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Glossary of Terms

 Glossary of Terms




An early stage in the reaction of certain thermosetting resins in which the material has not yet been cured.
Abrasion The wearing away by friction.
Absorption The state of one substance being taken up by another; for example a sponge absorbs water.
Accelerator (Promoter) An ingredient added to a resin-hardening mixture to speed up the reaction. Also see Curing Agent.
Adherend A body that is held to another body by an adhesive. Also see Substrate.
Adhesion The state in which two surfaces are held together by interfacial forces which may consist of valence forces or interlocking action, or both.
Adhesion Promoter Materials used to improve a coating or adhesive's ability to withstand mechanical separation from a substrate; to improve a system's adhesive strength.
Adhesive A substance capable of holding materials together by surface attachment.
Adsorption The adhesion in an extremely thin layer, of the molecules of gases of dissolved substances or liquids, to the surface of solid bodies with which they are in contact.
Aggregate A hard fragmented material used with an epoxy binder as a flooring or surfacing medium. A coarse filler.
Alkyd A special type of resin prepared by condensing polyhydric alcohols such as glycerine with polybasic acids such as phthalic acid.
Amide A curing agent used with epoxy resins, containing the –(C = 0)–NH2group in its molecular formula. Most amides are semi-solids or solids at room temperature and they are practically neutral. They are derived from a hydrogen replacement reaction between an organic acid and ammonia (NH3).
Amine A curing agent used with epoxy resins that is any of a class of ammonia derivatives.
Antioxidant A compound added to other substances to retard oxidation.
Aqueous Containing water; usually describes a water solution of something.
ASTM American Society for Testing Materials.
Auxiliary Catalyst See Curing Agent or Accelerator (Promoter).

An intermediate stage (between the A-stage and the C-stage) in the reaction of certain thermosetting resins in which the material softens when heated and swells when in contact with certain liquids.
Barcol Hardness The reading of a material's hardness on a pin point impression instrument, the scale of which is 0-100. Used on soft metals, harder plastics and epoxy resin coatings.
Binder An adhesive material used to hold together fillers such as sand, aggregate and other ingredients.
Biocide A chemical agent used to kill organisms responsible for microbiological degradation.
Bisphenol-A A standard resin intermediate along with epichlorohydrin, used in the production of epoxy resins. A condensation product formed by the reaction of two (bis) molecules of phenol with acetone (A).
Bleeding The diffusion of color through a coating from the substrate; discoloration arising from such diffusion.
Blender A machine or shearing device used to mix granular or liquid materials. Adhesives and coatings may be blended in this way to produce a finished product meeting certain specifications.
Blister An elevation on a surface; its boundaries may be indefinitely outlined and it may burst and become flattened. It may be caused by insufficient adhesive; inadequate curing time, temperature or pressure; or trapped air, water or solvent vapor.
Body A combination of properties of a material including consistency, firmness, resistance to melting, appearance, etc. In adhesives, body is a combination of pastiness, viscosity, tackiness, etc., which describe the overall consistency.
Bond The union of materials by adhesives; to unite materials by means of an adhesive.
Bond Strength The stress (tensile load divided by the area of bond) required to rupture a bond formed by an adhesive. (ASTM D952)
Breaking Load The required load that causes fracture in a tension, compression, flexure or torsion test.
Breaking Strength The term for flexural strength.
Brookfield Viscosimeter An instrument used to measure the viscosity or resistance to flow of materials under standard conditions of temperature. This commonly used instrument consists of a scale that measures the drag on various size spindles that rotate at a set speed.

