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Glossary

A Brief Glossary of General Terms Used in the Plastics Industry

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

A

 

Abrasion Resistance:

Capability of material to resist mechanical actions such as rubbing, scraping, erosion which wear down material. In general, the abrasion behaviour of plastics is good, especially in the case of sliding surfaces where foreign particles, as well as particles generated through abrasion, are pressed into the surface and thus lose their abrasive effect. This is why plastics mostly withstand sliding abrasion, grain abrasion and frictional abrasion better than metallic materials.

ABS

Acrylonitrile Butadiene Styrene is a thermoplastic copolymer that can withstand high temperatures and has good adhesive properties. It is one of the most widely used engineering thermoplastic . ABS extrusions are mainly used for indoor purposes. The plastic product has excellent surface appearance, strength and stiffness, toughness and chemical resistance—as well as its processing ease and versatility. ABS is often used for refrigerator door liners, interior automotive trims, and housings for business machines, small appliances, telephones, and other consumer electronics. Furthermore, ABS offers a broad processing window with resins tailored for plastic extrusion manufacture, injection moulding, sheet extrusion and coextrusion, plating, roto moulding, compression, cold forming, and blow moulding.

Acetal (POM):

Acetal is a highly crystalline thermoplastic engineering resin that offers high mechanical properties and resists many chemicals. There are two basic types of Acetal resins: homopolymer and copolymer. Acetal is known for its high strength, creep resistance, resilience, surface hardness and lubricity, toughness, and excellent solvent and petrol resistance. Additionally, it absorbs little water. Acetals can be processed by conventional extrusion and injection moulded techniques.

Application: Acetals are widely used for plastic pipes and tubes in plumbing and irrigation because they resist scale build-up, and have excellent thread strength. Furthermore this material is used for moulded and machined rollers, bearings, gears, conveyor chains, and housings. Automotive applications include, door handles, ventilation and cooling system parts, fuel system components, and many more.

Alloy:

Composites of polymers or copolymers with other polymers or elastomers, e.g. ABS/Polycarbonate. ABS/PC alloys are used to make structurally strong parts for use in such market areas as appliances, automotive, for building and construction, chemical processing, consumer goods, electronics, health care, and packaging.

Additive:

A compound or substance added to a polymer plastic to improve and alter characteristics of a polymer, such as a lubricant, stabilizer, plasticizer, etc.

Amorphous:

Non-crystalline. Most plastics are amorphous at extrusion processing temperatures. The material assumes a more random molecular structure when cooling.

Antiblock Agent:

Additive used to improve the electrical conductivity of the plastic extrusions or other plastic profiles so that any charge can readily go to ground and not remain in the part.

Antioxidant:

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

Antistatic Agent:

Additive which reduces or eliminates the build-up of static electricity in the material. This can be used in all processes including plastic extrusion manufacturing.

Application:

The act of applying or putting to use, i.e. What the plastic extrusion profile will be used for in its final form.

Aspect Ratio:

Ratio of total flow length to average wall thickness.

 

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B

 

Barrel:

Section of the extrusion machine that contains the plastic extrusion feed screw, which can be single or twin screw. This is also the section where resin heating and mixing occurs.

Biodegradation:

The process of reducing plastics by microorganisms while buried in the soil.

Bioplastics:

Bioplastics, such as thermoplastic starch, cellulose-based plastics, are a form of plastics derived from renewable biological material sources. Biodegradable bioplastics are used for disposable items, such as packaging and catering items (crockery, cutlery, pots, bowls, straws). Bioplastics are more sustainable because they can break down in the environment faster than fossil-fuel plastics.

Blend:

The mixing of polymer plastics with other polymer or copolymers.

Blister:

An imperfection on the surface of plastic extrusions or other plastic profiles caused by a pocket of air or gas beneath the surface.

Bloom:

Also known as migration – an undesirable greasy cloud effect or white powdery deposit on the surface of a plastic product usually caused by the exudation of an additive.

