Mechanical Properties Of Natural Rubber Composites Research Articles

Rapid formation of carbon nanotubes–natural rubber films cured with glutaraldehyde for reducing percolation threshold concentration

Carbon nanotubes (CNTs) filled natural rubber (NR) composites with various CNT contents at 0, 1, 2, 3, 4 and 5 phr were prepared by latex mixing method using glutaraldehyde as curing agent. This work aims to improve the electrical and mechanical properties of CNT filled NR vulcanizates. The CNT dispersion of NR composites was clarified using dispersion grader, optical microscopy and scanning electron microscopy. The electrical properties of NR composites in the existing of CNT networks were studied by following the well-known percolation theory. It was observed that the NR composites exhibited low percolation threshold at 0.98 phr of CNT. Moreover, a three-dimensional network formation of CNT in the NR composites was observed and it is indicated by the t-value of 1.67. The mechanical properties of NR composites in terms of modulus, tensile strength and hardness properties were increased upon the addition of CNT to the optimum mechanical properties at 1 phr of CNT. Therefore, the present work is found the novelty of the study that the conductive rubber latex film can be produced using GA as low-temperature curing agent which enhanced good electrical properties. Moreover, this work is found to be beneficial in case of conductive rubber latex film that requires high modulus at low strain. The additional advantage of this system is the curing process occurs at low-temperature using GA and it can be easily processed.Graphical abstract

Novel application of Zn‐containing Zeolitic Imidazolate Frameworks in promoting the vulcanization and mechanical properties of natural rubber composites

AbstractThree kinds of Zn‐containing Zeolitic Imidazolate Frameworks (Zn‐ZIFs, including ZIF‐8, ZIF‐11 and ZIF‐14) based on the zinc ions coordinating with different imidazolate ligands were added into the natural rubber (NR) using the DM and TMTD binary accelerators system, respectively. The influences of Zn‐ZIFs on the sulfur vulcanization behaviors and mechanical properties of NR matrix were evaluated. The results indicated that the addition of ZIF‐8 or ZIF‐14 could realize the fast vulcanization of NR at 130°C (the ordinary vulcanization temperature of NR is above 150°C), while ZIF‐11 did not show the obvious accelerating performance. Amongst the three Zn‐ZIFs, ZIF‐8 benefited NR matrix for the acquirement of the highest tensile strength and the largest crosslinking density. As an optimal additive, ZIF‐8 with 0.6 phr distinctly improved the physical‐mechanical, thermo‐oxidative aging resistance and dynamic mechanical properties of NR composites. It proved that Zn atom and its coordination porous network in Zn‐ZIFs played synergistic effects in accelerating vulcanization and enhancing mechanical properties of NR matrix besides its role of reinforcement filler. Then the above ZIF‐8/DM/TMTD vulcanization system was used to prepare the UHMWPE fibers/NR composites. The mechanical properties of the UHMWPE/NR composites were significantly improved in contrast to the pure NR matrix.

Natural Rubber Composites Reinforced with Green Silica from Rice Husk: Effect of Filler Loading on Mechanical Properties

Natural rubber (NR) composites filled with silica are typically used for tire tread applications owing to their low energy consumption and low rolling resistance. Tire tread properties vary broadly depending on the compound formulation and curing conditions. Silica loading is recognized as a critical factor influencing the mechanical properties of the composites. In this work, we aim to investigate the effect of silica loading (10–50 phr) on the mechanical properties of NR composites. Silica was prepared from rice husk waste via chemical treatment and subsequent calcination at 600 °C. Prior to the compound mixing process, silica was modified by a silane coupling agent to improve compatibility with the NR matrix. The NR compounds reinforced with silane-modified silica from rice husk were prepared using a two-roll mill machine. The scorch and cure times increased as the silica loading increased. The mechanical properties of the NR composites, including tensile strength, elongation at break, modulus, hardness, and abrasion loss, were examined as a function of silica loading. Tensile strength increased and reached the maximum value at 20 phr but decreased at high loading owing to the agglomeration of silica in the NR matrix. With increasing silica loading, hardness and modulus increased, whereas elongation at break and abrasion resistance decreased slightly. These results indicate that NR composites filled with silica are stiffer and harder at a higher silica loading due to the strong interaction between silica and the NR matrix, inhibiting the segmental mobility of rubber chains. We anticipate that the compound formulation presented in this work could potentially be adapted to tire tread applications.

Modified nanocrystalline cellulose partially replaced carbon black to reinforce natural rubber composites

AbstractAs a renewable nanomaterials, nanocellulose was generally considered as a green filler for reinforcing polymer. In this study, nanocrystalline cellulose (NCC) isolated from softwood pulp was successfully modified, and the modified nanocrystalline cellulose (m‐NCC) was used to partially replace carbon black (CB) to reinforce natural rubber (NR). Then, the dispersion of m‐NCC in the rubber matrix and the mechanical properties of NR composites were studied. The results showed that the surface modification of NCC improved its dispersion in the NR matrix and the filler‐rubber interfacial interaction. In addition, the m‐NCC partly replaced the CB‐reinforced NR composite with a lower stress at 300% elongation, but the tensile strength, elongation at break, tear strength, and wear resistance of the composites were significantly improved. Besides, the dynamic compression fatigue heat built‐up of the composites in which m‐NCC partially replaced CB was increased, but DIN abrasion and the flex cracking resistance was improved. From these properties, it can be seen that the partial replacement of CB by NCC could basically approach or even achieve the effect of NR composites reinforced by CB, indicating that the NCC had good rubber reinforcement ability.

