Preparation of High Modulus Poly(Ethylene Terephthalate): Influence of Molecular Weight, Extrusion, and Drawing Parameters

Jian Min Zhang,Yuling Zhao,Emiliano Bilotti,Qingsong Hua,Ton Peijs,Christopher T. Reynolds,Jie Tang,Zuoqiang Dai

doi:10.1155/2017/2781425

Abstract

Poly(ethylene terephthalate) (PET) which is one of the most commercially important polymers, has for many years been an interesting candidate for the production of high performance fibres and tapes. In current study, we focus on investigating the effects of the various processing variables on the mechanical properties of PET produced by a distinctive process of melt spinning and uniaxial two-stage solid-state drawing (SSD). These processing variables include screw rotation speed during extrusion, fibre take-up speed, molecular weight, draw-ratio, and drawing temperature. As-spun PET production using a single-screw extrusion process was first optimized to induce an optimal polymer microstructure for subsequent drawing processes. It was found that less crystallization which occurred during this process would lead to better drawability, higher draw-ratio, and mechanical properties in the subsequent SSD process. Then the effect of drawing temperature (DT) in uniaxial two-stage SSD process was studied to understand how DT (<Tg or close to Tg or close to Trec) would affect the crystallization, draw-ratio, and final mechanical properties of PET. The designed process in current work is simulated to an industrial production process for PET fibres; therefore, results and analysis in this paper have significant importance for industrial production.

Highlights

There are a number of technical routes to improve the mechanical properties of polymeric materials
By comparing the endothermic melting peaks in Differential Scanning Calorimetry (DSC) heating traces for three kinds of Poly(ethylene terephthalate) (PET) grades, it is found that the widths of melting peaks are different for grades H (∼40∘C), M (∼30∘C), and L (18∘C)
The DSC tests are performed under a constant heating and cooling rate of 10∘C⋅min−1; it indicates that grade H has the longest relaxation time during melting

Summary

Introduction

There are a number of technical routes to improve the mechanical properties of polymeric materials. Various methods have been investigated by previous researchers, involving spinning, drawing, and annealing processes [1,2,3,4,5,6,7,8] These methods, including vibrating hot drawing, zone-drawing, cold-drawing, horizontal isothermal bath, draw by using high pressure CO2, and high speed in-line drawing, are quite different from each other; the fundamentals are the same. During these processes reorganization of amorphous and crystalline phases in the PET microstructure occurs, and it is widely accepted that orientation in both the amorphous phase and the crystalline phase is essential to achieve high mechanical properties for these fibres. It was proposed in literature [9, 10] that the orientating process will transform initial microstructure into a fibrillar one, which is a good way of explaining how various properties are affected by orientation

Methods

Results

Conclusion