Effect of rice straw fiber and Polyethylene glycol on polylactic acid/polyhydroxybutyrate-valerate blends

Abstract

Biodegradable polymer is one of the alternatives that have potential to overcome serious environmental problem and depletion of crude oil. The materials that have been used in this study are polylactid acid (PLA), polyhydroxybutyrate-valerate (PHBV), rice straw (RS) fiber and polyethylene glycol (PEG). PLA and PHBV are one of biopolymer that can complement each other properties. The mixing process of these composites was carried out using heated two-roll mill (DW5110). The blends between PLA and PHBV slightly reduced tensile strength but increased Eb. Besides, it also increased the Young’s modulus. The optimum ratio of the blends is 50% PLA with 50% PHBV. This study also focused on the effect of RS fiber and PEG as plasticizer on PLA/PHBV blends. The RS fiber content was varied from 5 to 25 wt%. 5 wt% PEG based on RS fiber content was added. The addition of RS fiber into the blends reduced the mechanical properties and thermal stability however the water absorption increased. The incompatibility of RS fiber with PLA/ PHBV blends was proven by SEM micrographs. PLA/PHBV blends show high modulus and high tensile strength but it is quite brittle. . The goal of adding plasticizer to PLA/ PHBV blend with RS fiber is to enhance the polymer elongation and to reduce the brittleness while maintaining optimum polymer strength and stiffness. After the addition of PEG, the tensile strength reduced, while the Eb and Young modulus increased. The amphiphilic properties of PEG slightly reduced the water absorption. From FTIR spectra, it can be seen that the presence of PEG into PLA/PBV blends filled with RS fiber reduced the –OH group intensity. Natural weathering and soil burial test until 6 months were performed to determine the biodegradability of the polymer and were confirmed by evaluating the mechanical, morphological, carbonyl index and crystallinity. The addition of RS fiber had reduced the mechanical strength but carbonyl index and crystallinity increased. The crack, pores and fungus colonization was shown in SEM micrograph, indicated that the biodegradation was more pronounced with the addition of RS fiber. The addition of PEG also helps to increase the degradability by increasing the surface area for microbial attack. In conclusion, the addition of RS fiber increased the degradability and the presence of PEG as plasticizer improved the Eb between the blends.