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    Is PTFE a thermoset or a thermoplastic?

    Many assume that polytetrafluoroethylene is a thermoset because it seems unaffected by heat.  However it is a linear polymer chain and a melt transition point can be detected at 327oC but the melt viscosity is so high that it does not appear to soften at all.  Consequently conventional extrusion and injection moulding are out of the question.

    Initially PTFE powder from the polymeristation reactor was compressed and heated (sintered) to create solid blocks, sheets and rod. From these more detailed shapes could be machined.  Innovative processors produced film and wire coating by loading up the PTFE powder with lubricant to extrude the shape, extract the lubricant and sinter the extrudate to give a cohesive film or coating.

    The sheath of fluorine atoms round the carbon backbone not only gives PTFE excellent heat, electrical and chemical resistance but it is responsible for the low coefficient of friction and non-stick qualities.

    When polytetrafluoroethylene was introduced almost 70 years ago, engineers were quickly seduced by its outstanding properties. However, they often overlooked the fact that at room temperature it is in its thermoplastic rubbery state. Although it is a very stiff rubbery state due to the exceptionally high crystallinity.  Mechanically PTFE is not much to write home about, particularly when it comes to creep.

    Trade names:  Fluon, Hostaflon, Teflon 

    I leave you with a conundrum.  If PTFE has such good non-stick properties how do you get it to stick to metal frying pans?

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    Coping with weld lines

    In injection moulding, weld lines (knit lines) form when two melt fronts meet. If the melt fronts do not coalesce completely, at best there will be a cosmetic flaw. At worst there will be a mechanical weak-spot, with strengths of the order of 10 - 90 % of the material potential.

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    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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    Polypropylene: the Workhorse of the Plastics Industry

    Polypropylene. Little did Karl Zeigler or Giulio Natta realise, 60 years ago, when they were developing a catalyst system to produce a useful thermoplastic from the inexpensive monomer, propylene, that their work would have such far reaching consequences.

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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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    The Long and the Short of Fibre Reinforcement of Thermoplastics

    Fibre Reinforcement. The advantages of adding glass fibre to thermoplastics to increase stiffness (modulus), strength, heat distortion resistance and dimensional stability are well known.

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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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    Transparent ABS can be a clear winner

    Transparent ABS. Mentioning transparency in the context of ABS moulding materials can raise a few eyebrows. This is because ABS is normally taken to be opaque and indeed the vast majority of grades of ABS are opaque.

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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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