Synthesis of Polyblends from Sulfonated Polystyrene and Bacterial Polyhydroxybutyrate and Its Characterizations

The increasing volume of plastics used has caused the increase plastic wastes in our environmental, which are usually made from non-biodegradable material. If it is not solved immediately, it can make environmental pollution. This problem has motivated many researches to make biodegradable polymers, such as modifying polymers that are used as plastic material with a biopolymer in order to obtain plastics which can be decomposed by microorganisms in environment. In this research, polystyrene (PS) obtained from styrofoam was sulfonated to be sulfonated polystyrene (PSS), and then blended with polyhydroxybutyrate (PHB) as a biopolymer. PS in this research was isolated from styrofoam, while the PHB was obtained commercially from PHB from Aldrich Chemical Inc. The first, PHB had been hydrolyzed in order to decrease its molecular weight. The sulfonation reaction was done to give polar group to PS, so that PS could be a homogeneous membrane with PHB, because PS and PHB have different polarity. The sulfonation degree of PSS synthesized in this research was 9.10%. The polyblend membranes were made by solvent casting method. PSS was dissolved in toluene:n-butanol with composition 7:3 and PHB in chloroform, then the polymer solutions mixed together until homogeneous. Afterwards, this solution was casted in petri dish and dried up in room temperature. Polyblend membranes prepared in this research were PS/PHB (80/20), PSS/PHB (90/10), PSS/PHB (80/20), PSS/PHB (70/30), PSS/PHB (60/40), and PSS/PHB (50/50). Those membranes were characterized by functional group analysis using FTIR (Fourier Transform Infra Red), crystallinity analysis using XRD (X-Ray Diffraction), thermal stability analysis using TGA/DTA (Thermal Gravimetric Analysis/Differential Thermal Analysis), mechanical properties analysis using Autograph (tensile strength), biodegradability analysis in activated sludge, and morphology analysis using SEM (Scanning Electron Microscope). FTIR results show peaks of the functional groups of polymer in the polyblend. Between PS/PHB (80/20) and PSS/PHB (80/20) polyblend, the higher crystallinity was obtained in PSS/PHB (80/20) polyblend. It was shown that sulfonation process could increase crystallinity, and if comparing between PSS/PHB (80/20) with PSS/PHB (50/50), the crystallinity increases with the increasing PHB composition, while the thermal stability and elasticity modulus (mechanic properties) decrease. The biodegradation test during 5, 10, 20, dan 30 days show that there were decreasing of polyblend mass with increasing the time of biodegradation. After 30 days, polyblend that shows highest degradation was PSS/PHB (80/20). SEM results show the difference between PSS/PHB (50/50) before and after biodegradation. The holes in surface of polyblend after biodegradation were bigger than that before biodegradation. This was indicated that bacteries in activated sludge could degrade the biopolymer part of polyblend. Based on the characterization results, the polyblend which was potential to be applicated as biodegradable plastic was PSS/PHB (80/20), due to PSS/PHB (80/20) had the similar mechanical and thermal stability properties to PS/PHB (80/20), but the value of % mass decrease of PSS/PHB (80/20) for biodegradation test was quite high.

Keywords: biodegradable polymer, sulfonated polystyrene, polyhydroxybutyrate, polyblend