Filler characterization, mechanical properties, x-ray diffraction and crosslink density analysis of starch/natural rubber biopolymer composites

Abstract

Starch fillers were extracted from three plant sources namely amora tuber, Tacca lentopeteloides; sweet potato, Ipomoea batatas; yam starch, Dioscorea rotundata and their particle size, pH, amylose, and amylopectin percentage decomposition determined accordingly. The starch was introduced into natural rubber in liquid phase (through gelatinization) by the latex compounding method and compounded according to standard method. The prepared starch/natural rubber composites was characterized by Instron Universal testing machine (UTM) for tensile mechanical properties. The composites was further characterized by x-ray diffraction and crosslink density analysis. The particle size determination showed that amora starch granules has the smallest particle size (156 × 47 μm) followed by yam starch (155 × 40 μm) and then sweet potato starch (153 × 46 μm) with the biggest particle size. The pH test also revealed that amora starch has a near neutral pH of 6.9, yam 6.8, and sweet potato 5.2 respectively. Amylose and amylopectin determination showed that yam starch has a higher percentage of amylose (29.68), followed by potato (22.34) and then amora starch with the lowest value (14.86) respectively. The tensile mechanical properties testing revealed that yam starch produced the best tensile mechanical properties followed by amora starch and then sweet potato starch. The structure, crystallinity/amorphous nature of the product composite was confirmed by x-ray diffraction, while the nature of crosslinking was confirmed by swelling test in toluene solvent using the Flory-Rehner approach. The increasing values of crosslink density in the starch/rubber composite is a clear evidence of good interfacial adhesion between the starch fillers and the rubber, hence good dispersion of starch fillers in the rubber. This research has rendered a workable strategy for enhancing interfacial interaction between a hydrophilic filler (Starch) and hydrophobic polymeric matrix (natural rubber) yielding moderately good tensile mechanical properties with prospects for the rubber processing industry. The studied fillers can partially replace carbon black as natural rubber fillers with reduced cost, no risk to human health and also an environment friendly approach .