Controlling polymeric composite properties by understanding the influence of mixing parameters
Deeptangshu Chaudhary, Margaret Jollands, Ferenc Cser
Rheology and Materials Processing Centre
Australia
Keywords: silica-ash, mixing, analysis
In 2000, Australia added approximately 0.21 million tonnes of rice hulls, a mere 0.2 %, to the world production of about 110 million tonnes. Rice hulls, a by-product of the rice industry, is classified as an industrial waste. Burning rice hulls – as a preparative step for energy production – is a useful solution to the growing environmental concern where the desirable situation would be the economic use of the resulting ash. Though the hull ash contains 60-90 % silica, its usefulness as a filler in polymers has been marred by filler-polymer incompatibility, which results in poor composite mechanical properties. Mixing has been identified as a crucial stage that can significantly alter the final properties.
To obtain a deeper understanding of the influence of mixing parameters and/or their interactions on the composite properties, the incompatible components (rice hull ash and polypropylene) were mixed in a Haake batch mixer and mixing time, mixing chamber temperature and rotor speed (rotor rpm) were varied. Tensile and flexural moduli were measured for each set of process conditions. A full factorial experimental design was set up using two levels, then the data was analysed using statistical software. The results were used to formulate a model that represents the system behaviour in terms of mechanical properties.
The model could be used to optimise the mixing process for either tensile or flexural modulus; however, it is only applicable to this system. It was found that mixing time was the most influential parameters for both the responses, and a higher temperature accompanied by an increased mixing time was detrimental to the composite mechanical properties, which was attributed to degradation. On the other hand, mixing speed, showed positive influence on composite mechanical properties in the range considered.