Environmental Engineering Reference
In-Depth Information
So, a lot of care must be taken when interpreting the results at room temperature.
TGA measures the quantity and rate of change in the mass of a sample as a function 
of temperature or time in controlled conditions. It is used mainly to determine
the thermal and oxidative stabilities of polymer samples and their compositional
properties [20]. Several currently used TGA devices can emit the burn-off gas to an 
IR spectrophotometer to determine its composition. 
DSC determines the heat low into or out of a specimen as a function of time and
temperature. DSC measures the glass transition temperature, the temperature of
crystallisation and the melting temperature of the polymer [20, 33]. It is a relatively
fast technique and requires a small amount of sample.
Thermal analysis alone cannot provide suficient data. Thus, development of integrated
techniques for simultaneous analysis can be very useful. Integration of TGA with 
MS can provide additional information. The simultaneous application of TGA with 
DSC can yield more information.
The most common mechanical properties used to monitor degradation of polymers
are tensile strength, bending, and compressive properties as described in the American
Society for Testing and Materials (ASTM) standards.
Mechanical properties such as tensile strength are very sensitive to changes in MW
of the polymer. Mechanical properties of the polymer would change only if there is
a signiicant change or loss of mass. In the case of enzyme induced depolymerisation,
the polymer undergoes only surface erosion but the inner part remains undamaged
with very little loss of mass and minimum change in mechanical properties. But for
abiotic degradation, mechanical properties may alter signiicantly with almost no
loss of mass. This is because of the solubilisation of degradation intermediates [9].
Thus, change in mechanical properties to monitor degradation is good in the case
of abiotic degradation.
MW change of biodegradable aliphatic polyesters, such as poly( ɛ -caprolactone),
and poly[( R )-3-hydroxybutyrate] during biodegradation is insigniicant but the
tensile strength and Young's modulus of the ilms decreases considerably. This can be
attributed to the formation of pores and cracks in these ilms during biodegradation
[36].
Similar to the measurement of MW and weight loss, mechanical property measurement
can only give information about the early stages of the biodegradation process, and
do not provide information on the extent of mineralisation. Thus, this method always
has to be employed with caution and veriied with other techniques.
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