Natural Rubber Compounds Research Articles

An innovative approach to utilize waste silica fume from zirconia industry to prepare high performance natural rubber composites for multi-functional applications

Silica fume (SF) is silica-rich amorphous waste by-product obtained during zirconium silicate electrofusion process. The key objective of the study was to determine the efficiency of SF as a reinforcing filler in Natural Rubber (NR) compounds vis a vis the conventional filler, high abrasion furnace (HAF) black. Inter-particle distance and particle size distribution analysis from Transmission Electron Microscopy exhibited homogeneous dispersion of filler in hybrid composite (NR SF20/HAF30) with Bis[3-(triethoxysilyl)propyl] tetrasulfide (TESPT). NR composite with 20 phr SF loading improved modulus by 107%, tensile strength by 12%, and tear strength by 28% over gum NR. Hybrid composite showed 111% increase in modulus than NR SF20 composite. Theoretical modelling of Young's modulus with volume fraction of filler quite fit with Guth-Gold equation. Hybrid composite with TESPT showed 72% reduction in heat build-up compared to NR HAF50 composite. Thermal stability improved by 6 °C and rolling resistance reduced by 64% for hybrid TESPT composite compared to NR HAF50 composite. Constrained region in NR composites obtained from dynamic mechanical analysis showed improved rubber-filler interaction in hybrid TESPT composite. Hence, this work not only provides a new approach to utilize industrial waste but also provides for a high performance NR composite at low cost.

The effect of modified Cu(II) kaolinite on interactions with rubberizing components

The interactions of modified Cu(II) kaolinite with rubberizing components, such as stearic acid (SA), zinc oxide (ZnO), sulphur (S) and benzothiazole (Btz) after heating to 150 °C cure temperature were investigated. More over the given prepared modified kaolinite was used for investigation of its effect in model rubber composites. Commercially calcined kaolinite (Kaol) was chemically treated using 0.5 M copper acetate solution in presence of NaOH solution. The modified resulting sample was designated as KCu sample. Different techniques such as Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction patterns analysis (XRD), thermogravimetry/differential thermal analysis (TG/DTA) and scanning electron microscopy (SEM) were used to characterize kaolinite and KCu samples. The different techniques (mainly FTIR an XRD) demonstrated that the copper acetate treatment of kaolinite resulted in formation of monohydrate copper hydroxy acetate complex, which influenced the clay surface. XRD pattern and FTIR spectrum of the modified KCu proved that copper acetate treatment did not affect the clay structure significantly. High-temperature X-ray diffraction patterns analysis (HTXRD) was also used for investigate the interactions of modified KCu with rubberizing components. Heating process of KCu and SA without or with ZnO caused the formation of copper stearate and zinc stearate respectively and it let to the occurrence of the stretching vibrations of the carboxyl group (νCOO−). K-Cu2(OH)3Ac·H2O complex on the clay surface influenced the mutual interaction with benzothiazole and it can be seen in IR spectra involving stretching vibrations (νCH) of aromatic ring and the stretching vibrations of functional groups ν(N=CS) and ν(C=N). Finally, for the supplementation of the results, the model rubber composites, filled with kaolinite and KCu and ranged 5, 10 and 20 phr, were prepared. The effect of modified kaolinite on the curing characteristics (minimum torque – ML, maximum torque – MH, optimal vulcanization time – t90, coefficient of vulcanization rate – Rv) and mechanical properties (tensile strength at break – TSb, elongation at break – Eb and hardness) in sulphur-cured natural rubber (NR) composites was investigated. A low viscosity of the NR compounds was achieved throughout the kaolinite and KCu fillers used. The cure time increased by KCu dosing in amount of 10 and 20 phr. The decrease of the maximum torque (MH) value indicates a lower stiffness as well as the viscosity of the mixture at the end of vulcanization. However, the mechanical properties of the vulcanizates with KCu showed significant improvement of TSb and Eb, compared with standard and mixtures with non-modified kaolinite. The modified Cu(II) form of kaolinite had positive effect on the properties of rubber compounds in amount of 5 and 10 phr.

