Shinyoung Kaang

Electrical properties of polyaniline/sulfonated polycarbonate blends

Abstract A conducting composite using polyaniline (PANI) as the conducting polymer and polycarbonate (PC) as a matrix was prepared by a blending method. Chloroform was used as a solvent in the blending. The PANI was protonated using camphor sulfonic acid (CSA) or a dodecylbenzene sulfonic acid (DBSA) such as alkylbenzenesulfonic acid. A sulfonic group was introduced into the structure of the PC in order to enhance the coulombic interaction between each phase of the composite. The effect of ionic groups in sulfonated PC (SPC) was monitored using measurements of both the mechanical and thermal properties. Using the presence of protonating agents and the amount of PANI complex, both the electrical conductivity and morphology were measured. Electrical conductivity increased to 7.5 S/cm with the amount of PANI complex protonated with DBSA having a long alkyl chain.

Melt free‐radical grafting of hindered phenol antioxidant onto polyethylene

A monomeric antioxidant (3) was prepared by reacting 3,5-di-tert-butyl-4-hydroxybenzyl alcohol (1) with N-[4-(chlorocarbonyl) phenyl] maleimide (2). This reactive antioxidant was grafted onto polyethylene (PE) by melt processing with free-radical initiators in a mini-max molder. The IR spectra of the grafted PE showed that the monomeric antioxidant was introduced onto the PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Also, the extent of crosslinking was indicated by the gel content. Grafting occurred in the following order: dicumyl peroxide (DCP) > benzoyl peroxide > 2,2′-azobisisobutyronitrile. The influences of the DCP concentration and monomeric antioxidant on the extent of grafting were studied. The effects of the reaction time and temperature were also determined.

Some Physical Characteristics of Double-Networked Natural Rubber

ABSTRACT: A double-networked natural rubber (DNNR) was prepared by a ‘‘two-stepcrosslinking’’ method, in which the crosslinking was achieved while the natural rubberwas in a stretched condition. The swelling behavior, tensile properties, creep, recovery,and permanent set were investigated. Generally, the observed mechanical propertiesof DNNR, such as the Young’s modulus, tensile strength, toughness, creep, recovery,and permanent set, were considerably improved as the residual extension was in-creased. They were, however, rather inferior to those of a single-networked naturalrubber and showed a minimum at a lower residual extension of about 1.55. The degreeof crosslinking and elongation at break were not greatly affected by the residual exten-sion. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 917–924, 1997 Key words: natural rubber; double networks; swelling; tensile property; creep andrecovery INTRODUCTION having different strain conditions. Based on thetheory, the degree of permanent set can be de-When a rubbery material is crosslinked in a state scribed quantitatively by using only two factors:of macroscopically zero strain, i.e., in the typical (1) the relative ratio of the number of the twomanner of the rubber industries,

Enhanced adhesion of steel filaments to rubber via plasma etching and plasma-polymerized coatings

Zinc-plated steel filaments were coated with RF plasma polymers of acetylene or butadiene in order to enhance adhesion to rubber compounds. Plasma polymerization was carried out as a function of the plasma power, deposition time, and gas pressure. In order to maximize adhesion, argon plasma etching was performed and carrier gases such as argon, nitrogen, and oxygen were used. Plasma polymer coatings were characterized by FT-IR, Alpha-Step, and a dynamic contact angle analyzer. The adhesion of steel filaments was evaluated via a tire cord adhesion test (TCAT). The best results were obtained from a combined process involving argon etching (90 W, 10 min, 30 mTorr) and acetylene plasma polymer coating (10 W, 30 s, 30 mTorr) with argon carrier gas (25/5, acetylene/argon). These samples exhibited a pull-out force of 285 N, which is comparable to that from the brass-plated steel filament (290 N).

Fatigue crack growth of double-networked natural rubber

Tensile stress—strain behaviour, hysteresis and crack propagation resistance were investigated for various double-networked natural rubbers, prepared using a two-step crosslinking technique. Partially cured rubber is strained and then further crosslinked. They were compared with those of a conventional network (single network). The double-networked natural rubbers were found to show a significant improvement in tensile modulus, tensile strength at break, and strain energy density in the direction parallel to the cure stretching direction. The resistance to crack propagation across the residual strain direction was also greatly enhanced. Moreover, no significant deterioration in crack resistance was observed, even in the direction parallel to the residual strain direction. The morphology of the torn surfaces of the double networks generally resembled that of the single networks, except the cross-hatched pattern was somewhat developed and slanted to the residual strain direction.

