NR Compound Research Articles

Organic radicals stabilization in natural rubber: Discerning the influence of thermo-oxidation using chemically modified or unmodified lignin as antioxidant

We have implemented a lignin compatibilization strategy through silylation and elaborated NR compounds with lignin and silylated lignin. Then, the lignin’s contribution to the preservation of physico-mechanical properties and stability of the materials obtained against thermo-oxidation was studied. Thus, our work considered the indirect study of the antioxidant activity on NR compounds by determining the physico-mechanical properties before and after accelerated thermo-oxidative aging, which allowed us to determine that the increase in crosslinking density during the initial hours of accelerated aging was the main observed cause associated with a higher tensile strength retention rate (TSRR: 13.4 %) in NR compound with 5 phr of lignin (CL5) versus a TSRR: 4.7 % for the compound with 5 phr of silylated lignin (CL5Si1). On the other hand, the direct study of the antioxidant capacity by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) using oxygen atmosphere indicated greater thermal stability in NR compounds when lignin is not silylated. The maximum degradation temperature for the CL5 compound was 341.6 °C, while for the CL5Si1 compound it was 328.6 °C. The oxidation induction temperature (OITtemp) in the CL5 compound was 190.9 °C with a peak at 221.0 °C, while for CL5Si1 it was 170.3 °C with a peak at 194.1 °C, indicating again that unsilylated lignin is more suitable as an antioxidant. Finally, through Electron Paramagnetic Resonance (EPR), we determined that the radical quenching effect due to the presence of lignin was significant as the lignin content increases, with a reduction in radical presence close to 50 % compared to a reference compound without lignin.

Technical research of pyrolytic carbon black prepared on rotating moving bed equipment

Nowadays, waste tires have been one of the worst environmental pollution sources. How to solve the waste tires is a hot potato for the environment. Pyrolysis is one of the most commonly used method. In China, rotary kiln reactor has been widely used for pyrolysis and can be used as a large-scale production equipment form, but there is no mature case of rotating moving bed. In this paper, CBp was produced in rotating moving bed. The continuous pyrolysis device, rotating moving bed, which is a new type of equipment to replace the batch reactor. Temperature is studied as the most important character in the cracking process. The results showed that the productivity of CBp, Pyrolytic oil and gas were obviously affected by temperature. The oil could improve the compatibility of CBp with rubber, increasing the dispersion in rubber, resulted in the good reinforce property. High temperature causes more groups be detected on the surface of CBp by FT-IR spectrometer. The Payne effect of CBp reinforced NR compound increases with the increasing of pyrolysis temperature.

In-situ preparation of TBIR/CB nanocomposites and its regulation in structure and properties of NR based composites

In order to construct the rubber nanocomposites with desired dual network structures, the trans -1,4-poly (butadiene-co-isoprene) copolymers (TBIR)/carbon black (CB) nanocomposites were prepared by in-situ polymerization in the presence of large amounts of CB using TiCl 4 -type Ziegler-Natta catalysts. It was found that the addition of CB had no obvious negative effects on the catalytic behaviors. Further, the TBIRCB were used to modify NR and the NR/TBIRCB vulcanizates were investigated. Compared with the NR compound, the NR/TBIRCB compounds presented weakened Payne effects and increased bound rubber contents with the increase in CB filling in TBIRCB. Compared with NR and NR/TBIR vulcanizates, the NR/TBIRCB46 vulcanizate with features like excellent filler dispersion and high CB in-situ filling, enhanced interaction between CB and rubber matrix and special polymer network structure constructed from NR/TBIR matrix, showed outstanding comprehensive properties, including greatly reduced rolling resistance, much lower heat built-up and increased abrasion resistance. • Synthesis of new synthetic rubber composites by in-situ polymerization. • NR/TBIRCB46 vulcanizate improve the dispersion of filler in natural rubber. • The rolling resistance, heat build-up and wear of NR/TBIRCB composites are significantly reduced.

Effect of composition ratios and mixing steps on properties of BR/NR/NBR blends and blends foam

This research is aimed to prepare foam from BR/NR/NBR blends which should integrate key property of these three rubbers. BR possesses high abrasion resistance but low tensile strength while NR possesses high tensile strength [1]. The addition of NBR was advantage for non-polar solvent resistance [2]. The effect of the mixing steps of rubber with vulcanizing additives on vulcanization of rubber and on mechanical properties and foaming of BR/NR/NBR were reported. The ratios of BR/NR/NBR were various as 60/20/20, 40/40/20 and 20/60/20. The vulcanizing additives used for rubber compounding were 5 phr ZnO, 2 phr stearic acid, 1.5 phr MBTS and 2 phr sulfur. The first part of the work was to study the effect of mixing step on rubber blends. Compounding system I was carried out by masticated BR, NR and NBR on a two-roll mill after that vulcanizing agent was added consecutively obtaining BR/NR/NBR rubber compounds with various rubber compositions. Rubber compounds were then characterized and vulcanized in order to investigate vulcanizate properties. In System II, three rubbers were mixed separately with required vulcanizing additives on the two-roll mill, obtaining BR, NR and NBR compound containing the same content of vulcanizing agent. Then the compounds were blended to obtain compound blended for the same blend ratios in System I. The blended rubber compounds were then characterized and vulcanized for their properties. In term of rubber blend foaming these two mixing systems were also used to compound the rubbers by addition foaming agent into the compound during mastication or blending of rubber on the two-roll mill. The results showed that mixing step affected the properties of rubber compound and vulcanizate in rubber blend. As various rubbers were mixed in different step resulting in different viscosity and hence affect foaming of rubber and subsequently properties of rubber foam.

