Subhas Chandra Debnath

EFFECT OF ZINC DITHIOCARBAMATES AND THIAZOLE-BASED ACCELERATORS ON THE VULCANIZATION OF NATURAL RUBBER

Abstract Several zinc dithiocarbamates (ZDCs) as accelerator derived from safe amine has been exclusively studied in the presence of thiazole-based accelerators to introduce safe dithiocarbamate in the vulcanization of natural rubber. Comparison has been made between conventional unsafe zinc dimethyldithiocarbamate (ZDMC) with safe novel ZDC combined with thizole-based accelerators in the light of mechanical properties. The study reveals that thiuram disulfide and 2-mercaptobenzothiazole (MBT) are always formed from the reaction either between ZDC and dibenzothiazyledisulfide (MBTS) or between ZDC and N-cyclohexyl-2-benzothiazole sulfenamide (CBS). It has been conclusively proved that MBT generated from MBTS or CBS reacts with ZDC and produces tetramethylthiuram disulfide. The observed synergistic activity has been discussed based on the cure and physical data and explained through the results based on high-performance liquid chromatography and a reaction mechanism. Synergistic activity is observed in all...

Controlled growth of in situ silica in a NR/CR blend by a solution sol–gel method and the studies of its composite properties

Silica is grown in situ into a natural rubber (NR)/chloroprene rubber (CR) blend (at 40/60 ratio), by a solution sol–gel method, where the silica content in rubber blend is increased in a controlled manner exceeding the limit found for the same blend ratio in the soaking sol–gel method. Reaction conditions have been optimized to get adequate conversion of tetraethoxysilane (TEOS, a silica precursor) to silica. Rheological, thermal, mechanical and viscoelastic properties of all the composites are compared with those of the unfilled rubber blend at similar conditions. Thermal and mechanical properties of the composites are found to improve consistently as silica content in the composite increases owing to increased rubber–filler interaction as revealed in dynamical mechanical analysis (DMA). Further improvement in the properties is observed for a particular composite where a silane coupling agent ((γ-aminopropyl)trimethoxysilane, γ-APS) is used in the reactive sol–gel system during in situ generation of silica. This is attributed to the uniform distribution of silica in the rubber matrix and strong rubber–filler interaction, caused by bifunctionality of silane, as revealed by morphology and DMA studies respectively. The reinforcement effect of silica is evaluated by comparing the experimental results with theoretical values obtained from the Guth–Gold model and the modified Guth model. The present study supplements the in situ silica generation in NR/CR blend of 40/60 ratio, following the solution sol–gel method, to the earlier study involving the soaking sol–gel method where the maximum reinforcement was found for this composition.

Impact of surface modification on the properties of sol–gel synthesized nanotitanium dioxide (TiO2)-based styrene butadiene rubber (SBR) nanocomposites

AbstractThe present paper provides a modern route to reinforce styrene butadiene rubber (SBR) nanocomposites by the proper utilization of sol–gel synthesized nanotitanium dioxide (TiO2). In order to achieve proper dispersion within the SBR matrix, the surface of nano-TiO2 is modified by cationic surfactants cetyltrimethylammonium bromide (CTAB) and tetraethylammonium bromide (TEAB). The surface modification of nano-TiO2 is characterized by Fourier transform infrared spectra and field emission scanning electron microscopy. The result reveals that after surface modification, sol–gel derived nano-TiO2 is much more efficient to improve the cure, mechanical and thermal properties of SBR nanocomposites in comparison with unmodified nano-TiO2. This is due to the excellent dispersion of modified nano-TiO2 within the SBR matrix, leading to the good compatibility between SBR and nano-TiO2, as confirmed from morphological analysis. Further, CTAB-treated nano-TiO2 has superior ability to enhance the resulting properties of SBR nanocomposites in comparison with either untreated or TEAB-treated nano-TiO2. Graphical Abstract

