Mooney Viscosity Stability and Polymer Filler Interactions in Silica Filled Rubbers

Abstract

The change in Mooney viscosity (ML1+4) with aging was followed for silica filled compounds containing various silanes and polar additives. Several mechanisms for the aging stability are postulated and evaluated through experimentation. The type of silane or polar additive used can cause the ML1+4 to increase or even decrease during aging. When bis(triethoxy silanes) are used in silica filled rubbers, the ML1+4 growth during aging is caused by hydrolysis. Silica-silica bridging was found to be responsible for the ML1+4 growth in rubber compounds containing a more thermally stable polysulfide or a sulfur-free bis(triethoxy silane). When the bis(triethoxy silane) is bis(3-triethoxysilylpropyl) tetrasulfide (TESPT), a fraction of TESPT is attached to the unsaturated rubber to give polymer-silica attachments. These attachments further enhance the hydrolytic ML1+4 increase during aging. Chemical coating of the silica with a monofunctional silane or a physical coating with a trialkyl amine compound effectively stops the ML1+4 increase upon aging. The prevention of ML1+4 growth is so efficient that a reduction in the ML1+4 can be realized by absorption of ambient moisture. The extent of ML1+4 reduction caused by moisture depends on the degree of hydrophobation of the coated silicas. Hydrolytic stability was also studied with an amine or a sugar fatty acid ester that formed either strong or weak polar associations to the silica.

Silane grafted natural rubber and its compatibilization effect on silica-reinforced rubber tire compounds

“…Mooney viscosity, bound rubber content and Payne effect For filled rubber compounds, the viscosity increment depends on several factors, to include mastication time [29], mixing time [30], filler types [31,32], filler contents [32,33], compatibilizer or coupling [36]. The change of compound viscosity is strongly influenced by the levels of filler-filler and filler-rubber interactions which consequently have an influence on the final properties of the filled rubber.…”

Reduction of volatile organic compound emission. II. Use of alkoxy‐modified silsesquioxane for compounding silica‐filled rubbers

“…The detailed procedure to measure the latent alcohol in rubbers was described in previous publications. 9,18 RESULTS AND DISCUSSIONS Processing assessment on using AMS for compounding silica-filled rubbers For the first evaluation of AMS as a silica-dispersing, silica-shielding, or silica-processing agent in an all silica formulation, the first three stocks (1, 2, and 3) of Table V were prepared from which a list of selected critical properties from the uncured stocks were tabulated in Table VI. An effective silica dispersion, shielding, or processing agent should be able to interact with silica filler during preparation of rubber compounds such that workable rubber slabs are produced for extrusion and tire formation.…”

“…9 The test was performed using a large rotor at 130 C for the filled rubbers and 100 C for gum rubbers. The sample was preheated at the test temperature for 1 min before the rotor started and then the Mooney viscosity (ML 4 ) was recorded as the torque after the rotor had rotated for 4 min at 2 rpm (average shear rate about 1.6 s…”

“…An effective silica dispersion, shielding, or processing agent should be able to interact with silica filler during preparation of rubber compounds such that workable rubber slabs are produced for extrusion and tire formation. Either a bifunctional polysulfane of TESPT and TESPD [2][3][4][5][6] or a monofunctional silane of OTES, 9,18,19 or the physical processing aids such as sugar fatty acid esters 20,21 are capable of coating the silica aggregates during the mixing stage that effectively reduces the compound Mooney viscosity (ML 4 ) for processing. Comparisons of these stocks show that the AMS (stock 3) and the OTES (stock 2) containing stocks had similar ML 4 values that were significantly lower than stock 1, which contained no silica-dispersing or shielding agent.…”

“…Such a delayed reaction leads to the entrapment of the alcohol byproducts as blisters or tread porosity and results in an undesirable increase in the compound viscosity upon storage. 9 As a result of the delayed reaction, the speed of processing, mixing, and tread extrusion will be reduced, and thus significantly decrease the plant productivity. The use of alkoxymodified silsesquioxane (AMS) compounds will be shown to alleviate the above issues.…”