Sugata Chakraborty

Effect of vulcanization temperature and vulcanization systems on the structure and properties of natural rubber vulcanizates

Abstract The effect of vulcanization temperature (150°–180°C) on the structure and technical properties of gum natural rubber vulcanizates with four different 2-(morpholinodithio)-benzothiazole: sulphur ratios (A, 0.6:2.4; B, 1.5:1.5; C, 2.4:0.6; D, 3.0:0.0) at the respective optimum cure times has been determined. The influence of cure temperature on (a) the chemical crosslink density; (b) the distribution of crosslink types; (c) the extent of sulphidic main chain modifications and (d) the zinc sulphide formation was investigated. Results show that elevated cure temperatures produce a network with lower crosslink density, in particular a lower polysulphidic crosslink density. The formation of intramolecular sulphidic groups and zinc sulphide increase with increasing cure temperatures. The possibility of chain scission during vulcanization, as examined by a quantitative analysis of the sol—gel data, was found to be negligible. The network results have been correlated with the technical properties.

Composition Analysis of Carbon Black-Filled Polychloroprene Rubber Compound by Thermo-Oxidative Degradation of the Compound

This study describes a method for the composition analysis of the carbon black-filled polychloroprene rubber (CR) compound. Good agreement of the experimental data with the actual value was found. The method is based on three experiments namely thermogravimetric analysis, solvent extraction, and newly developed thermo and thermo-oxidative degradation of the vulcanized CR compound in the presence of nickel catalyst. Thermogravimetric analysis experiment gives the amount of inorganic material in the rubber compound. Solvent extraction gives the extractable amount. Thermo-oxidative degradation experiment gives the polymer amount. In thermo-oxidative degradation experiment, liberated chloride ion was titrated by Mohr’s method, and the amount of CR was back calculated from the chlorine content.

Coagulated Styrene-Vinylpyridine-Butadiene Ter-polymer latex as Secondary Accelerator in Sulfonamide—Sulfur Curing System

In the present study, coagulated styrene-vinylpyridine-butadiene ter-polymer latex (VP latex) is used as a secondary accelerator to increase the cure rate in the sulfonamide—sulfur curing system in natural as well as synthetic rubber-based compounds. The activation energy is observed to be lower when coagulated VP latex is used as a secondary accelerator. All other physical properties are observed to be comparable. It is found that a small amount of coagulated VP ter-polymer is sufficient to increase the reaction rate. However, it is also found that coagulated VP latex alone is not a satisfactory accelerator.

Stearyl Amine Ethoxylate (SAM) Grafted Montmorillonite Clay-Styrene Butadiene Rubber (SBR) Nanocomposites

The present study describes the modification of montmorillonite clay (kunipia F) surface by grafting Stearyl Amine Ethoxylate (SAM). Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) provided the evidence of formation of a nanocomposite. The interlayer spacing of the kunipia clay was increased from 1.22 nm (unmodified) to 1.53 nm (modified). The TEM study revealed the intercalated and partially exfoliated nature of the nanocomposites. When the modified clay was compounded with SBR rubber, the interlayer spacing was further increased to 1.88 nm. Remarkable improvements in the mechanical properties were found by the addition of a small amount of modified clay.

Effect of Ozone, Thermo, and Thermo-oxidative Aging on the Physical Property of Styrene Butadiene Rubber-Organoclay Nanocomposites

The present study describes the effect of thermo, thermo-oxidative, and ozone exposure on the retention of physical property of organoclay nanocomposites. Accelerated thermal aging is carried out at 130°C for 30 h. Accelerated thermo-oxidative aging is carried out at 105°C for 7 days. Samples are exposed to 50 pphm ozone atmosphere for 24 and 48 h. The result indicates that the retention of physical property is better in nanocomposites compared to carbon black-filled compounds under thermal and thermo-oxidative aging. Besides, ozone resistance is also relatively superior for nanocomposites. The superior barrier property of the nanocomposites is attributed to the better retention of the physical property after aging.

Mathematical Correlation of Polydispersity using Gel Permeation Chromatography and Rubber Process Analyzer for Raw Rubbers

In this study, an attempt has been made to correlate the polydispersity value measured through gel permeation chromatography (GPC) and that obtained through rubber process analyzer (RPA 2000). The tanδ at higher and lower frequencies is measured using RPA 2000. The inverse of tanδ difference at higher and lower frequencies obtained through RPA 2000 is correlated with the polydispersity data measured from GPC for different grades of raw rubbers like ethylene propylene diene rubber (EPDM) and butyl rubber (IIR). Polydispersity as predicted by RPA 2000 shows excellent correlation with that measured through GPC. The coefficient of correlation is found to be 0.98 for EPDM and 0.99 for IIR. The predicted polydispersity value obtained through RPA 2000 is within ±8% from that measured through GPC.

Shellac as a Multifunctional Additive (MFA) in a Typical Truck Tyre Sidewall Compound

This study reports some unexplored features of naturally occurring Indian shellac present in a typical truck tyre sidewall compound, at low doses with the intention of replacing stearic acid in the formula. The chemical characterization of shellac was determined using Fourier transform infrared (FTIR) spectroscopy, along with information from earlier published reports, revealing the presence of different fatty acids, alcohols, esters and quinone-based dyes. The substitution of stearic acid with shellac shows that 50% replacement of the acid with shellac obtained comparable rheometric and physical properties with the control compound. The presence of different components in shellac further helped to improve ageing and reversion resistance. The volatile loss from shellac is much lower compared with commercial stearic acid. Some essential properties for sidewall application such as extrudate shrinkage and die swell behaviour were also found to be suitable when 50% of the commercial stearic acid was replaced with shellac in the formula.

Technical Analysis of Euphorbia caducifolia Haines Latex of South-East Asian Origin - Part I

Identification and characterization of the latex from Euphorbia caducifolia Haines has been thoroughly described in this article. The average total solid content (TSC) of the latex was 27% and pH was found to vary between 6 to 7. About 70% by weight of the whole coagulum (Cog) was found soluble in toluene; rest was insoluble. Toluene soluble portion (TE) was mainly composed of terpenes and terpenoids of three different molecular weights; the lowest molecular weight fraction being the dominant (82%) one. Presence of about 8% natural rubber (NR, a polyterpene), mostly of cis configuration, was also identified from the composition analysis of that portion. Due to dominant low molecular weight mass, it was tackier as compared to Cog portion when manually felt. Thermal characterization showed a low temperature melting behavior (starting at 70°C for Cog and at 104°C for TE), ideal for a tackifier resin. Both Cog and TE portions were found to exhibit high thermal decomposition temperature ensuring high process safety. The ash was rich in magnesium oxide and has a great potential to be used as the cure retarder in certain rubber compounds. Absence of any deleterious metals like copper, manganese etc. was also a great positive point towards its application standpoint.

Use of crystal violet to prepare SBR-montmorillonite clay nanocomposites

Abstract Present study describes the preparation and characterization of crystal violet modified-montmorillonite clay nanocomposites by latex blending technique. Coagulation of the latex-clay slurry produced nanocomposites master batch. The master batch was compounded with Styrene Butadiene rubber (SBR). WAXD and TEM provided the evidences of formation of nanocomposite. Remarkable improvements in the mechanical properties were found by addition of small amount of modified clay.