(217w) Effect of Stearic Acid-Grafted Starch On Processability and Properties of Polyethylene/Thermoplastic Starch Blends

Polyethylene (PE) is a versatile thermoplastic: it is cheap, chemically inert, and easy to convert into various shapes and sizes of plastic products.  Therefore, PE film has been used in a wide variety of applications, e.g. plastic bags, packaging, labels, building construction, and landscaping.  However, PE is a petroleum-based plastic and cannot be degraded under normal composting condition, leading to plastic waste in the environment.  Full or partial substitution/replacement of PE with other biodegradable materials is an alternative way to solve this problem.  Thermoplastic starch (TPS) is a bio-based material made from starch, which is renewable, cheap, non-toxic, biodegradable, compostable and environmentally friendly.  Although TPS is the cheapest bio-based and biodegradable plastics and possesses the highest biodegradation rate among those, its hydrophilicity restricts the miscibility or compatibility with hydrophobic PE.  Improvement of hydrophobicity of TPS before blending with PE and/or addition of compatibilizer to the PE/TPS blend system have been known to be effective strategies to improve miscibility between PE and TPS phases.  In the past, most organic compatibilizers for PE/TPS blends were PE derivatives such as PE-g-maleic anhydride and poly(ethylene-co-vinyl alcohol) (EVOH); there has not been a systematic study on the use of starch derivative for the miscibility purpose of PE and TPS.  Although PE-g-maleic anhydride is an effective compatibilizer for PE based blend, it might be unsafe in contact with food and human tissue.  Therefore, the aim of the present work is to improve the miscibility between PE and TPS using stearic acid-grafted starch as a compatibilizer.  PE and TPS were melt blended in a twin screw extruder using a weight ratio of PE:TPS of 60:40.  The obtained PE/TPS blend resins were then converted to film by blown film extrusion.  Processability in blown film extrusion of PE/TPS blends was improved when stearic acid-grafted starch with a content of 0.3-5.0 parts per hundred parts of matrix (phm) was incorporated.  Melt processability of PE/TPS blend increased (~ 80-350 %) by the addition of stearic acid-grafted starch at a content of 0.3-1.5 phm; however, a larger content of 3.0-5.0 phm caused decreased melt flow characteristics.  PE/TPS blend films showed improved tensile strength (~30-60 %) and ductility (~ 2-15 %) when stearic acid-grafted starch was added.