Reinforcement of natural rubber

In this article, we report on recent investigations on filled natural rubber. These investigations include a mechanical characterization as well as a molecular analysis based on measurements of chain orientation. It is demonstrated that at intermediate strains, the increase in the moduli can be explained by the inclusion of rigid particles in the soft matrix and from molecular interactions between the rubber and the filler. These interactions can be evaluated by equilibrium swelling and by orientational measurements. With regard to the unfilled formulation, carbon black– and silanized‐filled natural rubber exhibit increases in the cross‐linking density ascribed to filler‐polymer links, whereas a large decrease in the orientational level, evidenced by birefringence and by infrared dichroism, is observed when silica is added without any coupling agent. Finally, two specific effects—the Payne and Mullins effects, both related to energy dissipation phenomena—are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2301–2316, 2002     

Length scale dependent deformation in natural rubber

Strong length scale dependent deformation has been previously observed in the elastomer polydimethylsiloxane by indentation type experiments at micro‐ to nanometer length scales with a sharp conical tip. To examine if other nonsilicone based elastomers exhibit similar length scale dependent deformation behavior, natural rubber has been chosen in this study. Performing indentation type tests with a nanoindentation system, the universal hardness and the elastic modulus are determined at different probing depths ranging from about 90 to 5 μm to characterize length scale dependent deformation behavior in natural rubber. The testing with a Berkovich tip resulted in an amazing increase in the universal hardness with decreasing probing depth indicating that the deformation mechanisms at the micrometer length scales are significantly different as compared to those at the macroscopic length scales. The observed length scale dependent deformation is associated with an increase in rotation gradients with decreasing probing depth. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42683.     

Comparison of the effects of collagen and modified collagen fillers on the properties of XNBR rubber

The aim of this study was to compare the effects of 5 to 30 parts by weight of unmodified and modified collagen on the properties of XNBR rubber vulcanized with a cross‐linking system. This study is a part of experimental series concerning polymeric materials that are biodegradable due to their filling with a waste protein such as collagen. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Transient effects in dynamic modulus measurement of silicone rubber,part 2: Effect of mean strains and strain history

The strain‐dependent dynamic storage modulus of a poly(dimethyl‐siloxane‐co‐methylvinyl‐siloxane‐co‐methylphenyl‐siloxane)‐based silicone elastomer (PVMQ), which is reinforced with fumed silica and crosslinked with peroxide, is investigated. The time dependence of the dynamic storage modulus on the magnitude of the mean strain at a particular test condition is investigated. The dynamic modulus results are shown to depend on the time of cycling as well as the relative magnitudes of the dynamic and mean strains. The relaxation of the force required to maintain the mean strain is observed to depend on the magnitude of the dynamic strains and the data are shown to be consistent with static stress relaxation experiments in the limit of zero dynamic strain. Recovery of the dynamic modulus from the exposure to higher strain cycling is seen to be facilitated by dynamic cycling with higher cycling strains yielding faster recovery rates. The observed phenomena are interpreted in terms of the role of entanglements in the polymer phase on the dynamic behavior of the elastomer material. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2197–2204, 2007     

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

Dichlorocarbene 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 T_g 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     

Influence of filler–rubber interactions on the viscoelastic properties of carbon‐black‐filled rubber compounds

The specific role of filler–rubber interactions in dynamic properties was investigated. Natural rubber compounds, filled with N330 carbon black, were used, and the filler surface was modified through a gas treatment in the solid phase. The effects of this filler surface treatment on the dynamic properties were systematically studied at equal filler dispersion levels. The dynamic properties were assessed for both uncured and vulcanized compounds, and a number of advanced investigative techniques were used to characterize not only the modification of the carbon particle surface by an oxidative treatment but also the structure of the filled rubber compounds. Particular attention was paid to techniques that gave access to the segmental mobility to explain the benefit observed with modified carbon black. A molecular interpretation, based on NMR measurements, was considered that took into account physicochemical parameters. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 577–588, 2004     

