Narongrit Sombatsompop

Dynamic mechanical properties and swelling behaviour of NR/reclaimed rubber blends

Abstract The dynamic mechanical properties and swelling behaviour of two natural rubber (NR) (STRVS60 and STR20CV) vulcanizates filled with different reclaimed rubber contents were examined with respect to loss tangent (tanδ) and the change in glass transition temperature. Tanδmax was found to shift to higher temperature, and the peak height reduced with increasing reclaimed rubber content. An increase in the overall width of the tanδ peaks was associated with the presence of styrene-butadiene rubber (SBR) in the reclaimed rubber. Tg was found to increase with reclaim content due to an increased cross-link density, and presence of carbon black in the reclaim. The change in cross-link density was more dependent on the vulcanizing recipe than the initial molar mass of the rubber. The equilibrium swelling of the NR vulcanizates was observed to reduce with increasing reclaimed rubber content due to the increases in cross-link density and the polymer–solvent interaction.

A modified method for calculating the Impact Factors of journals in ISI Journal Citation Reports: Polymer Science Category in 1997-2001

This article introduces a new modified method for calculating the impact factor of journals based on the current ISI practice in generating journal impact factor values. The impact factor value for a journal calculated by the proposed method, the so-called Cited Half-Life Impact Factor (CHAL) method, which is based on the ratio of the number of current year citations of articles from the previous X years to that of articles published in the previous X years, the X value being equal to the value of the cited half-life of the journal in the current year. Thirty-four journals in the Polymer Science Category from the ISI Subject Heading Categories were selected and examined. Total citations, impact factors and cited half-life of the 34 journals during the last five years (1997-2001) were retrieved from the ISI Journal Citation Reports and were used as the data source for the calculations in this work, the impact factor values from ISI and CHAL methods then being compared. The positions of the journals ranked by impact factors obtained from the ISI method were different from those from the CHAL method. It was concluded that the CHAL method was more suitable for calculating the impact factor of the journals than the existing ISI method.

Dynamic mechanical properties of SBR and EPDM vulcanisates filled with cryogenically pulverized flexible polyurethane foam particles

The dynamic mechanical properties of rubber vulcanisates filled with cryogenically pulverized polyurethane foam particles, used as a reinforcing filler, were investigated with respect to storage modulus (E′), loss modulus, and the variation of glass transition temperature. Two rubbers were using styrene–butadiene rubber (SBR) and ethylene–propylene copolymer (EPDM). The effects of filler concentration and filler characteristics (such as particle size and moisture content) were also monitored. It was found that the optimum dynamic mechanical properties of the compounds were obtained when introducing the PU particles of 40–50 parts per hundred (pph) rubber in the SBR and 30 pph in the EPDM, the properties being affected by the size of PU particles and moisture content.

Measurement of thermal conductivity of polymers using an improved Lee's Disc apparatus

Abstract An improved Lees Disc apparatus was designed and utilised to measure the thermal conductivity of various commercial polymers such as low-density polyethylene, polystyrene, polypropylene and poly(ether ether ketone) over a wide range of test temperatures from 40 to 400 °C. The measurements were carried out under vacuum such that convective heat losses were minimised. It was found that the thermal conductivity of semi-crystalline polymers, below melting temperature (Tm), was dependent on their density and degree of crystallinity and, above Tm, on the chain mobility and degradation effects. The thermal conductivity of the amorphous polymer was dependent on mobility of polymer chains below the glass transition temperature (Tg) and on the density above Tg The effect of density, degree of crystallinity and heating/cooling were also separately investigated and found to influence the thermal conductivity of the polymers used.

Mechanical Characterization of E-Chopped Strand Glass Fiber Reinforced Wood/PVC Composites

E-chopped strand glass fibers with different initial fiber lengths and contents are introduced into wood-polyvinyl chloride (PVC) composites having the wood content of 50 parts per hundred (phr). The initial fiber lengths and glass fiber contents varied from 3, 6, and 12 mm, and 10, 20, and 30 phr, respectively, and the mechanical and morphological properties of the wood/PVC composites are then monitored. The results suggest that the tensile and flexural moduli and strengths of the wood/PVC composites increase with increasing glass fiber contents. The tensile and flexural moduli and strengths of the WPVC composites at 10—20 phr glass fiber loadings are more dependent on carbonyl (C=O) content on the fiber surface, but those at 30 phr glass fiber loadings are influenced by the average final length of glass fibers. The impact strength of the wood/PVC composites progressively increase with increasing glass fiber content. The elongation at break is found to slightly decrease with increasing glass fiber content due to increases in fiber-end effects and stress concentrations in the wood/PVC composites. The effect of initial fiber length on the degree of composite shrinkage is very small, the values ranging from 0.3 to 1.3%.

