Synthesis and Characterization of Polyethylene Composites Based on Polysaccharide

Abstract

Some novel biodegradable polymer composites were synthesized, using polyolefin as a matrix with various natural polymers including chitosan, starch and carboxymethyl cellulose as biodegradable additives. The compatibility of the components was enhanced with different silane coupling agents. The materials were heat mixed in brabender plasti- corder mixer using roller rotor. During mixing, different temperatures were used to mix and decompose the initiator to start the grafting of silane and crosslinking of the polymer. The blended materials were hot pressed into sheets. The hydrolysis and the condensation reactions of silane were carried out in hot water at 95°C for 20 hours. After crosslinking reactions, the prepared sheets were dried in vacuum oven for 16 hours before characterization. The structural analysis of the non-crosslinked and crosslinked composites was carried out using Fourier Transform Infrared (FTIR) and Scanning Electron Microscope (SEM) techniques. The crosslinking reaction was confirmed by FTIR spectra, which revealed the important absorption peaks of siloxane (Si-O-Si) and Si-O-C bonds. SEM images also revealed that crosslinking has improved the dispersion and interaction between polymer and the additives. The degree of crosslinking as determined by gel content analysis was found to be directly proportional to the amount of chitosan in HDPE/chitosan composite. In LLDPE/starch/sepiolite composite, it decreased with high sepiolite loading. Thermogravimetric analysis showed higher thermal stability of the crosslinked composites. Differential scanning calorimetry showed decreasing trend of percentage crystallinity with increasing amount of additive. This behavior is associated to the network structure and the disorder of close packing of polyethylene chains. Rheological studies of crosslinked composites showed linear viscoelastic behavior with high complex viscosities (*) and dynamic shear storage moduli (G`) reflecting a strong interaction between matrix-filler interphase and the elastic nature of the crosslinked samples. High tensile strength (TS) and reduced elongation at break (Eb) values were observed in all the crosslinked samples of HDPE/chitosan and HDPE/carboxymethyl cellulose composites. However, the TS and Eb values of non-crosslinked and crosslinked formulations for LLDPE/starch/sepiolite composite showed decreasing trends with high starch and sepiolite loading. Creep experiments indicated a small deformation in crosslinked composites, which showed that silane effectively coupled the immiscible components.