Effects of Blend Composition and Mixing Method on Mechanical and Morphological Properties of Zinc Dimethacrylate-Reinforced Acrylonitrile-Butadiene Copolymer Nanocomposites

Abstract Two kinds of rubber composites were prepared by melt mixing of acrylonitrile-butadiene rubber (NBR) with zinc dimethacrylate (ZMA). In one system ZMA was added in the form of powder; and, in another system, the ZMA was prepared by in-situ reaction of ZnO and methacrylic acid (MA) during melt mixing. Both systems showed similar tensile strength, however the elongation at break, tear strength, and fatigue resistance were higher for the in-situ prepared system. The composite prepared by direct addition of ZMA powder showed a corresponding peak for ZMA particles in the wide angle x-ray diffraction (WAXD) spectra, indicating the existence of two phases, while there was no such peak for the in-situ prepared blend. The comparison of cross-link densities of these two blends showed a higher proportion of total cross-link density (calculated from covalent and ionic cross-linking) for the blend prepared from the direct addition method. The morphology of torn surfaces based on field-emission scanning electron microscopy (FE-SEM), showed a different nature of fracture behavior in these blends. The mean particle size and distribution of ZMA in NBR matrix as measured by atomic force microscopy (AFM) and small angle x-ray scattering (SAXS) indicated the formation of nanostructured domains of ZMA of particle size in the range of 10–40 nm with more uniform distribution in the in-situ blends.

Specific heats of rubber compounds

The specific heats of rubber compounds are very important not only for the thermodynamic calculations in various rubber processings; mixing, extrusion, calen- dering, and vulcanization, etc., but also for the service life of the final products under repeated stressing conditions. In this study, the specific heats of various compounding ingredients and their compounds for tires were determined using a differential scan- ning calorimeter (DSC) in the temperature range from 45 to 95°C. The determined specific heats, Cp, were compared with the previous published results for natural rubber (NR), styrene- butadiene rubber (SBR), polybutadiene rubber (BR), and isopre- ne-isobutyl rubber (IIR). The effects of carbon black loading and vulcanization on the specific heats were investigated. The measured specific heats of the compounds were compared with the calculated values based on the fractional summation of the specific heat of each compounding ingredient.

An improved test method of abrasion of rubber in a blade abrader

Abstract An improved laboratory test method for the abrasion of rubber is suggested based on a modified version of the previous blade abraders. In the modified apparatus, a constant normal load, N , is applied to the knife blade, which is mounted and fixed over a frictionless linear slider by means of a pulley and string system such that the knife blade can press the flat surface of a rotating rubber disk, and the frictional torque, M , is monitored and measured during each measurement. A precise potentiometer is used to measure the displacement, d , of the knife axis, and the measured values are carefully examined to assess whether they can be used as an alternative way of determining the rate of wear of rubber. The rates of wear from the newly designed abrader were found to be in good agreement with those of the previous results when they were compared in terms of frictional work input, W f , for some selected rubber compounds: unfilled polybutadiene (UBR), unfilled natural rubber (UNR), and filled polybutadiene (FBR). It was also found that the direct measurement of the displacement of knife axis can be used as an alternative test method of the abrasion of rubber, instead of the conventional way of measuring the weight loss.

Rheological and Mechanical Properties of Styrene-Butadiene Rubber Compounds

The cure behavior, rheological property, and tensile strength of styrene-butadiene rubber (SBR) compounds containing different sizes of rubber powder vulcanizates (RPV) were investigated by varying the loading from 0 to 40 phr. Six different sizes of RPV were selected to see the effect of particle size. A typical reclaimed rubber powder was also used to see the reclaiming effect. The average particle size of the RPVs ranged from 70 to 2,000 μm. In the cure characteristics, as the powder loading was increased, the maximum torque, scorch time, and optimum cure time decreased, while minimum torque increased. At lower shear stresses (or shear strains) the viscosity of the rubber compounds increased noticeably with the addition of RPV. This increase was diminished at higher shear stresses. However, the die swell decreased when RPV was added. With increased powder loading the tensile strength decreased dramatically at lower powder concentrations, ∼ 10 phr, and then the rate of this decrease became slower at higher concentrations. A power-law relation was observed between the tensile strength reduction and the particle size of the RPV.

The Effect of Surface Area of Silicas on Their Reinforcing Performance to Styrene-butadiene Rubber Compounds

The effect of the surface area of silicas on their reinforcing performance to styrene-butadiene rubber (SBR) compounds was systematically investigated. The feasibility of the Brunauer-Emmett-Teller surface area (SBET) as a parameter representing the characteristics of the silicas was discussed compared to the mesopore volume, c value, oil absorption, and uptake of silane. The increase in SBET of silicas caused a considerable increase in Mooney viscosity, minimum torque, and hysteresis loss of the silica-filled SBR compounds, while significantly enhancing their abrasion property. These changes were explained by the attrition between the hydrophilic silica surface and the hydrophobic rubber chains. As expected, the change in SBET did not induce any remarkable changes in the cure, processing, tensile, and dynamic properties of the silicafilled SBR compounds because the crosslinking density of the rubber chains mainly determined these properties.