recycling

Article The Recycling of Waste Laminated through Decomposition Technologies

L’ubomír Šooš, Miloš Matúš * , Marcela Pokusová , Viliam Caˇckoandˇ Jozef Bábics

Faculty of Mechanical Engineering, Slovak University of Technology in Bratislava, Námestie Slobody 17, 812 31 Bratislava, Slovakia; [email protected] (L’.Š.);[email protected] (M.P.); [email protected] (V.C.);ˇ [email protected] (J.B.) * Correspondence: [email protected]; Tel.: +421-257-296-573

Abstract: Laminated glass is ever more frequently used nowadays. This applies to the automobile industry and the construction industry. In cars, this refers mostly to the front and rear windows, whereas in construction, technical is used for railings and window glass. The task of this type of glass is to provide sufficient resistance against mechanical impact and unpleasant weather conditions. At the same time, if it is damaged, it has to break into the smallest possible pieces, or, wherever possible, the glass should remain intact on the interlayer film to prevent shards from injuring people and animals in the immediate vicinity. The paper deals with the recycling of laminated glass, especially with the effective separation of glass (in the form of cullet) from the (PVB) interlayer film. The experimental research is focused on the mechanical separation of glass from the interlayer film by vibration, and also on the chemical cleaning of PVB film in order to allow subsequent recycling of both materials. The results quantify the efficiency of

 mechanical separation in the form of weight loss of the sample of laminated glass and define the  particle size distribution of glass cullet, which is an important parameter in the possibility of glass

Citation: Šooš, L’.;Matúš, M.; recycling. The research leads to a methodology proposal for the separation of glass and PVB film and Pokusová, M.; Caˇcko,V.;ˇ Bábics, J. the design of equipment for this method. The Recycling of Waste Laminated Glass through Decomposition Keywords: laminated glass; ; recycling; PVB recycling; automotive waste; mechanochem- Technologies. Recycling 2021, 6, 26. ical separation https://doi.org/10.3390/ recycling6020026

Academic Editor: Michele John 1. Introduction The significance of recycling glass is very great from the ecological, energy, and Received: 28 December 2020 technical standpoints, and accordingly, glass is an important secondary raw material in the Accepted: 12 April 2021 Published: 15 April 2021 form of waste. According to data from The International Organization of Motor Vehicle Manufacturers (OICA), global car production is about 90 million cars per year. Assuming

Publisher’s Note: MDPI stays neutral that one vehicle windshield contains approximately 13 kg of glass and 1 kg of PVB film, with regard to jurisdictional claims in the total amount of glass for windshield production is approximately 1170 mil. kg and published maps and institutional affil- 90 mil. kg of PVB film per year. The total worldwide amount of PVB film produced for the iations. automotive and construction industries is estimated at around 170 mil. kg per year [1–4]. Production lines of world-renowned manufacturers such as Solutia, DuPont, Sekisui, and Kuraray produce thousands of tons of PVB film per year for automotive and construction use, which is further pressed into laminated glass. Worldwide, 65% of all PVB films are used in automotive applications [1,4]. By-products from processed PVB films (5%) and Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. trimmed films (less than 10%) must also be included in the total produced quantities. This This article is an open access article represents a total amount of 105 million kg of waste of PVB films per year. According to distributed under the terms and the estimates of the Automotive Industry Association of Slovak Republic [5], each year conditions of the Creative Commons in Slovakia, there is at hand available about 13,200 t of flat glass waste from the building Attribution (CC BY) license (https:// trade and from automobile glass, around 3600 t. creativecommons.org/licenses/by/ Researchers and recycling companies are increasingly focusing on the recycling and 4.0/). recovery of end-of-life vehicle (ELV) materials. This is due to various strict government

Recycling 2021, 6, 26. https://doi.org/10.3390/recycling6020026 https://www.mdpi.com/journal/recycling Recycling 2021, 6, 26 2 of 13

directives and environmental regulations, such as the Resource Conservation and Recovery Act (RCRA) of the USA [6], K-REACH [7], and the EU directive on ELV [4]. European directive number 2000/53/CE represents a challenge for the automotive industry since it sets a recovery limit of 95% by weight of ELV, of which 85% by recycling. The automotive industry supports these efforts in all EU countries. However, material recycling has generally been oriented to materials such as steel and aluminum and not on less attractive wastes such as glazing [8]. Clearly, it is necessary to significantly increase the efficient recycling of as well. The removal of glazing is nonetheless given an explicit mention in the minimum operations obligations when ELV comes to dismantling [9]. The recovery priority should be the reuse of secondary raw material from the waste glass as input material for manufacturing new glass. When the secondary raw material fulfills the required technical parameters, the quality of the product is equal to a product manufactured from the primary material. By recycling glass waste, we save mainly primary material resources, energy, and water and avoid the overloading of landfills. Energy demands on the production of container glass fluctuate around 4.5–5 GJ per ton of molten glass [10]. If the proportion of shards in a batch increases by 10%, the energy intensity of the glass production will decrease by 2.5% (starting value is a 35% batch of shards). For container glass, the emission factor varies at present between 350 and 400 kg CO2/t of molten glass. If the batch contains 35% of shards, the volume of CO2 emissions is reduced by about 18.5%, and with a 60% share of shards, the volume of CO2 emissions is reduced by up to 32% [10]. The technology for manufacturing laminated glass depends on the usage of a type of interlayer. In the process of technical layering, elastic material with good adhesiveness to glass is placed between the glass panes. The materials usually used include polyvinyl butyral (PVB), ethyl vinyl acetate (EVA), or the ionoplast SentryGlassPlus (SGP). PVB is the most frequently used material for the manufacture of interlayer film in laminated glass. Laminated glass with film is usually produced under high pressure and temperature in an autoclave. Two glass planes are mostly joined by a film with a strong adhesive bond. However, this adhesion is an obstacle in the recycling process because the separation of the laminated film from the glass cullet causes the biggest problems. It is possible to obtain clean glass by separation, but the polymer is often contaminated with glass or other foreign substances to such an extent that it is unsuitable for further use or recycling and ends up mostly in landfills. This is because the large glass content precludes burning it [2]. For perfect separation and achieving clean phases of the laminate, according to the literature [1,4,11–14], a wet method of separating the layers of glass from the film seems to be the only usable one. This uses the reverse effect of the connecting technology— with a decreasing mixture of the film, its adhesion to glass increases. The basis of the decomposition technology is therefore the decrease of the PVB adhesiveness through an increasing content of water in the film. The problem with this method is the economic effectiveness of the entire technological process. Based on scientific publications and research reports in this field [1,4,9,13,15–19], the technology of combined separation must always be used for the effective separation of PVB film from the glass. This includes mechanical treatment by breaking the glass or separating the glass (either with or without breaking the film), followed by chemical separation under the thermal influence, and finally mechanical, e.g., hydrodynamic cleaning, washing, and drying. All the mentioned technological influences affect the properties of the recycled PVB. Therefore, it is necessary to pay attention to research into changes in the PVB properties during processing and their impact on recycling.

