Relationship among mechanical properties,heat ageing resistance,cut growth behaviour and morphology in natural rubber: Partial replacement of clay with various types of carbon black at similar hardness level

In this experiment, various types of carbon black (CB) were employed to partially substitute the calcined clay for preparing natural rubber (NR) compounds of similar hardness. At similar hardness, the compounds containing both clay and CB give the better tensile strength, edge-cut tensile strength, tear strength and thermal ageing resistance compared to the control, but the control had better gas barrier property. In addition, the cracking behaviour of the vulcanizate has a transition from simple lateral growth to oblique crack with partial substitution of the clay with CB, and the vulcanizate containing N330 exhibits the greatest longitudinal cracking corresponding to its highest edge-cut tensile strength. This means the presence of N330 causes the greater orientation of the NR chains along the applied force. Furthermore, the vulcanizate containing N330 yields the highest tensile and tear strength, and lowest resilience, although it has the lowest volume fraction of filler. The explanation is given as the higher reinforcing efficiency of N330 and the better filler dispersion shown in SEM micrographs.     

Highly enhanced electrical and mechanical properties of methyl methacrylate modified natural rubber filled with multiwalled carbon nanotubes

Developing conductive networks in a polymer matrix with a low percolation threshold and excellent mechanical properties is desired for soft electronics applications. In this work, natural rubber (NR) functionalized with poly(methyl methacrylate) (PMMA) was prepared for strong interfacial interactions with multiwalled carbon nanotubes (MWCNT), resulting in excellent performance of the natural rubber nanocomposites. The MWCNT and methyl methacrylate functional groups gave good filler dispersion, conductivity and tensile properties. The filler network in the matrix was studied with microscopy and from its non-linear viscoelasticity. The Maier-Göritze approach revealed that MWCNT network formation was favored in the NR functionalized with PMMA, with reduced electrical and mechanical percolation thresholds. The obvious improvement in physical performance of MWCNT/methyl methacrylate functionalized natural rubber nanocomposites was caused by interfacial interactions and reduced filler agglomeration in the NR matrix. The modification of NR with poly(methyl methacrylate) and MWCNT filler was demonstrated as an effective pathway to enhance the mechanical and electrical properties of natural rubber nanocomposites.     

Thermal properties of compatibilized and filled natural rubber/acrylonitrile butadiene rubber blends

The thermal behaviour of natural rubber/acrylonitrile butadiene rubber (NR/NBR) was studied using thermogravimetry (TG) and differential scanning calorimetry (DSC) in terms of blend ratio, crosslinking systems, fillers and compatibilizer (neoprene) were analyzed. The presence of NBR markedly increases the thermal stability of their blends and it lies in between NR and NBR. DSC studies revealed the thermodynamic immiscibility of the NR/NBR blends by the presence of two distinct glass transition temperatures and the immiscibility was prominent even in the presence of a compatibilizer.     

Strain‐induced crystallization and mechanical properties of functionalized graphene sheet‐filled natural rubber

The effects of functionalized graphene sheets (FGSs) on the mechanical properties and strain‐induced crystallization of natural rubber (NR) are investigated. FGSs are predominantly single sheets of graphene with a lateral size of several hundreds of nanometers and a thickness of 1.5 nm. The effect of FGS and that of carbon black (CB) on the strain‐induced crystallization of NR is compared by coupled tensile tests and X‐ray diffraction experiments. Synchrotron X‐ray scattering enables simultaneous measurements of stress and crystallization of NR in real time during sample stretching. The onset of crystallization occurs at significantly lower strains for FGS‐filled NR samples compared with CB‐filled NR, even at low loadings. Neat‐NR exhibits strain‐induced crystallization around a strain of 2.25, while incorporation of 1 and 4 wt % FGS shifts the crystallization to strains of 1.25 and 0.75, respectively. In contrast, loadings of 16 wt % CB do not significantly shift the critical strain for crystallization. Two‐dimensional (2D) wide angle X‐ray scattering patterns show minor polymer chain alignment during stretching, in accord with previous results for NR. Small angle X‐ray scattering shows that FGS is aligned in the stretching direction, whereas CB does not show alignment or anisotropy. The mechanical properties of filled NR samples are investigated using cyclic tensile and dynamic mechanical measurements above and below the glass transition of NR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Properties of rubber filled with montmorillonite with various surface modifications

