振荡剪切对聚乳酸熔体分子链解缠结的研究

刘天宇; 蒋维娇; 杨卫星; 张琴; 傅强

doi:10.11777/j.issn1000-3304.2018.18053

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振荡剪切对聚乳酸熔体分子链解缠结的研究

研究论文 | 更新时间：2021-01-26

- 振荡剪切对聚乳酸熔体分子链解缠结的研究
- Disentanglement of Polylactide Melt by Oscillatory Shear Stress Field
- 高分子学报 2018年0卷第8期页码：1107-1115
- 作者机构：
  
  四川大学高分子材料科学与工程学院高分子材料工程国家重点实验室　成都 610065
- 作者简介：
  
  E-mail: qiangfu@scu.edu.cn Qiang Fu, E-mail: qiangfu@scu.edu.cn
- 基金信息：
  
  国家自然科学基金(基金号 21627804，51721091)资助项目()
- DOI：10.11777/j.issn1000-3304.2018.18053
  中图分类号：
- 纸质出版日期：2018-8，
  
  收稿日期：2018-2-9，
  
  修回日期：2018-3-24，
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刘天宇, 蒋维娇, 杨卫星, 张琴, 傅强. 振荡剪切对聚乳酸熔体分子链解缠结的研究[J]. 高分子学报, 2018,0(8):1107-1115.

Tian-yu Liu, Wei-jiao Jiang, Wei-xing Yang, Qin Zhang, Qiang Fu. Disentanglement of Polylactide Melt by Oscillatory Shear Stress Field[J]. Acta Polymerica Sinica, 2018,0(8):1107-1115.
刘天宇, 蒋维娇, 杨卫星, 张琴, 傅强. 振荡剪切对聚乳酸熔体分子链解缠结的研究[J]. 高分子学报, 2018,0(8):1107-1115. DOI： 10.11777/j.issn1000-3304.2018.18053.

Tian-yu Liu, Wei-jiao Jiang, Wei-xing Yang, Qin Zhang, Qiang Fu. Disentanglement of Polylactide Melt by Oscillatory Shear Stress Field[J]. Acta Polymerica Sinica, 2018,0(8):1107-1115. DOI： 10.11777/j.issn1000-3304.2018.18053.

摘要

利用哈克旋转流变仪在一定的温度和压力条件下对聚乳酸(PLA)熔体施加应变为正弦变化的振荡剪切场，从而对PLA分子链进行高效的降黏解缠. 结果表明，当温度为190 °C、样品厚度为1.5 mm时，PLA熔体在振动频率和剪切应变分别为3.5 Hz和50%处呈现最佳的降黏效果，其黏度相比于未经处理的熔体黏度下降了3 ~ 4个数量级. 同时，凝胶渗透色谱(GPC)测试结果表明经过振荡剪切处理的PLA其分子量基本不变，表明熔体黏度的大幅下降是由PLA分子链有效解缠结导致而非分子链降解. 示差扫描量热仪(DSC)结果表明，解缠效果最佳的PLA样品相比于未经处理的样品呈现出更低的玻璃化转变温度和较高的结晶度，进一步验证了熔体解缠的效果. 不仅如此，我们研究了不同退火时间(1 ~ 30 min)和温度(180 ~ 200 °C)对PLA分子链重新恢复缠结的影响，发现随着退火温度和时间的增加，PLA在120 °C下等温结晶的半结晶时间不断增加，并向未经解缠处理的PLA样品的半结晶时间不断靠近，表明振荡剪切导致的解缠能在低温度下保持较长时间，在高温下快速复缠.

Abstract

The Haake rotational rheometer was employed to disentangle the polylactide melt by well-controlled oscillatory shear stress with sinusoidal strain and to monitor the melt viscosity in real time. Fisrtly

a PLA sample was disentangled with different strains at various frequency ranges

and the results indicated that the PLA melt represented the lowest melt viscosity which was four orders of magnitude lower than that of the PLA without any treatment when the strain was 50% with the frequency at 3.5 Hz. Then

the molecular weights of all these PLA were measured by gel permeation chromatography (GPC) and almost no change was detected after the oscillatory shear. Taken into account the results of the melt viscosity and the molecular weight measurement

it was reasonable that the significant reduction of PLA melt viscosity was attributed to the effective disentanglement of PLA chains

rather than their degradation. Furthermore

the effect of oscillatory shear on glass transition

crystallization and melting behavior was also studied. It was found that the effective disentanglement of PLA chains was achieved by oscillatory shearing

leading to a lower glass transition temperature and a cold-crystallization temperature together with largely improved crystallinity of PLA. Simultaneously

when compared to the PLA melt without any treatment

the isothermal crystallization of PLA at 120 °C with the lowest melt viscosity also demonstrated that the oscillatory shear could disentangle the PLA melt and thus accelerated the crystallization of PLA. More importantly

the influence of annealing time (1 − 30 min) and temperature (180 − 200 °C) was investigated as well. The semi-crystallization time at 120 °C of disentangled PLA constantly increased with the increasing annealing time and temperature

which got gradually closer to that of PLA without any treatment. These results demonstrated that the disentanglement could be maintained at relatively low temperature and re-entangled rapidly at relatively high temperature. In summary

the Haake rotational rheometer

the common test instrument for the rheological properties of polymer melt

can be employed for the investigation of the disentanglement of polymer melt

which is not merely a simple and effective method to disentangle the polymer melt

but also a well-controlled and real-time monitoring approach for systematically investigating the disentanglement of polymer melt.

关键词

振荡剪切聚乳酸熔体解缠结等温结晶行为

Keywords

Oscillatory shearPolylactide meltDisentanglementIsothermal crystallization behavior

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