Chemical Modification Of Natural Rubber Research Articles

Improvement of mechanical and dynamic properties of high silica filled epoxide functionalized natural rubber

In this research, 3 different low degrees (4, 8, and 14 mol%) of epoxide functionalized natural rubber were prepared via chemical modification of natural rubber, which was then vulcanized. Each of them was mixed with silica (50 parts per hundred of rubber) without a silane coupling agent and investigated their properties. It was found that the tensile and tear properties, as well as abrasion resistance of the silica filled epoxide functionalized natural rubber vulcanizates were higher than the silica filled natural rubber vulcanizate. These properties improvements could be attributed to the interaction of the silanol groups of the silica with the epoxide groups of the modified rubber chains via chemical and physical interactions. This could be supported by the occurrence of tear parts from the morphology investigation of the tensile fractured surface of the modified rubber vulcanizates using a scanning electron microscope. The presence of silicon elements in the rubber matrix was evidenced by scanning electron microscopy and energy dispersive X-Ray spectrometer. Moreover, the silica filled epoxide functionalized natural rubber having 14 mol% epoxide content without a silane coupling agent exhibited low abrasion loss, low heat build-up and enhancement in loss tangent at 0 °C, hence improved wet skid resistance, compared to the silica filled natural rubber without a silane coupling agent. This work demonstrated that the prepared low degree of epoxide functionalized natural rubber could be potentially applied to the tire tread rubber application without the use of a silane coupling agent.

Sustainable Epoxidized Guayule Natural Rubber, Blends and Composites with Improved Oil Resistance and Greater Stiffness.

Production of petroleum-based synthetic rubbers (SRs) causes an enormous carbon footprint for the rubber industry. Carbon footprint would be reduced if natural rubber (NR) could take a larger market share and replace significant quantities of SR. However, some SRs have higher oil resistance than NRs, and, in applications where these properties are needed, chemically modified NR will be required. Epoxidation is a chemical modification of NR which partially converts unsaturated bonds on the backbone of NR to epoxy groups. In this research, epoxidized guayule natural rubber (EGNR)/guayule natural rubber (GNR) blends and GNR were used to make carbon black (CB) filled composites. The processability, mechanical properties, swelling behaviors and dynamic mechanical properties were characterized at various epoxide fractions. Composites made with EGNR/GNR had higher oil resistance, wet traction and stiffness than GNR composites, although tensile strength and elongation at break were reduced by epoxidation. EGNR is expected to lead to the development of new NR products with similar properties to SR, eroding SR markets and increasing the sustainability of the rubber industry.

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.

Effect of urea deproteinization on catalytic hydrogenation of natural rubber latex

Natural rubber is unsaturated biopolymer which has low resistance to heat, oxygen, and ozone. Chemical modification of natural rubber by catalytic hydrogenation can improve its oxidative property. In this study, the catalytic hydrogenation of natural rubber was investigated in latex phase after reduction of protein content with urea. Hydrogenation of deproteinized natural rubber latex was performed by using diimide which generated insitu from hydrazine hydrate/hydrogen peroxide and catalyst (boric acid, cupric sulfate and cupric acetate) at 70°C for 5 h. The hydrogenation system was stabilized with sodium dodecyl sulphate. The hydrogenation of deproteinized natural rubber (HDPNR) was confirmed by FTIR analysis. The result indicated that cupric sulphate was extremely active catalyst which was showed by the elimination of C=C transmittance bands at 1660 cm-1 on HDPNR spectra and highest degree of hydrogenation. Furthermore, urea deproteinization increased possibility of side reactions during catalytic hydrogenation as seen on the reduction of gel content compared to undeproteinized natural rubber.

PROPERTIES OF NR AND NR/ENR BASED RUBBER COMPOUNDS REINFORCED WITH CHOPPED AND SIZED CARBON FIBER

High elasticity, mechanical resistance and antivibration characteristic s of natural rubber (NR) are essential issue in the main area of vehicle tyres and high modulus demanding bearing applications. In this study, especially in bearing applications, where natural rubber modulus properties are limited, natural rubber has been reinforced with chopped and hydrocarbon sized carbon fiber to get improved tensile modulus. Besides, epoxidized natural rubber (ENR), which was produced by chemical modification of natural rubber, blended with NR and the compounds have been reinforced with epoxy sized carbon fiber. NR and NR/ENR based rubber compounds’ rheological, mechanical, and aging properties have been systematically investigated and evaluated.

Carboxy terminated rubber based on natural rubber grafted with acid anhydrides and its adhesion properties

The chemical modification of natural rubber by grafting of various polar functional molecules is an essential method, improving the versatility of rubber in applications. This research investigated the preparation of natural rubber-graft-citraconic anhydride (NR-g-CCA), natural rubber-graft-itaconic anhydride (NR-g-ICA), and natural rubber-graft-maleic anhydride (NR-g-MA), with the anhydrides grafted to natural rubber in toluene using benzoyl peroxide as an initiator. Variations of monomer content, initiator content, temperature and reaction time of the grafting copolymerization were investigated. The maximum degrees of grafting were 1.06% for NR-g-CCA, 4.66% for NR-g-ICA, and 5.03% for NR-g-MA, reached using 10 phr citraconic anhydride, 10 phr of itaconic anhydride, or 8 phr of maleic anhydride, 3 phr benzoyl peroxide, at 85, 80 and 80°C for 2, 2 and 3 hrs, respectively. Solvent-based wood adhesives were formulated from these copolymers with various contents of wood resin in the range 10-40 phr. The maximal 289 N/in cleavage peel and 245.7 KPa shear strength for NR-g-MA (5.03% grafting) were obtained at 40 phr wood resin.

