China Eager for Eco-friendly Rubber Manufacturing

By Xu Chunhua, China Rubber Industry Association

The development of China's tire industry has been boosted for years by the soaring automobile industry. In 2012, about 19.3 million automobiles were sold in China, up 4.3% year-on-year. Meanwhile, the output of tires in China totaled 483 million pcs, up 6% year-on-year, and 89% of them are radial tires. It is expected that 5 million hybrid/electric vehicles will be manufactured in China by 2015. With the product structure adjustment of China's automobile industry, especially the development of new-energy vehicles, the development of green tires and fuel-efficient tires will be greatly promoted. Moreover, the current rapid development in industries such as transportation, aerospace, aviation, highways and high-speed rail offers many excellent opportunities for China to develop various high-performance rubber products. In 2011, the total length of highways in China was 85 000 km; the figure increased to 96 000 km in 2012 and is expected to reach 108 000 km by the end of 2015. The total length of China’s railways is 96 000 km. The total length of high-speed railways in China, the world’s longest, will continue to increase and reach 18 000 km by the end of 2015.
　　In 2012, the European Commission started the implementation of Regulation No. 1222/2009 on the labelling of tires (amended by Regulation 228/2011). The regulation is a tremendous impetus to the production and use of green tires. Currently, several countries including the United States, Japan, South Korea and Brazil are planning to implement labeling regulations, too. China is also actively establishing related standards and green tire industrial regulations as well as constructing tire testing centers. China’s tire industry should take this opportunity to promote green tire manufacturing and to upgrade technologies of the industry. Reportedly, if all vehicles in China were using fuel-efficient tires, 410 kt of oil or RMB 3 billion could be saved each year, and the reduced carbon dioxide emissions could be more than 3 million tons.
　　Although 27 Chinese companies were listed in the top 75 tire producers in the world in 2012, their combined sales revenue, US$20.95 billion, was less than that of either Japan's Bridgestone (US$28.45 billion) and France’s Michelin (US$22.515 billion). At one time, there were over 120 tire producers in the United States. However, after decades of integration, the number decreased to only six or seven in 1980s. Meanwhile, the number of automobile makers in the United States decreased from over 3000 to only three at present. Therefore, China’s tire industry should restructure enterprises and improve the competitiveness of tire products.
　　
I. Adjusting product structure of raw materials
　　In recent years, one of the major strategic measures in China’s rubber industry has been to develop eco-friendly raw materials, and the results have already been fruitful. Table 1 shows the statistics of the output of major raw materials in China’s rubber industry since 2001.
　　
　　Table 1 Output of China's major rubber raw materials since 2001 (kt)
　　
Year    2001    2002    2003    2004    2005    2006    2007    2008    2009    2010    2011
Synthetic rubber    1052    1133    1272    1380    1630    1840    2220    2383    2755    3100    3480
Natural rubber    478    527    565    574    511    538    588    548    630    687    720
Carbon black    763    826    1019    1381    1610    1850    2300    2430    2830    3375    3850
Rubber chemicals    138    180    206    246    298    389    470    517    595    701    757
Steel cord    50    89    160    309    460    562    725    695    916    1204    1360
Polyester cord    12    18    17    24    23    46    76    71    86    117    130
Nylon cord    228    236    256    316    325    266    270    243    247    268    254

