Dictionary of Plastic Industry Terms

A

• Amorphous Polymers: Polymers lacking structure or order. Amorphous polymers do not contain crystalline regions or an ordered structure. They are often described as being like a bowl of cooked spaghetti noodles.
• Anti-Block: An additive added to plastics that are processed into film. Anti-block additives help to prevent the film from sticking to itself.
• Anti-Fog Additive: Anti-fog additives function by increasing the surface tension of the polymer surface, allowing the molecules of water to wet the surface, forming a continuous later of water which does not scatter light or interfere with transparency.
• Anti-Oxidant: Additives that are added to a polymer to improve the thermal-oxidation resistance during processing as well as in elevated temperature end use applications.
• Anti-Stat: An additive added to polymers to reduce or eliminate static buildup. This helps to reduce static related issues such as dust build-up.
• Autoclave Reactor: Autoclave reactors are high pressure, stirred vessels used to produce Low Density Polyethylene, EVA and a number of other ethylene copolymers. Autoclave products have a broad molecular weight distribution and a high level of long chain branching and are often used in blow molding or other processes where high melt strength is desirable.

B

• Barefoot Resin: Resins made with no additives. Often associated with polyethylene that contains no slip, anti-block or other additives.
• Bimodal Polyethylene: High density polyethylene that has two separate molecular weight distributions. The lower MWD provides for good processability while the higher MWD provides for better mechanical properties.
• Bio-Polymer: A polymer produced from renewable resources such as corn, rice, tapioca or starch.
• Blown Film: Film produced by a continuous extrusion process whereby the molten polymer is forced through an annular die and the resulting tube is inflated with air (blown) forming a bubble. After cooling the film bubble is collapsed and wound up.
• Branched polymer: A polymer, such as low density polyethylene or EVA that has many long, side chains. In many cases the branches can be as long as the main polymer chains
• Butene: A comonomer used to produce linear low density polyethylene. Also referred to as C4.

C

• Clarified: A polymer that contains a clarifier additive. Clarifiers help to increase the clarity of a polymer and are commonly used in polypropylene random copolymers.
• Compatibilizer: A substance used to stabilize blends of incompatible polymers. For example, to compatibilize a blend of nylon and polypropylene which are incompatible with each other.
• Copolymer: A polymer made with two different monomers.
• Coupling Agent: A compatibilizer that is used specifically to bond inorganic material to the polymer matrix. For example, to bond calcium carbonate to the polypropylene polymer.
• Crate grade: High density polyethylene with a melt index of 7 to 10 grams/10 minutes.

D

• Desiccant: An additive added to a plastic to help absorb moisture. Often used in film packaging applications.
• DEGRADATION: Any deleterious change in the chemical composition, appearance, physical or mechanical properties of a plastic material.
• DISCOLORATION: Any change from original color. Discoloration is often caused by overheating, light exposure, irradiation or chemical attack.
• DUROMETER: A numerical scale for measuring the hardness of rubber or plastic based on the depth of penetration of an indenter point on the surface of the test specimen.

E

• Environmental Stress Cracking (ESC): Cracking caused by the combined influence of a mechanical stress and a chemical or surface active substance. Environmental stress cracking results in a brittle failure, especially in amorphous polymers.
• Environmental Stress Cracking Resistance (ESCR): The ability of a polymer to resist slow crack growth or environmental stress cracking.
• Extrusion Coating: Extrusion coating is the coating of a thermoplastic polymer onto a substrate material. Substrate materials are often paper, paperboard, cardboard, foils, non-wovens or plastic film.
• Extrusion Lamination: A process for joining two webs of material by feeding them through a machine that extrudes a thin layer of plastic between them to act as an adhesive.

F

• FLAME TREATING: A method of increasing the surface energy of a plastic object to be more receptive to paints, inks, adhesives, etc. Flame treatment causes oxidation on the surface of the plastic object to improve bonding and adhesion.
• FLUORINATION: A process in which a thermoplastic object, such as a bottle or container, is exposed to fluorine gas. The fluorine creates improved barrier resistance to absorption and permeation of solvents and fuels.
• Functionalized: When chemical functional groups are attached to the polymer backbone. For example, polyethylene can be functionalized with maleic anhydride or glycidyl methacrylate. This gives the non-polar polyethylene some polarity and/or chemical reactivity.

