拉伸温度对α'-型聚乳酸结构与性能的影响

Effect of Drawing Temperature on Structure and Properties of α'-Phase of Poly(lactic acid)

α'-晶型聚乳酸(PLA)膜被制备和单轴拉伸.通过凝胶渗透色谱仪(GPC)、全反射红外光谱(ATR-IR)、差示扫描量热仪(DSC),X射线衍射(XRD)及Raman光谱等测试技术研究了拉伸温度梯度变化对α'-晶型PLA膜的分子量及其分布、分子链构象、结晶度、晶型转变和取向行为的影响.在恒定拉伸速度与应变下,拉伸温度对PLA膜的应力-应变曲线,特别是屈服强度、拉伸模量产生了较大的影响,其值随拉伸温度的增加而降低.GPC测试结果表明,在不同的温度下拉伸后,PLA会发生一定程度的降解,分子量降低;ATR-IR,XRD,DSC和Raman光谱测试结果表明,在不同的温度下拉伸后α'-型PLA没有发生晶型的转变,即没有由α'-晶体转变为α-或β-晶体.结果表明PLA的结晶度、分子链取向程度强烈依赖于拉伸温度:当拉伸温度低于100℃时,α'-型PLA膜的结晶度与沿着拉伸方向的变形程度随拉伸温度的增加而增加,分子链的高度取向诱导了PLA结晶;当拉伸温度超过100℃后,PLA的分子链沿着拉伸方向上的有序度与结晶度将降低.

Poly（lactic acid） （PLA） films consisting of a＇-forms were prepared and uniaxially drawn. The effects of the drawing temperatures above the glass transition temperature on molecular weight and molecu lar weight distribution, chain conformation, degree of crystallinity and crystalline phase transformation were investigated by a combination of vibrational spectroscopy （infrared and Raman）, gel permeation chromatog raphy （GPC）, differential scanning calorimetry （DSC）, and Xray diffraction （XRD）. The eeneral appnearanceof stress-strain behaviour of drawn PLA, and in particular its yield stress and Young＇s modulus, is strongly affected by the drawing temperatures. The values decreas.e with increasing the stretching temperatures. The GPC results showed that the molecular weight decreases and its distribution becomes wider after drawing at various drawing temperatures. It was established that the a＇-forms phase of PLA films does not transform into either an a or β crystals upon uniaxial drawing with various temperatures at a fixed draw ratio of 4. However, compared with undrawn a＇-forms PLA films, the crystallinity and the degree of orientation of PLA products are greatly influenced by the drawing temperatures. The crystallinity is significantly increased upon deformation. The crystallinity and orientation of PLA products increase with increasing the draw tempera ture when the stretching temperature is 〈 100 ℃, however, the degree of crystallinity and deformation will decrease when the temperature is ≥100 ℃C. While the overall changes in physical properties can be attrib uted to changes in the degree of crystallinity as a function of drawing temperatures, polarized Raman spectra and XRD clearly illustrated changes and the differences in the amorphous and crystalline orientation as a function of processing conditions.