Fundamentals resin viscosity

As discussed in this chapter, a VARTM prcx ess is affected by many fundamental factors such as resin viscosity, fiber preform compaction, fiber preform permeability, resin cure kinetics and temperature control. Flow modeling and curing process modehng can help one to avoid these potential problems during the resin infusion and the curing cycle. 

Epoxy resins and curing agents must have a relatively low viscosity so that formulation compounding can be accomplished easily and without a great deal of energy or degradation of the components. Viscosity is defined as the resistance of a liquid material to flow. It is usually measured in fundamental units of poise (P) or centipoise (cP). Table 3.2 shows a relationship between various common fluids and their viscosity as measured in centipoise. 

In Section 4, we have examined, from a fundamental point of view, how temperature and cure affect the dielectric properties of thermosetting resins. The principal conclusions of that study were (1) that conductivity (or its reciprocal, resistivity) is perhaps the most useful overall probe of cure state, (2) that dipolar relaxations are associated with the glass transition (i.e., with vitrification), (3) that correlations between viscosity and both resistivity and dipole relaxation time are expected early in cure, but will disappear as gelation is approached, and (4) that the relaxed permittivity follows chemical changes during cure but is cumbersome to use quantitatively. 

In a fundamental study of the factors affecting the growth of the rubber domains in a CTBN-toughened DGEBA epoxy resin cured by piperidine (Manzione and GilUiam, 1981) the kinetics of phase separation were linked to the diffusivity, Uab, of the rabber (A) dissolved in the epoxy resin (B). The relevant dependence on the molar volume of the rubber (proportional to the radius of the rubber molecules when dissolved in the epoxy resin) at the viscosity for the temperature T of reaction is given by the Stokes-Einstein equation ... 

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