Thermosets and Thermoset Materials

Thermosets and thermoset materials are crosslinked polymers that are cured or set using heat or heat and pressure. Cured thermoset resins may soften when heated, but do not melt or flow. They generally have a higher resistance to heat than thermoplastics. Vulcanization is a thermosetting reaction that uses a crosslinked compound or catalyst. In rubber-like materials, vulcanization results in greatly increased strength, stability, and elasticity. Traditionally, sulfur is used as the vulcanizing agent for natural rubber. Thermosets and thermoset materials may contain filler materials such as powders or fibers to provide improved strength and/or stiffness. Fibers can be either chopped or wound, and commonly include glass, fiberglass, or cloth. Some products contain solid lubricant fillers such as graphite or molybdenum disulfide. Others contain aramid fibers, metal powders, or inorganic fillers with ceramics and silicates.  

Many types of thermosets and thermoset materials are available. Filled or reinforced products consist of resins and modifiers such as pigments, plasticizers, or chopped fibers. By contrast, unfilled resins, base polymers, and raw materials do not contain additives. Typically, raw materials are available as pellets, powders, granules, or liquids. Stock shapes such as bars, sheets, and film are also available. Molding compounds are designed for processes such as reaction injection molding (RIM) and resin transfer molding (RTM). Composite materials consist of a matrix and a dispersed, fibrous or continuous second phase. Casting resins include a catalyst or hardener. Electrical resins and electronic-grade polymers and elastomers are used in potting or encapsulating compounds, conductive adhesives, and dielectric sealants. Specialized elastomers and rubber materials are used in optical and photonics applications and in mold and tooling fabrication. Monomers and intermediates are commonly available.

Thermosets and thermoset materials are based on a variety of chemical systems. Examples include polyamide, polybutadiene, polyether block amide (PEBA), polyetherimide, polyimide, polyurea, polyurethane (PUR), silicone, and vinyl ester. Phenolic, melamine and urea formaldehyde resins offer strong bonds and good resistance to high temperatures. Silicones products use acetic acid and other compounds as curing agents. Fluropolymers such as polytetrafluorethylene (PTFE) and polyvinylidene fluoride (PVDF) provide superior chemical resistance.

Important specifications for thermosets and thermoset materials include mechanical, thermal, electrical, optical, processing, and physical properties. Mechanical properties include flexural strength or yield, tear strength, ultimate tensile strength (UTS), yield strength (YS), tensile modulus or modulus of elasticity, elongation, and impact toughness as measured with an Izod test and a notched sample. Thermal properties include maximum use temperature, deflection temperature at 264 psi or 1.8 MPa, glass transition temperature, thermal conductivity, and coefficient of thermal expansion (CTE). Electrical and optical properties include electrical resistivity, dielectric strength, dielectric constant or relative permittivity, index of refraction, and light transmission. Processing and physical properties include bulk or apparent density, water absorption, viscosity, process temperature, shrinkage, and melt flow index (MFI).

Thermosets and thermoset materials provide a variety of features. Products that are designed for electrical and electronics applications often provide protection against electrostatic discharge (ESD), electromagnetic interference (EMI), or radio frequency interference (RFI). Materials that are electrically conductive, resistive, insulating, or suitable for high voltage applications are commonly available. Flame retardant materials reduce the spread of flames or resist ignition when exposed to high temperatures. Thermal compounds form a thermally conductive layer on a substrate, either between components or within a finished electronic product. Purging compounds are used to clean molding machines between runs of different colors or compositions. Gap filling or underfill compounds are used to fill in gaps or spaces between two surfaces to be bonded or sealed.

• Thermoset Composites
  Thermoset matrix systems dominate the composites industry because of their reactive nature and ease of impregnation. They begin in a monomeric or oligomeric state, characterized by very low viscosity....
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• Polyurethane
  Extremely wide variations in forms and in physical and mechanical properties are available in polyurethanes. Grades can range in density from 0.5 lb/ft3 in cellular form, to over 70 lb/ft3 in solid...
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• Predicting plastic part life
  Dynamic mechanical analysis helps designers build longer lasting products. Edited by Jean M. Hoffman DMA testing helps determine the effect of different curing conditions on thermoset polyester...
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Part Numbers for Thermosets and Thermoset Materials