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    How can a thermoplastic elastomer be both thermoplastic and elastomer ?

    Thermoplastic elastomer?

    The class of polymers known as thermoplastic rubbers (TPR), or thermoplastic elastomers (TPE), describes pretty well what it says.  As thermoplastics these materials soften with heat. They can be melt processed, by extrusion or injection moulding, but regain their soft solid properties when cooled.  As elastomers they conform to the ASTM definition of materials. The definition being materials which ‘can be stretched repeatedly to twice their length and, on release of the stress, will recover, with force, to the original length’.

    Most linear polymers above their glass transition temperature can be easily stretched but few have the ability to recover elastically.  Traditional vulcanised rubbers achieve elastic recovery by inserting strong chemical bonds between the polymer chains (irreversible crosslinks) to create loose networks.  Thermoplastic elastomers acquire recovery from reversible ‘physical’ crosslinks (domains, crystalline regions or ionic bonds), created by close association of the ‘hard’ parts of the polymer chains.

    TPEs have been synthesised to mimic the properties (mechanical and chemical) of traditional vulcanised elastomers. However, they perform less well at elevated temperatures, as one might expect.  However the considerable savings in processing costs make them attractive in many applications.  The real boost to TPE development came when designers discovered their ‘soft-touch’ properties for hand-held appliances like electric shavers and keypads.

    TPEs also struggle to match the compression set resistance and creep resistance of vulcanised elastomers.  I’ve witnessed rejection of TPEs as replacement for vulcanised elastomers because they couldn’t match the compression set resistance imposed in the specification. This wasn’t because compression set had any relevance in the application but because it happened to be on the data sheet of the material being replaced.

    TPE Families:

    • Styrenic (SBS, SIS, SEBS)
    • Olefinic (TP), TPV)
    • Polyester copolymers
    • Thermoplastic polyurethanes (TPU)
    • Ionomers
    • Ethylene vinyl acetate (EVA)

    Search results

    What determines friction between thermoplastic components?

    Friction is an important property for thermoplastics in bearings and gears but also has a part to play in assembly of plastic parts (snap-fit and interference-fit) and ejection during moulding.

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    Will Styrenic thermoplastics evolve further to meet design demands ?

    Styrenic thermoplastics?

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    What makes medical grade plastics so special?

    Toughness and transparency are important properties for the constituents of intravenous lines.

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    What causes mouldings (and moulders) to be off-colour?

    When mouldings are not the intended colour, the first thing to check is the raw material, particularly the dosing rate, if you are using masterbatch, and the quality of regrind.

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    Where are Engineering Thermoplastics Blends going ?

    The timeline of appearance of materials for the plastics industry can be viewed as several overlapping phases.

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    Understanding the difference between SBS & SEBS thermoplastic elastomers?

    The difference between SBS and SEBS thermoplastic elastomers explained.

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    Is MFR really much help to moulders these days ?

    Often a moulder has to change material grades. One of the first properties to be consulted on the new data sheet is usually the MFR. This is to establish if the new grade has the same melt viscosity performance.

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    What gives Moulders a Warped View on Life?

    Warping is one of the most frustrating injection moulding faults. This is because it does not always appear immediately, the causes are complex and prevention is difficult.

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    Colour your thinking on the Optical Properties of Thermoplastics

    Very few commercial polymers have chemical groups (chromophores) which absorb light in the visible region of the spectrum. Consequently the base polymers are colourless.

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    Understanding the causes of silvering in injection mouldings .

    Silvering. Water is essential for human and plant life but can prove inconvenient for thermoplastics.

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