1.1. Use and Properties of Recycled Materials Processed clear glass, in the form of cullet, can be reused in the manufacture of glass products, and it is a replacement for conventional raw materials. The glass industry enjoys two advantages by recycling glass cullet—cullet is relatively cheaper than the primary Recycling 2021, 6, 26 3 of 13

material (silica) and less electricity is used to melt it in the furnace [4]. In addition to these economic benefits, cullet recycling saves many natural resources. The method of recycling and the applicability of cullets depend on their purity and fraction size. Larger clean cullets are immediately suitable in the glass industry for the production of glass products. The small size of the glass fractions in the form of glass powder can be successfully used for the production of foam glass as thermal insulation for buildings and acoustic insulation. This application is analyzed in detail in works [20–22]. The properties of this material are also investigated in detail in works [23,24]. Waste glass of various fractions and purity is widely used in the construction industry. Much scientific research deals with new perspectives of recycled glass in concrete, mortars, and building materials [25–36]. Experimental research [12] investigating the impact of recycling on the properties of PVB film has shown that the reuse of recycled PVB film in laminated glass is conditioned by quantification of the plasticizer loss that occurred during the windshield recycling and the preparation process of PVB blends. The amount of plasticizer affects the ratio of the viscosity of the dispersed phase and the PVB matrix, which in turn controls the morphology of PVB blends and their properties. The results of scientific research [4] show the characteristics of recycled PVB, in com- parison with new PVB, depend on the effect of temperature in order to determine the suitability for reuse. Recycled PVB changes due to temperature were evaluated by means of thermal gravimetric analysis (TGA). Research has shown that the stable decomposition of new PVB begins at 200 ◦C, but a rapid decomposition follows from 300 ◦C In con- trast, recycled PVB has two different temperature ranges with rapid decomposition, i.e., 180–350 ◦C and 350–550 ◦C. The first rapid decomposition is caused by the decomposition of plasticizers in recycled PVB in the temperature range 180–350 ◦C. Very similar exper- imental results are reported by the study [1]. The average weight loss of recycled PVB, caused only due to the decomposition of plasticizers, was 13.62% in the temperature range 250–350 ◦C. In this study, the content of plasticizers in PVB was found to be 20 and 25% by weight by mass spectroscopy. The investigated tensile properties of samples of new and recycled PVB film reported in work [1] were measured at room temperature on standard tensile samples in the form of a “dumbbell”. They were cut directly from the films. Recycled and new PVB had very similar properties, but recycled PVB achieved higher tensile strength. Research has shown that the recycled material did not differ significantly from the original PVB polymers since they had a similar chemical composition and weight fraction of plasticizer. Original and recycled material can be mixed together, while there were no incompatibilities between different varieties. Problems may arise due to the loss of plasticizer from recycled material depending on the selected processing conditions. However, the addition of dibutyl sebacate can compensate for this deficiency. It has also been found in the laboratory that recycled types of PVB can be used to laminate without loss of optical purity.

1.2. Separation Technologies Literature and patent studies have shown [4,37,38] that there are, in general, four valid methods for the separation of laminated glass waste—mechanical, thermodynamic, chemi- cal, and combined methods. The most frequently used is the mechanical disintegration way, based on the principle of multiple disintegrations of glued waste and the consequent separation of the particles of glass and film. On lines for the recycling of laminated glass, purely mechanical or combined separation is mostly applied, depending on the required final product and its quality. From the standpoint of working media present in the sepa- ration process, the methods and their appertaining technologies can be grouped into two categories—the so-called dry (mechanical or thermodynamic separating) and wet methods (e.g., chemical separation). Recycling 2021, 6, 26 4 of 13

