Development of "Green" Rubber Additives     

By Xu Chunhua, China Rubber Industry Association   

After 58 years of development, China has become the world's largest producer and consumer of rubber additives. In 2009, China produced around 660 000 tons of rubber additives (accounting for more than 50% of the world's total), achieving a total industrial output value of about RMB12 billion. Thirty percent of the rubber additives that China produced were exported. China's output of antioxidant 4020, accelerator NS, scorch agent CTP and silane coupling agent Si-69 occupied leading positions in the world.

China's output of rubber additives from 2001 to 2009
       (thousand tons)
Year    Antioxidant    Accelerator    Insoluble sulfur    Processing aids*    Total
2001    38.0    72.0    8.6     19.0    137.6
2002    41.0    66.0    16.3    56.7    180.0
2003    62.5    83.5    11.2    48.8    206.0
2004    69.5    93.0    18.0    65.5    246.0
2005    82.6    138.0    17.2    60.2    298.0
2006    113.0    163.9    23.3    89.0    389.2
2007    135.0    195.0    25.0    115.0    470.0
2008    168.0    213.3    19.2    116.6    517.1
2009    205.2    232.1    36.3    111.7    585.3
* Including output of the adhesive series additives
Note: only the output of member enterprises of China Rubber Industry Association was included.



1. Changing the products layout and speeding up the substitutions for toxic and harmful rubber additives

1). Accelerator NOBS and antioxidant D

Rubber additives that have been identified to be highly toxic or harmful to the human body mainly include beta - naphthylamine, nitrosamines-emitting products such as antioxidant D (N-phenyl - beta - naphthylamine), and secondary amine accelerators such as NOBS (2 - morpholinyl benzothiazole sulfenamide).
   In recent years, China's rubber additives manufacturers have sped up the development of primary amine accelerator NS (N-tert-butyl-2-benzothiazolyl sulfonamide) to replace NOBS and achieved remarkable progress. In 2001, China's NS output was less than 2 000 tons, but in 2007, it rose to 42 200 tons, 7.03 times the output of NOBS. At the same time, the output of NOBS has declined year by year. In 2007, its market share was less than 5%. In 2008, NOBS and antioxidant D were included by China's Ministry of Environmental Protection into the high-risk, high-pollution product catalog.

2) Thiuram accelerator TMTD and thiophenol peptizers

In addition to NOBS, thiuram accelerator TMTD (tetramethyl thiuram disulfide) is also a secondary amine product and can also emit nitrosamines. Although this accelerator does not account for a high proportion in the rubber compound formula, it has a wide range of uses, and its output has increased rapidly. Currently, its total annual output in China has exceeded ten thousand tons. At home and abroad, scientists have developed TBZTD (tetrabenzyl thiuram disulfide) as an alternative of TMTD. TBZTD also belongs to secondary amine family. But because of its high molecular weight, a small dosage and a low nitrosamines emission, it can be used as an alternative of TMTD and similar products. Some Chinese enterprises have realized large-scale production of TBZTD. It is expected that in a relatively short period of time, TBZTD will replace TMTD and its similar products.
    Bayer's Renacit 7 is an example of pentachloro-thiophenol chemical peptizers. It has now been replaced by Renacit 11 (2,2'- diphenyl acylamino disulfide) and other types of peptizers. China's annual output of pentachloro-thiophenol chemical peptizers is about 3 000 tons. At present, the alternative products, such as Renacit 11 (DBD) and organic metal complexes CPA and ZD-8, have been successfully developed by Chinese companies, so their applications will be sped up.

3) Development of excellent alternative products

P-phenylenediamine 4020 series and quinoline RD are excellent antioxidants, and their output now accounts for 82% of China's total antioxidant output. They will continue to be the leading antioxidant products in China. Sulfenamide accelerators CZ and NS, thiuram accelerator TBZTD and thiazole accelerators M and DM will be leading accelerator products in China. Currently, the combined output of CZ and NS account for 40% of China's total accelerator output, accelerators M and DM together account for 30%. With the issue and implementation of various laws and regulations, new alternative products of toxic and harmful rubber additives that can emit nitrosamines will be constantly developed, and it is not far off for rubber additives to bid farewell to the harm of nitrosamines.

4) Replacement of polycyclic aromatic hydrocarbons (PAHs) containing aromatic oil

Rubber oil is a type of important softening agent in processing rubber; the main examples are aromatic oil, naphthenic oil and paraffin oil. Because aromatic oil has good compatibility with rubber and can effectively improve the mixing, extrusion, calendaring and curing performances of rubber compounds, its consumption is the largest (accounting for about 77%, and having a global annual sales of more than 200 000 tons). With the public awareness of the harm of PAHs, replacement of PAHs-containing aromatic oil is getting increasing attention. At present, China's environmentally friendly aromatic oil products are mainly imported or produced by foreign-funded enterprises. Speeding up the development of environmentally friendly aromatic oil products and naphthenic oil has become an inevitable trend.

2.  Making efforts to achieve
the cleaner production of
rubber additives

The drive for cleaner production of rubber additives affects the product structure, the production process and waste treatment in the whole chain from raw materials to intermediates to rubber additives. Although China has been the world's largest producer and consumer of rubber additives and has made a number of advances in cleaner production technologies, it is still far from the full realization of cleaner production. To promote further implementation of cleaner production, China's Ministry of Science and Technology has invested large amounts of money to support research in green rubber additives. To meet domestic needs China is expected in the next three years to produce sufficient high-thermal-stability insoluble sulfur, rubber homogenizing agents and pre-dispersed rubber additives, all of which have been imported up to now.

(1) Cleaner production
with accelerator M

The cleaner production opportunities offered by rubber accelerator M is a global research priority. At present, most Chinese manufacturers use aniline, carbon disulfide and sulfur as raw materials to synthesize crude