Surface modification of microcrystalline cellulose from parawood sawdust via mechanochemical process for reinforcement in polypropylene composites

Abstract

The objective of this study is to prepare and modify parawood microcrystalline cellulose (PW-MCC) for applying as reinforced material for polypropylene composites. PW-MCC was prepared from parawood sawdust using acid hydrolysis method with pulp to acid ratio at 1:15 and temperature at 80oC for 2 hours. The obtained PW-MCC exhibited the cellulose type I with CrI at 60%. Moreover, PW-MCC had higher thermal stability than parawood sawdust. PW-MCC was further modified with various types of coupling agent such as maleic anhydride-grafted-polypropylene (PP-G-MA), organosilane, and acid chloride. Vinyltrimethoxysilane and three different acid chlorides such as benzoyl chloride, hexanoyl chloride, and lauroyl chloride were used to modify PW-MCC under mechanochemical method using planetary ball milling at ambient temperature. The optimized condition for each modification and properties of modified PW-MCC were studied and characterized. The functional group from FTIR and surface composition from XPS of silane treated PW-MCC confirmed the chemical bonding between PW-MCC surface and silane coupling agent. The esterified cellulose presented carbonyl stretching of ester peak at 1740 cm-1. Then, PW-MCC and the modified PW-MCC were applied to prepare polypropylene composites at 5-30 wt% loading content without a compatibilizer using an internal mixer for compounding. The compound was fabricated into specimens by injection process. The results of the PP composites revealed that PW-MCC was an effective reinforcing material. The modified PW-MCC enhanced compatibility between PW-MCC and PP matrix resulting in an increasing of mechanical properties, water resistance, and thermal stability of PP composites. Besides, the type of coupling agents was also affected to composites properties. The results indicated that modified PW-MCC with fatty alkyl chain provided a better compatibility than using benzoyl group and organosilane. In addition, using long chain fatty grafted on PW-MCC exhibited a plasticizing effect to composites resulting to the reduction of modulus of the composites. Nevertheless, the suitable content for using modified PW-MCC was 5wt%. Comparatively, cellulose laurate was an effective reinforcing agent for applying in PP composite. Cellulose laurate/PP composite exhibited an increasing of elongation at break and impact strength at 21% and 23%, respectively. In addition, water resistance was increased approximately 80% and thermal stability at Td50% was shifted from 431 to 462oC with char residue at 4.23% which was higher than those of the PW-MCC/PP composites.