The final stage in the reaction of certain thermosetting resins in which the material is fully cured.
Catalyst A substance used to change the rate of a chemical reaction without itself undergoing permanent change in composition.
Centigrade A scale of temperature that features 0° as the freezing point and 100° as the boiling point of water. To convert Centigrade to Fahrenheit, multiply by 1.8 and add 32.
Centipoise 1/100th of a poise (dyne-sec/cm²); a viscosity measurement unit.
Clarity Degree of clearness.
(Coalescing Agents)
Additives used to obtain/promote good film formation.
Co-Catalyst See Curing Agent or Accelerator (Promoter).
Cold Flow The dimensional change or deformation that occurs over a period of time when a material is subjected to constant stress at a constant temperature; also called creep.
Compatibility The ability of a material to become or remain homogenous before, during or after cure.
NOTE: Serious incompatibility is exemplified by separation of components, loss of clarity, "sweating out," loss of adhesion, etc.
Compression Modulus The ratio of the compressive stress to the resulting compressive strain (the latter expressed as a fraction of the original height or thickness in the direction of the force). May be either static or dynamic.
Compression Set The deformation that remains in a material after it has been subjected to and released from a specific compressive stress for a definite period of time at a prescribed temperature. Used to evaluate creep and stress relaxation properties.
Compressive Strength The maximum stress a material can sustain under crush loading. It is calculated by dividing the maximum load by the original cross-sectional area of a specimen.
Compression Test The method for determining behavior of materials under crushing loads. The specimen is compressed, and deformation at various loads is recorded. Compressive stress and strain are calculated and plotted as a stress-strain diagram that is used to determine elastic limit, proportional limit, yield point, yield strength and compressive strength.
Corrosion The eating and wearing away of a material by chemical action (pitting, rusting).
Corrosion Inhibitors Compounds used to prevent the oxidation of metal.
Crater Small, shallow, crater-like surface imperfections.
Creep The dimensional change or deformation that occurs over a period of time when a material is subjected to constant stress at a constant temperature; also called cold flow.
Cross-Link Tying together large molecules and changing the physical properties of the material.
Cure The changing of physical properties of a material by chemical reaction—usually to a harder or more permanent form. Sometimes cure is synonymous with set.
Cure Cycle The schedule of time periods under specified conditions to which a reacting composition is subjected in order to reach a specified property level.
Cure Temperature The temperature to which a system is subjected in order to cure it. Note that the temperature attained by the system in the process of curing may differ from the temperature of the atmosphere surrounding the system.
Cure Time The period of time during which a system may be subjected to heat or pressure to cure. In two-component systems, it is the time lapse between the addition of the curing agent (hardener) to the resin, and completed polymerization.
Curing Agent (Hardener) A catalytic or reactive agent used to promote, enhance or control the curing reaction and aid in property development. The addition of a curing agent to an epoxy resin causes polymerization.

A surface-active agent used to reduce or eliminate foam. It stops the foam and breaks the bubble once it has been formed.
Deformation under Load Deformation under LoadThe measure of the ability of a material to withstand permanent deformation; the ability of a material to return to its original shape after deformation.
Degree of Cure The percentage of the optimum level of a specified property attained by a reacting composition under given cure conditions.
Delamination The separation of layers in a laminate because of failure of the adhesive, either in the adhesive itself or at the interface between the adhesive and the adherend, or because of cohesive failure of the adherend.
Density The ratio of a substance's mass to its volume at a given temperature and pressure.
Deterioration (Degradation) A permanent change in the physical and/or chemical properties of a material evidenced by impairment of these properties.
Diluent A reactive or non-reactive modifier used to reduce the viscosity and extend the material to which it is added.
Discoloration Any change from an initial color possessed by a material, either due to environmental or internal conditions. A lack of uniformity in color where color should be uniform over the whole area of a material.
Drying Time The period of time during which an adhesive or a system is allowed to dry with or without the application of heat or pressure or both.
Dispersion A heterogenous system in which a finely divided material is distributed in another material.

The property of a material by which it tends to recover its original size and shape after deformation.
Elongation The increase in gauge length of a tension test specimen, usually expressed as a percentage of the original gauge length.
Enamel A protective coating that may contain a number of base resin types, capable of forming an especially smooth surface.
Encapsulation The covering of an item by a protective coating. Also called potting.
Epichlorohydrin The basic epoxidizing resin intermediate used in the production of epoxy resins. It contains an epoxy group and is highly reactive with polyhydric phenols such as bisphenol-A.
Exotherm The liberation of heat energy during a chemical reaction.
Extender A material added to a compound to lower cost with minimal degradation of properties.

Failure, Adhesive
The failure at the bond line between a substrate and an adhesive; when the adhesive separates entirely from the substrate.
Failure, Cohesive Failure within the adhesive under a stress, resulting in a broken bond with all adhered surfaces still covered with adhesive.
Failure, Substrate The failure of the substrate material itself upon subjecting the bonded adherend surfaces to a stress.
Fatigue The permanent structural change that occurs in a material that has been subjected to fluctuating stress and strain.
Filament Winding The manufacture of cylindrical casings by the winding of a continuous strand of glass made up of a gathering of many individual glass filaments each impregnated with an epoxy-anhydride product. These casings are used for rocket motors, reinforced epoxy pipe, pressure vessels, and in heavy electrical apparatus.
Filler A particulate solid material added to a resin-curing agent system to change properties and/or to lower cost.
Film The thin, level application of an adhesive or coating to a surface. Thickness is not typically greater than 0.010 inch.
Flexibility A state of matter, usually synonymous with higher elongation or lower modulus.
Flexibilizer An additive used to increase system flexibility.
Flexural Strength The ability of a material to withstand failure due to bending.
Fungicide An additive used to destroy, retard or prevent the growth of fungi and spores.