G

• Gamma Stabilizer: Additives that are added to a polymer to improve its resistance to gamma sterilization.
• Gas Fading: Gas fading is a yellow or pink discoloration that occurs when atmospheric pollutants like nitrogen oxide gases react with phenolic-type antioxidants. It is common in polyethylene and polypropylene films.
• Gas Phase Polymerization: Gas phase polymerization is a widely used polymerization technique for gaseous monomers such as ethylene, vinyl chloride and polytetrafluoroethylene. This method has the advantage that it does not require any solvent and that no residual catalyst remains in the powder or pellet after polymerization.
• Glass Transition Temperature: The temperature where a polymer changes from a rigid, glassy material to a soft, viscous material. For amorphous polymers a temperature of 15-20°C below the glass transition temperature represents the upper useful temperature limit.

H

• Haze: Haze is a measure of clarity. A resin with a haze of 5% allows 95% of the light to pass through the film.
• Hexene: A comonomer used to produce linear low density polyethylene. Also referred to as C6.
• High Load Melt Index (HLMI): Used to measure the melt index of high molecular weight, very low flowing materials, most notably polyethylene.
• Homopolymer: A polymer produced from using only one monomer.
• Hydrogen Bonding: A bond that is primarily an electrostatic force of attraction between a hydrogen atom and another electronegative atom bearing a lone pair of electrons. Hydrogen bonds are responsible for many of the physical and chemical properties of compounds containing nitrogen, oxygen and fluorine.

I

• Impact Modifier: A rubber or elastomer modifier added to a polymer to improve the toughness and impact resistance.
• Impact Strength: Impact strength or toughness of a material is defined as its ability resist to fracture by a blow or a sudden applied load or force.
• Injection Blow Molding: A blow molding process where a pre-form is first injection molded, then is re-heated and blown. Pre-forms typically have fully formed threads that have high dimensional tolerances that cannot be achieved in extrusion blow molding.
• Injection Stretch Blow Molding (ISBM): Similar to injection blow molding, except that during the blowing phase, the pre-form is stretched and blown in the radial and longitudinal directions.

J

• Jet Molding: A modified version of an injection molding technique characterized by the fact that more heat can apply to the material rather than from a heating cylinder, as is done in ordinary processes.
• Jetting: A defect in injection molding that occurs when the molten plastic is injected at a high velocity and does not make initial contact with the mold wall. Also called snaking.
• J Fold: The folding of a plastic film along its length to obtain a two layered product with one layer wider than the other.

K

• KEVLAR: A strong, synthetic heat resistant fiber. Kevlar was first used as a replacement for steel wire in racing tires. Kevlar fiber is used in plastic compounds for friction and wear applications.
• Kirksite: An alloy of aluminum and zinc used in the construction of molds. It is known for its high thermal conductivity.
• KNIT LINES: Also known as weld lines or mold lines, it can occur when the mold or material temperatures are set to low or when the melt reforms after going around a mold feature.

L

• Let Down Ratio (LDR): The level at which a masterbatch is added into a base polymer. Typical let down ratios for color and additive masterbatches are 1% to 5%.
• Long Chain Branching (LCB): Long chain branches are formed in the high pressure polymerization process used to make low density polyethylene (LDPE) and ethylene vinyl acetate (EVA). These long chain branches occur at random intervals along the length of the main polymer chain. The long chain branches themselves can contain branches.
• Long Term Heat Aging (LTHA): Special additives that are added to a polymer (often polypropylene) to provide retention of properties at elevated temperatures and long periods of time.
• Low Water Carry-Over (LWCO): Special additives used in polypropylene to help reduce water from adhering to the surface of PP films and tapes when they pass through cooling water baths. Any water adhering to the film surface can cause issues further down the manufacturing process.

