Azizon Kaesaman

The grafting of maleic anhydride onto natural rubber

Abstract Graft copolymers of natural rubber and maleic anhydride (NR-g-MA) or maleated natural rubber (MNR) were synthesized in a toluene solution. Benzoyl peroxide (BPO) was used to initiate the free radical graft copolymerization. Influence of monomer and initiator concentrations together with effect of the reaction temperature and reaction time were investigated. Quantities of the grafted anhydride (MA) were determined by titration of the carboxylic acid functions derived from the anhydride functions. Estimation of the grafted MA level was also performed using IR absorbance ratio of the peaks at 1780–1784 cm−1 plus 1854 cm−1 to 835 cm−1. We found that quantities of the grafted MA on NR molecules increase with increasing monomer and initiator concentrations. The increase in reaction time and reaction temperature also causes increasing levels of the grafted MA. We also found that the glass transition temperature of the MNR was higher than that of the pure NR. Furthermore, the Tg values increase with increasing the monomer concentration used in the graft copolymerization.

Rheological properties of maleated natural rubber and natural rubber blends

Two types of natural rubber (ADS and STR 5L) were used to prepare maleated natural rubber (MNR). Melt rheological properties of MNRs (i.e. MNR-ADS and MNR-STR) and their blends with the same type of natural rubber were quantified. We found that the Mooney viscosities of MNR-ADS/ADS blends were higher than those of MNR-STR/STR 5L blends. The log additive rule was applied to the Mooney viscosity data. Positive deviation blends (PDB) were observed. A power law model was also applied to the shear flow data at a wide range of shear rates. The pseudoplastic (shear-thinning) behavior for all sets of MNR/NR blends were observed with the power law index, n, lower than 1. According to the log additive rule, plots of the consistency index against MNR levels in the blends also indicated positive deviation blends. Shear viscosity data of the blends also confirmed the shear-thinning behavior and the positive deviation blends. From the rheological property point of view, we therefore concluded that the MNR/NR blends were compatible.

Rheological and curing properties of reactive blending products of epoxidised natural rubber and cassava starch

Abstract Epoxidised natural rubber (ENR) has been prepared and used as a blending ingredient together with a compatibiliser for blending of natural rubber (air dry sheet, ADS) and cassava starch. Mooney viscosities of the blends were quantified at 100°C and rheological properties in terms of shear stress and shear viscosity were plotted against shear rates. The results showed that pure ENR gave a lower Mooney viscosity, shear stress, and shear viscosity than blends with cassava starch. Mooney viscosity, shear stress, and shear viscosity for the blends increased with increasing levels of starch. At the same level of cassava starch blended, the highest values of these quantities were observed for the blends with ENR. The blend of ADS with ENR as a compatibiliser showed lower values than those of ENR itself, but higher than those of ADS with the starch. The results are described in terms of the level of chemical interaction between polar groups in ENR and in cassava starch. Curing behaviour for compounds of ENR, ADS, and ADS with ENR as a compatibiliser were studied. The results found that ENR exhibited a long delay (∼ 10 min) before the vulcanisation took place compared with 1 min for ADS compounds. In the curing curve for ENR, an equilibrium value at maximum torque was not found indicating that the stiffness of the ENR compounds still increased with increasing testing time until 60 min. Stiffness of the ENR compounds also increased with increasing levels of cassava starch.

Electrical, dielectric, and dynamic mechanical properties of conductive carbon black/epoxidized natural rubber composites:

Electrically conductive epoxidized natural rubber filled with conductive carbon black was prepared. The AC conductivity (σAC), dielectric constant (ɛ′), loss factor (tan δ*) and dynamic mechanical properties of the composites were studied. It was found that the epoxide groups in epoxidized natural rubber molecules positively contributed to AC conductivity, dielectric constant, and tan δ* of the composites. Especially, the composite with epoxidized natural rubber containing 50% mol epoxide (epoxidized natural rubber–50) showed better electrical and dynamic mechanical properties than the composites with epoxidized natural rubber–25 or NR. The effects of conductive carbon black loading level on electrical conductivity and dielectric constant of the epoxidized natural rubber–50/conductive carbon black composites was also studied. The percolation threshold was found at very low content of conductive carbon black at volume fraction of 0.07 with the critical exponent value 2.04. Furthermore, the glass transition temperatures of epoxidized natural rubber–50/conductive carbon black composites were higher than those of epoxidized natural rubber–25/conductive carbon black or NR/conductive carbon black composites, and increased with conductive carbon black content.

