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Thermosets, Thermoplastics and Elastomers: A Primer

July 30, 2015

Okay, let’s start out with a few basic concepts…

Thermoplastics are formed into products when they are molten: their ultimate shape and internal structure is determined by cooling.  If a malformation occurs, they can be re-heated, then reshaped, if need be.  The polymer chains of thermoplastics, whether branched or linear, will stay separated and distinct from each other.

Thermoset polymers, on the other hand, can exist in three distinct states:

Stage 1: Sometimes known as a resole, this is the stage where  the thermoset resin can still be fused easily and remains soluble.

Stage 2:  This is the stage where the thermosets are almost insoluble but can still be molded.  Thermosets can only remain in this molten state for only a short period,  as the heat will eventually cause cross-linking of the material which leads to…

Stage 3: This is the final stage of polymerization where the cross linking reaction takes place at the time of molding the product under controlled impact of heat and pressure over time.

In short, the final structure of thermosets is not complete until all three stages are complete, creating a three-dimensional internal structural network of highly cross-linked polymer chains. The final product cannot be re-molded by the addition of heat, and is insoluble.

Elastomers share the properties of both thermosets and thermoplastics. Initially, they behave like thermoplastic polymers, with distinct chains, that only afterward develop a covalent crosslink network, like thermosets.  Unlike thermosets, however, elastomers form a crosslink network in a distinct vulcanization step known as post-polymerization.

Glass transition temperature differs between all three polymer classes.  This is the temperature at which polymers reversibly transmute between glassy and rubbery states. The glass transition temperature is below ambient temperature for elastomers.  However, the glass transition temperature is above the ambient temperature for thermosets and thermoplastics.

Well, there you have it… sort of.  Stay tuned for a continuation of this primer in future posts.




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