扩链改性对PBAT挤出发泡成型的影响研究

Study on the Influence of Chain Extension Modification During a PBAT Extrusion Foaming Process

摘要:

挤出发泡是一种可制备轻量化聚合物发泡材料如发泡网套、发泡片材等的连续加工工艺。近年来在“双碳”政策背景下，市面常见的水果网套原材料聚乙烯（PE），作为典型不可生物降解的石油基聚合物，已逐渐被可生物降解材料替代。聚对苯二甲酸-己二酸丁二醇酯(PBAT)是一种高强高韧且可生物降解材料，其制品广泛应用于包装、农业等领域。探究了扩链改性对PBAT的流变行为、结晶行为以及挤出发泡成型过程的影响。结果表明，扩链改性使得支化结构逐渐增加并诱导PBAT链网络发生凝胶化，PBAT的基体模量增加。此外，扩链剂可以充当异相成核剂，导致扩链改性PBAT的结晶温度升高超30 ℃。挤出发泡成型结果表明，随着扩链剂含量增加，网套样品的膨胀倍率逐渐降低，横向延展性先增加后降低，横向拉伸断裂伸长率在扩链剂的质量分数为0.25%时达到600%。因此，在挤出发泡过程中，采用扩链改性的方法可以快速提高PBAT的熔体强度，提升PBAT基体在发泡膨胀过程限制气体快速逃逸的能力。同时，扩链改性可以快速提高PBAT在降温结晶过程的结晶温度，这有利于PBAT在口模处挤出后更快地结晶从而稳定泡孔。然而，过度的扩链改性将造成PBAT发泡网套的膨胀倍率过低。结合扩链改性对PBAT挤出发泡膨胀过程及降温结晶过程的影响，当扩链剂质量分数为0.25%、挤出发泡机加工温度分别为130 ℃(加料区)-180 ℃-180 ℃(进气口)-145 ℃-110 ℃-110 ℃-115 ℃(换网器)-115 ℃(模头)、进气压力约为18 MPa时，PBAT网套的综合性能较为合适。其中，网套的密度为0.03 g·cm^-3，发泡倍率φ约为36倍，横向拉伸断裂伸长率超过600%，具备实际应用价值。

Abstract:

Polybutylene terephthalate-adipate （PBAT） is a high-strength， tough and biodegradable material， and its products are widely used in packaging and agriculture. This study investigates the effects of chain extension modification on the rheological behavior， crystallization behavior， and extrusion foam molding process of PBAT. The results showed that the chain extension modification gradually increases in the branched structure and induced gelation of the PBAT chain network， resulting in a gradual increase in the matrix modulus of PBAT. Additionally， the crystallization temperature of the chain extension modified PBAT increased more than 30 ℃ because the chain-extender （CE） could act as a heterogeneous nucleating agent. The results of extrusion foam molding showed that with the increase of CE content， the expansion ratio of the PBAT mesh gradually decreased but the transverse ductility initially increased and then decreased， and the transverse tensile elongation at break reached 600% at a CE content of 0.25 wt.% of CE. Therefore， in the extrusion foaming process， the use of chain expansion modification can rapidly increase the melt strength of PBAT， thereby enhancing the ability of the PBAT matrix to limit the rapid escape of gases during the foaming process. At the same time， the chain expansion modification can rapidly increase the crystallization temperature of PBAT during the cooling crystallization process， which is conducive to the faster crystallization of PBAT after extrusion at the die to stabilize the foam pores. However， excessive chain expansion modification would result in too low expansion ratio of the PBAT mesh. Therefore， in combination with the effect of chain expansion modification on the expansion process and the cooling crystallization process of PBAT extrusion foaming， with the content of CE of 0.25 wt%， the processing temperature of the extrusion foaming machine at 130 ℃ （feed hopper）-180 ℃- 180 ℃ （air inlet）-145 ℃-110 ℃-110 ℃-115 ℃-115 ℃ （die）， and the inlet pressure of about 18 MPa， the comprehensive performance of the PBAT mesh is more suitable. Among them， the density of the mesh was 0.03 g·cm^-3， the foaming ratio φ was about 36， and the transverse tensile elongation at break was more than 600%， which has the practical application value.