Synergistic effect by high specific surface area carbon black as secondary filler in silica reinforced natural rubber tire tread compounds

The partial replacement of silica by high specific surface area and high structure Carbon Black (CB) N134 as secondary filler, keeping the same total filler content at 55 phr, shows a clear synergistic effect on overall performance. At low content of CB, i.e. in the range of 0–36 wt% of CB relative to total filler amount, the Payne effect and tan delta at both 0 °C and 60 °C change marginally, but thereafter gradually increase. Cure times are shortened in the presence of CB, facilitating an increase of productivity. Bound rubber content and mechanical properties show an optimum at 18 wt% of CB relative to total filler amount or at a ratio of silica/CB 45/10 phr. With regard to tire performance as indicated by the laboratory test results, the abrasion resistance, wet grip and ice traction can therefore be enhanced while maintaining the tire rolling resistance at the optimum level for this silica/CB ratio.     

Effects of epoxidized natural rubber as a compatibilizer in melt compounded natural rubber-organoclay nanocomposites

Nanocomposites containing natural rubber (NR) as matrix, epoxidized natural rubber (ENR) as compatibilizer and organophilic layered clay (organoclay) as filler were produced in an internal mixer and cured using a conventional sulphuric system. The effects of ENR with 25 (ENR 25) and 50 mol% epoxidation (ENR 50), respectively, were compared at 5 and 10 parts per hundred rubber (phr) concentrations. The organoclay content was fixed at 2 phr. Cure characteristics, clay dispersion, (thermo)mechanical properties of the nanocomposites were determined and discussed. Incorporation of ENR and organoclay strongly affected the parameters which could be derived from Monsanto MDR measurements. Faster cure and increased crosslink density were attributed to changes in the activation/crosslinking pathway which was, however, not studied in detail. The organoclay was mostly intercalated according to X-ray diffraction (XRD) and transmission electron microscopic (TEM) results. The best clay dispersion was achieved by adding ENR 50. This was reflected in the stiffness of the nanocomposites derived from both dynamic mechanical thermal analysis (DMTA) and tensile tests. The tensile and tear strengths of the ENR 50 containing nanocomposites were also superior to the ENR 25 compatibilized and uncompatibilized stocks.     

Preparation of purified spent coffee ground and its reinforcement in natural rubber composite

Spent coffee ground (SCG) contains a variety of organic compounds such as fatty acids, amino acids, polyphenols, polysaccharides, etc. In this study, purification of SCG was carried out by alkalization and bleaching treatment and the purified SCG (PSCG) was characterized by various techniques, i.e., FTIR, XRD, BET, SEM and TGA. PSCG was later treated with Bis-triethoxysilylpropyl tetrasulfide (TESPT). Both PSCG and TESPT-treated PSCG were then incorporated into natural rubber (NR) to investigate their reinforcement magnitude in the bio-composite. Results revealed the eradication of lignin and other non-polysaccharide components after the purification leading to the significant increases in specific surface area and cellulose content of PSCG. Although the addition of PSCG into NR showed cure time reduction in association with the increased modulus and hardness, its reinforcement was not very high due to the large particle size and the abundance of hydroxyl groups in PSCG. The TESPT treatment significantly improved the reinforcement of PSCG due to the increases in rubber-filler interaction and crosslink density. However, the reinforcement of both PSCG and TESPT-treated PSCG is still relatively low compared to the commercial nanofillers and, thus, they can be considered as a cheap and eco-friendly filler in NR.     

Comparative study of natural rubber and acrylonitrile rubber reinforced with aligned short aramid fiber

The aims of this paper are three-fold. The first is to determine the reinforcement of high performance short aramid fiber in two representative rubber matrices, namely natural rubber and acrylonitrile rubber. The second is to ascertain the effect of rubber polarity on the reinforcement. The third is to establish a pattern of reinforcement for use with less studied fibers. The rubbers were reinforced either with only aramid fiber or with a hybrid of aramid fiber and carbon black. The fiber contents were varied at 0, 2, 5 and 10 parts (by weight) per hundred rubber (phr) while those of carbon black were 0, 10, 20 and 30 phr. Conventional sulfur vulcanization was used. It was found that aramid fiber can reinforce both rubbers in the low strain region effectively, although to a significantly different degree. The hybrid carbon black provides additional reinforcement at low to medium strains and allows high strain stress upturn to occur in both rubber matrices. The findings enable the preparation of rubber composites having a wide, controllable range of mechanical behavior for specific high-performance engineering applications. Significantly, they also serve as a benchmark for developing reinforced systems from alternative fibers, particularly those from natural sources.     

Stabilization effect of lignin in natural rubber

A series of carbon black filled natural rubbers containing lignin was tested from the view point of their thermo-oxidative aging. Lignin is biopolymer that belongs to the main components of wood. Mechanical properties and crosslink density of lignin stabilized vulcanisates were measured before and after thermo-oxidative aging for 24, 72, 168, 240 and 408 h at 80 °C. The results were compared with those from NR vulcanisates stabilized with the commercial rubber antioxidant N-phenyl-N-isopropyl-p-phenylene diamine (IPPD). The results obtained show that lignin exerts a stabilizing effect in carbon black filled natural rubber. Its effect is comparable with that of conventional synthetic antioxidant. Moreover, the addition of lignin increased the stabilizing effect of IPPD.     

