Engineering Design Process of Face Masks Based on Circularity and Life Cycle Assessment in the Constraint of the COVID-19 Pandemic

sustainability

Article Engineering Design Process of Face Masks Based on Circularity and Life Cycle Assessment in the Constraint of the COVID-19 Pandemic

Núria Boix Rodríguez 1,* , Giovanni Formentini 1 , Claudio Favi 1 and Marco Marconi 2

1 Department of Engineering and Architecture, University of Parma, 43124 Parma, Italy; [email protected] (G.F.); [email protected] (C.F.) 2 Department of Economics, Engineering, Society and Business Organization, Università degli Studi della Tuscia, 01100 Viterbo, Italy; [email protected] * Correspondence: [email protected]; Tel.: +39-0521-90-6344

Abstract: Face masks are currently considered key equipment to protect people against the COVID-19 pandemic. The demand for such devices is considerable, as is the amount of plastic waste generated after their use (approximately 1.6 million tons/day since the outbreak). Even if the sanitary emergency must have the maximum priority, environmental concerns require investigation to ﬁnd possible mitigation solutions. The aim of this work is to develop an eco-design actions guide that supports the design of dedicated masks, in a manner to reduce the negative impacts of these devices on the environment during the pandemic period. Toward this aim, an environmental assessment based on life cycle assessment and circularity assessment (material circularity indicator) of different types of masks have been carried out on (i) a 3D-printed mask with changeable ﬁlters, (ii) a surgical Citation: Boix Rodríguez, N.; mask, (iii) an FFP2 mask with valve, (iv) an FFP2 mask without valve, and (v) a washable mask. Formentini, G.; Favi, C.; Marconi, M. Results highlight how reusable masks (i.e., 3D-printed masks and washable masks) are the most Engineering Design Process of Face sustainable from a life cycle perspective, drastically reducing the environmental impacts in all Masks Based on Circularity and Life categories. The outcomes of the analysis provide a framework to derive a set of eco-design guidelines Cycle Assessment in the Constraint of which have been used to design a new device that couples protection requirements against the virus the COVID-19 Pandemic. and environmental sustainability. Sustainability 2021, 13, 4948. https:// doi.org/10.3390/su13094948 Keywords: face masks; life cycle assessment; LCA; environmental analysis; eco-design; product

Academic Editor: development process; circularity; engineering design; COVID-19 Ali Bahadori-Jahromi

Received: 18 March 2021 Accepted: 23 April 2021 1. Introduction Published: 28 April 2021 It is almost a year since the World Health Organization (WHO) classiﬁed the COVID-19 disease caused by the new SARS-CoV-2 virus as a pandemic [1], and by March 2021, more Publisher’s Note: MDPI stays neutral than 100 million people had been infected [2] around the world, causing a global emer- with regard to jurisdictional claims in gency that will continue until effective health care, prevention and/or medical treatment published maps and institutional afﬁl- solutions (e.g., vaccines) are widely implemented. iations. During this period, the world has seen how human interaction, work and personal hygiene habits, as well as daily routines, have changed. The most common method of disease diffusion is through respiratory droplets, meaning that the virus can be transmitted while people are breathing or speaking [3,4]. There are various methods of spreading the Copyright: © 2021 by the authors. virus: by direct contact with surfaces/people on which these droplets have been deposited Licensee MDPI, Basel, Switzerland. (large droplets > 20 µm) and airborne transmission, during which infection occurs when This article is an open access article people inhale the droplets in the air (small droplets < 5–10 µm) [5–7]. Given this context, distributed under the terms and the importance of using devices that can reduce the spread of these particles has become conditions of the Creative Commons more evident, facial masks being the most recommended and effective device to reduce Attribution (CC BY) license (https:// contagion, along with the limitation of contact between people (such as lockdowns carried creativecommons.org/licenses/by/ out in various countries) [8–10]. That is why WHO guidelines and several research studies 4.0/).

Sustainability 2021, 13, 4948. https://doi.org/10.3390/su13094948 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, 4948 2 of 26

recommend the use of masks both in closed and open spaces [8,11–13]. These devices act as a physical barrier to prevent particle dispersion, thus filtering the exhalation of infected individuals [14]. For this reason, masks should be worn during daily activities (work, public transport, etc.) by a large part of the population during 2021, especially in places where ventilation is not good [7,13–15]. The WHO has estimated that 89 million medical masks are needed per month [16], a huge quantity that caused limited stocks in many countries during the initial period of the pandemic [17–19]. Moreover, their production entails a large consumption of fossil-based materials and the generation of large amounts of waste (difficult to manage), which can cause an environmental issue. This problem should not be forgotten although, at this time, efforts should be focused on solving the current health emergency. These sustainability issues are due to the fact that masks (surgical and PPE, or personal protective equipment) are usually disposable devices, generally produced by using different layers of nonwoven fibers made of thermoplastic polymers [20] and sometimes functionalized to improve their filtering properties [21,22]. This type of devices is very difficult to recycle, which makes the end of life (EoL) of the product another critical and impactful aspect to manage since most of the masks end up being discarded in municipal/sanitary landfills or incinerated [23], with considerable emissions of greenhouse gases (GHGs) [24]. Furthermore, masks potentially represent a source of microplastics, which are very dangerous for microorganisms living in water and can reenter the human food chain, causing severe health problems [25,26]. This is the reason why studies are being promoted to obtain masks with biodegradable materials [27], which should facilitate their end-of-life disposal. With the aim of improving the sustainability of the health sector, the focus is being placed on increasing the lifespan of these devices, mainly through their reuse [28]. In this way, some governments (i.e., Spain) [29] are taking measures that promote the manufacture and use of reusable hygienic masks (specified in UNE 0065 standard). Additionally, various investigations have focused on giving biocidal properties to masks to increase their useful life and reduce bio-infectious waste [30,31]. Studies such as those by McGain et al. [32] and Ertz and Patrick [28] have exposed the economic and environmental benefits of reusing medical devices. Klemeš et al. [33] have conducted research focused on the energy and carbon footprint associated with masks and PPE during the COVID-19 pandemic period. The result of this study shows that if a proper selection of materials is made, a suitable design is used, and user guides are drawn up, reusable PPE leads to a reduction in energy consumption and environmental footprint. Kumar et al. [34] have carried out an environmental analysis and sustainable waste management study of PPE kits (surgical mask, gloves, goggles, suit), considering different scenarios such as end-of-life landfill disposal or incineration (centralized and decentralized), finding, as a result, that the most unfavorable situation is landfill disposal. Allison et al. [35] carried out an investigation comparing single-use masks with reusable ones, considering various scenarios, finding that the use of reusable masks reduces the amount of waste entering general waste streams. Results obtained by Schmutz et al. [36] and Boix et al. [37] comparing surgical and reusable masks instead highlight the great dependence that the impact calculations have on the use phase (personal behavior) and materials used. However, these studies do not offer a global comparison of the different models of masks available on the market, a clear vision when comparing the different impacts (environmental, circularity, etc.), or facilitate decision making from the eco-design perspective. Only a few and preliminary life cycle assessment (LCA) studies and eco-design analyses have been carried out on this topic (the environmental impact of face masks) [38,39]. The main goal of this research paper is to develop an eco-design actions guide that helps engineers and designers during the process of product development of new masks, with the objective to reduce the negative impacts of these devices on the environment during this pandemic period. To achieve this objective, an LCA analysis on different types of masks was carried out: (i) M1—3D-printed mask with changeable filters, (ii) M2—surgical mask, (iii) M3—FFP2 mask with valve, (iv) M4—FFP2 mask without valve, and (v) M5— Sustainability 2021, 13, x FOR PEER REVIEW 3 of 28

Sustainability 2021, 13, 4948 3 of 26 during this pandemic period. To achieve this objective, an LCA analysis on different types of masks was carried out: (i) M1—3D-printed mask with changeable filters, (ii) M2— surgical mask, (iii) M3—FFP2 mask with valve, (iv) M4—FFP2 mask without valve, and washable(v) M5—washable mask. The mask. study The was study performed was performed considering considering the Italian the scenario; Italian scenario; Italy was Italy one ofwas the one first of EU the countries first EU tocountries face the to pandemic face the pandemic emergency, emergency, therefore having therefore the having necessary the datanecessary available data for available the analysis. for the However, analysis. the However, study can the be study transferred can be and transferred replicated and to otherreplicated countries. to other This countries. paper has This the paper ambition has the to provideambition a to scientific providebasis a scientific to reduce basis the to wastereduce produced the waste during produced this during pandemic, this pandemic, increase the increase circularity the circularity of these devices of these (through devices the(through study ofthe the study material of the circularity material indicator circularity (MCI)), indicator and increase(MCI)), theand overall increase sustainability the overall ofsustainability face masks. of All face analyses masks. enable All analyses the definition enable of the a framework definition forof a the framework development for the of andevelopment eco-sustainable of an mask, eco-sustainable which undoubtedly mask, wh canich beundoubtedly of great relevance can be duringof great the relevance current seriousduring healththe current situation serious in thehealth world. situation The novelty in the world. of the paperThe novelty is to overtake of the paper the main is to limitationsovertake the of generalmain studieslimitations regarding of general the environmental studies regarding performance the ofenvironmental face masks, providingperformance a study of face that masks, allows providing having a globala study vision that ofallows the impacts having of a theglobal masks vision currently of the onimpacts the market of the andmasks facilitating currently eco-design on the market decision and facilitating making. eco-design decision making. TheThe restrest ofof thethe articlearticle isis organizedorganized asas follows:follows: SectionSection2 2describes describes the the methodology methodology followedfollowed toto developdevelop thethe LCALCA analysis,analysis, thethe calculationcalculation ofof thethe circularitycircularity index,index, asas wellwell asas thethe eco-designeco-design guidelinesguidelines andand maskmask developmentdevelopment process;process; SectionSection3 3 presents presents the the results results obtainedobtained forfor the the different different masks, masks, their their most most critical critical aspects aspects and alsoand developsalso develops an eco-design an eco- guide,design inguide, addition in addition to proposing to proposing a framework a framework for the developmentfor the development of a sustainable of a sustainable mask; Sectionmask; 4Section discusses 4 thediscusses main outcomesthe main of outcom the research.es of Finally,the research. Section 5Finally, summarizes Section the 5 conclusionssummarizes and the possibleconclusions future and developments. possible future developments. 2. Materials and Methods 2. Materials and Methods The following study has been carried out using a methodology composed of three The following study has been carried out using a methodology composed of three easily identifiable phases: (i) assessment of environmental and circularity key performance easily identifiable phases: (i) assessment of environmental and circularity key indicators (KPIs), (ii) a knowledge-based system for eco-design, and (iii) ask development performance indicators (KPIs), (ii) a knowledge-based system for eco-design, and (iii) ask process. The workflow and the main activities of each phase are reported in Figure1 and detaileddevelopment in the process. following The subsections. workflow and the main activities of each phase are reported in Figure 1 and detailed in the following subsections.