Influence of Reaction Volume on the Properties of Natural Rubber-g-Methyl Methacrylate

Graft copolymer of natural rubber and poly(methyl methacrylate) was prepared using CHP/TEPA redox initiators at 50°C and a reaction time of 3 h. Various reaction volumes (i.e., 0.5, 100, and 200 L) were used to prepare the graft copolymer which was then characterized by Fourier transform infrared spectrophotometer and proton nuclear magnetic resonance spectrophotometer (1H-NMR) techniques. It was found that conversion of monomer to polymer and grafting efficiency slightly decreased with increasing reaction volumes. Quantity of grafted poly(methyl methacrylate) was calculated based on the integrated peak areas of the 1H-NMR spectra and quantitative analysis by extraction method. It was found that both techniques gave similar level of the grafted poly(methyl methacrylate) onto the natural rubber backbone. Furthermore, Mooney viscosities, glass transition temperature (Tg) and degradation temperature (Td) of the natural rubber and poly(methyl methacrylate) were slightly decreased with increasing the reaction volumes.

Effect of Nanoclay Addition on Morphology and Elastomeric Properties of Dynamically Vulcanized Natural Rubber/Polypropylene Nanocomposites

Abstract Thermoplastic vulcanizate (TPV) nanocomposites based on 60/40 (%wt) natural rubber (NR)/polypropylene (PP) blends were prepared by melt blending in an internal mixer. Sodium montmorillonite (Na-MMT) was first added in natural rubber latex to obtain natural rubber/clay masterbatch, which was subsequently dynamically crosslinked while mixing with molten PP. The effect of Na-MMT content were examined concerning elastomeric properties of NR/PP blends dynamically vulcanized using phenolic resin as a curing agent. Morphology characterization observed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and 3D microfocus X-ray computerized tomography showed that the dynamic vulcanization with nanoclay addition changed the blend morphology from a co-continuous-like structure to droplet-like phase one, and the clay remained within NR phase in intercalated and aggregated forms. Furthermore, the presence of clay induced the decrease in crosslinking of NR, but promoted the mixing between NR and PP during dynamic vulcanization. This suggested that nanoclay worked as a kind of morphology modifier during dynamic vulcanization. The addition of clay marginally enhanced the 100 % modulus and tensile strength, but led to the decrease of the elongation at break. The optimal level of tensile strength improvement was obtained with loading of 5 phr clay. The permanent set of the NR/PP/Clay TPV nanocomposites was well maintained at the acceptable level as elastomer. The resistances to oil and heat were improved with incorporation of clay, proportional to clay loading. The experimental results indicated that the nanoclay had a positive effect on improving the 60/40 NR/PP blend morphology, which provided a little benefit to strength of the TPVs. However, the addition of nanoclay offered an improvement in oil and thermal resistances due to a combined effect of the clay dispersion and improved morphology of NR and PP blends.

Thermoplastic Natural Rubbers Based on Blending of Ethylene-Vinyl Acetate Copolymer with Different Types of Natural Rubber

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.

Thermoplastic Natural Rubber Based on Blending of Maleated Natural Rubber and Copolyester: Effect of Blend Ratios on Mechanical, Thermal, Dynamic and Morphological Properties

Maleated natural rubber (MNR) was synthesized and formulated to prepare thermoplastic natural rubber (TPNRs) by blending with copolyester (COPE). It was found that tensile strength and hardness of the TPNRs increased with increasing proportions of COPE, while the elongation at break decreased. Furthermore, tension set decreased with increasing proportions of MNR in the blends which reflects enhancing of rubber elasticity. Themogravimetry analysis (TGA) was used to characterize the TPNRs. It was found that the decomposition temperature (Td) of the blend increased with increasing proportions of COPE. Morphological properties were also determined by SEM technique. It was found that the MNR/COPA simple blends with the proportion of rubber 40, 50 and 60 wt % exhibited the co-continuous phase structures.

Effect of Modified Natural Rubber on Properties of Thermoplastic Natural Rubber Based on Co-Polyamide Blends

Thermoplastic elastomers (TPEs) based on natural rubber (NR)/co-polyamine (COPA) blends with different types of NR (i.e., unmodified NR, MNR, ENR-30 and ENR-50) were prepared using simple blend technique. Mechanical, elastic, oil resistant and morphological properties were investigated. The main objective was to prepare TPEs based on NR with good set property and oil resistance. It was found that the blends with modified NRs exhibited higher moduli, tensile strength, oil resistance and elastic properties than the blend with NR. This is due to higher interaction between functional groups of modified NRs (i.e., ENR and MNR) and COPA. Furthermore, the blends using modified NRs showed finer grain morphology than the blend with NR. This may be caused by higher interfacial adhesion between rubber phase and COPA matrix.

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.