A comparison between polyethylene glycol (PEG) and polypropylene glycol (PPG) treatment on the properties of nano-titanium dioxide (TiO2) based natural rubber (NR) nanocomposites

The purpose of the present article is to modify the surface of nano-titanium dioxide (TiO2) and to investigate the reinforcing effect of both unmodified and surface-modified nano-titanium dioxide (TiO2) on the mechanical properties and thermal stability of natural rubber (NR) nanocomposites. Surface of nano-TiO2 is modified by polyethylene glycol (PEG) and polypropylene glycol (PPG). The effective surface modification of nano-TiO2 is evaluated by Fourier transform infrared (FTIR) spectra and field emission scanning electron microscopy (FESEM). The result notifies that the final properties of NR nanocomposites are dramatically improved in the presence of surface-modified nano-TiO2 in comparison to unmodified nano-TiO2. The excellent reinforcing capability of surface-modified nano-TiO2 is due to its better hydrophobicity and uniform dispersion within the NR matrix, as confirmed from morphological analysis. Furthermore, due to its small size PEG is better surface modifier for nano-TiO2 than PPG.

Surface modification of sol–gel derived nano zinc oxide (ZnO) and the study of its effect on the properties of styrene–butadiene rubber (SBR) nanocomposites

Very recently, nano zinc oxide (ZnO) has been successfully introduced as a cure activator for the reduction of ZnO level in the rubber industry. The purpose of the present work is to examine the appropriateness of surface-modified nano ZnO in the vulcanization of styrene–butadiene rubber (SBR). In the experimental part, the surface of nano ZnO is modified by stearic acid and bis[3-(triethoxysilyl)propyl]tetrasulfide (Si-69). Si-69-treated nano ZnO causes considerable enhancement in many properties such as maximum rheometric torque, modulus, tensile strength, elongation at break, cross-linking degree of SBR nanocomposite in comparison to conventional ZnO and unmodified or stearic acid-treated nano ZnO. Thermogravimetric analysis (TGA) reveals that Si-69-treated nano ZnO imposes better thermal stability than untreated or stearic acid-treated nano ZnO in the SBR vulcanizates. Morphological study indicates uniform dispersion of Si-69-treated nano ZnO within the SBR matrix and this fact accounts for better mechanical and thermal properties of SBR nanocomposite in the presence of Si-69-modified nano ZnO. This study concludes that Si-69-modified nano ZnO can be effectively applied as cure activator in place of nano ZnO to reduce the ZnO level in SBR compounds. This will lead to both economic advantages and environmental safety in the rubber industry.

Silica-coated nano calcium carbonate reinforced polychloroprene rubber nanocomposites: influence of silica coating on cure, mechanical and thermal properties

The main objective of the present work is to compare the influence of silica-coated nano calcium carbonate (SNCC) with uncoated nano calcium carbonate (NCC) as filler on the property enhancement of polychloroprene rubber (CR) composites. The CR nanocomposites containing SNCC exhibit superior curing, mechanical and thermal properties in comparison to NCC-filled CR nanocomposites. The fantastic enrichment in the resulting properties of CR nanocomposites containing SNCC is mainly due to better rubber–filler interaction resulting from the reasonably excellent dispersion of SNCC within the CR matrix. The more uniform distribution of SNCC in comparison to NCC within the rubber matrix is also confirmed from morphological analysis. Thus, in this article, we report SNCC as a new type of efficient filler to reinforce the ultimate properties of CR nanocomposites for the first time.

