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Flashcards in Chapter 8 Deck (20):

Define: Polymer

Compound consisting of long-chain molecules with each molecule made up of repeating units connected together.


Define: Thermoplastic

Are solid materials at room temperature but that become viscous liquids when heated to temperatures of only a few hundred degrees. Can be repeatedly heated and cooled without significant degradation to the polymer.


Define: Thermoset

Cannot tolerate repeated heating cycles. Once initially heated , they soften and flow for molding but the elevated temperatures produce a chemical reaction that hardens the material into an in-fusible solid.


Define: Elastomer

Rubbers; polymers that exhibit extreme elastic extensibility when subjected to relatively low mechanical stress.


Define: Monomer

The small units that make up the chain like structures (macromolecules) in polymers. Generally simple unsaturated organic molecules such as ethylene, C2H4.


Define: Macromolecule

The combination of many small molecules (monomers) into large molecules that possess a chain-like structure.


Define: Chain Polymerization

The process by which long chains of repeating "mers" are formed. It is initiated by a chemical catalyst (initiator) to open the carbon double bond in some of the monomers. with unpaired electrons, these monomers capture other monomers to begin forming chains that are reactive.


Define: Degree of Polymerization

The number of repeating "mers" in polymerization is known as "n" and the mean value of "n" is the degree of polymerization for the batch. Higher DP increases mechanical strength but also increases viscosity in the fluid state.


Define: Molecular Weight

In a polymer, is the sum of the molecular weights of the "mers" in the molecule ("n" times the molecular weight of one "mer")


Define: Linear Polymer

When polymers form in chain-like structures, they are classified as linear polymers. Is a characterization of a thermoplastic polymer.


Define: Cross-Linked Polymer

When multiple linear polymers are connected by branches and other molecules at certain connection points (spider web)


Define: Degree of Crystallinity

The proportion of crystallized material in the mass. As crystallinity increases in a polymer, density, stiffness, strength, and heat resistance also go up.


Define: Glass-Transition Temperature

The point when cooling molten polymer in which the thermal expansion of the amorphous material becomes lower (change in slope). Below this temperature, the material is hard and brittle.


Define: Fillers

Solid materials added to a polymer usually in particulate or fibrous form to alter its mechanical properties or to simply reduce material cost.


Define: Plastizers

Chemicals added to a polymer to make it softer and more flexible and to improve its flow characteristics during forming.


Define: Lubricants

Additives to a polymer to reduce friction and promote flow at the mold interface. Also help in releasing the part from the mold in injection molding.


Define: Thermal Aging

The long-term effect found in thermoplastic polymers where there is degradation and chemical deterioration due to continuous elevated temperatures or thermal cycling.


Define: Vulcanization

The process of heating rubbers with sulfur to prevent melting and hardening in various temperatures.


Define: Rubber

Deprived primarily from latex, is an elastomer that will become stiff in cold weather and sticky in hot weather (without vulcanization)


Define: Bioplastics

Also "Completely Biodegradable Plastics"; consists of a polymer and filler that are both derived from natural and renewable sources. (ex. starch, cellulose)