Impact of Repetitive Recycling on Optical Properties of Virgin and Recycled Polypropylene Blends Based on Material Value Conservation Paradigm

Abstract

Implementation of material value conservation (MVC) needs to be proven through research to determine impact upon plastic properties such as optical properties of virgin plastic and recycled plastic blends. Optical properties such as colour, transparency and gloss are important parameters for appropriate quality of plastic packaging. Degradation of optical properties occurs during recycling processes of plastic materials and the declining properties of recycled products could be improved by blending them with virgin materials. This research aims to reveal the impact of repetitive recycling on optical properties of virgin and recycled polypropylene (PP) blends based on MVC paradigm. The first step of this research was to determine composition of virgin PP and recycled PP blends. Proportion of 70% virgin PP and 30% recycled PP was selected as a blend composition. The next step of this research was repetitive recycling of virgin PP and recycled PP blends with implementation of MVC up to the 8th recycling stage. The specimens of plastic blends were made from the 1st, 2nd, 4th and the 8th recycling stage and then their optical properties were tested with the American Society for Testing Materials (ASTM) methods. Generally, degradation level of optical properties will increase during the recycling processes. Testing results show a slightly change of colour properties. Degradation level of gloss properties is gradually increased by a maximum degradation level at the 8th recycling stage as 17.46%. However, transparency had a maximum degradation level at the 4th recycling stage as 20.93%. It means that the plastic blends can be used as viable raw materials based on their optical properties with more attention to the gloss. Furthermore, the implementation of MVC will provide more benefits through extending the life cycle of recycled products, reducing virgin plastic consumption, optimizing the use of plastic waste and reducing plastic waste generation.