ANALYSIS OF CURE CHARACTERISTICS ON CROSS-LINK DENSITY AND TYPE, AND VISCOELASTIC PROPERTIES OF NATURAL RUBBER

Abstract The interrelation of degree and type of cross-linking and viscoelastic properties of sulfur-cured natural rubber (NR) vulcanizates was investigated by altering accelerator concentration, cure time, and cure temperature. Constants C 1 and C 2 from the Mooney-Rivlin equation were given via stress-strain measurement to estimate the cross-link density, cross link type, and effectiveness of forming cross-links, coupled with a thiol-amine chemical probe technique. The dynamic mechanical properties, such as storage modulus, damping behavior, and variation of the glass transition temperature, were found to be not necessarily dependent on the overall cross-link density but were a function of the percentage proportion of cross-link types generated in the NR compounds; these were varied by the compounding and curing conditions. The effects were explained based on desulfuration and decomposition reactions of the cross-links; these are also associated with additional heat built up during vulcanization.

Investigation of Swelling Behavior of NR Vulcanisates

Abstract A relationship between swelling behavior and the Mooney-Rivlin constant (C 2), which has been suggested as being associated with intermolecular forces between cross-linked polymer chains and flexibility of the NR network structure, was observed under a constrained swelling condition of 100% elongation (by length). It was found that determination of the C 2 value can be used to estimate the degree of swelling of the NR vulcanisates under equilibrium condition when different cross-link characteristics were involved and compared. The swelling results from the use of the C 2 value were compared to those from a sorption method—the results from two methods under the equilibrium state being in good agreement. The degree of swelling of the NR vulcanisates with a similar cross-link density was examined in detail by varying cross-link type and structure. In addition, the effects of molecular size and shape of swelling solvents and the molar mass of the rubber on the degree of swelling were monitored.

An evaluation of research performance for different subject categories using Impact Factor Point Average (IFPA) index: Thailand case study

SummaryThe research performance of Thai researchers in various subject categories was evaluated using a new mathematical index entitled “Impact Factor Point Average” (IFPA), by considering the number of published papers in journals listed in the Science Citation Index (SCI) database held by the Institute for Scientific Information (ISI) for the years 1998-2002, and the results compared with the direct publication number (PN) and publication credit (PC) methods. The results suggested that the PN and PC indicators cannot be used for comparison between fields or countries because of the strong field-dependence. The IFPA index, based on a normalization of differences in impact factors, rankings, and number of journal titles in different subject categories, was found to be simple and could be used with equality for accurate assessment of the quality of research work in different subject categories. The results of research performance were found to be dependent on the method used for the evaluations. All evaluation methods indicated that Clinical Medicine was ranked first in terms of the research performance of Thai scholars listed in the SCI database, but exhibited the lowest improvement of performance. Chemistry was shown to be the most improved subject category.

Effects of chemical blowing agents on swelling properties of expanded elastomers

Two commercial chemical blowing agents, azodicarbonamide (ADC) and oxybisenzenesulphonylhydrazide (OBSH), were used alone and in blends for expanded natural rubber vulcanisates. The expanded rubber vulcanisates were characterised with respect to the apparent foam density, degree of crosslinking, tensile properties and swelling behaviour. For a given blowing agent, the apparent foam density and crosslink density were found to change with blowing agent content. The swelling behaviour greatly changed with OBSH content, but was unaffected by ADC content. The OBSH blowing agent seemed to generate more voids in the vulcanisates as compared to the ADC blowing agent and thus increased swelling. The swelling ratio of the NR vulcanisates having blended blowing agents tended to be more influenced by OBSH than ADC blowing agents.

Dynamic Rebound Behavior of Silica/Natural Rubber Composites: Fly Ash Particles and Precipitated Silica

This article investigated the elastic response of natural rubber (NR) compounds filled with silica from fly ash particles (FASi) and commercial precipitated silica (PSi), through a dynamic rebound test. The effects of silica content and initial drop‐height on the height and number of rebounds, dynamic stiffness, and the energy loss were of interest. The results suggested that the unfilled NR vulcanizates exhibited a greater elastic response than the FASi and PSi‐filled vulcanized composites. For given silica contents, the NR compounds with FASi had better elastic response than those with PSi, where the elastic response decreased with an increase in silica content. The greater the silica contents, the higher the dynamic stiffness of the composites. The initial drop‐height had no effects on the elastic response change for the unfilled NR compound, but resulted in an increase in the energy loss for the silica‐filled NR composites. The differences in the elastic responses for the NR compounds filled with silica from FASi and PSi were associated with the differences in crosslink density and the filler–filler interaction influenced by content of bis(3‐triethoxysilylpropyl) tetrasulfane (designated as Si69) used.