Mechanical Properties Of Natural Rubber Research Articles

The Effect Of Accelerators On Vulcanization Of Natural Rubber Compounds

The effect of accelerator type on vulcanization characteristics and mechanical properties of natural rubber was investigated. Also, the effect of growing quantity of MBTS on vulcanization characteristics and mechanical properties of natural rubber was investigated. The results show that the fastest cure time is obtained with thiurams and dithiocarbamates for natural rubber. Sulphenamides, especially TBBS gives the best tensile strength. Elongation at break first increases by increasing dose of MBTS and then decreases. The higher elongation at break is obtained with DPG.

Bismuth oxyiodide nanorods towards improvements in fire safety and mechanical properties of natural rubber

Fire safety represents an enduring challenge in the realm of polymer-based nanocomposites, significantly limiting their application. The utilization of bismuth oxyiodide in flame retardant applications offers advantages such as increased surface area for improved interaction with combustible materials, the formation of a uniform flame retardant layer at the interface, and enhanced thermal stability. Hence, this work explored a facile strategy to synthesize bismuth oxyiodide nanorods by hydrothermal method combined with ball milling in anticipation of constructing an efficient flame retardant system. The bismuth oxyiodide nanorods dispersed relatively uniformly in the natural rubber matrix and endowed natural rubber nanocomposites with enhanced mechanical properties and fire-safety. The resultant natural rubber nanocomposite containing 5 wt.% of bismuth oxyiodide showed a 36% improvement in the tensile strength and a 39% increase in the tear strength compared to those of the neat natural rubber. Cone calorimeter tests revealed that the introduction of 5 wt.% bismuth oxyiodide to natural rubber matrix remarkably reduced the peak of heat release rate and peak smoke production release by 22% and 25%, respectively. A rational flame retardant mode of action for bismuth oxyiodide nanorods was proposed based on the analysis of pyrolysis fragments and char residues. Hence, this work provides a green and feasible method to prepare bismuth oxyiodide nanorods for flame retardant natural rubber products.

Revealing the Effect of the Length of Chains on Rubber Mechanical Properties by the Two‐Component Quantum Mechanical Gaussian Model

AbstractThe special mechanical properties of natural rubber originate from the stretching of the network chains (i.e., cis‐1,4‐polyisoprene chains) in the rubber network. The chains with various lengths exhibit various relative extensions, leading to various normalized energy contributions to the mechanical properties of rubber. However, the stretching behaviors of cis‐1,4‐polyisoprene chains with different lengths are not studied clearly. Here, the stretching behavior, which is the basis for analyzing the normalized energy contribution, is obtained by the modified freely jointed chain model. Next, using a new statistical model, i.e., the two‐component quantum‐mechanics Gaussian (TCQMG) model, the relative extension–length relationship of network chains is determined. Combining the above results, the energy contributions of network chains with different lengths are analyzed. The results show that long and short chains show different stretching states. The following can be explained by these results: short chains play an important role in the mechanical properties of rubber. As the network chain density increases, the average length of the chains decreases, leading to the variation of the normalized extensions. It is found that the variation of the normalized extensions is responsible for both the effects of the network chain density and network chain length on the mechanical properties of rubber.

Characterization and Application in Natural Rubber of Leucaena Leaf and Its Extracted Products.

Leucaena is a fast-growing tree in the legume family. Its leaf contains a significant amount of protein and is thus widely used as fodder for cattle. To broaden its application in the rubber field, the effects of Leucaena leaf powder and its extracted products on the cure characteristics and mechanical properties of natural rubber were investigated. The extraction of Leucaena leaf was carried out by using a proteolytic enzyme at 60 °C. The digested protein was separated from the residue by centrifugation. Both digested protein and residue were then dried and ground into powder, namely digested protein powder and residual powder, respectively, before being characterized by Fourier transform infrared spectroscopy, scanning electron microscope, thermogravimetric analysis, X-ray diffraction, particle size determination, and protein analysis. After being added to natural rubber at 3 parts per hundred rubber, they significantly reduced both the scorch time and the optimum cure time of the rubber compounds, probably due to the presence of nitrogen-containing substances, without a significant sacrifice of the mechanical properties. For instance, the optimum cure time decreased by approximately 25.5, 35.4, and 54.9% for Leucaena leaf powder, residual powder, and digested protein powder, respectively. Thus, they can be used as green and sustainable fillers with a cure-activation effect in rubber compounding.

