Environmental Engineering Reference
In-Depth Information
much on further strain, until it finally breaks. The breaking extension is
the “ultimate extensibility (%),” and the corresponding stress is the “tensile
strength”(MPa).Typicalstress-straincurvesshownin
Figure3.10
illustrate
theinitiallinearpartofthecurveandthestiffeningeffectofglassbeadfillers
at different weight fractions on the properties of LDPE.
Figure 3.10
Left
: Change in shape of the dog-bone test piece.
Right
:
Tensile stress-strain curves for glass bead-filled LDPE at different volume
fractions of beads.
Source: Reprinted with permission from Liang et al. (1998).
Source: Reprinted with permission from Coppieters et al. (2011).
3.4.2 Thermal Properties: DSC (Differential Scanning
Calorimetry)
The range of physical and chemical changes that occur on heating polymers
can be monitored using DSC and thermogravimetry (TGA). These thermal
techniques are commonly used in plastics industry to characterize plastics.
DSC is generally used to obtain information on properties including (i)
the Tg of polymers, (ii) percent crystallinity, (iii) thermal stability or
degradation on heating, (iv) cross-linking or thermal curing, and (v) the
purity of materials. The main features of a DSC instrument are shown in
Figure 3.11
. Essentially, it consists of two identical pans (each equipped
with sensitive temperature sensors), enclosed in an oven. This arrangement
allows the pans to be slowly heated over a range of temperature and the
