Aqueous Dispersions of Rubber Chemicals

Manufacturer: We are encountering poor dispersion of rubber chemicals such as sulphur, accelerators and antioxidants used for latex compounding. This has resulted in sedimentation to the extent of forming hard cakes that are difficult to be re-dispersed. We would appreciate very much if you could give us some guidance to overcome this problem.

John Woon (Senior Latex Consultant): Achievement of a well milled and well dispersed rubber chemical in water entails a lot of details which cannot be sufficiently covered in this forum. If you want, I can prepare a comprehensive report for you.

However, in the mean time, you should pay close attention on all factors that allow you to achieve the following:

• Wetting of Chemical Particles: All the air from the particle surface and between the particles of the aggregates and agglomerates must first be replaced by the solution of a dispersing agent or agents. The particle/gaseous interface should then be transformed into a solid/liquid interface.
• Milling or Grinding and Separation: The composite from above mentioned step is then subjected to mechanical energy via impact and shear forces. As a result, the agglomerates are broken up  into smaller units and evenly dispersed.
• Stabilization of the Chemicals Particles in Suspension: The chemical dispersion is stabilized by dispersing agents via the adsorption of molecules of these dispersing agents (usually some surfactants) at the chemical particle surface. This prevents or minimizes sedimentation and phase-separation.  

Let me know if you require a more comprehensive report with recommended recipes for the dispersion of each chemical you are using.