Octylamine regulating the mechanical robustness of natural rubber by involving in the construction of crosslinking network

The formation of three dimensional network structure is critical in determining mechanical properties of natural rubber (NR). Consequently, it is vital to regulate crosslinking network of NR by controlling vulcanization process. Inspired by our previous studies on contribution of non-rubber components (NRCs) to the excellent properties of NR, we find octylamine in NRCs decreases the activation energy (Ea) of vulcanization from 82.73 kJ/mol to 44.34 kJ/mol, thereby reducing vulcanization time from 18.67 min to 2.71 min. From microscopic perspective, octylamine tends to coordinate with zinc ions to improve dispersion of ZnO in NR. And octylamine promotes ring-opening reaction of S8 to favor formation of polysulfide intermediates.Therefore, the incorporation of octylamine remarkably improves vulcanization efficiency, which contributes to the formation of a more homogeneous network with higher crosslinking density, enhancing remarkably the strength and toughness of NR. As a result, the tensile strength and fracture energy of samples are as high as 31.15 MPa and 68.88 kJ/m2, respectively. In addition, even with a 60 % reduction in ZnO content, the NR samples still maintain high vulcanization efficiency and excellent mechanical properties after the addition of octylamine, which provides a green and feasible way to alleviate the environmental pollution caused by ZnO.

Exploring buckling and post-buckling behavior of incompressible hyperelastic beams through innovative experimental and computational approaches

The objective of this paper is to conduct a comprehensive investigation into the buckling and post-buckling behavior of hyperelastic beams through both computational and experimental means. Natural rubber is used in the construction of a beam with a square cross-section. To determine the mechanical properties of natural rubber, a uniaxial tensile test is performed in accordance with ASTM D412. In finite element modeling (FEM), the nonlinear behavior of rubber is modeled using hyperelastic theory and the Yeoh strain energy function. The Static-Riks method is also implemented using Abaqus for the analysis of nonlinear buckling. To validate the present investigation results with FEM, an experimental test of digital image correlation (DIC) is conducted. The critical buckling force obtained via numerical methods exhibits an error of nearly 5% when compared to the corresponding results obtained from experimental testing. In order to ascertain the impact of various design parameters on the buckling behavior of the system, a comprehensive parametric analysis has been conducted. The parameters studied include the cross-sectional thickness, length of the structure, eccentric loads, as well as the mechanical properties of the materials used in the system. Consistent with the FEM outcomes, the critical buckling force exhibited by the hyperelastic beam demonstrates a positive correlation with increasing levels of hardness, cross-sectional thickness, and eccentric loads. The buckling behavior of the system is adversely affected by increasing its length. To ultimately validate the precision and reliability of the model, a supervised neural network (NN) learning method is employed.

Structure and mechanical properties of natural rubber vulcanized with various zinc oxide nanoparticles

AbstractEffect of zinc oxide (ZnO) nanoparticles on vulcanization mechanism of natural rubber and crosslinking structure of its vulcanizate was investigated by rubber‐state NMR spectroscopy. Natural rubber was compounded with various ZnO nanoparticles (c‐ZnO, NC105, NC205, NC23, NC234(STA), and AZ12N), stearic acid, N‐tert‐butyl‐2‐benzothiazole sulfonamide (TBBS), N‐(1,3‐dimethylbutyl)‐N′‐phenylenediamine (6PPD), and sulfur. Vulcanization of the compounded natural rubber was analyzed with a moving die rheometer. The resulting natural rubber vulcanizates were characterized by swelling method, rubber‐state NMR spectroscopy, and tensile test. The rubber‐state NMR measurements revealed that natural rubber was efficiently vulcanized with NC205 and AZ12N but not with c‐ZnO, NC234, and NC234(STA). A relationship between the structure of vulcanized natural rubber and surface activity, surface structure, and particle size of the ZnO nanoparticles was investigated in this study. The mechanical properties of vulcanized natural rubber were found to depend on not only strain‐induced crystallization but also amount of effective CS linkages.

