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

Environmental protection of rubber productsSpecial topic, rubber additives that produce carcinogens and their alternatives
It is required that the rubber products produced do not contain dangerous substances exceeding the limit value, and do not use banned dangerous substances to avoid harming human health.

1. Heavy metal

The model and grade of raw materials for rubber products will affect the content of heavy metals. Therefore, attention should be paid to avoid or reduce the use of raw materials containing chromium and nickel (for example, zinc chrome yellow contains hexavalent chromium, and antioxidant NBC contains nickel). The chromium plating layer of the mold and frame will also bring chromium elements into the rubber compound, so it is necessary to develop a new chromium plating technology that uses trivalent chromium instead of hexavalent chromium. The rubber shoe industry should pay attention to the heavy metal limit values ​​of textile and leather dyes, and limit the use of metal complex dyes containing copper, chromium, and nickel to avoid the consequences of my country’s shoes being found to contain high levels of nickel and azo dyes at the end of 2005. Troubled to Italy’s “Toxic” Investigation.

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

Since the EU ELV directive and the EEE RoHS directive have been implemented, the formula design and production process of rubber products have become “lead-free” and have become an important issue.

① Adopt 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 composed of thiadiazole vulcanizing agent/BaCO3 acid absorbing agent, vulcanizing agent XL-21 The system composed of (2,3)-dimercaptocarbamate methylquinoline)/Ca(OH)2 acid absorbent is a lead-free vulcanization system for chloroether rubber, which has replaced NA-22/Pb304 or ” The leaded vulcanization system of “disaldehyde” 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 chlorinated polyethylene rubber (CM) can be used to replace CSM in production.

② Cancel the lead vulcanization process of rubber hose

Use the overmolding process 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 established in Volume 1 of the Monographs of the International Center for Research on Cancer (IARC), and two directives of the European Community (67/548/EEC and 76/769/EEC ) also classifies lead and lead compounds as hazardous substances and stipulates limit values. At that time, European hose manufacturers were about to abandon lead-coated units. At this time, my country’s hose industry started a craze for the introduction of continuous lead-coated units. Many production lines were introduced from Europe, and some production lines are still in operation. Moreover, the cable industry was also promoting its application at that time, and developed domestic lead-coated units. This was a decision-making error caused by a lack of environmental awareness and information at the time, and we should take warning from this.

③ Use environmentally friendly adhesives

Some rubber/metal thermal vulcanization adhesives (such as Kemlock 220, 250, 252) contain lead compounds in their components, which may cause the lead in the product to exceed the standard. At present, the British Westbond cilbond 24C has been developed, which is a lead-free, non-toxic solvent-based high-performance adhesive that meets the requirements of the International Raw Materials Data System (IMDS). Used for thermal vulcanization bonding between various rubbers and metals, plastics and other hard substrates.

2. Brominated flame retardants

According to relevant EU directives, polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE) are prohibited/restricted. Although it is currently difficult for the rubber and plastics industry to find effective flame retardants 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 appears to give decaBDE legal status for the time being. However, some foreign electrical and electronic equipment manufacturers still insist on banning/restricting the use of “mono-” to “deca-bromo” diphenyl ethers. There are two reasons: the directive EU-D-2003/11/EC) restricting the use of pentabromodiphenyl ether and octabromodiphenyl ether is still valid and they are not exempted; in the synthesis process of decabromodiphenyl ether, there are 2% by-products – octabromodiphenyl ether and nonabromodiphenyl ether.

Tetrabromobisphenol A, another commonly used flame retardant, is also undergoing a “hazard assessment” in the European Union.

Therefore, the development and application of halogen-free flame retardants, especially bromine-free flame retardants, is a common urgent task for rubber additive manufacturers and rubber product factories.

3. Polycyclic aromatic hydrocarbons

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

Studying which raw materials are responsible for the PAHs detected in rubber and plastic products has always been a major problem that has troubled enterprises. Although the author has searched for literature, it has not been fully elucidated. It is only preliminary believed that coal tar and petroleum It is a possible suspect, and the main suspicious raw materials are carbon black and processing oil.

① Carbon black

The raw material oils for carbon black mainly include clarified oil, ethylene tar and coal tar. The raw material oil for carbon black in my country is mainly coal tar. Coal tar is an extremely complex mixture, the main components of which are aromatic compounds and heterocyclic compounds. There are thousands of species, of which more than 500 species have been isolated and identified. Chromatographic analysis of the intermediate products of the raw oil reaction in various parts of the carbon black reactor revealed the presence of a variety of PAHs, among which the most abundant ones arePyrene, benzo(a)pyrene, benzo(c)pyrene, etc. Ethylene tar also contains certain amounts of PAHs. Tests have shown that domestically produced oil furnace carbon black, which is currently widely used, can cause PAHs to exceed standards even if used in a small amount in the rubber formulation.

Currently, carbon black factories have not provided test reports or control indicators for PAHs content to rubber product factories, which is also a very confusing issue for rubber product manufacturers.

② Processing oil

Rubber processing oils include aromatic oils, paraffin oils and naphthenic oils. Aromatic hydrocarbon oil cannot be used in rubber products with environmental protection requirements because it contains a large amount of PAHs, which also limits the application of oil-extended rubber filled with high aromatic hydrocarbon oil (such as SBRl712, etc.). Although we have developed oil-extended rubbers with lower PAHs content (such as SBRl723), the types and amounts of PAHs they contain have not been reported, and it is not yet known whether they can meet EU environmental protection requirements. In paraffin oil and naphthenic oil, the PAHs content varies greatly due to different origins and processing techniques. So far, the author has not seen PAHs data provided by domestic and foreign companies that produce rubber processing oils, making it difficult to make environmental evaluations of various oil products.

Currently, we are still unclear about the sources of PAHs in raw materials. In addition to carbon black and processing oil, there may be many other raw materials that cause PAHs to exceed standards, and we need to step up screening and determination. Otherwise, once the EU formally legislates PAHs, we will be in a very embarrassing situation.

4. Specific amines

EU Directive 2002/61/EC and the ecological textile standard “Oeko-Tex-Standard 100” restrict the sale and use of hazardous azo dyes. The so-called “specific amines” refer to carcinogenic aromatic amines produced from azo dyes decomposed under specific (i.e. reducing) conditions. There are 24 types in total.

Azo dyes mainly involve dyes for textiles and leather, but now purchasers also require testing of specific amines in rubber products. Analysis believes that some organic pigments (colorants) in the rubber, especially azo colorants, may contain these specific amines, such as bright red powder and golden red, oil-soluble candle red, rubber bright red LG and other colorants contain Dichlorobenzidine.

For footwear products, special attention should be paid to whether the fabrics and leather materials used contain banned dyes. There are now more than 300 environmentally friendly dyes to choose from.

5. N-nitrosamine

Certain rubber additives with a secondary amine structure react with nitrosating agents (nitrogen oxides NOx) to generate carcinogenic N-nitrosamines. German regulation TRGS552 (effective in January 1988) stipulates the ban on 12 types of carcinogenic N-nitrosamines, involving a variety of rubber additives currently widely used in China. In particular, the “White Paper on Future Chemicals Policy Strategy” published by the European Union lists the vulcanizing agent DTDM and certain thiuram accelerators (such as TMTD, etc.) as chemicals to be phased out within a time limit, which is not only harmful to rubber product manufacturers, but also to tires. There are threats to all industries. Therefore, we should use safe and environmentally friendly additives. For example, domestic tire factories are using accelerator NS to replace NOBS.

Rubber additives and their substitutes that produce carcinogens