1. New synthetic rubber products
   In 2011, China's total consumption of synthetic rubber, 370 million tons, exceeded that of natural rubber. Due to a lack of natural rubber resources, more than 75% of natural rubber consumed in China is imported. Isoprene rubber, which has a molecular structure close to that of natural rubber, spurred new growth of synthetic rubber. China became the most important growth region of isoprene rubber, where the production capacity is expected to increase 300 kt/a in the next few years.
   Neodymium-catalyzed polybutadiene is the perfect polymer for tread rubber of fuel-efficient tires due to its advantages such as narrow molar mass distribution, better structural regularity, less branching, excellent physical and mechanical properties, and low rolling resistance. LANXESS (Germany) is now constructing the world’s largest rare earth butadiene rubber unit in Singapore. China should also accelerate the pace of industrializing rare earth butadiene rubber.
   SIBR, a tri-block copolymer of styrene, butadiene and isoprene, synthesized through molecular design, can replace rubber blends since it has advantages of several rubber products and can balance various properties of tire rubber such as wear-resistance, rolling resistance and wet skid performance. Sinopec Beijing Yanshan Petrochemical Company has successfully developed SIBR and is preparing to expand its production scale.
   Thermoplastic elastomer (TPE) is an emerging polymer material, which is developing fast worldwide and has wide applications. Styrenic TPE, e.g. SBS, has been grown steadily and now has the largest production and sales scale among all TPEs. About 30% of TPEs are produced in China. Thermoplastic vulcanizates (TPVs), a class of materials developed jointly by the Beijing University of Chemical Technology and Shandong Dawn Polymer Co., Ltd by using a new catalyst and dynamical vulcanization technology, was awarded the second prize of National Scientific and Technological Inventions. TPVs can be used to replace thermally cross-linked rubber for the production of elastomer products with complex shape due to its excellent anti-fatigue property.
　　Polyurethane tread rubber, which has excellent mechanical properties such as high abrasion and puncture resistance and low rolling resistance, is an excellent raw material for green tires. It can be molded by casting, which can significantly decrease energy consumption. The related technology passed technical appraisal in 2009 and will be vigorously promoted in the 12th Five-Year Plan period. A production line for polyurethane tread radial tires which has a capacity of 400 000 pcs per annum has already been built in China.
2. Eco-friendly rubber chemicals
　　Currently, the output of rubber chemicals in China accounts for more than 60% of the world total. Driven by the implementation of the national scientific and technological supporting policies from 2006 to 2010, more than 90% of rubber chemicals are now eco-friendly, and breakthroughs in clean production technologies of rubber chemicals have been achieved. From 2011 to 2015, the development of China's rubber chemicals will continue to follow the principles of green chemical process such scientific and technological progress, environmental protection, safe production and energy conservation.
　　(1) The technology of using NS to replace NOBS, which produces nitrosamines, has been popularized. Some nitrosamine-generating accelerators such as thiuram and dithio carbamates will gradually be replaced from 2011 to 2015. Currently, substitutes such as TBzTD and ZBEC have been successfully developed and their market shares will continue to increase with deceasing production costs.
　　(2) Replacing pentachlorothiophenol peptizer with DBD has become the trend. At present, the output of pentachloro thiophenol peptizer Sj-103 is less than 3000 t/a.
　　(3) A clean production process for resorcinol that can minimize the impact to the environment has not been developed yet.  
　 (4) Rubber accelerator D (diphenyl guanidine) is extensively used in silica-reinforced rubber products. Its consumption is increasing sharply with the widespread use of silica in rubber. However, clean production technologies for accelerator D need to be developed.
　　(5) Solvent extraction refining processes for vulcanization accelerator M (2-mercaptobenzothiazole) and oxidation processes for other accelerators should be improved and popularized in the 12th Five-Year Plan period.
　　In addition, the development of multi-purpose rubber chemicals and eco-friendly aromatic oil should be strengthened; the eco-friendly rubber chemicals that have excellent yellowing resistance still have much room for development.
　　At present, most of China's large rubber chemical producers comply with the European Union REACH Regulation. The product structure of China's exported rubber chemicals will be further adjusted.

3. Silica and silica dispersants
   Silica is closely related to green tires. The wear resistance of rubber increases with increasing dispersibility of silica in rubber. It is expected that at the end of 2015, the global consumption of silica in rubber will reach 2.1 million t/a, while the demand for silica in China will reach 1.2 million t/a. China will become a major producer and consumer of silica. With the successful development of silica varieties that can be easily dispersed and the application of silica dispersants such as AT-BTK, HST and XT280, the content of silica in rubber can be as high as 50 to 80%. Thus the rolling resistance of tires can be greatly reduced and the development of green tires can be strongly accelerated.