Blow moulding:

It is also known as blow forming. It is a manufacturing process whereby hollow plastic parts are formed, e.g. bottles, tanks. In general, there are three main types: extrusion blow moulding, injection blow moulding, and stretch blow moulding. D W Plastics does not manufacture blow mouldings. It specialises in plastic extrusions.

Blown Film:

It is a process that involves extruding a continuous thin walled tube of plastic material, and inflating the material immediately after the plastic leaves the die. Air is trapped within the blow tube (bubble) between the die and collapsing rolls which converts it to lay flat plastic film to facilitate winding onto a roll. D W Plastics only specialises in plastic extrusions and does not manufacture blown film.

Blushing:

The tendency of plastic products to turn white or chalky in areas where pressure is applied.

Breaker Plate:

A thick metal piece with many holes drilled through it which reinforces the screen pack through which the molten plastic travels when leaving the barrel of the plastic extrusion machine. Breaker plate and screen combination also converts "rotational memory" of the molten plastic into "longitudinal memory".

Brittle Temperature:

The temperature at which plastic extrusions and other plastic profiles rupture by impact under specific conditions.

 

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C

 

Cable extrusion:

Process of extruding cables for wire sheathing or coating. Various plastic materials can be used for this process, such as PVC, HDPE, depending on the application of the extruded plastic profile.

Calcium Carbonate:

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

Cellular Plastic:

Plastics containing numerous small cells, some interconnected others not, distributed throughout the mass. Used for lighter weight plastic extrusions and other PVC products.

Clarifiers:

Additives used in resins to improve the transparency or translucency of the finished plastic extrusion profiles and other plastic products.

Coating:

Plastic that has not been recycled commonly has coating of a substrate by extruding a thin film of molten polymer plastic and pressing it onto the substrate.

Coefficient of Thermal Expansion (CTE):

Describes how the size of an object changes with a change in temperature

Coextrusion:

The process of combining two or more layers of plastic extrusions to produce a multiple layer product in a single step using one tool. A co-extrusion requires compatible PVC materials that will bond together to form a strong finished part. It can be either a dual hardness (rigid/flexible PVC) co-extrusion or a two-colour co-extrusion where two colours are extruded together.

Colour pigment:

Also known as masterbatch. A concentrated blend of pigment, additives, filler, etc., that are added to the base plastic polymer in appropriate amounts to achieve the required colour.

Colour Concentrate:

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

Compound:

These are chemical combinations of materials which include all the materials necessary for the finished product.

Compression zone:

Also called the transition or melting zone. Zone in the extruder’s screwbarrel. Most of the plastic compound is melted in this section, and the channel depth gets progressively smaller.

Copolymer:

Polymers resulting from the polymerization reaction of two monomers that are chemically altered.

Corrosion Resistance:

Term that applies to the ability of plastics to resist degradation in many environments.

Cross Linking:

The forming of chemical bonds between the molecular chains of a plastic during curing, so that it cannot be re-softened and re-moulded, thus becoming a thermoset.

Curing:

The forming of a polymer by polymerization and/or Cross Linking.

 

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D

 

Decompression zone:

Zone in a double screw extruder, about two-thirds down the screw, the channel suddenly gets deeper, which relieves the pressure and allows any trapped gases (usually moisture or air) to be drawn out by vacuum.

Degradation:

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.

Density:

Weight per unit volume of a substance.

Die:

A steel block/tool containing an opening through which plastic is extruded, shaping the plastic extrusions to the desired form.

Die Gap:

Distance between the metal faces forming the die opening within the material.

Die Lines:

Vertical or horizontal marks on the extruded plastic and in the finished plastic products caused by contamination held up in the die area.

Drawdown:

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

Durometer:

Instrument for measuring the hardness of a material. Plastic materials can have different shore hardnesses depending on the requirements of the plastic extrusion’s final applications. The durometer measures the depth of an indentation in the material created by a given force on a standardized presser foot.

