Thermoplastic natural rubber based on polyamide-12 (PA-12) blend was prepared by melt blending technique. Influence of blending techniques (i.e., simple blend and dynamic vulcanization) and types of natural rubber (i.e., unmodified natural rubber (NR) and epoxidized natural rubber (ENR)) on properties of the blends were investigated. It was found that the simple blends with the proportion of rubber $ 60 wt % exhibited cocontinuous phase structure while the dynamically cured blends showed dispersed morphology. Furthermore, the blend of ENR exhibited superior mechanical properties, stress relaxation behavior, and fine grain morphology than those of the blend of the unmodified NR. This is attributed to chemical interaction between oxirane groups in ENR molecules and polar functional groups in PA-12 molecules which caused higher interfacial adhesion. It was also found that the dynamic vulcanization caused enhancement of strength and hardness properties. Temperature scanning stress relaxation measurement revealed improvement of stress relaxation properties and thermal resistance of the dynamically cured ENR/PA-12 blend. This is attributed to synergistic effects of dynamic vulcanization of ENR and chemical reaction of the ENR and PA-12 molecules. Furthermore, the dynamically cured ENR/PA-12 blend exhibited smaller rubber particles dispersed in the PA-12 matrix.

A simple blend (i.e., blend without curative) of 60/40 rubber/nylon-12 with three different types of natural rubber (i.e., air-dried sheet natural rubber (ADS) and epoxidized natural rubbers (ENR) with 25 and 50 mol% epoxide) was prepared by the melt-mixing process. Influence of different types of PROPERTIES OF EPOXIDIZED NATURAL RUBBER AND NYLON-12 BLENDSrubbers and the level of epoxide groups in ENR molecules on the properties of the blends were investigated. It was found that all the blends exhibited a co-continuous phase morphology. Furthermore, the ENR/nylon-12 blends exhibited superior mechanical properties, stress relaxation behavior, thermal and rheological properties, and a finer grain morphology than that of the ADS/nylon-12 blend. This may be attributed to the higher interfacial adhesion between the ENR and nylon-12 phases via a chemical interaction of epoxide groups in ENR molecules and polar functional groups in the nylon-12 molecules. Temperature scanning stress relaxation (TSSR) measurement was also performed. Improvement in stress relaxation and thermal resistance of the blends with ENR was observed. Moreover, the higher temperature coefficient and lower glass transition temperature (T g ) of the nylon-12 phase in the ENR-50/nylon-12 blends were found. C 2011 Wiley Periodicals, Inc. Adv Polym Techn 00: 1-12, 2011; View this article online at wileyonlinelibrary.com.

in Wiley InterScience (www.interscience.wiley.com).ABSTRACT: Thermal and mechanical degradation of natural rubber (NR) mixed with N-(1,3-dimethylbutyl)-N 0 -phenyl-p-phenylenediamine (6PPD), polymerized 1,2-dihydro-2,2,4-trimethyl-quinoline (TMQ), and 50/50 weight basis mixture under high temperature and shearing conditions were investigated using a moving die processability test and FTIR spectroscopy. Relationship between dynamic properties in terms of tan d value and chemical changes of NR molecules during degradation were correlated. The results indicated that the NR mixed with antioxidants caused decreased level of chain scission and oxidative degradation. The 6PPD provided better protection of NR against degradation at elevated temperature than TMQ. Furthermore, it was found that a prolonged mixing time caused more pronounced oxidative degradation on NR molecules than increased mixing temperature. The antioxidative capability of those antioxidants on NR was ordered based on their effectiveness as follows: 6PPD > 6PPD mixed with TMQ > TMQ. It was also found that the moving die processability test and FTIR spectroscopy are efficient routes to estimate the oxidative degradation of NR molecules. Therefore, the techniques could be applied to assess or compare antioxidative capability of various types and amounts of antioxidants used in the rubber formulation within a reasonable testing time.

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 sulfurcured system.

Thermoplastic natural rubber (NR) of dynamically cured 60/40 NR/polyamide (PA) blends has been prepared by using three types of NR: unmodified air dried sheet NR, epoxidized NR (ENR) with 25 and 50 mol% epoxides. Plasticizer (i.e. dioctyl phthalate (DOP)) and processing oils (i.e. treated distillate aromatic extract and paraffinic oils) were incorporated in the blends. Stress relaxation, rheological, mechanical, and thermal properties of the blends were investigated. It was found that mixing torque, shear viscosity, tensile strength, and hardness of the oil-extended blends exhibited lower values compared with the blends without oil. But higher elongation was observed due to the distribution of oil into PA-12 and rubber phases. Furthermore, an increasing trend of stress relaxation behavior and rubber index was observed in the blends with DOP, which revealed an improvement in elastic properties. It was also found that the incorporation of DOP caused an enhancement in thermal behavior in terms of T 10 , T 50 , T 90 , and integral values, but a reduction in the glass transition temperature (T g ) of NR phase and crystallization temperature (T c ) of PA-12 matrix was also observed. This is attributed to the similar solubility parameter of DOP compared with the blend components. It was also found that the dynamically cured blends showed smaller rubber Downloaded from domains dispersed in PA-12 matrix. However, the addition of DOP resulted in an increase in the size of vulcanized rubber particles.