P

Paste
Word used to usally describe a highly viscosity adhesive made from starch or flour such as rice or wheat, generally prepared by heating together a mixture of starch and water and subsequently cooling the resulting product. This in turn may be diluted with water to produce the required texture.

Peel adhesion
Adhesive's resistance to be stripped from a bonded joint with the stripping force applied at a predetermined angle and rate. (more about adhesive testing)

Peel strength
The amount of force required to peel a material off a substrate. Expressed in Pascals (Pa).

Phenolic / Phenol Formaldehyde, PF (extended definition)
Made from chemicals of the phenol group and formaldehyde.

Photo-initiator
Agent which when exposed to a specific wavelength of energy forms a reactive species which starts the chain reaction to cause polymer formation. Most commercial photo-iniators for radical curing reactions contain benzoil groups, which are mainly responsible for the absorption of energy from light. Aryl sulfonium salts can generate both radical type and cationic active centers.
Syn. Photo-curing material

Pigment
Fine solid particle used to colored products and substantially insoluble in the vehicle.
Note: In contrast, a dye is soluble.

Plasticizer
Compounding material used to enhance the deformability of a polymeric compound. A plasticizer is soluble in the polymer and decreases the glass transition temperature (Tg) value, softens and adds flexibility to the product.

Plastisol (extended definition)
Modified PVC or PMA dispersion which requires heat to harden. The resultant joints are often resilient and tough.

Polyamide, PA (extended definition)
Polymer formed by the reaction of a diamine and a diacid. Nylons are commercial polyamides characterized by toughness, solvent resistance, and sharp melting point.

Polychloroprene (extended definition)
Rubber-like compound.
Syn. Chlorobutadiene, Neoprene

Polyester
Polymer in which the structural units are linked by ester grouping. See Saturated Polyesters, SP and Unsaturated Polyester, UP.

Polyether
Polymer containing ether linkages. Polyethers used in polyurethane technology contain reactive hydroxyl end groups.

Polyol
Chemical substance containing one or more hydroxyl groups. Diol, triol and tetrol contain 2, 3 and 4 hydroxyl groups respectively. Polyols are reacted with isocyanates to make polyurethanes.

Polysulfide rubber, PSR (extended definition)
Mercaptan terminated, long chain aliphatic polymers containing disulfide linkages. Can be converted to rubber at room temperature without shrinkage upon addition of a curing agent. Used for exterior sealant and sealed insulating glass sealant.

Polyurea
Diisocyanates react with diamines to yield polyureas. Reaction is very fast and results in a strong polymer, popular for coatings applications.

Polyurethane, PU (extended definition)
Polymer made by the reaction of polyols with a multi-functional isocyanate. Its molecular structure may cross-link and become a thermosetting plastic, or stay linear and remain thermoplastic.

Polyurethane prepolymer
Polyurethane reaction intermediate made by reacting an isocyanate with a polyester or polyether polyol, in which one component (usually the isocyanate) is in considerable excess of the other.

Polyvinyl acetate, PVAc (extended definition)
Colourless, transparent solid. Used in adhesives which are themselves also referred to as PVA or PVA adhesives.

Polvinyl Alcohol, PVOH
Resin formed by polymerizing vinyl alcohol.

Polvinyl Chloride, PVC
Thermoplastic resin produced by the polymerization of the gas vinyl chloride [CH2CHCl]. Used in soft, flexible films for food packing. Also used in rigid products such as pipes.

Pot Life
The length of time an adhesive remains usable for mixing. Usually an important factor with adhesives mixed together that begin curing almost immediately.
Syn. Shelf life

Potting
Enclosing and article in an envelope of adhesive. Often used in the electronic industry to protect sensitive components.
Syn. Encapsulating

Precipitated Calcium Carbonate, PCC
Precipitated calcium carbonate is a versatile additive for use as rheological modifier in PVC, silicone, polysulphide and polyurethane sealants for the automotive, construction, aerospace, appliances and other industries.

Preformed tape
Preformed tapes are generally elastomeric rubber extruded into a ribbon of a width and thickness suitable for specific application. Preformed tapes are usually used in the Building and Construction market, chemically compatible to glass, metal, or wood.

Preservative
Substance added to protect, prevent, or retard decay, discoloration, or spoilage under conditions of use or storage. (see Biocide, Fungicide)

Pressure sensitive adhesive (PSA) (extended definition)
Adhesive that remains tacky after curing or setting. Firmly adheres to a variety of dissimilar surfaces upon mere contact without the need of more than finger or hand pressure.

Primer
Chemical material that improves the bond of the sealant to the substrate.

Processing aid
Compounding material that improves the processability of a polymeric compound.
Note : Examples of improvements attributable to processing aids include reduced nerve, better dispersion of dry materials, increased extrusion rates, reduced powder consumption during mixing, smoother surfaces on calendered and extruded products and improved knitting.

Putty
Thick, mastic type material, often made from calcium carbonate and a linseed oil, used for setting glass in wood frames, filling cracks, holes and open defects.