A new process for the production of carbon black master batches with enhanced mechanical properti... more A new process for the production of carbon black master batches with enhanced mechanical properties has been developed. The unit operations in the process are the preparation of carbon black slurry in the presence of a suitable surfactant, addition of the slurry to the fresh natural rubber (NR) latex under stirring, coagulation of the mixture by the addition of acid, dewatering of the coagulum and drying to obtain carbon black incorporated NR. The competence of the new technique was established by comparing the characteristics of the carbon black incorporated NR by mill mixing process (control). The mechanical properties of the vulcanisates obtained from the latex stage and the dry rubber incorporated mixes were evaluated. The effect of aging on the mechanical properties was also discussed. The carbon black filled mixes prepared by the new process showed better cure characteristics as compared to the dry rubber incorporated mix. The mechanical properties, like tensile strength, modulus, tear strength and hardness, were superior for the vulcanisates prepared by the new method. Comparatively better aging resistance was also recorded by these vulcanisates. The improvement shown by the vulcanisates prepared by the new process was attributed to the better filler dispersion evidenced from the result of filler dispersion data and the scanning electron micrograph studies along with the attainment of a higher level of vulcanisation.
This paper focuses on the use of styrene butadiene rubber (SBR) as a viscosity modifier in novel ... more This paper focuses on the use of styrene butadiene rubber (SBR) as a viscosity modifier in novel blends of natural rubber (NR) and dichlorocarbene modified styrene butadiene rubber (DCSBR). The processing characteristics, vulcanisation kinetics, stress-strain behaviour, mechanical properties and low temperature transition of the blends have been examined in order to analyse the influence of SBR in the blends. The
Mill mixed blends of epoxidized NR (with 50 mol % epoxidation) and carboxylated nitrile rubber un... more Mill mixed blends of epoxidized NR (with 50 mol % epoxidation) and carboxylated nitrile rubber undergo self-vulcanization during moulding at elevated temperature (150°C) in absence of any vulcanizing agent. The self-vulcanization characteristics are evident from studies on Monsanto rheometer, infrared spectrophotometer, differential scanning calorimeter, thermogravimetric analyses and solvent swelling. The extent of vulcanization depends on blend ratio, the maximum occurring at 50:50 blend. Both processing behaviour and physical properties are found to depend on blend composition
Progress in Rubber, Plastics and Recycling Technology, 2017
Carbon black filled natural rubber (NR) vulcanisate with known composition and properties were me... more Carbon black filled natural rubber (NR) vulcanisate with known composition and properties were mechanically devulcanized by shearing in a laboratory two roll mill. The efficiency of devulcanisation was determined through crosslink density measurements. In order to simulate the end-of-life rubber products, mechanical devulcanisation of samples aged at standard laboratory conditions were also carried out. The devulcanized rubber prepared from un-aged and aged samples were incorporated in fresh compounds at three different proportions viz. 85/15, 75/25 and 60/40. A comparative study of such blends, where the filler present in the devulcanized rubber is also considered active and corresponding reduction is made in the formulation and the other case where the filler present in the devulcanized rubber is rendered passive, showed that there is a chance to optimize the vulcanizate properties of the blends of virgin rubber and devulcanized rubber by adjusting the compounding strategies. A co...
The issue of recombining of the radicals formed from cross-link scission and the consequent refor... more The issue of recombining of the radicals formed from cross-link scission and the consequent reformation of once-cleaved cross-links during mechanical devulcanization of carbon black–filled NR vulcanizates was investigated in a two-roll mill by the addition of the stable free radical 4-hydroxy-TEMPO (4HT), formerly 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl free radical. The effect of concentration of 4HT (0–6 pounds per hundred of rubber [phr]) and the effect of cure system, that is, conventional, semi-efficient (EV), and EV, used for vulcanization of the original sample on the efficiency of devulcanization were determined from the residual cross-link density of the gel part of the devulcanized rubber and the percent devulcanization, and further from revulcanizate properties. Chemical probe analysis of the devulcanized sample disclosed that (i) mechanical shearing predominantly breaks the majority cross-link type that decides the associated percent devulcanization; (ii) shear...