Large deformation analysis of a hyperplastic beam using experimental / FEM/ meshless collocation method

In the present study, nonlinear numerical and experimental static bending analyses of hyperelastic beams are surveyed. Timoshenko's beam theory is used to obtain the Cauchy-Green deformation tensor. The governing equations are extracted using the neo-Hookean strain energy and Euler–Lagrange relation. Afterward, the nonlinear governing equations are solved numerically using the meshless collocation method (MCM). To validate the present investigation, a comparison study is accomplished between the acquired results from MCM and the experimental test of digital image correlation (DIC) and finite element method (FEM). The hyperelastic beam is made of natural rubber. Also, loading and boundary conditions are considered as concentrated force and clamped–clamped, respectively. In addition, the displacement contour is extracted by the DIC. The uniaxial tensile test based on the ASTM D412 standard is performed to extract the mechanical properties of natural rubber. The hyperelastic theory and neo-Hookean strain energy function are utilized to model the nonlinear behavior of rubber in the FEM. The error for the maximum displacement of system obtained from both numerical methods is less than 12% compared to the DIC. Additionally, it can be observed that in large deformations, unlike the FEM, MCM is able to predict the system's response with high accuracy.

Characterization and mechanism of natural rubber composites reinforced by modified calcium sulfate whisker

AbstractThis study concentrated on the mechanical properties of natural rubber (NR) composites [modified calcium sulfate whisker (MCSW)] and the reinforcement mechanism of MCSW on NR. First, anhydrous CSW with an orthogonal crystal system bottom center structure was prepared by hydrothermal method. Subsequently, MCSW was obtained by treating whiskers with inorganic, organic compounds, which effectively coated the surface of the whiskers with an average thickness of 40.85 nm, making the surface change from hydrophilic to hydrophobic. The CSW/MCSW filler was added to the NR under the optimum experimental conditions of 70°C, 12 min, 5 times of rolling, 140°C, and 1 h of curing time. The results showed that the tensile strength, elongation at break, and crosslink density of the NR composites with 15 phr of MCSW added were increased by 80.8%, 9.0%, and 80.2%, respectively, compared with the NR without the filler. The mechanism of MCSW improving the performance of composites was revealed from vulcanization kinetics and interfacial thermodynamics. In this work, a new type of high‐efficiency environmental protection NR filler reinforcing agent was developed.

Comparison of two compounding techniques for carbon nanotubes filled natural rubbers through microscopic and dynamic mechanical characterizations

Natural rubber used in wave energy converters requires higher fatigue life and better energy harvesting efficiency to make it inexpensive compared to other renewable energy resources. Carbon nanotubes (CNTs) were extensively used to enhance the mechanical properties of natural rubber, however, its performance in a double-bonded shear condition was rarely investigated. In addition, the state of CNT dispersion was a critical factor for better energy harvesting efficiency and fatigue life. Therefore, this study was aimed to compare two different dispersion approaches in CNT synthesis so that better dynamic mechanical properties and lower hysteresis loss were achieved. One approach was done in the liquid state whereas the other one was carried out in dry condition. Although the former manifested a better CNT dispersion, no significant differences in terms of dynamic mechanical properties and dissipation losses compared to the latter compounding were obtained.

EFFECT OF VULCANIZATION SYSTEMS AND CROSSLINK DENSITY ON TENSILE PROPERTIES AND NETWORK STRUCTURES OF NATURAL RUBBER

The mechanical properties of natural rubber (NR) vulcanizate depend strongly on several factors, i.e., vulcanization systems and crosslink density. These two parameters are originally from the formulation design of the vulcanizate. To focus more on such details, influences of three different vulcanization systems (sulfur, peroxide, and phenolic resin) with variations in their crosslink densities were studied by focusing on the change of curing properties, crosslink densities, mechanical properties and network structures of the NR vulcanizates. The crosslink density of various vulcanization systems increased with increasing curing promotors, as revealed by temperature scanning stress relaxation measurement. The tensile modulus at 100% strain increased with increasing crosslink density in all systems but the tensile strength varied with the vulcanization systems and degree of crosslink density. At the same crosslink level, the greatest tensile strength was obtained when the sulfur was used as a crosslinker, which was 100% greater than those obtained from peroxide and 200% over phenolic systems. In comparison to the phenolic resin system, sulfur and peroxide crosslink systems had a more uniform distribution of the crosslink network structure. The size of the network structure was found to be independent of the tensile strength. The peroxide system had the most uniform distribution of the crosslink network structure.  

