Biodegradation of Cellulose Esters: Composting of Cellulose Ester-Diluent Mixtures

A number of polymers such as polylactic acid (PLA), polycaprolactone (PCL), polyhydroxybutyrate (PHB), Matter-Bi, cellulose acetate (CA) with different degrees of substitution (DS), and cellulose ester-diluent mixtures have been evaluated in a static, bench-scale simulated municipal compost environment. Of the polymers evaluated, cellulose acetate (DS > 2.2), poly(hydroxybutyrate-co-valerate) (PHBV), and PCL exhibited the fastest composting rates, completely disappearing after 14 days. Optically clear resins were prepared from CA (DS = 2.06) and triethylcitrate (TEC) by thermal compounding, and the resins were converted to compression-molded film and injection-molded bars for composting studies. A series of miscible blends consisting of cellulose acetate propionate (CAP) and poly(ethylene glutarate) (PEG) or poly(-tetramethylene glutarate) (PTG) were also prepared and evaluated in composting. In addition to measured weight loss, samples were removed from the compost at different intervals and evaluated by gel permeation chromatography and 1 H NMR. As expected, the CA/TEC films disappeared rapidly upon composting while the injection-molded bars exhibited weight losses of 10−12%. For the CAP/polyester blends, the type of polyester (PEG versus PTG) in the blend made no difference in composting rates. In general, as the DS of the CAP decreased and the amount of polyester in the blend increased, the rate of composting and the weight loss due to composting increased. When the CAP was highly substituted, almost all of the weight loss was ascribed to loss to polyester. When the DS of the CAP was below approximately 2.0, both components degraded.