Progress in Rubber, Plastics and Recycling Technology, 2006
Hydrogenated nitrile rubber (HNBR) could be blended with natural rubber (NR) to improve its oil a... more Hydrogenated nitrile rubber (HNBR) could be blended with natural rubber (NR) to improve its oil and aging resistance without affecting drastically the dynamic properties. The polarity difference between the polymers is reduced by incorporation of small quantities of dichlorocarbene modifi ed NR (DCNR) which is formed during the alkaline hydrolysis of chloroform in presence of NR. The enhancement in technical properties in presence of DCNR is due to its dipole interaction with the-CN group of the acrylonitrile segments in HNBR as revealed from a shift in the characteristic IR absorption peak. Thus modifi ed form of NR enables the formation of a more uniformly mixed blend of NR and HNBR resulting in more cross links as revealed from an increase in rheometric torque. In blends, the NR matrix cross links to a same extent as pure NR, while the level of cross-linking of HNBR matrix is lower than that obtained for the pure HNBR. However in the presence of DCNR there is the formation of interfacial cross-links as evaluated from selective solvent swelling. During aging at a comparatively lower temperature the NR matrix of the blend undergoes cross-linking reactions while at high temperatures it undergoes scission reactions. The scission reactions taking place in the NR matrix are reduced in presence of DCNR as observed from the application of two-network theory for samples subjected to high temperature stress relaxation. A reduction in chain scission reactions at high temperature results in better aging characteristics of the modifi ed blends.
International journal of biological macromolecules, Jan 12, 2017
Natural rubber latex was initially deproteinised (DNRL) and then subjected to physicochemical mod... more Natural rubber latex was initially deproteinised (DNRL) and then subjected to physicochemical modifications to make high functional membranes for drug delivery applications. Initially, DNRL was prepared by incubating with urea, sodiumdodecylsulphate and acetone followed by centrifugation. The deproteinisation was confirmed by CHN analysis. The DNRL was then chemically modified by grafting (dimethylaminoethyl methacrylate) onto NR particles by using a redox initiator system viz; cumene hydroperoxide/tetraethylenepentamine, followed by dialysis for purification. The grafting was confirmed by dynamic light scattering, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The grafted system was blended with a hydrophilic adhesive polymer PVA and casted into membranes. The membranes after blending showed enhanced mechanical properties with a threshold concentration of PVA. The moisture uptake, swelling and water contact angle experiments indicated an increa...
We investigate the reasons behind the observed low scorch during the revulcanization of devulcani... more We investigate the reasons behind the observed low scorch during the revulcanization of devulcanized rubber. Mechanically devulcanized carbon black filled natural rubber vulcanizates originally cured by conventional vulcanization (CV), semiefficient vulcanization (semi EV), efficient vulcanization (EV), and peroxide systems as well as buffing dust obtained from pre-cured tread with known formulation were used. Revulcanization of these devulcanized samples using sulfur/sulfonamide system led to the following observations; irrespective of the type of sulfur cure system used for the initial vulcanization of the rubber, (i) the devulcanized samples cured without pre-vulcanization induction time and (ii) devulcanized samples prepared from peroxide vulcanized rubber cured with scorch safety. Based on the earlier reports that solvent extraction of devulcanized rubber did not improve the scorch time during revulcanization, the role of zinc bound non-extractable moieties was investigated usi...
