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Cure characteristics and tear properties of epoxidized natural rubber (ENR-33) and natural rubber were studied. Three types of accelerators, namely 2-mercaptobenzothiazole (MBT), 2-morpholinothiobenzothiazole (MBS) and N-tert-butyl-2-benzothiazyl sulphenamide (TBBS) were used in this work. The conventional valcanization (CV) system was used. Cure characteristics were determined using a Monsanto Oscillating Disk Rheometer (ODR 2000) at 150ºC. Also, a systematic study of tear strength was carried out before and after ageing at 70ºC for 72 h. A Hounsfield tensometer (Model H10KS) operating at 500 mm/min was used to determine the tear strength using standard angle test pieces. The results indicated that scorch time and cure time of natural rubber are greater than those of ENR-33 compounds. However, the contrary was observed for the minimum and maximum torques and the torque differences. The observation is attributed to the activation of a double bond by the adjacent epoxide group in ENR-33. Furthermore, we found that the change in tear strength of aged ENR sample was greater than that of NR vulcanizates.

Para rubber wood particleboard (PB) was prepared using NR based adhesives and hot pressing processes. Two types of NR based adhesives were used; epoxidized natural rubber (ENR) and unmodified NR. The ENR latex was prepared using in situ performic epoxidation. Molecular weight of the ENR molecules was then reduced by incorporating of a reducing agent; sodium nitrite solution. A chain scission reaction and epoxidation simultaneous occurred via a chain-scission parallel epoxidation mechanism. Sulphur and multifunctional amine (i.e., hexamethoxymethylmelamine) curing systems were used to cure the adhesives. It was found that the hexamethoxymethylmelamine gave the PB with higher tensile strength than that of the sulphur vulcanization system. Furthermore, the tensile strength increased with increasing concentration of citric acid in the compounding formulation. Adhesion of the ENR adhesive with Parawood sawdust was observed to imporve by reducing molecular weight of the ENR molecules. That is, the highest tensile strength of the PB was observed for the ENR adhesive with the lowest [bar.M.sub.n] (i.e., 1.10 x [10.sup.5]). This may be attributed to the adhesive with lower molecular weight exhibited greater ability to wet or cover the wood particle surfaces. As a consequence, greater chemical interaction between the adhesive and the wood particles was observed. POLYM. ENG. SCI., 47:421-428, 2007. © 2007 Society of Plastics Engineers, INTRODUCTION With an increasing environmental concern and forest protection, a search is on for alternative sources of wood materials. Particleboard (PB) and medium-density fiberboard are practically inexpensive alternatives to solid [...]

Some properties of carbon nanotube (CNT) filled natural rubber (NR) composites were improved by adding an ionic liquid (IL), 1-butyl-3-methyl imidazolium bis (trifluoromethylsulphonyl)mide (BMI). In this work, the CNT and IL (CNT-IL) were mixed with NR by latex mixing method. Cure characteristics, thermo-mechanical properties, Payne effect, electrical conductivity and thermal stability were investigated. It was found that IL (BMI) accelerated vulcanization reactions and reduced scorch time. In addition, Fourier Transform Infrared (FTIR) results confirmed the role of IL in NR composites along with the reaction between CNT and NR molecules. The temperature scanning stress relaxation (TSSR) measurement was used to assess thermo-mechanical properties, and a relaxation peak of IL was found due to interactions of cations and anions in IL (BMI). Furthermore, the Payne effect was used to qualitatively analyze the roles of IL and CNT in three-dimensional CNT networks in the NR matrix. It was found that CNT dispersion was finer in the NR/CNT composites with IL. Furthermore, the NR/CNT-IL composite had higher electrical conductivity and lower percolation threshold concentration than the NR/CNT composite. [ABSTRACT FROM AUTHOR]

