Improved Dispersion of Carbon Nanoparticles Modified by Poly(Sodium 4-Styrenesulfonate) and Its Influence on the Properties of Natural Rubber Latex

A novel strategy of radical polymerization of sodium 4-styrenesulfonate on the surface of carbon black (CB) in the solid state was developed to prepare hydrophilic carbon nanoparticles (PNASS-CB). A high performance natural rubber latex (NRL)/PNASS-CB composite was produced by the latex compounding technique. Scanning electron microscope shows considerable improvement in the dispersion of PNASS-CB in rubber matrix. The lower degree of filler–filler networks and the stronger filler–rubber interaction of PNASS-CB in rubber matrix were confirmed by dynamic mechanical thermal analysis. Rheometric properties of NRL/PNASS-CB, like scorch time and optimum cure time, decreased. Tensile strength, tear strength, and elongation at break increased due to stronger interaction between the PNASS-CB and rubber matrix. Dynamic mechanical properties of the modified carbon nanoparticles further corroborated a significant contribution from the better dispersion and efficient load transfer of PNASS-CB on the static and dynamic mechanical properties of composites.     

Investigation of Carbon Black Network in Natural Rubber with Different Bound Rubber Contents

A new method was applied to modify the surface activity of virginal carbon black (VCB). LA‐57, one kind of hindered amine light stabilizer, was adsorbed onto the carbon black surface through a strong shear force induced by the screws of a HAAKE internal mixer. The modified carbon black (MCB) was characterized by FT‐IR and thermogravimetric analysis (TGA). The bound rubber content of the natural rubber (NR) compounded with MCB and VCB varied with the fraction of LA‐57 on the MCB surface. The nonlinear effect at small strains, generally referred as the Payne effect, was investigated in the rubber compounds based on the different bound rubber contents. The NR compound containing the lowest bound rubber content had an obvious Payne effect. Based on the bound rubber content, the types of filler network varied from direct contact mode to the joint rubber shell mechanism.     

Stress-Strain Behaviors and Crosslinked Networks Studies of Natural Rubber-Zinc Dimethacrylate Composites

The stress-strain behaviors of natural rubber (NR)-zinc methacrylate (ZDMA) composite have been studied by uniaxial tension. The results indicated that there was a large reinforcement by ZDMA and the NR/ZDMA composites exhibited a high stress-softening effect. Meanwhile, the recovery stretch curve was close to the second stretch curve; thus a weak stress recovery of the composites was shown. The analysis of crosslink density indicated that the damage to the crosslink network was mainly due to the breakage of ionic crosslinks at low strain (100%). A more developed ionic crosslink network was formed at a higher content of ZDMA. When the vulcanizate is subjected to loading in tension, the ionic crosslink network will suffer the force first. Next, the slippage of ionic bonds will take place under the stress. A new ionic crosslink network might be formed rapidly after the ionic bonds were broken during the stretching. Therefore, it could not return to the initial state. The analysis of crosslink density and stress recovery indicated that the rubber chains could be adsorbed to the ZDMA aggregates due to the formation of poly-zinc methacrylate (PZDMA). A molecular analysis of NR/ZDMA composites is proposed in the last part of this article.     

Properties of Natural Rubber Vulcanizates/Nanosilica Composites Prepared Based on the Method of In-situ Generation and Coagulation

Using the characteristics of silica sol dispersing well in water and easy formation of silica gel when the silica sol is heated, by mixing a system of concentrated natural rubber latex and silica sol, the silica sol can in-situ generate SiO₂ particles when heated. After coagulation of the mixed system, natural rubber/nanosilica composites C(NR/nSiO₂) were obtained. The composites C(NR/nSiO₂) and their vulcanizates were studied using a rubber processing analyzer (RPA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The influence of silica contents on the C(NR/nSiO₂) vulcanizates mechanical properties, cross-linking degree, Payne effect, dissipation factor (tanδ), and the particle size and dispersion of SiO₂ in NR were investigated. The results obtained were compared with the NR/SiO₂ composites based on traditional dry mixing of bale natural rubber and precipitated silica (white carbon black). The results showed that when using a sulfur curing system with a silica coupling agent (Si69) in C(NR/nSiO₂), the vulcanizate had better mechanical properties, higher wet resistance, and lower rolling resistance than those without Si69. In the composites C(NR/nSiO₂) and their vulcanizates, the SiO₂ particles’ average grain diameter was 60 nm, and the good-dispersion of the in-situ generated SiO₂ in the rubber matrix were a significant contribution to the satisfactory properties of C(NR/nSiO₂) composites and their vulcanizates.     

