materials | Performance PP
Figure 2: Modulus of elasticity of PP compounds with different mineral fillers – talc, wollastonite and Hybrifil T silicate – at 20% loading Source: HPF The Mineral Engineers
Figure 2: Shrinkage of PP compounds with different mineral fillers – talc, wollastonite and Hybrifil T silicate – at 20% loading Source: HPF The Mineral Engineers
polymer whereas the addition of the graphene nano- platelets is found to increase it by more than a factor of five,” they say.
Exploring net benefits Also in the UK, and not far from the Manchester team, researchers in a 12-month project led by the University of Bradford’s School of Engineering and Informatics are also investigating the use of graphene in PP compos- ites. The project team also involves graphene producer Thomas Swan, graphene functionaliser Haydale, and the UK-based division of high performance net and non-wovens manufacturer Delstar Technologies. The target application for the research is a special
type of filtration net that is produced by extruding a thin film layer, embossing a pattern onto the film and then stretching to produce holes. It is anticipated that, through the introduction of a small percentage of graphene into the base polymer, properties such as physical strength and operating temperature of the filtration nets can be improved. The aim is to allow PP to replace more expensive and denser plastics. The project, which runs until November of this year,
is exploring good dispersion and exfoliation of graphene platelets can be achieved within the plastic without damaging them. Characterisation has been completed, says project head Adrian Lee Kelly, and the most successful compound will soon be produced on a larger scale and formed into films, which will be stretched to mimic the industrial process. After the optimum formulation and process conditions have been deter- mined, an industrial scale batch of composite material (around 250kg) will be produced and used in production trials at Delstar. These demonstrator products will be
30 COMPOUNDING WORLD | August 2017
provided to customers for feedback in target markets. “In the short term, the rapidly emerging UK gra- phene industry will benefit from the knowledge of how graphene features, such as platelet size and functional- ity, can influence the properties of a commodity polymer such as PP,” the project prospectus says. “The polymer processing industry will benefit from a better under- standing of the optimum process conditions to produce improved composite properties by achieving high levels of dispersion and exfoliation.”
Mineral options While not as exotic as graphene, the end properties of technical thermoplastics have been successfully modified for many years through the use of mineral fillers. In the case of PP, the most prominent of these is talc but other mineral additives are used. “For special applications, long-needled wollastonite is also to be found in many recipes, because it enables distinctly higher degrees of rigidity and consequently higher heat distortion resistances as well,” says HPF The Mineral Engineers, the high performance fillers division of Quarzwerke. However, the pronounced needle structure and the shrinkage anisotropy associated with wollastonite (mar- keted by HPF under the Tremin name) means it cannot be used for all mouldings. “Each mineral offers specific advantages, but also has limits that are usually set by its specific morphology,” HPF says. The company has set itself the objective of influenc- ing these limits through the development of new types of special silicates which have already been tested in PP. It says its new special silicate Hybrifil T combines positive properties of different mineral fillers. “With
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