聚(3-羟基丁酸酯-co-3-羟基戊酸酯)中β晶的形成与转变

The Formation and Transformation ofβ-Form Crystals in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

本文通过同步辐射原位二维广角X射线(2D-WAXD)和原位红外光谱(FTIR)等手段,对聚(3-羟基丁酸酯-co-3-羟基戊酸酯)(PHBV)预取向膜二次拉伸过程及随后升温过程中的结构演化机制进行了系统研究。研究结果表明,二次拉伸过程中β晶的相对含量、取向程度和晶粒尺寸会随应变而升高;同时,体系的总α晶的取向度和晶粒尺寸变小,结晶度下降。这说明拉伸过程中,α晶会被破坏并转变为β晶。经过二次拉伸的PHBV膜,在升温过程中,α晶的取向、晶粒尺寸及总体结晶度会升高,而β晶的相对含量逐步下降到零。这说明在较高的温度下,β晶的分子链会重新排列,主要转变成了取向度高的α晶。β晶表现出从65℃到135℃的持续熔融转变。本研究初步阐释了PHBV薄膜中的β晶在拉伸和升温过程中的演化机制,为生物基聚酯薄膜的加工和性能调控提供了理论依据。

In this work,structural evolution of uniaxially oriented poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV)films during stretching and subsequent heating was studied.The mechanism for generatingβ-form crystals during the second drawing and the transformation ofβ-form during heating were investigated via in situ synchrotron wide-angle X-ray diffraction(WAXD)and Fourier transform infrared spectroscopy(FTIR),together with the measurement of stress-strain curves.It was found that relative contents,orientation and size ofβ-form crystals increased with the increase of strain,while the crystallinity,orientation and crystal size ofα-form decreased.These results revealed that the packing states of molecular chains inα-form lamellar crystals must be disordered for generating theβform chains.In the following heating process,crystallinity,orientation and crystal size ofα-form crystals increased with the increase of temperature,and theβ-form crystals gradually disappeared.This was mainly owing to the transformation of theβ-form into theα-form with higher orientation.The melting temperature of theβ-crystals ranges from 65℃to 135℃.This work provides new insight into the structural evolution of PHBV films,which will provide a theoretical basis for the processing and property control of bio-based polyester films.