Latex Stage Research Articles

Hydrogenation of natural rubber having epoxy group

Hydrogenation of epoxidized natural rubber (ENR) was performed to introduce hydroxyl group to hydrogenated natural rubber. The ENR was prepared by epoxidation of deproteinized natural rubber (DPNR) with peracetic acid in latex stage. Hydrogenation of epoxidized DPNR (EDPNR) was performed with p-toluenesulfonylhydrazide in p-xylene. The resulting product, hydrogenated EDPNR (HEDPNR), was characterized by nuclear magnetic resonance spectroscopy with various pulse sequences, i.e., two-dimensional correlation spectroscopy, two-dimensional heteronuclear correlation measurements. Carbons linking up to hydroxyl group were assigned to be quaternary and tertiary groups. The HEDPNR was proved to be a polyolefine elastomer through differential scanning calorimetry.

A comparative study of short nylon fiber—Natural rubber composites prepared from dry rubber and latex masterbatch

AbstractA novel method for the preparation of short nylon fiber–natural rubber composites was developed in which short fibers chopped to approximately 6 mm were incorporated in the latex stage and processed into sheet form. By this method, mixing cycle time was reduced without compromising the fiber dispersion. Fiber breakage during mixing was reduced. The new composites when compounded with a dry bonding system based on hexamethylenetetramine, resorcinol and hydrated silica (HRH) showed improved modulus, tensile strength and abrasion resistance compared to conventional composites. Tear strength, resilience, and compression set were similar to the conventional composites. SEM analysis indicated better interaction between matrix and fibers in the case of latex master batch. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Compatibility of liquid deproteinized natural rubber having epoxy group (LEDPNR)/poly (L‐lactide) blend

AbstractReaction after mixing of liquid epoxidized natural rubber/poly(L‐lactide) blend was performed to enhance the compatibility of the blend. The liquid epoxidized natural rubber was prepared by epoxidation of deproteinized natural rubber with peracetic acid in latex stage followed by depolymerization with peroxide and propanal. The resulting liquid deproteinized natural rubber having epoxy group (LEDPNR) was mixed with poly(L‐lactide) (PLLA) to investigate the compatibility of the blend through differential scanning calorimetry, optical light microscopy, and NMR spectroscopy. After heating the blend at 473 K for 20 min, glass transition temperature (Tg) of LEDPNR in LEDPNR/PLLA blend increased from 251 to 259 K, while Tg and melting temperature (Tm) of PLLA decreased from 337 to 332 K and 450 to 445 K, respectively, suggesting that the compatibility of LEDPNR/ PLLA blend was enhanced by a reaction between the epoxy group of LEDPNR and the ester group of PLLA. The reaction was proved by high‐resolution solid‐state 13C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Characterization of epoxidized natural rubber by 2D NMR spectroscopy

Assignment of signals in aliphatic region of 1H NMR spectrum for epoxidized natural rubber was carried out through NMR spectroscopy. The epoxidized natural rubber was prepared by epoxidation of purified natural rubber with peracetic acid in latex stage followed by degradation with propanal and ammonium persulfate. The resulting liquid epoxidized natural rubber was characterized through 1D- and 2D-NMR spectroscopy. The unknown signals in the aliphatic region of the 1H NMR spectrum were assigned through 13C NMR and two-dimensional heteronuclear shift correlation (HETCOR) measurement. The assignments were proved by two-dimensional inverse detected heteronuclear long-range shift correlation (HMBC) and two-dimensional homonuclear shift correlation (COSY) measurements, and they were supported with epoxidized squalene as a model compound through NMR spectroscopy.

Latex Stage Blending of Natural Rubber and Poly(Vinyl Chloride) for Improved Mechanical Properties

ABSTRACT A novel method of blending natural rubber with polyvinylchloride in the latex stage was developed, Dioctyl phthalate (DOP) and Amine terminated natural rubber (ATNR) were used as plasticisers, for improving the mechanical properties of these blends. Properties of the latex stage blends were compared with those of dry blends. Latex stage blends showed superior mechanical properties compared to the blends prepared in the dry state. The ageing resistance, oil resistance and processability were found to be improved by latex stage blending.