FigureFigure 1.1. Methodology.Methodology.

2.1.2.1. EnvironmentalEnvironmental andand CircularityCircularity KPIKPI AssessmentAssessment InIn orderorder toto meetmeet thethe objectivesobjectives ofof thisthis studystudy andand identifyidentify criticalcritical pointspoints ofof thesethese products,products, LCALCA methodologymethodology hashas beenbeen used,used, followingfollowingthe the ISOISO 14040,14040, ISOISO 1404414044 andand ILCDILCD Handbook,Handbook, whichwhich identiﬁesidentifies thethe followingfollowing fourfour phasesphases [[40]:40]: 1.1. Goal and scope deﬁnition;definition; 2.2. Life cycle inventory (LCI); 3.3. Life cycle impact assessment (LCIA); 4.4. Interpretation. ThisThis typetype ofof analysis analysis makes makes it it possible possible to to establish establish the the environmental environmental impacts impacts and and the resourcesthe resources used used during during the lifethe cyclelife cycle of the of product,the product, including including some some categories categories that that may may not benot taken be taken into into account account when when a simpler a simpler study study is conducted. is conducted. The functional unit chosen to carry out the comparison is “The use of a face mask that complies with UNI EN 149:2009 or UNI EN 14683:2019 standards and is able to prevent the emission of respiratory droplets, in a pandemic situation for Italian citizen during a month.” It Sustainability 2021, 13, x FOR PEER REVIEW 4 of 28

Sustainability 2021, 13, 4948 The functional unit chosen to carry out the comparison is “The use of a face mask4 ofthat 26 complies with UNI EN 149:2009 or UNI EN 14683:2019 standards and is able to prevent the emission of respiratory droplets, in a pandemic situation for Italian citizen during a month.” It was decided to take the time time reference reference of 1 mont monthh to facilitate facilitate the calc calculationulation of the impact duringduring the the entire entire pandemic due due to the uncert uncertaintyainty that exists regarding the end of this period, making it possible to obtain the total impact by multiplying the results obtained byby the the total total months. months. Italy Italy has has been been used used as as th thee reference reference country due to the available data necessarynecessary for for the the analysis; however, however, the obtain obtaineded results can be transferred to other EU countriescountries and and geographical geographical areas. ToTo facilitate comparative analysis, it was established that the reference flow flow is a face maskmask that that complies with with UNI UNI EN 149:2009 or UNI EN 14683:2019 in order to consider masksmasks that that assure a certain degree of safety for finalfinal users. The UNI EN 149:2009 is the referencereference standardstandard forfor PPEs PPEs that that foresees foresees a seriesa series of testingof testing and and marking marking requirements requirements (e.g., (e.g.,visual visual inspection, inspection, leakage, leakage, compatibility compatibility with skin, with flammability skin, flammability of material, of breathingmaterial, breathingresistance) resistance) for this kind for ofthis protective kind of protec equipmenttive equipment dedicated dedicated to the protection to the protection of nose and of nosemouth. and Among mouth. theAmong required the required performance performanc tests, thee tests, penetration the penetration of filter of material filter material is the istest the related test related to droplet to droplet emission emission (and (and inhalation). inhalation). The The penetration penetration of of filter filter materialmaterial is quantifiedquantified through the particle filtration filtration efficiency efficiency (PFE) parameter by following the test procedure in in accordance accordance with with the the UNI UNI EN EN 132 13274-7:2019.74-7:2019. According According to this to this test, test, masks masks can becan classified be classified into intothree three categories: categories: FFP1 FFP1 (PFE (PFE ≥ 80%≥ of80% PFE), of PFE), FFP2 FFP2(PFE (PFE≥ 94%),≥ 94%),and FFP3 and (PFEFFP3 ≥ (PFE 99%).≥ The99%). UNI The EN UNI 14683:2019 EN 14683:2019 is the isreference the reference standard standard for surgical for surgical masks masks that foreseesthat foresees requirements requirements and andtest test methods methods for for such such equipment, equipment, generally generally dedicated dedicated to medicalmedical environments. environments. The The standard standard includes includes requirements requirements about about material material breathability, breathability, splashsplash resistance,resistance, microbial microbial cleanliness cleanliness (bioburden), (bioburden), biocompatibility, biocompatibility, and bacteria and filtrationbacteria filtrationefficiency efficiency (BFE). The (BFE). latter The is thelatter key is parameter the key parameter that allows that the allows verification the verification of whether of whetherthe material the material used to used manufacture to manufacture the mask the ismask able is to able filtrate to filtrate a reference a reference pathogen, pathogen, the theStaphylococcus Staphylococcus aureus aureus, with, with a certain a certain efficiency: efficiency: BFE ≥BFE95% ≥ 95% for Type for Type I masks I masks and BFEand ≥BFE98% ≥ 98%for Type for Type II or II IIR or masks IIR masks (which (which are also are resistantalso resistant to splashes). to splashes). TheThe system boundaries boundaries considered considered in in the the LCA LCA study include (Figure 22)) (i)(i) maskmask production (material(material extraction extraction and, and, for thefor M1the mask, M1 mask, the manufacturing the manufacturing process (additiveprocess (additivemanufacturing)); manufacturing)); (ii) transportation (ii) transportation (distribution (distribution center and finalcenter user); and (iii)final usage user); phase; (iii) usage(iv) maintenance phase; (iv) maintenance (disinfection with(disinfection ethanol orwith wash); ethanol and or (v) wash); end of and life. (v) end of life.

Figure 2. System boundary. Figure 2. System boundary.

FiveFive different different types of masks available on the market have been selected as follows: • • M1—3D-printed model. model. This This commercial commercial mask mask uses disposable FFP2 filters.filters. This technologytechnology is is very very widespread widespread on on the the market market for for masks masks with with a a reusable reusable structure. structure. The 3D-printed part has to be disinfected to en ensuresure that it is safe to use. FFP2 filters filters guarantee a filtration efficiency of at least 94% and must be changed every 8 h of use [41]. SustainabilitySustainability 20212021,, 1313,, xx FORFOR PEERPEER REVIEWREVIEW 55 ofof 2828

