Topics on environmental protection of rubber products, rubber additives that produce carcinogens and their substitutes

Special topic on environmental protection of rubber products, rubber additives and their substitutes that produce carcinogens
It is required that the rubber products produced do not contain dangerous substances exceeding the limit value, and do not use prohibited dangerous substances, so as not to endanger human health.

1. Heavy metal

The type and grade of raw materials for rubber products will affect the content of heavy metals. Therefore, care should be taken to avoid or reduce the use of raw materials containing chromium and nickel (such as zinc chrome yellow containing hexavalent chromium, anti-aging agent NBC containing nickel). The chromium plating layer of the mold and the skeleton will also bring chromium elements into the rubber compound, so it is necessary to develop a new chromium plating technology that replaces hexavalent chromium with trivalent chromium. The rubber shoe industry should pay attention to the heavy metal limit value of textile and leather dyes, and limit the use of metal complex dyes containing copper, chromium, and nickel, so as to avoid the detection of high levels of nickel and azo dyes in Chinese shoes at the end of 2005. Troubled by ‘toxic’ investigation into Italy.

The content of heavy metals in rubber products does not only come from one or two key raw materials, but is the sum of the heavy metal content of all raw materials (including raw rubber). Although some raw materials contain very little heavy metals (such as white carbon black and kaolin), we should also pay attention to “accumulation makes more”.

Since the EU ELV Directive and EEE RoHS Directive have been implemented, the formulation design and production process of rubber products to achieve “lead-free” has become an important issue.

① Using lead-free vulcanization system

The system composed of vulcanizing agent TCY (2,4,6-trimercapto-s-triazine) and Ca/Mg acid absorbing stabilizer, the system consisting of thiadiazole vulcanizing agent/BaCO3 acid absorbing agent, vulcanizing agent XL-21 The system composed of (2,3)-dimercaptocarbamate methylquinoline)/Ca(OH)2 acid absorbing agent is a lead-free vulcanization system of epichlorohydrin rubber, which has replaced NA-22/Pb304 or ” The lead vulcanization system of “two salts” is used in automobile fuel hoses. In addition, the lead monoxide vulcanization system of chlorosulfonated polyethylene rubber (CSM) has serious environmental problems. It can be replaced by a lead-free vulcanization system (such as pentaerythritol), or CSM can be replaced by chlorinated polyethylene rubber (CM) in production.

② Cancel the rubber hose lead vulcanization process

Use overmolding instead of TPX resin (poly-4-methyl-1-pentene), nylon, polypropylene or nylon/polypropylene. As early as 1972, the carcinogenicity of lead and lead compounds was determined in volume 1 of the monograph collection of the International Cancer Research Center (IARC), and the two directives of the European Community (67/548/EEC and 76/769/EEC ) also classifies lead and lead compounds as hazardous substances and sets limit values. At that time, European rubber hose production plants were about to abandon lead-coated units. At this time, my country’s rubber hose industry set off an upsurge in introducing continuous lead-coated units. Several production lines were introduced from Europe, and some production lines are still in operation. Moreover, the cable industry was also promoting the application at that time, and developed a domestic lead-coated unit. This was due to a decision-making error caused by the lack of environmental protection awareness and information at that time, so it should be taken as a warning.

③ Use environmentally friendly adhesives

Some rubber/metal heat vulcanizing adhesives (such as Chemlock 220, 250, 252) contain lead compounds in the components, which will cause the lead in the product to exceed the standard. At present, cilbond 24C from Sibang, UK has been developed, which is a lead-free, non-toxic solvent-based high-performance adhesive that meets the requirements of the International Material Data System (IMDS). It is used for thermal vulcanization bonding between various rubbers and metals, plastics and other hard substrates.

2. Brominated flame retardants

According to the relevant EU directives, polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE) are prohibited/restricted. Although it is currently difficult for the rubber and plastic industry to find an effective flame retardant that can replace decabromodiphenyl ether, and the fire department also raised objections, the European Commission passed a resolution on October 13, 2005, deciding to exempt “decabromodiphenyl ether in polymer applications.” Diphenyl ether”. This seems to temporarily give decaBDE a legal status. However, some foreign electrical and electronic equipment manufacturers still insist on the prohibition/restriction of “monobromo” to “decabromo” diphenyl ethers. There are two reasons: Directive EU-D-2003/11/EC restricting the use of pentabromodiphenyl ether and octabromodiphenyl ether) is still in force and they are not exempted; during the synthesis of decabromodiphenyl ether, with 2% by-products – octabromodiphenyl ether and nonabromodiphenyl ether.

