Glossary

Course

Module

149 terms shown.

1. What Rubber Is

Monomer: The small molecule linked repeatedly to build a polymer.
Polymer: A large molecule made of many repeating monomer units.
Homopolymer / copolymer / terpolymer: A polymer made from one, two, or three different monomers.
Repeat unit: The section of chain that repeats along the polymer.
Degree of polymerization: The number of times the repeat unit repeats in a chain.
Elastomer: A polymer that recovers quickly and forcibly from large deformation.
Crosslink: A chemical bond joining two polymer chains, formed during vulcanization.
Compound: The complete mixture: base polymer plus filler, oil, protective chemicals, and cure system.
phr: Parts per hundred rubber. The elastomer totals 100 and all other ingredients are relative to it.
Thermoset: A crosslinked material that cannot be melted and reformed.
Thermoplastic: A material that softens on heating and hardens on cooling, repeatedly.
Thermoplastic elastomer (TPE): Rubber-like behaviour from hard physical domains rather than chemical crosslinks, so it can be reprocessed.
Mn (number average MW): Average molecular weight counting every molecule equally.
Mw (weight average MW): Average molecular weight weighted toward larger molecules.
MWD (Mw/Mn): Molecular weight distribution. Broad processes more easily; narrow performs better but is harder to process.
Tg (glass transition temperature): The range below which chain motion stops and the rubber stiffens. Sets the low-temperature limit.
Unsaturation: Carbon-carbon double bonds in the chain. The sites sulfur uses to cure and ozone uses to attack.
Saturated: Containing no carbon-carbon double bonds. Requires peroxide cure but resists ozone.
Cis / trans: Geometry about a double bond. cis-1,4-polyisoprene is natural rubber; the trans form is a hard thermoplastic.
Mooney viscosity: A standard measure of raw polymer or compound viscosity, reported as ML(1+4) at a stated temperature.
Entanglement: Physical looping of long chains around each other; what lets chain segments carry load between crosslinks.
Hysteresis: Energy lost as heat each time a compound is deformed and released.
Viscoelasticity: Behaving partly as an elastic solid and partly as a viscous liquid, depending on temperature and rate.
Crystallinity: Ordered packing of chain sections. Requires a regular chain structure.
Strain crystallization: Crystallization caused by stretching; reversible, and a source of strength in natural rubber.
Green strength: The strength of uncured compound; determines whether a shaped part holds together before cure.
Bound styrene: The styrene content of an SBR grade. A primary property variable.
Volume swell: Increase in volume after immersion in a fluid; primarily a property of the polymer chemistry.
Constant viscosity (CV) grade: Natural rubber treated to prevent storage hardening.
Vulcanization: The reaction that crosslinks polymer chains into an elastic network.
Modulus (rubber usage): Stress at a stated elongation, such as M100. Not a true modulus; see Module 10.
Reinforcement: The increase in strength and stiffness that filler gives a compound.
Accelerator: Chemical controlling how fast a compound cures and how long it can be worked first.

2. Vulcanization

Crosslink density: Number of crosslinks per unit volume. Controls most cured properties.
Monosulfidic / disulfidic / polysulfidic: Crosslinks containing one, two, or several sulfur atoms.
Conventional cure: High sulfur, low accelerator. Mostly polysulfidic; best tensile and fatigue, poor heat aging.
EV (efficient vulcanization): Low sulfur, high accelerator. Mostly monosulfidic; best heat aging, poorer fatigue.
Semi-EV: An intermediate cure system balancing aging resistance against fatigue life.
Sulfur donor: A chemical such as TMTD that supplies sulfur without adding elemental sulfur.
Activator: Zinc oxide plus stearic acid, which make the accelerator and sulfur work efficiently together.
Sulfenamide: Accelerator class giving delayed action then fast cure. The standard for high-volume production.
MDR (moving die rheometer): Instrument that plots torque against time at cure temperature.
ML / MH: Minimum and maximum torque on the cure curve.
ts2: Time to a two-unit torque rise above minimum. Rheometer scorch, the onset of cure.
t90: Time to 90 percent of maximum torque. The practical definition of optimum cure.
Scorch: Premature vulcanization during processing. Defines available working time.
Residual scorch time: The scorch time remaining after heat history already accumulated in earlier steps.
Marching modulus: Continued slow stiffening past the cure plateau.
Reversion: Loss of stiffness on overcure as unstable crosslinks break down.
10 °C rule: Rule of thumb that a 10 °C rise roughly halves cure time.
Coagent: A multifunctional monomer used with peroxides to raise crosslinking efficiency.
State of cure: How far the crosslinking reaction has progressed relative to its achievable maximum.
Induction period: The flat early region of a cure curve where accelerator chemistry proceeds but no crosslinks yet form.
Zinc stearate: The soluble zinc species formed from zinc oxide and stearic acid; the form in which zinc actually activates the cure.
PVI (prevulcanisation inhibitor): An additive that extends scorch time with little effect on cure rate or final modulus.
Retarder: An additive that delays cure onset, but at the cost of cure rate and modulus.
Bloom: Any ingredient migrating to the surface and becoming visible; wax bloom is intended, sulfur bloom is not.
Work-away stock: Previously processed compound reintroduced into a fresh batch; it carries heat history with it.
Resin cure: Crosslinking with a phenolic resin, giving all-carbon crosslinks with exceptional heat stability.
Compression set: The fraction of a compression not recovered after release; the key seal property.
Dispersion: Breaking agglomerates apart and distributing filler uniformly through the polymer.