Sustainability 2021, 13, 4948 5 of 26 guaranteeguarantee aa filtrationfiltration efficiencyefficiency ofof atat leastleast 94%94% andand mustmust bebe changedchanged everyevery 88 hh ofof useuse [41].[41]. •• M2—surgical mask. This type of device is for single use only and acts as a barrier to • M2—surgical M2—surgicalM2—surgical mask. mask.mask. This This typeThis type oftype device ofof devicedevice is for isis single forfor singlesingle use only useuse only andonly acts andand as actsacts a barrier asas aa barrierbarrier to toto preventpreventprevent droplets dropletsdroplets from fromfrom being beingbeing transmitted transmittedtransmitted during dudu breathingringring breathingbreathing or speaking. oror speaking.speaking. They TheyThey mainly mainlymainly protectprotectprotect other otherother people, people,people, not the notnot wearer, thethe wearer,wearer, although althoughalthough they cantheythey help cancan tohelphelp prevent toto preventprevent the user thethe fromuseruser fromfrom comingcomingcoming into into contactinto contactcontact with withwith a stream aa streamstream of liquid. ofof liquid.liquid. They TheyThey must mustmust be bebe discarded discardeddiscarded every everyevery 4 44 h hh of ofof useuse use [41[41].[41].]. •• • M3—FFP2 M3—FFP2M3—FFP2 with withwith exhalation exhalationexhalation valve. valve.valve. This ThisThis mask maskmask is for isis single forfor singlesingle use anduseuse isandand designed isis designeddesigned to toto facilitatefacilitatefacilitate breathing breathingbreathing through throughthrough its valve. itsits valve.valve. It protects ItIt protectsprotects the userthethe user fromuser fromfrom possible possiblepossible external externalexternal contamination,contamination,contamination, but it butbut does itit doesdoes not protect notnot protectprotect others. otheothe Theyrs.rs. TheyThey must mustmust be discarded bebe discardeddiscarded every everyevery 8 h of 88 hh ofof use [41useuse]. [41].[41]. • • M4—FFP2•• M4—FFP2M4—FFP2 without withoutwithout an exhalation anan exhalationexhalation valve. valve.valve. As in AsAs the inin previous thethe previousprevious case, case,case, it is for itit isis single forfor singlesingle use useuse but, sincebut,but, sincesince it does itit does notdoes have notnot havehave an exhalation anan exhalationexhalation valve, valvvalv it protectse,e, itit protectsprotects both thebothboth user thethe and useruser others. andand others.others. It ItIt needsneedsneeds to be toto discarded bebe discardeddiscarded every everyevery 8 h of 88 use hh ofof [ 41 useuse]. [41].[41]. • M5—washable•• M5—washableM5—washable mask. mask.mask. Mask MaskMask can becancan reused bebe reusedreused several severalseveral times, times,times, maintaining maintainingmaintaining its filtering itsits filteringfiltering efficiencyefficiencyefficiency for at forfor least atat least 50least washes. 5050 washes.washes. In this InIn case, thisthis case,case, maintenance maintenancemaintenance consists consistsconsists of washing ofof washingwashing the thethe productproductproduct in a washing inin aa washingwashing machine machinemachine at a atat recommended aa recommendedrecommended temperature temperaturetemperature between betweenbetween 40 40◦40C °C°C and andand 7575 75 ◦C[°C°C42 [42].[42].]. The lifeTheThe cycle lifelife cyclecycle inventory inventoryinventory (LCI) (LCI)(LCI) must mustmust consider considerconsider all materials allall materialsmaterials and energy andand energyenergy flows flowsflows (inputs (inputs(inputs and outputs)andand outputs)outputs) related relatedrelated to the toto functional thethe functionalfunctional unit so unitunit that soso they thatthat aretheythey quantified. areare quantified.quantified. The full TheThe description fullfull descriptiondescription of theofof LCI thethe (both LCILCI foreground (both(both foregroundforeground and background andand backgroundbackground data) is reported data)data) asisis Supplementary reportedreported asas SupplementarySupplementary Materials to makeMaterialsMaterials the study toto make fullymake reproducible. thethe studystudy fullyfully In this reproducible.reproducible. manuscript, InIn the thisthis LCI manuscript,manuscript, has been mainly thethe LCILCI divided hashas beenbeen into twomainlymainly parts: divideddivided the first intointo one istwotwo related parts:parts: to thethe materialsfirstfirst oneone used isis relatedrelated and manufacturing toto thethe materialsmaterials phase, usedused and andand the secondmanufacturingmanufacturing one is related phase,phase, to and theand use thethe phase. secondsecond The oneone LCI isis relatedrelated for the materialstoto thethe useuse and phase.phase. manufacturing TheThe LCILCI forfor thethe phasematerialsmaterials seeks to and knowand manufacturingmanufacturing exactly the components phasephase seeksseeks and toto knowknow materials exactlyexactly that thethe make componentscomponents up these products. andand materialsmaterials For thisthatthat purpose, makemake upup the thesethese five typesproducts.products. of masks ForFor thisthis studied purppurp wereose,ose, manuallythethe fivefive typestypes disassembled, ofof masksmasks andstudiedstudied each werewere componentmanuallymanually was disassembled,disassembled, weighed using theandand appropriate eacheach componcompon equipmententent waswas for weighedweighed it. Table 1using usingshows thethe the resultsappropriateappropriate of theequipmentequipment LCI manufacturing forfor it.it. TableTable phase 11 showsshows for each thethe typeresultsresults of ofof mask. thethe LCILCI manufacturingmanufacturing phasephase forfor eacheach typetype ofof mask.mask. Table 1. Life cycle inventory (LCI) of the mask production phase. TableTable 1.1. LifeLife cyclecycle inventoryinventory (LCI)(LCI) ofof thethe maskmask productionproduction phase.phase. Manufacturing Type Image Component Weight [g] Material TypeType Image Image Component Component Weight Weight [g][g] Material Material Manufacturing ManufacturingProcess ProcessProcess 0.500.50 PP—PolypropylenePP—Polypropylene FilterFilter 0.50 PP—Polypropylene N.A.N.A. Filter 0.500.50 PE—PolyesterPE—Polyester N.A. M1 M1M1 0.50 PE—Polyester StructureStructureStructure 30.0030.00 30.00PLAPLA PLA 3D 3D printingprinting 3D printing BandsBands Bands3.003.00 3.00SyntheticSynthetic rubber Syntheticrubber rubberN.A.N.A. N.A. 1.281.28 1.28PP—PolypropylenePP—Polypropylene PP—Polypropylene FilterFilter Filter N.A.N.A. N.A. 1.281.28 1.28PE—PolyesterPE—Polyester PE—Polyester M2 M2M2 NoseNose adapteradapterNose adapter 0.44 0.44 0.44 Aluminum Aluminum Aluminum Wire Wire drawingdrawing Wire drawing BandsBands Bands0.020.02 0.02CottonCotton Cotton N.A. N.A. N.A. Filter 5.00 PP—Polypropylene N.A. FilterFilter Filter5.005.00 5.00PP—PolypropylenePP—Polypropylene PP—Polypropylene N.A.N.A. N.A. ValveValve Valve5.005.00 5.00PP—PolypropylenePP—Polypropylene PP—Polypropylene InjectionInjection Injection moldingmolding molding M3 M3M3 NoseNose adapteradapterNose adapter 0.95 0.95 0.95 Aluminum Aluminum Aluminum Wire Wire drawingdrawing Wire drawing NoseNose protectionprotectionNose protection 0.05 0.05 0.05 PU—Polyurethane PU—Polyurethane PU—Polyurethane foamfoam foam N.A. N.A. N.A. BandsBands Bands3.003.00 3.00SyntheticSynthetic rubber Syntheticrubber rubberN.A.N.A. N.A. FilterFilter 5.005.00 PP—PolypropylenePP—Polypropylene N.A.N.A. Sustainability 2021, 13, x FOR PEER REVIEWFilter 5.00 PP—Polypropylene N.A. 6 of 28 NoseNose adapteradapter 0.95 0.95 Aluminum Aluminum Wire Wire drawingdrawing M4 M4M4 M4 Nose adapter 0.95 Aluminum Wire drawing BandsBands 3.003.00 SyntheticSynthetic rubberrubber N.A.N.A. Bands 3.00 Synthetic rubber N.A. 2.702.70 2.70PP—PolypropylenePP—Polypropylene PP—Polypropylene M5M5 FilterFilter Filter N.A.N.A. N.A. M5 Bands 1.002.702.70 2.70CottonPE—PolyesterPE—Polyester PE—Polyester N.A. Bands 1.00 Cotton N.A.

To define the inventory of the use phase, it must be taken into account that the study scenario is Italy where it is estimated that there is a daily need for masks of 40 million [43]. The daily mask estimation, together with the useful life of each type, allows us to know the total masks needed during the established period of time (one month), as can be seen in Table 2.

Table 2. Life cycle inventory (LCI) of the use phase.

Type Lifespan Units [million] Mask - 40 M1 Filter 8 h 600 M2 4 h 1200 M3 8 h 600 M4 8 h 600 M5 50 washes 40

Considering the use phase, M1 and M5 models require some type of “maintenance.” In the case of M1, the ethanol used to disinfect the 3D-printed mask was considered in the inventory. On the other hand, for the M5 model, the water, electricity, and soap that are consumed in a standard washing cycle performed with a washing machine were quantified. Concerning the end-of-life assessment, the hypothesis that all masks are disposed of in municipal landfills was established. For secondary data, datasets from Ecoinvent 3.5 were used. Life cycle impact assessment (LCIA) was carried out using a specific software tool (i.e., SimaPro 9.0.0.49). The selected impact indicators are the most suitable for the purpose of this article. Two different methods have been used: i) ReCiPe and ii) cumulative energy demand (CED). With the first method, it is possible to have an overview of the environmental loads using the midpoints (12 chosen categories, see Table 3) and endpoints (three categories, see Table 3), facilitating the interpretation of results [44]. On the other hand, the single-issue CED method was used to complement the information provided by ReCiPe concerning the LCIA of energy resources since CED allows us to take into account the energy consumption related to the product (directly or indirectly) during its life cycle [45].

Sustainability 2021, 13, 4948 6 of 26

To deﬁne the inventory of the use phase, it must be taken into account that the study scenario is Italy where it is estimated that there is a daily need for masks of 40 million [43]. The daily mask estimation, together with the useful life of each type, allows us to know the total masks needed during the established period of time (one month), as can be seen in Table2.

Table 2. Life cycle inventory (LCI) of the use phase.

Type Lifespan Units [million] Mask - 40 M1 Filter 8 h 600 M2 4 h 1200 M3 8 h 600 M4 8 h 600 M5 50 washes 40

Considering the use phase, M1 and M5 models require some type of “maintenance.” In the case of M1, the ethanol used to disinfect the 3D-printed mask was considered in the inventory. On the other hand, for the M5 model, the water, electricity, and soap that are consumed in a standard washing cycle performed with a washing machine were quantified. Concerning the end-of-life assessment, the hypothesis that all masks are disposed of in municipal landfills was established. For secondary data, datasets from Ecoinvent 3.5 were used. Life cycle impact assessment (LCIA) was carried out using a specific software tool (i.e., SimaPro 9.0.0.49). The selected impact indicators are the most suitable for the purpose of this article. Two different methods have been used: i) ReCiPe and ii) cumulative energy demand (CED). With the first method, it is possible to have an overview of the environmental loads using the midpoints (12 chosen categories, see Table3) and endpoints (three categories, see Table3), facilitating the interpretation of results [ 44]. On the other hand, the single-issue CED method was used to complement the information provided by ReCiPe concerning the LCIA of energy resources since CED allows us to take into account the energy consumption related to the product (directly or indirectly) during its life cycle [45].

Table 3. LCIA methods and indicators analyzed [44].

LCIA Method Indicator Acronym Unit

Global warming potential GWP [Kg CO2 eq] Ozone depletion potential ODP [kg CFC11 eq] Photochemical oxidant formation potential OFP [kg NOx eq] Particulate matter formation potential PMFP [kg PM2.5 eq] Terrestrial acidiﬁcation potential TAP [kg SO2 eq] ReCiPe Midpoints Freshwater eutrophication potential FEP [kg P eq] Terrestrial ecotoxicity potential TETP [kg 1.4-DCB] Freshwater ecotoxicity potential FETP [kg 1.4-DCB] Marine ecotoxicity potential METP [kg 1.4-DCB] Human toxicity potential HTP [kg 1.4-DCB] Fossil fuel potential FFP [kg oil eq] Water consumption potential WCP [m3] Human Health HH [-] ReCiPe Endpoints Ecosystem ED [-] Resources RA [-] Single Issue Cumulative energy demand CED [MJ]

Finally, the research work includes the analysis of the product circularity, sharing the vision of the EU and its purpose of achieving a circular economy [46]. In order to evaluate this factor, the material circularity indicator (MCI) was used. MCI studies the ﬂow of the product, indicating how restorative it is [47] and considering values in the range of Sustainability 2021, 13, 4948 7 of 26

0 and 1 (0 being fully linear and 1 being fully circular). The MCI calculator tool [48] was used to obtain the value of this parameter (in this tool, the minimum value that can be reached is 0.1, considering this result fully linear). A key parameter for the calculation of the MCI is the “utility,” which can be calculated using a simpliﬁed version of the method (Equation (1)) proposed by [47] as follows:

L X = (1) Lav

where • L represents the useful life of the product; • Lav refers to the average useful life of the industry.

