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Glossary

Pan Fibres

Carbon reinforcement fibre derived from the controlled pyrolysis of poly(acrylonitrile) fibre.


Parting Line

A mark on a moulded piece where the sections of a mould have met in closing.


PBT

Polybuthlene Therephthalate (Thermoplastic Polyester Resin).


Peel Ply

Layer of material applied to a prepreg layup surface that is removed from the cured laminate prior to bonding operations and leaves a clean resin-rich surface ready for bonding.


Peel Strength

Adhesive bond strength, as in pounds per inch of width, obtained by a stress applied in a peeling mode.


PET

Polyethylene Terephthalate (Thermoplastic Polyester Resin).


Pinhole

A tiny hole in the surface of, or through, a plastic material; usually occurring in multiples.


Pit

Small regular or irregular crater in the surface of a plastic, usually with width approximately of the same order of magnitude as its depth.


Pitch

A Residual Petroleum Product Used In The Manufacture Of Certain Carbon Fibres.


Plain Weave

A weaving pattern in which the warp and fill fibres alternate; that is, the repeat pattern is warp/fill/warp/fill, and so on. Both faces of a plain weave are identical. Properties are significantly reduced relative to a weaving pattern with fewer crossovers.


Plastic

A material that contains as an essential ingredient an organic substance of large molecular weight, 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.


Platens

The mounting plates of a press, to which the entire mould assembly is bolted.


Plied Yarn

A yarn formed by twisting together two or more single yarns in one operation.(Synonyms folded yarn, formed yarn.)


Ply

In general, fabrics or felts consisting of one or more layers (laminates, and so forth). The layers that make up a stack. Yarn resulting from twisting operations (three-ply yarn, and so forth). A single layer of prepreg. A single pass in filament winding (two plies forming one layer).


Polyacrylonitrile (PAN)

A product used as a base material in the manufacture of certain carbon fibres.


Polyamide

A polymer in which the structural units are linked by amide or thioamide groupings. Many polyamides are fibre-forming.


Polyester Combination Yarn

A polyester/fibre glass hybrid yarn.


Polyesters

Thermosetting resins, produced by dissolving unsaturated, generally linear, alkyd resins in a vinyl-type active monomer such as styrene, methyl styrene, and diallyl phthalate. Cure is effected through vinyl polymerisation using peroxide catalysts and promoters, or heat, to accelerate the reaction. The resins are usually furnished in solution form, but powdered solids are also available.


Polymer

A very large molecule formed by combining a large number of smaller molecules, called monomers, in a regular pattern.


Polymerisation

A chemical reaction in which the molecules of monomers are linked together to form polymers.


Porosity

The presence of visible voids within a solid material into which either air or liquids can pass.


Positive Mould

A mould designed to apply pressure to a piece being moulded with no escape of material.


Post-Cure

Additional elevated temperature cure, usually without pressure, to improve final properties and/or complete the cure. In certain resins, complete cure and ultimate mechanical properties are attained only by exposure of the cured resin to higher temperatures than those of curing.


Pot Life

The length of time a catalysed thermosetting resin system retains a viscosity low enough for it to be suitable for processing.


PPO

Polyphenylene Oxide (Thermoplastic Resin).


PPS

Polyphenylene Sulfide (Thermoplastic Resin).


Precursor

For carbon fibres, the rayon, PAN, or pitch fibres from which carbon fibres are made.


Preform

A preshaped fibrous reinforcement formed by distribution of chopped fibres by air, water flotation, or vacuum over the surface of a perforated screen to the approximate contour and thickness desired in the finished part. Also, a preshaped fibrous reinforcement of mat or cloth formed to desired shape on a mandrel or mock-up prior to being placed in a mould press. Also, a compact "pill" formed by compressing premixed material to facilitate handling and control of uniformity of charges for mould loading.


Pregel

An unintentional extra layer of cured resin on part of the surface of a reinforced plastic. (Not relating to 'gel coat.')


Premix

A moulding compound prepared prior to and apart from the moulding operations and containing all components required for moulding resin, reinforcement, fillers, catalysts, release agents, and other compounds.


Prepreg

Ready-to-mould material in sheet form which may be cloth, mat, or paper pre-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.


Pressure Bag Moulding

A process for moulding reinforced plastics in which a tailored, flexible bag is placed over the contact lay-up on the mould, sealed, and clamped in place. Fluid pressure, usually provided by compressed air or water, is placed against the bag, and the part is cured.


Pressure Intensifier

A layer of flexible material (usually a high-temperature rubber) used to ensure the application of sufficient pressure to a location, such as a radius, in a lay-up being cured.


Primer

A coating applied to a surface, before the application of an adhesive, lacquer, enamel, and so forth, to improve the adhesion performance or load-carrying ability of the bond.


Processing Window

The range of processing conditions, such as stock (melt) temperature, pressure, shear rate, and so on, within which a particular grade of plastic can be fabricated with optimum or acceptable properties by a particular fabricating process.


Pultrusion

An automated, continuous process for manufacturing composite rods, tubes and structural shapes having a constant cross section. Roving and other reinforcements are saturated with resin and continuously pulled through a heated die, where the part is formed and cured. The cured part is then cut to length.