Thermoplastics 251

abrasives

A material consisting of hard particles used to wear down, rub away, or machine material. Abrasives can damage some plastics.

ABS

Acrylonitrile-butadiene-styrene. A thermoplastic material with good heat, chemical, and impact resistance. ABS is used to manufacture medical equipment housing.

acetal

A semicrystalline thermoplastic that can withstand a wide temperature range. Acetal must be treated with additives in order to withstand ultraviolet radiation.

acrylic

An amorphous thermoplastic that is resistant to the damaging effects of weather and ultraviolet light. Acrylics are often used for optical products because they are transparent.

acrylic

An amorphous thermoplastic that is resistant to weather and ultraviolet light. Acrylics are often used for optical products because they are transparent.

acrylonitrile-butadiene-styrene

ABS. A thermoplastic material with good heat, chemical, and impact resistance. Acrylonitrile-butadiene-styrene is used to manufacture medical equipment housing.

additives

Any substance that is added to a material during manufacturing in order to improve or change the material's properties. Additives used in plastic include colorants and thermal stabilizers.

aluminum

A lightweight metal with high thermal conductivity. Aluminum molds used in thermoforming can help to maintain a consistent temperature for the plastic sheets.

amorphous regions

A molecular formation that lacks a definite repeating form, shape, or structure. Amorphous thermoplastics have a lower viscosity with increased temperatures.

antioxidants

An additive that prevents ultraviolet degradation. Antioxidants are often added to polypropylene.

atoms

The smallest particle of a substance that can be combined with other atoms to form a molecule. Atoms form the backbone of a polymer molecule chain.

blister packs

Packaging with clear plastic cavities or pockets on a rigid backing that is used for a variety of products. Blister packs are often thermoformed.

blow molding

A plastic shaping process in which a heated tube of resin is clamped in a mold while positive air pressure blows the resin into the desired shape. Blow molding can be done with either an injection molding machine or an extrusion machine.

carbon black

A soot-like residue that is used as a colorant and/or a protector against ultraviolet radiation in polymers. Carbon black is often applied to various acetals.

changeover time

The time it takes to convert a machine from one process, tool, or program to another. Changeover time in extrusion blow molding is faster than in injection blow molding.

clamping unit

The component of an injection molding machine that secures the mold while resin is injected and cooled. The clamping unit opens and closes the mold to eject the solidified part.

clamping unit

The part of the injection molding machine that physically opens and closes the mold to eject the solidified part. The clamping unit also helps to keep resin from leaking out of mold components.

cold-drawing

The process of stretching a nylon fiber until it will no longer stretch. Cold-drawing a fiber makes it thinner and stronger.

creep-resistance

A plastic's ability to resist any kind of distortion when under a load over an extended period of time. Creep-resistant plastics include polycarbonates.

cross-links

Primary bonds between polymer molecules. The number of cross-linked molecules and molecule chains in a polymer determines the properties of a plastic.

crystalline regions

Polymer molecules packed together into regular, repeating patterns. Crystalline regions in a thermoplastic result in a semi-crystalline plastic with some amorphous regions present, as no polymer is completely composed of crystalline regions.

die

A tool containing a recess that provides space for the shaping of plastic. The die in an extrusion machine shapes the molten plastic before it goes to the cooling tank.

electrical conductivity

The ability of a material to act as a medium for conveying electricity. Electrical conductivity levels of thermoplastics are generally low, unless manufacturers use additives.

extrudate

A material that has been shaped through a die in an extrusion machine. An extrudate exits the die assembly and is fed into a cooling tank.

extruder screw

A long screw that rotates inside the feed barrel of an extruder machine. The extruder screw uniformly heats and mixes the resin to push it through to the die.

extrusion

A molding process that forces raw material through a die opening. Extrusion is a continuous process that can create parts with a uniform cross section.

extrusion

A molding process that forces raw material through a die opening. Extrusion is a continuous process that can create parts with a uniform cross-section.

extrusion blow molding

A blow molding process in which the parison is formed using an extrusion machine. Extrusion blow molding has a higher production rate than injection blow molding.

fatigue

The structural weakening of a material due to stress from repeated loads. Fatigue levels of a material can vary depending on exposure to temperatures and chemicals.

feed barrel

The holding chamber of an extrusion or injection molding machine that contains the resin as it is melted and mixed. The feed barrel in an extrusion machine also contains the extruder screw.

feedthroat

The component on the extruder machine where resin pellets enter the feed barrel. The feedthroat connects the hopper and the feed barrel.

fiber optics

A bundle of thin, flexible fiber cables made of glass or plastic that transmit light signals. Fiber-optic cables can use acrylic and other plastics as insulators.

forming temperature

A temperature range for thermoplastic sheets used in thermoforming that makes the plastic pliable but not melted. Forming temperature varies depending on the specific material and can range from 248°F to 608°F.

glass transition temperature

The temperature at which a rigid solid becomes pliable and can be formed, shaped, or molded. The glass transition temperature of an amorphous thermoplastic is slightly below the melting point of a semicrystalline thermoplastic.

