Thermosets sheets, prepregs

Prepregs Prepregs are thin sheets of fibers impregnated with formulated thermoset precursors. The thermoset precursor formulation in the prepreg is in the so-called B-stage that characterizes an ungelled liquid of very high viscosity, but with the necessary tack, flexibility, and shelf life to facilitate part production. 

Courtaulds developed many products [153] based on carbon fibers prepreg as warp sheet and tape, random fiber mats, preferred orientation mats, chopped fiber, thermoset and thermoplastic molding compounds and polytetrafluroethylene (PTFE) impregnated tow. Oxidized PAN fiber was available as continuous tow, tops, yarns, woven and knitted fabrics. 

Prepreg Fibrous reinforcement held in position with polymeric matrix. May be sheet, tape or, tow. If the matrix is thermoset resin, may be partly cured to induce right level of tack, a condition known as B-stage. 

In the heater, the impregnated web is heated to boil away the solvent and to begin the polymerization of the thermosetting resin. This step is known as B-staging or prepreging. It is deshable to cure the resin enough so that the web is not tacky or dry and is handleable, but yet sufficiently uncured to permit an additional cure and flow at the lamination press. As the sheets exit the treater, they are sheared, stacked, and stored in temperature- and humidity-conholled rooms. 

In contrast to fibre reinforced thermoset systems, thermoplastics are easy to process. By consolidating a stack of prepregs, a laminate is formed which can be regarded as a sheet material like aluminium and steel. Organic sheet is a characterization which is sometimes found in the literature. 

Sheet-Molding Compound n (SMC) A fiberglass-reinforced thermosetting compound in sheet form, usually rolled into coils interleaved with plastic film to prevent Autoadhesion. This term was chosen to replace the term Prepreg which was deemed to be confusing and insufficiently definitive. SMC can be molded into complex shapes with little scrap, and is low in cost. 

An alternative approach to building up components in which the fibres are aligned in various directions, which is often favoured with carbon fibres, is to produce a pre-impregnated material, known as a prepreg. Unidirectional fibres are spread out thinly and impregnated with a thermosetting resin which is partially cured or B-staged. The sheet or roll material (which is a fraction of a millimetre in thickness)... 

---