Mathematical Model Development Using Commercial Polypropylene to Evaluate Degradation of Plastic Under the Thermal Fatigue Cycles; Modelling approach.

Abstract

Recycling of waste plastics is of great interest in solid waste management and characterization of waste plastic. The change of stress-strain behaviour of waste plastic depends on environment factors and the number of days exposed to heating at day time and cooling at night. Stress-strain behaviour of commercial grade polypropylene at the end of each thermal fatigue cycles was studied. Heating-cooling cycle was set to 8 hours for heating at a specified temperature (80°C, 100°C, 120°C 140°C and 160°C) and air cooling over night at ambient temperature. Toughness of each sample was calculated in two different ways, in one method it was calculated using regression equation based on stress values of strains at 0.5% , 1% , yield point, breaking point and strains at one third and two third of plastic region. In the other method, the geometrical area of the stress–strain curve was calculated using yield stress, breaking stress, elastic limit, young modules. Matching ratio of toughness (β) is defined as a new index to calculate the ratio of toughness calculated from regression equation and parameters of stress-strain curve. The percentage of relative difference of matching ratio (  %) of toughness is defined as another index. It is defined with respect to the matching ratio of commercial polypropylene samples without exposing to the thermal fatigue conditions ( 0  ).The percentage of the retention of plastic behaviour (RPB %) of commercial plastic product is defined as another index. It can be calculated when 0  is known. The proposed model can be used to calculates retention of plastic behaviour (RPB%) as a percentage with respect to the original state under the natural condition.