Depolymerization and ionic conductivity of enzymatically deproteinized natural rubber having epoxy group

Preparation of liquid epoxidized natural rubber (ENR) was made by oxidative depolymerization of ENR in latex stage without loss of epoxy group. Epoxidation of fresh natural rubber latex, which was purified by deproteinization with proteolytic enzyme and surfactant, was carried out with freshly prepared peracetic acid. The glass transition temperature ( T g) and gel content of the rubbers increased after the epoxidation, both of which were dependent upon an amount of peracetic acid. The gel content was significantly reduced by oxidative depolymerization of the rubber with (NH 4) 2S 2O 8 in the presence of propanal. The resulting liquid epoxidized rubber ( M n≈10 4) was found to have well-defined terminal groups, i.e. aldehyde groups and α-β unsaturated carbonyl groups. The novel rubber was applied to transport Li + as an ionic conducting medium, that is, solid polymer electrolyte.

Diimide reduction of carboxylated styrene–butadiene rubber in latex stage

Carboxylated styrene–butadiene rubber (XSBR) is selectively hydrogenated by diimide reduction technique in latex stage using hydrazine hydrate, hydrogen peroxide and Cu +2 as catalyst. The products are characterised by IR and NMR spectroscopy. Dynamic Mechanical Properties and Transmission Electron Micrographs of the hydrogenated products confirm the existence of ionic aggregates involving carboxyl (–COOH) groups of the substrate and externally added Cu +2 ions. Longer reaction time and higher amount of catalyst are required for hydrogenation of XSBR compared to that of SBR. An increase in the amount of carboxyl group decreases the extent of reaction.

Influence of styrene content on the hydrogenation of styrene-butadiene copolymer

A hydrogenated styrene–butadiene copolymer (HSBR) was prepared by a diimide reduction of SBR in the latex stage. The influence of the styrene content on various reaction parameters, namely, time, temperature, and concentration of the reactants and the catalyst was studied. A comparatively lower temperature, longer time, lesser amount of hydrogen peroxide, and higher amount of the catalyst are required to optimize the hydrogenation reactions of SBR with a higher styrene content. The diimide reduction of SBR is first order with respect to the olefinic substrate and the apparent activation energy increases with increase in the styrene level. All the hydrogenated copolymers were characterized with the help of IR, NMR, and DSC. The TGA data indicate a higher thermal stability of HSBR as compared to SBR in nitrogen, although an anomalous behavior is observed in air due to crosslinking and oxidation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1581–1595, 1999

Thermoplastic elastomeric hydrogenated styrene‐butadiene elastomer: Optimization of reaction conditions, thermodynamics, and kinetics

Thermoplastic elastomeric hydrogenated styrene—butadiene (HSBR) elastomer was prepared by diimide reduction of styrene-butadiene rubber in the latex stage. The products were characterized by infrared, 1H-NMR, 13C-NMR spectroscopy, and differential scanning calorimetry (DSC). The standard free energy change, ΔG0 at 298°K is −44.7 × 104 kJ/mol, indicating that the formation of HSBR is thermodynamically feasible. The value of heat change of the reaction at constant volume, ΔUT is −41.6 × 104 kJ/mol. The effect of different reaction parameters on the level of hydrogenation, calculated from nuclear magnetic resonance spectroscopy, was also investigated. The degree of hydrogenation increases with the increase in reaction time, temperature, the concentration of reactants and catalyst. A maximum of 94% hydrogenation was obtained under the following conditions: time, 4 h; temperature, 45 ± 2°C; pH, 9.36; cupric sulphate (CuSO4 · 5H2O) catalyst concentration, 0.0064 mmol; hydrazine concentration, 0.20 mol; and hydrogen peroxide concentration, 0.26 mol. The diimide reduction of SBR is first-order with respect to olefinic substrate, and the apparent activation energy is 9.5 kJ/mol. The glass transition temperature increases with the increase in saturation level due to development of crystalline segments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1151–1162, 1997

Thermoplastic elastomeric hydrogenated styrene-butadiene elastomer: Optimization of reaction conditions, thermodynamics, and kinetics