The principle of mechanical separation is the subject of patent EP0249094 [11]. The essence of the patent is multiple cycles of combined disintegration and separation of fragments of the laminated glass. Another mechanical separation variant is the American Patent US8220728 [39], which is primarily focused on the effective separating of recycled PVB film. The essence of the invention is that in the first step, multi-laminated glass is crushed and splintered in a cylindrical chamber equipped with crushing hammers of a specific shape, while the splinters fall through a screen to the bottom of the chamber. The problem of mechanical separation is also addressed by patent SK286370, which makes use of the principle of double rotating rollers situated around a longitudinal axis with a treated surface. One of the pair of rollers is placed immovably in a bearing structure, and the second is placed so as to be displaceable and adjustable. The pairs of rotating rollers are arranged vertically and behind each other at an established distance in the bearing structure, with the distance between the rollers of the following pair being less than that between the rollers of the preceding pair. One example of a combined wet technology is the continuous line from the company Xinology Co., Ltd., Hong Kong, for the recycling of laminated glass and the separation of PVB or EVA film from glass residues. Apart from the mechanical technology, the line also uses flotation technology, a washer, and a dryer [40]. The Danish company Shark Solution A/S also successfully undertakes mechanical recycling, and their patented technology produces ground glass with a particle size of 0–5 mm containing less than 1% contaminated materials and films, allowing it to be de- ployed in high-performance applications [41]. Our institute, in cooperation with the company MAVEBA s.r.o [42], has developed equipment that acts as a prototype for recycling automobile glass. In contrast to the patented solution EP0567876 [37], the processing of the waste laminated glass takes place in equipment based on the principle of two rotating shafts with chains, at the ends of which are steel impact hammers. The ground mixture is shifted to a rotating sorter where it is further sorted into individual batches of glass shards and film. The output of the mill for side and back windows is 200 kg/h, while its total annual capacity with a two-shift operation is 1600 t. Compared to the EP0567876 patent, Maveba technology has hammers mounted on chains rather than rigid bars.

1.3. Conclusion of Analysis From the results of the analysis, there arises one significant conclusion—that mechani- cal disintegration technology itself, along with the subsequent separation of the individual components of laminated glass, is cheap, but at the same time, the present technology is highly noisy and dusty. In addition, it does not facilitate the efficient recovery of waste. Even though there is interest in the film and chips, glass factories and chemical plants do not want to buy secondary raw materials that do not fulfill the required criteria for cleanliness. The recoverability of clean glass fragments and film available with currently available technologies is only 50–60%. The residue of the unseparated waste finishes up on landfills. In combination with other technologies, efficiency and the purity of the individual components will surely increase, but the price for this technology will also rise sharply and remain economically unviable for small processing activities. Accordingly, demand has arisen to develop a process and equipment that will be tech- nologically acceptable and economically viable for small- and medium-sized enterprises with an annual capacity of 1000–2000 t. The aim of our experimental activities was the research and verification of a variety of separation principles.

1.4. Scientific Hypothesis The basic scientific hypothesis that we adopted in the research for solving the given task was that the proposed technology should meet the requirement of keeping a “compact Recycling 2021, 6, x FOR PEER REVIEW 5 of 14

1.4. Scientific Hypothesis The basic scientific hypothesis that we adopted in the research for solving the given task was that the proposed technology should meet the requirement of keeping a “compact film” after the technological process of decomposition. In our opinion, in this way, we will achieve the highest degree of purity in the individual batches. This implies successfully designing a technology such that in the decomposition process disintegration of the glass waste does not occur. This process could take place in such a way that the separation of the glass could be achieved by breaking the glass and then by subsequently Recycling 2021, 6, 26peeling and scraping the shards from the film so that the film remains as integral as 5 of 13 possible.

2. Materials and Methods film” after the technological process of decomposition. In our opinion, in this way, we will 2.1. Materials achieve the highest degree of purity in the individual batches. This implies successfully For all the designingexperiments a technology described in such this that study, in the laminated decomposition glass was process used in disintegration the form of the glass of windshields wastefrom the does same not car occur. manufacturer This process brand. could The take tested place windshields in such a way consist that theof separation of two glass layersthe of a glass thickness could of be 2.5 achieved mm and by the breaking PVB interlayer the glass of and a thickness then by of subsequently 0.76 mm. peeling and All the tested windshieldscraping the samples shards were from made the film from so two that float the filmglass remains layers modified as integral to asheat- possible. tempered glass and with a PVB interlayer of Trosifol® Standard. 2. Materials and Methods 2.2. Laminated Glass2.1. MaterialsBreakage Tests Breakage tests Forof laminated all the experiments windshields described and testing in this of study, the laminatedsuitability glassof the was tool used in the form shape for breakingof windshields were realized. from Experiment the same caral work manufacturer for testing brand. various The punch tested profiles windshields consist of was carried outtwo in this glass stage. layers The of breakage a thickness tests of of 2.5 the mm windshield and the PVB samples interlayer (Figure of a1) thickness were of 0.76 mm. conducted to determineAll the tested the force windshield at which samplesthe glass weredeformed made and from at what two floatdegree glass of force layers modified to breakage occurred.heat-tempered Another very glass andimportant with a PVBoutput interlayer is the knowledge of Trosifol® Standard.of which tool geometry (sharp or rounded) allows the glass to crack into fragments of identical size. Two punches2.2. were Laminated used Glassfor the Breakage tests—the Tests first was a “V” shape with a top angle of 90° (Figure 1a), and Breakagethe second tests was of an laminated “S” cylinder windshields shape (Figure and testing 2a) with of the a radius suitability of 50 of the tool shape mm. The samplefor size breaking was ca. were 100 × realized. 70 mm. The Experimental usage of the work V punch for testing (Figure various 1b) showed punch profiles was that the glass layercarried was outto the in thisgreatest stage. degree The breakagebroken in teststhe area of the of the windshield punch edge, samples while (Figure 1) were the other parts ofconducted the glass sample to determine were only the forceslightly at cracked which the (Figure glass 1c). deformed It also remained and at what degree of firmly adhered forceto the breakage film. A force occurred. of 0.05 Another kN was very required important to crack output the glass, is the and knowledge a force of which tool higher than 2 kNgeometry was required (sharp to or achiev rounded)e full allows cracking the in glass the topressing crack into form. fragments of identical size.

