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