Gardner Color Scale
A system of color standards based on stable solutions of ferric chloride used in the evaluation of resins, lacquers, oils and varnishes. The Gardner Scale can be correlated roughly with other color standards such as FAC, ASTM, NPA and Lovibond.
Gel (1) A semi-solid system consisting of a network of solid aggregates in which liquid is held.
(2) The initial jelly-like solid phase that develops during the formation of a resin from a liquid.
Gel Coat The first coat of laminating resin laid up against a mold. The first layer of laminating material is then laid up on this resin after it has hardened or "gelled" slightly.
Gel Point (Time) The stage at which a liquid begins to gel or exhibit pseudo-elastic properties. This stage may be observed from the inflection point on a viscosity-time plot.

See Curing Agent.
Hardness A measure of the resistance of a material to surface indentation or abrasion; a function of the stress required to produce some specified type of surface deformation.
Haze The cloudy or turbid appearance of an otherwise transparent specimen caused by light scattered from within the specimen or from its surfaces.
Hot Melt A resinous thermoplastic compound adhesive that melts at relatively high temperatures (around 350°F). It is flexible and sets instantly when cooled.

Impact Strength
The ability of a material to withstand shock loading. It is an indication of the toughness of a material.
Inhibitor A substance that is used to slow a chemical reaction-often to prolong shelf or storage life.

A product made by bonding together two or more layers of material or materials.
Linear Shrinkage
(Mold Shrinkage)
The difference in linear dimensions of a specimen from the corresponding mold dimensions as a consequence of the polymerization reaction and the cure cycle used. Usually expressed in cm/cm, in/in, in/ft, etc.

Melting Point
The temperature at which a solid becomes a liquid.
Miscible The capability of being mixed; mutually soluble.
Mixing Ratio The proportionate combining weights or volumes of resin, curing agent, catalyst and other components of a two or more-component system, as specified by the supplier.
Modifier Any material that when added to a resin/curing agent combination causes a change in properties.
(Modulus of Elasticity)
The ratio of unit stress to unit strain.
Moisture Resistant Having some resistance to high humidity. The material will not easily change its chemical and physical properties due to moisture exposure.
Molecular Weight The sum of the atomic weghts of the atoms in a compound. The higher the molecular weight of a substance, the more viscous it is. Units are grams per mole.
Monomer A simple chemical that in the presence of a suitable catalyst combines with itself to form a polymer of much greater molecular size.

Newtonian Flow
The flow characteristic of a liquid that shows constant resistance to flow as stirring is continued at constant or varying rates of shear.
Novolak A linear thermoplastic B-stage phenolic resin that remains permanently thermoplastic unless a source of methylene groups is added.

The degree of obstruction to the transmission of visible light.
Orange Peel An uneven surface of a material somewhat resembling an orange peel.
Organosol A finely divided or colloidal dispersion of a resin in a plasticizer, with solvents or other materials.
Oxidation The process of combining with oxygen; the changes resulting from the affects of air or oxygen, such as the corrosion of metal surfaces.

A mixture of ingredients having a doughy or buttery consistency.
Peak Exotherm The maximum internal temperature reached by a reacting composition.
Peeling The loosening of a coating or layer from a base material.
Peel Resistance A measure of bond strength. The torque required in order to separate an adhesive and an adherend, as done in the climbing drum peel test (ASTM D-1781).
Peel Strength The measure of the strength of an adhesive bond. It is the average load per unit width of bond line required to part bonded materials where the angle of separation is 180 degrees and the separation rate is 6 in/min. (ASTM D-903).
Pencil Hardness A test for surface hardness using a numbered set of increasing hardness lead pencils. Surface hardness is designated by the first numbered pencil that will scratch the surface, starting with the softest pencil.
Penetration The entering of one material into another material, measured by the depth of penetration.
Permanent Set The deformation that remains after a specimen has been stressed in tension at a prescribed amount for a definite period of time and has been released for a definite period.
pH A simplified system of measuring acidity or alkalinity irrespective of the acid or alkali involved.
Phenolic Resin Compound Single-Stage: A phenolic resin compound in which the resin, due to its reactive groups, is capable of further polymerization by application of heat.

