Pub Date : 2024-09-04DOI: 10.1177/02624893241282002
George Youssef, Mark Smeets, Behrad Koohbor
The overarching goal in sports gears to achieve higher levels of impact protection without an increased weight penalty motivated the pursuit of density gradation in cellular solids. The research reported herein studied the impact performance of density-graded polyurea elastomeric foams, including different gradation and interfacing strategies. The latter leveraged the natural adhesion properties of polyurea foam slurry to sequentially assemble graded structures with seamless interfaces. Moreover, conventional discretely graded polyurea foam structures were manufactured using bulk polyurea adhesive by individually bonding pre-fabricated sheets. Six density-graded foam configurations were characterized, including bi- and tri-layered foams with naturally bonded or adhered interfaces. Additionally, standard mono-density polyurea and another benchmark foams were tested as controls. Extracted samples were submitted to impact loading using an instrumented drop weight tower. The impact efficacy of the foams was analyzed using three dynamic performance metrics (DPMs), including the specific energy absorptivity (SEA), absorption efficiency, and local buckling-induced undulation, based on the averaged stress-strain response. The mono-density polyurea foam reported the largest SEA, outperforming all density-graded foam configurations. The limited density gradation is attributed to the inferior performance of graded structures. A brief biomechanics case study is presented to assess the potential interrelationship between the investigated foam structures and the head injury criterion (HIC), showing the superior performance of adhered trilayer polyurea foams. Finally, the average stress-strain responses were fitted using an empirical model, elucidating the effect of strain rates and base materials on their overall impact behavior.
{"title":"The impact performance of density-graded polyurea elastomeric foams","authors":"George Youssef, Mark Smeets, Behrad Koohbor","doi":"10.1177/02624893241282002","DOIUrl":"https://doi.org/10.1177/02624893241282002","url":null,"abstract":"The overarching goal in sports gears to achieve higher levels of impact protection without an increased weight penalty motivated the pursuit of density gradation in cellular solids. The research reported herein studied the impact performance of density-graded polyurea elastomeric foams, including different gradation and interfacing strategies. The latter leveraged the natural adhesion properties of polyurea foam slurry to sequentially assemble graded structures with seamless interfaces. Moreover, conventional discretely graded polyurea foam structures were manufactured using bulk polyurea adhesive by individually bonding pre-fabricated sheets. Six density-graded foam configurations were characterized, including bi- and tri-layered foams with naturally bonded or adhered interfaces. Additionally, standard mono-density polyurea and another benchmark foams were tested as controls. Extracted samples were submitted to impact loading using an instrumented drop weight tower. The impact efficacy of the foams was analyzed using three dynamic performance metrics (DPMs), including the specific energy absorptivity (SEA), absorption efficiency, and local buckling-induced undulation, based on the averaged stress-strain response. The mono-density polyurea foam reported the largest SEA, outperforming all density-graded foam configurations. The limited density gradation is attributed to the inferior performance of graded structures. A brief biomechanics case study is presented to assess the potential interrelationship between the investigated foam structures and the head injury criterion (HIC), showing the superior performance of adhered trilayer polyurea foams. Finally, the average stress-strain responses were fitted using an empirical model, elucidating the effect of strain rates and base materials on their overall impact behavior.","PeriodicalId":9816,"journal":{"name":"Cellular Polymers","volume":"59 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142214591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-25DOI: 10.1177/0262489319981704002
A. Mahapatro, N.J. Mills, G.L.A. Sims
The density of chemically-blown low density polyethylene foam was altered by varying the amount of blowing agent, the degree of cross linking of the polymer, and the foam expansion temperature. A theory is proposed for the equilibrium density, based on the gas pressures in a Kelvin foam structure, and a rubber-elastic analysis of the biaxial stretching of the cell faces. The predicted densities are within 3 kg m -3of the experimental values. For commercial types of LDPE foams, the biaxial stresses in the cell faces are significant, but they only cause a minor increase in the foam density above the free-expansion limit. The molecular orientation in the cell faces must affect the foam properties. The diffusion of the nitrogen gas from the foam is insignificant.
通过改变发泡剂的用量、聚合物的交联程度和泡沫膨胀温度，改变了化学发泡低密度聚乙烯泡沫的密度。根据开尔文泡沫结构中的气体压力以及对泡孔表面双轴拉伸的橡胶弹性分析，提出了平衡密度理论。预测密度与实验值相差不超过 3 kg m-3。对于商用类型的低密度聚乙烯泡沫来说，泡孔表面的双轴应力很大，但它们只会导致泡沫密度在自由膨胀极限以上略有增加。泡孔表面的分子取向一定会影响泡沫特性。氮气从泡沫中扩散的影响微乎其微。
{"title":"Experiments and Modelling of the Expansion of Crosslinked Polyethylene Foams","authors":"A. Mahapatro, N.J. Mills, G.L.A. Sims","doi":"10.1177/0262489319981704002","DOIUrl":"https://doi.org/10.1177/0262489319981704002","url":null,"abstract":"The density of chemically-blown low density polyethylene foam was altered by varying the amount of blowing agent, the degree of cross linking of the polymer, and the foam expansion temperature. A theory is proposed for the equilibrium density, based on the gas pressures in a Kelvin foam structure, and a rubber-elastic analysis of the biaxial stretching of the cell faces. The predicted densities are within 3 kg m -3of the experimental values. For commercial types of LDPE foams, the biaxial stresses in the cell faces are significant, but they only cause a minor increase in the foam density above the free-expansion limit. The molecular orientation in the cell faces must affect the foam properties. The diffusion of the nitrogen gas from the foam is insignificant.","PeriodicalId":9816,"journal":{"name":"Cellular Polymers","volume":"31 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141783214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-25DOI: 10.1177/0262489319961502003
J.B. Blackwell, G. Buckley, S.W. Blackwell
A number of technologies are now available to replace ozone depleting chemicals and hazardous air pollutants in the manufacture of flexible polyurethane slabstock.In the U.S.A. the Environmental Protection Agency has made provisional recommendations regarding the Presumptive Maximum Available Control Technology. Two of the options - Variable Pressure Foaming (V.P.F.) and the Liquid C02 Injection process are compared on the following basis: Production Range; Economics of Production; Process Improvements; Environmental Considerations; Capital Costs Both V.P.F. and Liquid C02 fulfil the requirements of the Montreal Protocol.The comparisons illustrate that Liquid C02 is a part solution to the Environmental problem, V.P.F. is the more complete solution.