 

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E

 

Elasticity:

The processes of recovering original size and shape after deformation of the material. Most plastic materials have limited elasticity.

Elastomer:

A synthetic plastic with the flexible properties of rubber. See also TPEs.

Elongation:

The stretching of plastic material.

Ethylene Vinyl Acetate (EVA):

Copolymeric member of the polyolefin family derived from random copolymerization of vinyl acetate and ethylene. They are mainly used for foaming, coating, extrusion, and injection moulding applications for many industrial market sectors such as shoe soles, sheets, wire and cable, hot melt adhesive, and solar cell encapsulation.

Extrudate:

The plastic products delivered from a plastic extrusion manufacturer, for example PVC and UPVC tubes, pipe profiles, plastic rods to mention but a few extrusion profiles.

Extrusion:

The process of compacting and melting plastic compounds into continuous shaped lengths by forcing them through a die. Plastic extrusions can be manufactured in a wide variety of shapes, sizes and colours, and for customers across many industry sectors. Plastic extrusions are normally manufactured in high-volumes.

 

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F

 

Feed Zone:

Zone in the extruder’s screw which feeds the resin into the plastic extrusion machine, and the channel depth is usually the same throughout the zone.

Filler:

Inert material added to a polymer to improve its properties. Usually in powder or fibre form such as wood pulp, cotton flock and talc.

Foam:

Process for producing plastic profiles 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 compound manufacturers, flame retardants are reactive compounds and additive compounds to make the finished plastic extrusion products fire resistant. A flame retardant plastic is considered to be one that will not continue to burn or glow after the source of ignition has been removed.

Flow Rate:

The volume of plastic compound passing a fixed point per unit time.

 

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G

 

Gauge:

Thickness of recycled plastic or plastic film measured in decimal inches or mils.

Glass Fibre:

A family of reinforcing materials for reinforced plastics based on a filament of glass.

Gloss:

Brightness or shine of a plastic resulting from a smooth surface within recycled plastic and plastic material. Similar to a polished effect.

 

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H

 

Hardness:

The resistance of a material to compression, indentation and scratching. It also denotes the flexibility of the plastic extrusion or other plastic products. See also Shore Hardness and Rockwell Hardness.

Haze:

Cloudiness in plastic film that is measured as ‘percent haze’. Five percent and below is considered high clarity in plastic.

Heat Sealing:

Plastic manufacturers use this process of joining two or more thermoplastic films or plastic sheets by heating areas on the plastic to the temperature at which fusion occurs. Plastic heat sealing is usually reinforced by pressure.

Heat stabilizers:

Additives to increase the ability of the plastic materials to withstand the negative effects of heat exposure. They are used to increase the overall service temperature of the material.

HIPS:

High Impact Polystyrene is a low density, rigid, clear plastic extrusion material mostly used for indoor applications (see Polystyrene).

High-Density Polyethylene (HDPE):

This term is generally considered to include polyethylene plastics ranging in density from about 0.940 to 0.960 and over in recycled plastic and plastic materials. Its main usages are crates and boxes, bottles (for food products, detergents, cosmetics), food containers, toys, petrol tanks, industrial wrapping and film, pipes and houseware.

Homopolymer:

The result of the polymerization of a single monomer. In the plastic industry a homopolymer is a sequence of identical bases.

Hopper:

Container mounted on the plastic extrusion line in to which plastic raw material is filled to feed the extrusion barrel.

Hopper Dryers:

Auxiliary equipment for the plastic extrusion process that removes moisture from the resin pellets.

Hopper Loader:

Auxiliary equipment for automatically loading plastic pellets into the hopper.

 

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I

 

Impact Resistance:

The resistance of plastic extrusions or other plastic products to fracture under pressure applied at high speeds.

Impact Strength:

The ability of a plastic extrusion or other PVC profile to withstand shock loading.

