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    How to crystallise your thoughts on selecting a thermoplastic.

    When faced with selecting a thermoplastic for a new component, I find it helpful to view potential materials in two groups …. amorphous (non-crystalline) and crystalline (strictly speaking semi-crystalline because it is unusual to get close to 100% crystalline).  This helps me to focus in on three areas of properties.

    selecting a thermoplastic triangle

    Firstly amorphous thermoplastics have the potential for good transparency, unless incorporating pigments and fillers or blended with other thermoplastics.  Semi-crystalline thermoplastics, in their natural state, consist of two phases (amorphous and crystalline).  Each has a different density and hence different refractive index. So transmitted light will be scattered and the optical properties will be translucent to opaque.  It is possible to achieve transparency in semi-crystalline by an assortment of tricks but high transparency is not the norm.

    The second area is chemical resistance, or more specifically solvent resistance.  Amorphous thermoplastics will dissolve in an appropriate solvent (similar polarity) whereas a semi-crystalline grade will not dissolve in any solvent at ambient temperature, although it may be subject to slight swelling and, in certain cases, environmental stress cracking.

    The third property is mould shrinkage.  In their natural state semi-crystalline thermoplastics can have mould shrinkage values more than 3 times that of amorphous materials. However, this differential can be greatly reduced by adding fillers.   A toolmaker will not be pleased if a designer makes a late switch from amorphous to semi-crystalline… or vice versa.

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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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    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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    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 […]

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