Preformed resin system

Pines defend themselves against bark beetles and fungal pathogens by both a preformed resin system and an induced hypersensitive response. In the latter, the infected area at the site of beetle/fungal attack initially becomes soaked with resin. A layer... 

Bonnets for mini excavators manufactured by Kobe Steel, Japan, are molded by RTM using a modified acrylic resin and glass fiber fabric. The 850 mm wide x 420 mm high component has double curvature and is molded with a glass fiber strand preform with surface mat on the outer surface, preformed with an organic binder. The resin system contains 100... 

RIM is very similar to RTM. In the reinforced RIM (RRIM) process a dry reinforcement preform is placed in a closed mold. Next a reactive resin system is mixed under high pressure in a specialty designed mix head. Upon mixing, the reacting liquid flows at low pressure through a runner system to fill the mold cavity, impregnating the reinforcement in the process. Once the mold cavity is filled, the resin quickly completes its reaction. The complete cycle time required to produce a molded part can be as little as 1 min. (see Chapter 8 and Fig. 8-1). 

Advantages of RRIM are similar to those listed for RTM. However, RRIM uses preforms that are less complex in construction and lower in reinforcement content than those used in RTM. The RRIM resin systems currently available will build up viscosity rapidly, which results in a higher average viscosity during mold filling. This action follows the initial filling with a low viscosity resin. 

Resin systems that are used with such preforms are generally epoxies or polyester, but any resin suitable for laminate construction can be used. The fiber options are similar to those for filament winding. However, the single stiff fibers, such as boron or ceramic fiber, cannot endure the tight bend radii. 

High performance composites for this industry must have continuous reinforcement. This contrasts with the chopped fibres used in reinforced RIM (known as RRIM) [1], where short fibres are injected into the moulding via a slurry in one (or both) of the reactant streams. The use of a continuous reinforcement necessitates the placement of the reinforcing package (preform) in the mould prior to dispensing the epoxy resin system. This... 

Occasionally, fibers or tows are inserted or laid into a shape as a preform, and the whole preform is subjected to the injection of the resin system under pressure, such as resin transfer molding (RTM) vacuum-assisted resin transfer molding (VaRTM) or even partial injection of the resin or part of the resin system, with the same qualified resin transfer molding (SqRTM) process. In every case, there is the real possibility of fibers moving under the influence of the injected resin, producing considerable doubt as to the final formal structure, position, or integrity of the fibers after molding. 

However, when low profile additives were applied to these new chemically thickened formulations rather than the BMC and preform unthickened systems, problems were observed. The reaction of the unsaturated polyesters carboxyl groups with the magnesium oxide changed the compatibility between the resin and low profile additive. This caused a separation of the components which resulted in an exudate on the surface of the SMC. Not only did this complicate the compound handling but caused molding defects such as scumming, sticking and porosity. 

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acryHc (52). The acryhc-vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aHphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, soHd epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

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