Environmental degradation of poly(ethyleneterephthalate).
The degradation of amorphous and orientated PET is investigated by several
analytical methods. In this study, samples of both amorphous and orientated PET
material were exposed to wet and dry soil, various humidities and temperature as
well as UV irradiation.
Results of accelerated ageing studies indicate that the amorphous sheet and
biaxially orientated bottles degrade mainly due to de-esterification and oxidative
chain scission due to their low crystallinity.
At high temperatures (70-90)
breakdown, as characterisedb y viscosity and chain scission measurements,is
indicative of significant polymer deterioration.
Breakdown is enhanced by
increasing temperature, increasing relative humidity and UV irradiation.
regard the polyester bottles are more stable than sheet due to a greater degree of
orientation and hence higher degree of crystallinity.
However, the rate of
degradation is also a function of the surrounding environment. During the course
of degradation, an increase in crystallinity was observed for both sheet and
The rate of increase in crystallinity is initially rapid and is associated with
plasticization by moisture and subsequent annealing. The dry conditions and UV
irradiation cause negligible increase in crystallinity .
An increase in the number of end groups was observed which is due to chain
Whilst the carboxyl and hydroxyl end groups were increased at the
same rate asthermally degraded samples, the increase of carboxyl end groups for
UV degraded samples was significantly higher than hydroxyl end groups.
increase is initially sharp and then more gradual with almost the same rate as
hydroxyl end groups. A
higher level of carboxyl end groups is due to the release
of carbon dioxide and carbon monoxide mainly on the surface of the polymer.
In this work two methods were used to introduce stability to the polymer. The
first was preconditioning the polymer in an inert atmosphere for 48 hours at 600C
which had a better effect for bottles
This stabilizing effect was observed for both
thermal degradation and UV irradiation of polyester materials.
The second method was stabilizing polyester against UV irradiation by the
incorporation of naphthalenea nd benzophenoned erivatives to the structure of the
polyester. In this case the dihydroxybenzophenone showed the greatest
Hydroperoxide formation during hydrolytic degradation is found to be both
temperature and humidity dependent and appears to play a secondary role in