Natural rubber (NR) usage is widespread from pencil erasers to aero tyres. Carbon black and silic... more Natural rubber (NR) usage is widespread from pencil erasers to aero tyres. Carbon black and silica are the most common reinforcing fillers in the rubber industries. Carbon black enhances the mechanical properties, while silica reduces the rolling resistance and enhances the wet grip characteristics. However, the dispersion of polar silica fillers in the nonpolar hydrocarbon rubbers like natural rubber is a serious issue to be resolved. In recent years, cardanol, an agricultural by-product of the cashew industry is already established as a multifunctional additive in the rubber. The present study focuses on dispersion of silica filler in natural rubber grafted with cardanol (CGNR) and determination of its technical properties. The optimum cure time reduces and the cure rate increases for the CGNR vulcanizates as compared to that of the NR vulcanizates at all loadings of silica varying from 30 to 60 phr. The interaction between the phenolic moiety of cardanol and the siloxane as well as silanol functional groups present on the silica surface enhances the rubber-filler interaction which leads to better reinforcement. The crosslink density and bound rubber content are found to be higher for the silica reinforced CGNR vulcanizates. The physico-mechanical properties of the silica reinforced CGNR vulcanizates are superior to those of the NR vulcanizates. The CGNR vulcanizates show lower compression set and lower abrasion loss. The dynamic-mechanical properties exhibit less Payne effect for silica reinforced CGNR vulcanizates as compared to the NR vulcanizates. The transmission electron photomicrographs show uniform dispersion of silica filler in the CGNR matrix. V
Dichlorocarbene modification of SBR results in an enhancement in physical properties, improvement... more Dichlorocarbene modification of SBR results in an enhancement in physical properties, improvement of air aging behaviour and excellent oil resistance as compared to SBR. This chemical modification changes SBR from a soft elastomeric to hard thermoplastic material. A satisfactory level of vulcanization with sulfur or metal oxide is only possible when the chlorine content of modified sample is <25%.
George, B. and Alex, R (2013). Stable free radical assisted scorch control in peroxide vulcanizat... more George, B. and Alex, R (2013). Stable free radical assisted scorch control in peroxide vulcanization of EPDM. Rubber Science, 27(1): 135-145. This study demonstrates the capability of a nitroxide stable free radical, 2, 2, 6, 6-tetramethylpiperidine 1-oxyl (TEMPO), to induce sulphur/accelerator like scorch control in peroxide vulcanisation of EPDM. Two commercially used peroxides; butyl 4,4-di(tert-butylperoxy) valerate (BPV) and Di(tert-butyl peroxyisopropyl) benzene (BBPIB) with cure temperatures of 160 o C and 175 o C respectively were used for vulcanisation. TEMPO induced scorch in both systems and the cure curves resembling typical sulphur/ accelerator cure curves were obtained. The reduction in cross-link density with the addition of TEMPO was significantly less in BBPIB system. Addition of 4phr of trimethylolpropane trimethacrylate (TMPTM) could regain the loss of cross-links due to the scavenging action of TEMPO. The vulcanisate properties of the EPDM/ BBPIB /TEMPO/ TMPTM sy...
The effect of aluminum powder on the properties of natural rubber composites containing high abra... more 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 savin...
A process for production of carbon black/silica/nanoclay ternary filler masterbatch from fresh na... more A process for production of carbon black/silica/nanoclay ternary filler masterbatch from fresh natural rubber (NR) latex was standardized. The fillers, nanoclay, carbon black, and silica were incorporated in fresh NR latex by a modified coagulation process. The latex, mixed with filler dispersions, coagulated immediately on addition of acids. The coagulum containing fillers was dried at 70 °C in an air oven to get the latex filler masterbatch, which was further processed in the conventional way. The masterbatch compounds containing only silica/carbon black showed a higher level of vulcanization as compared with the corresponding dry mixes. The mechanical properties, such as tensile strength, modulus, tear strength, abrasion resistance, and hardness, increased with the proportion of nanoclay in the mixes up to 5 phr, and with a greater amount, the change was only marginal. Lower tan delta values were observed for all of the masterbatches containing nanoclay in the ranges of 3 to 10 p...
