Morphology-interface-toughness relationship in polyamide/polysulfone blends by reactive processing

By reactive blending of polyamide 6 (PA) with polysulfone (PSU) using a gra m-scale mixer (Mini-Max Molder), we prepared a series of PA/PSU (80/20 wt. ratio) blends with various diameters of PSU particles; 70 nm by using phtha lic anhydride-terminated PSU (PSU-PhAH), 0.4 mu m by epoxy-terminated PSU, 0.45 mu m by maleic anhydride-grafted PSU and 1.3 mu m by non-reactive PSU. By Light scattering (LS), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry, it was sho wn that there did not exist any difference in the crystalline morphology of PA matrix among the blends. Although difference in tensile strength among blends was small but on elongation it was large; the smaller PSU particles yielded larger elongation at break. The bulk-fracture toughness was shown t o be higher for the blend with smaller PSU particles, Especially, PSU-PhAH blend showed a remarkably high toughness. In this blend, ductile fracture w as shown by SEM observation. Transmission electron microscopic (TEM) observ ation confirmed the homogenous plastic deformation without interfacial debo nding in the two-phase material. In contrast, other blends showed brittle f racture accompanied with interfacial debonding. The adhesive strength betwe en PA and PSU-PhAH phases measured by asymmetric double cantilever beam met hod was shown to be much higher than in other systems. Thus, when the inter facial adhesive strength is high enough to provide adequate stress transfer , plastic deformation of brittle PSU particle can occur and hence the unifo rm plastic deformation of the whole material may render high toughness. The lower interfacial adhesion seems to yield in less massive plastic deformat ion to resulting in lower toughness. (C) 1999 Elsevier Science Ltd. All rig hts reserved.