Abstract:

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.

Key words: polylactic acid, meltblown technology, nonwoven material, melt flow rate, melt index, rheology property