Anoma Thitithammawong

The influence of mixed conventional sulfur/peroxide vulcanization systems on the mechanical and thermal properties of natural rubber/polypropylene blends

The role of mixed conventional sulfur/peroxide vulcanization systems on the mechanical and thermal properties of natural rubber/polypropylene thermoplastic vulcanizate (TPV) was investigated. Various proportions of peroxide in the mixed vulcanization system were used to dynamically vulcanize the natural rubber phase in the blend. The results show that using a mixed vulcanization system results in TPVs with superior properties in all areas studied, to those of TPVs cured by individual sulfur or peroxide systems. However, the peroxide content in the mixed vulcanization system has a strong effect on the variation in properties. A system containing 30 parts of peroxide to 70 parts of sulfur, results in a TPV with the best overall properties due to a balance of the effects of the sulfur and the peroxide curing agents in the blend. This ratio promotes optimum cross-link density, cross-link patterns, and low competing reactions of the peroxide and co-agents. As a result, improvements in the mechanical and thermal properties of the TPV are obtained with 30 parts of peroxide in the mixed system. Any further increase in the peroxide content results in a deterioration of those properties due to inefficient cross-linking with a high degree of competing reactions. Thus, close attention should be paid to the ratio of sulfur to peroxide or more specifically to the content of peroxide when selecting a mixed vulcanization system as a cross-link agent.

Thermoplastic Elastomer Based on Epoxidized Natural Rubber/Polyamide-12 and Co-Polyamide-12 Blends

Thermoplastic elastomers based on blending of epoxidized natural rubber with 30 mol% epoxide (ENR-30) with polyamide-12 (PA-12) (i.e., ENR-30/PA-12) and blending of ENR-30 with co-polyamide-12 (ENR-30/CO-PA-12) were prepared by dynamic vulcanization technique. It was found that the dynamically cured ENR-30/PA-12 blends exhibited higher tensile strength, Youngs modulus and hardness than those of the ENR-30/CO-PA-12 blends. However, the elongation at break of the ENR-30/PA-12 blend was very poor and hence the tension set could not be determined. On the other hand, the ENR-30 contents in the dynamically cured ENR-30/CO-PA-12 influence on various properties. These include lowering of stiffness and tensile properties together with enhancing elastic properties (i.e. lower tension set and tan ) of the blends.

A Comparative Investigation of Rice Husk Ash and Siliceous Earth as Reinforcing Fillers in Dynamically Cured Blends of Epoxidized Natural Rubber (ENR) and Thermoplastic Polyurethane (TPU)

The present work aimed to develop epoxidized natural rubber/thermoplastic polyurethane thermoplastic vulcanizates (ENR/TPU TPVs) having some specific properties, i.e., good processability and dynamic properties, and excellent heat and oil resistances. A comparative study on the effects of rice husk ash (RHA) and commercial siliceous earth (SE) as reinforcing fillers on alteration and enhancement of TPV properties was performed. It was found that the RHA-filled ENR/TPU TPVs showed an improvement of thermoelastic properties with outstanding thermal resistance relative to the pure TPU. This might be attributed to the synergistic effects of the dispersed vulcanized ENR domains and the RHA particles in the TPVs. Furthermore, the RHA-filled ENR/TPU TPVs had rather similar performance, processability and physical properties to the SE-filled ENR/TPU TPV. This indicates that the RHA has great potential as a filler in thermoplastic vulcanizates, in particular with ENR that is a renewable green resource.

Effects of crosslinked elastomer particles on heterogeneous nucleation of isotactic PP in dynamically vulcanized EPDM/PP and EOC/PP blends

The isothermal and non-isothermal crystallizations of PP in neat form and in the TPVs EPDM/PP and EOC/PP were investigated using differential scanning calorimetry (DSC). The crystallization of PP was systematically studied by fitting mathematical models, and was later confirmed by X-ray diffraction (XRD) and by scanning electron microscopy (SEM). The experiments revealed that crosslinked elastomer particles first accelerated the primary nucleation of the PP matrix, acting effectively as a nucleating agent that reduces the induction time while increasing the nucleation efficiency. In the secondary nucleation regime (growth of spherulites), the crosslinked elastomer particles enhanced crystal growth rate, reducing the nucleation energy contribution from PP chain folding. Moreover, the crosslinked elastomer particles increased the final thickness of PP lamellae from that of neat PP, and this was corroborated by the XRD results. On comparing the two types of elastomer, it was found that the EOC particles were more effective in heterogeneous cell nucleation than the EPDM particles. The morphological study by SEM revealed completely altered PP spherulite size and shape, as well as their altered distribution, affected by heterogeneous nucleation effects of the crosslinked elastomer particles.

Changes in Mixing Torque, Mechanical and Dynamic Rheological Properties of Epoxidized Natural Rubber and Copolyester Blends as Affected by Epoxidized Natural Rubber Contents

Thermoplastic natural rubber (TPNR) based on epoxidized natural rubber with 30 %mol epoxide (ENR-30) and copolyester (COPE) blends was prepared in a molten state by using roller rotor internal mixer. Effect of various ENR contents on mixing torque together with mechanical and dynamic properties of the ENR-30/COPE blends was investigated. It was found that the mixing torque and complex viscosity increased with increasing contents of the ENR in the blends. This was due to higher polarity the ENR molecules caused interaction and entanglement of the ENR molecular chains with higher viscosity. Furthermore, improvement of elastomeric properties of the ENR-30/COPE blends was clearly observed, especially in the blends with higher proportion of the ENR. These improved elastomeric properties with high elongation at break, low tension set and high storage modulus together with low tan δ. This observation correlated to higher elastic component in the blend caused promoting higher elastic response in combination with increasing of interaction between the ENR and the COPE phases.