Characterizing the Intrinsic Strength (Fatigue Threshold) of Natural Rubber/Butadiene Rubber Blends

ABSTRACT Tires require rubber compounds capable of enduring more than 108 deformation cycles without developing cracks. One strategy for evaluating candidate compounds is to measure the intrinsic strength, which is also known as the fatigue threshold or endurance limit. The intrinsic strength is the residual strength remaining in the material after the strength-enhancing effects of energy dissipation in crack tip fields are removed. If loads stay always below the intrinsic strength (taking proper account of the possibility that the intrinsic strength may degrade with aging), then cracks cannot grow. Using the cutting protocol proposed originally by Lake and Yeoh, as implemented on a commercial intrinsic strength analyzer, the intrinsic strength is determined for a series of carbon black (CB) reinforced blends of natural rubber (NR) and butadiene rubber (BR) typical of tire applications. The intrinsic strength benefits of the blends over the neat NR and BR compounds are only observed after aging at temperatures in the range from 50 to 70 °C, thus providing fresh insights into the widespread durability success of CB-filled NR/BR blends in tire sidewall compounds and commercial truck tire treads.

Influence of Activated Rubber Powder on the Mechanical Properties of Natural Rubber Compound

Influence of Activated Rubber Powder on the Mechanical Properties of Natural Rubber Compound

Effects of TESPT-Silane Coupling Agent on Torque Properties and Degree of Filler Dispersion of Silica Filled Natural Rubber and Epoxidized Natural Rubbers Compounds

The effect of the addition of a bis(triethoxysilylpropyl) tetra sulphide or TESPT-silane coupling agent on torque properties and degree of filler dispersion of silica-filled compounds of natural rubber (NR), epoxidized natural rubbers with 25% mole of epoxidation (ENR 25) and epoxidized natural rubbers with 50% mole of epoxidation (ENR 50) were investigated. All the rubbers were filled by silica filler at a fixed loading (30.0 parts per hundred rubber, phr) and the TESPT was added to each silica-filled rubbers compounds at 1.0phr. It was found that TESPT affected the torque properties of all the silica-filled rubbers compounds. The TESPT decreased the minimum torque of NR system but increased the minimum torque of ENRs systems and maximum and torque differences of the all rubbers systems. The minimum torque was decreased from 0.61 to 0.53 dN.m for NR; were increased from 0.23 to 0.49 dN.m for ENR 25 and from 0.07 to 0.34 dN.m for ENR 50.It was also found that the TESPT acted as an internal plasticizer for NR which improved the degree of silica dispersion. Presumably, for the ENRs, the TESPT acted as an additional cross linker with a more pronouncedly which poorer the degree of silica dispersion.

Base isolation fibre-reinforced composite bearings using recycled rubber

In the past few years, there have been a number of previous researches on the rubber isolators for resisting earthquakes. A typical bearing consists of natural rubber sheets and bonded to steel plates. For an application of using rubber bearings, numerous isolated buildings have been constructed to resist an earthquake across the countries which experience earthquakes over decades. Another application might be used in the bridge structures of railways and highways, in order to suppress vibrations and dynamic actions. The key idea is to use rubber isolators attached beneath the superstructures for attenuating the damage potential of seismic responses. This means that the rubber provides the isolators flexible in the horizontal direction and the steel makes them strong in the vertical direction. Anyways, most bearings are made of natural rubber or synthetic compound. These materials are costly and cannot be durable over time. This paper aims to develop a new design of bearing using recycled materials and fibre reinforcement. The concept is to design two models using the finite element method (FEM) as a square and circular shape for the investigation into the static and dynamic behaviour. Through, the finite element method will be conducted to evaluate structural response and effectiveness of the novel low-cost bearing. Bearing models from the analytical method based on the theory are verified by the FEM. The overall results show that the fibre square model is less effective than the fibre circular model due to the different shape factors, S. The outcome of this project will help to enable more eco-friendly bearing materials for structural, highway and railway engineers. However, a further study of designing recycled rubber bearings with the fibre-reinforced polymer should be carried out by experimental tests. The study should be also compared with the performance between the fibre and steel bearing model, in order to verify the models created by FEA more effectively.

