Namita Roy Choudhury

Thermal characterization of thermoplastic elastomeric natural rubber-polypropylene blends

Abstract The thermal behaviour of natural rubber-polypropylene (NR/PP) thermoplastic elastomeric blends has been studied by a number of different techniques, e.g. differential scanning calorimetry (DSC), thermogravimetry (TG) and dynamic mechanical analysis (DMA). The melting temperature ( T m ) for polypropylene is 165°C. DSC results show a drop in the T m value with increasing rubber content. The effect of 20 parts of an interfacial agent, like ethylene-propylene diene rubber (EPDM) or chlorinated polyethylene (CPE), is similar. Heat of fusion (Δ H ) values exhibit a similar trend indicating increasing isolation of the crystallizable component at high rubber content. There is a 79% drop in crystallinity with the incorporation of 70 parts of natural rubber. The glass transition temperature ( T g ) of the rubber phase, can be detected by this technique. The T g of the blends is higher than that of pure NR. The elevation of T g coupled with the depression of T m indicate the kinetic restriction on the crystallization process. The TGA shows that the onset of degradation for pure PP is delayed with the addition of rubber. Differential thermogravimetry (DTG) curves for the blends display two peaks. The highest thermal stability is attained with the addition of ethylene-propylene diene rubber to the NR/PP blend. Dynamic mechanical analysis shows the existence of two T g values—one corresponding with the amorphous phase and the other with the polypropylene phase—indicating the incompatibility of the blends. The values of the elastic modulus also display a sharp change in magnitude in the vicinity of the glass transition temperature. The intensity of the damping (tan δ) peak is found to be governed by the overall blend crystallinity. A new method for calculation of crystallinity by DMA is also suggested.

Influence of interaction promoter on the properties of thermoplastic elastomeric blends of natural rubber and polyethylene

The influence of a third component as interaction promoter on the properties of natural rubber-polyethylene thermoplastic blends, both uncured and cured, has been studied. The third component chosen has some structural similarity with polyethylene and is amorphous in nature. Ethylene propylene diene (EPDM) rubber, chlorinated polyethylene and chlorosulphonated polyethylene have been used as the third component. All the third components have better adhesion with the plastic phase and the rubber phase. The adhesive strength is highest with EPDM. The properties are improved by using the above third components both for cured and uncured blends. In comparing the properties, the strength of the composite is divided by the modulus of the composite to take care of the hard-phase contribution. The size of the dispersed domain is reduced by using the third component and is approximately 1.2 μm. All the properties could be explained in terms of the strengths of the individual phases, the morphology and the adhesion between components.

Strength of thermoplastic elastomers from rubber-polyolefin blends

The strength of different thermoplastic elastomers of varying compositions and interactions has been examined over a wide range of rates and temperatures and for a wide variety of test configurations. Fracture energy was calculated from various test specimens and found to be similar, and independent of the test configuration. Fracture energy values lie between 0.8 and 120kJm−2. The behaviour could be compared with that of rubbers. However, for a trouser-tear test piece, the fracture energy increases with increasing thickness of the torn path in the very small thickness region, as for the fracture of polyethylene. The fracture surface morphology of various composites indicates different mechanisms of crack propagation. The tensile rupture data over a wide range of rates and temperatures could be represented by a single parabolic curve — the “failure envelope”. The maximum elongation at break and tensile strength of the composites are related to the modulus.

Adhesion between individual components and mechanical properties of natural rubber-polypropylene thermoplastic elastomeric blends

Adhesion between individual components and the mechanical properties of natural rubber (NR)-polypropylene (PP) thermoplastic elastomeric blends with reference to adhesion have been studied. The adhesion strength between the component phases was varied by incorporating a third component, namely ethylene propylene diene rubber (EPDM) or chlorinated polyethylene (CPE), and their effects on the mechanical properties were also studied. It was observed that the level of adhesion between NR and PP is improved by incorporating 20 parts of EPDM or CPE in NR. The mechanical properties of the blends are also improved for a particular composition. The enhancement in the strength properties and modulus of an NR:X:PP (where X is the third component) (70:10:30 or 70:20:30) blend is apparent when a correction due to the hard-phase contribution of the blend is made by taking the ratio of the strength of the composite to the strength of the hard phase or modulus of the blends. When the three-component blends were compared ...