2.2. Knowledge-Based System for Eco-Design In order to minimize the consumption of resources and the impact on the planet, eco- design has to be adopted as a design method, using a life cycle thinking (LCT) approach in which the entire life cycle of the product is taken into account. Approximately 70% of a product’s cost, environmental impact, and functional requirements can be determined during the design phase, thus demonstrating the importance of eco-design in those stages of the project [49]. The application of scientific and technological principles to design and carrying out engineering activities in a sustainable way, together with the LCT approach to optimize the life cycle of a product in order to protect the environment and improve economic progress, are defined as life cycle engineering (LCE). There are different design support tools that have been in use for years, with a broad spectrum ranging from extremely easy to use (i.e., recommendations) to some with a very complex structure [50]. To carry out the knowledge-based system step, methodologies that have already been shown to be effective in literature were followed. An example is the “Ten Golden Rules” explained in the study by Luttropp and Lagerstedt, which presented a qualitative approach to the application and creation of an eco-design guide [50]. On the other hand, the guidelines of the international ISO 14006:2011 [51] (updated in 2020) standard were used, establishing a methodology and a flowchart that must be followed to incorporate eco- design during the development of a product. This methodology is based on the following six phases: • Define product functions; • Environmental analysis; • Environmental improvement strategies; • Develop environmental objectives; • Environmental product specification; • Develop technical solutions. During the environmental assessment phase, LCA analysis was used and integrated into the eco-design application. Articles that work with both methods (LCA and eco- design) were a source of inspiration [52,53], together with the detailed explanation and application of the methodology set out in the ISO 14006:2011, presented in the article by Navajas et al. [54]. Therefore, as reported in many of the reviewed existing success experiences, after an LCA analysis, the most impactful components are usually identified to create a database that has a key role in establishing which aspects should be the focus of attention for achieving a significant environmental improvement while maintaining the functionality of the product. In the present paper, to carry out this analysis and obtain an eco-design actions guide, the same methodology was followed by first establishing criticalities of each phase of the device’s life cycle (once the LCA and MCI analyses have been performed) and then developing specific measures to improve these aspects. Figure3 shows how this methodology has been customized for an application to the specific case study. Sustainability 2021, 13, x FOR PEER REVIEW 8 of 28

used, establishing a methodology and a flowchart that must be followed to incorporate eco-design during the development of a product. This methodology is based on the following six phases: • Define product functions; • Environmental analysis; • Environmental improvement strategies; • Develop environmental objectives; • Environmental product specification; • Develop technical solutions. During the environmental assessment phase, LCA analysis was used and integrated into the eco-design application. Articles that work with both methods (LCA and eco- design) were a source of inspiration [52,53], together with the detailed explanation and application of the methodology set out in the ISO 14006:2011, presented in the article by Navajas et al. [54]. Therefore, as reported in many of the reviewed existing success experiences, after an LCA analysis, the most impactful components are usually identified to create a database that has a key role in establishing which aspects should be the focus of attention for achieving a significant environmental improvement while maintaining the functionality of the product. In the present paper, to carry out this analysis and obtain an eco-design actions guide, the same methodology was followed by first establishing criticalities of each phase of the device’s life cycle (once the LCA and MCI analyses have Sustainability 2021, 13, 4948 been performed) and then developing specific measures to improve these aspects. 8Figure of 26 3 shows how this methodology has been customized for an application to the specific case study.

Sustainability 2021, 13, x FOR PEER REVIEW 9 of 28

Figure 3. Eco-design methodology applied to this study. Figure 3. Eco-design methodology applied to this study.

2.3. Mask Mask Development Development process process The process workflow workﬂow followed to carry ou outt the development of a new device is depicted in Figure 44..

Figure 4. Process workflow. Figure 4. Process workﬂow.

First ofof all, all, eco-design eco-design measures measures should shou be includedld be included in the list in of productthe list requirementsof product requirementsdeveloped by developed the same authors by the ofsame this authors paper and of this discussed paper and in depth discussed in [55 ],in along depth with in [55], the alongspecific with regulations the specific and regulations standards forand these standa devices.rds for A these list of devices. requirements A list of is requirements the collection isof the customer’s collection needs of customer’s that must beneeds satisfied that must by the be creation satisfied of by a physical the creation product of a or physical system. productIn it, together or system. with In environmental it, together with aspects, enviro othernmental factors aspects, such other as safety factors and such ergonomic as safety anddesign ergonomic were also design covered. were Table also 4covered. shows an Tabl examplee 4 shows of somean example sustainability of some requirements.sustainability requirements. Table 4. Excerpt of the list of sustainable requirements [55]. Table 4. Excerpt of the list of sustainable requirements [55]. Type Requirement Type Requirement Wish Might be made of sustainable materials WishDemand Might be made Might of sustainable be reusable materials DemandDemand Might be reusable Might be durable DemandWish Might be durable Might provide filtering status information Wish Might be recyclable Wish Might provide filtering status information Demand Need to allow to see the face WishWish Might be recyclable Might be personalized DemandWish Need to allow Need to see to the be cheapface for daily use WishDemand Might be personalized Need to be available for each person in very constrained time Wish Need to be cheap for daily use Demand Need to be available for each person in very constrained time

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It is interesting to notice that pillars of sustainability other than environmental factors have been considered. For example, the “Need to allow to see the face” has an important role in the social aspect of sustainability (facilitating comprehension during a conversation and improving safety in certain environments). This requirement is highly debated in the social context; indeed, face masks decrease speech intelligibility and make communication more difficult, especially for people with hearing loss, and few works have been developed to tackle this issue [56–58]. The first step of development was followed by the functional analysis of the product, applying the methodology proposed by Pahl and Beitz [59]. The Pahl and Beitz theory uses a black box to represent the main product function, while the flows of material, energy, and signal are transformed by the function itself passing through the black box. The main function is then divided into subfunctions with a hierarchical structure. and a complex tree structure is created. In order to carry out this analysis, the main function (characterized by a black box) must be defined (“Filter air from viruses and pollutants to protect a person”), which is also composed of various subfunctions related to each other through different fluxes (i.e., mass, signal, and energy fluxes). The result of the functional analysis represents the starting point for the modularization phase, following the heuristics method for product modularization proposed by Stone and Wood [60]. The lowest hierarchical level of the functional analysis is used to identify modules. This step consists of grouping functions by using three separate strategies (heuristics): (i) dominant flow (DF), (ii) branching flows (BF), and (iii) conversion–transmission modules (CTM). The main objective of the identification of the modules is to group the functions of the previous phase into categories that facilitate the identification of the technological implementation. To carry out the last product development phase, a morphological matrix [61] can be used, which allows us to analyze and compare the different possible solutions for a given problem. The morphological matrix allows generating an exhaustive set of solutions for a given problem (in this case, each product “module”), organizing them into a matrix in which rows identify modules and columns identify possible solutions (i.e., design options). The morphological matrix enables the analysis of all the engineering solutions that may occur during the development of the facial mask. It concerns the analysis and permutations of any possible solutions generated to fulfill each module identified within the previous step. Thus, the various solutions obtained in the morphological matrix can be combined to obtain the final product that meets all the requirements.

3. Results 3.1. Environmental and Circularity KPI Assessment This section presents the results obtained during the environmental and circularity investigations. Table5 shows the values of the LCA midpoints studied, considering the use phase of the product and its end of life. These results show that the highest values in all categories analyzed have been obtained for M3 (FFP2 mask with valve), then M4 (FFP2 mask without valve), followed by M2 (surgical mask), and with a large difference of up to an order of magnitude in some categories (i.e., GWP), M1 (3D-printed mask) and M5 (washable mask). Figure5 shows the percentage distribution for the GWP indicator; the rest of the ReCiPe midpoints are reported in Table5, and the percentage distribution is analogous. Sustainability 2021, 13, 4948 10 of 26

Table 5. ReCiPe midpoints (H).

Impact Category Unit M1 M2 M3 M4 M5 6 7 7 7 6 GWP [Kg CO2 eq] 3.9 × 10 2.7 × 10 5.6 × 10 3.8 × 10 1.5 × 10 ODP [kg CFC11 eq] 1.8 6.1 1.0 × 10 8.3 2.3 OFP [kg NOx eq] 1.3 × 104 1.0 × 105 1.9 × 105 1.4 × 105 5.7 × 103 PMFP [kg PM2.5 eq] 3.7 × 103 3.4 × 104 5.7 × 104 4.5 × 104 2.1 × 103 3 4 5 5 3 TAP [kg SO2 eq] 9.9 × 10 8.0 × 10 1.5 × 10 1.1 × 10 4.5 × 10 FEP [kg P eq] 5.9 × 102 5.3 × 103 1.0 × 104 7.7 × 103 4.2 × 102 TETP [kg 1.4-DCB] 4.9 × 106 2.9 × 107 4.8 × 107 4.3 × 107 1.9 × 106 FETP [kg 1.4-DCB] 1.2 × 105 1.0 × 106 3.4 × 106 3.1 × 106 4.5 × 104 METP [kg 1.4-DCB] 1.7 × 105 1.3 × 106 4.7 × 106 4.3 × 106 5.8 × 104 HTP [kg 1.4-DCB] 2.4 × 106 1.4 × 107 9.6 × 107 9.2 × 107 7.5 × 105 SustainabilityFFP 2021, 13, x FOR PEER [kg REVIEW oil eq] 1.2 × 106 7.3 × 106 1.7 × 107 1.1 × 107 4.1 × 10115 of 28

WCP [m3] 5.4 × 104 2.0 × 105 3.9 × 105 2.9 × 105 7.0 × 104

Figure 5. Percentage distribution of the GWP indicator. Figure 5. Percentage distribution of the GWP indicator.

