Environmental Engineering Reference
In-Depth Information
are a problem. Contact angle measurement alone cannot be used as a measure of
degradability. The techniques which combine contact angle and other surface property
measuring tools could be very useful.
EIS is a technique for monitoring paints and coatings [27−29]. EIS is one of the least
destructive techniques. This technique has also been used in the detection of microbial
degradation of polymers. It monitors the integrity of oxide layers on surfaces [29].
EIS uses a small magnitude of sinusoidal potential around an open circuit potential
(usually 5−10 mV rms), which does not affect the bioilm. Impedance is measured
directly in the frequency domain. Single frequency voltage is applied to the interface
and the phase shift and amplitude are measured. Reduction in the phase angle and
total impedance at low frequencies show the initiation of small pits that are too small
to be observed under a microscope [28, 30]. EIS is useful during the initial polymer
degradation as it is sensitive enough to detect small amounts of damage in a polymer
[30]. This technique has not yet been fully exploited.
6.1.2.3 Bulk Techniques
Gravimetry is the most widely used, simple method to monitor degradation of
polymers based on weight loss of a polymer. The change in mass can be measured
by comparing the mass before and after the degradation period [31]. The polymer
should be dried to a constant mass before taking the initial weight. After degradation
the sample should be properly washed to remove enzymes, impurities and so on, and
then dried until constant mass is reached [32]. Drawbacks of this method are: 1) a
large quantity of polymers is required, 2) the weight loss recorded may not be really
because of biodegradation because the weight loss could also be from biodeterioration,
3) loss of volatile and soluble impurities, 4) polymer fracture and cracking because
of environmental changes [2, 33], and 5) there is no facility available for on-line
measurement. Gravimetric results need to be correlated with other techniques. If the
problems mentioned here are addressed this could be a good technique.
Determination of the change in MW because of degradation is an important analysis.
Change in the MW of the polymer can be measured using GPC or viscometry
[32, 34, 35]. The MW measurement provides information on the early stages of the
biodegradation process, but does not provide data on the extent of the mineralisation.
Also it is a time consuming and involved process. An improved technique, which
could measure the MW of any polymer or blend would be highly desirable.
Another widely used technique to study biodegradation is thermal analysis. It is
studied using DSC, differential photo-calorimetry and TGA. The main drawback of
thermal analysis is that it measures what happens at a particular high temperature.