{"title":"Comparison of the VPF and Liquid C02 Foaming Processes","authors":"J.B. Blackwell, G. Buckley, S.W. Blackwell","doi":"10.1177/0262489319961502003","DOIUrl":"https://doi.org/10.1177/0262489319961502003","url":null,"abstract":"A number of technologies are now available to replace ozone depleting chemicals and hazardous air pollutants in the manufacture of flexible polyurethane slabstock.In the U.S.A. the Environmental Protection Agency has made provisional recommendations regarding the Presumptive Maximum Available Control Technology. Two of the options - Variable Pressure Foaming (V.P.F.) and the Liquid C02 Injection process are compared on the following basis: Production Range; Economics of Production; Process Improvements; Environmental Considerations; Capital Costs Both V.P.F. and Liquid C02 fulfil the requirements of the Montreal Protocol.The comparisons illustrate that Liquid C02 is a part solution to the Environmental problem, V.P.F. is the more complete solution.","PeriodicalId":9816,"journal":{"name":"Cellular Polymers","volume":"232 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141783215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-25DOI: 10.1177/0262489319961502001
R. Yerushalmi-Rozen, J. Klein
Stability of thin films of non-volatile liquids is a key issue in a variety of applications. Often a film is forced to spread on a substrate which is not wetted by the liquid. The film then ruptures within minutes and dewets. Common methods for achieving stability include the introduction of surface-active low molecular weight agents, or modification of the chemistry of the substrate. We describe here a mechanism for suppressing the rupture of the films by surface-attached polymers together with trace amounts of free polymers in the bulk of the film. The effect may have a kinetic origin, which is related to the entanglement of free chains and surface-attached polymer chains, or it may be due to a modification of the thermodynamic interactions.
{"title":"Stabilisation of Thin Liquid Films by Polymer Additives","authors":"R. Yerushalmi-Rozen, J. Klein","doi":"10.1177/0262489319961502001","DOIUrl":"https://doi.org/10.1177/0262489319961502001","url":null,"abstract":"Stability of thin films of non-volatile liquids is a key issue in a variety of applications. Often a film is forced to spread on a substrate which is not wetted by the liquid. The film then ruptures within minutes and dewets. Common methods for achieving stability include the introduction of surface-active low molecular weight agents, or modification of the chemistry of the substrate. We describe here a mechanism for suppressing the rupture of the films by surface-attached polymers together with trace amounts of free polymers in the bulk of the film. The effect may have a kinetic origin, which is related to the entanglement of free chains and surface-attached polymer chains, or it may be due to a modification of the thermodynamic interactions.","PeriodicalId":9816,"journal":{"name":"Cellular Polymers","volume":"89 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141783333","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-25DOI: 10.1177/0262489319981704003
M.R. Holl, M. Ma, V. Kumar, R.R. Kwapisz
The effect of the presence of commonly used additives on the processing and structure of microcellular PVC foams was investigated. It was found that the presence of additives leads to a polydisperse cell structure with large variations in cell sizes. The solubility of carbon dioxide in the additives and in the lubricants was found to be lower than in the PVC matrix. The presence of additives showed no adverse effect on the overall foam growth dynamics. It appears that target reductions in density of PVC can be achieved at lower processing temperatures when additives and processing aids are present.
{"title":"The Effect of Additives on Microcellular PVC Foams: Part 1 - Effect on Processing and Microstructure","authors":"M.R. Holl, M. Ma, V. Kumar, R.R. Kwapisz","doi":"10.1177/0262489319981704003","DOIUrl":"https://doi.org/10.1177/0262489319981704003","url":null,"abstract":"The effect of the presence of commonly used additives on the processing and structure of microcellular PVC foams was investigated. It was found that the presence of additives leads to a polydisperse cell structure with large variations in cell sizes. The solubility of carbon dioxide in the additives and in the lubricants was found to be lower than in the PVC matrix. The presence of additives showed no adverse effect on the overall foam growth dynamics. It appears that target reductions in density of PVC can be achieved at lower processing temperatures when additives and processing aids are present.","PeriodicalId":9816,"journal":{"name":"Cellular Polymers","volume":"85 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141783219","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-25DOI: 10.1177/0262489319961502004
M. Jeffs
{"title":"Polyurethane: A Polymer Addressing the Environmental Issues of the 21st Century","authors":"M. Jeffs","doi":"10.1177/0262489319961502004","DOIUrl":"https://doi.org/10.1177/0262489319961502004","url":null,"abstract":"","PeriodicalId":9816,"journal":{"name":"Cellular Polymers","volume":"119 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141783218","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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