Community Research and Development Information Service - CORDIS

Rational way to process rubber

In tyre manufacturing, rubbers (SBR) are mixed with a lot of ingredients, fillers as reinforcing agents, processing aids and curatives. SBR based compounds with silica as filler, are known to be hardly processable. Flow defects and poor rubber strength occur when compounds are extruded or injected. Flow and aspect defects can be only slightly postponed using:
- Processing promoters that reduce compound viscosity as well (the most effective are fatty acid Zn salts based);
- Covering the inner die surface that is in contact with the polymer with a layer that favours slippage. The addition of 2phr of DYNEON fluoroelastomer as slip promoter is completely inefficient, increasing flow defects and getting final compound properties worse.

The best way to postpone compound flow instabilities is:
- Use of polymer blends (two or more SBRs, blend with BR) to enlarge molecular weight distribution;
- Addition of a certain quantity of Carbon Black. It was found that 30phr of CB are enough to improve considerably elongational properties of green compound. Surface aspect is even better, very fair and smooth. Silica compound ageing was found very important in determining flow defects: the more you store the compound, the more it generates flow instabilities and surface defects. Elongational compound properties and viscosity measured in extensional rheometry seem to be more predictive than common shear viscosity. It is going to be proposed as a lab test for new compound development.

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