Degradable or not? Cellulose acetate as a model for complicated interplay between structure, environment and degradation.

Degradable and/or biobased plastics are advocated as possible solution to plastic waste problem. Although mechanical and chemical recycling or energy recovery are in many cases a preferred option to regain the material value, for some applications composting is ideal. However, to more generally ensure complete degradation of plastics within a relatively short time-frame in all-natural environments would be extremely challenging, if not impossible. It is also important to keep in mind that it is the chemical structure and composition in combination with degradation environment that determines whether the plastic will degrade and within what timeframe. Biobased materials can be as stable as the petroleum-based counterparts and face the same waste-management problems. One interesting group of biobased materials are the modified biopolymer-based plastics, such as cellulose acetate (CA). How different modifications affect the inherent degradability of biopolymers is still poorly understood, which is reflected in the contradictory literature. This mirrors the complex interplay between structure-environment-degradability, where structural changes such as degree of substitution in the case of CA and changes in selected degradation environment can lead to totally different end-results and conclusions. Understanding these interactions is a fascinating scientific question. The deposition of CA based products as common surface litter makes it also question of societal and environmental interest. The purpose of this review is to summarize the existing knowledge on degradation of CA and in larger perspective highlight the complicated nature of plastic and bioplastic degradation in natural environments and the interplay between different environmental parameters and material modifications on this process.