Theoretical Model Of Non-isothermal Cell Growth Of Polyamide Elastomer And Its Shrinkage Regulation Strategy

Thermoplastic polyamide elastomer（TPAE）,a new type of high-performance elastic material with alternating soft and hard blocks,integrates the elastic and impact resistance characteristics of rubber with the strength and wear resistance of polyamide resin.Therefore,due to the excellent performance of TPAE foam in resilience,heat insulation,low-temperature impact resistance,and other aspects,it is widely used in shoe materials,medical equipment,sports equipment,and other fields.Compared with the common polyamide 12-type TPAE,the polyamide 6-type TPAE adopted in this paper has greater development potential because of its common raw materials and low cost.However,due to the lack of matrix rigidity,poor melt strength,slow crystallization rate,and low elastic modulus of matrix caused by its linear molecular structure,combined with the high penetration rate of blowing agent,TPAE foam has serious shrinkage and uneven cell structure,which limits its industrial application.In response to these problems,this paper focuses on the improvement of the anti-shrinkage behavior of TPAE foam and the optimization of bubble structure.By constructing a theoretical study on the non-isothermal growth and contraction behavior of TPAE cell,multiple influencing factors are deeply explored from the theoretical level.The cell structure and anti-shrinkage behavior of TPAE foam were optimized by means of hard segment content regulation,the synergistic effect of chain extender and nucleator,introduction of crosslinking structure,and formation of open-cell structure.The research contents are summarized as follows:1.Based on the cell model,a TPAE cell non-isothermal growth model was established,and based on the iterative algorithm combined with the viscoelastic data during the cooling process,the influence of each parameter on the growth dynamics of the cell was discussed through numerical calculation,and the contribution of the wall viscosity and elasticity to the growth of the cell was calculated respectively.The results show that the diffusivity,zero shear viscosity,and relaxation time significantly affect the growth of the cell.At the same time,it is pointed out that wall viscosity plays a leading role in the early stage of cell growth,and wall elasticity is in the later stage.A new theoretical framework was proposed to analyze the shrinkage behavior of TPAE foam by considering the contraction caused by the pressure difference caused by gas displacement and the contraction caused by the internal stress caused by the cell wall during cell growth.The results show that in addition to improving the matrix rigidity of TPAE,increasing the elastic modulus of TPAE or reducing the penetration rate of the blowing agent can produce significant effects.2.Three kinds of TPAE with different hard segment content were used as research objects to systematically evaluate the effects of hard segment content on the chemical structure,crystallization,rheological behavior,mechanical properties,foaming properties,and anti-shrinkage behavior of TPAE.It was found that TPAE with higher hard segment content exhibited enhanced hydrogen bonding forces,excellent crystallization properties,improved melt viscoelasticity,and significant improvements in tensile properties,compressive permanence,and wear resistance despite a decrease in resilience.The increase of hard segment content not only significantly increased the expansion ratio of TPAE and optimized the uniformity of cell structure but also realized the preparation of low-shrinkage TPAE foam through the regulation of hard segment recrystallization behavior.3.To address the challenges associated with low melt strength and slow crystallization rate inherent in TPAE,the synergistic effects of epoxy chain extender KL-E4370B and crystallization nucleating agent TMN22 on rheological properties,crystallization behavior,foaming behavior,and anti-shrinkage properties of TPAE were investigated.The results demonstrated that the addition of KL-E4370B facilitated the formation of a long-chain branched structure in TPAE,thereby enhancing its melt strength,increasing the expansion ratio,and significantly improving cell merger and rupture issues.Simultaneously,the introduction of TMN22 enhanced molecular chain mobility in TPAE,accelerated the crystallization process and promoted rapid cooling and foam formation while improving foam structure rigidity.Consequently,this led to improved anti-shrinkage performance in TPAE foam.4.The low elastic modulus of TPAE was addressed by studying the effects of polyamide 6（PA6）on rheological properties,foaming properties,and anti-shrinkage behavior of the blending system by using anhydride SMA-725 as a crosslinking agent.Results indicate that the addition of PA6 promotes the formation of cross-linked network structure of TPAE,significantly enhances the viscoelasticity of TPAE melt,increases the elastic modulus of its matrix,and ensures that TPAE foam is in the range of resilient elastic strain.Ultimately,TPAE foam with an expansion ratio of approximately 13 times,a final shrinkage rate below 10%,and a rebound rate of 58%was achieved.Based on the TPAE foam shrinkage theory,the shrinkage and recovery mechanism of TPAE foam is analyzed from the Angle of elastic modulus5.Considering the impact of a high CO₂ penetration rate on TPAE foam shrinkage,four inorganic particles（Talc,Ca CO₃,Ca Si O₃,and WI）were combined with TPAE to create TPAE foam with varying opening degrees.The objective was to enhance the exchange rate between CO₂ and air,that is,to relatively reduce the penetration rate of CO₂,to improve foam shrinkage.It was observed that compared to Talc,Ca CO₃,Ca Si O₃,and WI exhibited higher interfacial tension and poor compatibility when combined with TPAE.Additionally,the melt viscoelasticity of these three composite systems also improved.A fundamental mechanism for how inorganic particles promotes an open-cell structure formation in TPAE foam was revealed.Consequently,TPAE foam with an open cell ratio exceeding 90%,an expansion ratio up to 20 times,and a shrinkage rate below 5%was successfully prepared.These improvements significantly enhanced its dimensional stability and adsorption properties.