InIn order order to to make make the the interpretation interpretation of of results results easier, easier, disposable disposable masks masks and and other other ones ones thatthat allow allow total total or or partial partial reuse reuse of of the the device device were were analyzed analyzed separately. separately. The The first first group group refersrefers to to M2, M2, M3, M3, and and M4; M4; it it should should be be kept kept in in mind mind that that the the useful useful life life of of M2 M2 is is half half of of M3 M3 andand M4 M4 but but entails entails fewer fewer environmental environmental impacts impact fors for its its manufacturing. manufacturing. M3 M3 greatly greatly differs differs fromfrom M4 M4 in in the the FFP, FFP, GWP, GWP, and and OFP OFP categories categories (about (about 36%, 36%, 32%, 32%, and and 27%, 27%, respectively), respectively), withwith the the average average difference difference of of 20%. 20%. The The variations variations within within these these two two models, models, which which have have thethe same same lifespan, lifespan, are are due due to, to, among among other other factors, factors, the the fact fact that that the the M3 M3 is is composed composed of of five five differentdifferent components, components, and and the the amount amount of of plastic plastic (PP) (PP) used used is is double double that that in in the the M4 M4 case. case. OnOn the the other other hand, hand, when when comparing comparing M4 M4 and and M2, M2, it it is is observed observed that that the the highest highest differences differences occuroccur in in the the HTP, HTP, METP, METP, and and FETP FETP categories categories (about (about 85%, 85%, 68%, 68%, and and 67%, 67%, respectively), respectively), withwith an an average average difference difference of of 40%. 40%. The The fact fact that that the the average average difference difference is is notably notably greater greater inin this this second second case case isis duedue to the the completely completely different different manufacturing manufacturing and and use use phases phases of ofM2 M2with with respect respect to toM4. M4. In In addition, addition, the the amount amount of material necessarynecessary toto fulfillfulfill the the overall overall demanddemand of of face face masks masks is is significantly significantly different different for for M4 M4 and and M2; M2; thus thus the the mask mask production production forfor M2 M2 has has a a greater greater impact. impact. AsAs regards regards reusable reusable solutions, solutions, after after comparing comparing M1, whichM1, which allows allows the reuse the ofreuse the maskof the structuremask structure since the since filters the are filters disposable, are disposable, with M5, with which M5, can which be reused can be up reused to 50 washesup to 50 withoutwashes losing without the losing filtration the filtration performance, performance, it is observed it is observed that the greatestthat the differencegreatest difference occurs inoccurs HTP, FFP,in HTP, and FFP, METP and (about METP 69%, (about 66%, 69%, and 66%, 66%, and respectively). 66%, respectively). By contrast, By contrast, the impact the ofimpact ODP andof ODP WCP and categories WCP categories of M5 are of higherM5 are thanhigher those than of those M1 (aboutof M1 (about 33% and 33% 30%, and respectively).30%, respectively). The fact The that fact WCP that is WCP higher is inhigher the case in the of M5 case is of due M5 to is the due cotton to the used cotton during used during the mask production phase (a critical material for this indicator) and the maintenance (i.e., washing) required by this mask during its useful life for the purpose of disinfection. Subsequently, a more in-depth analysis of the midpoints for each mask was carried out. Figure 6 shows the results for M3, which exhibits the highest levels of impact. Sustainability 2021, 13, 4948 11 of 26

the mask production phase (a critical material for this indicator) and the maintenance (i.e., washing) required by this mask during its useful life for the purpose of disinfection. Sustainability 2021, 13, x FOR PEER REVIEWSubsequently, a more in-depth analysis of the midpoints for each mask was carried12 of 28

out. Figure6 shows the results for M3, which exhibits the highest levels of impact.

FigureFigure 6.6.Midpoints Midpoints (H)(H) forfor M3M3 maskmask (percentage(percentage distribution). distribution).

AsAs cancan bebe inferred,inferred, inin almost almost allall categories, categories, thethe upstreamupstream productionproduction ofof thethe mask mask is is thethe phase phase causing causing the the most most impact impact during during its its life life cycle. cycle. Only Only in FETP,in FETP, METP, METP, and and HTP, HTP, the endthe end of life of causeslife causes the the highest highest impacts. impacts. This This distribution distribution of of the the impacts impacts of of contributions contributions isis quitequite similarsimilar toto thatthat ofof M1M1 andand M4M4 masksmasks (the(the otherother devicesdevices studiedstudied withwith FFP2FFP2 ﬁlters).filters). However,However, considering considering thethe givengiven functionalfunctional unit,unit,which whichrecalls recalls the the time time frame frame of of a a month month forfor thethe M2M2 andand M5, M5, the the inﬂuence influence of of volume volume of of masks masks required required is is higher higher in in all all categories categories withoutwithout any any exception. exception. GivenGiven itsits greatgreat relevance,relevance, thethe resultsresults ofof the the mask mask production production phase phase were were studied studied in in detail.detail. DueDue to to the the fact fact that that GWP GWP is is the the most most relevant relevant indicator indicator for for polymers polymers [62 [62–64],–64], Figure Figure7 shows7 shows the the comparison comparison of theof the different different models models studied studied in terms in terms of GWP. of GWP. As expected, As expected, M1 hasM1 thehas greatest the greatest value value due to due the to amount the amount of plastic of requiredplastic required to produce to produce its structure, its structure, but this initialbut this impact initial will impact be offset will duringbe offset the during use phase the use (due phase to the (due reuse to of the this reuse part of of this the mask).part of the mask).Endpoints (HH, ED, RA) were also analyzed, allowing a global overview of how each component affects each area of protection and thus facilitating decision making for eco-design. As can be inferred in Figure8, in the case of the M1 mask, the 3D-printed structure, which is also the reusable part of this device, is the part with the greatest impact during its production. This fact shows the importance of the material selection, seeking durable and easy-to-disinfect solutions.

Sustainability 2021, 13, 4948 12 of 26

Sustainability 2021, 13, x FOR PEER REVIEW 13 of 28

Figure 7. GWP [kg CO2-eq/functional unit] of the manufacturing phase.

Endpoints (HH, ED, RA) were also analyzed, allowing a global overview of how each component affects each area of protection and thus facilitating decision making for eco- design. As can be inferred in Figure 8, in the case of the M1 mask, the 3D-printed structure, which is also the reusable part of this device, is the part with the greatest impact during its production. This fact shows the importance of the material selection, seeking durable

Figureand 7. GWP easy-to-disinfect [kg CO2-eq/functional solutions. unit] of the manufacturing phase.

FigureFigure 8. Endpoints8. Endpoints (H) (H) for M1for (percentageM1 (percentage distribution). distribution).

ForFor M2 M2 (see (see Figure Figure9), the 9), nose the adapternose adapter (made (made of aluminum) of aluminum) is the component is the component that that hashas the the greatest greatest impact impact on HHon HH and ED,and whileED, while in the in case the of case RA, theof RA, material the material needed to needed to makemake the the mask mask (PP (PP and and PE) PE) represents represents the most the criticalmost critical ﬂow. flow. M3 is composed of ﬁve elements, with nose protection practically negligible. Once again, the nose adapter is the most relevant on HH and ED, while for the RA endpoint, the valve is the component that has the greatest impact, as can be seen in Figure 10.

Figure 9. Endpoints (H) for M2 (percentage distribution).

M3 is composed of five elements, with nose protection practically negligible. Once again, the nose adapter is the most relevant on HH and ED, while for the RA endpoint, the valve is the component that has the greatest impact, as can be seen in Figure 10. Sustainability 2021, 13, x FOR PEER REVIEW 13 of 28

Figure 7. GWP [kg CO2-eq/functional unit] of the manufacturing phase.

Figure 8. Endpoints (H) for M1 (percentage distribution).

Sustainability 2021, 13, 4948 For M2 (see Figure 9), the nose adapter (made of aluminum) is the component13 ofthat 26 has the greatest impact on HH and ED, while in the case of RA, the material needed to make the mask (PP and PE) represents the most critical flow.

Sustainability 2021, 13, x FOR PEER REVIEW 14 of 28 Figure 9. Endpoints (H) for M2 (percentage distribution). Figure 9. Endpoints (H) for M2 (percentage distribution). M3 is composed of five elements, with nose protection practically negligible. Once again, the nose adapter is the most relevant on HH and ED, while for the RA endpoint, the valve is the component that has the greatest impact, as can be seen in Figure 10.

Figure 10. Endpoints (H) for M3 (percentage distribution). Figure 10. Endpoints (H) for M3 (percentage distribution).

TheThe results results of of M4 M4 are are shown shown in in Figure Figure 11 11 and and are are analogous analogous to to the the previous previous ones ones but but withoutwithout the the valve valve and and the the nose nose protection. protection. Lastly, for the M5 mask, the bands (made of cotton) have the greatest impact on HH and ED, while for the RA endpoint, the material used as a ﬁlter causes the highest level of impact (see Figure 12).

Figure 11. Endpoints (H) for M4 (percentage distribution).

Lastly, for the M5 mask, the bands (made of cotton) have the greatest impact on HH and ED, while for the RA endpoint, the material used as a filter causes the highest level of impact (see Figure 12). Sustainability 2021, 13, x FOR PEER REVIEW 14 of 28

Figure 10. Endpoints (H) for M3 (percentage distribution). Sustainability 2021, 13, 4948 14 of 26 The results of M4 are shown in Figure 11 and are analogous to the previous ones but without the valve and the nose protection.

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FigureFigure 11. 11.Endpoints Endpoints (H) (H) for for M4 M4 (percentage (percentage distribution). distribution).

Lastly, for the M5 mask, the bands (made of cotton) have the greatest impact on HH and ED, while for the RA endpoint, the material used as a filter causes the highest level of impact (see Figure 12).

FigureFigure 12. 12.Endpoints Endpoints (H) (H) for for M5 M5 (percentage (percentage distribution). distribution).

Finally,Finally, in in order order to to understand understand in in more more detail detail the the energy energy resources resources used used during during the the lifelife cycle cycle of of these these devices, devices, the the results results of of the the CED CED are are shown shown (Table (Table6). 6).

TableTable 6. Cumulative 6. Cumulative energy energy demand demand for the for use the phase. use phase.