Layered silicate/natural rubber composites were prepared by direct polymer melt intercalation. Na‐montmorillonite Kunipia‐F and its organic derivates (organo‐clays) prepared by ion exchange were used as clay fillers. Silica (SiO₂) Ultrasil VN3, a filler commonly used in the rubber industry, was used in combination with clay fillers. The effect of clay or organo‐clay loading from 1 up to 10 phr without (0 phr) or with silica (15 phr) showed significant improvement of the tensile properties (stress at break, strain at break and modulus M100). Modification of montmorillonite by three alkylammonium cations with the same length of alkylammonium chain (18 carbons) and different structure resulted in altered reinforcing and plasticizing effects of the filler in composites with rubber matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of non‐rubber components on the mechanical properties of natural rubber

Effect of the nanomatrix structure on mechanical properties of natural rubber was investigated in relation to the strain‐induced crystallization. Structure of natural rubber was analyzed through Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction measurement and transmission electron microscopy. The nanomatrix of the non‐rubber components was found to be inevitably formed in natural rubber, in which natural rubber particles linking to fatty acids were dispersed in the nanomatrix of the proteins and phospholipids. The nanomatrix disappeared after deproteinization of natural rubber with urea. Tensile strength and modulus of natural rubber were reduced by removal of the fatty acids and the proteins, which resulted in disappearance of the nanomatrix structure. The effect of fatty acids on the crystallization of natural rubber in small particles as a dispersoid was proved by tensile test of blend of natural rubber and styrene butadiene rubber. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of alkaline treatment and acetone extraction of natural rubber matrix on properties of carbon black filled natural rubber vulcanizates

In this study, air dried sheet (ADS) showed higher molecular weight, proteins, lipids and more gel content than the low protein natural rubber (LPNR) from alkaline treatment or acetone-extracted natural rubber (AENR). After removal of proteins and lipids, LPNR and AENR had shorter scorch and cure times among the rubber compounds observed. This is due to higher content of free fatty acids, glycerides and sodium salts of fatty acid that might act as cure activators with sulfur curing. Furthermore, a finer dispersion of CB was found in ADS, due to chemical interactions of CB with proteins and lipids at terminal ends of NR molecules. Also, high molecular weight and gel in ADS could induce a higher reinforcing index (α) resulting to superior mechanical, dynamic, thermo-mechanical, hardness and crosslink density. In contrast, CB agglomerates occurred in LPNR and AENR with low molecular weight and reduced proteins and lipids, causing inferior mechanical, dynamic, thermo-mechanical, along with loss of stiffness and crosslink density.     

Improving the mechanical properties of short pineapple leaf fiber reinforced natural rubber by blending with acrylonitrile butadiene rubber

This work proposes a simple method for improving the rubber to filler stress transfer in short pineapple leaf fiber-reinforced natural rubber (NR). This was achieved by replacing some of the non-polar NR by polar acrylonitrile butadiene rubber (NBR). The amount replaced was varied from 0% to 20% by weight. The mixing sequence was designed so that the fiber would be coated with polar NBR before being dispersed in the NR matrix. A comparison system in which the mixing was carried out in a single step was also examined. Despite the fact that the two rubbers are immiscible, it was found that significant improvement of the stress transfer in the low strain region can be obtained. The mixing sequence affected the mechanical properties of the resulting composites. It is concluded that frictional stress transfer between the immiscible rubbers contributes more to the total stress transfer than does the frictional stress transfer between non-polar NR and polar cellulose fiber.     

The effects of a silane coupling agent on curing characteristics and mechanical properties of bamboo fibre filled natural rubber composites

The effects of a silane coupling agent on curing characteristics and mechanical properties of bamboo fibre filled natural rubber composites were studied. Scorch time, t₂ and cure time, t₉₀ of the composites decrease with increasing filler loading and with the presence of a silane coupling agent, Si69. Mooney viscosity also increases with increasing filler loading but at a similar filler loading shows lower value with the presence of Si69. The mechanical properties of composites viz tensile strength, tear strength, hardness and tensile modulus were also improved with the addition of Si69.     

Influence of ionizing radiation on rheological,mechanical and electrical properties of various sorts of natural and synthetic rubber

The influence of -radiation, upon elongation, resistance to tearing, module of elasticity, as well as upon the following electrical properties has been studied: , tg, and breakdown resistance, for various sorts of rubber.     

