Introduction to Plastics 131

3D printing

Three-dimensional printing. A process for making a physical object from a digital model by laying down many layers of material. 3D printers often use plastic resin as the raw material.

abrasion

Damage from repeated rubbing or scraping that is concentrated in the same place. Abrasion-resistant plastics include hard thermosets, such as phenolics.

additives

A substance that is added to a material during manufacturing in order to improve its properties. Additives perform a range of functions, from changing the color of plastic to improving its strength.

additives

A substance that is added to a plastic during manufacturing in order to improve or alter its properties. Additives can help add strength to a plastic.

additives

Any substance that is added to a material during manufacturing in order to improve its properties. Additives in plastics perform a range of functions, from changing the color to improving strength.

adhesive

A substance used to join two or more materials. Adhesives include phenolic resins due to the water-resistant properties of phenolics.

amber

Fossilized plant resin that forms over millions of years and involves a complex oxidation and polymerization process. Amber is used in varnishes, jewelry, and other ornamental items.

amorphous regions

A polymer molecule formation in thermoplastics that lacks a definite repeating structure. Amorphous thermoplastic materials form clear plastic parts.

antioxidants

An additive that prevents oxidation from damaging a plastic. Antioxidants can extend the life of a manufactured plastic part.

atoms

The smallest unit of an element. Atoms bond together to form molecules.

branched arrangement

A molecule chain with multiple branches or extensions of mer units. Branched arrangements of molecules can appear in both thermoplastics and thermosets.

brittle

A material's resistance to being drawn, stretched, or formed. Brittle materials can fracture when subjected to mechanical forces.

butyl rubber

An elastomer that is odorless and impermeable to air. Butyl rubber can form an airtight seal.

carbon

A common, non-metallic element. Carbon molecules bond with hydrogen molecules to form polyethylene.

carbon black

A soot-like additive that is used as a colorant and/or a protector against ultraviolet radiation in polymers. Carbon black is a type of light stabilizer.

ceramics

A hard, brittle material that can withstand high temperatures and resist corrosion. Ceramics include traditional materials such as brick and clay as well as advanced ceramics used in abrasives and cutting tools.

chemical reaction tank

A vessel designed to contain chemicals. Chemical reaction tanks require an inert material, such as polyethylene, in which to store chemicals.

chloroprene

An elastomer that effectively resists oil, weather, heat, and flame. Chloroprene was one of the first successful synthetic rubbers.

circuit boards

A thin, insulating board that supports electronic components and chips. A circuit board base can be made from plastic.

coating

A finish used for protective and decorative purposes in manufacturing. Coatings can include different plastics because of their low thermal and electrical conductivity properties.

coefficient of thermal expansion

The degree to which a material increases in size as temperatures increase. Plastic has a low coefficient of thermal expansion.

coloring agents

An additive that can be used to help a plastic absorb ultraviolet light or change the color of a plastic part. Coloring agents include dyes and pigments.

composite

A material made by combining a plastic resin with small particles of solid reinforcements. Composites often contain fillers, reinforcements, and other additives.

composites

A material made by combining two or more materials. Composites can contain laminar, particulate, or reinforced fibers.

corrosion

The deterioration of a material caused by exposure to environmental or chemical elements. Some plastics are designed to resist corrosion.

corrosion resistance

The ability of a material to resist deterioration and chemical breakdown due to surface exposure in a particular environment. Plastic is able to resist corrosion from most chemicals.

covalent bonds

A type of primary bond formed between atoms that holds polymer molecules together. Covalent bonds hold thermoset molecules together.

covalent bonds

A type of primary bond formed between atoms that holds polymer molecules together. Covalent bonds in thermosets result in a tougher plastic.

creep resistance

A material's ability to resist distortion when under a load over an extended period of time. Creep resistance in a plastic decreases as polymer molecules uncoil.

creep rupture

When an object breaks or permanently deforms after supporting a load over time. Creep rupture can occur when the molecules in a plastic begin to uncoil.

cross-linked

The covalent bonds that form between polymer molecule chains. The degree of cross-linking determines the characteristics of the plastic.

cross-linked

The covalent bonds that form between thermoset molecule chains. The degree of cross-linking determines the characteristics of the plastic.

cure

The process of using thermal energy or ultraviolet radiation to harden a polymer material so that it can be manufactured. Curing a thermoset creates a chemical reaction that permanently cross-links the molecules.