Dynamic Fatigue Behavior of Natural Rubber Reinforced with Nanoclay and Carbon Black

The dynamic fatigue behaviors of natural rubber (NR) filled with carbon black (CB) and both nanoclay (NC) and CB at same hardness was evaluated using the stepwise increasing strain test (SIST) and long-term testing. Compared with NR/CB composites, NR/CB/NC nanocomposites exhibited higher fatigue-limited strain, stronger dynamic stress relaxation, and longer compression fatigue life. By examining the fracture morphologies, nonlinear viscoelastic behavior, and hysteresis loss of filled NR, it was found that NR, synergisticly reinforced by NC and CB, exhibited improved anti-fatigue ability than NR filled with CB due to stronger filler–filler interactions between NC and CB (a local filler network) and the high aspect ratio and typical lamellar structure of NC.     

Tensile properties of styrene-butadiene rubber/silica composites with mercapto functional silane coupling agents: influences of loading method and alkoxy group number

The influences of alkoxy group number and loading method of silane coupling agents on the mechanical properties of a styrene-butadiene rubber/silica composite were investigated. Mercapto functional silane coupling agents with dialkoxy and trialkoxy structures were used. The pre-treatment method and the integral blend method were compared. Both the fracture stress and modulus at 200% strain were higher in the pre-treatment than in the integral blend for dialkoxy type composites. However, they were higher in the integral blend than in the pre-treatment for trialkoxy-type composites. The interaction between the silane chains on the silica surface and the rubber molecular chains at the interfacial region was estimated by ¹H pulse nuclear magnetic resonance spectroscopy using an unvulcanized silica/rubber mixture. It was found that the binding of rubber molecular chains by the silane chains was higher in the pre-treatment system for dialkoxy-type composites, whereas it was higher in the integral blend for trialkoxy-type composites. The reason is proposed as follows: in the pre-treatment for dialkoxy type, a linear silane chain formed in the case of multi-layer coverage. The silane chain entangled with the rubber chain in the interfacial region and improved the reinforcement effect. For the trialkoxy type, a network structure formed using the pre-treatment method, lowering the amount of entanglement. However, in the integral blend for trialkoxy type, the formation of the silane network and the entanglement progressed simultaneously during the preparation process. A well-entangled interfacial region was formed.     

Preparation and Characterization of Grafted Natural Rubber/Graphene Oxide Nanocomposites

Vinyltriethoxysilane (VTES) was grafted onto natural rubber (NR) in latex form, using potassium persulfate (KPS) as initiator. The VTES grafted NR (NR-g-VTES) was then further reinforced with graphene oxide (GO) by a mechanical mixing method with different GO loadings to get the rubber composite (GO/NR-g-VTES). The NR-g-VTES was characterized and confirmed by attenuated total teflectance-Fourier transforms infrared spectroscopy (ATR-FTIR). The effect of GO content on the curing characteristics and resulting mechanical properties of the GO/NR-g-VTES were studied and compared with neat NR filled with GO (NR/GO). The maximum and minimum torque and the tensile and tear strength of the NR-g-VTES/GO composites were higher than that of NR/GO. The samples containing low GO concentration showed maximum torque and tensile and tear strength. Dynamic mechanical analysis showed that the interaction between GO and NR-g-VTES was better than that of the GO-reinforced NR.     

Effect of Wood Flour on the Curing Behavior,Mechanical Properties,and Water Absorption of Natural Rubber/Wood Flour Composites

The preparation of natural rubber/wood flour (NR/WF) composites and the influence of WF content, modification, and particle size on the vulcanizing behavior, mechanical properties, and water absorption of NR/WF composites are described. Results show that the addition of WF into NR delayed the scorching time and vulcanizing time of NR. The appropriate WF contents can improve the mechanical properties of NR. However, the overloading of WF destroys the mechanical properties of NR. The addition of WF increased the water absorption of NR. The silicone couple agents that were used to modify the WF had little effect on the water absorption of NR/WF composites. Decreasing the WF particle size enhanced the water absorption of NR/WF composites because the water-absorbing surface area increased with decreasing WF particle size. The water absorption of sisal-fiber-filled NR-based composites was larger than that of the WF-filled NR-based composites. A useful equation, w=ktⁿ , was inferred from the water absorption results to calculate the water absorption (w) of the NR/WF composites as a function of time (t), where k was a constant concerning the compounds’ character that was primarily determined by the WF's character and n was the power of time that was related to the NR's inherent character, such as cross-linking density, and primarily determined the water absorption rate.     