New insights into the cold crystallization of filled natural rubber

This article is devoted to the cold crystallization of filled natural rubber with different types of filler such as carbon black, silica, and grafted silica. A large set of differential scanning calorimetry data is presented with various scanning rates, times, and temperatures of isothermal crystallization to display the factors affecting natural rubber (NR) crystallization. The crystallization kinetic measurements suggest that fillers can create a region with perturbed mobility where the kinetics of nucleation and/or growth are slowed down, the rest of the matrix being unperturbed. And, the final crystallization level indicates the existence of an excluded region for crystallization close to the filler surface. Furthermore, the presence of fillers appears less unfavorable to NR crystallization than chemical crosslinking. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 955–962, 2007     

Morphology and mechanical and viscoelastic properties of natural rubber and styrene butadiene rubber latex blends

The morphology and mechanical and viscoelastic properties of a series of blends of natural rubber (NR) and styrene butadiene rubber (SBR) latex blends were studied in the uncrosslinked and crosslinked state. The morphology of the NR/SBR blends was analyzed using a scanning electron microscope. The morphology of the blends indicated a two phase structure in which SBR is dispersed as domains in the continuous NR matrix when its content is less than 50%. A cocontinuous morphology was obtained at a 50/50 NR/SBR ratio and phase inversion was seen beyond 50% SBR when NR formed the dispersed phase. The mechanical properties of the blends were studied with special reference to the effect of the blend ratio, surface active agents, vulcanizing system, and time for prevulcanization. As the NR content and time of prevulcanization increased, the mechanical properties such as the tensile strength, modulus, elongation at break, and hardness increased. This was due to the increased degree of crosslinking that leads to the strengthening of the 3‐dimensional network. In most cases the tear strength values increased as the prevulcanization time increased. The mechanical data were compared with theoretical predictions. The effects of the blend ratio and prevulcanization on the dynamic mechanical properties of the blends were investigated at different temperatures and frequencies. All the blends showed two distinct glass‐transition temperatures, indicating that the system is immiscible. It was also found that the glass‐transition temperatures of vulcanized blends are higher than those of unvulcanized blends. The time–temperature superposition and Cole–Cole analysis were made to understand the phase behavior of the blends. The tensile and tear fracture surfaces were examined by a scanning electron microscope to gain an insight into the failure mechanism. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2189–2211, 2000     

Correlations between natural rubber protein content and rapid predictions of rheological properties,compression set and hardness of rubber compound

In this study the correlations between protein contents of different kinds of natural rubber were considered with rheological behavior, compression set and hardness of rubber compounds based on natural rubber. At the first stage, protein contents were obtained by Kjeldahl method and correlated with normalized absorbance of amine band in NR's attenuated total reflection Fourier transform infrared spectra and shown linear behavior. At the second stage, correlations between the protein contents obtained by the spectra were considered with rheological behavior, compression set and hardness of rubber compounds and shown second order fitting models. The introduced models were applied to predict these features in case studies. Results were shown that Mooney viscosity, torque difference, optimum cure time, scorch time, cure rate index and hardness can be predicted by lower than 10% while compression set can be estimated by lower than 20% error. This significant attitude is a nondestructive and fast technique that uses little quantity of NR for prediction of some NR based compounds properties, before compounding.     

Influence of gel content on the physical properties of unfilled and carbon black filled natural rubber vulcanizates

Recently, gel content has been considered as a standard property for evaluating commercial grade natural rubber (NR). In this study, NR containing various amounts of gel was prepared by accelerated storage hardening as a model to clarify the influence of gel content on the physical properties of both unfilled and carbon black filled vulcanizates. Furthermore, the NR samples were investigated to determine the effect of gel fraction on Mooney viscosity and the structure of the gel after mastication. The results revealed that Mooney viscosity was related to the percentage of gel fraction that has been proven to be the result of interactions between proteins and phospholipids at chain ends. After mastication, although the gel fraction of NR can be decomposed to ∼0% w/w, the interactions of proteins and phospholipids at the chain ends still existed, corresponding to the gel content of the raw rubber. In the case of unfilled vulcanizates, the gel content showed no effect on cure characteristics, crosslink density and ultimate tensile strength, whereas the upturn of stress occurred at a smaller strain when the gel content increased. However, in the case of carbon black filled vulcanizates, the gel content played a dominant role in the carbon black dispersion, which was poorer when gel content increased, contributing to a decrease of crosslink density and ultimate tensile strength.     