Thermoplastic elastomeric hydrogenated styrene—butadiene (HSBR) elastomer was prepared by diimide reduction of styrene-butadiene rubber in the latex stage. The products were characterized by infrared, 1H-NMR, 13C-NMR spectroscopy, and differential scanning calorimetry (DSC). The standard free energy change, ΔG0 at 298°K is −44.7 × 104 kJ/mol, indicating that the formation of HSBR is thermodynamically feasible. The value of heat change of the reaction at constant volume, ΔUT is −41.6 × 104 kJ/mol. The effect of different reaction parameters on the level of hydrogenation, calculated from nuclear magnetic resonance spectroscopy, was also investigated. The degree of hydrogenation increases with the increase in reaction time, temperature, the concentration of reactants and catalyst. A maximum of 94% hydrogenation was obtained under the following conditions: time, 4 h; temperature, 45 ± 2°C; pH, 9.36; cupric sulphate (CuSO4 · 5H2O) catalyst concentration, 0.0064 mmol; hydrazine concentration, 0.20 mol; and hydrogen peroxide concentration, 0.26 mol. The diimide reduction of SBR is first-order with respect to olefinic substrate, and the apparent activation energy is 9.5 kJ/mol. The glass transition temperature increases with the increase in saturation level due to development of crystalline segments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1151–1162, 1997

Storage Hardening of Natural Rubber

Abstract Natural rubber exhibits different storage properties when compared with synthetic polyisoprenes. Stored over an extended period of a few months, natural rubber is found to become progressively harder while the synthetic rubber is known to soften. This phenomenon of spontaneous crosslinking of natural rubber in storage is of considerable importance since it affects the processing properties. The process of storage hardening has been actively investigated and is believed to involve abnormal groups in the rubber molecules. This paper reviews the various proposals by different workers involving aldehyde, epoxide, and amino acids. Our recent results show that amino acids react with certain abnormal groups in rubber at the latex stage. The net effect of the reaction is to functionalize the rubber with carboxylic, hydroxylic, and amine groups in addition to the original abnormal groups. Storage of the dry rubber could lead to slow crosslinking reactions which are accelerated by anhydrous conditions.

Latex Stage Epoxidation of Natural Rubber: Effects of Agitation, Mode of Addition of Reagents, Neutralization Technique, and Secondary Acid

ABSTRACTLatex stage epoxidation of natural rubber (NR) with in-situ formed performic acid has been studied and the effects of speed of agitation, mode of addition of reagents, type of secondary acid and neutralization techniques on product quality are reported. Increase in agitation speed resulted in a more desirable product distribution but too high a speed created other problems like frothing and microcoagulation of rubber. The mode of addition of reagents, whether simultaneous or dropwise, was found to affect the product distribution. The extent of hydrofuranization was lower when acid of lower strength was used. Neutralization of the reaction mixture before coagulation gave products with improved aging properties.

Kinetic modeling of the epoxidation of natural rubber with in‐situ–formed peracid

AbstractIn the presence of excess hydrogen peroxide and formic acid the latex stage epoxidation of natural rubber is pseudo–first order in nature. A kinetic model is developed to predict the maximum extent of epoxidation for the reaction system and its variation with increasing acid concentration. Th dependence of the overall rate constant on acid concentration is also studied.

Effect of acid concentration and other reaction parameters on epoxidation of natural rubber latex

Latex stage epoxidation of natural rubber was studied under different reaction temperatures with in situ formed performic acid. Overall kinetics of the reaction and effect of acid concentration were studied. Product distribution and optimum acid concentration were determined from experimental data. It was found that with increasing acid concentrations initially the overall rate constant increased, reached a maximum, and then sharply decreased. The maximum epoxidation level decreased with increased acid concentration

Studies on the Epoxidation of Natural Rubber

Latex stage epoxidation of natural rubber with in-situ formed performic acid with and without acetic acid at room temperature were studied at various feed composition. Epoxidised natural rubber was characterised by IR, NMR and DSC. A simple kinetic model was developed from laboratory ex perimental data. Various side reaction products were detected. The H1-NMR spectra of product sample prepared in our laboratory and samples of ENR50 from Rubber Research Institute of Malaysia (RRIM) were compared.

Mechanisms of antioxidant action: Stabilisation of nitrile rubber by interpenetrating networks based on thiol adducts

Nitrile rubbers containing three thiol antioxidants ((I) to (III)) in bound form have been evaluated as masterbatch concentrates by dilution in unstabilised nitrile rubber both at the latex stage and in the polymer melt. Both procedures give effective substantive systems in the case of the hindered phenol (I) and the aromatic thiol amide (II). Both show a high level of antioxidant retention under very severe technological conditions (oil/air oven cyclical test at 150°C). Antioxidant (III), which has only a minor structural difference from (II), is very much less effective as a substantive antioxidant.