A new process for the production of carbon black master batches with enhanced mechanical properti... more A new process for the production of carbon black master batches with enhanced mechanical properties has been developed. The unit operations in the process are the preparation of carbon black slurry in the presence of a suitable surfactant, addition of the slurry to the fresh natural rubber (NR) latex under stirring, coagulation of the mixture by the addition of acid, dewatering of the coagulum and drying to obtain carbon black incorporated NR. The competence of the new technique was established by comparing the characteristics of the carbon black incorporated NR by mill mixing process (control). The mechanical properties of the vulcanisates obtained from the latex stage and the dry rubber incorporated mixes were evaluated. The effect of aging on the mechanical properties was also discussed. The carbon black filled mixes prepared by the new process showed better cure characteristics as compared to the dry rubber incorporated mix. The mechanical properties, like tensile strength, modulus, tear strength and hardness, were superior for the vulcanisates prepared by the new method. Comparatively better aging resistance was also recorded by these vulcanisates. The improvement shown by the vulcanisates prepared by the new process was attributed to the better filler dispersion evidenced from the result of filler dispersion data and the scanning electron micrograph studies along with the attainment of a higher level of vulcanisation.
This paper focuses on the use of styrene butadiene rubber (SBR) as a viscosity modifier in novel ... more This paper focuses on the use of styrene butadiene rubber (SBR) as a viscosity modifier in novel blends of natural rubber (NR) and dichlorocarbene modified styrene butadiene rubber (DCSBR). The processing characteristics, vulcanisation kinetics, stress-strain behaviour, mechanical properties and low temperature transition of the blends have been examined in order to analyse the influence of SBR in the blends. The
Mill mixed blends of epoxidized NR (with 50 mol % epoxidation) and carboxylated nitrile rubber un... more Mill mixed blends of epoxidized NR (with 50 mol % epoxidation) and carboxylated nitrile rubber undergo self-vulcanization during moulding at elevated temperature (150°C) in absence of any vulcanizing agent. The self-vulcanization characteristics are evident from studies on Monsanto rheometer, infrared spectrophotometer, differential scanning calorimeter, thermogravimetric analyses and solvent swelling. The extent of vulcanization depends on blend ratio, the maximum occurring at 50:50 blend. Both processing behaviour and physical properties are found to depend on blend composition
Progress in Rubber, Plastics and Recycling Technology, 2017
Carbon black filled natural rubber (NR) vulcanisate with known composition and properties were me... more Carbon black filled natural rubber (NR) vulcanisate with known composition and properties were mechanically devulcanized by shearing in a laboratory two roll mill. The efficiency of devulcanisation was determined through crosslink density measurements. In order to simulate the end-of-life rubber products, mechanical devulcanisation of samples aged at standard laboratory conditions were also carried out. The devulcanized rubber prepared from un-aged and aged samples were incorporated in fresh compounds at three different proportions viz. 85/15, 75/25 and 60/40. A comparative study of such blends, where the filler present in the devulcanized rubber is also considered active and corresponding reduction is made in the formulation and the other case where the filler present in the devulcanized rubber is rendered passive, showed that there is a chance to optimize the vulcanizate properties of the blends of virgin rubber and devulcanized rubber by adjusting the compounding strategies. A co...
The issue of recombining of the radicals formed from cross-link scission and the consequent refor... more The issue of recombining of the radicals formed from cross-link scission and the consequent reformation of once-cleaved cross-links during mechanical devulcanization of carbon black–filled NR vulcanizates was investigated in a two-roll mill by the addition of the stable free radical 4-hydroxy-TEMPO (4HT), formerly 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl free radical. The effect of concentration of 4HT (0–6 pounds per hundred of rubber [phr]) and the effect of cure system, that is, conventional, semi-efficient (EV), and EV, used for vulcanization of the original sample on the efficiency of devulcanization were determined from the residual cross-link density of the gel part of the devulcanized rubber and the percent devulcanization, and further from revulcanizate properties. Chemical probe analysis of the devulcanized sample disclosed that (i) mechanical shearing predominantly breaks the majority cross-link type that decides the associated percent devulcanization; (ii) shear...
