Relationship between tensile modulus and oxygen uptake of prooxidant loaded low-density polyethylene films during heal aging

摘要

Polyethylene (PE) films with pro-oxidants are commonly used in agricultural and packaging industries due to their inherent biodegradability when initially expose to heat and/or light in the presence of oxygen. The degradation of films is characterized by formation of oxidation products, weight changes and loss of mechanical properties. This study investigated the relationship between tensile modulus and oxygen uptake of low-density PE films with pro-oxidants under thermal treatment at 50 and 70°C. Blown-type films of varying colorants, thickness and pro-oxidant loading were formulated according to Taguchi design of experiments. Tensile modulus and oxygen uptake of thermally aged films were obtained from force-stroke curves and gravimetric tests, respectively. Results revealed that two out of nine formulated films showed tensile modulus to be significantly increasing with oxygen uptake at 50°C. Correlation was more evident at 70°C where seven out of nine formulations followed the same trend. The improvement in tensile modulus with oxygen uptake indicates increase in crystallinity of films during thermal aging. Increase in hydroxyl index of films with exposure time confirmed their degradation during heat aging. Consequently, concentration of carboxylic acids as major thermo-oxidation products was found higher at 70°C of aging,