5. Polymer degradation is a change in the properties
tensile strength, colour, shape, etc.
Polymer-based product under the influence of one or
more environmental factors such as heat, light or
chemicals such as acids, alkalis and some salts. These
changes are usually undesirable, such as cracking and
chemical disintegration of products.
7. Most polymers can be degraded by photolysis to give lower
molecular weight molecules. Electromagnetic waves with the
energy of visible light or higher, such as ultraviolet light-rays and
gamma rays are usually involved in such reactions.
Photo degradation of poly alpha –methyl styrene
---CH2 -cH2 -cH2 -cH2 –co-cH2 -cH2 -cH2 -cH2 -cH2 -cH2 -cH2 -
----
UV rays
---CH2 -cH2 -cH2 -cH2 –co-cH3+cH2 =cH2 -cH2 -cH2 -cH2 -cH2 -----
8. Chain-growth polymers like poly(methyl
methacrylate) can be degraded by hemolysis at high
temperatures to give monomers, oils, gases and water.
For example the PVC eliminates Hcl, under 100–120 °C.
CH2(Cl)CHCH2CH(Cl)→CH=CH-CH=CH+2HCl
9. Solvolysis
Step-growth polymers like polyesters, polyamides and
polycarbonates can be degraded by solvolysis and mainly
hydrolysis to give lower molecular weight molecules. The
hydrolysis takes place in the presence of water containing an acid
or a base as catalyst. Polyamide is sensitive to degradation by acids
and polyamide mouldings will crack when attacked by strong
acids
H2O
~~NH-CO~~ ~~~NH+HOOC~~
10. This degradation usally leads hardening,discolaration
as well as surface change .the degree of oxidative
degradation of the polymer depends on its structure.
Thus unstructured polymer such as polyisoperene or
polybutadiene containing double bonds are easily
attacted by oxygen.
11.
12. Biodegradable plastics can be biologically
degraded by microorganisms to give lower
molecular weight molecules. To degrade
properly biodegradable polymers need to be
treated like compost and not just left in a
landfill site where degradation is very
difficult due to the lack of oxygen and
moisture.
The mechanism of biodegradation is by anaerobic processes,
where oxygen is not present.
13. Biodegradable polymers are of significant interest to a
variety of fields including medicine, agriculture, and
packaging. One of the most active areas of research in
biodegradable polymer is in controlled drug delivery
and release