Tetrabromobisphenol A, another commonly used flame retardant, is also undergoing a “risk assessment” in the EU.

Therefore, the development and application of halogen-free flame retardants, especially bromine-free flame retardants, is an urgent task shared by rubber additives manufacturers and rubber product factories.

3. PAH

At present, there are 16 kinds of polycyclic aromatic hydrocarbons (PAHs) restricted by the EU and other countries. The most important PAH is the well-known benzo(α)pyrene. In recent years, the electrical and electronic products exported by my country have been repeatedly returned by European countries, some of which are related to the excessive PAHs of rubber and plastic products.

Which raw materials are responsible for the PAHs detected in rubber and plastic products has always been a major problem for enterprises. is a possible suspicious point, and the corresponding main suspicious raw materials are carbon black and processing oil.

① Carbon black

The raw material oil of carbon black mainly includes clarified oil, ethylene tar and coal tar. The raw material oil of carbon black in my country is mainly coal tar. Coal tar is an extremely complex mixture. The main components are aromatic compounds and heterocyclic compounds. There are thousands of species, and more than 500 species have been isolated and identified. The chromatographic analysis of the intermediate products of the raw oil reaction in various parts of the carbon black reaction furnace found that there are many kinds of PAHs, among which the most abundant ones are pyrene, benzo(a)pyrene,and (c) pyrene et al. Ethylene tar also contains a certain amount of PAHs. Tests have shown that domestic oil furnace carbon black, which is widely used at present, will cause PAHs to exceed the standard even if it is used in a small amount in the rubber compound formulation.

Currently carbon black factories have not provided testing reports or control indicators for PAHs content to rubber product factories, which is also a problem that confuses rubber product manufacturers.

② Processing oil

Rubber processing oils include aromatic oils, paraffinic oils and naphthenic oils. Aromatic oils cannot be used in rubber products with environmental protection requirements because they contain a large amount of PAHs, which also limits the application of oil-extended rubbers filled with high aromatic oils (such as SBR1712, etc.). Although we have developed oil-extended rubbers with lower PAHs content (such as SBR1723), the types and quantities of PAHs contained in them have not been reported, and it is unknown whether they can meet the EU environmental protection requirements. In paraffinic oil and naphthenic oil, due to different origins and processing techniques, the content of PAHs is also very different. So far, the author has not seen the PAHs data produced by companies producing rubber processing oil at home and abroad, so it is difficult to make an environmental assessment of various oil products.

Currently, the source of PAHs in raw materials is still unclear. In addition to carbon black and processed oil, there may be many other raw materials that cause PAHs to exceed the standard, which needs to be screened and determined. Otherwise, once the EU formally legislates on PAHs, we will be in a very embarrassing situation.

4. Specific amines

EU Directive 2002/61/EC and Ecological Textile Standard “Oeko-Tex-Standard 100” restrict the sale and use of dangerous substances azo dyes. The so-called “specific amines” refer to the carcinogenic aromatic amines produced from the decomposition of azo dyes under specific (ie reducing) conditions, and there are 24 kinds in total.

Azo dyes are primarily concerned with dyes for textiles and leather, but buyers are now also asking for specific amines in rubber products. According to the analysis, some organic pigments (colorants) in rubber materials, especially azo colorants, may contain these specific amines, such as big red powder and golden light red, oil soluble candle red, rubber red LG and other colorants contain Dichlorobenzidine.

Footwear products should pay special attention to whether the fabrics and leather materials used have banned dyes. There are more than 300 environmentally friendly dyes to choose from.

5. N-nitrosamine

Some rubber additives with secondary amine structure react with nitrosating agents (nitrogen oxides NOx) to generate carcinogenic N-nitrosamines. The German regulation TRGS552 (effective in January 1988) stipulates that 12 kinds of carcinogenic N-nitrosamines are prohibited, involving a variety of rubber additives widely used in China. In particular, the “White Paper on Future Chemicals Policy Strategy” published by the European Union includes vulcanizing agent DTDM and certain thiuram accelerators (such as TMTD, etc.) All industries are threatened. Therefore, we should use safe and environmentally friendly additives. For example, domestic tire factories are replacing NOBS with accelerator NS.

Rubber additives and their substitutes that can produce carcinogens