DEVELOPMENT OF POLYPROPYLENE COMPOSITES AND POLYLACTIC ACID COMPOSITES CONTAINING CELLULOSE FIBRIL PREPARED BY DISSOLUTION/PRECIPITATION TECHNIQUE

Abstract

The aim of this research is to develop polypropylene (PP) and polylactic acid (PLA) composites reinforced with cellulose fibril which prepared from the novel technique via the dissolution and precipitation of cellulosic materials. Cellulose fibril was prepared from the dissolution of microcrystalline cellulose in NaOH/urea/distilled water (7:12:81 by weight) solution at -5 °C, followed by the addition of starch solution which plays a role as the dispersing agent and performs the anti-coagulation effect. The mixed solution was precipitated in HCl solution to obtain cellulose fibril (CF) which has a web-like morphology with the diameter ranging from 10-40 nm. The high surface area of CF results in the increasing of water retention value (WRV). The surface of CF was modified with two different modifying agents including malenized soybean oil and hexadecyltrimethoxysilane. The results indicate that hexadecyltrimethoxysilane modified cellulose fibril (Silane-g-CF) is the more efficient reinforcement for polypropylene than malenized soybean oil modified cellulose fibril (Oil-g-CF), judged by the rising of onset thermal degradation temperature by 20 °C, the increasing of degree of crystallinity up to 11% and the shift of crystallization peak to higher temperature by 4 °C. Subsequently, Silane-g-CF reinforced PP and PLA composites with the filler content of 0.5, 1.0, 3.0 and 5.0 wt% were prepared by the twin screw extrusion, followed by the injection molding. The results indicate that Silane-g-CF can improve the thermal stability of PP and plays a role as the nucleating agent by increasing the crystallization temperature up to 5 °C as well as the degree of crystallinity. Silane-g-CF/PP composites show the higher impact resistance and Young’s modulus up to 20% and 10%, respectively when compared to neat PP. The enhancement of mechanical properties corresponds to the better compatibility and interfacial adhesion between CF and PP due to surface treatment, evidenced by the rough fracture surface of composites. In case of Silane-g-CF/PLA composites, the thermal stability is slightly increased. The nucleation effect of Silane-g-CF was observed clearly by DSC using the cooling rate of 1 °C/min. The glass transition temperature and the cold crystallization temperature are disappeared while the crystallization temperature is increased up to 5 °C as well as the increment of the degree of crystallinity by 30%. The addition of Silane-g-CF also improves the mechanical properties of PLA, resulting in the increasing of impact resistance up to 30%. At 0.5 wt% filler loading, the elongation at break of PLA is increased up to 50%. However, the decreasing of elongation at break, tensile strength, and Young’s modulus is observed when filler loading is increased, attributing to the plasticization effect caused by the long alkyl chain of organosilane modifying agent.