Nanocapsules embedded in natural rubber latex gloves

To prepare medical gloves containing disinfectant agent, poly(methyl acrylate) (PMA) with _w of 550 K was synthesized via the iniferter technique and then used for encapsulating disinfectant agent, i.e., chlorhexidine digluconate (CHD), droplets. The CHD‐PMA nanocapsules suspended in a sodium dodecyl sulfate aqueous solution having 93% encapsulation efficiency were successfully embedded between the outermost and inner layers of γ‐radiation vulcanized natural rubber (RVNR) latex films by the coagulant dipping process. A RVNR/CHD‐PMA nanocapsules/RVNR three‐layer structure was revealed by the contact angle measurement, ATR‐FTIR and SEM. Both the tensile strength and elongation at break of the three‐layer film were also measured. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Reinforcement and antioxidation effects of fullerenol‐containing natural rubber

Natural rubber (NR) containing fullerenol, C60‐OH, was prepared by two methods; one by mixing C60‐OH aqueous solution to NR latex followed by coagulation (wet method) and the other by mixing C60‐OH powder with solid rubber by an open roll mixer (dry method). C60‐OH mixed by wet method was homogeneously dispersed in the rubber, while one mixed by dry method was particles in the size up to 70 μm. The former exhibited large reinforcing and antiaging effect than the latter. The large antiaging effect was explained by the finding that C60‐OH had large radical scavenging ability and gel forming ability during heat treatment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Deformation behaviour of styrene/butadiene star block copolymer/hPS blends: influence of morphology

The influence of morphology on micromechanical deformation behaviour of blends consisting of a lamellar forming styrene/butadiene star block copolymer and polystyrene homopolymer (hPS) was studied by transmission electron microscopy (TEM). The pure star block copolymer and the microphase separated blends revealing lamellar structure with polystyrene (PS) lamella thickness in the range of about 20 nm showed homogeneous plastic deformation of the PS lamellae. The macrophase separated blends with PS particles in lamellar matrix exhibited debonding at the particle–matrix interface associated with extensive plastic deformation of the surrounding matrix. The blends containing PS matrix deformed via crazing.     

Microwave devulcanization of ground tire rubber and applicability in SBR compounds

Rubber recycling is a major environmental challenge, as their covalently crosslinked structure makes it impossible to reprocess via conventional polymer processing technologies. Devulcanization of rubber waste, whereby crosslinks are selectively broken, may provide a solution, as it allows it to be remolded into new shapes. We used two types of ground tire rubbers (GTRs) for this study; mechanically ground and waterjet-milled GTRs with different particle sizes. First, we revealed the effects of GTR particle size on the devulcanization process. We examined the sol content of the samples before and after devulcanization with two different microwave ovens, a power-controlled conventional one, and a temperature-controlled laboratory oven. In the latter one, heating rate and maximum temperature were controlled. We studied the effects of temperature, atmosphere in which the rubber was treated, heating rate, and holding time at maximum temperature. We prepared styrene-butadiene rubber-based rubber compounds containing GTR and optimally devulcanized GTR (dGTR_WJ). The physical and mechanical properties of the samples were assessed. The results indicate that both GTR_WJ and dGTR_WJ have an accelerating and a mildly softening effect on curing and dGTR_WJ has a less significant negative effect on mechanical properties: 15 phr GTR_WJ has the same effect as 45 phr dGTR_WJ. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48351.     