Injection Moulding:

The method of forming objects from granular or powdered thermoplastic materials using moulds. The mould gives the plastic product its shape by means of a confining cavity or matrix. This is a different process to plastic extrusion manufacture using different grades of plastic compounds.

 

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J

 

Jacket:

A tough sheath made of plastic material used to protect an insulated wire or cable, or to permanently group two or more insulated wires or cables.

Jig:

A tool for holding parts of an assembly during a manufacturing process.

 

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K

 

Kelvin:

The Kelvin scale is a thermodynamic temperature scale (metric).

 

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L

 

Light, UV Stabilizers:

Additives that increase the ability of the material to withstand the negative effect of light and ultra violet (UV) exposure. This increases the service life of the plastic extrusions and other plastic profiles.

Low-Density Polyethylene (LDPE):

LDPE is defined by a density range of 0.910–0.940 g/cm3. This plastic material is relatively soft, flexible and tough but breakable, and will withstand temperatures of 80 °C continuously and 95 °C for a short time. It is made in translucent or opaque variations. LDPE is widely used for the manufacture of various containers, dispensing bottles, wash bottles, tubing, plastic bags for computer components, and various moulded laboratory equipment. Its most common use is in plastic bags. Linear low density polyethylene (LLDPE) is a new type of low density polythene.

Lubricant:

Internal lubricants promote the flow of plastic resin. External lubricants promote release from metals which helps with the smooth flow of the plastic melt over the surfaces.

 

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M

 

Masterbatch:

A concentrated blend of pigment, additives, and fillers that are added to the base plastic polymer in appropriate amounts to achieve the required colour.

Material Safety Data Sheets:

Documentation regarding the toxicity or hazards associated with contact with some substances. Polymer manufacturers have to provide these data sheets.

Melt Conveying:

Also called Metering zone. This zone, in which channel depth is the same throughout the zone, melts the last plastic resin particles and mixes to a uniform temperature and composition.

Melt Flow:

Rate of extrusion of molten resin through a die of specified length and diameter.

Melt Fracture:

Is a phenomenon of melt extrudate in which the surface of plastic appears rough or wavy upon exit from the die. Melt fracture may appear uniformly or only in certain sections of plastic material.

Melt temperature:

Temperature at which plastic melts (ranging from 200°C (392 °F) to 275°C (527 °F) depending on the polymer.

Melting Point:

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

Melt Strength:

The strength of the plastic while in a molten state. This is an important factor in the process of plastic extrusion, blow moulding and drawing molten plastic resin from the die.

Melting zone:

Also called the transition or compression zone. Most of the plastic resin is melted in this section, and the channel depth gets progressively smaller.

Memory:

The tendency of plastic extrusions or other plastic products to revert in dimension to a size previously existing at some stage in its manufacture.

Metering zone:

Also called melt conveying. This zone, in which channel depth is the same throughout the zone, melts the last plastic resin particles and mixes to a uniform temperature and composition. The second metering zone in a twin screw extruder is the same as the first metering zone, but with greater channel depth, and it repressurizes the melt to get it through the resistance of the screens and the die.

Migration:

Also known as Bloom – an undesirable greasy cloud effect or white powdery deposit on the surface of a plastic product usually caused by the exudation of an additive such lubricant, stabilizer, plasticizer, etc.

Minimum Specification:

The minimum values, usually of mechanical properties, that compounds, plastic extrusions, or other PVC profiles must meet by Quality Assurance prior to shipment.

Molecular Weight:

The sum of the atomic weights of all atoms in a molecule. In plastics an average molecular weight is stated.

Mono layer:

A homogenous film formed by pumping molten polymer plastic from an extruder through a die assembly to form a plastic film.

Monomers:

The term that most often refers to organic molecules which form synthetic polymers, such as, for example, vinyl chloride, which is used to produce the polymer polyvinyl chloride (PVC).

 

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N

 

Neck-In:

The difference between the width of the extrusion die opening and the width of the coating on the plastic substrate, in extrusion coating.

 

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O

 

Octene:

A co-monomer used in the production of linear low-density polyethylene plastics.

