Development of durian skin fibre nanocomposite via in situ polymerization of lactic acid from kenaf

Abstract

Polylactic acid (PLA) recently gained a widespread popularity as a biodegradable polymers matrix. PLA is derived from renewable resources and easily processed due to its great tolerance towards thermal process. PLA however exhibits several limitations when in service such as in industrial applications that involve huge mechanical utilization. Therefore surface modification on the PLA was carried out. One of the methods to modify the surface of PLA is through reinforced with natural fibre to become a composite. The aim of this work is to develop PLA nanocomposite via in situ polymerization. The monomer used is based on lactic acid derived from kenaf biomass (KB). Polymerization is carried out in the presence of durian skin nanofibre (DSNF) as nanofiller. Through in situ polymerization method, the use of machineries may be avoided and the potential of enhancing the properties of the existing composite becomes possible. The process started with the optimization of KB pre-treatment with diluted H2SO4 acid and about 25.33% of glucose conversion that was attained from previous process. Next, about 17.14 g/L and 18.33 g/L of lactic acids that was yielded from the optimization of lactic acid fermentation in KB under varying conditions of medium compositions and processes. DSNF is isolated from DSF via biological method. The diameter of DSNF is in the range of 41-89 nm and length is 1.2-3.1 µm. As both lactic acid and DSNF are ready, then the polymerization process on the PLA (PLA from KB), which is the matrix in this study and followed by the addition of DSNF for fibre loading (1, 3 and 5 wt%). Gel permeation chromatography (GPC) revealed that the molecular weight of PLA from KB is 9.5 X10-3 g/mol. From FTIR analysis, it is found that the PLA from KB is successfully produced due to similar chemical bonding with the commercial PLA. However, there are impurities present in the PLA from KB as confirmed by nuclear magnetic resonance (NMR) analysis. The FTIR analysis unveiled that as the percentage of DSNF increased, there is significant improvement in the compatibility between the nanofibre and PLA. This is demonstrated by the wavenumber at around 1450-1000 cm-1 and 1150-1050 cm-1. Additionally, the TGA analysis of PLA/DSNF nanocomposites illustrated an improvement in the thermal analysis at the highest percentage of residue when 5 wt% of DSNF is added. The differential scanning calorimetry (DSC) revealed that glass transition temperature (Tg) and melting temperature (Tm) of PLA/DSNF nanocomposites are lower than the commercial PLA. Among those compositions of composites (1, 3 and 5 wt %), 5 wt% provided the highest rigidness but with poor distribution of DSNF as revealed under field emission scanning electron microscope (FESEM).