A brief review of the potential for microwave heating in the manufacture of fiberreinforced composites is presented, with particular emphasis on the Microwave Assisted Pultrusion (MAP). Manufacture of a 6 mm cylindrical glass reinforced profile, based on a number of latent-cure epoxy resins by MAP is described. These materials combine room temperature stability (long pot life) with rapid crosslinking at elevated temperature. The measured line speeds exceeded 2 m/min, using approximately 800 W of applied microwave power in a single mode TM,,, cavity operating at 2450 MHz. The measured pulling force was about 250 N, showing a stick-slip behavior for a crosslinked profile. The ultimate tensile strength and the interlaminar shear strength of the profiles increased after post curing, suggesting that the extent of crosslinking in the MAP die may be diffusion limited. Permeability of free space, 1.25 X lo4 H/m Relative permeability Electrical conductivity, siemens/m Density, kg/m3 Angular frequency, rad/s Heat of reaction, kJ/kg POLYMER COMPOSITES, AUGUST2000, Val. 21, No. 4 593 J. M . M e t h v e n , S . R. ( i y a n L, and A. 2. Abidin
This paper describes a new class of thermosetting polymer blends. The blends are now used commercially in the manufacture of sheet moulding compounds (SMC) where they exhibit important advantages compared with conventional systems. The new compositions comprise a cross-linkable base resin and unsaturated monomer in which the base resin is dissolved and a saturated additive resin which has a crystalline melting temperature T m below the temperature T r at which cross-linking occurs. Between T r and T m the additive and base resin form a single liquid phase, which on cooling thickens reversibly to a leathery sheet with no bulk phase separation. The paper describes the mechanisms underlying this viscosity switch phenomenon and the partial compatibility criterion used to select the resin-additive combinations which exhibit this behaviour.
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