Oleamide:

An ivory-coloured powder used as a slip additive in polyolefin plastics.

 

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P

 

Perforating:

Processes used by plastic manufacturers by which plastic film or plastic sheeting, or extrusions are provided with holes within the plastic material ranging from relatively large diameters for decorative effects to very small, even invisible, sizes on the plastic.

Permeation:

The passage or diffusion of a gas, vapour, liquid, or solid through a barrier within the plastic material without physically or chemically affecting the plastic.

Photodegradation:

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 UV portion of the spectrum this generates in the formation of free radicals and causes degradation in plastic materials.

Plastic:

Plastics are derived from organic products. The materials used in the production of plastics are natural products such as cellulose, coal, natural gas, salt and, of course, crude oil. Plastic contains as an essential ingredient of one or more organic polymeric substances of large molecular weight. It is solid in its finished state, and, at some stage in its manufacture or processing into finished plastic extrusions, can be shaped by flow. Common plastics, such as fossil-fuel plastics, are derived from petroleum, but bioplastics are a form of plastics derived from renewable biomass sources, for example. Plastics are lightweight, cost-efficient and durable materials.

Plastic Compound:

A mixture of resin(s) and additives to provide the end-user with a finished grade suitable for the required plastic extrusion profile or other manufactured plastic products.

Plastic Extrusions:

Plastic products extruded in a high-volume manufacturing process in which raw plastic material is melted and formed into a continuous profile. The first thermoplastic extrusion was made in Germany in 1935.

Plastic Extrusion Machines:

Machines used for the process of plastic extrusion. Extruders produce items such as pipe/tubing, weather stripping, plastic fence posts and railings, synthetic decking, window frames, plastic films, thermoplastic coatings, and wire insulation, to name but a few.

Plastic Extrusion Manufacturing:

Plastic extrusions are manufactured by loading plastic chips or pellets, in to a hopper before being fed into the screw barrel. The polymer resin is heated to molten state by a combination of heating elements and shear heating from the extrusion screw. The screw forces the resin through a die, forming the resin into the desired shape. The extrudate is cooled and solidified as it is pulled through the die or water tank.

A multitude of polymers are used in the production of plastic tubing, pipes, rods, rails, seals, and sheets or films.

Plastic Extrusion Tooling:

Tooling consists of the dies which are designed for bespoke PVC extrusions

Plastic Manufacturing:

Fabrication of plastic products by various processes such as thermoplastic extrusion, sheet/film extrusion, blown film extrusion, various forms of plastic moulding, for example injection moulding, and vacuum forming of plastic sheet.

Plastic Pellets:

Small plastic beads of uniform size, consisting of resins or mixtures of resins with compounding additives prepared for the plastic extrusion process, or other plastic manufacturing processes.

Plastic Recycling:

The process of recovering plastic scrap or waste plastic material and reprocessing the plastic material into useful recycled plastic products.

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.

Plasticity:

A material that has a tendency to say in shape or size has high plasticity. The opposite of elasticity.

Plasticizer:

A substance incorporated in a plastic compound to increase its flexibility, softness, or extensibility.

Polycarbonate:

A very tough thermoplastic, usually found as a substitute for glass, e.g. vandal proof telephone kiosks, bullet proof shields, baby bottles and picnic ware. It is also extensively used in the automobile industry.

Polyethylene (PE):

A thermoplastic material composed by polymers of ethylene. It is normally a translucent, tough, waxy solid which is unaffected by water and by a large range of chemicals. It can be supplied in high or low density depending on application and is suitable for indoor and outdoor uses. It has good resistance to chemicals and low temperatures.

Polyethylene Terephthalate (PET)

PET is one of the most commonly used plastics in Europe’s packaging industry for several reasons. It is very strong, it can withstand high pressures and being dropped without bursting. It has excellent gas barrier properties, so it keeps the fizz in carbonated drinks, and protects the taste of the drinks in the bottles.