Dynamically cured 60/40 epoxidized natural rubber (ENR)/polyamide 12 (PA-12) and unmodified natural rubber (NR)/PA-12 blends with different types of curing systems (i.e. sulfur- and peroxide-cured systems) were prepared. It was found that mixing torque, shear viscosity, tensile strength, hardness, stress relaxation, thermal, and oil resistance properties of the ENR/PA-12 blends were higher than those of the NR/PA-12 blends. This is attributed to the chemical interaction between polar functional groups in ENR and PA-12 molecules which caused the formation of ENR-grafted PA-12. Smaller vulcanized rubber domains dispersed in the PA-12 matrix was observed in the dynamically sulfur-cured ENR/PA-12 blends. This is attributed to higher shear and elongational viscosities during mixing operation at high temperature. However, the peroxide-cured blends exhibited higher relaxation property, oil resistance, and cross-link density than those of the sulfur-cured blends due to strong reversion effect observed in the sulfur-cured system. [ABSTRACT FROM AUTHOR]

Epoxidized natural rubber (ENR) and thermoplastic polyurethane (TPU) blends were prepared by simple blend and dynamic vulcanization. The main objective was to prepare a low-hardness TPU material with good damping and elastic and mechanical properties. It was found that the incorporation of ENR into the blend shows a reduction in Young's modulus, hardness (i.e. <70 Shore A), damping properties (i.e. tan δ < 0.3), and tension set (i.e. <20%) compared with the pure TPU. This indicates the formation of softer TPU materials with superior damping and elastomeric properties. However, incorporation of ENR sacrificed mechanical properties in terms of tensile strength and elongation at break, but these still remain in the range of applicability for industrial uses. It was also found that dynamic vulcanization caused enhancement of mechanical properties, relaxation, damping, rheological properties, and elasticity of the blends. Temperature scanning stress relaxation measurements revealed an improvement in stress relaxation properties and thermal resistance of the dynamically cured ENR/TPU blend. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Thermoplastic natural rubbers based on reactive blending of maleated natural rubber/ethylene-vinyl acetate copolymer and epoxidized natural rubber/ethylene-vinyl acetate copolymer blends were prepared via a simple blend technique. Phenolic-modified ethylene-vinyl acetate copolymer was used as a blend compatibilizer for the unmodified natural rubber, air dried sheet/ethylene-vinyl acetate copolymer blend. Dynamic, rheological, morphological, thermal, and mechanical properties of the blends were investigated. It was found that the epoxidized natural rubber/ethylene-vinyl acetate copolymer blend showed higher tensile modulus, tension set properties as well as smallest dispersion of the co-continuous phase than those of the maleated natural rubber/ethylene-vinyl acetate copolymer and air dried sheet/ethylene-vinyl acetate copolymer blends, respectively. Furthermore, the air dried sheet/ethylene-vinyl acetate copolymer and epoxidized natural rubber/ethylene-vinyl acetate copolymer blends exhibited similar values of tensile strength, while the maleated natural rubber/ethylene-vinyl acetate copolymer blend gave the lowest value. The air dried sheet/ethylene-vinyl acetate copolymer blend gave higher extensibility than that of the epoxidized natural rubber/ethylene-vinyl acetate copolymer and maleated natural rubber/ethylene-vinyl acetate copolymer blends. This is attributed to the molecular characteristics in terms of molecular mass and level of interaction between the chains. Furthermore, the blends showed higher thermal stability than pure rubber because of high heat resistance of the ethylene-vinyl acetate copolymer component. The epoxidized natural rubber/ethylene-vinyl acetate copolymer blend exhibited the highest heat stability because of higher chemical interaction between molecules and between phases. Also, the degree of crystallinity in the ethylene-vinyl acetate copolymer phase in the blends was lower than that of the pure ethylene-vinyl acetate copolymer. Among the various types of blends, the epoxidized natural rubber/ethylene-vinyl acetate copolymer blend showed the highest degree of crystallinity. [ABSTRACT FROM PUBLISHER]