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.

Mechanical Properties of Ternary-Filled Natural Rubber Composites

The aim of this study was to investigate the effect of each ternary filler component: carbon black (CB), modified bentonite (M-BNT), and raw bentonite (BNT), and their interactions, on the mechanical properties of natural rubber (NR) composites, using a third degree-simplex lattice mixture design of experiment. The efficiency of the two-step organic modification to produce M-BNT was confirmed by the results of Fourier transform infrared with attenuated total reflectance (FTIR-ATR) spectroscopy and x-ray diffraction (XRD) analysis. Synergistic effect between CB and M-BNT on the mechanical properties of NR composites with ternary filler composition 10/5/0 was observed. Reinforcement of NR matrix using this ternary filler enhanced its tensile properties: strength (69.43%), modulus (47.01%), stress at 100% strain (34.67%), stress at 200% strain (41.88%), and stress at 300% strain (50.82%), as well as its compressive properties: strength (40.89%), modulus (40.05%), stress at 20% strain (41.10%), stress at 40% strain (37.57%), and stress at 60% strain (40.79%). Significant improvement in the mechanical properties was also attributed to the surface modification of M-BNT resulting to better dispersion to NR matrix. The addition of pure BNT filler resulted to lowest tensile and compressive performance due to high clay loading and incompatibility with NR matrix. Trends of the generated contour plots based on reduced hierarchical models demonstrated synergy between CB and M-BNT as well as deterioration of mechanical properties upon addition of pure BNT filler 0/0/15.

Accelerated Aging and Lifetime Prediction of Graphene-Reinforced Natural Rubber Composites

Accelerated lifetime prediction is the key technology to assure the safety and reliability of rubber products in automotive components. In the present study, carbon black (CB), which has been a conventional reinforcing filler in the rubber industry, was partially replaced by graphene in natural rubber (NR) composite system. Due to the superior intrinsic thermal conductivity of graphene, it is getting much attention to reduce heat build-up problem of vibration mount for longer lifetime in its demanding performance. Therefore this study not only focuses on the effect of graphene loading on mechanical properties of NR composites but also on the accelerated lifetime prediction of graphene-reinforced NR composites. Hardness and compressive properties were linearly increased as CB was partially replaced by graphene (1-5 phr; parts per hundred rubber) showing better reinforcing effect. In accelerated lifetime experiments, hardness and compression set were significantly changed after 24 h when the samples were exposed to 85 °C and 70 °C, respectively. From the relationship between thermal aging temperature and lifetime, Arrhenius plot using least square method was drawn to predict the lifetime of NR composites resulting that the activation energy reached at a maximum when 3 phr of graphene was filled in NR composite. Through the accelerated thermal aging test, lifetime prediction of graphene-reinforced NR composites were successfully drawn particularly focusing on compression set property which is one of the most dominant factors for the aging of vibration mount.

Effect of replacing carbon black with surfactant-modified silica clay on mechanical properties of natural rubber composites

The effect of replacing carbon black (CB) with surfactant-modified silica clay (SMSC) on hardness and tensile properties of natural rubber (NR) composites was studied using a simplex-lattice design of experiment. SMSC was produced by treating silica clay (SC) with coconut diethanolamine (CDEA) and glycerol monostearate (GMS). Complete replacement of CB with SMSC resulted in the decrease of Shore A hardness and tensile stress at all elongations. At higher CB to SMSC ratio, SMSC modified with CDEA performed better than with GMS. However, at lower CB to SMSC ratio, GMS exhibited larger values in the mechanical properties of NR composites. This can be attributed to the surface morphologies of SMSC and the surface aggregation of surfactant to SC.

Effect of Fiber Surface Modification on Properties of Artificial Leather from Leather Fiber Filled Natural Rubber Composites

Artificial leather based on natural rubber (NR) filled with leather fibers was prepared using a hot pressing process. The leather fiber was obtained by shredding chrome-tanned leather into fibers with the sizes of 20-mesh. Three different modifying agents (i.e., 1% aqueous solutions of sodium hydroxide, urea, and sodium bicarbonate) were used in the modification of leather fibers. Mechanical properties of NR composites filled with 100 phr of modified or unmodified leather fibers were then investigated. The results showed that cure characteristics, tensile properties, tear strength and abrasion resistance of the composite combined with the modified leather fibers were clearly improved, compared to those of the simple unmodified leather fiber composite. Furthermore, interfacial adhesion between the leather fiber and natural rubber was found to improve. From this study, the result suggested that the urea solution provided the best property improvement when the other modifying agents were compared with.

