TENSILE BEHAVIOR OF BLENDS OF POLY(VINYLIDENE FLUORIDE) WITH POLY(METHYL METHACRYLATE)

Blends of poly(vinylidene fluoride) (PVF2) and poly(methyl methacrylate) (PMMA) were prepared over a wide concentration range and tested in tension at the same relative temperature below the glass transition. Testing was performed at strain rates ranging from 10 to 0.01 min-1 at test temperatures from Tg-40 to Tg-10. By normalizing the test temperature to fixed increments below Tg, blends and homopolymers can be compared on the basis of PVF2 and PMMA composition and crystallinity. In nearly all blends, under conditions favouring disentanglement, (decrease in strain rate, or increase in test temperature), the yield stress and drawing stress decreased while the breaking strain increased. For materials with about the same degree of crystallinity, those with a higher proportion of amorphous PVF2 exhibited brittle-like behaviour as a result of interlamellar tie molecules. In the semicrystalline blends, yield stress remains high as the test temperature approaches Tg, whereas in the amorphous blends the yield stress falls to zero near Tg. Results of physical ageing support the role of interlamellar ties which cause semicrystalline blends to exhibit ageing at temperatures above Tg. © 1990 Chapman and Hall Ltd.