PAN
See Polyacrylonitrile.

PAN FIBERS
Reinforcement fiber derived from the controlled pyrolysis of poly(acrylonitrile) fiber.

PARALLEL-LAMINATED
Laminated so that all layers of material are oriented approximately parallel with respect to the grain or strongest direction in tension. Also called unidirectional. This pattern allows the highest loading of reinforcement, but gives maximum strength in only one direction.

PARTING AGENT
See Mold Release.

PART CONSOLIDATION
A process of composites fabrication in which multiple discrete parts are designed and fabricated together into a single part, thus reducing the number of fabricated parts and the need to join those parts together.

PARTING LINE
A mark on a molded piece where the sections of a mold have met in closing.

PATTERN
The initial model for making fiberglass molds.

PEEL PLY
Layer of material applied to a 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
Strength of an adhesive bond obtained by stress that is applied "in a peeling mode."

PEROXIDES
Category of compounds containing an unstable O - O Group: Oxygen to Oxygen atoms.

Ph
A measure of acidity or alkalinity of a solution, with neutrality represented by a value of 7, with increasing acidity corresponding to progressively smaller values, and increasing alkalinity corresponding to progressively higher values.

PHENOLIC RESIN
Thermosetting resin produced by condensation of an aromatic alcohol with an aldehyde, particularily phenol with formaldehyde.

PIGMENT
the ingredient used in gel coats to impart color.

PIGMENT SEPARATION
A mottled (varied colors) appearance of the gel coat surface.

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 fibers.

PLANAR WINDING
A type of filament winding in which the filament path lies on a plane that intersects the winding surface.

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.

PLASTIC DEFORMATION
Change in dimensions of an object under load that is not recovered when the load is removed; opposed to elastic deformation.

PLASTIC TOOLING
Tools (mostly for the metal forming trades) constructed of plastics, generally laminates or casting materials.

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

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

PLUG
See Master - Both terms used to imply the same meaning.

PLY
The number of single yarns twisted together to form a plied yarn; one of the layers that make up a stack or laminate.

PLY SCHEDULE
Lay-up of individual plies or layers to form a laminate. Plies may be arranged in alternating fiber orientation to produce multi-directional strength in a part.

POISSON'S RATIO
The ratio of transverse strain to axial strength during axial load.

POLAR WINDING
A type of filament winding in which the filament path passes tangent to the polar opening at one end of the chamber and tangent to the opposite side of the polar opening at the other end of the chamber.

POLYACRYLONITRILE (PAN)
A product used as a base material in the manufacture of certain carbon fibers.

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

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 polymerization 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.

POLYESTER RESING (Unsaturated)
The 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
A very large molecule formed by combining a large number of smaller molecules, called monomers, in a regular pattern.

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

POLYMERIZE
To unite molecules of the same kind to form a compound having the elements in the same proportion but possessing much higher molecular weight and different physical properties.

POLYVINYL ALCOHOL (PVA)
A liquid water soluble release agent.

POROSITY
Small air bubbles in the gel coat film; too numerous to count. Generally smaller in size than pinholes.

POSITIVE MOLD
A mold designed to apply pressure to a piece being molded with no escape of material.

POST BAKE
See Post Cure.

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 that a catalyzed resin system retains a viscosity low enough to be used in processing.

POTTING
Similar to encapsulating, except that steps are taken to insure complete penetration of all the voids in the object before the resin polymerizes.

PRECURE
The full or partial setting of a resin or adhesive before the clamping operation is complete or before pressure is applied.

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

PREFORM
A preshaped fibrous reinforcement formed by distribution of chopped fibers 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 mold press. Also, a compact "pill" formed by compressing premixed material to facilitate handling and control of uniformity of charges for mold loading.

PREFORM MAT
Fiber reinforced mat shaped like the mold in which it will be used. It eliminates the need for overlapping the corners in molding.

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

PREHEATING
The heating of compound prior to molding or casting in order to facilitate the operation or to reduce the molding cycle.

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

PREPREG
Ready-to-mold material in sheet form which may be cloth, mat, 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.

PRE-RELEASE
The premature release of the gel coat or laminate from the mold.  Pre-release causes cosmetic or dimensional problems.

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.

PRESSURE
The force or load per unit area.

PRESSURE-BAG MOLDING
A molding technique in which a flexible bag is placed over the contact layup in the mold, sealed, and clamped in place, and pressure applied by compressed air, which forces the bag against the part while the part cures.

PRIMARY LAMINATE
Laminate applied after the skin coat has cured. Generally thicker than the skin coat.

PRINT THROUGH
"Telegraphing" of the image of glass strands through the gel coat film.

PROMOTER
See Accelerator.

PROTOTYPE
Process of creating a test part not intended for commercial release that establishes design, material and fabrication parameters for a new product. May entail multiple iterations to arrive at final/commercial part design.

PUCKERS
Local areas on prepreg where material has blistered and pulled away from the separator film or release paper.

PUNCTURE
Break in composite skin in sandwich structure that may or may not go through to the core material or completely through the part.

PULTRUSION
Reversed "extrusion" of resin-impregnated roving in the manufacture of rods, tubes and structural shapes of a permanent cross-section. The roving, after passing through the resin dip tank, is drawn through a die to form the desired cross-section.

PUTTY
A thickened mixture of resin made by adding fillers, thixotrophs and reinforcing fibers.

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Glossary Section (P) Last Updated: 9/3/99 1:11 PM

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