3. Elastomer Families

ESBR / SSBR: Emulsion and solution polymerized SBR. Emulsion processes more easily; solution performs better.
High-cis BR: Polybutadiene above about 90 percent cis-1,4. Best abrasion resistance and resilience.
Termonomer: The third monomer in a terpolymer, such as the diene in EPDM.
ENB / DCPD / 1,4-hexadiene: The common EPDM dienes. ENB cures fastest, hexadiene gives best set and scorch safety, DCPD is cheapest.
Halobutyl: Chlorinated or brominated butyl. Cures faster and co-cures with high-unsaturation rubbers.
ACN content: The acrylonitrile fraction in NBR. Higher means better oil resistance but worse low temperature.
HNBR: Hydrogenated nitrile. Most backbone unsaturation removed for heat and ozone resistance.
Cure compatibility: Whether two blended elastomers cure at similar rates rather than one drawing curatives from the other.
Microstructure: The proportion of cis, trans, and vinyl repeat units in a diene polymer; set by the catalyst.
Co-vulcanisation: Two compounds forming networks across their shared interface during cure.
Building tack: The ability of uncured compound to stick to itself, needed when assembling a part from layers.
Service group: The working classification into general purpose, solvent resistant, and temperature resistant.
Layered construction: Using an expensive polymer only as a thin liner where it contacts the aggressive fluid.

4. Fillers

Aggregate: The fused cluster of carbon black particles; the smallest unit that can be dispersed.
Agglomerate: A loose cluster of aggregates held by weak attraction; what mixing breaks down.
Surface area: Filler area per gram. The main driver of reinforcement, encoded in the ASTM grade digit.
Structure: How branched and irregular filler aggregates are. Drives viscosity, modulus, and green strength.
Hard / soft black: Hard blacks (N100–N300) are fine and highly reinforcing; soft blacks (N500 and above) are coarser.
Filler network: Aggregates touching each other at low strain; the main source of hysteresis in a filled compound.
Bound rubber: Polymer immobilised at the filler surface; a measure of filler-polymer interaction.
Silanol: The reactive hydroxyl group on a silica surface, responsible for silica's distinctive behaviour.
Silane coupling agent: A molecule bridging silica to polymer, restoring reinforcement and reducing cure interference.

5. Plasticizers and Antidegradants

Process oil: Petroleum plasticizer that lowers viscosity by separating chains without reacting with them.
Paraffinic / naphthenic / aromatic: The three process oil types, from least to most polar; matched to polymer for compatibility.
Bleeding: Oil migrating out of a compound to the surface, from incompatibility or overloading.
Extraction: Loss of plasticizer into a contacting fluid; can cause a part to shrink and harden rather than swell.
Antioxidant: Chemical that interrupts the free-radical chain reaction of oxidation; consumed as it works.
Antiozonant: Chemical that migrates to the surface and reacts with ozone before it attacks the polymer.
PPD: Paraphenylenediamine, the most common chemical antiozonant class. Staining.
Staining: Either the compound darkening itself, or an ingredient migrating out and discolouring what it touches.
Peptizer: Additive that permanently lowers viscosity by cutting polymer chains during mixing.
Tackifier: Additive that increases the ability of uncured compound to stick to itself.