Preparation and properties of natural rubber/rectorite nanocomposites

Natural rubber (NR)/rectorite nanocomposite was prepared by co-coagulating NR latex and rectorite aqueous suspension. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) were employed to characterize the microstructure of the nanocomposite. The results showed that the nanocomposite exhibited a higher glass transition temperature, lower tan δ peak value and slightly broader glass transition region compared with pure NR. The gas barrier properties of the NR/rectorite nanocomposites were remarkably improved by the introduction of nanoscale rectorite because of the increased tortuosity of the diffusive path for a penetrant molecule. The nanocomposites have a unique stress-strain behavior due to the reinforcement and the hindrance of rectorite layers to the tensile crystallization of NR.     

Alkanolamide as an accelerator,filler-dispersant and a plasticizer in silica-filled natural rubber compounds

A feasibility study was carried out on the utilization of Alkanolamide (ALK) on silica reinforcement of natural rubber (NR) by using a semi-efficient cure system. The ALK was incorporated into the NR compound at 1.0, 3.0, 5.0, 7.0 and 9.0 phr. An investigation was carried out to examine the effect of ALK on the cure characteristics and properties of NR compounds. It was found that ALK gave shorter scorch and cure times for silica-filled NR compounds. ALK also exhibited higher torque differences, tensile modulus, tensile strength, hardness and crosslink density of up to 5.0 phr of ALK loading, and then decreased with further increases of ALK loading. The resilience increased with increased ALK loading. Scanning electron microscopy (SEM) micrographs proved that 5.0 phr of ALK in the silica-filled NR compound exhibited the greatest matrix tearing line and surface roughness due to higher reinforcement level of the silica, as well as better dispersion and cure enhancement.     

Insight into vulcanization mechanism of novel binary accelerators for natural rubber

A novel TU derivative, N-phenyl-N′-(у-triethoxysilane)-propyl thiourea(STU), is prepared and its binary accelerator system is investigated in detail. Compared to the control references, the optimum curing time of NR compounds with STU is the shortest, indicating a more nucleophilic reaction occurs. The Py-GC/MS results present that the phenyl isothiocyanate fragment still remains in the NR/STU compounds with or without extracting treatment, but no silane segment can be found in the vulcanizate with extracting treatment. Vibrations of C=S, NH and aromatic ring in FTIR experiments and a new methyne carbon peak, as well as the peaks of phenyl group of STU, in the solid state 13C-NMR experiments are found in the NR/STU vulcanizate with extracting treatment. Moreover, the crosslinking density of vulcanizates with STU evolves to lower level, indicating the sulfur atom of STU does not contribute to the sulfur crosslinking. Therefore, a new vulcanization kinetic mechanism of STU is propounded that the thiourea groups can graft to the rubber main chains as pendant groups by chemical bonds during the vulcanization process, which is in accordance with the experimental observations quite well.     

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.     

Low temperature degradation and characterization of natural rubber

Low temperature degradation of natural rubber was performed with potassium persulfate (K₂S₂O₈, KPS) in the latex stage at 30 °C to accomplish a good processability of the rubber. Various grades of natural rubbers were used as a source rubber. Gel content, molecular weight and chemical structure of the rubbers were characterized by swelling method, size exclusion chromatography and ¹H NMR spectroscopy, respectively. The well characterized natural rubber was subjected to oxidative degradation with KPS at 30 °C. Mooney viscosity decreased when the latex was degraded with 1.0 phr of KPS and it was dependent upon the amount of KPS. Molecular weight and gel content of the degraded natural rubber were about one-half as low as those of the source rubber. Chemical structure of the rubber was analyzed through Fourier transform infrared and ¹H NMR spectroscopic methods. The degraded natural rubber was found to contain carbonyl and formyl groups as an evidence of the oxidative degradation. Tensile strength of a vulcanizate prepared from the degraded natural rubber was the same as that prepared from the source rubber, even though the gel content and the molecular weight of the degraded rubber were distinguished from those of the source rubber.     

Cytotoxicity and anticancer activity of natural rubber latex particles for cancer cells

To broaden the knowledge of cytotoxicity of natural rubber latex (NRL) nanoparticles we for the first time examined the latex biocompatibility in vitro against a panel of cancer cells (A549, A2780, and MDA-MB-231). Owing to fractionation of NRL nanoparticles by ultra-centrifuge, the effect of the non-rubber constituents (intermediate of 5.8 wt% and sediment of 0.2 wt%) on the cytotoxicity was clarified. For intermediate constituent, the half maximal inhibitory concentration (IC₅₀) values at 24 h was 1.05 mg/mL for A549 cells, which was one order of magnitude higher in toxicity as compared to that for A2780 (0.24 mg/mL) and MDA-MB-231 (0.36 mg/mL) cells. In addition, profound studies including cell cycle arrest abilities and apoptosis induction profiles against cancer cells were discussed in detail. It was found that the constituents exhibit some significant effect on the cell cycle arrest and trigger apoptosis for A2780 cells. This effective apoptosis induction profiles was more prominent in MDA-MB-231 cells incubated with NRL nanoparticles and sediment loading conditions. The percentage of apoptotic cells was ca. 6–8% of the total cells.     

