A technological breakthrough by Australian scientists has produced a solution for the world's mountains of waste truck and car tyres.

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In Australia about 70% of the estimated 11 million tyres discarded annually are still being dumped, used as landfill, or stockpiled. Tyres can now be recycled and used in shoe soles, automotive components, building products, coatings/sealants and containers for hazardous waste.

The technology has already been proven through the development of rubber ABS (Acrylonitrile-Butadiene-Styrene) composites for EcoRecycle Victoria. The composite uses 50% crumbed rubber to replace plastic, offering an economic alternative to Poly Vinyl Chloride (PVC) plastics.

Despite environmental concerns, incineration of scrap tyre rubber as a fuel source is currently the most widely used method of disposal. One example is burning tyres to fire cement kilns. Although burning a kilo of tyre rubber generates approximately 28,600 BTUs (British Thermal Units) of energy, it actually requires much higher energy (approximately 121,000 BTUs) to produce a kilo of raw rubber.

Since most common tyre recycling methods require less than 2,200 BTUs to process about a kilo of scrap tyres into clean crumb rubber, the use of crumb rubber in new products could offer considerable energy savings.

The mechanical segmenting method is highly energy efficient and is the first part of a process which incorporates downstream devulcanization* and activation phases resulting in high quality rubber powders.

The whole process will enable waste tyres to be turned back into high quality devulcanized and activated rubber powders (down to 80 - 120 mesh size) free of metal contamination for redevelopment as new products, such as new tyres and elasto-polymer based items.

Examples of applications include: Shoe soles, automotive components, tyres, non-pneumatic tyres, wheels, building products (roofing materials, insulating materials, window gaskets) coatings/sealants, containers for hazardous waste, industrial products (enclosures, conveyor belts, etc) and many more.

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MSc thesis from Luleå tekniska universitet (Luleå Univeristy of Technology/Maskinteknik/Polymer Engineering)

Author: Jinxia Li; [2008]

Keywords: Recycled EPDM rubber; Unvulcanized rubber; LDPE; EMA; Reactive compatibilization; Non-reactive compatibilization; Ethylene octene copolymer; Phenolic resins; Tensile properties; Tear strength; Microstructure; Pressing pressure; rubber recycling,

Abstarct: Blends containing recycled EPDM rubber and thermoplastics, EMA and LDPE were studied. Two compatibilization methods, reactive and non-reactive, were evaluated. Ethylene octene copolymer (EXACT 0210) was used as non-reactive compatibilizer. Phenolic resins (SP1045 & HRJ10518) were reactive agents. There existed an optimal composition of compatibilizers which were 25wt% in the case of reactive and non-reactive agents added to 15wt%EMA and 55-60wt% EPDM rubber.

EXACT-compatibilized blends gave high elongation at break while phenolic resin-compatibilized mixtures gave high stiffness in comparison with the chosen reference material. Comparison in compatibilizing capabilities HRJ-10518 and SP-1045 was carried out. The former one had better capabilities than the latter at high compatibilizer content. Talcum was used as anti-agglomeration agent but failed to work properly. Pressing pressure could be minimized without any adverse effect. Non-vulcanized rubber was used to enhance tear strength but its effect was small by assuming that there exists degradation of the interfacial surface at high temperature. SEM analysis revealed homogeneous microstructure in both kinds of compatibilization. EXACT 0210-compatibilized blends showed more plastic deformation of the matrix than reactive blends. Stable connection between phases was also observed.

Tensile strength of the LDPE based blends were a little lower than that of EMA based blends and the hardness was a little higher. Compared to EMA based blends, the elongation at break was much lower while the young's modulus was much higher with LDPE based blends. Compression set of both LDPE and EMA based blends was high compared to the reference materials supplied by Rerub AB, Piteå.

Download MSc thesis from Luleå University