Mechanical strength of natural rubber filled fly ash

In this present work, Fly ash was incorporated into natural rubber to form a natural rubber composite. The natural rubber composite was prepared by solution mixing method at the constant amount of fly ash at 80 phr. The fly ash particle was modified its surface by TESPT silane coupling agent before mixing with natural rubber latex. The surface morphology of natural rubber composites were examined by SEM image. The vulcanization parameters were examined by MDR technique. The results show that modified fly ash affects to natural rubber compound by shorten the vulcanization time and increase maximum torque. The mechanical properties were investigated from stress-strain curve. It reveals that the surface modification of fly ash improves tensile strength of natural rubber by 6 times. The increasing of strength may attribute to the formation of polymer-fillers interaction through TESPT molecules.

Microencapsulation and Surface Functionalization of Ammonium Polyphosphate via In-Situ Polymerization and Thiol–Ene Photograted Reaction for Application in Flame-Retardant Natural Rubber

A novel type of microencapsulated ammonium polyphosphate (MAPP) with a triallyl cyanurate (TAC)/SiO2 double-layered shell was synthesized through in-situ polymerization, followed by the thiol–ene photograted reaction. With a double bond in the TAC outer shell, MAPP could be utilized as a highly efficient flame retardant for intumescent flame-retarded natural rubber (NR). The chemical structure, morphology, and performance of MAPP were characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, water contact angle (WCA), scanning electron microscopy, and thermogravimetric analysis. MAPP exhibited a hydrophobic feature with a WCA of 101° because of its organic outer shell, which made MAPP well dispersed in the NR matrix as well as enhanced the compatibility between the MAPP and NR matrix. The resulting intumescent flame-retardant NR compounds not only achieved excellent flame-retardant performance but also obtain improved mechanical properties because of the presence of 3D-cr...

Novel CNC/silica hybrid as potential reinforcing filler for natural rubber compounds

ABSTRACTThis work describes the development of a low‐density, renewable, and high reinforcing filler for natural rubber (NR) compounds. The cellulose nanocrystal (CNC)‐based hybrid filler was synthesized by decorating the surface of CNCs with silica using a simple and efficient coprecipitation method. The properties of the prepared hybrid were investigated by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, nitrogen physisorption measurements, and Thermogravimetric analysis. Then, the prepared hybrid was incorporated in NR using two different approaches, namely, dry mixing and coprecipitation. The dynamic and tensile mechanical properties of the hybrid/NR compounds were evaluated indicating that: the coprecipitation method was found much more effective for homogeneous dispersion and the CNC/silica hybrid provided quite higher reinforcement to NR than reference silica; however, much lower density of the final compounds was obtained. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48332.

Effect of the cure system on aging resistance of natural rubber compounds

This work investigates natural rubber (NR) composites vulcanized with different combinations of accelerators in efficient cure systems. The NR compounds were characterized for cross-link density, hardness, tensile strength, and dynamical–mechanical properties, before and after aging. Among the cure systems used, that containing the highest amount of free sulfur presented the best mechanical performance, before and after aging; concerning dynamic properties after the aging, the composition with a lower number of cross-links was the best.

EXPERIMENTAL DETERMINATION OF THE QUANTITY AND DISTRIBUTION OF CHEMICAL CROSSLINKS IN UNAGED AND AGED NATURAL RUBBER. II: A SULFUR DONOR SYSTEM

ABSTRACTA series of unfilled and stabilized natural rubber compounds varying in concentration of tetramethylthiuram disulfide (TMTD) was analyzed using rheometry, hardness, dynamic mechanical properties, stress–strain (Mooney–Rivlin), equilibrium solvent swell (Flory–Rhener), and low-field nuclear magnetic resonance (NMR) by the double quantum (DQ) technique. Crosslinking level increased proportionately with TMTD concentration, and the reaction ratio of three TMTD molecules producing one crosslink was generally upheld. Unreacted TMTD acted as a pseudo-plasticizer and lowered the chain entanglement density with increasing TMTD content. DQ NMR confirmed that the elastic network was homogeneous and that the absolute chemical crosslink distributions broaden with increasing curative level. Upon mild heat aging, zinc complexes based on TMTD/ZnO are likely responsible for causing additional crosslinking, explaining the rise in crosslink density by equilibrium solvent swell and DQ NMR. The amine-based antioxidant, the generation of thiocarbamate radicals from TMTD, and the heat stability of the predominant monosulfide crosslinking system helped to limit network breakdown through chain scission. The chain entanglement increase is likely due to reduction of the plasticizing effect caused by unreacted curative. The distribution of crosslinks slightly broadens toward higher total crosslink density because of the generation of additional chemical crosslinks and chain entanglement densification.