In situ epoxidized natural rubber: Improved oil resistance of natural rubber

This study sought to synthesize an in situ epoxidized natural rubber (NR) from 20% dry rubber content latex stabilized by nonionic surfactant, 5 phr of Terric 16A16, in the presence of hydrogen peroxide and formic acid at the temperature of 50°C. The molar ratios of H₂O₂ and HCOOH to isoprene unit were equal, 0.75 : 0.75. Reaction was carried out for 3 to 8 h. This reaction yielded products of various epoxide contents depending on reaction time. Based on DSC characterization, epoxide contents of the in situ epoxidized natural rubbers (ENRs) were about 22–39 mol %. Tensile properties and tear resistance of the in situ ENRs were equal to, or better than, those of NR and commercial ENRs. The in situ epoxidation improved resistance to petroleum ether, but not to toluene. Changes in volume and weight of specimens immersed in ASTM no. 3 oil and automobile oils (various trade names: Shell engine oil, Shell gear oil, and Toyota motor oil) exhibited significant decrease after epoxidation, except in Shell brake fluid. Similar results were obtained from tensile testing of the oil‐immersed specimens. Tensile strength and elongation at break of the in situ ENRs were much higher than those of NR after immersion in those oils at room temperature for 7 days, except the immersion in brake fluid. Improved oil resistance of the in situ ENRs under severe condition was obtained in gear oil. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 261–269, 2003     

Fatigue crack growth dynamics in filled natural rubber

Abstract

We present fatigue experiments performed on filled natural rubber and study the correlations between crack growth dynamics and fracture morphologies imprinted by an irregular crack path. Slow crack growth dynamics is obtained by cyclic fatigue in a pure shear test. We will show that an unstable crack growth regime exists for high loads. We will also discuss the appearance of sawtooth striations which follow a scenario that significantly differs from previous results reported in the literature.     

Mechanical properties of natural rubber filled with flyash

The mechanical properties of flyash‐filled natural rubber were investigated and compared with those filled with calcium carbonate. A number of composites with varying percentage of the fillers were prepared using a two‐roll mill and molded on compression molding press. Specimens were subjected to mechanical testing. The properties studied were tensile strength, modulus at various elongations, hardness, density, etc. From the results it was observed that flyash‐filled composites were better in mechanical properties compared to those filled with calcium carbonate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 995–1001, 2002     

Isoprene rubber filled with silica generated in situ

We modified synthetic isoprene rubber by means of the in situ generation of silica particles through the sol–gel process starting from tetraethoxysilane (TEOS) as an inorganic oxide precursor. Different reaction conditions were investigated with variations in the initial TEOS content, the reaction time of the sol–gel process, and the presence of a coupling/surfactant agent (octyltriethoxysilane). Organic–inorganic hybrid materials with a silica content up to 70 phr were obtained with the complete conversion of TEOS to silica for a long enough sol–gel reaction time. A very homogeneous dispersion of silica particles was observed in all cases together with a very good adhesion between the filler and matrix. The size of the in situ generated silica was controlled by the appropriate addition of octyltriethoxysilane. Swelling and extraction tests and dynamic mechanical analysis indicated that the vulcanization process of isoprene rubber was perturbed by the sol–gel process; this led to a slight decrease in the crosslinking degree. However, a significant reinforcing effect due to the presence of silica particles was observed for all of the investigated samples. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of liquid media on lifetime predictions of nitrile rubber

Evaluating a material's suitability for an application includes determination of its expected service lifetime. For alternative fuels, this entails assessing, inter alia, their effect on the durability of polymeric engine components, e.g., seals, gaskets, and O‐rings. When this is governed by thermally activated chemical deterioration, the conventional approach to characterizing aging is laboratory measurements of property changes of the polymer subjected to accelerated conditions (usually higher temperatures), with the data analyzed by an Arrhenius analysis. However, this method is inefficient and time‐consuming when the number of candidate alternative fuels is large. Herein, we test the hypothesis that the activation energy governing thermal oxidation of elastomeric engine components is independent of the fuel; thus, while the aging rate may vary, the effect of temperature is independent of the contacting liquid. Accelerated testing of the thermal oxidation of nitrile rubber O‐rings were carried out in three liquids, including a fossil fuel and a bio‐fuel. The activation energy obtained from changes in crosslink density, = 82 kJ/mol, was the same for all liquids and consistent with the broad range of literature values for similar compounds aged in air. This result suggests the possibility that estimates of the lifetime of polymeric engine components require only a single accelerated aging test, with the known activation energy used to predict the durability at the service temperature. This would represent at least an order of magnitude reduction in testing requirements. The extension of the approach to the general aging of polymers exposed to different environments is obvious. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40296.     

