Environmental Engineering Reference
In-Depth Information
term that yields peaks (positive or negative) on the baseline of the specific
heat
C
P
versus
T
tracing in a DSC. Area under these peaks and the
temperatures at which they occur can yield information on changes in the
polymer responsible for these. The area under the melting peak (J/mol)
might be normalized against that for a 100% crystalline form of the polymer
(usually estimated) to estimate a value for the percent crystallinity of the
sample (D'Aniello et al., 2000). The area of interest is shown in the DSC
tracing of PP blends in
Figure 3.12
.
3.4.3 Thermal Properties: TGA
TGA involves accurate monitoring of the mass of a sample as a function of
either the temperature, or time at a constant temperature in the isothermal
mode. As the sample dries and disintegrates, its mass is reduced. The
techniqueallowsthemeasurementofvolatilesand/orthefractionoforganic
or inorganic filler present in a sample (Hatakeyema et al., 2005). The
technique is therefore used for quality control and characterization of
compounds that contain known amounts of fillers. It is also used to study
the stability of compounded plastics; chemical changes that evolve a
product, change the mass of sample that can be monitored as a function of
time. A balance with a precision of 0.01-0.001% is used in recent models of
the equipment to record the weight change. The temperature can be raised
at selected rates up to 1500°C and the samples can be heated in an inert
atmosphere, a specific gas or in air. Resolution of the data depends on the
scan rate (typically 10-20°C/min rates are used).
3.5 COMMON PLASTICS
Different fossil fuel-derived feedstock used in the manufacture of common
plastics are as follows:
Ethylene: PE, PP, PVC, PS, PET, and ABS
Propylene: PP, PS, ABS, PC, and nylons
Benzene: PS, ABS, PC, and nylon
Butadiene: PS, ABS, and nylon
Xylene: PET