damping

The ability to resist deformation through vibration. Damping capabilities in plastics are higher than the damping capabilities of metals.

ductility

The measure of a material's ability to be drawn, stretched, or formed without fracturing. The ductility of plastic depends on its molecular structure.

durometer

The testing instrument used in a Shore hardness test. A durometer has a needle and a spring on one end that presses into the plastic to measure hardness levels.

dyes

A liquid coloring agent that is mixed with resin. Dyes are an additive used to color a plastic throughout.

elastic

Having the ability to return to an original shape after being stretched or deformed. Most plastics exhibit elastic qualities.

elasticity

A measure of a material's ability to reshape itself after being stretched or deformed. A rubber band is an example of an object with elasticity.

elastomers

A type of plastic with slightly cross-linked molecules that can stretch and then return to its original shape once the stretching force is removed. Elastomers will eventually lose some elastic properties after repeated stretching.

electrical conductivity

The ability of a material to act as a medium for conveying electricity. Plastic has low electrical conductivity.

electron

A negatively charged particle that orbits the center of an atom. Tight electron bonds result in the low electrical conductivity of plastic.

extrusion

A plastic molding process in which melted resin is pushed out of the machine into a shaping die. Extrusion is a continuous process that creates parts with a uniform cross section.

feedstock material

A raw material used in additive manufacturing. Feedstock material for many 3D printing applications includes polymers.

fiberglass

A lightweight and strong material composed of fine glass fibers. Fiberglass particles are used as a reinforcement in many plastics.

fiberglass-reinforced plastic

FRP. A composite made from thermoset polyester resin and fiberglass particles. Fiberglass-reinforced plastic cannot be re-formed once it has hardened, due to the cross-linking that occurs during curing.

fillers

An inert particle added to plastic resin to take up space and lower costs. Fillers do not add significant amounts of strength to a material.

flame retardants

An additive that helps a material to resist igniting when exposed to a flame or elevated temperatures. Flame retardants are often added to polyurethane foam.

foam molding

A shaping process that involves pouring foamed plastic into a mold. Foam molding is a low-pressure molding process.

foaming agents

A substance that generates gases to produce foam. Foaming agents used in foam molding are added before the resin is molded.

hardness

The ability of a material to resist penetration, indentation, or scratching. Hardness properties in a plastic are increased by the presence of covalent bonds.

high-density polyethylene

HDPE. A common thermoplastic known for its high strength-to-density ratio. High-density polyethylene has a higher chemical resistance than low-density polyethylene.

hydrogen

A colorless, odorless gas that is the most abundant element on the planet. Hydrogen molecules bond to carbon molecules to form polyethylene.

hygroscopic

Able to effectively absorb moisture from the air. Hygroscopic plastics are often used in plastic wrap.

impact tests

Used to measure a material's ability to absorb the energy of a sudden impact without breaking. Impact tests measure the toughness levels of a plastic.

inert

The state of being non-reactive. Inert fillers are often added to plastics to take up space and save cost without affecting material properties.

injection molding

A shaping process in which resin is heated in a barrel and then injected into a mold. Injection molding uses high pressures to create complex parts.

injection molding

A shaping process in which resin is melted in a barrel and then injected into a mold. Injection molding uses high pressures to create complex parts.

insoluble

A substance that cannot be dissolved. Insoluble plastics can be a result of increased cross-link density.

insulator

A material with low electrical conductivity and a high resistance to electrical charges. Plastic has low electrical conductivity and is used as an insulator.

latex

A milky resin produced in plants that is the main source of natural rubber. Latex rubber is treated with heat and chemicals in order to be used commercially.

load

The weight or burden that a material supports. A constant load may cause deformation over time.

low-density polyethylene

LDPE. A translucent to opaque thermoplastic with loosely packed molecules. Low-density polyethylene is not as chemically resistant as high-density polyethylene.

macromolecules

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

magnetism

The power of attraction and repulsion that exists in some materials. Plastic is non-magnetic.

mechanical properties

The collection of properties that describe a material's ability to compress, stretch, bend, scratch, dent, or break. Mechanical properties of a plastic are determined by its molecular structure.

mer units

A single unit of atoms that chemically bonds to other similar units to form long, repeating polymer molecule chains. Mer units are also called monomers.

metals

A naturally occurring material with high electric and thermal conductivity. Metals include copper, iron, nickel, and lead.

molding

A plastic shaping process in which molten plastic is forced into a mold to form a shape and then released once it cools and solidifies. Molding involves higher pressure, whereas casting does not.

molecules

Two or more atoms joined together by chemical bonds. Large polymer molecules bond together to form long polymer chains.

monomers

A single unit of atoms that chemically bonds to other similar units to form long, repeating polymer molecule chains. Monomers are also called mer units.

