Ashley S. Hilton

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 effe...

Use of χ As a Function of Volume Fraction of Rubber to Determine Crosslink Density by Swelling

Abstract A technique is described allowing a relatively simple determination of χ as a function of vr from swelling in heptane. A good measure of the true νe of the cured elastomer at all values of...

Guayule extractables: Influence of extraction conditions on yield and composition

The yield and composition of the resin extracted from guayule will depend upon the choice of extraction medium. Water-soluble components, primarily polysaccharides, are entrained by solvent when the shrub is first deresinated with acetone (sequential extraction). Entrainment of water-soluble components does not occur when rubber and resin are both removed with a solvent such as the acetone-pentane azeotrope (simultaneous extraction). As a consequence, resin yield is substantially (68%) higher with sequential extraction. Resin from simultaneous extraction contains no detectable ash. While resin composition, including the levels of sesquiterpene esters, triterpene keto alcohols, and triglycerides, varies with the conditions of extraction, the total content of species bearing chemically reactive groups such as carbonyl shows little change (1.2–1.3 mmol g−1). This suggests that the water-soluble material in resin from sequential extraction contains components suitable for commercially valuable derivatization. Rubber yield and molecular weight are unaffected by the choice of extraction medium.

Allelopathic response of vegetables to guayule residue

Abstract Water leachates from guayule processing residues or residues mixed with peat moss or soil significantly delay germination onset and decrease percentage germination for the following crops: broccoli, cantaloupe, cauliflower, cotton, guayule, lettuce, pepper, and tomato. These effects can be ascribed to p-anisic acid present in leaf resin and a variety of substituted benzoic and cinnamic acids present as carboxylate salts in leaves and bagasse.

Model Reaction of Polysulfide with Olefin

A model polysulfide, t-butyl polysulfide (TBPS) and an olefin, cyclododecene (CDD), were used to study the reactivity of polysulfanes in silica filled rubbers. The TBPS has a similar sulfur rank and distribution as bis (3-triethoxysilylpropyl) tetrasulfide (TESPT) without the complication of reactivity of the triethoxysilyl group that would cause a loss of soluble components of the reactants and products by hydrolytic coupling. Thermal reaction between the polysulfide and olefin was investigated by following the TBPS loss in the CDD solution at 171 °C as a function of time. The loss of TBPS and the formation of reaction products during heating were followed, identified and quantified using HPLC. These include attachment of t-butyl sulfide group from the TBPS to CDD, coupling between CDD, and redistribution of the sulfur rank. It was found that after six minutes, less than 2 weight % of the sulfur in the TBPS was utilized to couple CDD molecules. Since these thermal conditions are more severe than what a rubber compound is normally subjected to, this sulfur coupling would not be expected to give a vulcanization problem during mixing. The model reaction was also followed in the presence of added peroxide or typical vulcanization ingredients. The strongest catalytic effect was seen with N-cyclohexyl-2-benzothiazolesulfenamide and zinc oxide.