Effects of lanthanum complex on the thermo-oxidative aging of natural rubber

Novel mixed antioxidants composed of antioxidant IPPD and lanthanum (La) complex were added as a filler to form natural rubber (NR) composites. Mechanical testing was carried out before and after the thermo-oxidative aging of NR composites. Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) was performed to observe the variation of internal groups. The thermal and thermo-oxidative decomposition of NR were investigated by thermogravimetric (TG) curves, and the thermo-oxidative aging kinetic parameters were determined by the Flynn-Wall-Ozawa (FWO) method. The results showed that the thermo-oxidative degradation of NR composites was a two-stage reaction. Compared with the pure antioxidant IPPD, the same mass of mixed antioxidants had better effects to improve the mechanical properties of NR composites, reduce the formation of aging products, and increase the activation energies (Ea) of the thermo-oxidative degradation. Based on the autocatalytic, free radical chain reaction of the thermo-oxidative aging of NR, different function mechanisms of antioxidant IPPD and La complex were also compared. As a result of strong coordination abilities, large coordination numbers, and decomposition of the hydroperoxides, this new rare-earth antioxidant could indeed enhance the thermo-oxidative aging resistance of NR composites. This research has important significance for the exploitation of rubbers with high resistance to thermo-oxidative aging.

Effect of coal gangue/carbon black/multiwall carbon nanotubes hybrid fillers on the properties of natural rubber composites

The objective of this study was to investigate three kinds of filler with completely different morphology on mechanical properties of natural rubber (NR). Coal gangue (CG) are derived from natural deposits are composed principally by illite and quartz. CG, carbon black (CB), and multiwalled carbon nanotube (CNT) were used as hybrid fillers in NR. CNTs were dispersed into NR latex by ultrasonic irradiation and then the mixed latex were coagulated to obtain the CNTs/NR masterbatch, then mechanical mixing method was employed to prepare the CG/CB/CNTs/NR composites. The addition of CG, CB, and CNTs to NR was varied with the total filler loading fixed at 35 phr. The mechanical properties of NR composites were studied in terms of tensile and dynamic mechanical analysis (DMA). The results showed that the tensile strength and modulus 300% (M300) of all hybrid samples were higher than the composites only loaded CG; and the highest tensile strength of NR loaded with hybrid fillers achieved at sample of loading amount of CG 17.5, CB 15.5, and CNTs 2 phr, whose M300 and elongation at break was obviously higher than that of only CB loaded NR composites; The inclusion CG improves the tensile strength of NR without the sacrifice of its extensibility, while CB and CNTs brings together the enhancement in the ultimate strength and the reduction in the extensibility. DMA results revealed that the existence of CG can improve the dispersion of CB and CNTs in NR matrix. POLYM. COMPOS., 37:3083–3092, 2016. © 2015 Society of Plastics Engineers

The Effect of Hydrochloric Acid Treatment on Properties of Oil Palm Ash-filled Natural Rubber Composites

The properties of non-treated and hydrochloric acid (HCl)-treated oil palm ash (OPA)-filled natural rubber (NR) composites were investigated in terms of swelling behavior, rubber-filler interaction, ageing resistance, dynamic mechanical analysis, and thermal stability. The incorporation of OPA resulted in a lower degree of swelling in the NR composites, which was even lower after HCl treatment. Concerning the rubber-filler interaction, the HCl-treated OPA had better interfacial interaction with the NR matrix than that of non-treated OPA, resulting in higher crosslink density and improved ageing resistance. The dynamic mechanical properties of NR composites were better with the incorporation of HCl-treated OPA compared to non-treated OPA, in that they showed a higher storage modulus and lower mechanical loss factor. Thermogravimetry analysis revealed that the HCl treatment process did not affect the thermal stability of OPA-filled NR composites.

Reinforcement of Natural Rubber with Quartz/Sericite/Wollastonite

In the paper, ultrafine quartz, sericite and wollastonite modified with silane coupling agents KH-570 were incorporated into natural rubber(NR). The synergisitc effect on reinforcing NR caused by the three types of fillers was investigated under a same vulcanizing formulation and process. The mechanical properties and microstructure of the vulcanizates were conducted through mechanical testing and scanning electron microscopy(SEM). The results of mechanical properties tests showed that when one of these three fillers was loaded within NR alone, the tear strength and permanent set of NR vulcanizates filled with quartz could reach 27.61 kN m-1and 16.0%, respectively, stress at 300% elongation of NR vulcanizates filled with sericite could attain 4.69 MPa, and the tensile strength and elongation at break of NR vulcanizates filled with wollastonite could get to16.64 MPa and 951.21%, respectively. Under the condition that the filler loadings were 40 parts per hundred parts of rubber(phr), and the mass ratio of quartz, sericite, wollastonite was 1:1:3, the tensile strength and tear strength could come up to 17.33MPa and 27.54 kN m-1. The mechanical properties of NR composites filled with mixtures were found to be complemented by those three types of minerals. SEM results revealed that the fillers are well dispersed in the rubber matrix in the parallel arrangement with a densest stack, and the synergistic reinforcment effect of the fillers on NR was obvious.