Rubber Accelerators

Novel Room Temperature Safe Accelerator Cure Compositions for use in Synthetic Polyisoprene Latex

Natural and synthetic polyisoprene rubbers are chemically very similar as they are made up of the same monomer unit 'isoprene'.

Synthetic polyisoprene provides the benefits of natural rubber and additionally eliminates the potential for Type 1 allergic reactions. However, there are some differences between natural and synthetic polyisoprene polymers and latices that result in processability challenges and difficulty in meeting the desirable physical properties of the final articles.

In practice, synthetic polyisoprene latex is more difficult to handle compared to natural rubber latex. The compounding and processing of synthetic polyisoprene is required at a much lower temperature compared to natural rubber latex to maintain an acceptable colloidal stability for dipping. This is a real challenge for the compounder as a very efficient cure system is required that can function effectively at a lower temperature. The choice of accelerators used and the accelerator system used is governed by many factors, such as toxicity and stability of the accelerator, commercial availability, sustainability, efficiency of vulcanisation at lower temperature, regularity approvals, customer demands and cost. One of the most stringent demands for dipped articles, made from polyisoprene rubbers, is meeting the N-nitrosamine and N-nitrosatable substances in the safety of toys standard EN 71-12:2013 regulations. These carcinogenic chemicals mainly arise from the use of conventional accelerators. Hence there is a requirement for an efficient cure system that can cure isoprene latex at room temperature within 24 hours but not give rise to irritant dermatitis, Type IV allergy or form carcinogenic N-nitrosamines and N- nitrosatable substances in the final product.

The paper describes parameters governing accelerator choice and their subsequent effectiveness in efficient room temperature curing of synthetic polyisoprene latex for dipped articles. Results are disclosed on new safer accelerator combinations based on Robac AS100, Arbestab Z and metal xanthates that produce vulcanisates with good physical properties. The accelerator compositions, after vulcanisation, are capable of producing dipped articles that should not give rise to irritant dermatitis, Type IV allergy or form carcinogenic N-nitrosamines and N-nitrosatable substances in the final product.

Ranvir S Virdi, Boyd W Grover, Dale Stroyde
Robinson Brothers Limited | United Kingdom