Characterization of Filler-rubber Interaction,Filler Network Structure,and Their Effects on Viscoelasticity for Styrene-butadiene Rubber Filled with Different Fillers

For styrene-butadiene rubber (SBR) compounds filled with the same volume fraction of carbon black (CB), precipitated silica and carbon–silica dual phase filler (CSDPF), filler-rubber interactions were investigated thru bound rubber content (BRC) of the compounds and solid-state ¹H low-field nuclear magnetic resonance (NMR) spectroscopy. The results indicated that the BRC of the compound was highly related to the amount of surface area for interaction between filler and rubber, while the solid-state ¹H low-field NMR spectroscopy was an effective method to evaluate the intensity of filler-rubber interaction. The silica-filled compound showed the highest BRC, whereas the CB-filled compound had the strongest filler-rubber interfacial interaction, verified by NMR transverse relaxation. The strain sweep measurements of the compounds were conducted thru a rubber process analyzer; the results showed that the CSDPF-filled compound presented the lowest Payne effect, which is mainly related to the weakened filler network structure in polymer matrix. The temperature sweep measurement, tested by dynamic mechanical thermal analysis, indicated that the glass transition temperature did not change when SBR was filled with different fillers, whereas the storage modulus in rubbery state and the tanδ peak height were greatly affected by the filler network structure of composites.     

Preparation of Water-suspensible Carbon Nanoparticles and Their Influence on the Properties of Epoxidized Natural Rubber Latex

A new kind of water-suspensible carbon nanoparticle was prepared by oxidizing carbon black (CB) using aqueous ammonium persulfate (APS) as an oxidant. The obtained water-suspensible carbon nanoparticles (APS-CBs) were still homogeneously distributed in water three weeks after sonication. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were employed to characterize the changes of the oxygen containing functional groups on the surfaces of the APS-CBs. Furthermore, a high performance of an epoxidized natural rubber latex (ENRL)/APS-CBs composite was obtained by a liquid latex blending method. The carbon nanoparticles were homogeneously distributed in the matrix. In comparison with the ENRL/pristine CBs composites, the APS-CBs improved the mechanical properties of the ENRL/APS-CBs composites. The dynamic rheological properties were also studied.     

Variation of the Payne Effect in Natural Rubber Reinforced by Graft-Modified Carbon Black

Carbon black (CB) was modified by liquid grafting and used for natural rubber (NR) reinforcement. Payne effects during NR reinforcement by the graft-modified carbon black (GCB) were analyzed in this paper. The results showed a proportional relationship between filler content and the Payne effect. Rubber compounds with GCB presented weaker Payne effects than their non-modified counterparts. Qualitative analysis of the correlation between filler network structure and filler content was conducted according to the relationship between bound rubber of a rubber compound and shear modulus. The impact of the storage period on the Payne effect was further studied, and the results demonstrated that the longer the storage period of the rubber compound, the stronger the Payne effect tended to be. The mechanisms by which the Payne effects were manifested differed according to the content of the filler in the rubber.     

Effects of Carbon Black on Chain Mobility and Dynamic Mechanical Properties of Solution Polymerized Styrene-Butadiene Rubber

The structure of the bound rubber, the ¹H NMR (nuclear magnetic resonance) relaxation time, and the crosslink density of the physical network and the glass transition, were studied for solution polymerized styrene-butadiene rubber (SSBR) filled by carbon black, to investigate the effects of carbon black on the chain mobility and dynamic mechanical properties. It was found by ¹H NMR analysis that the rubber chains were adsorbed on the surface of carbon black to form physical crosslinks and restrict the mobility of the chains, especially for some high-mobility units such as chain ends. It was calculated, according to the molecular weight between adjacent crosslinks, that the main motion units of the tightly adsorbed chains appeared to be similar in size to the chain segments. The glass transition temperature (T _g) obtained by differential scanning calorimetry (DSC) could not be used to judge the effect of carbon black on chain mobility, while the appearance and change of the loss-tangent (tan δ) peak at high temperature in dynamic mechanical thermal spectrometry (DMTS) test showed that there were three chain states: free chains, loosely adsorbed chains, and tightly adsorbed chains. The dynamic rheology test showed that the unfilled SSBR compound had the rheological characteristics of entangled chain networks; however the nonlinear viscoelasticities of the filled SSBR were related to the gradual disentanglement of adsorbed chains and free chains. The peaks in tan δ vs. temperature curves implied that the motion unit size decreased with the increase of bound rubber content, and the modulus vs. temperature curve showed an apparently lower mobility of adsorbed chains than that of free chains through the very low dependence of modulus on temperature for the highly filled compounds. The extremely high tensile modulus of the vulcanizate with 63.6% carbon black at room temperature also implied that the adsorbed chains were in the glass state due to their restriction by the carbon black.     