Influence of sizes of rubber particles in latex on mechanical properties of natural rubber filled with carbon black

The structures and properties of natural rubber (NR) obtained from latex with small and large rubber particles (SRP and LRP) are obviously different, while carbon black (CB)/SRP or CB/LRP composites have rarely been reported. In this work, SRP and LRP are separated from natural rubber latex (NRL). The properties of obtained NR/CB composites are systematically investigated as a function of SRP and LRP mass ratios. It shows that the nitrogen content of SRP (1.32%) is much higher than that of LRP (0.10%). Mechanical properties increase with the increase of LRP content because plenty of agglomerates exist in SRP/CB composite whereas LRP/CB composite shows a homogeneous dispersion. Furthermore, a possible model is proposed to illustrate the transformations of agglomerates during stretching and dynamic compressing process. This study provides a new perspective for the design of NR materials through the selection of rubber particles in NRL.

Dioctyl Phthalate-Modified Graphene Nanoplatelets: An Effective Additive for Enhanced Mechanical Properties of Natural Rubber.

Graphene has been extensively considered an ideal additive to improve the mechanical properties of many composite materials, including rubbers, because of its novel strength, high surface area, and remarkable thermal and electron conductivity. However, the pristine graphene shows low dispersibility in the rubber matrix resulting in only slightly enhanced mechanical properties of the rubber composite. In this work, graphene nanoplatelets (GNPs) were modified with dioctyl phthalate (DOP) to improve the dispersibility of the graphene in the natural rubber (NR). The distribution of the DOP-modified GNPs in the NR matrix was investigated using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The effect of the modified GNPs’ contents on the mechanical properties of the GNPs/NR composite was studied in detail. The results showed that the abrasion resistance of the graphene-reinforced rubber composite significantly improved by 10 times compared to that of the rubber without graphene (from 0.3 to 0.03 g/cycle without and with addition of the 0.3 phr modified GNPs). The addition of the modified GNPs also improved the shear and tensile strength of the rubber composite. The tensile strength and shear strength of the NR/GNPs composite with a GNPs loading of 0.3 phr were determined to be 23.63 MPa and 42.69 N/mm, respectively. Even the presence of the graphene reduced the other mechanical properties such as Shore hardness, elongation at break, and residual elongation; however, these reductions were negligible, which still makes the modified GNPs significant as an effective additive for the natural rubber in applications requiring high abrasion resistance.

REINFORCEMENT OF CHARCOAL ACTIVATED CARBON (CAC) IN NATURAL RUBBER (NR) COMPOUND: IN COMPARISON WITH CARBON BLACK

The physical and mechanical properties of natural rubber (NR) filled with Charcoal Activated Carbon (CAC) and Carbon Black (CB) were studied. NR is a high-quality, bio-based material that has a more environmentally friendly production system than synthetic rubbers. The incorporation of reinforcing fillers into the natural rubber can significantly improve the mechanical properties, and up to now, CB has been one of the widely used filler. CAC had its own set of benefits for polymer engineering applications, particularly as a potential new natural-based filler in rubber composites. SMR-10 was compounded with compounding ingredients using a two-roll mill by Conventional Vulcanization system. As a comparison study, commercial grade CB (N220) filled NR was compounded alongside with the CAC/NR at 10 phr and 15 phr (parts per hundred of rubber) loading. A cure test was performed to determine the scorch time (tS2) and the cure time (tC90). The density, tensile strength, M100 and M300 of CAC/NR were lower than CB/NR due to the poor interaction of CAC-rubber and the possibility of slightly polar. However, the mentioned properties showed a promising increment as the filler loading increased. The swelling index (%) of CAC/NR were higher which might be contributed by the porous structure of CAC that assisting in the penetration of the toluene. As a conclusion, CAC has the potential to be used as reinforcing filler for elastomer due to the porous structure which can provide greater surface area for interaction. However, if compared to CB, higher loading of CAC was required to obtain the properties of CB of lower loading.

