Influence of surface treatments and coupling agents on the thermal and thermo-mechanical properties of yerba mate/post-consumer polypropylene composites

The main objective of this work is to evaluate an interaction between yerba mate fibers (YM) and post-consumption polypropylene (r-PP) using the surface treatments and coupling agent. YM fibers were submitted to two different surface treatments: alkaline solution (NaOH 10%) and 3-aminopropyltriethoxysilane (APTS) (5 wt%). The influence of 5 wt% addition of maleic anhydride (MA)-grafted polypropylene copolymer (PP-g-MA) coupling agent in the composite processing was also evaluated. YM of 30 wt% was loaded into r-PP by extrusion, and then the specimens were prepared by injection molding. The results showed that all treatments were effective in improving thermal stability increase the maximum degradation temperature by approximately 5 degrees C, as also confirmed by differential scanning calorimetry analysis. Composite with PP-g-MA presented the greater increase in thermal stability and in the crystallization index (approximately 46% in relation to the r-PP/YM30 composite). DMA analysis revealed increases in the storage and loss moduli and a decrease in the damping factor for all composites produced with treated fibers and coupling agent. The enhancement of the analyzed properties of these composites is related to the better interfacial adhesion between YM fiber and r-PP, which was confirmed by scanning electron microscope micrographs.