Biodegradability additives

Upper LEVEL 1 Chronic toxicity Toxicity in soil and plants Additional mutagenicity Long-term toxicity Bioaccumulation Inherent biodegradability Additional abiotic degradability 100 t/annum or 500 t cumulative... 

A study using resuspended river sediment (Marchesi et al. 1991) illustrated the important interdependence of substrate attachment to particulate matter and its biodegradability. Addition of sodium dodecyl sulfate that is degradable resulted in a relative increase in the number of particle-associated bacteria, whereas this was not observed with the nondegrad-able analogs such as sodium tetradecyl sulfate or sodium dodecane sulfonate. 

The skeleton of the non-degradable polymers containing a high percentage of biodegradable additives survive the degradation and pollute the environment. 

One of the most-commercialized routes is the addition of starch-based materials but other biodegradable additives are used. Marketed solutions are numerous, for example, without claiming to be exhaustive. 

W. J. Bailey s(52,53) work with ketene acetals deserves mention as potentially a route to biodegradable addition polymers. Its novelty resides in the instability of the vinyl radical and rearrangement to introduce a polyester linkage into a radically produced polymer. As we shall see in the next section, polyesters are biodegradable hence, their Introduction into a polymer with a C-C backbone produces weak links which fracture the polymer into oligomers which we have seen are biodegradable. This chemistry is exemplified schematically, below. 

When a biodegradable additive is employed, microorganisms can easily utilize the additive. The porosity of the material is thereby increased and a mechanically weakened film is obtained. The surface area will be increased, and this film will be more susceptible than the original film to all degradation factors including biodegradation. 

This indicates the possibility of making addition polymers biodegradable by the introduction of ester linkages in to the backbone. Since the free radical ring-opening polymerization of cyclic ketene acetals, such as 2-methylene-1,3-dioxepane (1, Scheme I), made possible the introduction of ester groups into the backbone of addition polymers, this appeared to be an attractive method for the synthesis of biodegradable addition polymers. 

Muzafarov, Golly and Moller 646 have prepared similar poly(alkoxysilanes) that are easily hydrolyzed under acidic conditions and are thus biodegradable. Additional branched organosilicon polymers of interest include those of Ishikawa et al. fi4c ... 

Since the monomer I would copolymerize with a wide variety of comonomers with the introduction of an ester group into the main chain, this appeared to make possible the preparation of biodegradable addition polymers. Copolymerization of ethylene and the ketene acetal I at 120°C produced a series of copolymers containing ester groups in the backbone of the copolymer, again with quantitative ring opening. 

C02 method applied to linear polyethylene containing a biodegradable additive. J. Appl. Polym. Sci. Appl. Polym. Symp. 35 423-30. 

Further, the blends may contain biodegradable additives to enhance their disintegration and biodegradabUity in the environment. Examples of biodegradable additives include thermoplastic starch, microcrystalline cellulose, methyl cellulose, hydrox5rpropyl cellulose, PLA, poly(hydroxy butyrate), or poly(vinyl alcohol) (50). 

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