ImpactImpact Category Category Unit UnitM1 M1 M2 M2 M3 M3 M4 M4 M5M5 Fossil MJ 5.4 × 107 7 3.3 × 108 8 7.6 × 108 8 4.8 × 108 1.9 × 1077 Non Fossil MJ 5.4 × 10 3.3 × 10 7.6 × 10 4.8 × 10 1.9 × 10 Non 6 7 7 7 6 NuclearNuclear MJ MJ 3.73.7 × 10× 10 6 1.91.9 × ×1010 7 7.37.3 ×× 1010 7 3.93.9 × 10107 2.0 2.0× × 10106 renewablerenewable BiomassBiomass MJ MJ 4.24.2 × 10×310 3 5.55.5 × ×10103 3 1.21.2 ×× 10104 4 1.11.1 × 10104 6.2 6.2× × 101033 BiomassBiomass MJ MJ 3.53.5 × 10×610 6 3.73.7 × ×10106 6 1.31.3 ×× 10107 7 7.67.6 × 10106 1.6 1.6× × 101066 Renewable Wind,Wind, solar, solar, geothermal MJ 3.0 × 105 7.4 × 105 3.6 × 106 2.0 × 106 1.7 × 105 Renewable MJ 3.0 × 105 7.4 × 105 3.6 × 106 2.0 × 106 1.7 × 105 Watergeothermal MJ 1.1 × 106 1.4 × 107 2.3 × 107 1.8 × 107 6.4 × 105 TotalWater MJ MJ 1.16.3 × 10×610 7 1.43.7 × ×10107 8 2.38.7 ×× 10107 8 1.85.5 × 101078 2.3 6.4× × 101075 Total MJ 6.3 × 107 3.7 × 108 8.7 × 108 5.5 × 108 2.3 × 107 As in the previous cases, M3 has the highest values, followed by M4, M2, and with a large differenceAs in the previous (of an order cases, of M3 magnitude), has the high M1est and values, M5. The followed fact that by M1M4, and M2, M5 and are with not a large difference (of an order of magnitude), M1 and M5. The fact that M1 and M5 are not disposable masks makes their demand during the whole life cycle much lower. This result explains why their values of CED are lower, as in the other impact categories. From these results, it can be inferred that to reduce the impacts related to resources and energy (RA and CED), action must be taken on the filters. If the objective is the ecosystem and human health, the nose adapter is more relevant. After the LCA analysis, a study of the circularity of these devices was also carried out through the MCI (Table 7). The first analyzed mask was the 3D-printed (M1) mask, for which the utility parameter was based on lifespan. M1 is composed of the mask structure and filter, which have a very different useful life, thus MCI was calculated separately. For the 3D-printed structure, it is assumed that the durability is 300 times higher than an FFP2 mask, which is 8 h (X = 300). On the other hand, filters have a lifespan equal to the average of the FFP2 devices (X = 1). In all cases, it was considered that the source of input materials is “virgin” and that 100% of output materials have a landfill destination.

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disposable masks makes their demand during the whole life cycle much lower. This result explains why their values of CED are lower, as in the other impact categories. From these results, it can be inferred that to reduce the impacts related to resources and energy (RA and CED), action must be taken on the filters. If the objective is the ecosystem and human health, the nose adapter is more relevant. After the LCA analysis, a study of the circularity of these devices was also carried out through the MCI (Table7). The first analyzed mask was the 3D-printed (M1) mask, for which the utility parameter was based on lifespan. M1 is composed of the mask structure and filter, which have a very different useful life, thus MCI was calculated separately. For the 3D-printed structure, it is assumed that the durability is 300 times higher than an FFP2 mask, which is 8 h (X = 300). On the other hand, filters have a lifespan equal to the average of the FFP2 devices (X = 1). In all cases, it was considered that the source of input materials is “virgin” and that 100% of output materials have a landfill destination.

Table 7. Utility and MCI for different masks.

Type Utility MCI M1 ﬁlter 1 0.1 M1 structure 300 1.0 M2 1 0.1 M3 1 0.1 M4 1 0.1 M5 50 0.9

As can be seen in Figure 13, the M1 structure is a completely circular product (because of high utility), while the M1 ﬁlter (along with other disposable devices) is considered fully linear. In order to increase the circularity of this mask, recycled or reused sources for materials should be used, together with actions aimed at increasing utility. In general, eco-design actions should be mainly focused on masks considered fully linear since these devices have the worst circularity performance.

Figure 13. MCI chart.

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3.2. Knowledge-Based System for Eco-Design Through the results of various indicators revealed in the previous section and taking into account the objectives of this study, which seeks to create a guide of eco-design actions that allows reducing the negative impact on the environment due to the design and production of face masks, it can be established that the best alternative studied is M5, followed by M1. This demonstrates that totally or partially reusable products favor the reduction of negative impacts. By following the methodology described in Section 2.2, Table8 reports a list of eco-design actions to make face masks a more circular and sustainable product. To improve the usefulness of the identiﬁed guidelines, they have been divided according to the main phases of the mask life cycle: material and manufacturing, use, and end of life.

Table 8. Eco-design guidelines.

Lifecycle Phases Criticalities Related Eco-Design Guidelines • To choose the most sustainable and low energy-intensive 3D printing processes High impacts related to manufacturing • To evaluate if it is a large production process (3D printing) (M1) volume and change the manufacturing process to a more sustainable one (i.e., injection molding) • To reduce the number of components High impacts due to complex structure (integrate parts with same material) (M3) • To use as few diverse materials as possible Material and manufacturing • To avoid outlet valve • To choose more sustainable materials (i.e., PP instead of PE) • To avoid coupling PP and PE for the High impacts and low circularity due to manufacturing of filters (nonwoven fabric) the use of virgin materials (M1, M2, M3, • To use a mix of virgin and recycled input M4, M5) materials (or if possible, only recycled plastics) • To avoid the use of Aluminum as nose adapter • To prefer washable and reusable (fully or Disposable products (M2, M3, M4) partially) products • To increase useful life of the filters by Use modifying the material’s properties (i.e., Low duration of filters (M1) surface activated filters) [65–67] • To optimize weight and surface of filters • To use washable and interchangeable filters

Multimaterial for filters that reduces • To use single materials circularity (M1, M2) • To develop products according to the design for disassembly rules Difficulties in separating components and • To reduce the number of components End of life materials (M2, M3, M4) • To use easy to disassemble joints (i.e., snap-fit and press-fit) • To develop dedicated EoL processes for Open loop EoL (M1, M2, M3, M4, M5) material recycling • To organize dedicated collection systems

3.3. Mask Development Process As can be seen, LCA and MCI help to identify the critical factors of the product (face mask) and successively deﬁne eco-design actions that can be taken into account during the design of new masks, thus creating a framework for the development of these products in a sustainable manner. In this way, following the methodology proposed by Pahl and Beitz [59], a new product can be developed in a very short time, concentrating efforts Sustainability 2021, 13, 4948 17 of 26

on critical aspects and making the reaction to this health emergency swift and efﬁcient. Applying the process workﬂow explained in Section 2.3, it is possible to obtain a mask Sustainability 2021, 13, x FOR PEER REVIEW 18 of 28 prototype adapted to the needs expressed in the list of requirements. The main level of functional analysis is shown in Figure 14.

FigureFigure 14.14. FunctionalFunctional analysisanalysis (main(main level).level).

TheThe inputinput flowsflows identified identified in in terms terms of of materi material,al, signal, signal, and and energy energy can can be be defined defined as asfollows: follows: • • FreshFresh contaminatedcontaminated air:air: thethe materialmaterial neededneeded forfor breathing;breathing; • • ProtectionProtection signal:signal: thethe signalsignal toto activateactivate thethe protection;protection; •• HumanHuman force:force: thethe forceforce requiredrequired toto applyapply thethe protection.protection. OnOn thethe otherother hand,hand, twotwo outputsoutputs havehave beenbeen considered:considered: • Exhausted air: represents the result of the breathing process (contaminated air); • Exhausted air: represents the result of the breathing process (contaminated air); • Heat: generated by the breathing process. • Heat: generated by the breathing process. After having defined a detailed functional structure, results of the modularization After having defined a detailed functional structure, results of the modularization phase that takes only the dominant flow into account can be seen in Figure 15, identifying phase that takes only the dominant flow into account can be seen in Figure 15, identifying five modules and two auxiliaries: (i) import and regulate air, (ii) allow safely breathing; five modules and two auxiliaries: (i) import and regulate air, (ii) allow safely breathing; (iii) (iii) protect and cover exposed body parts; (iv) guarantee filter efficiency; (v) guarantee protect and cover exposed body parts; (iv) guarantee filter efficiency; (v) guarantee filter filter change; (Auxiliary 1) display filtering status; and (Auxiliary 2) personalize. change; (Auxiliary 1) display filtering status; and (Auxiliary 2) personalize. The full set of modules identified by the use of the three heuristic methods are reported in the following Table9.

Table 9. Modules retrieved by the use of the three heuristic methods.

ID Module Type DF CTM BF A Import and regulate air Main X B Allow safely breathing Main X C Protect and cover exposed body parts Main X D Guarantee filter efficiency Main X E Guarantee filter change Main X F Personalize Auxiliary X G Display filtering status Auxiliary X H Display protection sterilization Auxiliary X I Extract water after virus separation Auxiliary X X L Monitor protection efficiency Auxiliary X M Convert air Main X X N Dissipate exhaust air Main X X O Block water droplets after breathing Main X X P Ergonomic for fixation and adaptation Main X Q Dissipate heat Auxiliary X

Figure 15. Functional analysis including dominant flow heuristic methodfor module identification. Sustainability 2021, 13, x FOR PEER REVIEW 18 of 28

Figure 14. Functional analysis (main level).

The input flows identified in terms of material, signal, and energy can be defined as follows: • Fresh contaminated air: the material needed for breathing; • Protection signal: the signal to activate the protection; • Human force: the force required to apply the protection. On the other hand, two outputs have been considered: • Exhausted air: represents the result of the breathing process (contaminated air); • Heat: generated by the breathing process. After having defined a detailed functional structure, results of the modularization phase that takes only the dominant flow into account can be seen in Figure 15, identifying Sustainability 2021, 13, 4948 five modules and two auxiliaries: (i) import and regulate air, (ii) allow safely breathing;18 of 26 (iii) protect and cover exposed body parts; (iv) guarantee filter efficiency; (v) guarantee filter change; (Auxiliary 1) display filtering status; and (Auxiliary 2) personalize. SustainabilitySustainability 2021 2021, ,13 13, ,x x FOR FOR PEER PEER REVIEW REVIEW 1919 ofof 2828

TheThe fullfull setset ofof modulesmodules identifiedidentified byby ththee useuse ofof thethe threethree heuristicheuristic methodsmethods areare reportedreported in in the the following following Table Table 9. 9.