Effect of mica addition on the properties of natural rubber and polybutadiene rubber vulcanizates

The rheometric, mechanical, and dynamic mechanical properties as well as fracture surfaces of natural rubber–mica and polybutadiene rubber–mica vulcanizates were studied. Mica was used in the range of 0–30 phr and the rheometric study was carried out at 160°C. The results indicate that the mechanical properties are improved as filler addition increases. Dynamic mechanical testing was used to analyze the observed mechanical behavior. The two elastomers showed different fracture behaviors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2156–2162, 2003     

Toughening of polypropylene by combined rubber system of ultrafine full-vulcanized powdered rubber and SBS

A combined rubber system of ultrafine full-vulcanized powdered rubber (UFPR) and SBS was used for polypropylene toughening. The PP toughened with the combined rubber system shows not only higher impact strength as compared to each rubber component used alone but also good stiffness and heat resistance. Crystallization study shows that the UFPR is more efficient in promoting the crystallization of PP than SBS, leading to a higher crystallinity and an enhancement of stiffness and heat resistance of PP. The combined rubber system containing UFPR and a small amount of SBS still possesses a good nucleating ability. Transmission electron microscopy results indicate that the combined rubber system mostly forms an encapsulation structure of UFPR particles encapsulated by SBS phase. This morphology was also confirmed by scanning electron microscopy results through observing the fracture surfaces of toughened samples. A small amount of SBS was found to be helpful for a better dispersion of UFPR in PP matrix. The causes for the encapsulation morphology and the synergistic toughening effect were discussed. A tentative explanation was given by comparison of the solubility parameter of each component in the toughened samples.     

Sorption and diffusion of gold and silver nanoparticles in solution through nitrile rubber membrane

Mechanical and physical properties of the rubber material may be affected by swelling when brought into contact with solutions of engineered nanoparticles (ENP). As the rubber swells in the liquid carrier of the ENP, the polymeric chains of the network expand and the ENP can penetrate the structure being carried by the diffusion of the liquid. The aim of this work is to assess the influence of ENP and evaluate the effect of additives present in the solutions on the diffusion process through a rubbery structure. Swelling of membrane material specimens was evaluated by measuring mass gain and liquid diffusion was then deduced. The present study focuses on the contact of nitrile rubber membranes with commercial gold ENP (5 and 50 nm in diameter) and silver ENP (50 nm) in MilliQ water. Swelling tests were also conducted with MilliQ water and filtrates (the solutions from which the ENP were extracted). Results show that the diffusion coefficients of all the solutions of ENP are slightly different and are around 1.2 × 10^?10 cm² s^?1. However, it should be noted that these coefficients are notably higher for the filtrates and reach 2.4 × 10^?10 cm² s^?1 for the filtrate of the silver ENP. This result underscores the effect of the ENP on the liquid penetration process. We also found that the ENP has a noticeable effect on the Fickian diffusion mechanism of the penetrant; it was noticed that the presence of these nanoparticles lowers the diffusion mechanism index. Moreover, the size of the nanoparticles was found to have an impact on the diffusion coefficient of the solutions as well as their solubility. These findings help to better understand the diffusion phenomenon of the ENP through nitrile membrane materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45350.     

Homogenization of natural rubber network induced by nanoclay

Vulcanization gives birth to the nonuniformity of rubber network, the identification of which is the basis of improvement of performance of rubber products. We established a visco‐hyperelastic constitutive equation to reveal the quantitative distribution of the inhomogeneous network phases according to a three‐phase model. The cross‐linked network was assumed to be composed of the cross‐linking cluster, the low network chain density domain and the fluid‐like mass. The incorporation of clay with high specific surface area induced the effective uniformity of network structure by decreasing the content of the cross‐linking cluster and increasing that of the low network chain density domain. These structural variations were responsible for excellent mechanical properties and strong strain‐induced crystallization ability probed by the in situ synchrotron wide‐angle X‐ray diffraction. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40324.