Investigation on interfacial adhesion of short sisal/coir hybrid fibre reinforced natural rubber composites by restricted equilibrium swelling technique

Interfacial adhesion of sisal/coir hybrid fibre reinforced natural rubber (NR) composites has been characterized by restricted equilibrium swelling technique with special reference to the effects of fibre loading, orientation and bonding agent. The swelling parameters of NR composites with and without bonding agent were evaluated with three aromatic solvents, namely; benzene, toluene and xylene, by a sorption gravimetric method. As fibre content and penetrant size increase, the solvent uptake has been found to decrease due to the increased hindrance and good fibre–rubber interaction. The bonding agent added mixes showed enhanced restriction to swelling and it is seen that the ratio of change in volume fraction of rubber before and after swelling to the volume fraction of rubber before swelling (V ₀ – V _r/V ₀) is lower for bonding agent added composites, when compared to an unbonded one. The anisotropic swelling studies were carried out to analyse the extent of fibre alignment and fibre–matrix interaction. In strongly bonded composites, the swelling has been mainly observed to take place in the thickness direction, as attested by optical photographs. The rubber–fibre interaction has also been examined by Lorenz–Parks and Kraus equations.     

Carbon Black–Filled Styrene Butadiene Rubber Masterbatch Based on Simple Mixing of Latex and Carbon Black Suspension: Preparation and Mechanical Properties

An improved process was developed for the production of carbon black (CB)–filled styrene butadiene rubber masterbatch (SBR-CB-MB) using a simple latex/CB mixing technology; the improvement comprised processing the CB as an emulsifier-free aqueous suspension by high-rate shearing. Tensile and tear strength, dynamic compression behaviors, the Payne effect, equilibrium swelling and bound rubber of the SBR-CB-MB and dry mixing CB filled SBR (SBR-CB-DM), covering a wide range of CB loading (45–70 phr), were investigated and compared. It was found that the tensile and tear strength, heat buildup and compression set, abrasion volume loss, and the Payne effect of the SBR-CB-MB were lower than those of the SBR-CB-DM, while the bound rubber content were higher, indicating good CB/rubber interaction in the SBR-CB-MB. SEM analysis showed that no free CB could be found on the surface or inside of the granular SBR-CB-MB particles, indicating good CB dispersion in the rubber matrix.     

Interactions Between an Ionic Liquid and Silica,Silica and Silica,and Rubber and Silica and Their Effects on the Properties of Styrene-Butadiene Rubber Composites

An investigation of the effect of an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMI), on the properties of silica reinforced styrene-butadiene rubber (SBR), aimed to correlate the interactions between the ionic liquid and silica, silica and silica, and silica and rubber with the macro-properties and microstructure of SBR and SBR/silica vulcanizates is described. The interaction between the ionic liquid and silica was characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), the interaction between silica and silica was characterized by a rubber processing analyzer (RPA), and the interaction between rubber and silica was characterized by the bound rubber content. The FTIR analysis revealed that BMI can react with the hydroxyl groups on the surface of silica, improving the compatibility between the rubber and silica. The RPA and bound rubber testing indicated that the interactions between silica and silica particles were weakened and the interaction between silica and rubber increased with the incorporation of BMI into the SBR rubber. The bound rubber content showed a maximum with a BMI content of 3 phr. At the same time, the dispersion of silica in SBR was improved with the incorporation of BMI. With the increase of BMI content, the curing rate was greatly improved and the crosslink density increased. BMI also increased the tensile strength and abrasion resistance of the SBR vulcanizates. Most important, the BMI significantly improved the dynamic properties of the rubber composites, especially the wet-skid resistance and rolling resistance. However, excessive BMI (beyond 3 phr) acted as a plasticizer and was detrimental to the mechanical properties, resulting in a decrease of tensile strength and abrasion resistance.     

Influence of In-situ Grafting on the Dispersion of Carbon Black in Solvents and Natural Rubber

In-situ grafting of natural rubber (NR) onto the carbon black (CB) surface by a solid-state method was used to obtain grafted carbon black (GCB). The morphology of the original CB and GCB particles was observed by AFM and TEM. The original CB particles fused together and occurred as large dendritic agglomerates while the GCB particles occurred as small aggregates about 150 nm in diameter. The dispersion and dispersion stability of CB and GCB in toluene and cyclohexene were studied by zeta potential and a spectrophotometer. The results showed that the grafting procedure can improve both dispersion and dispersion stability of CB particles. The dispersion in NR was studied by DMA and observed by SEM. It was shown that GCB has better dispersion than CB in a NR matrix. As expected a weakened filler-filler interaction and enhanced filler-polymer interaction occurred after grafting modification.     

