Glossary of Adhesive & Sealant Terms

ABS (Acrylonitrile Butadiene Styrene Resin): A common polymer (plastic) with high resistance to heat, low-temperatures and impact. Bonds well with many adhesive families.

Accelerator (also see catalyst): Usually part B of an adhesive formula, it causes and/or speeds the resin’s curing process.

Acrylic: A semi-rigid, two-component adhesive which bonds to a large variety of substrates. Acrylics are known for their environmental resistance, fast setting time and flame retardant properties.

Activators: Chemicals which can be applied directly to a surface, substrate or mixed with an adhesive to speed up the solidification of an adhesive.

Adhesion: The bonding forces between two different materials (e.g. between an adhesive and substrate).

Adhesive: A material employed to attach one solid to another so that the two solids may function as a single unit.

Adhesive Failure: Loss of adhesion between the adhesive and substrate. The adhesive pulls cleanly away from the substrate.

Aerobic: An epoxy that requires exposure to oxygen to cure.

Anaerobic: A one-part sealant/adhesive that cures only in the absence of oxygen. Designed for locking screws, nuts, bolts or retaining bearings, shafts, etc.

Aqueous: Relating to or made with water.

Binder: A component of an adhesive composition which is primarily responsible for the adhesive forces that holds two bodies together.

Bond: The union of materials by adhesives.

Bond Line: The space or gap between two substrates which contain the adhesive.

Bond Strength: The amount of force a bond can sustain. Measured in Pounds per Square Inch (PSI).

Cartridge: A relatively rigid container used for storing unmixed adhesives in pre-measured quantities. Cartridges can either be side-by-side or coaxial.

Cast: To form a plastic material into a definite shape by pouring it into a mold and letting it harden without applying external pressure. Can be accomplished with or without application of external heat either before or after pouring.

Casting: The finished product of a casting operation. Should not be used as a synonym for molding.

Catalyst (also see accelerator): A substance which causes or speeds a chemical reaction. Usually part B of a two-part adhesive.

Centipoise (CPS): A measure of viscosity (water has a CPS of 1).

Coaxial (also see concentric): Sharing the same axis. When referring to cartridges, one part is contained inside the other part, as opposed to side-by-side.

Coefficient of Thermal Expansion: A measure of the tendency of an adhesive to expand with a temperature increase or contract with a temperature decrease. A higher number means a larger change up and down as the temperature rises and falls respectively.

Cohesion: The state in which the particles of a single substance are held together by primary or secondary valence forces.

Cohesive Failure: Loss of adhesion as a result of the adhesive rupturing, leaving adhesive on both substrates involved in the bond.

Cohesive Strength: The strength which holds a single material’s molecules together.

Composite: A material which is composed of two or more different substances.

Compression Strength: An object’s resistance to rupture under inward pressure.

Concentric (also see coaxial): Sharing the same center. With regard to cartridges, one part inside the other.

Crazing: Fine cracks that may extend in a network on or under the surface of or through a layer of adhesive.

Cure (also see setting): To change the physical properties of a material by chemical reaction through condensation, polymerization or vulcanization. Usually accomplished by the action of heat and catalysts, alone or in combination with or without pressure. Often referred to as hardening or setting.

Cure Inhibition: A poisoning of the catalyst in an addition cure product, such that there is a lack of a complete cure, usually at the interface of the adhesive and the other material.

Curing Agent: A chemical which reacts with an adhesive polymer to cause solidification. Approximately equal amounts of adhesive resin and curing agent are mixed together to form a solid adhesive. Usually Part A of a two-part adhesive.

Cyanoacrylate: A one-part adhesive that cures instantly on contact with mated surfaces. High strength, excellent adhesion to a wide variety of substrates, especially plastics. Poor shock resistance super glue.

Delamination: Separation of layers in a laminate because of adhesive failure.

Dielectric Strength: The maximum voltage a material can withstand without failure. Measured in volts per millimeter of thickness (of the material).

Dilatant Fluid: A fluid whose viscosity increases with increased shear rate.

Durometer: A device used to determine the hardness of a material.

Durometer Hardness: A measure of the hardness of a material as measured by a durometer. The resultant numerical rating of hardness in Shore A softer material (30 or 40) to higher numbered, harder material (80 to 90).

Elastomer: A synthetic rubber, plastic or other polymer which can be stretched to at least twice its original length then return to its original shape with force. The ability to return to its original shape is called memory.

Elongation: The amount a material will stretch before breaking. It is expressed as a percentage of the original length.

Encapsulate (also see potting): The process to surround and enclose an object in an adhesive. Often used in the electronic industry to protect sensitive components.