M

• Machine Direction (MD): The direction the film is being pulled through the machine.
• Magnetic Detectable Additives: Additives that are added to a plastic compound so that it can be detected by metal detectors. These additives are often used in plastic compounds that are used in the food processing industry. These additives help detect any plastic pieces that could potentially get into food products.
• Melt Flow Index (MFI): The mass of resin that exits the melt index tester in 10-minutes under specific test conditions of temperature and load. Inversely related to molecular weight. Melt Flow Index is typically used for materials other than polyethylene. The units are expressed as grams/10 minutes.
• Melt Flow Rate (MFR): The mass of resin that exits the melt index tester in 10-minutes under specific test conditions of temperature and load. Inversely related to molecular weight. Melt Flow Rate is the same as Melt Flow Index and is typically used for materials other than polyethylene. The units are expressed as grams/10 minutes.
• Melt Index (MI): The mass of resin that exits the melt index tester in 10-minutes under specific test conditions of temperature and load. Inversely related to molecular weight. Melt Index is typically only used in describing polyethylene. The units are expressed as grams/10 minutes.
• Melt Volume Rate (MVR): Similar to Melt Flow Rate except the test measures the volume of material through the die in 10 minutes, rather than the mass of material. Units are cm3/10 minutes. (3 should be superscript)
• Melting Point: The temperature where the crystalline regions of a polymer melt.
• Metallocene Catalyst: A single site catalyst that produces a polymer with a narrow molecular weight distribution and a narrow short chain branching distribution.
• Molecular Weight Distribution (MWD): Polymer chains rarely have the same length and molecular weight and there is always a distribution around the average value. The molecular weight distribution describes the relationship between the number of moles of each polymer species and the molecular weight of that species. Molecular weight distribution can be narrow to broad.
• Molecular Weight: Molecular weight is the molecular mass of a polymer chain. It can be obtained by multiplying the molecular mass of each repeating unit by the degree of polymerization.

N

• Neat Resin: A resin that contains no additional additives such as slip, anti-block or processing aids.
• NONPOLAR: A nonpolar molecule has no separation of charge, so no positive or negative poles are formed. Examples of nonpolar plastics are polyethylene, polystyrene and PTFE.
• NOTCH SENSITIVITY: The reduction of strength of a material caused by a notch or other stress riser.
• Nucleating Agent: Nucleating agents are additives which provide sites for crystal growth. This results in a finer crystal size which improves clarity and transparency and reduces processing cycle time.

O

• Octene: A comonomer used to produce linear low density polyethylene. Also referred to as C8.
• OLEFIN: Any of a group of unsaturated open chain hydrocarbons possessing one or more double bonds, the simplest which is ethylene.
• OPAQUE: A term describing a plastic or other material which will not transmit light.
• OXIDATION: The addition of oxygen to a compound. Oxidation can occur due to exposure to elevated temperature, UV or chemicals.

P

• Parison: A tube-like piece of plastic that is extruded at the beginning of the blow molding process. Once the parison is extruded, the mold closes, and air is blow into the parison to expand it to the shape of the mold.
• Peel Seal Film: A type of film designed to be able to seal to a package, but to also be able to easily peel open.
• Pinking: Pinking is a pink discoloration that occurs when atmospheric pollutants like nitrogen oxide gases react with phenolic-type antioxidants. It is common in polyethylene and polypropylene films.
• Plasticizer: A chemical added to a plastic to make it more flexible and less brittle. Plasticizers are commonly added to rigid PVC to turn it into flexible PVC.
• Polymeric Processing Aid (PPA): These are additives, often based on fluoropolymers, that help to improve the process efficiency and quality of high molecular weight polymers. They are often used to help eliminate surface defects such as melt fracture and shark skinning.

Q

• QUENCHERS: Types of additives used for UV stabilization. Quenchers work by quenching the energy that is generated during the photo-oxidation reactions, returning the excited molecules back to a ground state where they are less reactive.
• Quinacridones: Quinacridones are organic compounds used as pigments, most commonly in red-violet colors.

R

• Radio Frequency Welding: a method of welding thermoplastics using a radio frequency field to apply the necessary heat. Also called high frequency welding.
• REGRIND: A thermoplastic material from a processors production that has been cleaned and reground.
• RELEASE AGENT: A lubricant used to coat a mold cavity to prevent the molded piece from sticking to it.
• ROCKWELL HARDNESS: A test for hardness in which a hardened steel ball or diamond point is pressed into the material under a specific minor and major load.

