| Polymer foam materials are a new force in new materials,which endow polymers with new and excellent properties such as lightweight,shock absorption,noise reduction,and thermal insulation by introducing cellular structures into the materials.Polymer elastomer foam materials.as an important member of foam materials,are widely used in fields such as architecture,navigation,sports equipment,and shoe decoration due to their low density and good resilience.Especially in terms of shoe materials,elastic foam material is an important midsole material for sports shoes,and its performance directly determines the grade of sports shoes.At present,the mainstream elastomer foaming materials use thermoplastic elastomer as the matrix,and prepare foam materials by chemical foaming method or physical foaming method.However,although thermoplastic elastomers have good processability and can be repeatedly processed,they have poor solvent and corrosion resistance,and their mechanical properties are often poor compared to cross-linked elastomeric materials.In recent years,researchers have invented elastomer materials based on dynamic cross-linking bonds,which not only have excellent mechanical properties and solvent resistance of cross-linked elastomers,but also have the ability to be reprocessed repeatedly.They are expected to become the ideal matrix for the next generation of elastomer foam materials.However,there is currently little research in the industry and academia on the foaming of dynamically crosslinked elastomers and the structure-activity relationship between the pore structure and properties of foaming materials.Based on this,this paper first designed and constructed dynamic covalent crosslinked polyurethane and styrene ethylene/butene styrene(SEBS)elastomer,and prepared foam through supercritical carbon dioxide(CO2)foaming.The effects of dynamic crosslinked structure on the mechanical properties and cell structure of elastomer foam were explored.The research contents are as follows:(1)Firstly,PMDI monomer was prepared from pyromellitic dianhydride and 6-amino-1-hexanol,and then dynamic crosslinked polyurethane based on amide imide exchange was successfully prepared by two-step method.As the PMDI content increases to 10 mol%,the crosslinking density increases to 7.79×10-3 mol/cm3,the maximum tensile strength of dynamically crosslinked polyurethane is 9.89 MPa.Dynamic crosslinked polyurethane foam was prepared by supercritical CO2 foaming,and the effects of different crosslinking density and foaming conditions on cell structure were investigated.The results show that the porosity of foam increases with the increase of soaking time.The highest porosity is 78.8%when immersed in CO2 for 6 hours at 45℃ and 20 MPa;The effect of different cross-linking density on foaming was studied.Under the same foaming condition,the porosity of the foam with the highest crosslinking density reached 81.02%,and the cell density reached 1.32×1010 cells/cm3.(2)SEBS vitrimer materials based on dynamic ester bonds were successfully prepared through a simple solution co mixing and hot pressing curing method.SEBS vitrimers with different crosslinking densities were prepared by changing the dosage of bisphenol A epoxy resin(DGEBA).The mechanical properties of SEBS vitrimer are improved with the increase of DGEBA content.When the DGEBA content is 5 phr,the tensile strength reaches a maximum of 17.03 MPa.SEBS vitamer foam was prepared by supercritical CO2 foaming,and the effects of different foaming conditions and different raw material ratios on cell structure were investigated.With the increase of soakage time and foaming temperature,the porosity of foam increases first and then decreases.The results show that when the CO2 soakage time is 12h and the foaming temperature is 90℃,the highest porosity of foam is 82.49%;When the DGEBA content increased,the crosslinking density of SEBS vitrimer increased to 1151.68 mol/cm3,which affected the dissolution of gas in the matrix and restricted the porosity of foam from 82.49%to 75.76%. |
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