Chemical Modification of Natural Rubber in the Latex Stage by Grafting Cardanol, a Waste from the Cashew Industry and a Renewable Resource

Cardanol, an agricultural byproduct of the cashew industry, is a cheap and abundantly available renewable resource. The multifunctional activity of cardanol in the rubber and polymer industries has been well-established in recent years. The present study highlights the chemical grafting of cardanol onto natural rubber in the latex stage. The cardanol grafted natural rubber is characterized by FTIR and NMR spectroscopies. The grafting parameters have been optimized for maximum yield in terms of percent grafting and grafting efficiency by the Taguchi method. Four control factors, i.e., initiator concentration, cardanol concentration, reaction temperature, and reaction time, are chosen at three different levels. The optimum parameter combination is found to be the initiator concentration 2 phr, cardanol concentration 10 phr, reaction temperature 65 °C, and reaction time 6 h. The analysis of variance method is used to evaluate the percentage contributions of the different control factors on the percent grafti...

天然ゴム 天然ゴムの化学変性

The present review describes chemical modification of natural rubber, consisting of cis-1,4-polyisoprene, to introduce functional group. Natural rubber was first purified with urea in latex stage to remove proteins which inhibit precision control of the chemical modification. The resulting purified natural rubber was subjected to radical and ionic chemical reaction. Introduction of hydroxyl group, carbonyl group or functional polymer at allylic position of cis-1,4 isoprene unit was achieved with radical initiator to prepare liquid natural rubber and graft-copolymer, while it was reacted with hydrogen, peroxycarboxylic acid, carbon dioxide, water and polylactide to introduce hydrogen, epoxide, carbonate, hydroxy group and tetrahydrofuran, and ester at olefinic position, respectively.

Mechanical characteristics of hydrogenated natural rubber vulcanizates

AbstractMechanical properties of partially hydrogenated natural rubber (HNR) vulcanizates were evaluated regarding their chemical structure and crystallizable nature of HNR, and are reported here, to the best of our knowledge, for the first time. HNRs of three levels of hydrogenation (20.6, 29.0, and 40.6 mol%) were successfully prepared by the chemical modification of natural rubber (NR) latex using N2H4 and H2O2 as reagents, in a sufficient amount for preparing sulfur‐crosslinked samples to be subjected to mechanical and structural measurements. The three HNR vulcanizates were found to be crystallizable upon stretching; it is noted that even 40.6 mol% hydrogenation did not prevent HNR vulcanizates from crystallization upon stretching, while their onset strain of crystallization was higher than that of NR vulcanizate. The hysteresis loss and residual strain up to a stretching ratio of 2 for the HNR vulcanizates tended to become larger with the increase in the degree of the hydrogenation. Tensile and dynamic mechanical properties of 20.6 mol% hydrogenated HNR vulcanizate were comparable to those of NR vulcanizate. From differential scanning calorimetry and temperature dispersion of dynamic modulus or loss, the glass transition temperatures of HNR vulcanizates were found to be almost the same as that of NR vulcanizate, which is also notable. The thermal stability of HNR vulcanizates was better than that of NR vulcanizate. Thus, this chemical modification seems to give a promising NR derivative whose properties can be equivalent or even better than the mother polymer. Copyright © 2008 John Wiley & Sons, Ltd.

Dichlorocarbene modification of natural rubber and its role as a modifier in blends of natural rubber and hydrogenated nitrile rubber

AbstractDichlorocarbene modification of natural rubber (NR) carried out by alkaline hydrolysis of chloroform in presence of cetyl trimethyl ammonium bromide as phase‐transfer catalyst was investigated. Extent of chemical reaction was characterized by estimation of chlorine content and FTIR studies. Rate of dichlorocarbene addition depends on the time and temperature of reaction. Reaction carried out at 60°C for 2 h yielded a material with a chlorine content of 15%. Chemical modification of NR was accompanied by introduction of chlorine through cyclopropyl ring to the main chain of NR as revealed from FTIR studies. As level of chlorination increased, the physical nature of NR changed from a soft flexible state to a hard nontacky form. Blends of NR with hydrogenated nitrile rubber (HNBR) containing three to seven parts of dichlorocarbene‐modified NR (DCNR) of chlorine content 15% could be prepared by conventional mill mixing. Incorporation of DCNR into blends of NR and HNBR promoted polar interaction between the chlorine segments and acrylonitrile segments of the blend as shown from the shift in characteristic IR absorption peaks and shift in Tg from DSC studies. As a consequence, DCNR acted as an interface modifier in blends of NR and HNBR. Blends of NR and HNBR containing DCNR showed a considerable improvement in cure behavior, physical properties, and ageing characteristics in oil, ozone, and high temperature compared to pure blends of NR and HNBR. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4401–4409, 2006

