Baby Kuriakose

Melt rheological behaviour of natural rubber/poly(methyl methacrylate)/natural rubber-g-poly(methyl methacrylate) blends

Abstract Melt rheological behaviour of natural rubber (NR) and poly(methyl methacrylate) (PMMA) blends has been studied with reference to the effect of blend ratio, processing conditions and graft copolymer concentration as a function of shear stress and temperature. The viscosity of the blend increases as the amount of NR increases. The observed values of viscosity are found to be higher than that calculated from additivity rule. In the case of solution cast samples the melt viscosity increases as the percentage of graft copolymer increases and the blend becomes more sensitive to temperature in the presence of graft copolymers. The influence of dynamic vulcanization of the rubber phase on the flow behaviour of the blends has been analysed. The die swell of the NR/PMMA blends was also evaluated in the presence and absence of graft copolymers. The morphology of extrudates has been analysed as a function of composition, graft copolymer concentration and shear stress conditions. Addition of compatibilizer reduces the domain size of the dispersed phase and stabilizes the morphology. It is also noted that state of dispersion are affected by conditions of blend preparation and extrusion. A shear rate-temperature super position master curve is constructed to predict the melt viscosities of the system as a function of temperature. The rheograms of 50/50 NR/PMMA with varying graft copolymer concentrations are found to coalesce into a master curve using modified viscosity and shear rate functions.

Studies on the effect of blend ratio and cure system on the degradation of natural rubber—ethylene-vinyl acetate rubber blends

Abstract The effects of blend ratio and type of cross-link system on thermal ageing, γ-radiation and ozone resistance of blends of natural rubber and ethylene-vinyl acetate (EVA) rubber have been evaluated. The morphology of the blends is such that the EVA forms a continuous phase when its proportion in the blend is 40% or more. The resistance of the blends to thermal ageing, γ-radiation and ozone attack is better for those which contain a higher proportion of EVA. These properties are also highly dependent on the type of cure system used.

Effect of Adhesion on the Equilibrium Swelling of Short Sisal Fiber Reinforced Natural Rubber Composites

Abstract Solvent swelling of natural rubber composites, containing both untreated and acetylated short sisal fiber, has been investigated in a series of normal alkanes such as pentane, hexane, heptane and octane. The restriction on elastomer swelling exerted by sisal fiber as well as the anisotropy of swelling of the composite have been confirmed by this study. The results showed that increased fiber content and the addition of bonding agent reduced the swelling considerably. It has been demonstrated that with improved adhesion between short fiber and rubber, the factor, (VI−VF)/VI, decreases, where VI and VF are the volume fraction of rubber in dry and swollen samples, respectively.

Role of dichlorocarbene modified styrene butadiene rubber in compatibilisation of styrene butadiene rubber and chloroprene rubber blends

Abstract A study was conducted on the use of dichlorocarbene modified styrene butadiene rubber (DCSBR) for the compatibilisation of blends of styrene butadiene rubber (SBR) and chloroprene rubber (CR). Stress–strain behaviour, mechanical properties, and low temperature transitions of the blends were examined in order to elucidate the efficiency of the compatibiliser. It was found that effective compatibilisation was achieved when chlorine content of DCSBR was 25% and its dosage was 5 phr (parts per hundred rubber). Thermal analysis by DSC showed that an appreciable extent of molecular level miscibility has been achieved in SBR/CR blends by using DCSBR as a compatibiliser. The formation of interfacial crosslinks in the presence of DCSBR is evident from the cure characteristics and stress–strain isotherms. An increase in tensile strength, tear strength, resilience and hardness and a decrease in compression set was observed when the chlorine content and dosage of the compatibiliser increased from 15% to 25% and 5 phr, respectively. Compatibilised blends showed enhanced mechanical properties in the presence of reinforcing fillers such as HAF carbon black and precipitated silica.

Scanning electron microscopy studies on tensile, tear and abrasion failure of thermoplastic elastomers

