Characterization and properties of semi-biodegradable low density polyethylene/palm pressed fibre biocomposite film

Abstract

Semi-biodegradable low density polyethylene/press palm fibre (LDPE/PPF) biocomposite film was successfully prepared. PPF was treated with sodium hydroxide (NaOH) at various concentrations and soaking durations. Oil content analysis showed that the removal of oil residue was largely influenced by soaking time rather than NaOH concentration. The result was supported by a Fourier transform infra red analysis, where the peak intensities of carbonyl groups (C=0) at 1630-1700 cm'1 and alkene (C=C) at 1596 cm'1 decreased with soaking durations. Longer soaking duration led to fully-swollen PPF cellulose chains, thus allowing more oil to be easily removed from the surface of the fibre. However, the removal rate was gradually decreased after 6 hours, probably due to the difficulty to remove the oil trapped among the entangled-swollen cellulose chains. The crystalline phase of PPF was changed into the amorphous rich phase, as shown by the shifted of bonded-OH stretching band at 3280 cm'1 to freed-OH at 3345 cm'1. In addition, the decrease of area under the curve of melting temperature (Tm) and the heat of melting from the differential scanning calorimetry analysis supported the findings. Meanwhile, LDPE/PPF biocomposite was prepared by blending the LDPE resin with various percentages of PPF and glycerol. The mixtures were compounded using a single screw extruder prior to blown extrusion into films. Results from the melt flow index and rheological tests showed that the addition of PPF increased the shear stress and viscosity of samples, owing to the restriction of chain mobility of LDPE by PPF particles. Higher PPF loading had also decreased the tensile strength and elongation at break of the film due to agglomeration of PPF’s particles that caused phase separation between PPF-LDPE matrix, thus weakening the strength of the samples. The formation of a discrete phase observed on the micro-images taken from the scanning electron microscopy supported the results. Meanwhile, increasing the amount of PPF from 3wt% to 7 wt% had increased at about 43% water absorption in 30 days due to the formation of hydrogen bonding between the OH groups of PPF, glycerol and water. This condition provided a suitable environment for the growth of microorganisms thus increasing the biodegradation rate of the samples at an average of 31% weight loss in 12 weeks. However, Tm and the degree of crystallinity were unaffected with increasing PPF content as these properties are strongly influenced by LDPE.