plastics divided in two large kinds, they are thermoplastic and thermosets, in general, thermoset materials are stronger than thermoplastic materials due to this 3-D network of bonds, thermosets materials can not be softened on heating. In thermosetting polymers, the polymer chains are joined (or cross-linked) by intermolecular bonding, cross linking is what makes thermosets special.as we know thermoplastics can be re molded and made into other products. Thermosets, once cured, can not be transformed into another shape, their chemistry has been permanently altered.
History
Goodyear discovery of the vulcanization
of natural rubber in 1839 could be construed as the first successful commercial
venture based on thermosetting polymers. The plastics industry dates the
beginning of thermosetting plastics to the development by Leo Baekeland in
1909 of phenolic.
The Historical Milestones of Thermosets
1839 Goodyear discovered vulcanization of rubber.
1909 Baekeland granted his heat and Pressure・ patent for phenolic resins (Thermoset polycondensate)
1926 Alkyd introduced. Aniline-formaldehyde introduced in U.S.
1928 Urea-formaldehyde introduced commercially.
1931 Hyde began research on organo-silicon polymers.
1933 Ellis patented unsaturated polyester resins.
1935 Henkel made melamine-formaldehyde resins.
1937 Automatic compression molding introduced commercially. Polyurethanes first produced.
1938 Melamine formaldehyde introduced commercially. Used in molding compounds and food containers.
1939 First patent on epoxy was found in Germany
1941 Urethane-polyester type-introduced in Germany.
1942 Dow Coming made silicone industrially.
1943 Castan patent issued on epoxy.
1943 Thermoset polycondensate. Silicone (SI) used in computer chips, IC, cooking ware.
1946 Polyurethane elastomers introduced.
1947 Epoxy introduced commercially, thermoset polyadduct. Used in reactive molding compounds. Also used in adhesives.
1954 Polyurethane introduced in U.S.
1957 Urethane-polyether type-introduced in U.S.
1964 Polyimides introduced as a fabricated product.
Definitions
various definitions has explained by scientist, specially because the bond type of this polymer. Here some definitions
Thermosetting plastics (thermosets) are polymer materials that cure, through the addition of energy, to a stronger form. The energy may be in the form of heat (generally above 200 degrees Celsius), through a chemical reaction (two-part epoxy, for example), or irradiation.(wikipedia.org)
Goodman and Schwartz define thermoset as
a polymeric material which can be formed by the application of heat and pressure, but as a result of a chemical reaction, permanently crosslinks and cannot be reformed upon further application of heat and pressure
A polymer-based liquid or powder that becomes solid when heated, placed under pressure, treated with a chemical or via radiation. The curing process creates a chemical bond that, unlike a thermoplastic, prevents the material from being remelted (http://www.techweb.com/)
Resin or plastic compounds which in their final state as finished articles are substantially infusible and insoluble. Thermosetting resins are often liquid at some stage in their manufacture or processing,
which are cured by heat, catalysis, or other chemical means. After being fully cured, thermosets cannot be resoftened by heat. Some plastics which are normally thermoplastic can be made thermosetting by means of crosslinking with other materials. (Whittington Dictionary of Plastics)
Categories of Thermosets
based on individual families of plastic and the purpose we can divided thermosets as
1. General purpose
Phenolic, amino's, polyesters
2. Engineering Purpose
Epoxy, polyurethane
3. Specialty purpose
Silicones, allyls, high temperature thermosets, cross linked thermoplastic.
Thermosets Processing Methode
thermoset can be processed by molding, the kind of molding that can process thermosets are :
Injection Molding
Extrusion Molding
Compression Molding
Casting methode
( see the each explanation of those mold here)
the advantages of thermosets
Thermosets have many advantages:
* Excellent thermal propeties (epoxy)low creep over time.
* Excellent strength to weight ratio
* Rigid, Excellent fire performance,flame retardant.
* Cost competitive against metals & engineering thermoplastics
* No absorption of water
* Dimensionally stable at high temperatures
* Reliability
* High impact strength
* Electrical & thermal insulation properties
* Anti-stain / FDA applications
* Can achieve tight tolerances
* Withstands environmental extremes
* chemical and Corrosion resistant (epoxy)
* easy processed in low cost method and technology
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