Epoxy: A two-component adhesive with high strength and low shrinkage during cure. Epoxies are tough and known for their resistance to chemical and environmental damage, as well as their usefulness as structural adhesives. Some formulations are used as potting agents, while others are useful as thermal or electrical conductors.

Exothermic: Pertaining to a chemical reaction which releases heat.

Filled: An adhesive which contains particles not part of the chemical formula for the purpose of changing properties such as electrical conductivity or increasing volume.

Filler: A non-adhesive substance added to an adhesive to improve its working properties, permanence, strength and other qualities.

Fixture Time: The time at which an adhesive will hold a part in place. Fixture time is application specific and varies greatly depending on such parameters as part size and configuration, part weight, the particular adhesive used, thickness, temperature and relative humidity.

Formulator: A company which develops and makes adhesives.

FRP: Fiberglass Reinforced Plastic.

Gel: A description of an adhesive as it hardens from liquid to solid. More often a solid than a liquid.

Gel Time: The time (in minutes) required for a specific quantity of mixed resin and hardener to become unworkable (gelled).

Glass Transition: The reversible change in a substance from a pliable, rubbery condition to a relatively hard and brittle condition or vice-versa.

Glue: A hard gelatin obtained from the hides of animals.

Hardener: A substance added to an adhesive that promotes curing and controls hardness. Usually Part B of a two-part adhesive.

Hardness: A material’s resistance to indentation, scratching or cutting.

Hygroscopic: The ability to absorb and retain atmospheric moisture.

Impact Strength: The ability of a material to withstand a shock load.

Inhibitor: A substance that slows down a chemical reaction to prolong storage or working life.

Kelvin (K): A scale of temperature which has the same increments as Celsius but starts at absolute zero (-273.15°C or —459.67°F).

Laminate: To unite layers of materials with an adhesive.

Lap Shear: Shear stress acting on an overlapping joint.

Linear Shrinkage: The shrinkage encountered in an adhesive in one direction.

Load: The amount of force that a body, joint or bond will sustain. Also, the force applied to a body, joint or bond.

Luer Lock Adapter: A device used as a connector between a static mixer and an application tool such as a disposable needle.

Meter Mix and Dispense Machine (MMD): A machine designed to bring precisely measured volumes of material together from separate sources for mixing and dispensing.

Methacrylate: A modified acrylic adhesive.

Mold: The cavity or matrix into or on which the plastic composition is placed and from which it takes its form.

Motionless Mixer (also see static mixer): A device which uses passive (unmoving) means to combine two or more substances. Commonly found attached to cartridge systems or meter mix equipment.

Newtonian Fluid: A fluid whose viscosity is independent of shear rate. The term is useful in differentiating between thixotropic and dilatant fluids.

Nylon: A generic name for a specific family of plastics.

O-Ring: A circular piece of rubber which fits around the piston to help maintain the seal between the piston and cartridge wall.

Outgassing: A response to extreme conditions (e.g. high heat or the presence of a vacuum) to which the part is exposed. No relationship to by-products of the cure.

Peel Strength: The amount of force required to peel a material off a substrate.

Piston: A disc with a seal that fits tightly into the back of a cartridge against the contents and serves to expel the contents.

Plastic: A synthetic material made from organic compounds. Also can be defined as malleable (i.e. the ability to be molded into different shapes).

Plunger: A rod which is part of a dispensing tool and is used to force the piston (and thus the contents of the cartridge) to the front and through the nose of the cartridge.

Polymer: A complex chemical compound made of similar compounds linked together (e.g. acrylics, epoxies, silicones, urethanes).

Polypropylene: A typical material from which cartridges are often made. Benefits are low-cost, durability and flexibility.

Polyurethane: A one or two-part structural adhesive with excellent flexibility and durability. Cure requires a catalyst, heat or air evaporation. Short shelf-life with hydroscopic tendencies (water absorption). Excellent for potting or where flexibility is required. Good for bonding plastic substrates. Generally slower cure with more complicated handling and curing procedures.

Pot Life (also see work life): The length of time an adhesive remains usable for mixing. Usually an important factor with adhesives mixed together that begin curing almost immediately.

Potting (also see encapsulation): Similar to encapsulating. That is, filling a container of electrical components with an adhesive to provide environmental protection.

Primer: A coating applied to a surface, prior to application of an adhesive, to improve performance of the bond.

PSI (Pounds Per Square Inch): A measurement of pressure, shear, compression or tensile strength.

PVC (Polyvinyl Chloride): A polymer of vinyl chloride used in soft, flexible films for food packing. Also used in rigid products such as pipes.

Resin: A class of solid or semi-solid organic products of natural and synthetic origin, generally of high molecular weights with no definite melting point. Resins are generally water-insoluble and have little or no tendency to crystallize. However, certain resins, such as some polyvinyl alcohols and polyacrylates, are readily dispersible in water. Others, such as polyamides and polyvinylidene chloride, are readily crystallized.

