Rubber In Latex Stage Research Articles

Compatibility of epoxidized natural rubber and polyaniline blend

AbstractThe compatibility of binary blend of epoxidized natural rubber and polyaniline was investigated. Epoxidized natural rubber with 25 mol% of epoxy group content was prepared through epoxidation of deproteinized natural rubber in latex stage. Blends of epoxidized natural rubber and polyaniline with various ratios were prepared. The compatibility of the blends was examined through differential scanning calorimetry measurement and scanning electron microscopy observation. Obtained result showed that the presence of epoxy group significantly improved the compatibility of binary blends of epoxidized natural rubber and polyaniline blends. The compatibility significantly enhanced the electrical conductivity of epoxidized natural rubber/polyaniline blends.

Preparation and characterisation of liquid epoxidised natural rubber in latex stage by chemical degradation

Preparation and characterisation of liquid epoxidised natural rubber in latex by chemical degradation was successfully carried out. The effect of certain parameters, such as surfactant concentrations, incubation time of ENR latex in the presence of surfactant and pH condition on the reaction efficiency were studied. Effect of degrading agent concentrations and drying temperatures of LENR were also investigated. The molecular weight, i.e., Mw and Mn, which was determined by gel permeation chromatography (GPC) and gel content of LENR were decreased gradually as the degrading agent concentrations increased. Moreover, the drying temperatures, ranging from 333 to 423 K showed no significant changes in epoxidation levels and epoxy derivatives, as the drying period decreased from 24 to 4 h. The resulting LENR were further characterised using Fourier transform infra-red (FTIR) spectroscope, nuclear magnetic resonance (NMR) spectroscope, differential scanning calorimeter (DSC) and field emission-scanning electron microscope (FE-SEM). The glass transition temperature, Tg of LENR, i.e., 252 K was increased compared with ENR, i.e., 248 K. Besides, the latex particles morphology of LENR were found to be more uniform and larger compared with ENR. The functional groups such as carbonyl as functional end group, hydroxyl, epoxy, ester and furan groups were increased after degradation of ENR to form LENR. This indicates that the presence of functional polar groups at the LENR backbone play an important role which brings about the distinguished characters and properties of LENR.

Chemical modification of natural rubber in latex stage for improved thermal, oil, ozone and mechanical properties

In this work, chemical modification of natural rubber in latex stage was focused on a green condition and to improve thermal, ozone and mechanical properties. Two chemical modifications including epoxidation followed by hydrogenation of natural rubber latex (NRL) were carried out continuously in one-pot system. The NRL was treated with in situ performic acid generated from the reaction of formic acid and hydrogen peroxide to obtain partially epoxidized product or epoxidized natural rubber (ENR) latex which was then further modified its residual unsaturated units using hydrazine and hydrogen peroxide to perform hydrogenation reaction. The chemical structure of the obtained modified rubber so called hydrogenated epoxidized natural rubber (HENR) was characterized by 1H-NMR and ATR-FTIR. Two types of HENR including HENR-1 (27 mol% degree of hydrogenation and 17 mol% degree of epoxidation) and HENR-2 (25 mol% degree of hydrogenation and 28 mol% degree of epoxidation) were subjected to investigate their thermal properties compared to the NR, ENR and hydrogenated NR (HNR). It was found that the modified NRs possess higher thermal property and increased Tg as compared to NR, due to both incorporation of epoxide units and reduced unsaturation of the molecular chain. The prepared HENRs were found to maintain the strain induced crystallization character which is the feature of NR. The vulcanized HENR-1 and HENR-2 showed superior tensile strength compared to vulcanized NR. In addition, the oil and ozone resistances of modified NRs were also improved. The preparation of HENR in one-pot latex system is a facile condition and save energy for any solvent recovery. The procedure can be considered as a potential green and sustainable development of NR.

Preparation of phenyl‐modified natural rubber in latex stage

Phenyl‐modified natural rubber was prepared in latex stage by bromination of deproteinized natural rubber followed by Suzuki‐Miyaura cross‐coupling reaction. First, the bromination of natural rubber was carried out using N‐bromosuccinimide in latex stage. The bromine atom content increased as amount of N‐bromosuccinimide increased. Second, the allylic bromine atom was replaced with a phenyl group using phenyl boronic acid in the presence of a palladium catalyst, according to the Suzuki‐Miyaura cross‐coupling reaction in latex stage. The resulting products were characterized by nuclear magnetic resonance (NMR) spectroscopy. Signal at 7.13 ppm was assigned to the phenyl group of the product, while signals at 3.98, 4.14, and 4.44 ppm were assigned to the remaining allylic brominated cis‐1,4‐isoprene units. The estimated phenyl group content and the conversion of the Suzuki‐Miyaura cross‐coupling reaction were 1.32 and 23.7 mol%, respectively. Glass transition temperature (Tg) of deproteinized natural rubber increased from −62°C to −46.7°C, when the phenyl group was introduced into the rubber.