6. Cure System Design

Primary accelerator: The accelerator setting the basic character of the cure, chiefly scorch delay. Usually a sulfenamide.
Secondary accelerator: A faster accelerator added at low level to tune cure rate.
CBS / TBBS / MBS: The common sulfenamide primaries. MBS is secondary-amine derived and subject to nitrosamine concerns.
MBT / MBTS: Thiazole accelerators. MBTS gives safer processing than MBT.
TMTD: A thiuram accelerator that is also a sulfur donor, so it raises modulus as well as cure rate.
DPG: A guanidine secondary accelerator used to boost a sulfenamide.
ETU: Ethylene thiourea, the standard accelerator for polychloroprene metal oxide cures.
Insoluble sulfur: A polymeric sulfur form that resists blooming. It reverts progressively to the soluble form above roughly 105–110 °C, depending on temperature and residence time.
Acid acceptor: A metal oxide that neutralises hydrogen chloride released by halogenated polymers.
Nitrosamine: A carcinogenic compound that can form from secondary-amine derived accelerators; regulated in several regions.

7. Reading and Building a Formulation

Formulation: The complete list of ingredients and quantities that define a compound.
Specific gravity: Density relative to water; needed to convert a phr recipe into volume and batch weight.
Fill factor: The fraction of mixer chamber volume occupied by the batch, typically 0.70 to 0.75.
Batch weight: Chamber volume multiplied by compound specific gravity and fill factor.
Cost per volume: Cost per kilogram multiplied by specific gravity; the basis that tracks cost per part.
Starting formulation: A published or in-house recipe used as the basis for a new compound.
Property specification: A requirement defined by properties rather than by recipe, leaving formulation to the supplier.
Change control: The documented process for recording what was changed in a formulation, why, and what was tested.

8. Mixing

Internal mixer: An enclosed two-rotor mixer with a hydraulic ram; the main mixing machine in the industry.
Two-roll mill: An open pair of counter-rotating rolls used for cooling, sheeting, warming, and adding curatives.
Friction ratio: The speed difference between mill rolls; what generates shear in the nip.
Incorporation: Drawing ingredients into a single coherent mass wetted by polymer.
Distribution: Spreading material uniformly through the batch. Distinct from dispersion.
Ram pressure: Force applied by the ram to keep material in the rotor path.
Specific energy: Work done per unit mass of compound; the best single criterion for terminating a mix.
Drop temperature: Batch temperature at discharge; the most closely watched mixing parameter.
Upside-down mixing: Loading fillers and oils before polymer; faster, but less controlled peak shear.
Batch-off: Cooling and sheeting a mixed batch before storage.
Mastication: Deliberate breakdown of polymer molecular weight by shear, mainly for natural rubber.

9. Test Standards and Batch Release

Test method: A standardised procedure specifying specimen, conditioning, equipment, conditions, and reporting.
Repeatability: Agreement between results from the same operator, equipment, and material over a short period.
Reproducibility: Agreement between results from different laboratories. Always worse than repeatability.
Precision statement: The section of a method quantifying expected scatter within and between laboratories.
Conditioning: Holding a specimen at specified temperature and humidity before testing so it reaches equilibrium.
Batch release: The decision to allow a mixed compound into production, based on a small set of fast tests.
Qualification testing: Slower, less frequent testing establishing that a compound meets the full specification.
Fingerprint: The established set of release values characteristic of a compound, used for comparison.
Common cause variation: The ordinary noise of a stable process; reacting to it increases variation.
Special cause variation: Variation from an identifiable change; appears as a shift, trend, or outlier.
Measurement system variation: The share of observed variation contributed by the test rather than the material.

10. Physical and Product Testing

Shore A: The standard hardness scale for most rubbers, measuring resistance to indentation.
Ks: Static spring rate — force per unit deflection under steady load. A property of the part, not the compound.
Kd: Dynamic spring rate — the equivalent under cyclic load. Normally higher than Ks in filled compounds, and dependent on frequency, amplitude and temperature.
Kd/Ks: Dynamic-to-static ratio; how much a part stiffens under cyclic loading.
tan δ: Loss factor — the ratio of energy dissipated to energy stored per cycle.
Storage modulus (E′): The elastic component of the dynamic response; energy stored and returned.
Loss modulus (E″): The viscous component; energy dissipated as heat.
Payne effect: The fall in dynamic stiffness with increasing strain amplitude, caused by filler network breakdown.
Shape factor: The ratio of loaded area to free area; determines how much a bonded rubber block can bulge.
TR-10: Temperature retraction test estimating the lowest temperature at which a compound behaves elastically.
Brittleness point: The temperature at which a specimen fractures when struck or bent rapidly.
Typical value: The middle of a property distribution; roughly half of production falls below it.

11. Putting It Together

Last known good state: The most recent condition where everything behaved correctly; the right comparison point in an investigation.
Shared compound: A compound used across several parts, which couples those applications together when it changes.
Propagation: The way a change made for one reason produces consequences elsewhere, often in another department.
Blind spot: A failure mode that routine testing does not detect — dispersion is the classic example.