4. High-performance skeleton materials
   From 2011 to 2015, industrial production and application of high-performance Kevlar are expected to be achieved soon since it not only lowers the weight of products but also greatly decreases rolling resistance when added to tires, synchronous belts, toothed belts and conveyer belts; development of steel cord and bead wires with ultrahigh strength and varied structures should be strengthened so that the amount of steel skeleton materials in tires can be significantly reduced and properties such as light weight, high performance and low rolling resistance of tires can be achieved; the upgrading of high modulus, low shrinkage polyester skeleton materials, including the development of PEN, will be promoted; composites of BPO short fibers and rubber will be developed to meet the demand for high-performance rubber products; the application of ultra-high molar mass polyethylene in rubber will be promoted; clean production technologies for fibers and steel skeleton materials will be developed.

II. Green manufacturing relies on new technologies
1. Low temperature single-stage continuous mixing process
　　By utilizing the advantages of open mills such as low mixing temperature and good dispersity of carbon black, the new process can conduct all mixing processes including repeated low temperature mixing and sulphuration through one stage in several paralleled open mills. This is an enormous improvement over traditional internal mixers, which, after high temperature mixing, require that the rubber be taken out, cooled down and put back in for further mixing –  a process that might be repeated many times for a single batch. With the application of the new process, the energy and time needed for mixing can both be reduced by at least 40%; the mechanical strength of the final products is increased 10% ~ 15% on average; the lifetime of products is also significantly increased. Compared to the traditional multi-stage high temperature mixing process, the technology can save 30% of energy consumption and double the production efficiency. At present, several tire producers in China, including Triangle Group Co., Ltd, MESNAC, Guangzhou SCUT Bestry Technology Co., Ltd, Shandong Bayi Tyre Manufacture Co., Ltd and Beijing New Universal Science and Technology Co., Ltd, can provide the complete equipment set for the new process.

2. Energy-efficient wet mixing technology
   The technology is to blend latex with an aqueous silica suspension through high speed mixing and acquire wet mixed rubber through coprecipitation. The key techniques are the preparation and modification of a silica dispersant and the coprecipitation of the silica dispersant with latex. The technology enables adding a large amount of silica into rubber, which is important to green tires. Meanwhile, the technology enables a continuous mixing process, which can reduce the costs of mixing equipment, labor and energy. Free silica particles in rubber do not need to be separated, thus less environmentally harmful dust will be produced. According to tests, the wet mixing process can reduce energy consumption by more than 30%. The technology, which was patented by Cabot and then sold to Michelin, is limited to carbon black-reinforced rubbers. Several Chinese companies and institutes, including the China National Tire Process Control Engineering Technology Research Center, South China University of Technology, Hangzhou Zhongce Rubber Co., Ltd, South China Tire & Rubber Co., Ltd, Sailun Tire Co., Ltd, Zhuzhou Anbao Linfeng New Materails Co., Ltd and Beijing Wanhuiyifang Co., Ltd, have actively engaged in the development of the technology and successfully developed the first wet mixing technology for silica-reinforced rubbers. The new technology, which is expected to reach industrial scale soon, provides a good way to improve the content of silica in green tires.

3. Waste rubber recycling
   China is one of the largest producers of reclaimed rubber in the world. As an important supplement to rubber resources, about 3 million tons of reclaimed rubber was produced in China in 2011. The overall energy consumption in the production of reclaimed rubber products has decreased by 20% through the popularization of automated production lines. In particular, the production line of low temperature pyrolysis equipment developed by Qingdao University of Science and Technology provides a new way to develop the recycling economy of waste rubber utilization.