Larry R. Evans

Use of nonblack fillers in tire compounds

Abstract A variety of nonblack fillers are used in the rubber components of tires. Calcium carbonate, clay, precipitated silica, talc and titanium dioxide are used in white sidewall compounds to impart desired physical properties and appearance. Precipitated silica can be used in black sidewall compounds, including nonstaining EPDM black sidewalls, to significantly improve tear strength, cut-growth resistance and resistance to ozone aging. Precipitated silica is used extensively in wire coat compounds in conjunction with resorcinol and methylene donating resins, and can be used with organocobalt salts to improve adhesive properties, tear strength and cut-growth resistance. Calcium carbonate, clay, mica and talc are found in innerliner compounds, and precipitated silica can be used. Precipitated silica is used in the treads of off-the-road tires such as earthmover tires, in order to improve tear strength and cut-growth resistance. Clay and talc can be used in tire treads. Precipitated silica is also used i...

Polar copolymer–surface-modified precipitated silica

To improve the performance of rubber compounds using precipitated silica as a reinforcing filler, the silica surface was directly modified by (1) adsorption of a surfactant onto the surface, (2) adsolubilization of an organic monomer, (3) in situ polymerization of the monomer in the surfactant bilayer, and (4) partial surfactant removal. Silica was thus modified using copolymers of isoprene or 1,3-butadiene with vinyl acetate, acrylonitrile, 4-methoxystyrene, 4-chlorostyrene, and methyl methacrylate on the silica surface. 4-Methoxystyrene/butadiene modification afforded the most promising candidate based on evaluation in a silica-filled, natural/styrene-butadiene rubber shoe sole compound that also has been used as a model tire compound. Physical testing showed that cure times were decreased, and break strength, tear energy, elongation to break, and cut growth resistance were increased. Thus, surface modification of silica by the in situ polymerization of organic monomers has been shown to be a flexible process capable of producing unique materials useful in improving rubber cure properties and the cured compound physical properties.

Mechanism by Which Precipitated Silica Improves Brass-Coated Wire-To-Natural Rubber Adhesion

Quantitative determination of elements in the interfacial growth layer formed on brass-coated wire when reacted in sualene suspensions containing carbon black and curatives, with and without precipitated silica and an organocobalt adhesive, was accomplished by using direct surface characterisation techniques: Sacnning Electron Microscopy with Energy Dispersive Analysis of X-rays(SEM-EDX), Auger Electron Spectroscopy(AES), X-ray photoelectron Spectroscopy(XPS) and Proton induced X-ray Emission(PIXE) spectroscopy. The effects on elemental changes in the interfacial growth layer upon addition of silica and/or cobalt neodecanoate to the squalene suspensions were statistically analysed. Since the mechanism for silica improvement of brass-coated wire-to-rubber adhesion was previously shown not to be a simple effect of improving rubber physical properties, a chemical mechanism is proposed involving silica to reduce the thickness of the interfacial growth layer and to change the relative concentration of compounds formed in the interfacial growth layer

Microencapsulated antidegradants for extending rubber lifetime

Abstract Microcapsules containing rubber antidegradants were formed in a spray-drying process. Studies were carried out to select the proper wall material based on the processing properties, migration rate of the antidegradant through the capsule wall, thickness of the capsule wall, and overall capsule diameter. The resulting capsules were incorporated into a rubber article, providing a reservoir of antidegradant during the exposure lifetime. Testing of the rubber compounds with microcapsules having diameters less than 50 µm containing AN-(l,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine in a matrix of cellulose acetate showed a significant increase in the crack-free lifetime of the rubber when flexed in exposure to ozone.

Laser Mass Spectral Investigations of Rubber Compound Surface Species

Abstract Laser desorption mass spectrometry has proven a uniquely useful technique for the direct characterization of rubber-compound surface species. Mass spectra were obtained for intact molecular ions (M+) of organic chemical rubber additives such as the aromatic processing oil, and the aromatic antiozonant and antioxidants incorporated to protect the rubber. Molecular-weight information from the molecular ions and structural information from the fragmentation ions could be obtained without interference from the fragmentation peaks of the rubber backbone. Rubber compounding ingredients were also characterized by LDMS techniques. Differences in the structure of two carbon blacks were apparent, based upon the relative intensities of the various peaks present such as the significantly higher m/z 26 peak thought to be due to CN− compared to the m/z 24 peak thought to be due to C2−, and the peaks resulting from the presence of hydrogen atom(s) on the carbon clusters for the high NSA and DBPA black. Laser an...

Silica, Amorphous Silica

Amorphous silica, a three-dimensional, inorganic polymeric silicon dioxide, SiO2, does not have a crystalline structure as defined by the absence of definitive lines in x-ray diffraction measurements. Amorphous silica can be naturally occurring or synthetic, and either anhydrous or surface-hydrated with silanol groups. Synthetic amorphous silica can be divided into microamorphous silica and vitreous silica (glass) made by fusing quartz at temperatures greater than approximately 1700°C. A discussion of microamorphous silica is presented, including colloidal silica, ie, sol or stable dispersion of discrete particles; silicas gelled or precipitated from solution; and pyrogenic and fused silica. Amorphous silica is characterized by chemical composition, physical properties, and characteristics of its particles, with exact analytical procedures depending on the type and application. Various methods to prepare and characterize each type of amorphous silica, commercial applications including principal global manufacturers, and health and safety issues are discussed. Keywords: Silicon dioxide; Characterization; Silica sols; Colloidal silica; Silica gel; Precipitated silica; Pyrogenic silica; Fused silica; Naturally occurring amorphous silica; Diatomite

Direct Characterization of Rubber-Surface Chemistry Using Laser Desorption Mass Spectrometry

Abstract Laser desorption mass spectrometry (LDMS) was used to directly characterize the surfaces of vulcanized natural-rubber compounds with or without an antiozonant (AOz) and an antioxidant mixture. Molecular ions of five intact molecules were observed on the rubber surface using a single laser pulse. The molecular ions represent the AOz, the three components comprising the antioxidant mixture, and a production impurity in the AOz. The surface chemistry of the AOz, N-(1,3-dimethylbutyl)-.N′-phenyl-para-phenylenediamine (HPPD), was explored in order to investigate the mechanism of rubber-surface aging and protection. Two sets of samples were prepared: ozone-aged HPPD films that had been deposited on a glass plate and ozone-aged cured rubber strips containing HPPD. Rubber samples were continually stretched to 25% elongation and relaxed during exposure to ozone. The mechanisms of ozone reaction with HPPD on glass and on stretched rubber are similar, since many reaction products were identical based on the...