Devulcanization of natural rubber compounds by extrusion using thermoplastics and characterization of revulcanized compounds

Rubber recycling is a subject of high interest, regarding the complexity to develop a feasible method for material recovery without main chain degradation. In this research, Natural Rubber compounds were thermomechanically devulcanized in a continuous way through a co-rotating and intermeshing twin-screw extruder. Four process parameters were evaluated: screw rotation speed, barrel temperature, sulfur concentration and auxiliary thermoplastics (PP or EVA). Devulcanized samples were characterized by their soluble fraction, crosslink density, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR), demonstrating the rising of free natural rubber chains concentration after extrusion. Horikx theory was also used for qualitative analysis. The samples were revulcanized with or without virgin rubber compound addition and characterized by tensile, hardness and dynamic-mechanical tests (DMA). Better mechanical performances were achieved using thermoplastics due to greater second phase incorporation confirmed by scanning electron microscopy (SEM). Compounds extruded with EVA showed even better properties retention, with values around 86% for tensile strength, 110% for elongation at break and 99% for hardness, indicating this material as a promising assistant in vulcanized rubber recycling.

Natural Rubber Powder Production from Latex

Natural rubber-based products are widely used in everyday life. There are three types of upstream processed natural rubber, that are crumb rubber, conventional rubber, and concentrated latex. Latex is easily damaged by clotting and contains 35-40% w/w of water so that the packaging volume is relatively large and inefficient in transportation. Latex also contains ammonia as an anti-clotting agent so the packaging must be special to prevent unpleasant odour. This study aims to create a pilot plant of the spray drying latex from simulation results then test the performance, evaluate the performance test results, as well as making improvements to the production of rubber powder. The steps of this research are data collection for spray dryer design, design verification, construction of spray dryer, spray dryer appliance testing, and characterization of rubber powder produced. The heating system used in the spray dryer is LPG gas-fired furnace. Testing is done by varying the spray dryer drying air temperature of 120°C, 150°C, and 180°C, the water content of the feed latex 70% and 80% w/w, as well as non-stick material such as talc powder and MgO. Rubber powder characterized by water content with digital tools moisture meter and analysed spectra with Fourier Transform Infrared Spectroscopy (FTIR). The results showed the optimum operating conditions for the production of natural rubber powder is drying air temperature of 150°C and the water content of the feed latex 80% w/w. Natural rubber powder produced contains 10 to 13% w/w water but still sticky so that the powder grains stick to each other. The FTIR spectrum analysis of natural rubber powder products show similarity with bonding group of polyisoprene natural rubber compound. Natural rubber powder product can also be used as a substitute for crumb rubber.

SILICA-REINFORCED NATURAL RUBBER TIRE TREAD COMPOUNDS CONTAINING BIO-BASED PROCESS OILS. I: ASPECTS OF MIXING SEQUENCE AND EPOXIDE CONTENT

ABSTRACT A bio-based process oil for rubber compounds is one of the compounding ingredients to be used toward an eco-friendly and more sustainable rubber technology. This work investigates epoxidized palm oil (EPO) as an alternative for petroleum-based process oil in silica-reinforced natural rubber (NR) tire tread compounds. The effect of different incorporating steps of EPO on the properties of the rubber compounds is first studied, taking into account that the polar functional groups in the oil molecules may interact with the silanol groups on the silica surface. The properties of silica-reinforced NR compounds with EPO oil are compared with that of reference mixes with treated distillate aromatic extract (TDAE) and without oil. The compounds with EPO show a lower viscosity, filler–filler interaction, and flocculation rate constant but higher cure reaction rate constants compared with the compound with TDAE. The results indicate that the epoxide groups in EPO interact with the silanol groups on the silica surface, promoting a greater shielding effect on the polar surface and thus better silica dispersion and less interference with the vulcanization reaction. The different incorporating steps of EPO show no significant effect on the viscosity, filler–filler interaction, or flocculation rate constant but clearly affect the extent of crosslinking, as indicated by the cure torque difference. The presence of EPO in an early stage of the mixing together with the first half addition of silica and silane results in the lowest cure torque difference, modulus, and tensile strength (i.e., the highest tan δ at 60 °C), which indicates a possible obstruction for the interaction between the silanol groups and silane coupling agent by the EPO molecules. Comparing EPO with different epoxide contents in the range of 1–3 mol%, the increase in epoxide content gives similar Payne effects but enhances the cure reaction, resulting in improved tensile properties and tan δ at 60 °C. The results clearly prove that EPO can be used as a TDAE alternative.