MRI scanner

Magnetic Resonance Imaging. A medical device that uses a magnetic field and radio waves to produce a detailed image of the soft tissues and bones in the body. MRI scanners typically include hard plastic casings.

natural polymers

A polymer that occurs in nature. Natural, or organic, polymers are not synthesized by humans.

natural rubber

An elastomer that is extracted as a sap from tropical trees. Natural rubber must be hardened and treated with sulfur in order to be used commercially.

natural rubber

An important commercial elastomer that is harvested from the sap of tropical trees. Natural rubber is also a natural polymer.

opaque

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

oxidation

A material's chemical reaction with oxygen. Oxidation can damage a plastic, but manufacturers can use additives to prevent damage.

oxidation

A material's chemical reaction with oxygen. Oxidation can result in polymer degradation.

permeability

A measure of how easily moisture or gases pass through a material. Low permeability means that is difficult for liquids or gases to pass through a material.

petroleum

A fossil fuel that provides the raw base for many plastics through a chemical reaction called polymerization. Petroleum-based polyethylene is one of the most popular plastics.

phenolics

A rigid and relatively inexpensive thermoset with tightly cross-linked molecule chains. Phenolics are often used as an adhesive for plywood.

physical properties

A set of characteristics that describes how a material responds to environmental, thermal, electrical, and magnetic forces. Physical properties describe how a material reacts to forces other than mechanical forces.

pigments

A powder coloring agent mixed with resin. Pigments are an additive used to color the surface of a plastic product.

plastics

A lightweight polymer material that has high corrosion resistance, a high strength-to-weight ratio, and a low melting point. Most plastics are easily shaped and formed.

plywood

A thin, strong wooden board consisting of two or more layers glued and pressed together. Plywood often contains phenolic resins as an adhesive.

polyester

A plastic that can be used as a thermoplastic or a thermoset. Polyester is commonly combined with additives and reinforcements for numerous commercial uses.

polyester

A plastic that is highly compatible with additives or other chemicals that will give it desired characteristics. Polyester can be manufactured as a thermoplastic or a thermoset.

polyethylene

A thermoplastic in the polyester family that is highly resistant to electricity and heat. Polyethylene is often used to manufacture tough plastic bags and beverage containers.

polyethylene

A type of plastic formed from carbon and hydrogen molecules. Polyethylene can resist electricity and heat.

polylactic acid

PLA. A biodegradable thermoplastic in the polyester family. Polyactic acid is a natural polymer derived from corn starch and other renewable resources.

polymer

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

polystyrene

A thermoplastic that is transparent and easily shaped. Polystyrene has elastic qualities because of its secondary bonds.

polyurethanes

A plastic that can be manufactured as a foam or as a solid. Polyurethane can be used as a coating, in paints and varnishes, or in solid parts such as medical implants.

polyvinyl chloride

PVC. A thermoplastic that can be rigid or flexible. Polyvinyl chloride usage is controversial because of its potentially toxic environmental effects.

properties

The physical and mechanical characteristics of a material that distinguish it from other materials. The properties of plastic can be altered with additives.

reciprocating screw

A component of an injection molding machine that melts the resin and builds up pressure. Reciprocating screws inject melted resin into a mold cavity.

reinforcements

A material added to a plastic that provides strength, stiffness, and the ability to carry a load. Reinforcements are typically fiberglass or carbon fibers.

reinforcements

An additive that improves mechanical properties, such as toughness or strength. Reinforcements are added to most plastics during manufacturing.

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.

rigid

Unable to bend or resistant to bending. Rigid plastics can include polystyrene or polyvinyl chloride, depending on how they are manufactured.

rotational molding

A plastic shaping process in which resin is heated, rather than melted, inside a rotating mold. Rotational molding is a no-pressure process that creates hollow parts.

secondary bonds

A bond formed between atoms that holds the atoms in the polymer molecules together. Secondary bonds hold thermoplastic molecules together.

secondary bonds

A bond formed between atoms that involves an attraction between molecules without the transfer or sharing of electrons. Secondary bonds are found in thermoplastics.

secondary bonds

A type of chemical bond formed between atoms that involves an attraction between molecules without the transfer or sharing of electrons. Secondary bonds hold thermoplastic molecules together.

self-extinguishing

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

semicrystalline regions

A polymer molecule formation in thermoplastics in which the molecules follow an ordered and structured pattern as they cool. Semicrystalline thermoplastics have a higher melting point.

shaping

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

shaping die

A component of an extrusion machine that cuts or shapes material. A shaping die is used in extrusion while a mold cavity is used in injection molding.

shellac

A resinous substance that can be used as a coating. Shellac is a natural polymer that is chemically similar to synthetic polymers.

