Maxlink devulcanizing solutions are designed to recover maximum value from the recycling of scrap tyres to make reclaim rubber or to modify bitumen binders used in rubber modified asphalt – products that enjoy good market demand.
Vulcanization is a process where polyisoprene (natural rubber) is mixed with sulphur at a relatively high temperature and the resultant 3-dimensional cross-links of C-C, S-S and C-S bonds are extremely difficult to separate back to their original forms, giving vulcanized rubber its unique properties and making it an ideal material for high stress applications like tyres. Since tyres are designed and built to last, it may take more than 600 years for them to naturally degrade, and this accumulation of scrap tyres is posing a very serious environmental issue.
The urgency to find commercially viable and sustainable methods to recycle scrap tyres has mounted in recent years, focusing especially on reversing the vulcanizing process as this would allow the resource to be reuse and is the most ecological. This process called devulcanizing, attempts to selectively break the S-S and C-S links while keeping the C-C bonds relatively intact, in order to restore the desired properties of unvulcanized rubber.
However, rubber devulcanization technology has not enjoyed much development since Charles Goodyear received his US patent for vulcanizing rubber in 1844 because of one or more of the following reasons:-
- operating at very high (and unsafe) pressure – up to 4 MPa (40 Bar);
- operating at a very high temperature – higher than 300°C;
- subjected to extremely large shear forces, requiring high power consumption ;
- requiring to supply a special form of energy, e.g., ultrasonic and microwave radiation;
- subjected to a mixture of highly toxic reagents, catalysts and/or promoters;
- highly polluting to the environment due to discharge of water containing toxic oil and heavy metals and sulfur dioxide and carcinogenic dioxins into the air;
- requiring an unusually long processing time, even for partial devulcanization of cured rubber or elastomer; and
- only capable of devulcanizing the surface of rubber crumbs.
Maxlink’s thermo-mechanical devulcanizing technology, using our patented continuous screw devulcanizer operating at atmospheric pressure, where scrap tyres are recycled 100% with no residual waste or emissions, has however totally changed the outlook for devulcanized rubber products to being both eco-friendly and commercially viable.
Maxlink’s devulcanized rubber is used mainly for 3 reasons – as a source of rubber hydrocarbon or carbon black, or as a process aid. It generally contains about 50% rubber and 20% carbon and is less expensive than the virgin materials it replaces, and requires less mixing time and power consumption when processed. Thus, its prime benefit is cost reduction.
As a processing aid, the benefits that Maxlink devulcanized rubber offers include:-
- shorter mixing times
- lower power consumption
- lower heat buildup
- lower thermoplasticity
- minimum reversion
- better dispersion
- lower swelling and shrinkage
- higher cure rate
- lower deformation
- better aging
- improved tackiness
Devulcanized rubber is used in the manufacturing of tyres, retreading materials, tubes and flaps, shoe soles, conveyor belts, sports and playgrounds, adhesives and other moulded rubber products. China leads the world in the production and consumption of reclaim rubber, using 4 million tons in 2013. This is equivalent to the weight of 88 million truck tyres or 440 million PTE (passenger tyre equivalent).
Devulcanized rubber crumbs could be used together with polyolefin (e.g. polyethylene) to make bitumen modifier pellets used in preparing rubberized asphalt binder for asphalt concrete pavements. This proprietary technology which could be applied for both wet and dry blending methods, has exhibited better performance in high and low temperature cracking resistance, anti-stripping, flexibility, fluidity and workability. Pavements made using this WDRA bitumen modifier have also demonstrated superior drainage, grip, noise reduction and UV light resistance compared to conventional asphalt concrete. For some mixture designs, thinner layer of WDRA pavement is required to do the job, besides being easier to place and compact, leading to saving in both construction cost and time. From 2011 -2015, it is projected that 26.62 million tons of modified asphalt would be used for the construction and maintenance of China’s highways.
Maxlink’s solutions for the recycling of scrap tyres make products that are sustainable and easily marketable.