Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE Ground and spray-dried lignin powders are compared as fillers for polypropylene composites. Differences in powder preparation methods are associated with differences in powder characteristics and composite behavior after melt compounding. Spray-dried lignin produces smaller particles and fewer large agglomerates, while a 5 wt% lignin loading provides a more favorable balance of processability and overall composite performance than a 10 wt% loading.

ABSTRACT
Lignin, an environmentally friendly byproduct from pulping and biorefinery processes, was incorporated into polypropylene (PP) as ground and spray-dried powders. The effects of lignin morphology, particle size, and loading on the mechanical, rheological, viscoelastic, and thermal properties of PP composites were evaluated. Spray-dried lignin powders exhibited a smaller average particle size and a more uniform circularity distribution than ground lignin powders. After adding 5 wt% lignin to PP, the mechanical properties of neat PP decreased, with further reductions observed at 10 wt%. The incorporation of lignin powders reduced the complex viscosity of PP, with composites containing spray-dried lignin exhibiting lower viscosity than those containing ground lignin powders. The storage and loss modulus of PP decreased at a lignin loading of 5 wt% but increased at 10 wt%, with higher values observed in composites containing ground lignin than in those containing spray-dried lignin. The crystallization onset temperature of PP showed no significant change with lignin addition, whereas the degree of crystallinity decreased. The coefficient of thermal expansion (CTE) decreased at a lignin loading of 5 wt% but increased at 10 wt%, with spray-dried lignin exhibiting lower CTE values than ground lignin at the same loading.