FTIR spectra of plasticized grafted natural rubber–LiCF 3SO 3 electrolytes

Chemical modification of natural rubber (NR) has frequently been attempted to improve the performance in specific application. 30% poly(methyl metacrylate) (PMMA) grafted into NR (MG30) has been explored as a potential candidate for polymer electrolytes. The complexation effect of salt and plasticizer in polymer host electrolytes had been investigated using FTIR. The carbonyl stretch of MG30 locates at 1729 cm −1, with the addition of lithium trimethanesulfonate (LiCF 3SO 3) salt, new band evolves at lower frequency region at 1643–1645 cm −1. The nondegenerate vibrational mode of ν s(SO 3) of salted electrolytes appearing at 1031–1034 cm −1 comes from ‘free’ trimethanesulfonate anions and the 1040–1046 cm −1 absorption from the monodentate ion paired with triflates. These indicate MG30–salt interaction. When MG30 and ethylene carbonate (EC) formed film, the CH 3 asymmetric bend of MG30 appearing at 1447 cm −1 is shifted to 1449 cm −1 in the EC–polymer complex. The C O stretching at 1729 cm −1 also shifted to 1728 cm −1. Hence, the EC–MG30 system is complexed to each other. EC–LiCF 3SO 3 interactions are indicated by the shifting of C O bending band of EC from 718 cm −1 being shifted to 720 cm −1 in the complex. In Li +–EC interaction where the ring breathing region at 897 cm −1 in EC has shifted to 899 cm −1 in EC–salt spectrum. The band appearing at 1643–1645 cm −1 due to the coordination of Li + ← O–C is still under observation and new peaks at 1779 and 1809 cm −1 are responsible to the carbonyl stretches of EC in plasticized salt–polymer electrolytes.

FTIR and thermal studies of modified natural rubber based polymer electrolytes

Chemical modification of natural rubber (NR) has frequently been attempted to improve the performance in specific application. 30% poly (methyl metacrylate) grafted NR (MG 30) has been explored as a potential candidate for polymer electrolytes. The complexation effect of LiCF3SO3, ethylene carbonate (EC) and Al2SiO5 in polymer host electrolytes has been investigated using FTIR ICP-OES spectrometry. Thermal studies of the systems have displayed a stable trend of glass temperature transition at elevated salt concentration whereas incorporation of EC and filler into the system results in the same pattern in their Tg values.

Chemical modifications of polydiene elastomers: A survey and some recent results

By chemical modification of natural rubber, it is possible to modify its basic properties (for instance, improvement of gas permeability, resistance to oils or fire resistance) or to prepare new polymeric materials for specific applications (for instance, photocrosslinkable rubbers and rubbers support of active molecules). The purpose of the present paper is to give an overview of recent works carried out in the field of new rubber derivatives for specific applications, especially dealing with natural rubber degradation and products derived from liquid rubbers of type 1,4-polyisoprene (liquid natural rubbers, synthetic polyisoprenes) and/or their epoxidized forms. A reflexion on the perspectives of researches on natural rubber or its derivatives is given in conclusion. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1461–1477, 2000

Kinetic behavior of UV‐sensitive polymers from modified natural rubber

AbstractPhotosensitive copolymers have been obtained by chemical modification of natural rubber. The introduction of the photoreactive cinnamoyl group in different conversions has been carried out by the reaction of natural polyisoprene with maleic anhydride, followed by ring opening and condensation with some oxyalkylcinnamate esters. These reactions gave rise to five polymer series. Each series, for which the anhydride content was kept constant, is constituted of five copolymeric products, differing from each other in the size of the aliphatic chain between the chromophore and the main chain. The photosensitive products were submitted to UV irradiation, and their kinetic behavior has been investigated in order to correlate structural dissimilarities with the dimerization rate constants.

Infrared analysis of isomerized, vulcanized and oxidized natural rubber

AbstractThe purpose of this study was to follow by i.r. analysis double bond shifts and chemical modification of natural rubber. Accurate determination of the original rubber spectrum is facilitated by the use of an internal standard. Isorubber, prepared by thermal dissociation of rubber hydrochloride, contains about 50% of double bonds in the side groups. Although a similar double bond shift is observed in the cyclization of rubber, part of the absorption, in the 11 μ region, may here be due to ring formation. Vulcanization with accelerated sulfur mixtures does not produce changes in the i.r. spectrum, unless the rubber is transformed into a derivative by overcuring with S2Cl2 or during hard rubber formation. At least three types of oxidation reactions can be distinguished spectroscopically: (1 ) degradation of the rubber (by oxidation of a rubber solution with air) with the ultimate formation of only volatile oxidation products; (2 ) gradual formation of oxygenated derivatives (oxidation with ozone), with a distinguishable structure in the spectrum; (3 ) gradual formation of an oxidized and more saturated rubber (oxidation of solid rubber with air), with less characteristic broad absorption bands.