高熔融指数聚乳酸母粒的制备及其熔喷材料的可纺性

为制备综合性能优异的聚乳酸(PLA)熔喷非织造材料，探究不同熔融指数PLA母粒对其熔喷可纺性的影响。以纺丝级PLA为原料，采用催化降解法分别设计制备了熔融指数为200、400、600、1 000、1 400 g/(10 min)的PLA母粒，对其分子质量及其分布、流变性能、结晶性能以及热稳定性进行研究；然后进一步制备不同熔融指数的PLA熔喷材料，分析其形貌结构、纤维直径、力学性能。结果表明：随着熔融指数的升高，PLA熔喷母粒的重均分子量从75 566 g/mol降低到29 857 g/mol,分子质量分布变宽，而玻璃化转变温度、热结晶性能及热稳定性无明显变化；随着熔融指数的升高，熔喷纤维的直径逐渐减小，纤维直径为0.5～7μm,且熔喷材料的纵、横向断裂强度显著降低；当PLA熔喷母粒的熔融指数在400～600 g/(10 min)之间时，熔喷材料的可纺性和力学性能最佳。

Preparation of high melt index polylactic acid masterbatch and spinnability of its meltblown materials

Objective Meltblown polymer raw materials often require a relatively high melt index (MI), due to the fact that the polymer melt is extruded from the spinneret hole and then immediately subjected to high temperature and high speed airflow for rapid fiber formation. The melt flow must match its fiber formation speed, too high and too low MI will lead to the formation of melt droplets, seriously affecting the fiber formation process. In order to investigate the effect of different high melt index of polylactic acid (PLA) masterbatches on their meltblown spinnability, the preparation of PLA meltblown nonwoven materials for overall performance improvement was investigated.Method PLA masterbatches with melt indexes of 200, 400, 600, 1 000 and 1 400 g/(10 min) were designed and prepared by catalytic degradation method using spinning grade PLA as raw material, and their capillary rheological properties, molecular weight and its distribution, thermal-crystallization properties and thermal stability were investigated. Further, PLA meltblown materials with different melt indexes were prepared and their morphological structure, fiber diameter and mechanical properties were investigated.Results The melt of PLA meltblown masterbatch is typically "tangential thinning", which is characterized by a decrease in shear viscosity with increasing shear rate. The lower the melt index, the more significant the change in shear viscosity with shear rate, as shown in Fig. 2. No significant differences were found in glass transition temperature and melting point for PLA masterbatches with different melt indexes, and a significant cold crystallization peak appeared in the secondary temperature rise curves for MI=600,1 000 and 1 400 g/(10 min), as is shown in Fig. 4 and Tab. 2. It was also found that the crystallinity of the melt decreases as the MI increases. The higher the MI, the lower the molecular weight and the wider the molecular weight distribution (as shown in Fig. 3 and Tab. 1), which manifests itself in lower mechanical properties. The meltblown fiber with MI=400 and 600 g/(10 min) demonstrates the best uniformity and satisfactory mechanical properties, and the most fiber diameter around between 1 and 4 μm, as shown in Fig. 6-7.Conclusion In recent years, most of the domestic research on PLA has focused on the modification and functional finishing of this raw material, but the research on the meltblown spinnability of PLA masterbatches with high melt index and their influence on the performance of meltblown materials have not yet seen any systematic research. The research on meltblown spinnability of high melt index PLA masterbatches and its effect on the performance of meltblown materials have not been reported systematically. This study provides a theoretical basis and application guidance for the selection of high-quality PLA meltblown raw materials and the evaluation of their performance.