applied sciences Article Effect of Temperature Changes on the Vibration Transmissibility of XPE and PE Packaging Cushioning Material Péter Csavajda and Péter Böröcz * Department of Logistics and Forwarding, Széchenyi István University, Egyetem sqr 1, 9026 Gy˝or, Hungary; [email protected] * Correspondence: [email protected]; Tel.: +36-703352260 Abstract: Polyethylene (PE) and its variations are among the most traditional materials used for cushioning in packaging systems. The role of these materials is to prevent damages during handling and distribution processes from physical events such as vibration stress. This study presents new results on the characterization of properties of PE and XPE (cross-linked polyethylene) packaging materials, which have significant relevance as a protective mechanism due to their vibration trans- missibility and frequency curve properties. The main goal of this study is the evaluation of vibration transmissibility of PE and XPE cushion material at varied real temperature and static load conditions through a series of experiments using a vibration tester and climate chamber to determine the peak frequencies, vibration transmissibility, and damping ratios. The results can be used by engineers in the package-design process, and can be useful in different distribution conditions. Three different kinds of static loads and a 0.5 oct/min sine sweep of vibration test were used to find the peak frequencies and vibration transmissibility at −20 ◦C, 0 ◦C, 20 ◦C and 40 ◦C to estimate the damping ratios. The results provided a better understanding of the materials and can assist in the design of suitable protective packaging systems. Keywords: XPE (cross-linked polyethylene); PE (polyethylene); packaging; vibration transmissibility Citation: Csavajda, P.; Böröcz, P. Effect of Temperature Changes on the Vibration Transmissibility of XPE and 1. Introduction PE Packaging Cushioning Material. Physical events such as vibration are generated by vehicles and handling equipment Appl. Sci. 2021, 11, 482. https:// during distribution in different kinds of temperature conditions. Therefore, packaging has doi.org/10.3390/app11020482 a particular importance in avoiding or dampening those vibration stresses, which can affect the integrity of packaging and its protective mechanism, as well as product properties. Received: 9 December 2020 Furthermore, sensitive products like electrical or medical devices, or porcelain and glass Accepted: 4 January 2021 products, require a thorough and professional implementation of the packaging material Published: 6 January 2021 used in package-design processes. One of the most important aims of this process is to find cost-effective materials that offer enough protection of the product against the hazards of Publisher’s Note: MDPI stays neu- supply chains. Cushioning materials account for the balance between product ruggedness tral with regard to jurisdictional clai- and distribution hazards. The role of the materials is to absorb the energy of impact shock ms in published maps and institutio- or the dynamic oscillation of vibration. nal affiliations. Generally, the appropriate material and placement of cushioning material used in a packaging system within a container or parcel requires a necessary isolation between the packaged item (Figure1). M 1 is the critical element of the product (M2) that can be Copyright: © 2021 by the authors. Li- damaged easily under impact loading. This component should be an important focus censee MDPI, Basel, Switzerland. during the package-design process. The primary goal of the container (M3) is to store and This article is an open access article hold together the product and inner packaging during the distribution. The secondary distributed under the terms and con- goal of the container is to absorb the kinetic energy of impacts during transportation, ditions of the Creative Commons At- but this is neglected in the package-design process [1]. The protection element in the tribution (CC BY) license (https:// packaging system, which is known as a package cushion, usually is constructed using creativecommons.org/licenses/by/ plastic foams [2,3]. The packaging material usually used for cushioning is a lightweight, 4.0/). Appl. Sci. 2021, 11, 482. https://doi.org/10.3390/app11020482 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 of 18 Appl. Sci. 2021, 11, 482 2 of 18 neglected in the package-design process [1]. The protection element in the packaging sys- tem, which is known as a package cushion, usually is constructed using plastic foams [2,3]. The packaging material usually used for cushioning is a lightweight, inexpensive material inexpensivethat has high material strength-to-weight that has high and strength-to-weight stiffness-to-weight and ratios, stiffness-to-weight and has favorable ratios, cush- and hasioning favorable characteristics cushioning and vibration characteristics transmissibility. and vibration These transmissibility. materials, usually These plastic materials, foam usuallyor paper plastic packaging, foam orhave paper been packaging, widely applied have been in secondary widely applied (master) in secondaryand tertiary (master) (trans- andportation) tertiary packaging (transportation) to protect packaging products to such protect as medical products or suchelectronic as medical devices or and electronic instru- devicesments, or and fragile instruments, products. or [4–6]. fragile products [4–6]. Figure 1. The conceptual structure of a packaging system using cushioningcushioning material.material. In the design of protective cushionscushions forfor packaged-product systems, the most widely accepted method for the development of optimizedoptimized systems is the Six-Step method, which includes the following stepssteps [[7]:7]: 1. DefineDefine the the shipping shipping environment The damage potential must be evaluated and quantifiedquantified based on recording thethe realreal shipping environment duringduring thethe transportationtransportation ofof aa testtest package,package, oror onon anan estimation.estimation. 2. DefineDefine product product fragility During this step, the natural ability of the product to withstand shocks and vibrations from the transportationtransportation environmentenvironment shouldshould bebe quantified.quantified. 3. ImproveImprove the the robustness robustness of the product In some cases,cases, thethe packaged-productpackaged-product system system can can be be made made more more economical economical through through a redesigna redesign to to increase increase the the robustness robustness of of the the product, product, which which can can reduce reduce packaging packaging costs. costs. 4. Evaluate the performance of cushioning material 4. Evaluate the performance of cushioning material For optimal packaging design, the vibration transmissibility and shock attenuation For optimal packaging design, the vibration transmissibility and shock attenuation of of the cushion material must be considered. Transmissibility amplification/attenuation the cushion material must be considered. Transmissibility amplification/attenuation plots plots and cushion curves can be developed and applied to acquire this information. and cushion curves can be developed and applied to acquire this information. 5. Packaging design 5. Packaging design In this step, all previously collected information about the shipping environment, product,In this and step, cushioning all previously material collected are used information to create a packaging about the design. shipping environment, product, and cushioning material are used to create a packaging design. 6. Test and validate the packaged-product system 6. TheTest prototype and validate packaged-product the packaged-product system systemis tested to ensure that all design goals were achieved.The prototype packaged-product system is tested to ensure that all design goals were achieved.This technique takes into the consideration the requirements of cushioning material for protectionThis technique from shocks takes into and the vibration consideration resonance. the During requirements this process, of cushioning different material aspects for protection from shocks and vibration resonance. During this process, different aspects are considered by packaging professionals. The thickness of cushioning materials and the load-bearing area should offer enough protection against the different dynamic inputs to Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 18 Appl. Sci. 2021, 11, 482 3 of 18 are considered by packaging professionals. The thickness of cushioning materials and the load-bearing area should offer enough protection against the different dynamic inputs to minimize the cost ofof productproduct damage.damage. However, However, these these factors factors should should be be also also minimized minimized to tokeep keep the the package package costs costs and and volumes volumes down. down. The cushion characteristics characteristics of of a a polymer polymer foam foam are are affected affected by by their their mechanical mechanical prop- prop- erties. Based Based on on a astudy study by by Gibson Gibson and and Ashby Ashby [8], [8 these], these are are related related to the to theproperties properties of the of polymer’sthe polymer’s cell wall cell walland cell and geometry cell geometry and can and be can understood be understood in terms in of terms bending, of bending, elastic buckling,elastic buckling, and plastic and collapse. plastic collapse. New simple