GLOSSARY OF TERMS
P

Phenolic Resin: thermosetting resin produced by the condensation of an aromatic alcohol with an aldehyde, particularly of phenol with formaldehyde. Used in high-temperature applications with various fillers and reinforcements. Schmelzer Industries offers veils and mats with phenolic binders.

Pigment: A colorant added to gel coat or resin.

Pinholes: small holes on the exposed gel coated surface. They are about the diameter of common pins and may be easily counted. Veils can help reduce the appearance of pinholes.

Plastic: material that contains as an essential ingredient an organic polymer of large molecular weight, hardeners, fillers, reinforcements, and so forth; is solid in its finished state, and, at some stage in its manufacture or its processing into finished articles, can be shaped by flow. Made of plastic. A plastic may be either thermoplastic or thermoset.

Plasticizer: material incorporated in a plastic to increase its workability and flexibility. Normally used in thermoplastics. A lower molecular weight material added to an epoxy to reduce stiffness and brittleness, thereby resulting in a lower glass transition temperature for the polymer.

Plug: A composite industry name for a pattern or model.

Polyester (unsaturated): product of an acid-glycol reaction commonly blended with a monomer to create a polymer resin. In its thermosetting form it is the most common resin used in the FRP industry.

Polymer: chain molecule composed of many identical groups, commonly found in plastics.

Polymerization: chemical bonding of polymer molecules during the curing reaction.

Porosity: entrapped gas bubbles or voids in a gel coat film.

Prepreg: either ready-to-mold material in sheet form or ready-to-wind material in roving form, which may be cloth, mat, unidirectional fiber, or paper impregnated with resin and stored for use. The resin is partially cured to a B-stage and supplied to the fabricator, who lays up the finished shape and completes the cure with heat and pressure. The two distinct types of prepreg available are (1) commercial prepregs, where the roving is coated with a hot melt or solvent system to produce a specific product to meet specific customer requirements, and, (2) wet prepreg, where the basic resin is installed without solvents or preservatives but has limited room-temperature shelf life.

Pressure Bag: A membrane which conforms to the inside of a laminate laid up on a mold. The membrane or bag is then inflated applying pressure which consolidates and densifies the laminate.

Print Through: distortion in the surface of a part which allows the pattern of the core or fiberglass reinforcement to be visible through the surface. Also known as print out, telegraphing or read through.

Pultrusion: continuous process for manufacturing composites that have a constant cross-sectional shape. The process consists of pulling a fiber-reinforcing material through a resin impregnation bath and through a shaping die, where the resin is subsequently cured.

Putty: thickened mixture of resin made by adding fillers and reinforcing fibers

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