Figure 1. BreakingFigure 1.laminatedBreaking glass laminated by “V” glass punch by “V”on laboratory punch on testing laboratory press. testing press.

Two punches were used for the tests—the first was a “V” shape with a top angle of 90◦ (Figure1a), and the second was an “S” cylinder shape (Figure2a) with a radius of 50 mm. The sample size was ca. 100 × 70 mm. The usage of the V punch (Figure1b) showed that the glass layer was to the greatest degree broken in the area of the punch edge, while the other parts of the glass sample were only slightly cracked (Figure1c). It also remained Recycling 2021, 6, x FOR PEER REVIEW 6 of 14 firmly adhered to the film. A force of 0.05 kN was required to crack the glass, and a force higher than 2 kN was required to achieve full cracking in the pressing form.

Figure 2. BreakingFigure 2.laminatedBreaking glass laminated by “S” glass punch by on “S” laboratory punch on testing laboratory press. testing press.

The “S” punch (Figure 2b) was simulated in conformity with the presumed cylinder profile of the future tool. Right from the first stroke of the press, the sample was more significantly cracked than with the V punch. This sample in the press was then progressively broken five times in succession, with the glass turned through 180° after each crunch (Figure 2c). The breaking force delivered onto the glass after each turning was always about 2 kN, with the exception of the final turning when the glass was so shattered that it bent under its own weight. The results of the testing on the “S” punch showed the glass stayed stuck to the film, even though it required very little force to release it. The output of these pretests is the value of the effective cracking force that is needed to crack the glass on pieces of similar shape and size without breaking the PVB interlayer. We, therefore, focused our further attention on finding accompanying operations or procedures to address the issue of separating the broken glass from the film. The next step was an experiment for separating the broken glass by the action of heat. Pieces of dimensions of less than 5 × 5 mm could be easily mechanically separated from the film of PVB interlayer, but pieces of larger dimensions were harder to separate or could not be separated from the film at all. The next step was to test the reaction of the broken windshield glass to heating with a hot air pistol and then rapid cooling in a liquid of temperatures down to −25 °C. The liquid was injected by syringe onto the broken glass, between the glass and the film layers. After heating the sample of crushed laminated glass and then injecting the frozen liquid (a solution of methanol and distilled water) on the border between the glass and the film, it became possible to separate the glass easily because the liquid reached under the individual fragments, as a result of which the final degradation of the adhesive strength occurred.

2.3. Vibration Tests The second stage of the experimental work continued on the laboratory model of vibration equipment constructed for this purpose. The experimental equipment using mechanical vibration for grinding the samples of laminated glass is documented in Figure 3. The functional part of the machine is made up of two iron plates of 400 × 400 mm. The plates are connected together by a hinge at the bottom, and flexibly by springs on top. One plate is fixed to the base, while a vibrator (0.18 kW, 2880 rpm, centrifugal force 2.26 kN) is placed on the second plate. The working surfaces of both plates are made as a profile from rasterized horizontally placed cylindrical rods of 10 mm diameter. Recycling 2021, 6, 26 6 of 13

The “S” punch (Figure2b) was simulated in conformity with the presumed cylinder profile of the future tool. Right from the first stroke of the press, the sample was more significantly cracked than with the V punch. This sample in the press was then progres- sively broken five times in succession, with the glass turned through 180◦ after each crunch (Figure2c). The breaking force delivered onto the glass after each turning was always about 2 kN, with the exception of the final turning when the glass was so shattered that it bent under its own weight. The results of the testing on the “S” punch showed the glass stayed stuck to the film, even though it required very little force to release it. The output of these pretests is the value of the effective cracking force that is needed to crack the glass on pieces of similar shape and size without breaking the PVB interlayer. We, therefore, focused our further attention on finding accompanying operations or procedures to address the issue of separating the broken glass from the film. The next step was an experiment for separating the broken glass by the action of heat. Pieces of dimensions of less than 5 × 5 mm could be easily mechanically separated from the film of PVB interlayer, but pieces of larger dimensions were harder to separate or could not be separated from the film at all. The next step was to test the reaction of the broken windshield glass to heating with a hot air pistol and then rapid cooling in a liquid of temperatures down to −25 ◦C. The liquid was injected by syringe onto the broken glass, between the glass and the film layers. After heating the sample of crushed laminated glass and then injecting the frozen liquid (a solution of methanol and distilled water) on the border between the glass and the film, it became possible to separate the glass easily because the liquid reached under the individual fragments, as a result of which the final degradation of the adhesive strength occurred.

2.3. Vibration Tests The second stage of the experimental work continued on the laboratory model of vibration equipment constructed for this purpose. The experimental equipment using mechanical vibration for grinding the samples of laminated glass is documented in Figure3 . The functional part of the machine is made up of two iron plates of 400 × 400 mm. The plates are connected together by a hinge at the bottom, and flexibly by springs on top. One plate is fixed to the base, while a vibrator (0.18 kW, 2880 rpm, centrifugal force 2.26 kN) is Recycling 2021, 6, x FOR PEER REVIEWplaced on the second plate. The working surfaces of both plates are made as a profile from7 of 14

rasterized horizontally placed cylindrical rods of 10 mm diameter.

