E. Sheng

Effects of ozone oxidation on carbon black surfaces

Surface effects of ozone treatment with a fluidized bed-type reactor on carbon black have been studied. It has been observed that the surface oxygen level is proportional to the total volume of ozone supplied per unit area of carbon black surface. The ozone treatment increases the acidity of the carbon black surface. A limiting pH value has been obtained at a surface oxygen concentration of around 6 at %. The surface oxygen introduced on the carbon black is most likely present as carboxylic acid groups as indicated by both high-resolution X-ray photoelectron spectroscopy and Fourier transform-infrared spectroscopy results. The ozone treatment of a carbon black decreases the tensile strength for a natural rubber (non-polar), but increases the tensile strength for a nitrile butadiene rubber (polar).

Effects of a multifunctional additive on bound rubber in carbon black and silica filled natural rubbers

The effects of a multifunctional additive (MFA), i.e. a diamine salt of a carboxylic acid, on the bound rubber in carbon black and silica filled natural rubber compounds in o-xylene, have been studied. For the carbon black filled compound, the bound rubber initially decreases with the MFA concentration and then does not change significantly above an MFA concentration which approximately corresponds to the monolayer surface coverage of the carbon black. This phenomenon has been explained in terms of the release of immobilised rubber within the carbon black agglomerates. Bound rubber measured at high temperatures indicated that the MFA did not improve the chemical interaction between the carbon black and the rubber in an unvulcanised rubber mix. The MFA has no pronounced effects on the bound rubber for silica. This may be caused by the combined effects of improved filler dispersion and silica-rubber interfacial interaction. The ozone oxidation of the carbon black significantly increases its surface oxygen concentration but has little effect on its specific surface area. The oxidation has been found to decrease the bound rubber.

Effects of the chromic acid etching on propylene polymer surfaces

The chromic acid etching of three propylene polymers has been investigated by contact angle measurement, X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared (ATR-IR), scanning electron microscopy (SEM), and an adhesion test. It has been shown that etching with such an oxidative acid has a much more significant effect on the receding contact angle than on the advancing contact angle of a test liquid. Significant water and diiodomethane contact angle hystereses were found and were attributed mainly to surface chemical heterogeneity caused by the acid etching. Surface roughness resulting from the etching may also account for the contact angle hystereses in some cases. The acid etching significantly increased the surface oxygen concentration of all three polymers. Chemical derivatisation with trifluoroacetic anhydride (TFAA) and hydrazine have indicated that the acid etching introduced C=O/COOH but there is no evidence of -OH groups on the polymer surfaces. The adhesion level of the p...

A quantitative XPS study of spherically shaped powders coated with an overlayer

Effects of the spherical shape of a small size (< 1 μm) powder and the thickness of a uniform overlayer on the surface elemental compositions measured by X-ray photoelectron spectroscopy (XPS) have been studied. The angular and radial dependence of the path length of photoelectrons generated within the substrate and the overlayer was taken into account in the calculation. The difference in photoelectron inelastic mean free path (IMFP) between the substrate and the overlayer was also considered in calculating the photoelectron intensity. Spherically shaped zinc oxide powder coated with a hydrocarbon overlayer was taken as an example.

The effect of carbon black particle size on multifunctional additive-carbon black interaction

The effects of carbon black particle size on multifunctional additive (MFA)-carbon black interaction have been studied. A monolayer coverage of the carbon black is found to correspond to the MFA level for optimum mechanical properties. This optimum MFA level was found to vary with the surface area of the carbon black used. A mechanism of adsorption has also been proposed to explain the mode of action of MFA at the rubber-filler interface.

Surface studies of polyethylene modified by flame treatment

Effects of flame treatment on polyethylene (PE) surfaces have been studied using contact-angle measurements, attenuated total reflection infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS), and an adhesion test. A significantly higher level of surface oxidation was induced by flame treatment on PE than on polypropylene (PP) under a given set of conditions, and unlike the case of PP the oxidation of PE is not confined to the XPS sampling depth on the polymer surface even for a mild flame treatment. High-energy resolution XPS has revealed several different functionalities on the surface and ATR-FTIR has clearly detected the peak at 1715 cm–1 which can be attributed to CO groups. Large contact-angle hysteresis was obtained and was attributed to chemical heterogeneity on the surface. Good adhesion with an epoxy adhesive has been obtained after flame treatment.

Studies of vapour-phase chemical derivatisation for XPS analysis using model polymers

Vapour-phase chemical derivatisation carried out on a vacuum adsorption rig has been investigated. Model polymers were used to evaluate the reactivity and selectivity of trifluoroacetic anhydride (TFAA) and hydrazine. Results have shown that TFAA is a good derivatising reagent for hydroxyl groups, while hydrazine is not suitable for carbonyl groups. Chemical derivatisation with TFAA of flame-treated polypropylene surfaces has shown that under various flame conditions an aoproximately constant proportion (ca. 20%) of the oxygen introduced by flame treatment was present as hydroxyl groups. Selective removal of OH groups by derivatisation has a large effect on the adhesion of a flame-treated polypropylene surface to a reactive polyurethane paint, evidence of chemical reaction at the interface.

An X-ray photoelectron spectroscopy study of flame treatment of polypropylene

Abstract X-ray photoelectron spectroscopy (XPS) has been used to study the effects of flame treatment on three propylene polymers, i.e. a homopolymer, an ethylene-propylene copolymer and a rubber-modified polypropylene. Angle-resolved XPS has shown an enrichment in oxygen concentration at the near surface for all three propylene polymers when treated with a mild flame. A depletion in oxygen has been shown at the near surface of the rubber-modified polypropylene treated with an intense flame. The use of simple surface composition models shows that the oxidation depth induced by a mild flame treatment is around 50 A, and that oxygen-containing functional groups may have reoriented or migrated a few angstroms away from the near surface of the rubber-modified polypropylene during the treatment with an intense flame.

Heat of immersion calorimetry studies of carbon blacks

Abstract Immersional heats of carbon blacks into n -heptane and water have been investigated. It has been found that the dispersioncomponent of the carbon black surface free energy ( ψ s d ) calculated from heat of immersion data slightly decreases with the surface oxygen concentration, which is suggested to be caused by the partial perturbation of the graphitic structure on the carbon black surface. ( ψ s d ) was also calculated from the nitrogen adsorption data and compared with that from heat of immersion data. The heat of immersion in water increases with the carbon black surface oxygen concentration. The ozone oxidation of the carbon black has been found to improve the filled-rubber properties for a polar rubber (nitrile butadiene rubber), but to decrease the properties for a non-polar rubber (natural rubber).

Flame Treatment and Surface Characterisation of Rubber-Modified Polypropylene

Abstract The flame treatment of a rubber-modified polypropylene has been studied using XPS, contact angle measurement, SEM, vapour-phase derivatisation, and a composite butt adhesion test. Optimum air-to-gas ratio and the distance from the inner cone tip to the polymer surface were found to be ∼ 11:1 and ∼ 0.5 cm, respectively. The lack of correspondence between contact angle and surface oxygen concentration was proposed to be due to the reorientation/migration of surface functional groups that had been incorporated during flame treatment. SEM shows changes in surface topography induced by intense flame treatment. Trifluoroacetic anhydride (TFAA) was found to derivatise-OH groups selectively by using model polymers. About 30% of the incorporated oxygen on flame-treated polypropylene surfaces was found to be present as-OH. Under most flame conditions studied, the interfacial adhesion with an epoxy adhesive or a polyurethane paint was found in excess of the polymers cohesive strength. The results obtained ...