Two-Stage: A phenolic resin compound in which the resin is essentially not reactive at normal storage temperatures, and contains a reactive additive which causes further polymerization upon the application of heat. It is less sensitive to heat below a critical temperature and has a longer shelf life than a single-stage resin.
Pigment A fine, solid, typically inorganic particle used in the preparation of colored products. It is substantially insoluble in the vehicle versus a dye, which is soluble.
Plastic Deformation The deformation that remains after the load causing it has been removed. The permanent part of the deformation beyond the elastic limit of the material. Also called plastic strain and plastic flow.
Plasticity The tendency of a material to remain deformed after reduction of the deforming stress, to a value equal to or less than its yield strength.
Plasticizer An additive used to improve flexibility or to facilitate compounding.
Plastisol A colloidal dispersion (suspension) of a resin in a plasticizer without a solvent.
Poise The Bureau of Standards unit for measuring viscosity.
Polyester A resin composed of polymeric esters in which the recurring ester groups are an integral part of the main polymer chain. Unsaturated polyesters contain carbon double bonds that permit cross-linking and thus conversion of the resin to a substantially infusible and insoluble product.
Polymer A compound formed by the reaction of simple molecules having functional groups that permit their combination to proceed to high molecular weights under suitable conditions. Polymers may be formed by polymerization or polycondensation. When two or more monomers are involved, the product is called a copolymer.
Polymerization A chemical reaction in which the molecules of a monomer are linked to form large molecules whose molecular weight is a multiple of that of the original substance. When two or more monomers are involved, the process is called copolymerization.
Post Cure The additional operations to which a cured composition is subjected to enhance one or more properties.
Pot Life The period of time during which a resin, after being mixed with the curing agent, can be used for its extended purpose.
Potting The covering of an item (such as coils in motors and generators) by a protective coating. Also called encapsulation.
Prepreg A reinforcing material impregnated with resin, and ready for molding.
Prepolymer A low polymeric intermediate between that of the monomer and the final polymer or resin.
p.s.i. Pounds per square inch; a unit of measure of pressure.
Promoter See Accelerator.

Reactive Diluent
Materials used to decrease viscosity. Becomes an integral part of the final coating/adhesive by chemical reaction with itself or with other components of the formulation.
Reduction The reverse of oxidation; the removal of oxygen or the addition of hydrogen.
Resin, Epoxy Viscous liquids or clear, brittle solids, the most widely used being the glycidyl ethers of diphenols, such as the reaction products of e pichlohydrin and bisphenol A. Usually cured with an amine or a polyamide, they are used for coatings, castings and adhesives.

The conversion of a system into a fixed or hardened state by chemical or physical action such as condensation, polymerization, oxidation, vulcanization, gelation, hydration or evaporation of volatile constituents.
Shear Strength The maximum shear stress that can be sustained by a material before rupture. The ultimate strength of a material subjected to shear loading, as determined in a torsion test.
Shelf Life The useful life or period of time during which a material maintains its properties when stored at the specified temperature. Also called storage life.
Shrinkage The decrease in volume or contraction of a material by the escape of any volatile substance, or by a chemical or physical change in the material.
Slippage The movement of adherends with respect to each other during the bonding process.
Solids The dry ingredients remaining after evaporation of volatile solvents or water.
Solubility The property of a substance to dissolve in another and form a solution.
Solvent In a solution, the substance that dissolves another. A material used for thinning down a fluid or for cleaning purposes.
Specific Gravity The ratio of the weight of any volume of a mass or substance to the weight of an equal volume of water at a given temperature. The specific gravity of a substance times the density of water equals the density of the substance.
Stability The ability of a substance to remain unchanged, constant. The ability to restore to original condition after being disturbed by some force.
Staining Discoloration caused by a foreign matter that chemically affects the base material.
Storage Life The time period during which a packaged material can be stored under specified temperature conditions and remain suitable for use. Also called shelf life.
Strain The change per unit length in a linear dimension of a specimen, usually expressed in percent (%). In most mechanical tests, strain is based on the original length of the specimen.
Stress An applied force or pressure such as tension or shear that is exerted on a body to produce a resultant strain on the material. The ability of the material to withstand a stress depends on the strength of its cohesive force or molecular resistance.
Substrate A material upon the surface of which an adhesive-containing substance is spread for any purpose, such as bonding or coating. Also see Adherend.
Surface Active Agent
A wide variety of materials used to alter surface phenomena. Wetting agents reduce surface tension and improve wetting and spreading; dispersants aid in the dispersion of pigments; defoamers inhibit foam formation; and emulsifiers cause or improve emulsion formation.
Surface Hardness The apparent resistance of a surface to deformation by an impinging object.
Surface Tension The property of a liquid that causes the surface to pull into the smallest area for a maximum volume, hence, drops are spherical.
Surfactant See Surface Active Agents.