Morphology of peroxide-prevulcanised natural rubber latex: effect of reaction time and deproteinisation

A non-uniform mesh structure, i.e. a dense network near the surface of peroxide-prevulcanised natural rubber latex particles, was observed under transmission electron microscopy. In the initial period of prevulcanisation, the swelling ratio of the latex sheet decreased with longer reaction time while an increase in crosslink density of rubber particles containing polystyrene, prepared using the phase transfer/bulk polymerisation process, was noticed. The modulus of the rubber sheet increased up to maximum crosslinking and thereafter decreased. After removal of proteins from the latex membrane layer, derived from protein-lipid originally existing at the rubber particle surface, could not be detected. The absence of proteins, which act as free radical scavengers, resulted in a rapid diffusion of alkoxy radicals into the rubber phase of deproteinised latex and, therefore, a uniform crosslink distribution inside each particle was obtained.     

Effect of montmorillonite intercalant structure on the cure parameters of natural rubber

Two quaternary phosphonium salts (aromatic and aliphatic) have been used as intercalants for Na-montmorillonite and the effect of intercalant structure on clay morphology and natural rubber vulcanization kinetics was investigated. Due to its lower rigid structure the aliphatic salt was easier to intercalate into the clay galleries giving rise to a higher interlayer distance and facilitating the rubber intercalation obtaining an exfoliated structure in the nanocomposite. The vulcanization process was sensibly accelerated by this organoclay and a higher crosslinking degree was observed in the nanocomposite which gave rise to materials with improved processing and physical characteristics.     

Radiation-induced grafted UHMW–PE chopped fibers as reinforcing filler in polychloroprene

Ultrahigh molecular weight polyethylene (UHMW-PE) has been grafted with acrylonitrile using gamma radiation. The graft yield of the monomer was controlled by the proper choice of radiation dose and monomer concentration. The grafted chopped fibers were introduced in polychloroprene (CR) rubber mixes in order to improve the interfacial adhesion between fibers and matrix. It has been found that the improvement in the mechanical properties of rubber composites obtained depended markedly on the fiber concentration in the rubber mixture. Scanning electron micrographs showed the presence of a continuous phase of rubber adhered to the surface of grafted fiber. © 1997 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.     

Liquid natural rubber (LNR) as a compatibiliser in NR/LLDPE blends—II: the effects of electron-beam (EB) irradiation

Electron-beam (EB) irradiation technique has been used to improve the properties of 60/40 blends of NR/LLDPE in the presence of compatibilisers such as LNR-6 and LNR-16. Improvement in the physical properties of the blend correspond with the increase in the interactions created by EB irradiation as measured by gel content. For this blend ratio, the radiation dose of 200 kGy is found to be optimum. While LNR-6 shows some complimentary effects when it is used together with EB irradiation technique; LNR-16, however, causes an imperfection effect in the blend. The crosslinking process that takes place as a result of EB irradiation occurs at the expense of crystalline arrangement of the semi-crystalline LLDPE. For the morphological fixation purposes EB irradiation technique is found to be very effective.     

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.     

Prevulcanisation of skim latex: morphology and its use in natural rubber based composite material

The prevulcanisation of skim latex, a by-product of field natural rubber (NR) latex concentrated by centrifugation, using sulphur and peroxide systems was investigated. Compared to the peroxide prevulcanisation, the lower swelling ratio of film casted from sulphur-prevulcanised skim (SPVS) latex was observed. The latter was then employed for preparation of NR/SPVS core–shell particles by using heterocoagulation technique whose driving force was an interpolymer complex between poly(ethylene oxide) (PEO) moieties of a non-ionic surfactant (Nonidet) adsorbed on small SPVS particles and the indigenous surfactant (protein–lipid) on a large NR particle. The value of zeta potential of heterocoagulated particle and the better oil resistance of films casted from the composite latex when compared to that of the NR film revealed the NR/SPVS core–shell structure.     

Comparative study of natural rubber/clay nanocomposites prepared from fresh or concentrated latex

Rubbers are usually compounded with different chemicals and fillers in order to modify their properties to suit the end applications. Natural rubber (NR) contains different natural occurring materials and this brings about subtle complexities in controlling compound and vulcanizate properties. Thus, the aim of this paper is to illustrate that the properties of compounds and vulcanizates of NR/clay prepared from fresh field latex and from concentrated latex are different. Different amounts of pristine clay were added to the two latices and their viscosity determined. The latex mixtures were next coagulated to form solid filled rubbers and their properties examined. Vulcanizates of these solid rubbers were then prepared and their properties, also, were determined. The cause of an observed variation is attributed to soluble proteins in the fresh field latex. Structural models to explain this are proposed.     

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.