Polymer:

Another word for plastic material made from chains of molecules of one or more monomers. Polymers (plastics) are organic substances of high molecular weight, made from hundreds or thousands of molecules linked together in a repeating chain pattern.

Polymer Process Aid (PPA):

Additives incorporated into plastic material as a modifier to help in the extrusion of plastic materials.

Polymerization:

The chemical process of linking monomers to form new compounds called polymers.

Polyolefin:

The class of polymer plastics, made by polymerizing relatively simple olefins. Polyolefins is the collective description for plastics types that include polyethylene - low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) - and polypropylene (PP).

Polypropylene (PP):

A tough, lightweight, rigid plastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst. It has a good resistance to chemical environments and can withstand high temperatures. Polypropylene is available in high and low density formulation. It is used in the manufacture of food packaging, including yoghurt, margarine pots, sweet and snack wrappers, microwave-proof containers, carpet fibres, garden furniture, medical packaging and appliances, luggage, kitchen appliances, and pipes.

Polystyrene:

A lightweight, rigid, water-white thermoplastic produced by the polymerization of styrene. The electrical insulating properties of polystyrene are excellent and the material is relatively unaffected by moisture. It is also has very good thermal insulating properties. See Styrene for its usages.

Polyurethane (PUR):

Polyurethane is categorised as a polymer. It is a resilient, flexible and durable material that can be rigid or soft, protective like varnish, elastic like rubber, or have adhesive qualities. Polyurethanes are used in the manufacture of flexible, high-resilience foam seating; rigid foam insulation panels, microcellular foam seals and gaskets, elastomeric wheels and tires, automotive suspension units, high performance adhesives, surface coatings and surface sealants, synthetic fibres, carpet underlay, and hard-plastic parts (e.g., for electronic instruments). Polyurethane is also used for the manufacture of hoses and skateboard wheels as it combines the best properties of both rubber and plastic.

PVC

Polyvinyl Chloride is a thermoplastic material composed of polymers of vinyl chloride. PVC is a versatile thermoplastic resins that can be formulated to be rigid or flexible. This material is durable and light, strong, fire resistant, with excellent insulating properties and low permeability. By varying the use of additives in the manufacturing of PVC products, features such as strength, rigidity, colour and transparency can be adjusted to meet most applications. PVC is used in a broad range of plastic extrusion applications. As a flexible it is used in wire and cable jacketing, flooring, garden hoses, and medical tubing. As a rigid it is used most commonly in building and constructions. For exterior siding, windows, pipe fitting, sprinkler systems and office furniture edging. It has outstanding resistance to water, alcohols, and concentrated acids and alkalies. Compounded with plasticizers it yields a flexible material superior to rubber in ageing properties. It is widely used for cable and wire coverings, in chemical plants, and in the manufacture of protective garments.

 

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Q

 

Quality Assurance/Control

Like any other industry the plastics sector has stringent industry regulations and standards. These require constant monitoring and have to be reflected in quality control systems right across the board, from the plastic resin suppliers through to the finished plastic extrusions or other plastic products and their application.

 

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R

 

Recycled Plastic:

A plastic prepared from used articles which have been cleaned and reground, then re-introduced into the manufacturing process. See also Regrind, Rechip or Reprocessed.

Reformulated Plastic:

Recycled plastic that has been upgraded to alter or improve performance capability or to change characteristics through use of plasticizers, fillers, stabilizers, pigments, etc.

Regrind/Rechip:

Recycled plastic material which has been reclaimed by shredding or granulating from all fabrication processes including plastic extrusion manufacture. Regrind is often mixed with a percentage of virgin compound for re-use.

Reinforced Plastics:

These plastic materials consist of base resins to which fibrous reinforcements have been added to increase the strength of the finished plastic products.

Reprocessed Plastic

A thermoplastic prepared from scrap industrial plastic by other than the original processor (see also regrind, recycled plastic).

