Cellulose acetate (CA) is a family of bio-based semi-synthetic plastics, some of which are biodegradable and home compostable at the end of their useful life. To be certified compostable, the product must break down into water, CO2, and biomass at a rate consistent with other biomaterials. Also, there must be no negative chemical effects on the final compost, which is ensured through eco-toxicity testing. Thermoplastic types are recyclable.

Cellulose is an abundant renewable material, found in plants, algae and some bacteria. The raw materials used for industrial cellulose acetate production, such as wood and cotton, are converted into useable monomer through a process of esterification. The pulp is processed with acetic acid and acetic anhydride in the presence of sulphuric acid to produce acetate flake from which products are made. All manner of cellulose containing materials may be used in the production of these bio-based plastics, including bamboo, eucalyptus and bacteria. While the choice can affect the efficiency of the process and overall sustainability, it will not affect the properties – these are determined more by the manufacturing process.

The disadvantage of cellulose acetates, is they need plasticiser to be useful. This additive is mixed with the polymer in order to make it more flexible, durable, and processable. A balance must be struck, because these advantages come at the cost of strength and hardness. In the past, phthalate esters were the most common. These are being phased out, especially in toys and food packaging, and replaced with alternatives due to the health risk associated with their use – they are considered harmful and carcinogenic to humans.

The type of plastic depends on the degree of substitution of hydroxyl groups with acetyl types. During the manufacture of triacetate (TAC) the cellulose is completely acetylated (>92%), whereas in regular cellulose acetate or cellulose diacetate, it is only partially acetylated. Partially acetylated types are used in fibre, textiles, filters, films, drug delivery, membranes and moulded products. Triacetate, used in film and fibre, is significantly more heat resistant than acetate and diacetate types – with increasing acetyl content, the permeability to gas and moisture decreases whereas the chemical resistance, heat resistance and stiffness increases.