Lignin as a Compounding Ingredient for Natural Rubber

Abstract Important claims have been made in recent years regarding the capacity of lignin to reinforce natural and synthetic rubber. In 1949 Dawson reviewed the literature on the use of lignin in rubber and drew particular attention to the work of Keilen and Pollak who had shown that in certain circumstances lignin could be considered to rival EPC black in its ability to yield strong GR-S vulcanizates with high resistance to tear. Raff and his coworkers subsequently showed that the reinforcement of GR-S by lignin is enhanced if the lignin, before coprecipitation with the latex, is subjected to oxidation; other workers studied the application of lignin to the reinforcement of different elastomers, the influence of coprecipitation conditions on the properties of the product, and the problem of overcoming the delaying effect of lignin on vulcanization of lignin-natural rubber coprecipitates. Keilen and Pollak in their experiments incorporated lignin into rubber by coprecipitation at the latex stage, but they indicated that similar results could be obtained if lignin “in the gelled state” was added to rubber by milling. No reinforcement was observed however when lignin was added to rubber as a dry powder. Lignin is potentially an abundant and cheap material which according to the above claims should extend the range of useful compounds available to rubber manufacturers. The present paper describes work undertaken to gain firsthand knowledge of the technique of coprecipitating lignin with natural rubber from preserved latex, to learn something about the properties of natural rubber compounds prepared from lignin coprecipitates, and to study possible ways of incorporating lignin into rubber by means other than coprecipitation. It also records test results for masterbatches prepared by the Rubber Research Institute of Malaya from fresh latex on a pilot plant scale.

Vulcanization of Latex. Differences in the Behavior of Fresh, Old, and Purified Latex

Abstract Patents granted to Schidrowitz show that when latex is vulcanized and then dried at room temperature, the product has the properties of vulcanized rubber. Films produced in this way show tensile strengths and elasticity which correspond to those of latex films vulcanized in the dry state. It is apparent, however, that when fresh latex is vulcanized under certain definite conditions, the product has fair tensile strength and elasticity only at a relative humidity of zero, but which under ordinary atmospheric conditions is brittle, seems to be overcured, and is practically without tensile strength. This tensile strength, however, is increased by additional dry vulcanization, so there can be no question of overcure. Just as soon as vulcanization has proceeded to a point where brittle films without tensile strength are obtained, the latex, when treated with acid, does not coagulate, but merely flocculates. Nor can such vulcanized fresh latex at this stage be made to coagulate coherently by other means. This form of latex is not sticky. The flocculate referred to can be obtained only by vulcanizing fresh latex in the presence of zinc oxide, and under conditions such that hydrolysis of the nonrubber substances is a minimum. It is, therefore, desirable to have recourse to ultra-accelerators and to be sure that the vulcanization temperature is not too high. By keeping fresh latex alkaline, or by purifying it, it will not flocculate. Latex that has been purified or aged may occasionally, under similar conditions, give a brittle and incoherent coagulum, whereas in other cases a normally coherent but somewhat brittle coagulum results. The nature of the coagulum is governed by the degree of purification and hydrolysis of the nonrubber substances; hence all transition stages between a flocculate and a completely coherent coagulum may occur. By adding serum from fresh latex to purified latex, the behavior of such purified latex changes in the sense that it behaves more like fresh latex. In studying experimentally the difference in behavior of fresh latex and purified latex, the first thing considered was the combination of sulfur. It was found that sulfur first dissolves in the serum, after which it dissolves in the rubber itself. Only then does vulcanization take place. This became evident from the definite acceleration of the combination of sulfur in the latex stage, when before vulcanization, latex was heated with sulfur alone. By this preparatory treatment too, dry vulcanization at room temperature was accelerated, but there was no noticeable effect on dry vulcanization at 80° and 110° C. At 30° C, about 1 per cent of the sulfur dissolved in the rubber particles, in the form of free sulfur. From this it was concluded that it is not possible to remove by mechanical means (as by clarification) excess free sulfur from vulcanized latex. No essential difference could be found between the combined sulfur of fresh latex and that of purified old latex.