FigureFigure 3.3.Vibration Vibration equipment.equipment. The actual measuring took place on three intact test samples of the windshield The actual measuring took place on three intact test samples of the windshield (Figure 4), each of 395 × 295 mm. Each sample was crushed by its own weight six times (Figure4 ), each of 395 × 295 mm. Each sample was crushed by its own weight six times (three times from each side) while moving through the equipment. The samples’ weight (three times from each side) while moving through the equipment. The samples’ weight was measured before the tests and after each individual crushing cycle. The measured was measured before the tests and after each individual crushing cycle. The measured values of the samples’ weight are shown in Table 1. values of the samples’ weight are shown in Table1.

Figure 4. Sample of windshield before tests.

Table 1. Evolution of weight loss of analyzed samples over six vibration cycles.

Sample Weight (g) Original After 1st Cycle After 2nd Cycle After 3rd Cycle After 4th Cycle After 5th Cycle After 6th Cycle Sample 1 1300 862 558 396 307 192 99 Sample 2 1271 934 594 470 352 213 98 Sample 3 1294 844 540 433 345 225 105 Sample 4 1296 886 572 416 312 198 97 Sample 5 1283 910 580 450 349 217 106 Sample 6 1284 846 540 433 345 215 101 Average Value 1288 880 564 433 335 210 101 Average Weight Loss - 408 326 131 98 125 109 The glass that peeled off the PVB film during the vibration cycles was captured in a collection vessel situated below the laboratory vibration equipment. The separated glass was subjected to granulometric analysis to determine the weight and proportion of glass in five-size cullet samples. To classify the glass particles, a Retsch AS 200 sieving device was used. The results of the granulometric analysis are presented in Table 2. From the table, it can be inferred that the highest weight ratio of cullet sample II with particles of size 2–4 mm is 36% in all the cases. The individual samples of glass after sieve analysis and the final PVB interlayer film are shown in Figure 5. Recycling 2021, 6, x FOR PEER REVIEW 7 of 14

Figure 3. Vibration equipment. The actual measuring took place on three intact test samples of the windshield (Figure 4), each of 395 × 295 mm. Each sample was crushed by its own weight six times Recycling 2021, 6, 26 (three times from each side) while moving through the equipment. The samples’ weight7 of 13 was measured before the tests and after each individual crushing cycle. The measured values of the samples’ weight are shown in Table 1.

FigureFigure 4.4.Sample Sample ofof windshieldwindshield beforebefore tests. tests.

Table 1.TableEvolution 1. Evolution of weight of lossweight ofanalyzed loss of analyzed samples samples over six over vibration six vibration cycles. cycles. Sample Weight (g) Original After 1st Cycle After 2nd Cycle After 3rd Cycle After 4th Cycle After 5th Cycle After 6th Cycle After 1st After 2nd After 3rd After 4th After 5th After 6th SampleSample Weight 1 (g) Original1300 862 558 396 307 192 99 Sample 2 1271 Cycle 934 Cycle 594 Cycle 470 Cycle 352 Cycle213 Cycle98 SampleSample 1 3 13001294 862844 558540 396433 307345 192225 99105 SampleSample 2 4 12711296 934886 594572 470416 352312 213198 9897 SampleSample 3 5 12941283 844910 540580 433450 345349 225217 105106 SampleSample 4 6 12961284 886846 572540 416433 312345 198215 97101 SampleAverage 5Value 1283 1288 910880 580564 450433 349335 217210 106101 AverageSample Weight 6 Loss 1284- 846 408 540326 433131 34598 215125 101109 Average Value 1288 880 564 433 335 210 101 Average Weight Loss -The 408 glass that peeled 326 off the PVB 131 film during 98 the vibration 125cycles was captured 109 in a collection vessel situated below the laboratory vibration equipment. The separated glass was subjected to granulometric analysis to determine the weight and proportion of glass in five-sizeThe glass cullet that samples. peeled off To the classify PVB filmthe glass during particles, the vibration a Retsch cycles AS was200 sieving captured device in a collectionwas used. vessel The results situated of belowthe granulometric the laboratory an vibrationalysis are equipment. presented in The Table separated 2. From glass the wastable, subjected it can be to inferred granulometric that the analysis highest toweight determine ratio theof cullet weight sample and proportion II with particles of glass of insize five-size 2–4 mm cullet is 36% samples. in all the To classifycases. The the individual glass particles, samples a Retsch of glass AS 200after sieving sieve analysis device wasand used.the final The PVB results interlayer of the film granulometric are shown analysisin Figure are 5. presented in Table2. From the table, it can be inferred that the highest weight ratio of cullet sample II with particles of size 2–4 mm is 36% in all the cases. The individual samples of glass after sieve analysis and the final PVB interlayer film are shown in Figure5.

Table 2. Particle size analysis of cullet after vibration tests of glass samples 1 to 6.

Cullet Sample I Cullet Sample II Cullet Sample III Cullet Sample IV Cullet Sample V (above 4 mm) (2–4 mm) (1–2 mm) (0.5–1 mm) (under 0.5 mm) Glass sample 1 (g) 42 423 342 164 212 Glass sample 2 (g) 45.5 404 340 160 203 Glass sample 3 (g) 37 442 329 159 205 Glass sample 4 (g) 42 422 340 158 210 Glass sample 5 (g) 41.5 415 331 160 203 Glass sample 6 (g) 38 432 328 165 209 Average weight (g) 41 423 335 165 209 Average weight ratio (%) 3.5 36.2 28.8 13.8 17.7 Recycling 2021, 6, 26 8 of 13 Recycling 2021, 6, x FOR PEER REVIEW 8 of 14

