Processing, thermosets pultrusion

Composite processing uses specialized methods. For thermoplastics, glass mat thermoplastic (GMT) is the main method but prepreg, lay-up, tape winding, pultrusion are also used to produce composites. SMC/BMC are the main processes for thermosets but lay-up is currently used for large parts and prepregs are used for high-tech parts. 

The characteristics of the three most common thermoset resin systems used in pultrusion are compiled in Table 11.2 [3]. It is noteworthy that unreinforced polyesters and vinylesters shrink 7-9% upon crosslinking, whereas epoxies shrink much less and tend to adhere to the die. These epoxy characteristics translate into processing difficulties, reduced processing speed, and inferior component surface finish. It is normal practice to use resin additives to improve processability, mechanical properties, electrical properties, shrinkage, environmental resistance, temperature tolerance, fire tolerance, color, cost, and volatile evaporation. It is normally the resin, or rather its reactivity, that determines the pulling speed. Typical pulling speeds for polyesters tend to be on the order of 10-20 mm/s, whereas speeds may exceed lOOmm/s under certain circumstances. Apart from the resins characterized in Table 11.2, several other thermosets, such as phenolics, acrylics, and polyurethanes, have been tried, as have several thermoplastics (as will be discussed in Sec. 11.2.6). 

As pointed out in the beginning of the chapter—and perhaps also noticeable from the process description earlier—the pultrusion process at first appears rather simple and straightforward however, several intricacies arise on closer inspection. The key technology issues of pultrusion of thermoset-matrix composites are usually considered to be resin formulation, temperature control, material guidance, and die design (not in order of importance). It is typically the skill in these areas that distinguishes a successful pultruder from his hapless competitor. 

Recendy, storm doors have been constmcted of advanced thermoplastic composites. Stampable, glass-mat reinforced polypropylene sheet is used to create a high strength outer skin. These compression molded skins are welded together using a friction or ultrasonic process then injection molded with a polyurethane foam core to produce an insulated structure. New technology for window frames incorporate the pultrusion of frame channels to produce a thermoset composite channel that can be filled with fiber glass for further insulation enhancement (12,31,33,34,48,49,54—56,60—67). 

Pultrusion [PHENOLIC RESINS] (Vol 18) [PLASTIC PROCESSING] (Vol 19) [REINFORCED PLASTICS] (Vol 21) [COMPOSITEMATERIALS - SURVEY] (Vol 7) resin properties required for [COMPOSITE MATERIALS - POLYMER-MATRIX - THERMOSETS] (Vol 7)... 

In the pultrusion process, continuous fibers are impregnated by the thermoset precursors and are pulled through a heated die where the cure takes place this produces continuous profiles of different shapes at a rate of the order of 1 m min-1. 

If the filaments are not wound onto a mandrel but simply gathered into relatively large bundles and led slowly into a heated consolidation zone, emerging from a die partly or completely cured, the primitive essentials of pultrusion are present (Fig. 2.3(b)). This process began as the thermosetting resin equivalent of extrusion, that is, it was a continuous operation for manufacturing profiles, such as rod and channels. The method has been extended to fibre reinforced thermoplastics. 

CAS 21645-51-2 EINECS/ELINCS 244-492-7 Uses Flame retardant, smoke suppressanL processing aid, water resist, aid, antistat for wire/cable, elec, insulators, printed circuit boards, potting resins, molded and extruded polyolefins, flooring compds., conveyor belting, fabric coatings, polyester and aciylic pultrusion compds., thermosetting resins (BMC, SMC), PVC, EVA, EPDM, XLPE, EEA, thermoplastic elastomers, silicone rubber, NR, SR, acrylic resins, unsat. polyesters... 

Two processes for the forming of reinforced thermosets (a) pultrusion and (b) filament winding. 

These thermosetting resins contain a urethane prepolymer in methyl methacrylate monomer. Although they are cured in a similar fashion to polyesters, their initial viscosity is much lower and the cure reaction is more rapid. The speed of cure along with the odour of the monomer preclude the use of open mould processes, but these resins are especially suitable for fast processing by methods including pultrusion and resin... 

Pultrusion is a modern technique used for producing continuous fiber-reinforced profile in which the orientation of the fiber is kept constant during cure. Although this process is utilized for both thermoplastic and thermoset resins, it is mainly suitable for thermosetting resins like polyester, epoxy and phenolic resin systems. Jute, available in continuous forms such as mat, roving, tapes, yarn, etc., is impregnated with... 

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