Carbon Black and Lignin Hybrid Filler in Designing NR Based Cushion Gum Composite Formulation

Lignin has high potential to be used as rubber cushion gum compound ingredient due to its unique properties. Cushion gum is an adhesive used to bind a new tread to the surface of used tires in a retread tire factory. An experiment was carried out to evaluate the performance of hybrid filler consisting of carbon black and lignin in affecting the physical and mechanical properties of natural rubber (NR) based cushion gum composite. The composition of carbon black/lignin was arranged at 40/10 phr and 35/15 phr. Carbon black grade N220, N330, and N550 were used in this research. Meanwhile, the lignin was specifically in the form of sodium lignosulfonate. The cushion gum compound was also formulated with the addition of pine tar oil as bio-based plasticizer. Commercial cushion gum was used as a comparison. The result showed that the hybrid filled NR cushion gum composite with N330/lignin at 40/10 (coded as SP2) was the most appropriate formula. Compared to commercial cushion gum, the SP2 hybrid filled cushion gum had comparable or even better processability and mechanical properties, attributed to high crosslink density. The excellent adhesive strength of the SP2 NR cushion gum composite was due to the presence of high content of the phenolic functional group in lignin and pine tar oil.

Synergistically enhanced thermal control ability and mechanical properties of natural rubber for tires through a graphene/silica with a dot-face structure

Synergistically enhanced thermal control ability and mechanical properties of natural rubber for tires through a graphene/silica with a dot-face structure

The Influence of Colloidal Properties of Carbon Black on Static and Dynamic Mechanical Properties of Natural Rubber.

The influence of carbon black (CB) structure and surface area on key rubber properties such as monotonic stress-strain, cyclic stress–strain, and dynamic mechanical behaviors are investigated in this paper. Natural rubber compounds containing eight different CBs were examined at equivalent particulate volume fractions. The CBs varied in their surface area and structure properties according to a wide experimental design space, allowing robust correlations to the experimental data sets to be extracted. Carbon black structure plays a dominant role in defining the monotonic stress–strain properties (e.g., secant moduli) of the compounds. In line with the previous literature, this is primarily due to strain amplification and occluded rubber mechanisms. For cyclic stress–strain properties, which include the Mullins effect and cyclic softening, the observed mechanical hysteresis is strongly correlated with carbon black structure, which implies that hysteretic energy dissipation at medium to large strain values is isolated in the rubber matrix and arises due to matrix overstrain effects. Under small to medium dynamic strain conditions, classical strain dependence of viscoelastic moduli is observed (the Payne effect), the magnitude of which varies dramatically and systematically depending on the colloidal properties of the CB. At low strain amplitudes, both CB structure and surface area are positively correlated to the complex moduli. Beyond ~2% strain amplitude the effect of surface area vanishes, while structure plays an increasing and eventually dominant role in defining the complex modulus. This transition in colloidal correlations reflects the transition in stiffening mechanisms from flexing of rigid percolated particle networks at low strains to strain amplification at medium to high strains. By rescaling the dynamic mechanical data sets to peak dynamic stress and peak strain energy density, the influence of CB colloidal properties on compound hysteresis under strain, stress, and strain energy density control can be estimated. This has considerable significance for materials selection in rubber product development.

In-situ observation of spatial organization of natural rubber latex particles and exploring the relationship between particle size and mechanical properties of natural rubber