Recycling 2021, 6, x FOR PEER REVIEW 9 of 14

Figure 5. Samples of glass cullet after sieve analysis, and the final polyvinyl butyral (PVB) inter- thatFigure the highest 5. Samples average of glass value cullet of afterseparated sieve analysis, glass weight, and the about final polyvinyl 36.2%, was butyral in size (PVB) section layer film. II-culletinterlayer sample film. II, with parts from 2 mm to 4 mm, and the least, about 3.5%, occurred in size3. section Results I, andwith Discussion glass particles above 4 mm. The percentage share of the individual sections3.1.3. Results Vibration is illustrated and Test Discussion in Figure 6. 3.1. VibrationA summary Test and evaluation of the results attained from experimental measurements, Table 2. Particle size analysis of cullet after vibration tests of glass samples 1 to 6. the averageA summary of the and original evaluation weight, of the the results averages attained of the from weights experimental of the samples, measurements, and the Cullet Sample I Cullet Sample II Cullet Sample III Cullet Sample IV Cullet Sample V developmentthe average of of the average original weight weight, loss the after averag each vibrationes of the cycleweights are of shown the samples, in Table 1and. the development(aboveFrom 4 mm) Table of 1average, it follows (2–4 weightmm) that loss the after average (1–2 eamm)ch original vibration weight (0.5–1cycle mm) are of the shown selected (under in Table 0.5 sample mm) 1. of Glass sample 1 (g) automobile 42From Table glass, 1, 1288it follows 423 g, has that been the reduced average 342 byoriginal the mechanical weight 164 of separationthe selected 212 method sample toof Glass sample 2 (g) 45.5 404 340 160 203 a weight of 101 g, which represents a loss of weight of 92.16% and an approximately Glass sample 3 (g) automobile 37 glass, 1288 g, 442 has been reduced 329 by the mechanical 159separation method 205 to a weight Glass sample 4 (g) correspondingof 101 42 g, which weight represents of 422 PVB a loss film of (Figure weight6 340 ).of From 92.16% the and calculated an 158approximately average losses corresponding 210 of weight, Glass sample 5 (g) itweight is clear41.5 of thatPVB the film greatest (Figure 415 loss 6). tookFrom place the calculated after331 the firstaverage vibrations, losses 160 of when weight, it was it 203 is possible clear that to Glass sample 6 (g) watchthe greatest 38 larger loss cullet took of glassplace 432 fallingafter the from first the 328vibrations, PVB film, when and theit 165 was weight possible fell byto watch 209about 408larger g, Average weight (g) i.e.,cullet 31.68%, 41 of glass from falling the from original 423 the PVB weight. film, On and 335 the the other weight end fell of by the 165 about scale, 408 the g, least i.e., 31.68%, 209 weight from was Average weight ratio (%) 3.5 36.2 28.8 13.8 17.7 lostthe original after the weight. fourth vibratingOn the other cycle, end when of the the scal originale, the least weight weight fell bywas on lost average after the 98 g.fourth vibrating cycle, when the original weight fell by on average 98 g. On the basis of known data on the PVB interlayer, such as its density ρ, film thickness glued into the automobile glass h, and the dimensions, it was possible to calculate the weight m of the original clean PVB interlayer as follows: 𝑚=𝜌 × ℎ × 𝑎 × 𝑏 = 1.07 × 0.076 × 39.5 × 29.5 =94.75 g (1)

where • ρ is the density of the PVB film; ρ = 1.07–1.2 g.cm−3; for the calculation, this was the lowest mean value; • h is the thickness of the interlayer film in the automobile glass; h = 0.76 mm; • a, b is the average dimension of the sample with PVB film; a = 395 mm, b = 295 mm. The difference between the calculated film weight and the cleaned film weight is 6.25 g. The measured and calculated values from the particle size analysis for all six samples Figure 6. Percentage share of cullet fraction size. Figuresubjected 6. Percentage to mechanical share of cullet recycling fraction are size. shown in Table 2. The results of the analysis showed

3.2. Washing of Interlayer Film The next test was focused on examining the possibilities for removing remaining glass fragments from PVB film following vibration (Figure 5) by the action of heat and a water solution CaCl2. The prepared solution of water and CaCl2 (700 mL H20, 280 g CaCl2) was heated in a container to 60 °C. The PVB film was then soaked in the solution for a period of 5 min and washed by hand. The glass powder fragments were removed from the film by the hot solution and slid off. The quality of the surface cleanliness and the continuity of the recycled PVB film is documented in Figure 7.

Figure 7. PVB interlayer film after washing, sample No. 1. Recycling 2021, 6, x FOR PEER REVIEW 9 of 14

that the highest average value of separated glass weight, about 36.2%, was in size section II-cullet sample II, with parts from 2 mm to 4 mm, and the least, about 3.5%, occurred in size section I, with glass particles above 4 mm. The percentage share of the individual sections is illustrated in Figure 6.

Table 2. Particle size analysis of cullet after vibration tests of glass samples 1 to 6.

Cullet Sample I Cullet Sample II Cullet Sample III Cullet Sample IV Cullet Sample V

(above 4 mm) (2–4 mm) (1–2 mm) (0.5–1 mm) (under 0.5 mm) Glass sample 1 (g) 42 423 342 164 212 Recycling 2021, 6, 26 9 of 13 Glass sample 2 (g) 45.5 404 340 160 203 Glass sample 3 (g) 37 442 329 159 205 Glass sample 4 (g) 42 422 340 158 210 Glass sample 5 (g) 41.5 415 331 160 203 Glass sample 6 (g) On the 38 basis of known data 432 on the PVB interlayer, 328 such as its 165 density ρ, film thickness 209 Average weight (g) glued into 41 the automobile glass 423 h, and the dimensions, 335 it was 165 possible to calculate 209 the Average weight ratio (%) weight m 3.5 of the original clean 36.2 PVB interlayer 28.8 as follows: 13.8 17.7

