Silica reinforced rubber

#Both natural rubber and alkadiene based synthetic rubbers are useless for many purposes unless reinforced. Many different reinforcing and cross-linking agents have been developed in the art for rubbers. Sulfur curing of rubber is a technology that has been discovered very early. Using carbon black for reinforcement purposes in rubber is a very widespread technology today. A third approach to the problem of reinforcing rubber is the incorporation of mineral fillers such as silica or certain clays.

#Silicas and clays are often used with organosilane additives whose function is to improve certain properties of the rubber.

#The various reinforcing agents for rubber are developed with respect to specific properties of the rubber reinforced by those compositions. One of the important properties of a reinforced rubber is its hysteresis, i.e. its tendency to convert mechanical energy into heat. This property is very significant for instance for the rubber components of automotive tires. Tires are subjected to very significant mechanical working by bending and stretching. Mechanical losses result in heat build-up which may be severe enough to cause failure of the tire. Even when no such failure occurs the dissipation of energy increases fuel consumption of the vehicle on which tires are mounted.

#Reinforcing promoter-modified silica was prepared by slowly adding 3 M HCl to 286 g of water glass (29.3% SiO.sub.2 by analysis) diluted with 1260 mL. of water until the pH of the solution reached 8.0. This precipitation reaction was conducted at 100.degree. C. with constant stirring. 3-Azidopropyltrimethoxysilane (3.2 g) was then added with continued stirring and the aqueous slurry maintained at 100.degree. C. for one hour. The precipitated silica was filtered, reslurried with water and the pH adjusted to 7.01. The silica was filtered, washed twice with isopropyl alcohol, and dried at 105.degree. C. under reduced pressure. A control sample of silica was prepared using the same procedure with the exception that no azide was added.

#The azide-modified silica and the control silica were evaluated in the standard formulation shown above. An amount of the azide promoter was compounded into the blend containing the control silica at a level which was equivalent to the amount present in the azide-modified silica. Evaluation data for these reinforced rubber samples are shown in Table II.

#TABLE II __________________________________________________________________________ Heat Tensile 300% Mooney Hard- CTAB Surface Buildup Strength, Modulus Viscosity ness, Run Area, m.sup.2 /g .DELTA.T, .degree.C. Resilience % MPa MPa ML-4 Shore A __________________________________________________________________________ a 90 22.2 74.5 19.7 15.7 43 64 b 88 18.1 80.3 13.9 12.3 38 62 __________________________________________________________________________ a) The azide promoter and nonmodified precipitated silica were added separately to the blend during compounding. b) Azidemodified silica prepared by adding azide to silica slurry following precipitation and prior to heat treatment was compounded into blend.