Taber Abrader
An instrument used to test the abrasion resistance of a material.
Tack The property of a surface that imparts instantaneous adhesion (stickiness) when another surface is brought into contact with it. The tendency to adhere.
Tack-Free Time The period from the time of application to the time when a surface no longer imparts tack (stickiness) to another surface.
Tear Resistance The measure of the ability of a material to resist tearing or being pulled apart or lacerated upon when being subjected to a tearing force.
Tensile Strength The pulling force necessary to break a specimen divided by the cross sectional area. The ultimate strength of a material subjected to tensile loading. Units are given as lb/in² (psi).
Thermal Conductivity The ability of a material to conduct heat; the physical constant for quantity of heat that passes through a unit of volume of a substance in a unit of time when the difference in temperature of two opposite faces is 1°.
Thermal Expansion
(Coefficient of Linear)
The amount of change in the length of a specimen per unit length, for a unit change in specimen temperature. Usually expressed as in/in/°F or in/in/°C.
Thermoplastic A material which when heated, softens, melts or becomes more pliable, and when cooled, regains its former rigidity.
Thermoset A material which, when cured by application of heat or chemical means, changes into a substantially infusible and insoluble product.
Thixotrope An additive used in a liquid to change Newtonian Flow to thixotropic flow.
Thixotropic Flow The flow characteristic of a liquid that shows decreasing resistance to flow as stirring is continued, both at a constant rate of shear and at an increasing rate of shear. The resistance to flow is time dependent.
Thixotropic Index The ratio of stress (viscosity) at two different shear rates; usually expressed as the quotient of the viscosity value at a low shear rate divided by the viscosity value at a high shear rate.
Tint A color produced by the mixture of a small amount of colored pigment or tinting paste with a predominant amount of white base material. The tint of a color is much lighter and much less saturated than the color itself.
Toxicity The degree of harmfulness or poisonousness to humans of any substance.
Translucent The ability of a material to allow the passage of some light to pass through itself.

The liquid portion of an adhesive or coating. Anything that is dissolved in the liquid portion is a part of the vehicle.
Viscosimeter An instrument used to measure the viscosity or resistance to flow of materials under standard conditions of temperature. The Brookfield Viscosimeter, a commonly used instrument to measure viscosity, consists of a scale that measures the drag on various size spindles that rotate at a set speed.
Viscosity The property of resistance of flow exhibited within the body of a material. It can be expressed as the ratio between applied shearing stress and resulting rate of strain in shear. It is expressed in poise (dyne-sec/cm²).
Viscosity Coefficient The shearing stress necessary to induce a unit velocity flow gradient in a material. In actual measurement, the viscosity coefficient of a material is obtained from the ratio of shearing stress to shearing rate. It is expressed in poise (dyne-sec/cm²).
Volatility The tendency of a substance to pass into a vapor stage (vaporize) at a relatively low temperature.
Void An unfilled space in a material that is substantially larger than the characteristic individual cells of the material. These spaces are often filled with trapped air or some other gas.

The dimensional distortion in an object after molding or other fabrication.
Water Absorption The ability of a material to take up and retain water.
Wetting The thorough impregnation of a material by a liquid. The more viscous a fluid, and the higher its surface tension, the more difficult it is for the liquid to "wet" materials. Certain additives, such as surfactants, improve wetting properties, allowing the material to flow out more easily.
Wetting Agent A material usually added to aqueous solutions to facilitate spreading or to increase the solution's ability to evenly wet or penetrate the surface. See Surface Active Agents.
Working Life The period of time during which a resin after mixing with a curing agent, remains workable and suitable for use.

Yield Strength
The indication of maximum stress that can be developed in a material without causing plastic deformation.
Young's Modulus The modulus of elasticity in tension or compression.

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