S

• Semi-Crystalline Polymers: Polymers that contain both amorphous regions as well as crystalline, ordered regions in their structure. The crystalline regions are highly ordered and have well defined melting points.
• Shear Thinning: When a polymers viscosity decreases as the shear rate in increased. Branched polymers like LDPE and EVA have high shear thinning characteristics.
• Short Chain Branching (SCB): Shorth chain branches are short chains, typically less than 8 carbon atoms long. In polyethylene, short chain branches are based on butene, hexene or octene. Short chain branches break up the crystallinity and reduce the melting point of the polymer.
• Slurry Loop Reactor: Slurry loop reactors are primarily used to make high density polyethylene. In this process the slurry consists of undissolved polymer in a liquid mixture of diluent, ethylene, comonomer, and catalyst. The diluent and comonomer must be separated from the slurry exiting the reactor.
• Solution Reactor: Solution reactors are used to produce linear low density polyethylene utilizing Ziegler Natta catalysts in a solution. The resulting polymers have a high molecular weight and a medium density. Comonomers used include 1-butene, 1-hexene and 1-octene.
• Static Dissipative: Static dissipative polymers have a conductivity of between 10⁵ and 10¹⁰ ohm/square and allow electrical charges to dissipate within milliseconds.

T

• Tackifier: Chemical compounds used in formulating hot melt adhesives to help improve the tack or stickiness. They are usually low molecular weight chemicals (high flow) with high glass transition temperatures.
• Transverse Direction (TD): Cross direction, or 90° orientation to the machine direction.
• Tubular Reactor: A type of reactor that consists of a tube where the flow is continuous and is configured so that the reaction takes place based on the position in the reactor rather than based on time. LDPE produced in tubular reactors have a narrower molecular weight distribution compared to LDPE produced in autoclave reactors and is commonly used for film applications.

U

• Underwriters Labs (UL): UL is one of the world's leading providers of product safety and certification testing services. UL94 flammability testing is very commonly used in the plastics industry to certify the flammability of plastic materials for use in electrical devices.
• U Sheeting: A double layer of film, folded on both sides, with a center section cut out on one side.
• UV Stabilizers: Additives added to a polymer to help protect it from degradation from sunlight and weathering.

V

• Vapor Corrosion Inhibitor: A compound added to film for the prevention of oxidation or corrosion of packaged parts.
• Virgin Material: Any plastic compound or resin that has not been subjected to use or processing other than that required for its original manufacture.
• Viscosity: The viscosity of a liquid, or thermoplastic, is its resistance to deformation, or flow, at a given shear rate.
• Volatile Organic Compounds (VOCs): Organic chemical compounds that have a high vapor pressure at room temperature. VOCs can be found in many products such as plastics, paints, pharmaceuticals, and refrigerants.

W

• WARPAGE: A dimension distortion where the molded part does not follow the intended design shape. Warpage in molded parts is caused due to differential shrinkage because of temperature variations, molecular and fiber orientation, and variable packing such as under-packaging at remote locations and over-packaging at gates.
• Wettability: The ability of a liquid to spread on the surface. Adhesion and printing operations on a plastic surface depend on the substrate’s wettability, or its ability to allow a liquid to spread on its surface.
• Wollastonite: A calcium inosilicate mineral (CaSiO3) used as a reinforcement in plastic compounds.

X

• Xenon Arc Weathering: An accelerated weathering test using a xenon-arc gas discharge lamp. This test is used to reproduce the weathering effects that occur when materials are exposed to sunlight and moisture in actual use.
• X-Ray Fluorescence: Also called XRF, it is a common spectrographic method used for the analysis and identification of additives in polymers.

Y

• Yellowing: A discoloration that can be caused by excessive temperature or time at elevated temperature.
• Yellowness Index: A number calculated from spectrophotometric data that describes the change in color of a test sample from clear or white to yellow.
• Youngs Modulus: Modulus of elasticity in tension.

Z

• ZERO WASTE: A set of principles focused on waste prevention. The primary goal of a sustainability/recycling program is for zero trash to be sent to oceans and landfills.
• Ziegler-Natta Catalyst: Ziegler-Natta catalysts are prepared by reacting certain transition metal halides with organometallic reagents. These are the most common catalysts in the plastics industry used to produce polyethylene and polypropylene polymers.
• Zinc Stearate: A zinc salt of stearic acid, a naturally occurring fatty acid used as a lubricant or mold release additive.

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