m = ρ × h × (a × b) = 1.07 × 0.076 × (39.5 × 29.5) = 94.75 g (1)

where • ρ is the density of the PVB film; ρ = 1.07–1.2 g.cm−3; for the calculation, this was the lowest mean value; • h is the thickness of the interlayer film in the automobile glass; h = 0.76 mm; • a, b is the average dimension of the sample with PVB film; a = 395 mm, b = 295 mm. The difference between the calculated film weight and the cleaned film weight is 6.25 g. The measured and calculated values from the particle size analysis for all six samples subjected to mechanical recycling are shown in Table2. The results of the analysis showed that the highest average value of separated glass weight, about 36.2%, was in size section II-cullet sample II, with parts from 2 mm to 4 mm, and the least, about 3.5%, occurred in size section I, with glass particles above 4 mm. The percentage share of the individual sectionsFigure 6. is Percentage illustrated share in Figure of cullet6. fraction size.

3.2.3.2. WashingWashing ofof InterlayerInterlayer FilmFilm TheThe next next test test was was focused focused on on examining examining the possibilitiesthe possibilities for removing for removing remaining remaining glass fragmentsglass fragments from PVB from film PVB following film following vibration vibration (Figure (Figure5) by the 5) actionby the ofaction heat andof heat a water and a solutionwater solution CaCl2. CaCl The prepared2. The prepared solution solution of water of andwater CaCl and2 (700CaCl mL2 (700 H2 mLO, 280H20, g 280 CaCl g2 CaCl) was2) ◦ heatedwas heated in a container in a container to 60 C.to The60 °C. PVB The film PVB was film then was soaked then in soaked the solution in the for solution a period for of a 5period min and of washed5 min and by washed hand. The by glasshand. powder The glass fragments powder were fragments removed were from removed the film from by thethe hot film solution by the andhot slidsolution off. The and quality slid off. of theThe surface quality cleanliness of the surface and the cleanliness continuity and of thethe recycledcontinuity PVB of filmthe recycled is documented PVB film in Figureis documented7. in Figure 7.

FigureFigure 7. 7.PVB PVB interlayerinterlayer filmfilm afterafter washing, washing, sample sample No. No. 1.1.

The weighing of the interlayer film after washing showed an average weight value of 96.72 g. The difference between the original weight of the primary film (94.75 g) and the film after washing is therefore +1.97 g. In an analysis of the recorded values, we can conclude that 99.85% efficiency in the decomposition of laminated glass by mechanical treatment and washing can be attained by the proposed technology.

4. Design of Technology Line Structure The essence of construction in the design of the technological equipment for processing waste laminated glass resides in the fact that it is made up of a multistage set of variable modules. Due to this particular feature, it is possible on one device to process glued glass of various sizes and thicknesses, including multilaminated glass. In this way, new variable Recycling 2021, 6, x FOR PEER REVIEW 10 of 14

The weighing of the interlayer film after washing showed an average weight value of 96.72 g. The difference between the original weight of the primary film (94.75 g) and the film after washing is therefore +1.97 g. In an analysis of the recorded values, we can conclude that 99.85% efficiency in the decomposition of laminated glass by mechanical treatment and washing can be attained by the proposed technology.

4. Design of Technology Line Structure The essence of construction in the design of the technological equipment for Recycling 2021, 6, 26 processing waste laminated glass resides in the fact that it is made up of a multistage10 of 13set of variable modules. Due to this particular feature, it is possible on one device to process glued glass of various sizes and thicknesses, including multilaminated glass. In this way, new variable configurations for the specific requirements of different customers become configurationspossible. The described for the specific modules requirements are capable of of different working customers independently become orpossible. together Thewith describedaccompanying modules technology. are capable Mutual of working movements independently and interaction or together can withbe linked accompanying up due to technology.the frequency-controlled Mutual movements drive of and individual interaction rollers can be and linked the upfrequency due to theof the frequency- selected controlledindustrial drivevibrator. of individual On the one rollers hand, and the the individual frequency customer of the selected can acquire industrial “tailor-made” vibrator. Onmachines, the one while, hand, theat the individual same time, customer their “modular can acquire conception” “tailor-made” allows machines, for the while,broad atemployment the same time, of such their machines “modular in conception” the processing allows of waste for the laminated broad employment glass, mainly of suchin the machinesconstruction in theand processing automobile of industries. waste laminated glass, mainly in the construction and automobile industries. In the minimal configuration (Figure 8) [43], the line is made up of one breaking In the minimal configuration (Figure8)[ 43], the line is made up of one breaking module (Figure 9b), in which the glass is broken in both transverse and longitudinal module (Figure9b), in which the glass is broken in both transverse and longitudinal directions between two pairs of breaking profile rollers. The second line module is a directions between two pairs of breaking profile rollers. The second line module is a vibration module (Figure 9c), in which a broken but compact car windshield can be shaken vibration module (Figure9c), in which a broken but compact car windshield can be shaken between a vibrating tool with pyramidal needles. The final module in this minimal between a vibrating tool with pyramidal needles. The final module in this minimal makeup makeup is the stripper module (Figure 9d) in which, on the basis of the various is the stripper module (Figure9d) in which, on the basis of the various frequencies of the frequencies of the stripper rollers, mechanical cleaning of the PVB film is carried out. stripper rollers, mechanical cleaning of the PVB film is carried out.

Recycling 2021, 6, x FOR PEER REVIEW 11 of 14

FigureFigure 8.8.Minimum Minimum lineline configuration: configuration: A-breaking A-breaking module, module, B-vibration B-vibration module, module, and and C-stripper C-stripper module. module.