Strain-dependent dynamic properties of filled rubber network systems

A model for strain-dependent dynamic properties of filler loaded rubber systems has been derived based on the Links-Nodes-Blobs (L-N-B) model of percolation theory. It is the first time that a L-N-B model is applied in the study of dynamic properties of filled rubbers. The density distribution function of the number of singly connected bonds f_1a(ϵ) and the apparent yield strain amplitude ϵ_app that corresponds to the on-set point of corruption of the filler network are introduced in the model. Simulation results indicate that both f_1a(ϵ) and ϵ_app control the break-down and recombination of the filler network. Two recombination mechanism are adopted in this study. Results of simulations from the extreme ends recombination mechanism match the experimental data better than those from the zero strain recombination mechanism. Also, via the proposed model, the strain-dependent storage modulus correlates well with the peak loss modulus at a low strain range of around 0.1% to 100%. Moreover, a universal plot of the normalized storage modulus (Z_L-N-B) as a function of the normalized Log strain amplitude (ϵ₀/ϵ_app) for different rubber systems is obtained. The loss moduli of systems are also simulated by the L-N-B model.     

Dynamic mechanical properties of polymers filled with agglomerated particles

The filler particles in most filled polymers are not perfectly dispersed but are more or less agglomerated. The degree of agglomeration and the strength of the agglomerates, which can be modified by surface treatments, have a very great effect on the dynamic mechanical properties. Filler agglomerates which are wetted by the polymer matrix produce higher elastic moduli than similar agglomerates which are not wetted. The relative damping in most filled polymers is very temperature-dependent. A qualitative explanation is given for this temperature dependence. The degree of agglomeration and the strength of the agglomerates are important factors in determining the damping.     

Enhancement of mechanical properties of natural rubber with maleic anhydride grafted liquid polybutadiene functionalized graphene oxide

An effective procedure has been developed to synthesize the functionalized graphene oxide grafted by maleic anhydride grafted liquid polybutadiene(MLPB-GO). Fourier transform spectroscopy and X-ray photoelectron spectroscopy indicate the successful functionalization of GO. The NR/MLPB-GO composites were then prepared by the co-coagulation process. The results show that the mechanical properties of NR/MLPB-GO composites are obviously superior to those of NR/GO composites and neat NR. Compared with neat NR, the tensile strength, modulus at 300% strain and tear strength of NR composite containing 2.12 phr MLPB-GO are significantly increased by 40.5%, 109.1% and 85.0%, respectively. Dynamic mechanical analysis results show that 84% increase in storage modulus and 2.9 K enhancement in the glass transition temperature of the composite have been achieved with the incorporation of 2.12 phr MLPB-GO into NR. The good dispersion of GO and the strong interface interaction in the composites are responsible for the unprecedented reinforcing efficiency of MLPB-GO towards NR.     

Styrenated phenol modified nanosilica for improved thermo-oxidative and mechanical properties of natural rubber

The present work aims to prepare thermal and oxidation resistant Natural Rubber (NR) composites using antioxidant-modified nanosilica (MNS). The thermo-oxidative aging performance of the composites was evaluated by the variations in mechanical properties after aging at 100 °C for 24 h. The performance was further monitored through Scanning Electron Microscopy, Fourier Transform Infrared spectroscopy, Thermogravimetric Analysis, and Dynamic Mechanical Analysis. NR nanocomposite with 1–7.5 phr nanosilica (NS) and 3 phr MNS were prepared and its rheological properties were studied. A comparative study of the theoretical models yielded that modified Guth-Gold equation predicted Young's modulus better than other models. Thermal stability of natural rubber MNS composite was improved by 10 °C with pre-eminent mechanical properties like tensile strength and heat build-up. A linear relationship of compression set with modulus of all composites were also established. Equilibrium swelling test revealed improved crosslink density in NR MNS composite. The strong interaction between antioxidant and nanosilica enabled low migration of antioxidant in NR MNS composite. Hence its protective function after aging showed more effective than NR NS composites. These versatile functional properties of NR MNS composite suggest its potential application in electrical, electronic and high performance rubber products.