Evaluation of chain scission during mixing of filled compounds

Whether chain scission takes place during mixing of black-filled compounds has been a debatable subject which is yet unsettled. The uncertainty originates from the material system which contains gel. A direct method to evaluate scission is to quantify the change in the number of chain ends, since two chain ends will be newly created on each event of scission. It requires determination of an average molecular weight of the linear components which constitute the gel-containing system. The degree of polymerization defined in the Charlesby-Pinner theory, derived for crosslinking study by means of sol-gel analysis, could be conveniently used for the purpose. The theory, however, cannot be directly applied for black-filled compounds because the composite Structure in the compounds does not allow one to satisfy the assumptions made in the theory, ie., an equal chance of crosslinking for every reactive site: Anew technique is developed so that the assumption is satisfied and the sol-gel analysis can be carried out even with black-filled compounds. This technique is applied for numbers of compounds, with the same formulation but mixed under various conditions. A NR and an SBR formulations are used here. The results clearly indicate that chain scission takes place during mixing of both NR and SBR.