Study On Preparation And Shrinkage Behavior Of Polyamide Elastomer Foam

Thermoplastic polyamide elastomers（TPAE）are high-performance elastomers made from alternating blocks of rigid polyamide and flexible polyether or polyester polymers with excellent elasticity and mechanical properties.Polyamide 6 elastomer foams offer better durability than ethylene vinyl acetate（EVA）foams,higher resilience than thermoplastic polyurethane elastomer（TPU）foams and lower costs than polyamide 12 elastomer foams（Pebax）.Therefore,it has broader application prospects in the footwear industry.However,the localization of polyamide 6 elastomer has not been long,and there are some shortcomings,such as narrow foaming temperature range,low expansion ratio and poor dimensional stability.Starting from the essence of TPAE foam shrinkage,this paper explores and optimizes TPAE materials and foaming properties by improving TPAE material properties,balancing foaming agent diffusion,and changing cell structure.（1）The epoxy chain extender KL-4370B and anhydride chain extender SMA-725 were used for chain extension reaction with TPAE.The reaction process and principles of chain-expanding TPAE were studied by torque rheometry and infrared spectroscopy,and the rheological and crystallization properties of chain-expanding TPAE were investigated by rotational rheometry and differential scanning calorimetry.Finally,the foaming properties of chain extension TPAE were investigated by intermittent foaming process.The results showed that TPAE could react with two chain extenders and produce gel structure at a high content.After chain extension,the expansion ratio of TPAE was increased by 3-4 times,the foaming temperature range was expanded by20℃,and the cell quality was significantly improved,but the shrinkage problem was not significantly improved.（2）TPAE and PA6 were blended under the action of chain extender SMA.The reaction process and principle of modified TPAE were investigated by torque rheometry and infrared spectroscopy.The rheological and viscoelastic properties of modified TPAE were investigated by rotational rheometry and dynamic mechanical thermal analysis,and the crystallization properties,foaming properties and resilience properties of modified TPAE were investigated by differential scanning calorimetry,kettle foaming and falling ball resilience respectively.The results show that the TPAE modified by PA6+SMA,on the one hand,reduces the crystallinity of the hard phase to facilitate gas penetration and reduce the effect of negative pressure on foam shrinkage;on the other hand,micro-cross-linked shape enhancements modulus of elasticity and increases strain recovery and increases strain recovery.The foaming temperature range of the modified TPAE foaming material is significantly broadened,the recovery performance is significantly improved,the shrinkage rate is reduced to less than 10%,the maximum foaming ratio is up to 11-13times,the foam cell is more uniform and complete,and the rebound performance is increased by 12%.（3）Through the CO₂-N₂ composite blowing agent intermittent foaming device built independently,the solubility of single and composite blowing agents were measured respectively,and the theoretical formulae for calculating the solubility of single and composite blowing agents were derived,and finally the effect of different gas ratios on the foaming performance of TPAE was investigated using the device.The use of N₂-CO₂ composite gas as a physical foaming agent can generate synergistic effects.When the content of N₂ was 20-30%,TPAE foam with 11-12 times initial expansion ratio and less than 5%shrinkage could be prepared.（4）TPAE was melt blended with CaSiO₃ and the surface morphology of blended materials was studied using scanning electron microscopy,the rheological and crystallographic residences of the combos have been studied by way of rotational rheometry and DSC test,and subsequently the foaming homes of the combinations had been studied by using an intermittent foaming process.The results indicated that after blending CaSiO₃,TPAE foam could form an open cell structure with an opening ratio of more than 87%,the maximum expansion ratio increased from 8 to 18.77 times,and the shrinkage decreased from 65.98%to 2.86%,which greatly improved the expansion ratio and dimensional stability of TPAE foam.