Development of a suitable nanostructured cure activator system for polychloroprene rubber nanocomposites with enhanced curing, mechanical and thermal properties

Nanostructured zinc oxide (ZnO) and magnesium oxide (MgO) are synthesized by sol–gel method and characterized by X-ray diffraction and field-emission scanning electron microscopy. The curing characteristics, mechanical, thermal and aging resistance properties of polychloroprene rubber (CR) composites in presence of both nanostructured and conventional cure activators in different combinations are determined. The CR composite containing 2 phr (parts per hundred parts of rubber) nano-ZnO along with 2 phr nano-MgO shows an excellent improvement in the curing characteristics as well as in the values of modulus and tensile strength in comparison to CR composite containing conventional cure activator system, i.e., 5 phr conventional ZnO along with 4 phr conventional MgO. Morphological analysis confirms the uniform distribution of nanosized cure activators within the CR matrix in comparison to conventional cure activators. Thermogravimetric analysis reveals that rapid degradation region for CR composite starts at higher temperature in presence of nanostructured cure activator system in comparison to conventional cure activator system. This study reveals that only 2 phr nano-ZnO in combination with 2 phr nano-MgO can successfully replace conventional cure activator system containing 5 phr conventional ZnO along with 4 phr conventional MgO with the enhancement of cure, mechanical and thermal properties of CR composites.

Synthesis, structure, and biological properties of a Co(II) complex with tridentate Schiff base ligand

Abstract A new Co(II) complex of general formula [Co(L)2] has been synthesized from a NNO tridentate Schiff base ligand, 2-[(piperidin-2-ylmethylimino)-methyl]-phenol (L). The title complex is characterized by elemental, spectroscopic, antibacterial, and single crystal X-ray structural studies. X-Ray crystallography reveals that the complex shows a distorted octahedral geometry around the Co(II) ion. The complex was tested against several bacteria and shows good antibacterial activities against almost all of the bacteria. The interactions of the title complex with calf thymus deoxyribonucleic acid (CT-DNA) have been investigated by electronic absorption and fluorescence spectroscopy, showing that the complex interacts with CT-DNA via partial intercalation. Thermogravimetric analysis (TGA) of the complex has also been reported and the result shows that the complex is thermally stable up to 134 °C.

A square pyramidal copper(II) complex of a Schiff base ligand: synthesis, crystal structure, antibacterial and DNA interaction studies

A mononuclear Cu(II) complex [Cu(L)Cl2] has been synthesized from a tridentate Schiff base ligand, piperidin-2-ylmethyl-pyridin-2-ylmethylene-amine (L). The single-crystal X-ray structure of the complex shows a square pyramidal geometry. The complex was tested against several bacteria and showed good antibacterial activities against almost all of the bacteria. The interactions of the title complex with calf thymus DNA (CT-DNA) have been investigated by electronic absorption and fluorescence spectroscopy, showing that the complex interacts with CT-DNA via partial intercalation.

Modulation of physiological responses with TiO 2 nano-particle in Azolla pinnata R.Br. under 2,4-D toxicity

The present work is emphasised with the herbicidal tolerance of Azolla pinnata R.Br. and its modulation with TiO2 nano-particle. Both carbohydrate and nitrogen metabolism were effected with 2,4-D as herbicide and in few cases TiO2-NP had recovered few detrimental effects. From the nutrient status in Azolla it recorded the recovery of nitrogen as well as potassium by TiO2-NP but not in case of phosphorus. However, a conversion of nitrate to ammonium was more induced by TiO2-NP under herbicidal toxicity. Similar results were obtained for inter-conversion of amino acid–nitrate pool, but no changes with glutamine synthase activity with TiO2-NP. Initially, the effects of 2,4-D was monitored with changes of chlorophyll content but had not been recovered with nanoparticle. Photosynthetic reserves expressed as both total and reducing sugar were insensitive to TiO2-NP interference but activity of soluble and wall bound invertase was in reverse trend as compared to control. The 2,4-D mediated changes of redox and its oxidative stress was ameliorated in plants with over expressed ADH activity. As a whole the Azolla bio system with TiO2 supplementation may be useful in sustenance against 2,4-D toxicity through recovery of nitrogen metabolism. Thus, Azolla-TiO2-NP bio system would be realised to monitor the herbicidal toxicity in soil and its possible bioremediation.