TableTable 9. 9. Modules Modules retrieved retrieved by by the the use use of of the the three three heuristic heuristic methods. methods.

IDID ModuleModule Type Type DFDF CTMCTM BFBF AA Import Import and and regulate regulate air air Main Main X X BB AllowAllow safely safely breathing breathing Main Main X X CC Protect Protect and and cover cover exposed exposed body body parts parts Main Main X X DD GuaranteeGuarantee filter filter efficiency efficiency Main Main X X EE GuaranteeGuarantee filter filter change change Main Main X X FF PersonalizePersonalize Auxiliary Auxiliary X X GG Display Display filtering filtering status status Auxiliary Auxiliary X X HH Display Display protection protection sterilization sterilization Auxiliary Auxiliary X X II Extract Extract water water after after virus virus separation separation Auxiliary Auxiliary X X X X LL Monitor Monitor protection protection efficiency efficiency Auxiliary Auxiliary X X MM ConvertConvert air air Main Main X X X X NN DissipateDissipate exhaust exhaust air air Main Main X X X X OO Block Block water water droplets droplets after after breathing breathing Main Main X X X X P Ergonomic for fixation and adaptation Main X P Ergonomic for fixation and adaptation Main X Q Dissipate heat Auxiliary X Q DissipateFigureFigure heat 15. Functional 15. Functional analysis analysis including including dominant dominant ﬂowflow Auxiliary heuristic heuristic methodfor method formodule module identification. identiﬁcation. X

TheThe technological technological implementationimplementation waswas was carriedcarried outout takingtaking intointo accountaccount allall thethe eco-eco- designdesign actions actions (i.e., (i.e., type type of of filter ﬁlterfilter material, material, ease ease of of disassembly), disassembly),disassembly), creating creating a aa morphological morphologicalmorphological matrix.matrix. An An excerpt excerpt of of the the results results is is shown shown in in Figures Figures 1616 andand 17.1717..

Figure 16. Morphological matrix for Module 2. FigureFigure 16. 16. MorphologicalMorphological matrix matrix for for Module Module 2. 2.

Figure 17. Morphological matrix for Module Auxiliary 1. FigureFigure 17. 17. MorphologicalMorphological matrix matrix for for Module Module Auxiliary Auxiliary 1. 1.

Sustainability 2021, 13, x FOR PEER REVIEW 20 of 28 Sustainability 2021, 13, 4948 19 of 26

All the design steps previously described were carried out by the same authors of this workAll the following design steps the design previously process described described were by carried [59]. In out particular, by the same a systematic authors of requirementsthis work following analysis the (also design known process as describedrequirements by [59engineering)]. In particular, was aadopted, systematic and re- severalquirements tools analysiswere used (also to knowndefine the as requirementslist of requirements engineering) (i.e., market was adopted, analysis, anddiscussion several forum,tools were checklist) used to define[68]. theAs list previously of requirements mentioned, (i.e., market for analysis, the development discussion forum, of functional/modularchecklist) [68]. As previously decomposition, mentioned, the approa for thech development proposed by of Pahl functional/modular and Beitz [59] was de- adoptedcomposition, for the the functional approach proposedanalysis, while by Pahl the and heuristic Beitz [ 59method] was adopted developed for theby Stone functional and Woodanalysis, [60] while was theused heuristic for the method module developed derivation. by StoneFinally, and the Wood last [step60] was dealt used with for the the definitionmodule derivation. of the morphological Finally, the last matrix, step dealtwhich with was the carried definition out ofwith the morphologicalbrainstorming sessionsmatrix, whichbetween was the carried authors out withof this brainstorming work, other sessions researchers, between and the students authors of of thisthe work, other researchers, and students of the mechanical engineering course, including mechanical engineering course, including systematic analysis of the industrial patents. systematic analysis of the industrial patents. After all analyses, it was possible to obtain a final mask result, combining the After all analyses, it was possible to obtain a final mask result, combining the different different solutions identified in the morphological matrix in order to fulfill the solutions identified in the morphological matrix in order to fulfill the requirements pre- requirements previously established and taking into account the eco-design guidelines viously established and taking into account the eco-design guidelines identified through identified through the initial LCA and MCI analyses. The device proposed in Figure 18 is the initial LCA and MCI analyses. The device proposed in Figure 18 is the simplest ver- the simplest version, which only considers the main modules, and it was developed by sion, which only considers the main modules, and it was developed by the authors of the authors of this work, together with classroom work performed with the students of this work, together with classroom work performed with the students of the mechanical the mechanical engineering course. engineering course.

FigureFigure 18. 18. FaceFace mask mask prototype prototype developed developed by by the the authors authors of of this this work. work.

InIn this device,device, respirationrespiration (inhalation(inhalation andand exhalation) exhalation) is is carried carried out out by by natural natural de- depressionpression (thus (thus avoiding avoiding electronic electronic devices, devices,which which increaseincrease thethe numbernumber of components withwith the the corresponding corresponding economic economic and and environm environmentalental impacts). impacts). For For the the filtering filtering phase, phase, a a widelywidely used used N95 N95 filter filter was was chosen, chosen, minimizing minimizing the the surface surface in in order order to to reduce reduce the the amount amount ofof material material used. used. In In addition, addition, it it was was decided decided to to activate activate the the filter filter surface surface with with metallic oxideoxide coating coating to to guarantee guarantee its its efficiency efficiency and and antimicrobial antimicrobial properties properties [22,67]. [22,67]. In In order order to to simplifysimplify the filterfilter changingchanging process,process, a a snap-fit snap-fit fixing fixing system system for for the the mask mask structure structure and and the thecover cover ofthe of the filter filter was was chosen chosen in order in order to have to have an economic an economic and and easy-to-use easy-to-use solution. solution. Fur- Furthermore,thermore, to optimizeto optimize shape shape and dimensions and dimensions based onbased the anthropometric on the anthropometric and ergonomic and ergonomiccharacteristics, characteristics, the mask wearability the mask wearability was studied was with studied a virtual with human a virtual model human (Figure model 19). (FigureThe ergonomic 19). The analysisergonomic was analysis performed was perf by theormed authors by the of authors this work of this using work a virtual using fita virtualassessment fit assessment method (by method means (by of CAD means environment) of CAD environment) to design a facialto design mask a thatfacial fits mask with thatpeople fits presentingwith people different presenting anthropometric different anth featuresropometric (e.g., the features distance (e.g., from the the distance ear’s tragus from theup toear’s the tragus top point up to in the bridgetop point of thein the nose, bridge the height of the ofnose, the tipthe ofheight the nose, of the skull tip width,of the nose,the distance skull width, between the eyes, distance nose width,between etc.) ey [69es,]. nose The studywidth, was etc.) developed [69]. The using study 3D was face developedscan data ofusing more 3D than face a scan hundred data of people more tothan find a hundred the most people proper to shape find the of a most facial proper mask. Since this phase is not the focus of this work, the ergonomic analysis is not discussed in detail. Sustainability 2021, 13, x FOR PEER REVIEW 21 of 28

Sustainability 2021, 13, 4948 20 of 26 shape of a facial mask. Since this phase is not the focus of this work, the ergonomic analysis is not discussed in detail.

FigureFigure 19. 19. ExampleExample of of the the developed developed facial facial mask mask during during the the ergonomic ergonomic test. test.

4.4. Discussion Discussion AfterAfter the the LCA LCA and and MCI analyses,analyses, itit is is possible possible to to observe observe that that a reduction a reduction of 650,000 of 650,000 tons (extending results to one year) in terms of CO2 eq. emissions can be obtained in Italy by tons (extending results to one year) in terms of CO2 eq. emissions can be obtained in Italy simply choosing reusable devices such as M5 instead of disposable masks such as M3. by simply choosing reusable devices such as M5 instead of disposable masks such as M3. In this way, benefits at the environmental level and the improvement of the circularity In this way, benefits at the environmental level and the improvement of the circularity can can be appreciated. This decision allows reducing GHGs and also leads to an economic be appreciated. This decision allows reducing GHGs and also leads to an economic benefit. After the development of the new mask designed by following the proposed benefit. After the development of the new mask designed by following the proposed methodology and the identified eco-design suggestions, an environmental impact analysis methodology and the identified eco-design suggestions, an environmental impact of this innovative prototype was carried out in order to make a comparison with M1 analysis of this innovative prototype was carried out in order to make a comparison with since both are devices with similar characteristics (reusable structure of the mask and M1 since both are devices with similar characteristics (reusable structure of the mask and disposable filters). For this new mask, the manufacturing process selected was injection disposable filters). For this new mask, the manufacturing process selected was injection molding, based on the guidelines defined above, highlighting the 3D printing process as a molding, based on the guidelines defined above, highlighting the 3D printing process as criticality. It was verified that the optimized model produced by injection molding using PP aas criticality. material It for was the verified mask structure that the obtainsoptimized better model results produced in almost by allinjection the indicators molding studied. using PPFigure as material 20 shows for the the normalized mask structure results; obtains in this better way, theresults percentage in almost advantage all the indicators obtainable studied.with the Figure new solution 20 shows can the be normalized inferred. The results; only categoryin this way, in which the percentage the new design advantage has a obtainablegreater impact with isthe FFP, new due solution to the usecan ofbe a inferred. fossil-based The materialonly category (i.e., PP). in which However, the thesenew Sustainability 2021, 13, x FOR PEER REVIEW 22 of 28 designimpacts has can a begreater mitigated impact by substitutingis FFP, due thisto the type use of plasticof a fossil-based with a well-known material and(i.e., largely PP). However,used bio-based these impacts plastic (i.e., can PLA)be mitigated [70]. by substituting this type of plastic with a well- known and largely used bio-based plastic (i.e., PLA) [70].