Micromechanism of failure of thermoplastic rubber

The fracture surface morphology of various thermoplastic rubber and rubber vulcanizates based on natural rubber (NR), ethylene propylene diene rubber (EPDM), nitrile rubber (NBR), polyethylene (PE) and polypropylene (PP), namely NR-PE, NR-PP, EPDM-PE, EPDM-PP and NBR-PP, has been studied over a range of blend ratios, levels of interaction, rates, temperatures and modes of testing. The fracture surface changes with changes in blend ratio. Incorporation of a third component like EPDM or chlorinated polyethylene (CPE) to a certain percentage does not change the fracture morphology. Sulphur curing in the NR-PE blend generates a ductile matrix like rubber whereas large fissures are observed for peroxide-cured systems. Modification of both rubber and plastic also changes the surface morphology. The samples tested at various temperatures, rates and modes show similar features on the fracture surface.

Ageing of natural rubber-polyethylene thermoplastic elastomeric composites

Abstract Ageing of natural rubber-polyethylene thermoplastic elastomer composites with various levels of interaction has been carried out in air at various temperatures and times of ageing. Changes in technical properties such as tensile strength, modulus and elongation at break have been studied as functions of composite composition and time and temperature of ageing.

Studies on Adhesion Between Natural Rubber and Polyethylene and the Role of Adhesion Promoters

Abstract Studies on adhesion between natural rubber (NR) and polyethylene (PE) with different levels of interaction (physical and chemical) have been carried out. Ethylene propylene diene rubber (EPDM) and chlorinated polyethylene (CPE) were used as physical promoters and epoxidised natural rubber/modified polyethylene (ENR/PEm) and sulfonated ethylene propylene diene rubber/modified polyethylene (S-EPDM/PEm) were used as chemical adhesion promoters. The failure surfaces were examined with the help of scanning electron microscopy (SEM), optical photography and electron spectroscopy for chemical analysis (ESCA) techniques. The peel strength between natural rubber and polyethylene as measured in this study is 140 J/m2. With the incorporation of physical promoters such as EPDM, the peel strength increases twenty fold because of structural similarity of EPDM with PE and the rubbery nature of EPDM. Similarly, the other promoters show significant improvement in peel strength. At high temperature and low rate of...

Thermostable insulating thermoplastic elastomers from rubber polycarbonate blends

Thermoplastic elastomeric blends based on polycarbonate (PC) (30 parts) and elastomers (70 parts) of varying polarity, e.g., ethylene propylene diene rubber (EPDM), chlorinated polyethylene (CPE), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), acrylic rubber (ACM) have been studied and characterized by various methods, e.g., stress-strain measurement, surface energy estimation, thermogravimetric analysis, dynamic mechanical analysis and volume resistivity measurement. The highest tensile strength and best processability are found to be attained with the CPE/PC and HNBR/PC blends. The surface energy mismatch is also low for these systems. EPDM/PC and HNBR/PC offer excellent thermal stability. The amount of carbonaceous residue is found to depend on the elastomer structure present in the blend. The activation energy for degradation lies in the range of 210-320 kJ/mol and the order of reaction in the range of 0.8-1.2. Dynamic mechanical analysis shows existence of two separate glass transition temperatures (T.) classically associated with an immiscible system. The values of elastic modulus display a sharp change in magnitude in the vicinity of glass-rubber transition temperature and follow a linear relationship with frequency. The apparent activation energy for glass rubber transition of the blends lies in the range of 275-296 kJ/mol and that for high temperature relaxation of the polycarbonate phase lies in the range of 563-590 kJ/mole. All the blends show good electrical insulation characteristics. The amount of polycarbonate in the blend exerts a profound influence on the volume resistivity. The level of unsaturation and the polarity of the elastomer phase also affect the resistivity values.

Effect of contact time and temperature on adhesion between components of rubber-polyethylene thermoplastic composites

—The effect of contact time and temperature on the adhesion between rubber and polyethylene has been studied. The degree of adhesion between natural rubber (NR) and polyethylene (PE) was varied by using physical (EPDM) and chemical interaction promoters (ENR/PEm). It was observed that the peel strength increases with an increase in time of contact at a particular temperature. The adhesion strength varies with the square root of the contact time for all the systems with the exception of NR/PE/DCP at 75 and 100°C, EPDM/PE at 100°C, and NR/ENR/PEm/PE at 100°C. With an increase in temperature, however, only EPDM-containing systems show higher values of adhesion between components. EPDM enhances the strength of the interface of the NR/PE joint, especially at longer contact times and higher temperatures. However, the chemical modifier is active only when the joining temperature is 150°C. On mastication of NR up to 15 min, the adhesion between natural rubber and polyethylene increases. The tack strength of NR-PE...