Influence of Curing Systems on Mechanical, Dynamic, and Morphological Properties of Dynamically Cured Epoxidized Natural Rubber/ Copolyamide Blends

Thermoplastic elastomers (TPEs) based on dynamically cured epoxidized natural rubber/copolyamide (ENR/COPA) blends were prepared. Influence of curing systems (i.e., sulphur, peroxide, mixed sulphur and peroxide and phenolic resin cured systems on mechanical, dynamic and morphological properties of the blends were investigated. It was found that the blend with phenolic cured system exhibited superior mechanical and set properties. That is higher tendency to recover to its original shape after a prolong extension. It was also found that the blend with peroxide cured system exhibited higher storage modulus and complex viscosity than those of the blends with mixed sulphur and peroxide, phenolic and sulphur cured system, respectively. Furthermore, the TPVs blend with peroxide cured system showed the smallest vulcanized rubber particles.

Assessment of Mixing Efficiency of Intermeshing Rotor Mixers on Morphological and Mechanical Properties and Crosslink Density of Dynamically Vulcanized EPDM/PP Blends

The mixing efficiency of intermeshing rotor internal batch mixers for the preparation of rubber-rich thermoplastic vulcanizates (TPV) based on ethylene propylene diene terpolymer (EPDM) and polypropylene (PP) blends was investigated. Two laboratory scale mixers, namely intensive batch mixer (INS) and kneader batch mixer (KND), were used. The mixer choice at controlled mixing conditions was investigated to determine its effects on morphological and mechanical properties and crosslink density of the prepared EPDM/PP TPVs. Such effects were found on the degradation of the polymer, on the distribution of the EPDM phase in the blend morphology, particularly the size of EPDM inclusion, and on the crosslink density of the EPDM phase. In summary, the different mixing efficiencies of INS and KND type mixers affect the EPDM/PP TPVs and their properties. Also, the INS mixer has higher mixing efficiency than the KND mixer.

Mixing Methods Influencing on Properties of Epoxidized Natural Rubber/Polypropylene Thermoplastic Vulcanizates

Epoxidized natural rubber (ENR)/Polypropylene (PP) thermoplastic vulcanizates were prepared by melt mixing method in an internal mixer. Influences of different mixing methods for incorporation of processing oil into the TPVs on tensile and dynamic mechanical properties of the TPVs and crystallinity of the PP were investigated. Results show that distribution of processing oil in the ENR/PP TPV is important due to the processing oil can promote and in the same time can interrupt an improvement in elastomeric properties of the TPV. Incorporation of processing oil into the ENR phase by preparation of oil extended ENR (the mixing method 1) before mixing with the PP was the better way to produce the TPV. It promoted the TPV with superior tensile and dynamic mechanical properties than the TPVs prepared from the mixing method 2 and 3 in which the processing oil was directly added into the PP phase. Furthermore, the TPV from the mixing method 1 had less effect of processing oil on the PP crystallization.

Application of Benzyl Ester of Modified Vegetable Oils as Rubber Processing Oils

Benzyl esters of fatty acids based on three types of vegetable oils (i.e., coconut, palm, and soybean oils) were in-house prepared. They were used as alternative rubber processing oil to replace conventional aromatic oil which has been banned by European community since December 2009. Fatty acids were first prepared by hydrolysis of vegetable oils and thereafter esterified with benzyl alcohol in the presence of sulfuric acid as a catalyst. The reaction based on molar ratio of fatty acid:benzyl alcohol:sulfuric acid was set at 1.5:1.0:0.05 gave yield of benzyl esters higher than 80%. Rubber compounds containing different types of benzyl ester were prepared according to the standard formulation of ASTM 3184. It was found that the processing oil in the form of benzyl esters is possible to use instead of aromatic oil in rubber formulation. Various parameters and properties include mixing energy, Mooney viscosity, curing, mechanical and dynamic mechanical properties of rubber compounds and vulcanizates have been investigated.

Effect of N-Phenyl-p-Phenylenediamine Modified Vegetable Oils on Properties of ENR/PP Thermoplastic Vulcanizates: A Comparative Study

This research focuses on feasibility study of using n-phenyl-p-phenylenediamine modified vegetable oils as processing oil in the blend formulation of epoxidized natural rubber (ENR) /polypropylene (PP) thermoplastic vulcanizates (TPVs). Effect of n-phenyl-p-phenylene-diamine modified vegetable oils on tensile and dynamic mechanical properties of the ENR/PP TPVs was investigated. For a comparison purpose, vegetable oils, epoxidized vegetable oils, and white oil were selected and also used in our experiment. Results show that all types of oils used in this study did not give the TPVs with significantly different values of tensile strength. The TPVs with petrochemical based white oil obviously provided the best elongation at break and tension set. However, by using n-phenyl-p-phenylenediamine modified palm oil (pA-m-EPO) the ENR/PP TPVs showed superior elastomeric properties (higher storage modulus together with lower tension set, tan δ and complex viscosity) than those of other TPVs. This means that the pA-m-EPO performed good compatibility with the TPV and had good distribution in the ENR molecules.