Resin (Synthetic):

The term is synonymous with plastic used to label any polymer that is a basic material for plastics.

Rigid PVC

Polyvinyl chloride characterized by a relatively high degree of hardness.

Rockwell Hardness:

A measure of the surface hardness of a material. The Rockwell hardness test method consists of indenting the test material with a diamond cone or hardened steel ball indenter. See also Shore Hardness.

 

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S

 

Scrap:

Any waste plastic product that is not useable as the primary product. A certain amount of scrap is usually generated during plastic extrusion manufacture and other plastic manufacturing processes. This scrap can normally be recycled.

Screen (pack):

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

Screw:

The plastic extrusion feed screw, which can be single or twin screw, is part of the plastic extrusion machine. It sits in the barrel of the machine forcing the plastic material along the barrel.

Shear Strength:

The maximum load required to shear the material specimen. In materials science, the strength of a material is its ability to withstand an applied stress without failure.

Sheeting:

Sheets are distinguished from films in the plastics industry only according to the thickness. Plastic sheeting is most commonly made by sheet extrusion and casting in the plastics industry. Post extrusion processes for plastic sheet is thermoforming and vacuum forming.

Shelf Life:

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

Shore Hardness:

A method of determining the hardness of a plastic material using a scelroscope or durometer. The Shore Scleroscope measures hardness in terms of the elasticity of the material. The device consists of a small conical hammer fitted with a diamond point which falls inside a glass tube. The hammer is made to strike the material under test and the degree of rebound is noted on a graduated scale. Generally, the harder the material the greater will be the rebound. See also durometer.

Shrinkage:

Contraction upon cooling of all areas of the plastic extrusions, or other plastic products.

Shrinkage Allowance:

Dimensional allowance which must be made to compensate for shrinkage of the plastic profile/compound on cooling.

Slip Agent:

Additive used to provide lubrication during and immediately after the processing of plastics.

Specific Gravity:

SG is the ratio of the density of a material compared to the density of water at standard atmospheric pressure (1 ATM) and room temperature 23ºC.

Specific Heat:

The amount of heat required to raise a specified mass in plastic by one unit of a specified temperature.

Stabilizer:

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

Static Eliminators:

Mechanical devices frequently used by plastic material manufacturers for removing electrical static charges from plastic articles.

Stearamide:

A slip additive used by most plastic product distributors in polyolefins. It is used in process industries as release agents, antistatic agents, and antifoaming agents.

Stress:

The force causing deformation in a plastic material measured by the force applied per unit area.

Styrene

Styrene is the key building block for styrenic polymers. This includes materials such as Polystyrene, ABS, EPS or Expandable polystyrene, to name but a few. Plastic manufacturers use styrene-based resins to produce a wide variety of everyday goods ranging from cups and utensils to furniture, bathroom, and kitchen appliances, hospital and school supplies, boats, sports and recreational equipment, consumer electronics, automobile parts, and durable lightweight packaging of all kinds.

 

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T

 

Tack:

The stickiness of an adhesive, measurable as the force required to separate an adherent from it by viscous or plastic flow of the adhesive.

Talc:

A natural hydrous magnesium silicate, used frequently as an additive in plastic compounds.

Tear Resistance:

Also called tear strength, is the measure of how well a plastic material can withstand the effects of tearing. Natural rubber and polyurethane, for example, have a high tear resistance. Materials with low tear resistance tend to have poor resistance to abrasion and will quickly fail when damaged.

Tensile Strength:

The maximum tensile stress sustained by a material before failure in a tension test. Plastic materials have different tensile strengths.

Thermocouples:

Temperature sensor for measurement and control and can also be used to convert a temperature gradient into electricity. These are used on plastic extruder machines.

Thermoforming:

This is a process whereby a plastic sheet is heated and formed into a plastic product using a mould.

Thermoplastics:

Resins or plastic compounds in the form of small beads which, in their final state as formed plastic products, are capable of being repeatedly softened by an increase of temperature and hardened by a decrease of temperature.

