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Pure Appl. Chem.
76(2), 389-413, 2004
Pure and Applied
Vol. 76, Issue 2
Rheological and mechanical properties of poly(a-methylstyrene-co-acrylonitrile)/
poly[(methyl acrylate-co-methyl methacrylate)] blends in miscible
and phase separated regimes of various morphologies.
Part IV: Influence of the morphology on the mechanical properties (IUPAC
L. de Lucca Freitas, and D. W. Schubert
Abstract: Influences of the morphology on the thermal and mechanical
properties of poly(a-methylstyrene-co-acrylonitrile)/poly[(methyl
acrylate-co-methyl methacrylate)] (PaMSAN/PMMA)
blends have been investigated. DSC measurements confirm that all blends
were phase-separated due to the temperature at which they have been
extruded and squeeze-molded. Based on the cloudpoints of 17 blends and
TEM micrographs, the interaction parameters as a function of temperature
and composition were calculated for the lower critical solution temperature
(LCST) system. Varying the morphology by annealing without changing
the composition of the system resulted in a finer morphology for the
85/15 blends, while the 40/60 blend showed an increase in the domain
size with annealing time. Tensile strength and fracture toughness indicate
that the PaMSAN domains in the tougher PMMA
matrix cause a deterioration in the mechanical properties of the blends,
while the PMMA domains in the PaMSAN matrix
improve the mechanical properties. No clear conclusions on the influence
of morphology on fracture toughness could be drawn because in one case
(40/60 blend) the fracture toughness decreases slightly by annealing
and in the other case (85/15 blend) fracture toughness values increase
slightly with decreasing phase separation by annealing. In situ strained
thin sections in the TEM indicated no effect of annealing on the micromechanical
behavior. Shear deformation was observed as the prevailing deformation
mechanism in the PaMSAN and fibrillized crazing
in the PMMA-rich blends. From fatigue crack growth experiments it was
concluded that the fatigue crack propagation threshold is higher for
PMMA than for PaMSAN. Tests on the annealed
samples of PaMSAN/PMMA 85/15 and 40/60 showed
that the differences in morphology did not affect the fatigue crack
growth resistance significantly. From the features of the fracture surface
investigated by SEM, the conclusion can be drawn that the fatigue crack
propagates faster in the more brittle PaMSAN
phase, but the overall advance of the crack front is controlled at the
interphases, resulting in a crack propagation gradient along the interphase.
* Corresponding author.
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