The morphology gradient through the thickness of an injection-moulded blend of 10% by weight acrylonitrile-butadiene-styrene (ABS) and 90% by weight polycarbonate (PC) has been characterized. Brittle fracture surfaces were etched and examined both parallel and perpendicular to the injection direction in the scanning electron microscope. In the centre of the plaque, the morphology was isotropic with the ABS phase dispersed in the PC matrix as large composite rubber particles about 1 pm in diameter and smaller particles of free styrene-acrylonitrile (SAN) about 0.3 #m in diameter. About half the distance from the centre to the edge, the morphology of the free SAN phase changed from predominantly spherical to predominantly string-like. The SAN strings connected the rubber particles to form an oriented ABS bead-and-string structure that was essentially continuous in the injection direction. It was thought that the free SAN was highly extended under elongational or shear flow while remaining attached to the rubber particles because of miscibility with grafted SAN. The bead-and-string structure was retained near the edge where the melt solidified most rapidly. In the centre of the plaque, the low shear rate during mould filling and longer cooling time after mould filling favoured relaxation of the bead-and-string structure. The morphology gradient through the thickness was created by the competition between the relaxation rate and the cooling rate after mould filling. In this case, relaxation was thought to occur by interfacial-tension-driven break-up and end-pinching mechanisms to produce the dispersion of rubber and free SAN particles. Evidence to support the break-up mechanism was obtained when annealing above the glass transition temperature of PC for a matter of seconds, the timescale of mould cooling, caused the bead-and-string structure to convert to a dispersion of composite rubber particles and SAN particles.
Посилання на статтю:
Formation and break-up of a bead-and-string structure during injection moulding of a polycarbonate/acrylonitrilebutadiene- styrene blend / M.-P. Lee, A. Hiltner* and E. Baer // Polymer. – 1992. – Vol 33. – P. 675-684.