Thermoplastic Elastomers (TPE )

TPEs are a family of polymers that can be repeatedly stretched without permanently deforming the shape of the part. Unlike rubber-like elastomers, they do not require curing or vulcanization, as they are true thermoplastics. TPEs may be processed by conventional thermoplastic techniques such as injection moulding, plastic extrusion and blow moulding. They are used for automotive, building and construction plastic profiles, soft touch grips and handles, caster treads and rollers.

Thermoplastic screw:

The screw in the barrel of the plastic extrusion machine. There are single screw and vented (two-stage/twin) screws. Often screw length is referenced to its diameter as L:D ratio. For instance, a 6-inch (150 mm) diameter screw at 24:1 will be 144 inches (12 ft) long, and at 32:1 it is 192 inches (16 ft) long. An L:D ratio of 24:1 is common, but some machines go up to 32:1 for more mixing and more output at the same screw diameter. Two-stage (vented) screws are typically 36:1 to account for the two extra zones.

Thermosets:

Resins or plastic compounds which in their final state as finished resin or plastic articles are substantially infusible and insoluble (see also Cross-Linking).

Transition Temperature:

The temperature at which a polymer of the plastic changes from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one.

Tool:

Term also used to describe the die in the manufacture of plastic extrusions.

Transluscent:

Descriptive of a material or substance capable of transmitting some light, but not clear enough to be seen through

Transparent:

Descriptive of a material or substance capable of a high degree of light transmission, e.g. glass. Some polypropylene extrusions and acrylic mouldings are outstanding in this respect.

Treater:

Equipment and process generally used by plastic manufacturers used to render a surface of inert plastics, such as polyethylene plastic.

Twin Screw Extruder:

Twin screw extrusion used in plastic extrusion manufacturing offers several advantages over single screw extrusion. It has better feeding and more positive conveying characteristics which allow the extruder to process hard-to-feed materials. In addition a better mixing and larger heat transfer area allows good control of stock temperatures, which are key elements in the extrusion of thermally sensitive materials.

 

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U

 

UPVC

Unplasticized polyvinyl chloride is a rigid plastic polymer. UPVC is low maintenance and has strong resistance against chemicals, sunlight, and oxidation from water. Rigid PVC can be used for thermoplastic extrusion and is supplied in a variety of colours and strengths. Unplasticised PVC one of the stiffest polymers at ambient temperatures and is very durable. It is extremely versatile and is used for a wide variety of applications in most industry sectors.

UV Stabilizer:

Any chemical compound which, when mixed with a thermoplastic resin, selectively absorbs UV rays. It slows down the degradation through UV rays which occurs in most plastics.

 

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V

 

Vacuum Forming:

A process whereby a heated plastic sheet is drawn against a mould surface by withdrawing the air between it and the mould. It is a different process to plastic extrusion manufacturing.

Vapour Barrier:

A layer of plastic material through which water vapour will not pass.

Virgin Material:

A plastic material that has not been subjected to use or processing other than that required for its initial manufacture. It can be in the form of pellets, granules, powder, flock, or liquid.

Viscosity:

Resistance to flow of a liquid.

 

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W

 

Warpage:

A non-uniform change in internal stresses resulting distortion or warp of the plastic profile or part.

Water Absorbtion:

The amount of water absorbed by a plastic article when immersed in water for a certain period of time. All plastics will absorb moisture to some extent.

Water bath:

Used during the extrusion process to cool plastic extrusions.

Water White:

A grade of colour which looks like clear water.

Wrinkle:

A plastic surface imperfection in plastic films that has the appearance of a crease or wrinkle in plastic material.

WPC

Wood/Plastic Composite material made of recycled plastic and wood waste.

 

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X

 

(no entry)

 

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Y

 

Yellowness Index:

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

Young’s Modulus:

The modulus of elasticity in tension. It is concerned with how stiff, flexible, springy or floppy a material is.

 

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Z

 

(no entry)

 

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