Carbon Black Filled Powdered Natural Rubber

Carbon black (CB) filled powdered natural rubber [P(NR/N234)] was prepared using a patented method of latex/CB coagulation technology. The influence of curing recipes and CB contents on the curing, mechanical, and dynamic properties were studied in depth, and the results were compared with that of NR/N234 compounds based on traditional dry mixing of bale NR and CB. The results showed that, compared with NR/N234, P(NR/N234) showed higher tensile strength, tear strength, rebound elasticity and flexibilities, and the antiabrasion properties were similar, while the dynamic temperature-build-up and dynamic compression permanent set were about 50% of that of NR/N234. The analysis based on scanning electron micrographs (SEM) and the Payne effect showed that the fine dispersion of CB in the rubber and the enhanced interaction between CB and rubber contributed to the excellent properties of P(NR/N234), sufficient that they make P(NR/N234) a potential material for the tread compounds of heavy-duty all-steel cord radial tires.     

Influence of filler type on wet skid resistance of SSBR/BR composites: Effects from roughness and micro-hardness of rubber surface

The wet skid resistance (WSR) of SSBR/BR(solution styrene-butadiene rubber/butadiene rubber) composites filled with carbon black, silica, and nano-diamond partly replacing carbon black or silica, respectively, was measured with a portable British Pendulum Skid Tester (BPST). A dynamic mechanical thermal analyzer was used to obtain the viscoelasticity of the composites. A 3D scanning white-light interfering profilometer was used and the scratch test performed to characterize surface roughness and micro-roughness, respectively, of the composites. WSR of the silica-filled composite was better than that of the carbon black-filled one, and further enhancement of WSR was obtained by replacing silica with nano-diamond. Tan δ of the composites at 0 °C, 10 Hz, and tensile strain of 2% did not show good correlation with WSR. The surface roughness of the composites had effects on WSR. The scratch test indicated that the higher the hardness of the filler in the composite, the higher the micro-hardness and the better the WSR. Therefore, the surface micro-hardness of the composites is an important factor affecting WSR, besides viscoelasticity and surface roughness.     

Chain orientation in natural rubber, Part II: 2H-NMR study

Stress-induced crystallisation (SIC) and stress-induced melting (SIM) in natural rubbers (NR), unfilled and filled with carbon black (CB) have been studied by ²H-NMR measurements. Various materials have been swollen with small amount (< 2%) of deuterated alkane chains. The orientation of the amorphous chains, then the local deformation of the amorphous chains during deformation cycles and during stress relaxation, permits to clarify the SIC and SIM processes during hardening and recovery. By mechanical, WAXS and NMR measurements one determines the same critical draw ratio for appearance λ_A and disappearance λ_E of the crystallites. It is demonstrated that the hysteresis observed by the different techniques (stress σ, crystallinity χ, NMR splitting Δν) are due to the supercooling effect ( λ_A > λ_E, at constant temperature). During hardening at constant strain rate it is found that the local draw ratio remains constant and equal to λ_A, whereas the crystallinity increases linearly with the macroscopic draw ratio λ. The hardening σ ∼ (λ - λ_A)² is then interpreted as a reinforcement effect due to the crystallites, which act as new crosslinks. This confirms the prediction of Flory. In filled rubber the same effects are observed, and the stress amplification factor is determined as a function of the CB content. It is found that the fillers act as nucleation centres for the NR crystallites. The reinforcement of such materials is due principally to this nucleation effect and to the presence of a super network formed by both the NR crystallites and the CB fillers.     

Study of stress-strain characteristics of SBR and blended NR/SBR rubber

The effect of temperature and carbon black (CB) on the mechanical characteristics of styrene-butadine rubber (SBR) and natural rubber (NR) was studied at various temperatures. The relation obtained between true stress and true strain for both types of rubber showed three regions at room temperature and two regions at high temperature. The optimum CB concentration was found to be 95 phr for the unblended samples as it increases the stiffness of the SBR rubber materials at a maximum value. It was also found that the addition of NR to SBR increases the elasticity in the plastic region. The activation energy at the fracture of SBR samples decreased from about 2.7×10^–20 to 1.8×10^–20 J while for the blended samples NR/SBR it increased from 8×10^–20 to 10.1×10^–20 J with increasing CB concentration.