Biomedical Engineering Reference
In-Depth Information
10.6.3 Infra-red spectroscopy
A thin film was made by scraping off the outer surface of the polymer insert
and dissolving it in decalin solvent to create a thin (30 mm thick) film. The IR
spectrum recorded on the thin film showed the polymer to be a polypropylene
copolymer with ethylene, but it also showed an anomalous peak at 1735.7
cm
-1
(Fig. 10.29). This is the characteristic position of the carbonyl group
(C=O) produced by premature oxidation of the polymer:
-[CH
2
-CH · CH
3
]- + O
2
Æ -[CO -CH · CH
3
]- + H
2
O
Further oxidation occurs at carbonyl group, eventually splitting the
chain:
-[CO-CH · CH
3
]- + O
2
Æ -CO
2
H + HOCH · CH
3
-
The extent of oxidation was judged by comparing the height of the carbonyl
peak with that from a standard sample, and it indicated a very high level
of degradation, so explaining the deterioration in the tensile strength of the
insert.
10.6.4 Conclusions
The cause of the premature fracture which injured Mrs s lay in a defective
plastic insert at the arm rest of the crutch. The polymer used, polypropylene-
61.24
C = O absorption
14.4
4000 3500 3000 2500 2000
1500
1000
Wavenumber cm
-1
10.29
Infra-red spectrum of polypropylene from crutch insert
showing oxidation peak.
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