Fatty-diamine cationic surfactants in rubber compounds : synthesis, mixing and properties

Fatty diamine cationic surfactants are a recent entrant into the rubber mix formulation and have significant effects on the processing and properties of rubber compounds. Six new fatty diamine cationic surfactants, based on oleic acid, linoleic acid, rubber seed oil, 1,2-ethane diamine and 1,6-hexane diamine, were synthesised; and a simple method of their isolation and purification was developed. The effects of the experimental surfactants as combined activator and accelerator in rubber compounds were investigated. The rubber compounds containing them exhibited high activation energy of vulcanisation; and the surfactants functioned effectively as both activator and accelerator in SBR mixes. One of the new salts (l,2-ethane diamine dioleate, EDDO) and two commercial materials (EN444 and Duomeen TDO) were applied in standard NR and SBR mixes, and their effects on vulcanisation, rheological and vulcanisate properties investigated. Mixes containing the multi functional additives processed better, cured faster and had improved physical/mechanical properties over control mixes containing the same level of fillers. NRJEDDO mixes containing Si69 require a twostage mixing technique for further improvement in vulcanisate properties; similar SBR mixes were only slightly affected. Compounds were prepared in a Farrel (BR model) Banbury and a Francis Shaw KI Intermix internal mixers. Cure measurements were made on a Wallace Precision Cure Analyser and Monsanto (ODR) curemeter. Tensile properties were measured with a Hounsfield electronic tensometer (model SOOL). Filler dispersion was measured by SEM and "dark field" image analysis. Carbon black (N330)-filled NR compounds containing EDDO exhibited higher shear viscosity, higher activation energy of viscous flow and higher extrudate swell than a control compound which contained the same level of RAF black. Silica-filled mixes containing the MF A exhibited higher extrudate swell but lower shear viscosity than the control mixes containing the same level of silica filler. Melt flow measurements were carried out using a Davenport Capillary Rheometer and a Negretti TMS Rheometer. The effects of temperature and die length on shear viscosity, extrudate swell, melt flow behaviour index, n', and extrudate defonnation were investigated. The combined effect of MFA (EN444) level and mixing energy on properties of carbon black (N330)-filled natural rubber compounds was investigated by a factorial design experiment. No dependence of vulcanisation rates and elastic modulus on mixing energy was observed. Vulcanisation rates, mixing time and modulus (M300) showed a decrease with increase in MF A level. Other vulcanisate properties, including tensile strength, tear strength and j hardness, are optimised at MF A level of 2phr and above this level suffered significant deterioration.