Chemistry Reference
In-Depth Information
for Testing and Materials (ASTM) D-638-V standards. Sample powders of
1.5 g were applied to tensile bar wells in a stainless steel mold and heated in
a hydraulic press (Model C, Carver Inc., Wabash, IN) at 125-150 1C under a
pressure of 89.6 MPa per mold for 20 min. Tensile bars were evaluated using
an Instron Universal Testing Machine (Model 4201, Instron Corporation,
Norwood, MA) using a cross-head speed of 10 mm min
1
, a gauge length of
7.62 mm and a 1 kg load cell.
The mechanical properties [tensile strength (s
u
), Young's modulus (E),
and elongation-at-break values (%El)] of the CAGs were affected by the
curing process, see Figure 7.2. Additional thermal curing generally resulted
in CAGs with significantly higher s
u
and %El values compared to the un-
cured CAG samples. However the E values were unaffected by curing, which
reflects the high degree of brittleness of the polyesters. Evidently, the uses of
additional curing caused additional polymerization through cross-linking
and esterification, as evidenced by the improved mechanical properties. It is
dicult to compare these mechanical results with the mechanical results of
other investigators working with carboxylic acid glycol polyesters because of
the differences in ingredients, preparation and heating procedures em-
ployed. However, the tensile strength and stiffness properties of the CAG
bars are several times greater than those reported in the literature for other
carboxylic acid glycol polyesters. However, the elongation-at-break values
were much inferior to other carboxylic acid glycol polyesters studies. This
is to be expected since high stiffness is at odds with high elongation.
Furthermore, the CAG tensile bars exhibited mechanical properties that are
comparable with thermoplastic resins, see Table 7.4.
Figure 7.2 Effect of curing duration on the mechanical properties of citrate glycer-
ides. Means and standard errors are presented.
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