Latex-state NMR spectroscopy for quantitative analysis of epoxidized deproteinized natural rubber

Method of quantitative analysis through latex-state 13C NMR spectroscopy was established for in situ determination of epoxy group content of epoxidized natural rubber in latex stage. The epoxidized natural rubber latex was prepared by epoxidation of deproteinized natural rubber with freshly prepared peracetic acid in latex stage. The resulting epoxidized deproteinized natural rubber (EDPNR) latex was characterized through latex-state 13C NMR spectroscopy. Chemical shift values of signals of latex-state 13C NMR spectrum for EDPNR were similar to those of solution-state 13C NMR spectrum for EDPNR. Resolution of latex-state 13C NMR spectrum was gradually improved as temperature for the nuclear magnetic resonance (NMR) measurement increased to 70°C. Signal-to-noise ratio of latex-state 13C NMR measurement was similar to that of solution-state 13C NMR measurement at temperature above 50°C. The epoxy group content determined through latex-state NMR spectroscopy was proved to be the same as that determined through solution-state NMR spectroscopy. Copyright © 2017 John Wiley & Sons, Ltd.

Preparation and characterization of poly(stearyl methacrylate) grafted natural rubber in latex stage

An attempt to prepare graft copolymer of natural rubber, NR and poly(stearyl methacrylate), PSMA, was made to improve mechanical properties of NR, since the grafted PSMA was composed of crystallizable stearyl groups as a nucleating agent and methacrylate units. The graft-copolymerization of stearyl methacrylate (SMA) onto deproteinized natural rubber (DPNR) was performed in latex stage with tert-butylhydroperoxide (TBHP)/tetraethylenepentamine (TEPA) as an initiator, after purifying the rubber with urea and sodium dodecyl sulphate followed by centrifugation. The optimal conditions for the graft-copolymerization were determined as follows: 3.3 × 10−2 mol/kg-rubber of initiator, 1.5 mol/kg-rubber of monomer and 30 w/w% of dry rubber content (DRC). The conversion and grafting efficiency of SMA were 95 mol% and 60 mol%, respectively. After graft-copolymerization, the melting temperature of PSMA increased from 304.1 K to 306.2 K. The morphology showed that the DPNR particles, which were about 1 μm in average diameter, were well dispersed in PSMA nanomatrix. The stress at break increased about three times, i.e. 13 MPa, as high as that of DPNR. The increase in the mechanical properties was promoted by the nucleating effect of stearyl group of PSMA.

Preparation and graft‐copolymerization of hydrogenated natural rubber in latex stage

ABSTRACTPreparation and graft‐copolymerization of hydrogenated natural rubber are performed in latex stage after removal of proteins from the rubber with urea and surfactant. Hydrogenation of deproteinized natural rubber (DPNR) latex is carried out with palladium catalyst under hydrogen atmosphere. The hydrogenated DPNR (HDPNR) is crosslinked with a peroxide followed by graft‐copolymerization of styrene (Sty) and acrylonitrile (AN) in latex stage in order to prepare a graft‐copolymer of crosslinked HDPNR with poly(Sty‐co‐AN) (HDPNR‐graft‐PSAN). Characterization of the products is performed by nuclear magnetic resonance spectroscopy. The conversion of hydrogenation is investigated with respect to the catalyst feed, acidity (pH), and dry rubber content. In the resulting HDPNR‐graft‐PSAN, mole fraction of AN and Sty is 1.4 and 5.8 mol %, respectively. The graft‐copolymer is used to improve properties of PSAN as an impact modifier. The Charpy impact strength of crosslinked HDPNR‐graft‐PSAN/PSAN is about eight times as high as that of PSAN. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42435.

ラテックスの状態におけるエポキシ化天然ゴムの水素化

ヒドロキシ基を有する水素化天然ゴムは，天然ゴムの耐熱性や耐候性を向上させるだけでなく，架橋点への変換が期待される官能基が導入された植物資源由来のゴムである．本研究では，天然ゴムのエポキシ化と脱タンパク質化によりエポキシ化脱タンパク質化天然ゴム(EDPNR)ラテックスを調製し，ラテックスの状態でEDPNRの水素化を行った．得られた水素化EDPNR (HEDPNR)のキャラクタリゼーションはNMRにより行った．EDPNRの水素化の条件検討を行い，水素化率90.7%，二重結合残存率5.6%，ヒドロキシ基含有率1.5%のHEDPNRが調製されることを明らかにした．

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.