It is generally known that secondary cellulose acetate (with 53 to 56% acetyl groups) is suitable for thermoplastic processing. With appropriate plasticizers a plastic material is obtained which excels in transparency and pleasant texture, and it is therefore often used for tool handles, combs, spectacle frames, and the like. In principle, cellulose acetate with such a degree of substitution is biocregradable, although degradation proceeds extremely slowly. However, when common plasticizers are substituted by specific esters and other low molecular components (at least 30% by weight), the ''plastic material'' has the same thermoplastic properties but will decompose in soil or water within just a few years. For example, a cellulose acetate cup buried in sewage sludge lost more than 70% of its original weight within about 18 months. In an aqueous environment (Sturm's test), the decomposition amounted to more than 60%. Under appropriate composting conditions or conditions of anaerobic fermentation, the degradation process is likely to be even faster. However, the material can also be recycled or incinerated without residue. This new kind of biodegradable plastics can be processed on conventional injection molding machines or on extruders adapted to their specific processing properties. They can be turned into granular materials, strips and films, and into injection molded and extrusion blow-molded shapes. The material properties are comparable to those of the known cellulose ester-based plastics. Films and thin-walled hollow bodies are highly transparent. The mechanical properties compare well with those of conventional packaging materials. The thermal resistance is somewhat lower, but the permeability to steam and oxygen is relatively high compared to that of standard plastics. The material is resistant to oils and fats and, for a short while, even to weak acids and alkalies.