Progress in Rubber, Plastics and Recycling Technology, 2006
Hydrogenated nitrile rubber (HNBR) could be blended with natural rubber (NR) to improve its oil a... more Hydrogenated nitrile rubber (HNBR) could be blended with natural rubber (NR) to improve its oil and aging resistance without affecting drastically the dynamic properties. The polarity difference between the polymers is reduced by incorporation of small quantities of dichlorocarbene modifi ed NR (DCNR) which is formed during the alkaline hydrolysis of chloroform in presence of NR. The enhancement in technical properties in presence of DCNR is due to its dipole interaction with the-CN group of the acrylonitrile segments in HNBR as revealed from a shift in the characteristic IR absorption peak. Thus modifi ed form of NR enables the formation of a more uniformly mixed blend of NR and HNBR resulting in more cross links as revealed from an increase in rheometric torque. In blends, the NR matrix cross links to a same extent as pure NR, while the level of cross-linking of HNBR matrix is lower than that obtained for the pure HNBR. However in the presence of DCNR there is the formation of interfacial cross-links as evaluated from selective solvent swelling. During aging at a comparatively lower temperature the NR matrix of the blend undergoes cross-linking reactions while at high temperatures it undergoes scission reactions. The scission reactions taking place in the NR matrix are reduced in presence of DCNR as observed from the application of two-network theory for samples subjected to high temperature stress relaxation. A reduction in chain scission reactions at high temperature results in better aging characteristics of the modifi ed blends.
International journal of biological macromolecules, Jan 12, 2017
Natural rubber latex was initially deproteinised (DNRL) and then subjected to physicochemical mod... more Natural rubber latex was initially deproteinised (DNRL) and then subjected to physicochemical modifications to make high functional membranes for drug delivery applications. Initially, DNRL was prepared by incubating with urea, sodiumdodecylsulphate and acetone followed by centrifugation. The deproteinisation was confirmed by CHN analysis. The DNRL was then chemically modified by grafting (dimethylaminoethyl methacrylate) onto NR particles by using a redox initiator system viz; cumene hydroperoxide/tetraethylenepentamine, followed by dialysis for purification. The grafting was confirmed by dynamic light scattering, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The grafted system was blended with a hydrophilic adhesive polymer PVA and casted into membranes. The membranes after blending showed enhanced mechanical properties with a threshold concentration of PVA. The moisture uptake, swelling and water contact angle experiments indicated an increa...
We investigate the reasons behind the observed low scorch during the revulcanization of devulcani... more We investigate the reasons behind the observed low scorch during the revulcanization of devulcanized rubber. Mechanically devulcanized carbon black filled natural rubber vulcanizates originally cured by conventional vulcanization (CV), semiefficient vulcanization (semi EV), efficient vulcanization (EV), and peroxide systems as well as buffing dust obtained from pre-cured tread with known formulation were used. Revulcanization of these devulcanized samples using sulfur/sulfonamide system led to the following observations; irrespective of the type of sulfur cure system used for the initial vulcanization of the rubber, (i) the devulcanized samples cured without pre-vulcanization induction time and (ii) devulcanized samples prepared from peroxide vulcanized rubber cured with scorch safety. Based on the earlier reports that solvent extraction of devulcanized rubber did not improve the scorch time during revulcanization, the role of zinc bound non-extractable moieties was investigated usi...