Figure 9. PrototypesFigure of9. Prototypes decomposition of decomposition line modules line (utility modules design (u intility SR design No.SK8786). in SR No.SK8786). Reprinted with Reprinted permission from ref. [44]. 2020,with Owner: permission Slovak University from ref. [44] of Technology. 2020, Owner: in Bratislava. Slovak University of Technology in Bratislava.

For thick andFor multi-laminated thick and multi-laminated glass, any glass,of the any modules of the modulesmay be mayrun a be number run a number of of times times (Figure(Figure 10). In10 ).the In interest the interest of increa of increasingsing the the efficiency efficiency of of processing processing and and the the cleanliness cleanliness ofof the the final final film film product, product, the the line line configuration configuration is isfinished finished up up with with reception reception tables by tables by reception modules (Figure 9a) and washing modules for the cleaning of the PVB film in a heated water solution.

Figure 10. Example of wide line configuration (D-reception module, A-breaking module, B- vibration module, C-stripper module, and E-washing module).

5. Conclusions The main aim of the contribution presented here is a description of the research, development, and design leading to the construction of an effective high-efficiency technology for decomposition waste from multilayer glued glasses. On the principle of the proposed technology, it is possible to modify the optimal line configuration for economically efficient processing of laminated glass with an annual capacity of 500–2000 tons. The proposed technology begins with the hypothesis that waste glued glass is not crushed in the process of processing but rather subjected to a decomposition process based on the principle of retaining the integrity of the PVB film. In comparison with classical mechanical technologies, the proposed technology is not as dusty or noisy and does not require such machine input. The principle of film “integrity” ensures the attainment of cleanliness with an adhering glass content of up to 100 ppm. This residual Recycling 2021, 6, x FOR PEER REVIEW 11 of 14

Figure 9. Prototypes of decomposition line modules (utility design in SR No.SK8786). Reprinted with permission from ref. [44]. 2020, Owner: Slovak University of Technology in Bratislava.

Recycling 2021, 6, 26 For thick and multi-laminated glass, any of the modules may be run a number11 of of 13 times (Figure 10). In the interest of increasing the efficiency of processing and the cleanliness of the final film product, the line configuration is finished up with reception tables by reception modules (Figure 9a) and washing modules for the cleaning of the PVB filmreception in a heated modules water (Figure solution.9a) and washing modules for the cleaning of the PVB film in a heated water solution.

Figure 10. Example of wide line configuration (D-reception module, A-breaking module, B-vibration Figure 10. Example of wide line configuration (D-reception module, A-breaking module, B- module, C-stripper module, and E-washing module). vibration module, C-stripper module, and E-washing module). 5. Conclusions 5. Conclusions The main aim of the contribution presented here is a description of the research, devel- opment,The andmain design aim of leading the contribution to the construction presented of anhere effective is a description high-efficiency of the technology research, development,for decomposition and wastedesign from leading multilayer to the glued construction glasses. Onof thean principleeffective ofhigh-efficiency the proposed technologytechnology, for it is decomposition possible to modify waste the from optimal multilayer line configuration glued glasses. for economically On the principle efficient of theprocessing proposed of laminatedtechnology, glass it is with possible an annual to modify capacity the of 500–2000optimal line tons. configuration for economicallyThe proposed efficient technology processing begins of laminated with the glass hypothesis with an thatannual waste capacity glued of glass 500–2000 is not tons.crushed in the process of processing but rather subjected to a decomposition process based on theThe principle proposed of technology retaining the begins integrity with of the the hy PVBpothesis film. that In comparison waste glued with glass classical is not crushedmechanical in the technologies, process of theprocessing proposed but technology rather subjected is not as to dusty a decomposition or noisy and doesprocess not basedrequire on such the machineprinciple input.of retaining The principle the integrity of film of “integrity” the PVB film. ensures In comparison the attainment with of classicalcleanliness mechanical with an adhering technologies, glass contentthe propos of uped totechnology 100 ppm. Thisis not residual as dusty amount or noisy of glassand doesis acceptable not require for the such industrial machine recycling input. ofThe PVB principle foils. PVB of filmfilm separated “integrity” in thisensures way willthe attainmentbe prepared of for cleanliness repeat extrusion with an andadhering the production glass content of new of up PVB to film100 ppm. for laminated This residual glass. Another significant advantage of the proposed technology is that it ensures the greatest cleanliness of the individual types of waste. An essential advantage of the proposed technology is the up to 99.85% yield of glass shards. The multistage module technology for the processing of laminated glass may be modified simply according to the performance, type, and amount of waste to be processed. Finally, the design of the link also allows for a mobile arrangement.

6. Patents The work reported in this manuscript results in one utility design in SR (SK8786) [44] and one patent application (SK: PP 107-2019): Method of Effective Recovery of Waste Laminated Glass and Modular Construction of the Device [43].

Author Contributions: Conceptualization, L’.Š. and M.M.; methodology, L’.Š.; validation, L’.Š. and M.M.; formal analysis, M.M. and M.P.; investigation, J.B. and V.C.;ˇ resources, M.M.; data curation, L’.Š.; writing—original draft preparation, M.M. and L’.Š.; writing—review and editing, M.M.; supervision, L’.Š.; project administration, L’.Š.; funding acquisition, L’.Š. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the Slovak Research and Development Agency, grant number APVV-18-0505, and by the Ministry of Education, Science, Research, and Sport of the Slovak Republic under the Contract-University and industrial research and education platform of a recycling company (UNIVNET). Data Availability Statement: The data presented in this study are available on request from the corresponding author. Conflicts of Interest: The funders had no role in the design of the study; in the collection, analyses, or interpretation of data, in the writing of the manuscript, or in the decision to publish the results.

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