Circularity potential
Low
Strength
Medium
Production energy
High
Stiffness
Low
Embodied CO2
Medium
Density
Medium

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.



Cellulose acetate (CA) resin is moulded into products, such as eyewear (spectacle frames), tool handles, household products, tableware (cutlery handles) and sports goods. They are amorphous and transparent, and can be produced in brilliant, saturated colours.

The mechanical properties differ with proportion of plasticiser. Lower levels yields a harder and stiffer product with higher heat resistance. Increasing the plasticiser content improves impact strength (toughness). Its relatively low softening point, and pliability, means it can be worked easily by hand, and manipulated with a range of forming and polishing processes. Multicolour spectacle frames and jewellery, for example, are produced through a series of cutting and reforming processes, whereby layers of cellulose acetate are built up and compressed into large slabs to create organic repeating patterns.

Cellulose-based engineering plastics may be blended with non-bio chemistry to enhance specific properties. For example, Eastman Treva contains 45% cellulose sourced from sustainably managed forest. It boasts improved dimensional stability over existing bioplastics, as well as strong chemical resistance, including skin oils, sunscreen and cleaners, making it well suited for high-durability items that come in contact with the skin. In addition, low birefringence eliminates the rainbow effect some plastics experience with polarised light, giving the material some potential advantage in electronic device screens and retail displays. Competing with polycarbonate (PC) and acrylonitrile butadiene styrene (ABS), is used in packaging, eyewear and consumer product housings, for example.

Cellulose acetate foam, produced with physical blowing agent, has similar in mechanical properties to expanded polystyrene (EPS). With the right plasticisers (food safe), it is potentially suitable for biodegradable foamed food trays, as well as more demanding protective packaging applications.


Design properties
Carbon footprint kgCO2e/kg
1.5-5.5
Density kg/m3
1330
Tensile modulus GPa
2.4-4.1
Shear modulus GPa
0.85-1.5
Brinell hardness HB
1
Heat deflection temperature ÂșC
52-63
Thermal conductivity W/mK
0.17-0.34
Thermal
insulator
Electrical
insulator