Natural rubber (NR) usage is widespread from pencil erasers to aero tyres. Carbon black and silic... more Natural rubber (NR) usage is widespread from pencil erasers to aero tyres. Carbon black and silica are the most common reinforcing fillers in the rubber industries. Carbon black enhances the mechanical properties, while silica reduces the rolling resistance and enhances the wet grip characteristics. However, the dispersion of polar silica fillers in the nonpolar hydrocarbon rubbers like natural rubber is a serious issue to be resolved. In recent years, cardanol, an agricultural by-product of the cashew industry is already established as a multifunctional additive in the rubber. The present study focuses on dispersion of silica filler in natural rubber grafted with cardanol (CGNR) and determination of its technical properties. The optimum cure time reduces and the cure rate increases for the CGNR vulcanizates as compared to that of the NR vulcanizates at all loadings of silica varying from 30 to 60 phr. The interaction between the phenolic moiety of cardanol and the siloxane as well as silanol functional groups present on the silica surface enhances the rubber-filler interaction which leads to better reinforcement. The crosslink density and bound rubber content are found to be higher for the silica reinforced CGNR vulcanizates. The physico-mechanical properties of the silica reinforced CGNR vulcanizates are superior to those of the NR vulcanizates. The CGNR vulcanizates show lower compression set and lower abrasion loss. The dynamic-mechanical properties exhibit less Payne effect for silica reinforced CGNR vulcanizates as compared to the NR vulcanizates. The transmission electron photomicrographs show uniform dispersion of silica filler in the CGNR matrix. V
Dichlorocarbene modification of SBR results in an enhancement in physical properties, improvement... more Dichlorocarbene modification of SBR results in an enhancement in physical properties, improvement of air aging behaviour and excellent oil resistance as compared to SBR. This chemical modification changes SBR from a soft elastomeric to hard thermoplastic material. A satisfactory level of vulcanization with sulfur or metal oxide is only possible when the chlorine content of modified sample is <25%.
George, B. and Alex, R (2013). Stable free radical assisted scorch control in peroxide vulcanizat... more George, B. and Alex, R (2013). Stable free radical assisted scorch control in peroxide vulcanization of EPDM. Rubber Science, 27(1): 135-145. This study demonstrates the capability of a nitroxide stable free radical, 2, 2, 6, 6-tetramethylpiperidine 1-oxyl (TEMPO), to induce sulphur/accelerator like scorch control in peroxide vulcanisation of EPDM. Two commercially used peroxides; butyl 4,4-di(tert-butylperoxy) valerate (BPV) and Di(tert-butyl peroxyisopropyl) benzene (BBPIB) with cure temperatures of 160 o C and 175 o C respectively were used for vulcanisation. TEMPO induced scorch in both systems and the cure curves resembling typical sulphur/ accelerator cure curves were obtained. The reduction in cross-link density with the addition of TEMPO was significantly less in BBPIB system. Addition of 4phr of trimethylolpropane trimethacrylate (TMPTM) could regain the loss of cross-links due to the scavenging action of TEMPO. The vulcanisate properties of the EPDM/ BBPIB /TEMPO/ TMPTM sy...
The effect of aluminum powder on the properties of natural rubber composites containing high abra... more 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 savin...
A process for production of carbon black/silica/nanoclay ternary filler masterbatch from fresh na... more A process for production of carbon black/silica/nanoclay ternary filler masterbatch from fresh natural rubber (NR) latex was standardized. The fillers, nanoclay, carbon black, and silica were incorporated in fresh NR latex by a modified coagulation process. The latex, mixed with filler dispersions, coagulated immediately on addition of acids. The coagulum containing fillers was dried at 70 °C in an air oven to get the latex filler masterbatch, which was further processed in the conventional way. The masterbatch compounds containing only silica/carbon black showed a higher level of vulcanization as compared with the corresponding dry mixes. The mechanical properties, such as tensile strength, modulus, tear strength, abrasion resistance, and hardness, increased with the proportion of nanoclay in the mixes up to 5 phr, and with a greater amount, the change was only marginal. Lower tan delta values were observed for all of the masterbatches containing nanoclay in the ranges of 3 to 10 p...
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