Shore hardness test

A hardness test designed for elastic materials. The Shore hardness test uses a durometer that attempts to indent the plastic to determine hardness.

silicone

A thermoset that is both heat resistant and water repellant. Silicone can be a liquid, gel, rubber, or hard plastic.

solubility

The measure of a material's ability to dissolve in a solvent. The solubility of plastic depends on its molecular structure.

solubility rating

A rating system that gauges a material's likelihood of dissolving in a solvent. A low solubility rating is assigned to plastic that is not likely to dissolve in a solvent.

solute

A material that dissolves in a chemical. When testing the chemical reactions of plastics, the plastic material is the solute.

solvent

A chemical that attempts to dissolve another material. Solvents are rated by their solubility.

solvents

A chemical that attempts to dissolve another material. Solvents are rated by their solubility.

soot

A black powder that forms when wood or coal is burnt. Soot and carbon black are similar, but soot is an unwanted byproduct whereas carbon black is produced in a controlled environment.

stabilizers

An additive that helps prevent a plastic from breaking down when exposed to adverse environments. Stabilizers protect a plastic from ultraviolet radiation by absorbing ultraviolet rays.

strain

The physical deformation that occurs in an object when it is under stress. Strain in a plastic can exist while the object is under stress but can also exist once the force has been removed.

stress

A force that attempts to deform an object. Common forms of stress include compression, shear, and tensile.

surface finishes

The degree of roughness and variation on the surface of a manufactured part. Surface finish affects how a plastic component will function.

synthetic

An artificial or human-made material that does not occur in nature. Plastic and nylon are examples of synthetic materials.

synthetic polymers

A polymer that is chemically manufactured. Synthetic polymers include many different types of plastic.

tensile stress

A force that attempts to pull apart or stretch a material. The ability to withstand tensile stress is a measure of ductility.

tensile test

Stretching a material until it breaks or fails. Tensile tests determine different mechanical properties of plastics.

thermal conductivity

A physical property that indicates how well heat travels through a material. Plastic has low thermal conductivity.

thermal degradation

Deterioration of a material due to overexposure to heat or sun. Thermal degradation can accelerate oxidation in a plastic.

thermoplastic

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

thermoset

A group of plastics that is permanently hardened by heating. Thermosets, also known as thermosetting plastics, have covalent bonds and cross-linked molecule chains.

thermosetting plastics

A group of plastics that is permanently hardened by heating. Thermosetting plastics, also known as thermosets, have covalent bonds and cross-linked molecule chains.

toughness

The measure of a material's ability to absorb mechanical forces before it breaks. Toughness includes specific categories such as impact toughness.

transparent

Having the ability to allow light to pass through. Transparent plastics, such as polystyrene, are useful in eyeglass lenses or food packaging.

ultraviolet degradation

UV degradation. The deterioration of a material due to overexposure to the ultraviolet radiation in sunlight. Ultraviolet degradation is typically associated with plastics.

ultraviolet rays

UV rays. Potentially harmful wavelengths from the sun that are invisible to the naked eye. Ultraviolet rays can damage a plastic at the molecular level.

viscoelastic

Having both elastic and viscous properties. Viscoelastic materials have the ability to return to their original shape after undergoing stress, but they will lose shape over time.

viscoelasticity

The ability to be both elastic and viscous when undergoing deformation. Viscoelasticity allows some plastics to be recycled and reshaped.

viscosity

A measure of a material's resistance to flow. Heating a plastic decreases its viscosity and improves flow.

viscosity

A measure of a material's resistance to flow. Viscosity in a plastic decreases when the material is heated, resulting in improved flow.

vulcanized

Increasing the number of cross-linked bonds in an elastomer by using additives, chemicals, heat, and pressure. Vulcanization adds strength and toughness to an elastomer.

wood flour

Wood that has been finely ground to have the consistency of powder. Wood flour is an inert filler in many plastics.