Tensile and rheometric properties of calcium carbonate-filled natural rubber compounds without/with lauryl alcohol

The tensile and rheometric properties of CaCO3, calcium carbonate-filled natural rubber (NR) compounds without and with lauryl alcohol (LA) as a new rubber additive were examined. The NR was filled by CaCO3 with a certain addition, thirty phr. The LA was synthesized from palm kernel oil and incorporated into CaCO3-filled NR compounds at 1, 3, 5 and 7 phr. From the overall results, the LA was a curative and also plasticizing material. As a curative material, LA enhanced both tensile strength and difference in torque up to a five phr of addition. As a plasticizing material, LA reduced tensile moduli but enhanced elongation at break of CaCO3-filled NR vulcanizates. A five phr of LA was an optimum addition.

Study of physical characteristic of rubberized hot mix asphalt based on various dosage of natural rubber latex and solid rubber

Currently, the implementation of rubberized asphalt technology become the main concern of Government in natural rubber producing countries, especially Thailand, Indonesia, and Malaysia. The policy is intended to increase natural rubber domestic consumption and support national infrastructure project. Rubberized asphalt is made from the mixture of hot asphalt with polymer such as natural rubber either in the form of latex or compound. For field implementation, rubberized asphalt should be mixed with aggregate to form rubberized hot mix asphalt. The research was conducted to study the rubberized hot mix asphalt characteristic at laboratory scale. Types of natural rubber were used consist of cationic natural rubber latex (L2), 4 hours prevulcanized natural rubber latex (L3), and semi-efficient solid natural rubber compound (KP2). The base asphalt used asphalt penetration 60/70, while the aggregate was obtained from Subang District, West Java, Indonesia. The trials were run at three stages i.e. analysis of pure asphalt and aggregate properties, determination of mixing and compaction temperature, followed with characterization of rubberized hot mix asphalt physical properties by using Marshall and Wheel Tracking Machine. The dosage of natural rubber addition was varied at 3,5,7 and 9%. Hot mix asphalt without rubber addition was used as control. The result showed that the addition of natural rubber into the asphalt penetration 60/70 raised the Marshall stability of rubberized hot mix asphalt. The initial Marshall stability value was 986 kg for pure hot mix asphalt became 1097 kg for 7% of cationic natural rubber latex, 1103 kg for 5% of 4 hours prevulcanized natural latex, and 1110 kg for 7% of semi-efficient solid natural rubber compound. Thus, it could be concluded that the addition of 5-7% natural rubber improved the physical characteristic of rubberized hot mix asphalt as indicated by the increasing of Marshall stability value.

Grafting polyisoprene onto surfaces of nanosilica via RAFT polymerization and modification of natural rubber

In this contribution, we reported the investigation of natural rubber (NR) reinforced by silicon dioxide‐graft‐polyisoprene (SiO2‐g‐PIP) core–shell nanoparticle. First, the hydroxyl on the surface of the SiO2 nanoparticles was reacted with 2‐methyl‐2‐[(dodecylsulfanylthiocarbonyl) sulfanyl] propanoic acid to produce trithioester‐capped SiO2 (denoted as SiO2‐CTA). SiO2‐CTA was used as a nanoparticle chain transfer agent, and SiO2‐g‐PIP core–shell nanoparticles were synthesized via reversible addition‐fragmentation chain transfer polymerization (RAFT). The results of FTIR spectroscopy and TGA showed that the grafting weight of the PIP block in SiO2‐g‐PIP was 2.1 wt%. SiO2‐g‐PIP and SiO2 were simultaneously incorporated into NR. The curing properties of the NR compounds showed that the vulcanization rates of the NR/SiO2‐g‐PIP compounds were much higher than those of NR/silica compounds. The results of scanning electron microscopy showed that SiO2 microdomains in the NR/SiO2‐g‐PIP vulcanizate were much better disperse and distribute than SiO2 microdomains in the NR/SiO2 composite. The filler–rubber interaction of the NR/SiO2‐g‐PIP composite endowed the composite with improved mechanical properties. POLYM. ENG. SCI., 59:1167–1174 2019. © 2019 Society of Plastics Engineers

