Laboratory-Scale Composting Test Methods to Determine Polymer Biodegradability: Model Studies on Cellulose Acetate

Entrapment of Hydrophobic Biocides into Cellulose Acetate Nanoparticles by Nanoprecipitation

This contribution reports an efficient method for the production and use of biocide-loaded cellulose acetate nanoparticles. As well-known model biocides 4-Hexylresorcinol and Triclosan were used for in situ nanoparticle loading during a nanoprecipitation process. We show that the nanoparticle size can be well-controlled by variation of the cellulose acetate concentration during nanoprecipitation. Apart from strong evidence suggesting cellulose acetate particle formation according to a nucleation-aggregation mechanism, we further show that the biocide loading of the particles occurs by a diffusion process and not via co-precipitation. The quantity of particle loading was analyzed by ¹H-NMR spectroscopy of re-dissolved nanoparticles, and it was observed that a decisive factor for high packaging efficiency is the use of a biocide with low water solubility and high hydrophobicity. SEM studies showed no influence on the particle morphology or size by both biocides 4-Hexylresorcinol and Triclosan. Finally, an aqueous nanoparticle dispersion can be coated onto model paper sheets to yield pronounced antimicrobial surface-properties. Nanoparticles loaded with the biocide Triclosan showed a high antimicrobial activity against Bacillus subtilis, a cellulase producing bacteria, if applied to model paper substrates, even at extremely low coating weights of 1-5 g/m², respectively. Additional long-term efficacy renders these nanoparticles ideal for various applications.

Biodegradable polymers for the environment

Biodegradable polymers are designed to degrade upon disposal by the action of living organisms. Extraordinary progress has been made in the development of practical processes and products from polymers such as starch, cellulose, and lactic acid. The need to create alternative biodegradable water-soluble polymers for down-the-drain products such as detergents and cosmetics has taken on increasing importance. Consumers have, however, thus far attached little or no added value to the property of biodegradability, forcing industry to compete head-to-head on a cost-performance basis with existing familiar products. In addition, no suitable infrastructure for the disposal of biodegradable materials exists as yet.

Enzymatic degradation of cellulose acetate plastic by Novel degrading bacterium Bacillus sp. S2055

Cellulose acetate (CA)-degrading bacteria were isolated from samples obtained from environments at a population size of 6.7 x 10(1) to 1.0 x 10(8) halo-forming cfu/ml-water or g-solid, suggesting their ubiquitous presence. The classification of 35 isolated strains of CA-degrading bacteria into 15 genera indicates that CA-degrading activity is over a wide range of taxonomical groups. From these isolates, Bacillus sp. S2055 was found to be the most efficient CA-degrading bacterium, and its CA-degrading enzyme(s) was partially characterized. The weight loss of CA plastic film (degree of substitution (DS)=1.7) in the culture of S2055 was less than 12% after a 35-d culture while that in the crude enzyme solution extracted from the culture supernatant reached 62% after the same period. Lipase and cellulase activities were detected in the culture supernatant of strain S2055. The crude enzyme solution contained three major protein fractions that have different mean molecular weights (MWs). Fraction I with the highest MW exhibited both lipase and cellulase activities, while fraction II and III exhibited only lipase activity. Fraction I significantly deacetylated CA (DS 1.5) and fragmented CA plastic film into pieces while the other fractions failed to do so even when used in combination with commercially-available cellulases and lipases. The lipase activity of fraction I against various substrates differed considerably from those of known lipases. It was thus suggested that deacetylation of CA mediated by an enzyme with such a peculiar lipase-like activity is a requisite for the efficient biodegradation of CA plastics.

Relevance of aquatic biodegradation tests for predicting degradation of polymeric materials during biological solid waste treatment

The aquatic biodegradability of cellulose and cellulose acetate with degrees of substitution (d.s.) in the range of 1.5 to 3.0, was compared with the mineralization under laboratory controlled composting conditions. In line with previous observations, it was found that cellulose acetates with d.s. < or = 2.5 were readily mineralized to CO2 in the controlled composting test. The degradation rate was clearly affected by the degree of substitution (d.s. 1.5 > d.s. 2.5 > d.s. 3.0). Surprisingly, however, biodegradation of cellulose acetate materials was not observed in the aquatic Strum test. Modifications of the pH and the inoculum source in an attempt to improve the activity of fungi and actinomycetes in the aquatic environment, did not increase CO2-evolution. It is concluded that the relevance of modified Strum tests is limited for predicting complete biodegradation of polymeric materials during biological waste processing. For evaluation of the compostability of polymeric products or packaging materials, more relevant laboratory controlled composting tests should be used.