Chakrit Sirisinha

Kevlar reinforcement of polyolefin-based thermoplastic elastomer

Composite systems of Kevlar, poly(p-phenylene terephthalamide), and Santoprene, a polyolefin-based thermoplastic elastomer, were studied. Kevlar pulp was used as-received in one system, and modified in the other. The as-received Kevlar pulp was found to reinforce Santoprene to a certain degree. It was found that with increasing amount of Kevlar in the composite, low-strain modulus and tensile strength increased, while the elongation at break decreased sharply. To improve mechanical properties of the composite, hydrolysis of Kevlar pulp surface was employed in conjunction with maleic anhydride-grafted-polypropylene (MA-g-PP), a reactive compatibiliser. It was found that the treated Kevlar pulp greatly improved the low-strain modulus, tensile strength, and elongation at break of the composite. Dynamic mechanical analysis showed that the storage modulus of the Kevlar/MA-g-PP/Santoprene composite was significantly higher than the as-received Kevlar composite. A slight increase in transition temperatures of polypropylene matrix was also observed. As a result of the fact that low-strain modulus and tensile strength of the composite were improved when hydrolysed Kevlar pulp and MA-g-PP were used, it is suggested that such a combination might have increased the interfacial adhesion of the fibre and the matrix, and effective fibre volume fraction, resulting in a better distribution of stress along the reinforcing fibre.

Improvement of interfacial adhesion of poly(m-phenylene isophthalamide) short fiber–thermoplastic elastomer (SEBS) composites by N-alkylation on fiber surface

A composite of short-fiber, poly(m-phenylene isophthalamide), and thermoplastic elastomer styrene (ethylene–butylene) styrene (SEBS), was investigated. The fiber surface was modified by N-alkylation (heptylation and dodecylation) to improve their compatibility with a less polar SEBS matrix. Observation of fiber-surface morphology by SEM revealed surface roughness after N-alkylation. Nearly complete coating of the polymer matrix on the fiber was observed on a fractured surface of the composite, which is evidence for the improvement of fiber–matrix adhesion. It was found that the modulus of the composites grew with increasing fiber loading to approximately the same extent for both unmodified and modified fiber composites. Tensile strength of the modified fiber composites was found to improve significantly over that of the unmodified fiber composite. This suggests that the presence of the alkyl group on the fiber surface is responsible for an improvement of interfacial adhesion.

Properties of Natural Rubber Reinforced by Carbon Black-based Hybrid Fillers

Properties of natural rubber (NR) filled with hybrid fillers were compared. Loading of the primary filler, carbon black (CB), was fixed whereas that of the secondary fillers, carbon nanotube (CNT) and conductive carbon black (CCB), was varied. The increase of secondary filler loading results in loss of elasticity but the increases of viscosity, vulcanization rate, cross-link density, hardness, modulus, thermal and electrical conductivities and tan δ. Obviously, CNT gives stronger effect than CCB. However, CCB gives improvement in tensile and tear strengths when added up to 3 phr whereas the addition of CNT shows no significant effect on the strengths.

Changes in morphology and properties of NR–NBR blends. Effect of viscosity ratio modified by liquid natural rubber and epoxidised liquid natural rubber

Abstract Changes in rheological properties, morphology, and oil resistance in NR–NBR blends by viscosity ratio have been investigated. In this study, the viscosity ratio was modified by mechanical mastication and addition of liquid natural rubber (LNR) and epoxidised liquid natural rubber (ELNR). The results reveal that as viscosity ratio increased from 0·5 to 1·0, Mooney viscosity of the blends increased, and then decreased sharply as the viscosity ratio further increased from 1·0 to 2·0. The addition of LNR and ELNR for plasticising NR and NBR, respectively, does not significantly affect cure properties of the blends. The phase size of the NR dispersed phase depends strongly on the viscosity ratio. The high viscosity of the matrix and/or the low viscosity of the dispersed phase promote breaking up of the dispersed phase. Unexpectedly, a decrease in size of the dispersed phase by the modification of viscosity ratio via the use of low molecular weight rubber (i.e. LNR and ELNR) did not result in an improvement in oil resistance.

Relationship among thermal ageing degradation, dynamic properties, cure systems, and antioxidants in natural rubber vulcanisates

The present work aims to study the relationship among the thermal ageing stability, dynamic properties, cure systems, and antioxidants in natural rubber (NR) vulcanisates. Thermal degradation behavior of NR vulcanisates has been investigated and correlated to the changes in cross-link density, tensile and dynamic mechanical properties. The results obtained show that thermal ageing properties of NR vulcanisates depend strongly on cross-link density, which changes during thermal oxidative ageing or the so-called postcuring effect. In addition, the increases in ageing temperature and time lead dominantly to the postcuring and linkages scission phenomena in vulcanisates cured with CV and EV systems, respectively. With increasing ageing temperature, the tensile strength shows sharp drop at ageing temperature higher than 70°C and 100°C for the specimens cured with CV and EV systems, respectively. The sharp drop of tensile strength of vulcanisates cured with CV system is attributed to the too high cross-link density, which is caused by the postcuring effect. In the case of the vulcanisates cured with EV system, the linkage scission causes the sharp drop of tensile strength. The addition of amine-based antioxidant appears to improve ageing properties. However, the excessive antioxidant reduces tensile properties via a decrease in cross-link density.

