K.K.G. De Silva, M. Taylor, R. Nilmini, S. Kariyawasm, J. Vithanachchi
NZ Product Accelerator - University of Auckland,
Keywords: natural rubber, Plasticized PVC, supply chain engagment, durability
Summary:Rigid PVC is flexibilized by the addition of plasticizers such as phthalates to obtain the properties of elastomers. These plasticizers in the polymer matrix are not covalently bound to the main polymer chain, which makes them susceptible to leaching. The potential risks related to phthalates include degradation of the polymer during service causing surface embrittlement and micro-cracking, yielding micro-particles that persist in the environment. The use of phalates is becoming under increasing pressure in Europe and in February 2007, the Technical and Scientific Advisory Committee of the US Green Building Council released its report concluding that the risk of dioxin emissions from PVC puts it consistently among polymeric materials interms of human health impacts. On the other hand, the combination of unique morphology, excellent physical and mechanical properties, cost effectiveness and sustainability make natural rubber (NR) an appealing constituent for many industrial applications including tyres, rubber springs and vibration mounts. NR has high structural regularity, providing it with unique and valuable characteristics such as high tensile and tear strength, good resilience, high elasticity, excellent impact resistance and good low temperature performance. These inherent properties of NR make it an ideal material for the case study on research into flexible pylons used in harness horse racing tracks that require properties such as good resilience, impact resistance, flexibility and excellent overall performance and durability in service conditions. The Product Accelerator (PA) model of engagement through technology partners and service providers to commercialize new products into local and international markets has prompted undertake this project to improve performance of pylons in service. The attempts made were not to improve the performance of plasticized PVC that become brittle losing its integrity due to plasticizer migration in service but to develop a new product based on environmentally friendly sustainable NR that would fulfil all the requirements of flexible pylons. The pylons have been developed at an international technology partner institution and commercialized through consultancy and technology inputs from the PA network. An evaluation of the performance of rubber pylons is discussed in detail here. As an extension to this work, the possibility exists of replacing organic antioxidants that could leach out in hot sun with bio-based polymeric antioxidants increasing the life cycle of the pylons. This approach constitutes another aspect of Product Accelerator research contributions engaging its network partners as reported elsewhere. Processing parameters such as cure characteristics, mechanical and tensile properties and retention of properties after ageing at elevated temperatures were recorded and compared with the controls. The controls used in this study include the commercial antioxidants, 6PPD and SKF powder. These compounds have some drawbacks such as surface blooming and volatilization, with a consequent loss of activity. Other problems with these compounds include, leaching and migration in service and deterioration of mechanical properties by causing disruption of the stress propagation through the polymer chains. These problems can be solved by using a polymeric bio-based antioxidant which is thermally stable, nontoxic and compatible with the base polymer.