Natural rubber (NR), an important source of elastomeric material, has superior comprehensive properties compared to synthetic high cis-1, 4-polyisoprene, which are attributed to its peculiar architecture. However, it is a challenge to identify the precise structure of NR, especially the structure of NR particles, as there are no direct characterization methods to perform in-situ investigation of structure of NR particles at an intact state. In this study, we used cryogenic transmission electron microscopy (cryo-TEM) to directly explore the morphology of NR particles existing in the latex without drying or chemical fixation. Then, the spatial organization of proteins and phospholipids on the surface of NR particles was visualized by stochastic optical reconstruction microscopy (STORM). The results show that NR particles are spherical particles with an average particle size of 88 ± 15 nm, and the exterior of NR particles is a mixed monolayer of proteins and phospholipids (ca. 4.6 ± 0.77 nm in thickness). Thus, a more complete model for the Hevea brasiliensis rubber particles was proposed. Moreover, we explicated the relationship between the particle size of NR particles, molecular characteristics, and mechanical properties of NR. The Mnand Mw of small rubber particles (SRPs) with a particle size of 106 nm are (1.56 ± 0.06) × 106 g/mol and (2.21 ± 0.07) × 106 g/mol respectively, which are much larger than those of the large rubber particles (LRPs) with a particle size of 628 nm (Mn: (0.41 ± 0.05) × 10 6 g/mol; Mw: (1.63 ± 0.10) × 106 g/mol). After vulcanization, the SRPs have better mechanical properties. Compared with LRPs, SRPs exhibit a 4.3-fold increase in tensile strength (from 5.7 to 24.6 MPa) and a 3.5-fold increase in toughness (from 12.9 to 44.9 kJ/m2). This work not only provides rational design for the new biomimetic synthetic rubber with unique hierarchical structures and excellent properties, but also offers a new possibility for tuning the mechanical properties of NR by preparation of LRPs/SRPs blend of various ratios.

Effect of Chemically Modified Castor Seed (Ricinus Communis) Shell Powder on The Mechanical Properties of Natural Rubber Vulcanizate

Mechanical properties of natural rubber filled with modified castor seed shell powder for some engineering applications were studied. Castor seed shells were obtained and treated with 20% NaOH for 1h, washed and dried at 75oC and were pulverized and sieved to 75μm. Treated castor seed shell (TCSS) powder showed improved characteristics when compared to the untreated (UCSS) in terms of pH, bulk density, moisture content, lignin content, cellulose content, hemicelluloses content, thermal stability, SEM and FTIR spectra respectively. Natural rubber was compounded at varying filler loadings of 0, 10, 20, 30, 40 and 50phr on a two-roll mill. The cure characteristics of the compounded rubber were determined using a Mosanto Rheometer (model MDR 2000) and the result obtained were used for vulcanization in a hydraulic press. The cure characteristics, mechanical and morphological properties of the vulcanizates were analysed and compared with carbon black filled samples. The preliminary results showed that castor seed shell is hydrophilic which was chemically treated to decrease the hydrophilicity. The maximum and minimum torques increased with filler loadings. The result of the natural rubber filled vulcanizates showed improved mechanical properties such as; tensile strength, modulus, tear strength, hardness, abrasion resistance which increased with increased filler loadings while elongation at break, flex fatigue, compression set, impact strength and rebound resilience decreased with filler loadings. The TCSS filled vulcanizate showed superior abrasion resistance and compression set when compared with UCSS and CB filled. The sample morphology at 30phr revealed that TCSS was well dispersed due to strong interfacial adhesion between the filler and the matrices contributing to the improved mechanical properties investigated when compared to UCSS filled with poor interfacial interaction. The result reveal that TCSS is a reinforcing filler that can be used for the production of natural rubber-based products for some engineering applications.

Combustion and mechanical properties of natural rubber based on carboxyl modified carbon nanotubes and intumescent flame retardant

ABSTRACT The flame retardant natural rubber (NR) composites were prepared using carboxyl modified multi-walled carbon nanotubes (CMCNTs) and traditional intumescent flame retardant with the ratio among ammonium polyphosphate (APP), melamine (MEL), and pentaerythritol (PER) of 3/1/1. The flame retardancy and thermal stability, and mechanical properties of NR composites were investigated by the LOI test, UL-94 test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), and tensile test, respectively. The results showed that NR/IFR3/2.0CMCNT had good flame retardancy and past the UL-94 test V-2 rating. The peak of heat release rate (pHRR), the peak of smoke production rate (pSPR), and the total smoke production (TSP) of NR/IFR3/2.0CMCNT were lower than those of NR/IFR3, which were reduced by 4.4%, 12.1%, and 26.3%, respectively. In addition, CMCNTs can improve the elongation at the break of NR composites with the increase of CMCNTs under the condition of low load CMCNTs.