A study of relationships between state‐of‐mix, rheological properties, dynamic properties, and bound rubber content

The relationships between state-of-mix, rheologic properties, dynamic properties, and bound rubber content in N330 carbon black filled styrene butadiene rubber (SBR) were investigated. Shear viscosities measured from both Mooney viscometer and capillary rheometer decrease with increasing state-of-mix. By contrast, the stress relaxation determined from the Mooney relaxation viscometer (PR80) decreases with an increase in state-of-mix. In addition, glass transition temperature (Tg) is not strongly affected by a change in state-of-mix, whereas the magnitude of damping peak (tan δ) increases with state-of-mix. Bound rubber content appears to decrease as the state-of-mix increases. The concept of a change in an amount of immobilized rubber can be used to explain the results obtained.

Reinforcement of multiwalled carbon nanotube in nitrile rubber: in comparison with carbon black, conductive carbon black, and precipitated silica

The properties of nitrile rubber (NBR) reinforced by multiwalled carbon nanotube (MWCNT), conductive carbon black (CCB), carbon black (CB), and precipitated silica (PSi) were investigated via viscoelastic behavior, bound rubber content, electrical properties, cross-link density, and mechanical properties. The filler content was varied from 0 to 15 phr. MWCNT shows the greatest magnitude of reinforcement considered in terms of tensile strength, modulus, hardness, and abrasion resistance followed by CCB, CB, and PSi. The MWCNT filled system also exhibits extremely high levels of filler network and trapped rubber even at relatively low loading (5 phr) leading to high electrical properties and poor dynamic mechanical properties. Although CCB possesses the highest specific surface area, it gives lower level of filler network than MWCNT and also gives the highest elongation at break among all fillers. Both CB and PSi show comparable degree of reinforcement which is considerably lower than CCB and MWCNT.

Properties of Natural Rubber Filled with Ultra Fine Acrylate Rubber Powder

Properties of natural rubber (NR) filled with various loadings of ultra-fine vulcanized acrylate rubber powder (ACMP) were investigated. ACMP loading was varied from 0 to 20 phr and, after compounding, the compound properties were determined. Results reveal that increasing ACMP loading leads to improved processability, as evidenced by the reduction of both mixing energy and Mooney viscosity. ACMP, however, has negative effect on cure, that is, both scorch time and optimum cure time are prolonged while the state of cure is reduced with increasing ACMP loading. Due to the reinforcing effect of the fine ACMP particles, both modulus and hardness are found to increase consecutively with increasing ACMP loading. The tensile strength is also found to improve with increasing ACMP loading up to 10 phr. However, due to the cure retardation effect and the high thermoplastic nature, the presence of ACMP causes deterioration of elasticity. As ACMP is highly polar and fully saturated, the addition of ACMP enhances the resistance to oil and thermal aging of the NR vulcanizate. Significant improvement of thermal aging resistance is found when 10 phr or more of ACMP is added.

A STUDY OF CARBON BLACK DISTRIBUTION AND PROPERTIES IN BR/NBR BLENDS: ROLES OF COMMERCIAL HOMOGENIZER AND SLIPPING AGENT

Effects of commercial processing aids, Struktol NS60 (hydrocarbon resin) homogenizer and Struktol WB16 (a mixture of metal salt and a fatty acid amide) slipping agent on the distribution of carbon black and physical properties in BR/NBR blends have been investigated. It was found that Struktol 60NS and Struktol WB16 in blend systems migrate preferentially to BR phase due to the strong interaction between Struktol and BR phase, leading to a decrease in viscosity of BR phase and thus an increase in carbon black residing in BR phase. Mechanical properties of unfilled compounds are strongly affected by blend ratio and loading of processing aids. However, in the case of filled compounds, the influence of carbon black distribution in each phase of the blends override those blend ratio and additive loading effects.

Effects of Blend Ratio and SBR Type on Properties of Carbon Black-Filled and Silica-Filled SBR/BR Tire Tread Compounds

This work aimed at investigating the effects of blend ratio between styrene butadiene rubber (SBR) and butadiene rubber (BR) and SBR type (E-SBR and S-SBR) on properties of SBR/BR tire tread compounds. Influences of these parameters on properties of the tread compounds reinforced by 80 parts per hundred rubber (phr) of carbon black (CB) and silica were also compared. Results reveal that hardness, strengths, and wet grip efficiency were impaired whereas rolling resistance was improved with increasing BR proportion. Surprisingly, the presence of BR imparted poorer abrasion resistance in most systems, except for the CB-filled E-SBR system in which an enhanced abrasion resistance was observed. Obviously, S-SBR gave superior properties (tire performance) compared to E-SBR, particularly obvious in the silica-filled system. Compared with CB, silica gave comparable strengths, better wet grip efficiency, and lower rolling resistance. Carbon black, however, offered greater abrasion resistance than silica.