(217fg) Effect of Preparation Procedure On Polyethylene/Thermoplastic Starch/Zeolite ZSM-5 Composite

Polyethylene (PE) is widely used in rigid and flexible packaging applications due to its optimal combination of high strength, toughness, and moisture resistance.  After usage, however, when the polymer is improperly discarded, it causes environmental pollution.  To mitigate this problem, there has been an increasing interest in reducing the use of PE by blending it with thermoplastic starch (TPS), which is fully biodegradable and compostable.  Unfortunately, these two materials are immiscible, and their blends possess poor mechanical properties.  Incorporating suitable compatibilizers can potentially improve both the miscibility and mechanical properties of polymer blends, as shown by our previous work where the presence of zeolite 5A significantly improved the miscibility of PE/TPS blend.  Thus, the aim of this work was to investigate the effects of zeolite ZSM-5 (ZSM5) and preparation method on the morphological and mechanical properties of PE/TPS blend.  PE/TPS/ZSM5 composites were prepared by extrusion process with a weight ratio of PE to TPS of 7:3 and ZSM5 concentrations of 1–5 wt%.  Two processing routes were used for preparing PE/TPS/ZSM5 composite pellets: (i) melt compounding of PE with ZSM5 was carried out to obtain ZSM5-PE pellets before melt blending with TPS to produce ZSM5-PE/TPS composite; and (ii) TPS was melt compounded with ZSM5 to prepare ZSM5-TPS pellets prior to blending with PE to obtain ZSM5-TPS/PE composite.  The composite pellets from both methods were then converted into films by blown film extrusion, and investigated for their morphological, thermal, and tensile properties.  Differential scanning calorimetric analysis revealed that addition of ZSM5 had no effect on the glass-transition, melting, and crystallization temperatures of PE/TPS blend.  However, the presence of ZSM5 slightly decreased thermal decomposition temperature of the blend by ~5–8 °C.  The matrix of ZSM5-TPS/PE composite showed greater miscibility than that of ZSM5-PE/TPS.  Tensile strength, modulus, and elongation at break of ZSM5-TPS/PE composite were significantly higher than those of PE/TPS blend.  Increasing ZSM5 content resulted in increased tensile strength and modulus of the ZSM5-TPS/PE composite, without affecting its ductility.  In contrast, tensile properties of ZSM5-PE/TPS composite were lower than those of PE/TPS blend and ZSM5-TPS/PE composite.  The results indicate that preparation method plays a significant role in determining the properties of polymer blends.