Figure 20. Normalized midpoints for the manufacturing phase (3D-printed mask vs. new mask Figure 20. prototype).Normalized midpoints for the manufacturing phase (3D-printed mask vs. new mask prototype). Results for the use phase, when disposable filters are used, are analogous to those ones shown in the mask production phase, confirming the design improvement. In addition, if filters are substituted with washable ones (following the eco-design guidelines that recommend the use of nondisposable filters), the proposed mask prototype has the lowest impact on the use phase of all devices studied, even lower than M5 (see Figure 21). This result is in line with recent work [71] developed on the same subject but using a different metric than LCA (i.e., the environmental impact index (EI)). Indeed, the mentioned work highlights that quilt and cotton are appropriate cloth-from-cotton material for making a nonmedical mask with the highest quality of filtration efficiency and breathability while having the lowest environmental impact, whereas polypropylene fabric is the worst material in terms of environmental impact. Alternatively, another interesting research work [72] tried to investigate the adoption of recycled material from reprocessed FFP2 face masks. The study demonstrated how the reprocessed material has a lower environmental impact and financial burden than new disposable face masks without compromising qualifications and filtration efficiency. Concerning the maintenance phase for this mask, the use of ethanol for the main structure (mask body) and soap and water for the filters allows combining the advantages of the M1 and M5. This significant benefit is mainly due to the fact that the greatest efforts of the eco-design process are concentrated on the improvement of the use phase. Sustainability 2021, 13, 4948 21 of 26

Results for the use phase, when disposable filters are used, are analogous to those ones shown in the mask production phase, confirming the design improvement. In addition, if filters are substituted with washable ones (following the eco-design guidelines that recommend the use of nondisposable filters), the proposed mask prototype has the lowest impact on the use phase of all devices studied, even lower than M5 (see Figure 21). This result is in line with recent work [71] developed on the same subject but using a different metric than LCA (i.e., the environmental impact index (EI)). Indeed, the mentioned work highlights that quilt and cotton are appropriate cloth-from-cotton material for making a nonmedical mask with the highest quality of filtration efficiency and breathability while having the lowest environmental impact, whereas polypropylene fabric is the worst material in terms of environmental impact. Alternatively, another interesting research work [72] tried to investigate the adoption of recycled material from reprocessed FFP2 face masks. The study demonstrated how the reprocessed material has a lower environmental impact Sustainability 2021, 13, x FOR PEER REVIEW 23 of 28 and financial burden than new disposable face masks without compromising qualifications and filtration efficiency.

Figure 21. Normalized midpoints for the use and EoL phases (new mask prototype with washable Figurefilters vs. 21. washableNormalized mask). midpoints for the use and EoL phases (new mask prototype with washable filters vs. washable mask). Summarizing, it is possible to affirm that the usefulness of this type of methodologies and approachConcerning to developing the maintenance new sustainable phase face masks for this has mask,been clearly the usedemonstrated of ethanol for the main structureby this study. (mask Despite body) the fact and that soap to date and itwater has only for been the applied filters in allows the context combining of face the advantages masks development, it can be certainly used for the development of other widely used ofprotection the M1 anddevices M5. (e.g., This suits, significant gloves), benefitreplicating is mainly the process due towith the factthe thatneeded the greatest efforts ofcustomizations the eco-design (e.g., processthe definition are concentratedof specific eco-design on the guidelines, improvement use of appropriate of the use phase. KPIs Summarizing,for each product) and it is obtaining possible environm to affirmental that improvements the usefulness also in these of this products. type of methodologies and approachFinally, some to limitations developing of this new study sustainable should be mentioned. face masks For hasexample, been a clearlyunivocal demonstrated by EoL scenario was studied. If sanitary landfills would have also been considered an end- thisof-life study. scenario, Despite a reduction the fact in impacts that to could date have it has resulted, only been especially applied in the in case the of context M3 of face masks development,and M4 devices, itwhich can beare certainlythe ones that used genera forte the the developmentmost plastic waste. of otherHowever, widely it is used protection devicesclear after (e.g., studying suits, the gloves),results of this replicating research that the even process if a sanitary with end the of needed life had been customizations (e.g., theconsidered, definition the values of specific of the circularity eco-design index guidelines, would not have use changed of appropriate since the method KPIs for each product) andused obtaining to calculate environmental MCI makes no improvementsdistinction between also landfill in these types. products. To avoid this limitation, the circularity study can be extended using other additional indicators. Despite incinerationFinally, shows some high limitations GWP (as confirmed of this studyby the study should [34]) be it is mentioned. a promising option For example, for a univocal EoLthe management scenario was of this studied. waste compared If sanitary with landfills landfilling would among haveall the also others been impact considered an end- of-lifecategories. scenario, a reduction in impacts could have resulted, especially in the case of M3 and M4Lastly, devices, it should whichalso be taken are theinto consider ones thatation generate that the results the of most the M5 plastic mask vary waste. However, it depending on the material used and the number of times it can be washed without losing isfiltering clear afterproperties, studying this being the a results key factor of for this both research the environmental that even and ifa circularity sanitary end of life had beenperformance. considered, the values of the circularity index would not have changed since the method used to calculate MCI makes no distinction between landfill types. To avoid this limitation, the circularity study can be extended using other additional indicators. Despite incineration shows high GWP (as confirmed by the study [34]) it is a promising option for the management of this waste compared with landfilling among all the others impact categories. Sustainability 2021, 13, 4948 22 of 26

Lastly, it should also be taken into consideration that the results of the M5 mask vary depending on the material used and the number of times it can be washed without losing ﬁltering properties, this being a key factor for both the environmental and circularity performance.

5. Conclusions The present paper focuses on the proposal of an eco-design methodology to support designers in the development of environmentally sustainable face masks. The work was performed by using well-known methods for the environmental and circularity analysis of products (i.e., LCA, MCI). Consolidated procedures to formalize useful knowledge on past experiences (i.e., the definition of eco-design guidelines) and to reuse it for product improvement projects (i.e., systematic approach to design with specific constraints due to the pandemic situation) were followed to derive eco-design action in the development of sustainable facial masks. To date, this study can be considered the first attempt in the protection devices sector to contribute to the preservation of the natural environment while facing the world COVID-19 emergency, with a preventive approach to be applied during the design phase. More generally, considering that the risk of future unexpected events such as the COVID-19 pandemic is not null, it can be affirmed that this kind of methodology will be useful each time a very high demand for disposable fossil-based products (as face masks) will be needed to face an emergency situation. Results obtained with the first methodology step allow having an overview of the environmental performance of five common face masks and lay the foundation for the successive definition of design best practices. Reusable masks (M1 and M5) have clear advantages, compared to disposable products (M2, M3, and M4). However, these products also cannot be considered really sustainable, and different criticalities were identified (e.g., use of fossil-based or impactful materials, open-loop end of life). The proposed redesigned project demonstrated that by starting from the knowledge of the environmental performance of well-known products, it is possible to obtain significantly improved face masks in all the used KPIs by preventing observed criticalities and applying the best design choices concerning material selection, sustainable manufacturing processes, and durability of mask components. Future developments will regard the following points: • LCA analysis refinements: an extension of the environmental and circularity analyses, which include additional details (e.g., specific inventory for the nonwoven fabrics manufacturing, the inclusion of the waste collection phase within the system boundaries, etc.) will help in a definition of more specific guidelines and actions; • LCA analysis scenarios: additional scenarios (e.g., sanitary landfill EoL, different typologies of washable masks, etc.) will allow defining a larger set of design guidelines ad to provide the best solution for policymakers in this complex context; • Consequential LCA: since the production and disposal of anti-SARS-CoV-2 masks are becoming of global importance for the socioeconomic management of the pandemic, an additional consequential LCA will be able to estimate how the global environmental burdens are affected by the production and use of this product. Consequential LCA could bring some additional important conclusions to couple with the results of this study. Another direction of research could be the definition of multiobjective design methodologies dedicated to the sustainable development of face masks looking at the promotion of two combined targets: (i) the minimization of negative environmental impacts (as in the present paper) and (ii) the maximization of other performance (e.g., filtration efficiency, cost estimation, etc.).

Supplementary Materials: The following are available online at https://www.mdpi.com/article/10 .3390/su13094948/s1, Excel ﬁle. Sustainability 2021, 13, 4948 23 of 26

Author Contributions: Conceptualization, C.F.; methodology, M.M.; software, N.B.R. and C.F.; validation, M.M.; formal analysis, G.F.; investigation, G.F., N.B.R. and M.M.; resources, C.F. and M.M.; data curation, M.M.; writing—original draft preparation, N.B.R.; writing—review and editing, C.F., G.F. and M.M.; visualization, C.F. and M.M.; supervision, C.F.; project administration, C.F. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conﬂicts of Interest: The authors declare no conﬂict of interest.

List of Acronyms

Abbreviation BF Branching flows BFE Bacteria Filtration Efficiency CED Cumulative Energy Demand CTM Conversion-transmission modules DF Dominant flow ED Ecosystem EoL End of Life EU European Union FEP Freshwater eutrophication potential FETP Freshwater ecotoxicity potential GHG Greenhouse gas GWP Global warming potential HH Human Health HTP Human toxicity potential KPI Key Performance Indicator LCA Life Cycle Assessment LCE Life Cycle Engineering LCI Life Cycle Inventory LCIA Life Cycle Impact Assessment LCT Life Cycle Thinking M1 Mask type 1 M2 Mask type 2 M3 Mask type 3 M4 Mask type 4 M5 Mask type 5 MCI Material Circularity Indicator METP Marine ecotoxicity potential ODP Ozone depletion potential OFP Photochemical oxidant formation potential PE Polyester PFE Particle Filtration Efficiency PLA Polylactic acid PMFP Particulate matter formation potential PP Polypropylene PPE Personal Protective Equipment PU Polyurethane RA Resources TAP Terrestrial acidification potential TETP Terrestrial ecotoxicity potential UV Ultraviolet WCP Water consumption potential WHO World Health Organization Sustainability 2021, 13, 4948 24 of 26

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