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A compound or substance added to a polymer plastic to improve and alter characteristics of a polymer.  Additives are used to expand or extend material properties, enhance processability, modify aesthetics or increase environmental resistance.  Additives enhance properties like flame retardancy and UV light stability.


An additive, when exposed to ambient air, inhibits the degradation and oxidation of material.

Antistatic Agent

Additive which renders a remote degree of electrical energy to plastics, permitting the dispersion of electricity.


The mixing of polymer plastics with other polymer or copolymers

Calcium Carbonate

A chemical compound filler and extender used in thermoplastics, commonly found in rock.

Coefficient of Thermal Expansion

a.k.a. COE, the amount of movement of a material due to temperature change.  Generally all materials expand when heated and contract when cooled, continuously.  Not the same as Heat Shrinkage, which happens basically one time.


The process of extruding two or more materials through a single dies with two or more orifices arranged so that the extrudates merge and weld together into a laminar structure before chilling.

Color Concentrate

 Is a plastic’s compound containing high pigment that is blended into base resin.


A mixture of resin and the ingredients necessary to modify the resin to a form suitable for processing into finished articles.


The process of selection of additives and their incorporation into a polymer.  Compounding is done to obtain desirable properties for particular uses.  Modification of the polymer properties is done by ingredients such as polymeric resins, plasticizers, fillers, reinforcing agents, various stabilizers, lubricants, coloring agents, flame retardants, etc.

Compression Set

A physical property, and measurement of a materials’ ability to rebound back from deformation – like in a sealing application.



Caused by exposure to heat, light, oxygen, or weathering, degradation is a destructive change in the chemical structure, physical properties, or appearance of plastic materials.


Weight per unit volume of a substance.


A steel block containing an orifice through which plastic is extruded, shaping the extrudate to the desired form.

Die Lines

Vertical or horizontal marks on the extrudate plastic and in the finished plastic product caused by contamination held up in the die land. 


Typically used by most manufacturers, the drawdown process is pulling the extrudate away from the die at a linear speed higher than that at which the melt is emerging from the die.




The processes of recovering original size and shape after deformation of the material. 


The stretching of material.


Compacting and melting plastics and forcing them through an aperture in a perpetual fashion.

Flexural Modulas

The physical property and measurement of a materials’ relative stiffness relative to deflecting under pressure.



Process for producing extruded plastic articles with a cellular construction. Either a chemical or gaseous blowing agent is introduced into the polymer plastic melt while the plastic melt is being prepared in the extruder barrel. As the plastic melt exits the die, it expands a predetermined amount forming a cellular wall.

Flame Retardant

Used by recycled plastic and plastic material manufacturers, flame retardants are reactive compounds and additive compounds to render a polymer plastic fire resistant. Reactive compounds become an integral part of the polymer plastic.



Brightness or luster of a plastic resulting from a smooth surface within recycled plastic and plastic material.


Heat Sealing:

Plastic manufacturers use this process of joining two or more thermoplastic films or plastic sheets by heating areas on the plastic, in contact with each other to the temperature at which fusion occurs.  Plastic heat sealing is usually aided by pressure.

Heat Distortion Temperature

a.k.a. HDT, the temperature at which all stresses in a material will relax.  Generally a material properties failure temperature – rigid plastics are no longer rigid.  All stresses holding the part to shape and length will relax.

Heat Shrinkage

The phenomenon where plastics contract when heated up to or near their Heat Distortion Temperature and are starting to stress relieve.  Not the same as COE.

High-Density Polyethylene

This term is generally considered to include polyethylene plastic’s ranging in density from about 0.940 to 0.960 and over in recycled plastic and plastic materials.

Impact Strength

A physical property and measurement of the relative impact strength of different materials.  Most meaningful when done using a drop dart impact tester.


Linear Low-Density Polyethylene

Includes polyethylene plastic’s ranging in density from 0.915 to 0.935.

Low-Density Polyethylene

This term used by plastic material manufacturers is generally considered to include polyethylene plastic’s ranging in density from about 0.915 to 0.925. In low density polyethylene plastic’s, the ethylene monomeric units are linked in random fashion, with the main chains having long and short side branches. This branching prevents the formation of a closely knit pattern, resulting in plastic material that is relatively soft, flexible and tough, and which will withstand moderate heat.


Melting Point

The temperature at which a resin in plastic changes from a solid to a liquid form of the plastic material.

Modulus of Elasticity

The ratio of stress to strain below the yield point of the plastic material.




Permeability is the property of a plastic material.  Plastic manufacturers use this as a degree to which it allows permeation to occur.


Degradation of plastics due to the action of light. In the recycled plastic and plastic material industry, most plastics tend to absorb high-energy radiation in the ultraviolet portion of the spectrum this generates in the formation of free radicals and causes degradative reactions in plastic materials.

Plastic Orange Peel

An uneven surface texture of a plastic article or its finished coating somewhat resembling the surface of an orange.

Plastic Pellets

Plastic tablets of uniform size, consisting of resins or mixtures of resins with compounding additives which have been prepared for plastic molding operations by shaping by plastic extrusion and chopping into short plastic segments.

Plastic Virgin Material

Any plastic compound or resin that has not been subjected to use or processing other than that required for the plastic compound or resin’s original manufacture.


A substance or material incorporated in a material (usually a plastic or an elastomer) to increase its flexibility, workability or extensibility.


The class of polymer plastics, made by polymerizing relatively simple olefins.


Used in the plastics industry, polyethylene is a family of resins obtained by polymerizing the gas ethylene of plastic.


A tough, lightweight, rigid plastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst.  Plastic manufactures do this at low temperatures and pressures.



An organic substance commonly used by plastic manufactures, of natural or synthetic origin in plastic material characterized by being polymeric in nature.


Woven metal screens are installed across the flow of plastic in an extruder in plastic manufactures. Supported by a breaker plate, the screens strain out contaminants and increase back pressure.

Shelf Life

The length of time over which a product, such as plastics, will remain fit for use during storage under specific conditions.

Specific Heat

The amount of heat required to raise a specified mass in plastic by one unit of a specified temperature, usually expressed as Btu/lb/°F. or cal/g/°C in plastic.


Ingredient used in the formulation of some polymer plastics to assist in maintaining the physical and chemical properties of the compounded plastic materials.


The force producing or tending the plastic material, to produce deformation divided by the area over which the force is applied to the plastic material.


A natural hydrous magnesium silicate, used frequently as filler such as steatite, talcum, mineral graphite in plastic materials.

Tear Resistance

Consistently used by plastic manufacturers, resistance of a material, such as plastic material, to a force acting to initiate and then propagate a failure at the edge of a test specimen.

Tensile Strength

The maximum tensile stress sustained by the specimen before failure in a tension test by plastic material and plastic product distributors. The cross-sectional area used is that of the original specimen, not at the point of rupture.


Resins or plastic compounds which, in their final state as finished plastic articles, are capable of being repeatedly softened by an increase of temperature and hardened by a decrease of temperature within resins or plastic compounds.  PE, PP, PVC and all extrudable polymers are thermoplastics.


Resins or plastic compounds which in their final state as finished resin or plastic articles are substantially infusible and insoluble.


A physical property related to a materials’ ability to resist the degrading effects of sunlight, moisture, and airborne chemicals.

Yellowness Index

A measure of the tendency of plastics to turn yellow upon long-term exposure to light or heat



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