Tensile Properties and Dynamic Mechanical Behaviour of Natural Rubber Compound Filled with Rice Husk Silica Produced via Solvent-Thermal Extraction Method

This study highlighted the effect of incorporation of rice husk silica (RHS) on the tensile properties and dynamic mechanical behaviour of natural rubber (NR) compounds. High purity RHS was synthesised by solvent-thermal extraction method, which was inspired by TAPPI T204 cm-97 and TAPPI T264 cm-97 standards with some modifications. The extraction method had successfully produced RHS with 99.9% of silica content and surface area of 234.25 m2/g. The incorporation of RHS in NR showed increment in tensile properties compared to unfilled NR. Further improvement was recorded by surface modification of RHS with 1 wt. % bis (triethoxysilylpropyl) tetrasulfide (TESPT). The modification of RHS with TESPT increased the rubber-filler interaction between RHS and NR matrix, hence enhancing the strength-related properties. The modified RHS-NR also recorded highest storage modulus, and the presence of RHS in the NR compound had slightly shifted the glass transition temperature (Tg) to a higher value. This confirmed that the strong rubber-filler interaction had increased the rigidity of the compounds and restricted the mobility of the rubber chains.

Silica-Reinforced Natural Rubber: Synergistic Effects by Addition of Small Amounts of Secondary Fillers to Silica-Reinforced Natural Rubber Tire Tread Compounds

Modern fuel-saving tire treads are commonly reinforced by silica due to the fact that this leads to lower rolling resistance and higher wet grip compared to carbon black-filled alternatives. The introduction of secondary fillers into the silica-reinforced tread compounds, often named hybrid fillers, may have the potential to improve tire performance further. In the present work, two secondary fillers organoclay nanofiller and N134 carbon black were added to silica-based natural rubber compounds at a proportion of silica/secondary filler of 45/10 phr. The compounds were prepared with variable mixing temperatures based on the mixing procedure commonly in use for silica-filled NR systems. The results of Mooney viscosity, Payne effect, cure behavior, and mechanical properties imply that the silica hydrophobation and coupling reaction of the silane coupling agent with silica and elastomer are significantly influenced by organoclay due to an effect of its modifier: an organic ammonium derivative. This has an effect on scorch safety and cure rate. The compounds where carbon black was added as a secondary filler do not show this behavior. They give inferior filler dispersion compared to the pure silica-filled compound, attributed to an inappropriate high mixing temperature and the high specific surface area of the carbon black used. The dynamic properties indicate that there is a potential to improve wet traction and rolling resistance of a tire tread when using organoclay as secondary filler, while the combination of carbon black in silica-filled NR does not change these properties.

Performance of binary accelarator system on natural rubber compound

Accelerator system provides different response onto the rubber compound, and in turn influences its final properties. Accelerators, such as 2,2'-Dithiobis (benzothiazole) (MBTS), N-Cyclohexylbenzothiazole-2-Sulfenamide (CBS) and diphenyl guanidine (DPG), has been selected for the study. Response of paired accelerator, MBTS/DPG and CBS/DPG in various ratio, on natural rubber (NR) compound was evaluated. Rheological properties and cure characteristics of the compounds were analyzed using Mooney viscometer and moving die rheometer (MDR) typically. Results findings showed that incorporation of DPG into the system has increased the viscosity of the compound and effected the molecular weight during the process. Further, the addition of DPG also shortened the induction period by reducing the scorch time (ts2) and decreasing the cure time (t90). Binary paired accelerator resulted in poor flow characteristic as a result of strong domination of elastic element. In general, the CBS-based system provided more balance characteristic than those of MBTS-based.