hard

A material's resistance to surface penetration. Hard plastics such as acrylic and polystyrene can resist damage from penetration or indentation.

high-density polyethylene

HDPE. A lightweight and high-strength thermoplastic. High-density polyethylene polymer chains are packed tightly together, forming semicrystalline structures.

high-density polyethylene

HDPE. A lightweight semicrystalline thermoplastic. High-density polyethylene polymer chains are packed tightly together.

hopper

A large, funnel-shaped device located on top of the feed barrel on extrusion and injection molding machines. The hopper serves as the entryway for resin into the feed barrel.

injection blow molding

A blow molding process in which the parison is formed using an injection molding machine. Injection blow molding does not produce scrap.

injection molding

A molding process in which resin is heated in a barrel and then injected into a mold by a reciprocating screw. Injection molding can produce large items such as car dashboards and smaller items such as packing peanuts.

intravenous

IV. A medical solution inserted directly into a vein. Intravenous bags can be made of flexible polyvinyl chloride.

linear

A straight or nearly straight line. Linear molecule chains are found in thermoplastics.

low-density polyethylene

LDPE. A flexible and translucent polyethylene with semicrystalline molecule formations. Low-density polyethylene is often used to make transparent plastic wrap used in food manufacturing.

lubricants

An additive used to reduce friction. Lubricants added to polyvinyl chloride can help the material flow during the manufacturing process.

macromolecules

A large molecule that consists of repeating molecular units. Polymers consist of long chains of multiple macromolecules.

melting point

The temperature at which a crystalline material changes from a solid to a liquid. Semicrystalline thermoplastics have a melting point, while amorphous thermoplastics have a glass transition temperature instead.

molecular weight

The mass of a molecule. High molecular weight is a characteristic of thermoplastic molecules.

molecules

Two or more atoms held together by chemical bonds. A molecule contains all of the properties of the atoms forming it.

nylon

A semicrystalline thermoplastic that gains strength when the fibers are stretched. Nylon was originally developed as a substitute for silk.

opaque

Unable to transmit or reflect light. Opaque materials are not transparent.

optical

Relating to vision. Optical products can include acrylic and other plastic materials.

organic chemicals

A chemical found in nature. Organic chemicals can damage a plastic if the plastic is not resistant or is not treated with additives.

oxidizing agents

A substance that adds oxygen to a polymer, resulting in the breakdown of that polymer. Oxidizing agents can damage a plastic.

parison

A cylindrical tube of molten resin that is placed between mold halves in a blow molding process. Parisons expand to fill mold cavities.

plastic

A lightweight polymer material that generally has high corrosion resistance, a high strength-to-weight ratio, and a low melting point. Plastic is composed of large polymer molecules.

polycarbonates

A group of amorphous thermoplastics with high heat resistance. Polycarbonates are used in products such as safety helmets and appliance housings.

polyethylene

PE. A semicrystalline thermoplastic that is highly resistant to electricity and heat. Polyethylene is the most common commercial plastic.

polyethylene

PET. A common synthetic thermoplastic that is highly resistant to electricity and heat. Polyethylene is used in many products, including durable plastic bags and water bottles.

polymer

A material made of very large molecules of multiple repeating units. Polymers are either natural or synthetic.

polypropylene

PP. A semicrystalline thermoplastic that is resistant to fatigue. Polypropylene is used in a wide range of products, from laboratory equipment to microwavable soup cans.

polystyrene

PS. An amorphous thermoplastic that can be molded or foamed. Polystyrene is often used in insulation.

polyvinyl chloride

PVC. A thermoplastic that can be manufactured to produce both rigid and flexible materials. Polyvinyl chloride is a high-viscosity plastic that is often manufactured with lubricants that improve flow.

polyvinyl chloride

PVC. A thermoplastic that can be manufactured to produce both rigid and flexible materials. Polyvinyl chloride is used to manufacture many common products such as corrosion-resistant pipes.

pressure box

A component used in pressure thermoforming that encloses a plastic sheet in a mold and applies positive pressure to assist in forming. A pressure box is used in conjunction with vacuum force that sucks a thermoplastic sheet into the mold.

pressure thermoforming

A thermoforming process that uses compressed air pressure and vacuum force to shape a part around a mold. Pressure thermoforming is used to produce larger parts such as truck liners and vehicle door panels.

primary bonds

A bond between atoms that involves the exchange or sharing of electrons. Primary bonds in thermosets form strong connections within molecules.

properties

A physical or mechanical characteristic of a material that distinguishes it from other materials. The properties of a plastic depend largely on its molecular formations.