The tensile strength, tear resistance and abrasion resistance of four different types of commercial thermoplastic elastomers have been studied and their fracture surfaces examined by scanning electron microscopy. Thermoplastic polyurethane (TPU) showed elastic deformation under tensile fracture, whereas in 1,2 polybutadiene (1,2 PB) the fracture was initiated by craze formation and propagated by tear failure. Styrene-isoprene-styrene block copolymer (K1107) showed ductile type failure whereas in styrene-butadiene-styrene block copolymer containing a higher proportion of styrene and silica filler (K5152), the fracture occurred by shearing action. The tear failure surfaces of the thermoplastic elastomers showed different fracture patterns which could be correlated with the tear strength of the materials. The tear fracture surface of 1,2 PB showed stick-slip tear lines and that of TPU had a broad tear path with vertical striations. The fracture surfaces of K5152 and K1107 had the characteristics of laminar tearing and uninterrupted continuous tearing processes, respectively. The abrasion resistance of the samples was in the order TPU>1,2 PB>K5152, which was manifested through the type of ridge patterns formed on the abraded surfaces. Abraded surfaces of TPU, 1,2 PB and K5152 showed closely spaced stable ridges, widely spaced ridges bridged by elongated fibrils and highly deformed ridges, respectively.

Short sisal fibre reinforced natural rubber composites: high-energy radiation, thermal and ozone degradation

Abstract The effects of acetylation and bonding agent on thermal ageing, γ-radiation and ozone resistance of short sisal fibre reinforced natural rubber composites have been evaluated. At high fibre loadings the composites showed better resistance to ageing, especially in the presence of bonding agent. Acetylation of fibre and fibre orientation were also found to reduce the extent of degradation. The dosage of γ-radiation was found to influence the extent of the retention/degradation process.

Scanning electron microscopy studies on tensile, tear and abrasion failure of plasticized poly (vinyl chloride) and copolyester thermoplastic elastomers

Scanning electron microscopic observations on the tensile, tear and abrasion failure of plasticized poly (vinyl chloride) (PVC) and copdyester (Hytrel 40D) thermoplastic elastomers showed that the patterns developed on the fracture surfaces could be correlated with the strength and type of failure of these materials. Hytrel was found to undergo ductile failure whereas PVC showed shear fracture under tensile stress. The higher tear and abrasion resistances of Hytrel than those of PVC were also manifested by the difference in fracture patterns on the failure surfaces of these samples.

Scanning electron microscopy studies on tensile failure of thermoplastic elastomers from polypropylene-natural rubber blends

Abstract The tensile properties of thermoplastic polypropylene [pp]-natural rubber [NR]blends have been evaluated with special reference to the effect of blend ratios and dynamic cross-linking of the elastomer phase. The effects of silica filler and silane coupling agent on the tensile properties of the 30:70 PP:NR blend have also been studied. Analysis of the stress-strain curves and scanning electron microscopic examination of the tensile fracture surfaces of the blends have been used to correlate the test results on tensile properties.

Effect of vulcanization systems and antioxidants on discoloration and degradation of natural rubber latex thread under UV radiation

The effect of accelerator combinations and antioxidants on UV radiation degradation of natural rubber (NR) latex thread with a conventional and efficient vulcanization system is presented. Zinc diethyl dithiocarbamate (ZDEC), zinc dibutyl dithiocarbamate (ZDBC), zinc mercaptobenzothiazole (ZMBT), and tetramethyl thiuram disulfide (TMTD) were used as accelerators. The antioxidants used were reaction products of butylated p-cresol and dicyclopentadiene (Wingstay-L), Tris-nonylated phenyl phosphite (Crystol EPR 3400), styrenated phenol (SP), and polymerized 1,2-dihydro 2,2,4-trimethyl quinoline (HS). The thread samples were exposed to UV radiation and the appearance and physical properties of the thread were examined. The results indicated that the threads having ZDBC + ZDEC and ZDBC + ZMBT combinations as accelerators are more resistant to UV radiation than the thread having the ZDEC + ZMBT combination. The antioxidants Wingstay-L and SP + HS are effective in retaining the physical properties of the thread after UV exposure, and Crystol EPR 3400 is better in reducing discoloration.

Effect of Aluminum Powder on Filled Natural Rubber Composites

Abstract The effect of aluminum powder on the properties of natural rubber composites containing high abrasion furnace black (HAF), general purpose furnace black (GPF), acetylene black, china clay and precipitated silica was studied. In all cases the total filler content including aluminum powder is fixed at 40 parts per hundred rubber (phr). Gradual replacement of these fillers by aluminum powder showed a marked increase in thermal conductivity. This increased thermal conductivity of aluminum powder filled composites decreased the vulcanization time and led to uniform curing throughout the material, especially for thick articles. Mechanical properties like tensile strength, tear strength, rebound resilience, heat build-up, hardness, compression set, etc., are comparatively better for these composites. Aluminum powder incorporated vulcanizates also showed good resistance against thermal aging and oxidative degradation. Thus, use of aluminum powder in rubber compounds can lead to energy saving in the vulca...