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The influence of pigments on the mechanical properties of High Density Polythylene (HDPE).

Lodeiro, M J; Tomlins, P E; Pearce, A (2000) The influence of pigments on the mechanical properties of High Density Polythylene (HDPE). NPL Report. CMMT(A)258

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It is widely known that some organic pigments affect the crystallisation behaviour of polyethylene and polypropylene. These pigments appear to act as nucleating agents and produce marked changes in microstructure that can cause excessive shrinkage and warpage in mouldings manufactured from these materials. It is suspected that these changes in morphology may also influence the mechanical performance of pigmented mouldings. This is particularly important for closures containing tensioners where functionality is critically dependent on material performance.
This report presents the results from a study on the mechanical properties of injection moulded high-density polyethylene. The commonly used design parameters: Young’s modulus, maximum yield stress, strain-to-failure and impact energy were used to characterise the effects of organic pigments (irgalite yellow and phthalocyanine blue) and processing conditions on performance.
The results show that the addition of organic pigments (in particular phthalocyanine blue) to high-density polyethylene does affect the principal mechanical characteristics. There is also evidence to suggest that the carrier and wetting agent used to manufacture masterbatches may play an important role in modifying the effects of pigments. The presence of small amounts of phthalocyanine blue causes an increase in ductility shown by a marked reduction in Young’s modulus and yield stress and an increase in failure strain. These consequences can be attributed to morphological differences in levels of crystallisation, spherulite size and number. In addition, the increase in crystallisation temperature enhances the effects of processing variables, such as molecular orientation and skin-core ratio.
These results could be used by manufacturer’s to allow for changes in pigmented mouldings in design or to counter the effects induced by pigmentation through modification of processing parameters in the production cycle.

Item Type: Report/Guide (NPL Report)
NPL Report No.: CMMT(A)258
Subjects: Advanced Materials
Advanced Materials > Polymers
Last Modified: 02 Feb 2018 13:17
URI: http://eprintspublications.npl.co.uk/id/eprint/1596

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