PVC

Polyvinyl chloride. A thermoplastic that can be manufactured to produce both rigid and flexible materials. PVC is a high-viscosity plastic that is often manufactured with lubricants that improve flow.

reciprocating screw

A device in the barrel of an injection molding machine that rotates and moves back and forth to melt, mix, and inject molten resin through to a mold. Reciprocating screws are similar to extruder screws, but they move back and forth while also rotating in the barrel.

reinforced plastics

A combination of a polymer resin and fiber particles. Reinforced plastics are also called composites.

resin

A raw polymer, usually in the form of beads or pellets, that is not yet molded into its final shape. Resin is melted to form plastic parts.

rigging

The process of lifting and moving heavy loads with ropes, chains, and mechanical devices. Rigging operations often use nylon rope due to its ability to gain strength when stretched.

rigid

Unable to bend or resistant to bending. Rigid plastics include polyethylene and polystyrene.

rubber

A natural polymer that is extracted as a sap from tropical trees. Natural rubber must be vulcanized, or heated with sulfur, before it can be used commercially.

scrap

Any material not used to create the final part. Scrap from thermoplastic processes can be reused.

secondary bonds

A bond that involves attraction between molecules but no transfer or sharing of electrons. Secondary bonds in thermoplastics are not as strong as primary bonds.

self-extinguishing

The inability to support flame after the source of the flame is withdrawn. Self-extinguishing plastics include polyvinyl chloride.

semicrystalline regions

A molecular region in a thermoplastic with both amorphous and structured formations of molecules. Semicrystalline thermoplastics are melted at higher temperatures than amorphous thermoplastics because more heat is needed to encourage molecular movement.

shaping

The process of forming plastic resin. Shaping processes include injection molding and extrusion.

solvent resistance

A material's ability to resist chemicals or solvents that would otherwise cause material degradation. Solvent-resistant plastics include acrylonitrile-butadiene-styrene.

solvents

A chemical that attempts to dissolve another material. Solvents can damage a plastic if the plastic is not resistant or has not been treated with additives.

strength-to-density ratio

A material's strength divided by its mass. The high strength-to-density ratio of high-density polyethylene results in a strong and lightweight plastic.

synthetic polymers

A chemically manufactured polymer. Synthetic polymers include common types of plastic such as nylon and polyester.

thermal degradation

The molecular breakdown of a material due to overexposure to heat or the sun. Thermal degradation in some plastics can be prevented by using thermal stabilizers.

thermal stability

The ability of a material to resist changes in physical shape or size as its temperature changes. Thermal stability of the molten resin in an extrusion machine helps to create a uniform part.

thermal stabilizers

An additive that helps polymers endure the effects of elevated temperatures. Thermal stabilizers in polyvinyl chloride help lower the risk of decomposition when polyvinyl chloride is exposed to elevated temperatures.

thermoforming

A secondary plastic shaping process that forces heated plastic sheets around a mold. Thermoforming processes use mechanical, air, or vacuum pressure.

thermoplastic sheets

Flat pieces of solid plastic resin that will be reheated and shaped during a secondary shaping operation. Thermoplastic sheets are produced by injection molding or extrusion.

thermoplastics

A group of plastics that can be repeatedly heated, cooled, and shaped. Thermoplastic molecules are not cross-linked.

thermosets

A group of plastics, also known as thermosetting plastics, that cannot be reheated or re-formed after their initial heating. Thermoset molecule chains become permanently cross-linked during the manufacturing process.

thermosetting plastics

A group of plastics, also known as thermosets, that cannot be reheated or re-formed after their initial heating. Thermosetting plastic molecule chains become permanently cross-linked during the manufacturing process.

thick-gauge thermoforming

A thermoforming process that heats and forms thick plastic sheets into parts. Thick-gauge thermoforming can be used to create coverings for large medical equipment.

thin-gauge thermoforming

A thermoforming process that heats and forms thin plastic sheets into parts. Thin-gauge thermoforming is often used to create packaging materials and other small parts.

tolerances

An acceptable deviation from a desired dimension that still meets specifications. Tight tolerance specifications can be difficult to manufacture using extrusion because of the low pressures used.

toxins

A poisonous substance produced within living cells or organisms. Toxins can be released when manufacturing polyvinyl chloride because of the high chlorine gas content in polyvinyl chloride.

twin-sheet thermoforming

A thermoforming process in which two plastic sheets are heated separately and then pressed into molds. Twin-sheet thermoforming can produce large, hollow parts that look similar to blow-molded parts.

ultraviolet degradation

UV degradation. The deterioration of a material due to overexposure to the ultraviolet radiation in sunlight. Ultraviolet degradation in plastic can be prevented by using additives during the manufacturing process.

ultraviolet light

UV light. Light that is invisible to the human eye because it consists of wavelengths shorter than those of visible light. Ultraviolet light can be used during the curing process for acrylics.

UV radiation

Ultraviolet radiation. Energy transmitted as invisible yet damaging wavelengths. UV radiation can cause thermal degradation in plastics if additives are not used.

vacuum thermoforming

A thermoforming process that uses negative air pressure to force sheet plastic against a mold. Vacuum thermoforming is used to produce smaller parts such as blister packs and clamshell packaging.

viscosity

A material's resistance to flow. Viscosity decreases as temperatures increase.