Environmental Engineering Reference
In-Depth Information
6.1.2.2 Surface Analysis
Polymer biodegradation can be examined by physical, mechanical, biological, chemical
and electrochemical methods [8]. Biodeterioration of polymers leads to changes in
the surface properties and structures of the polymer. Surface characteristics used to
describe degradation include: morphological changes which involve roughening of the
surface, formation of holes or cracks, de-fragmentation, changes in colour, changes in
amorphous and crystalline regions. These characteristics can be observed using SEM, 
optical microscopy and AFM microscopy [9, 10]. Changes in surface chemistry of
polymers can be measured with FTIR, XRD, XPS and contact angle measurements. 
Despite the availability of so many techniques to characterise the degradation of
polymers, the tools have not all been completely exploited.
Microscopy is a method commonly used to identify and enumerate microorganisms
in biofilms. Many different microscopic techniques have been used to study
bioilms, polymers and biodegradation of polymers. These include: light microscopy,
epiluorescence, SEM, CLSM, and AFM. Among these SEM, AFM and CLSM have 
been extensively used in biodegradation studies because of their higher resolution.
The presence of deposits on the surface can also help to identify the type of
microorganism involved in degradation. Despite the availability of various microscopic
techniques, their use in industry for bioilm identiication, polymer degradation
and monitoring has been limited, because this technique is considered impractical.
There are a few problems associated with these techniques, which include: sample
preparation, a high vacuum requirement, real time visualisation and cost. But with the
use of luorescent tagging and online microscopic investigation the use of microscopes
for monitoring bioilms has increased [6].
SEM provides high resolution and qualitative characterisation of the modiications in 
surface morphology, however, it distorts and damages the samples because it requires
dehydration of the samples and a high vacuum. This leads to limitations in the way
that certain specimens are prepared and imaged [11]. Environmental SEM (ESEM), 
a recent improvement in microscopy, differs from conventional SEM because of 
the presence of a gas in the specimen chamber. So the samples can be viewed under
low vacuum, including hydrated and wet samples [11]. Polymers being electrically
non-conductive, require preparation techniques to make the surface conductive
which further deforms the surface. Although ESEM has been in use for a number 
of years as a technique, it is substantially underexplored. A new imaging technique:
wet scanning transmission electron microscope (STEM), was pioneered by Bultreys 
and Thollet a few years ago [11]. Wet-STEM or STEM-in-SEM actually refers to the 
STEM-in-SEM applied to ESEM, which beneits from the improved ield emission 
[11]. It allows straightforward transmission observations and characterisation of
wet samples including biological samples at nanoscales in a liquid layer. The wet-
 
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