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Customised Nanocomposites Based on Rubber Matrices for High Demand Applications

Final Report Summary - NANORUB (Customised Nanocomposites Based on Rubber Matrices for High Demand Applications)

The rubber industry is a sector displaying many paradoxes. Whilst it is clearly dominated by SMEs and only 75 companies worldwide with sales over EUR 40 million, just three of these companies (Goodyear, Michelin and Bridgestone) combine for more than EUR 30 billion in sales, 35 % of the global market. Furthermore, while a plethora of products are manufactured using rubber (sheets, hoses, floorings, transmission belts, roofings, membranes, linings, expansion joints, rollers, inflatable products, plugs, diving suits, etc.), just one product - tyres - accounts for around 70 % total sales of the sector. This, combined with the inherent difficulties of manufacturing rubber products, has forced companies to operate with universally accepted compositions in well-established mixing, processing and vulcanisation conditions, thus limiting innovation.

Factors which have to be considered when developing a rubber product include the amount of filler, which largely varies the properties and ease of manufacture, the type of filler used, mainly high-structure or low-structure carbon black, mixing conditions, with intense processes leading to better mixing but also breaking the nodules of high structure carbon black, and vulcanisation conditions, with intense vulcanisation resulting in superior hardness, stiffness, lower vapour transmision and better resistance to abrasion, but also in a loss of elastomeric properties.

The improvements already obtained in plastic composites should be largely attainable for rubber matrices, with the added value that the use of small amounts of nanoparticles will not likely disturb the delicate equilibrium between composition-processing and vulcanisation conditions, therefore not introducing undesirable effects. Nanoparticles to be used are nanoclays (montmorillonite), largely due to price considerations, which to be suitable for rubber composites must be chemically modified by the use of quaternarium ammonium salts or similar, sheared to a workable size of 35 to 50 nanometres and covered with coupling agents (liquid rubber of macroradicals) to avoid clustering and promote bonding in the matrix. The price for treated nanoclay (around 26 euros / kg) is reasonable considering its benefits and the low percentages to be used (max 5 %).

The product to be manufactured by the (SME) end users is a purpose-designed nano-filler for rubber products, obtained through treatment with quaternary ammonium salts, which increase the spacing of the nanoclay layers by shearing them to platelets of 30 nanometres size, followed by addition of a coupling agent to avoid agglomeration and provide organophilic effect. Coupling agents envisaged include modified liquid rubbers or rather large organic molecules modified with peroxidic-like radicals. The end result will be a filler in the shape of a masterbatch, easy to handle and which can be used directly in conventional rubber processing equipment. A cost estimation of the process up to the introduction of the coupling agent can be derived from available data, being about 17.1 euros / kg. The costs of addition of the coupling agent are more difficult to evaluate, but will be less than 5 euros / kg. Therefore a final price for the nanofiller of 26 euros / kg would result in a commercial margin of 15 %. At this price, a standard nanorubber composite, with 36 % carbon black and 4 % nanoclay would command a price in the range of 2.8 euros / kg, which has been found acceptable by the companies manufacturing rubber products provided that the final nanocomposite results in at least 3 times better abrasion resilience, 50 % improved stiffness, 30 % improved strength and 20 % delayed ignition. In this situation, sales of nanofiller in the order of 200 tonnes p/a are considered reasonable, with a market value of EUR 5.2 million, and resulting in approx. 5 000 tonnes of nanorubber composites for a value of approximately EUR 14 million. The direct market of approximately EUR 20 million p/a created by Nanorub indeed justifies the RTD expenses (approximately EUR 1 million) envisaged.

The innovative step in this research is the development of fundamental materials science that allows the rubber industry to move away from empirical trial and error techniques. Without government this project would not go ahead in the form presented. Individual companies may invest in a small area of R&D related to the use of nanofillers, but this is not likely to develop specific nanofillers for rubbers and any knowledge developed would be proprietary and not disseminated in the interests of the industry.

The overall target of the NANORUB project was to develop a suitable industrial scale technology for the production of high performance elastomeric components based on sophisticated, interfaceoptimised nanoclay / rubber composites. It is also required that the process should be validated by the cost efficient manufacture of prototypes for anti-vibration mounts, ball joints, roller covering and insulation matting. All of these products must achieve the most demanding requirements of their intended applications. The properties, constraints and costs defined for the material, together with the compliance with the relevant standards for the product will provide the framework of properties and requirements to be exceeded by the prototypes of the moulded components to be built in nanorubber composites.