Tuesday, November 18, 2014

FACTORS AFFECTING DEGRADATION



Synthetic polymers are inherently resistant to biological attack. But susceptibility to biodegradation varies and is affected by:
ADDITIVES
Various compounding ingredients may have nutritive value for microorganisms and hence may invite microbial attack. Most of the plasticizers, lubricants, thickening agents, starch and cellulose fillers are susceptible to microbial attack.
PLASTICIZERS
Plasticizer tends to force the chain apart, giving them greater freedom of movement and also reducing van der Waals’ forces between the chains. All plasticizers are affected by fungal or bacterial attacks. Susceptibility of microbial attack increases as the plasticizer level increases.
THE TYPE OF CHEMICAL BOND
Various chemically degradable polymer bonds are: polycyanoacrylates, polyanhydrides, polyketals, polyorthoesers, polyacetals, poly (2-hydroxy-esters), poly (E-caprolactone), polyphosphazenes, polyB-Hydroxyesters, polyamino carbonates, polypeptides, polycarbonates, polyphosphate esters.
WATER UPTAKE
The hydrolysis of the polymer backbone requires water. Degradation rates increase when the hydrophilic component contents are increased.
CRYSTALLINITY AND MOLECULAR WEIGHT
Crystalline polymers degrade slower than amorphous polymers. High molecular weight leads to slower degradation.
PH
pH changes can modify hydrolysis rates by orders of magnitude.
COPOLYMER COMPOSITION
The presence of variety of functional groups having different hydrolysis rates affects degradability.
ENZYMATIC DEGRADATION
Biodegradable polymers can be hydrolyzed passively or actively via enzymatic catalysis.

2 comments:

  1. Thank you med.
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