Rheology: The study of the flow of matter, especially the non-Newtonian flow of liquids and plastic solids.

Room Temperature: 70°F/21°C.

RTV (Room Temperature Vulcanizing): The tendency of an RTV adhesive to vulcanize (i.e. cure) at room temperature. Changes from a liquid/paste state to a solid, flexible rubber.

Sag: A decrease in the thickness of a section.

Sealant: A material which adheres to two adjoining parts of an assembly and prevents the passage of gases, dust, liquids, etc. into or out of the assembly at that point.

Set: To convert an adhesive into a fixed or hardened state by chemical or physical action.

Setting Temperature: The optimal temperature in which to promote the setting of an adhesive.

Setting Time: The period of time during which an assembly is subjected to set the adhesive.

Shear: The effect of forces acting in opposite but parallel directions.

Shear Strength: The maximum shearing force, per unit area, an adhesive bond will endure before failure. A shearing force on an adhesive bond is created when the two substrates adhered together are forced in opposite directions in the same plane as the bond. Usually expressed in pounds per square inch (psi).

Shelf-Life: The usable storage time of a material. Most adhesives have a shelf-life of 6 to 12 months. The shelf-life of an adhesive may be increased by refrigeration and is usually shortened by exposure to heat.

Silicone: Any member of a family of polymeric products whose molecular backbone is made up of alternating silicon and oxygen atoms and which has pendant hydrocarbon groups attached to the silicon atoms. Used primarily as a sealant, silicone is known for its ability to withstand large variations in temperature (-100°F to +600°F). Silicone is reliable and is relatively easy to handle.

Solids Content: The non-solvent content of an adhesive by weight, expressed as a percentage. 100% solids means there are no additives. 75% solids has 25% solvents.

Solvent: A substance capable of dissolving another substance.

Static Mixer: A device which consists of a series of internal baffles or elements within a plastic tube. As adhesive components are forced through the mixer, the components are repeatedly divided and recombined, thus creating a complete and uniform mixture. Most static mixers attach in one of two ways: a "bell-mouth" type which requires a retaining nut or a "twist-and-lock" (bayonet) type which requires no additional hardware.

Substrate: Materials to be bonded together (e.g. wood to wood, wood to metal, metal to metal, etc.).

Synthetic: Something produced by chemical means that does not occur naturally.

Tack: Adhesive stickiness on a surface that is not yet completely cured.

Tack Free Time: The time required for a one-component silicone to cure enough to develop a skin which is non-tacky.

Tear Strength: The force required to propagate a tear in a silicone which has been nicked or cut. Expressed in lbs./in. of width.

Tensile Strength: The maximum stress a material subjected to stretching can withstand without tearing.

Thermoplastic: A material which repeatedly softens as temperatures rise and hardens as temperatures fall.

Thermosetting: A material in a relatively infusible state.

Thermoset: A material which hardens when first exposed to high temperatures and pressure but cannot be remelted without destroying its attributes.

Thixotropic: A material with paste-like consistency at rest but flows under pressure or agitation (e.g. cold cream or grease).
Thixotropic Fluid/Liquids: Fluids/liquids which reduce their viscosity as agitation is increased (e.g. ketchup, latex paint).

Urethane: A flexible, two-part structural adhesive known for its durability. Urethanes make good potting compounds and bond well to plastics. Generally a slower cure process than other adhesive formulations.

Viscosity: The resistance of a fluid to flow (i.e. "thickness"). Measured in centipoise (cps).

VISCOSITY TABLE Approximate viscosities of common materials at room temperature - 70°F
	Material Water Milk SAE 10 Motor Oil SAE 20 Motor Oil SAE 30 Motor Oil SAE 40 Motor Oil Castor Oil Karo Syrup Honey Chocolate Syrup Ketchup Mustard Sour Cream Peanut Butter Shortening	Viscosity in Centipoise (cps) 1 CPS 3 CPS 85-140 CPS 140-420 CPS 420-650 CPS 650-900 CPS 1,000 CPS 5,000 CPS 10,000 CPS 25,000 CPS 50,000 CPS 70,000 CPS 100,000 CPS 250,00 CPS 1,200,000 CPS

Voids: Gas or air pockets trapped within a material.

Volatile Organic Compounds (VOC): Any organic molecules which evaporate easily. They are often associated with unpleasant odors or noxious fumes.

Wetting: The coating of a substrate surface with an adhesive.

Wicking: The flow of a liquid along a surface into a narrow space (much like capillary action).

Work-Life (see also pot life): The period of time after an adhesive has been mixed with its curing agent that it will remain useful or pliable.

Working-Time: Same as gel time.