Molecular weight biodegradation

Polymers differ in their chemical composition and content of plasticizers, additives, colorants and stabilizers. The leaching of compounds from polymers can promote microbial growth by providing a utilizable carbon source. It is interesting to note that a polymer surface, enriched in low-molecular-weight biodegradable components may allow more colonies of... 

Less volatile low-molecular-weight biodegradation products, were characterized by gas chromatography-mass spectroscopy (GC-MS). Higher molecular weight compounds were characterized by gel permeation chromatography (GPC), membrane filtration, dialysis and nuclear magnetic resonance (NMR). 

To characterize high-molecular-weight biodegradation products, an Amicon Model 202 Diafiltration Apparatus was used sequentially with XM300, PMIO and UM2 membranes at 10, 17 and 55 psl N2 pressure, respectively. The samples tested were water-soluble biodegradation products that had never been freeze-dried. Concentrations of the various fractions were determined on aliquots so that GPC curves could be determined on samples that had always been in solution. 

Gu et al. reported that a high-molecular-weight biodegradable lactic acid polymer was successfully synthesized in two steps. First, the lactic acid monomer was oligomerized to low-molecular-weight hydroxyl-terminated prepolymer the molecular weight was then increased by chain extension using 1,6-hexamethylene diisocyanate as the chain extender. The results showed that the obtained polymer had an M of 27,500 g-mol" and an Af of 116,900 g mol after 40 min of chain extension at 180°C [13]. 

Certain bacterial species produce polymers of y-hydroxybutyric acid and other hydroxyalkanoic acids as storage polymers. These are biodegradable polymers with some desirable properties for manufacture of biodegradable packaging materials, and considerable effort is being devoted by ICI Ltd. and others to the development of bacterial fermentation processes to produce these polymers at a high molecular weight (66). 

Ozone caimot be employed for the disinfection of distributed water because of its short lifetime. Unless removed from the treatment plant, the presence of low molecular weight, oxygenated, and biodegradable organics that ozone produces can promote biological growth. 

Lower molecular weight polymers are more susceptible to biodegradation. 

Other high molecular weight hydrocarbon polymers are not biodegradable, but oligomers of <7j -l,4-isoprene (83), butadiene (84), and styrene (85), are degradable. And there has been further confirmation of biodegradation of oligomeric ethylene (86). 

Anaerobically, poly(ethylene glycol) degrades slowly, although molecular weights up to 2000 daltons have been reported (177,178) to biodegrade. 

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