Understanding and predicting environmental effects on degradation of oxo-degradable polyethylene blown films

Abstract

Polyethylene (PE) based films are commonly used in agriculture for different applications such as mulching, walk-in tunnel and mini greenhouse. In the case of mini greenhouse, the thin film creates a confined environment providing favourable conditions for crop growth, such as increased temperature and moisture retention, hence reducing the need for irrigation and agrochemical treatments. However, in this specific application, it is necessary to control the rate of degradation of the film above ground to enable healthy crop growth. Several studies have investigated the photo-and/or thermo-oxidation of PE in sunlight and when buried in soil or compost. However the degradation rate is not well controlled and the degradation mechanisms are not fully understood. The service lifetime of polymer films is controlled by the chemical reactions leading to chain scission and mediating environmental factors. For application in agricultural cropping films, a controlled accelerated degradation is required. The rate of PE film degradation can be influenced by its intrinsic properties (such as polymer grade, concentration and/or type of pro-degradants) but also by environmental factors, such as UV dose, temperature and humidity. However, in practice, these are not the only factors controlling the polymer lifetime, with poor translation from model (laboratory based) accelerated ageing studies to in-field application. This creates a challenge in accurately predicting the useful iii rate of photo-oxidation. Overall, additional environmental factors to solar dose and temperature were influencing the rate of PE photo-degradation. The key factors were found to be the presence of condensed water and soil type. For the latter factor, the specific soil properties of importance with respect to film degradation appeared to be associated with organic matter, although the impact of soil on PE photo-oxidation was found to be complex and likely dependent at least in part v on soil components that varied between different soil types, consequently influencing their photo-chemistry. This knowledge could assist in designing a modelling tool to recommend the appropriated time-controlled PE film suitable for a specific crop cycles at specific sites across Australia. These findings could also be transferred to other degradable PE film applications, such as mulch films, plastic bags and other packaging products. vi Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, financial support and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have...