APPLICATION OF THE RESIN DERIVED FROM THE NATIVE EUPHORBIA CADUCIFOLIA HAINES AS MULTIFUNCTIONAL ADDITIVE IN FILLED NATURAL RUBBER COMPOUNDS

ABSTRACT The whole coagulum (Cog) and its toluene-soluble fraction [toluene extract (TE)] obtained via the coagulation of the latex of Euphorbia caducifolia Haines was used as a green, multifunctional additive in a filled NR compound. The actions of Cog and TE were compared with two commercial resins, non-heat-reactive octyl phenol-formaldehyde (PF) and coumarone-indene (CI), at equal doses and also with conventional aromatic oil (through replacement). Both Cog and TE exhibited comparable tack strength with CI, but lower tack strength with PF. In addition, TE improved the cure rate index, unlike Cog and the commercial resins. When the aromatic oil was replaced with TE and Cog at different levels, we observed that TE could replace 100% of the original oil content, whereas Cog could only replace 33% of the original oil content from the recipe without deterioration of physico-mechanical properties. Both forms of natural resins decreased the intrinsic elasticity of the compounds and improved the aging resistance of the vulcanizates.

Influence of flow pattern development at die entrance and inside annular die on extrudate swell behavior of NR compound

This research studies influence of the flow pattern at annular die entrance through the inside of annular die flow channel of capillary rheometer on the swell behavior of NR compound. The annular die used in this research was specifically designed to create the specific pattern of Vortex Flow at Die Entrance (VFE) of NR compound. Results of the study showed that the thickness swell ratio was higher than diameter swell ratio by an average of 20% at every die gap size. It was also found that the VFE flow pattern had direct significant influence on the swell behavior of NR compound while extrudating through annular die. Results from the study of the flow pattern could be used to explain why the thickness swell ratio is higher than the diameter swell ratio in every test condition.

양기능성 커플링제 실란에 의한 실리카-천연고무 복합소재의 계면간 결합 고찰

양기능성 실란 커플링제인 bis(triethoxysilylpropyl)tetrasulfide(TESPT)가 실리카/천연고무 복합소재 내에서 실리카의 hydroxy기와 고무 계면간에 화학적 결합반응을 하여 실리카-실란-고무간의 3차원 사슬구조를 형성한 것을 열분해 가스 크로마토그래피 질량분석기(Py-GC/MS)와 주사전자현미경(SEM)을 통해 관찰하였다. TESPT의 첨가로 배합물 내의 황 함유율이 증가하여 스코치 시간(<TEX>$t_{10}$</TEX>)은 감소하고, TESPT 내 sulfur donor 역할을 하는 황이 활성화제 및 촉진제와의 복합반응으로 가교반응이 지속적으로 이루어짐에 따라서 가교속도지수(CRI)의 값이 감소하였다. 또한 TESPT가 첨가된 컴파운드는 첨가되지 않은 컴파운드에 비해 가공성 및 기계적 물성이 향상되었다. 결과적으로, 실리카로 충전된 천연고무 복합소재에 실란 커플링제(TESPT)가 첨가되어 화학반응으로 실리카-실란-고무간의 3차원 사슬구조가 형성됨을 관찰하였고 이에 따라 가교밀도가 증가하여 복합소재의 물성 증가에 기여함을 보여주었다. Formation of a strong 3-dimensional interfacial network structure via chemical reaction between hydroxyl group on silica surface and NR chain by the addition of bis(triethoxysilylpropyl)tetrasulfide (TESPT) into silica-filled NR compound was observed by using Py-GC/MS and SEM. Addition of TESPT into silica-filled NR compound decreased scorch time (<TEX>$t_{10}$</TEX>) due to increased sulfur content, and reduced cure rate index (CRI) via continuous reaction between sulfur atoms in TESPT, which acted as a sulfur donor, and activators and/or accelerators. Addition of TESPT in the compound improved processability and mechanical properties of the compound. Overall, we observed that the addition of TESPT into the silica-filled NR compound formed a silica-TESPT-NR network, and thus the degree of crosslinking was increased resulting in improved mechanical properties.

Influence of &lt;i&gt;N&lt;/i&gt;-Phenyl-&lt;i&gt;p&lt;/i&gt;-Phenylenediamine Modified Epoxidized Palm Oil on Properties of Carbon Black Filled Natural Rubber Compound and Vulcanizate

Modified epoxidized palm oil (pA-m-EPO) was prepared by a reaction of epoxidized palm oil (EPO) with n-phenyl-p-phenylenediamine. Chemical structure of the pA-m-EPO was characterized by using FT-IR spectrophotometer. Influence of the pA-m-EPO on bound rubber content, total mixing energy, Mooney viscosity and curing characteristics of carbon black filled natural rubber compound together with mechanical and morphological properties of carbon black filled natural rubber vulcanizates was later studied. Results showed that the NR compound and vulcanizate with using the pA-m-EPO gave inferior properties than those of using the aromatic oil. However, they provided better properties than those of the treated distillate aromatic extract (TDAE) excepting filler dispersion. Furthermore, the pA-m-EPO can be claimed as non-carcinogenic processing oil with low polycyclic aromatic hydrocarbons.

Silica-Reinforced Natural Rubber Compounds Compatibilized through the Use of Epoxide Functional Groups and TESPT Combination

Epoxidized natural rubber (ENR) and bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT) were used to improve the properties of silica-filled NR. The use of ENR containing 51 mol% epoxide groups (ENR-51) as a compatibilizer without TESPT was optimized at 7.5 phr, based on the results of Payne effect and tensile strength. By using 7.5 phr of ENR-51 with varying amounts of TESPT in a range of 2 to 5 wt% relative to the silica, the properties of compounds were compared to those of the ones with optimum TESPT content (i.e. 8.6 wt% relative to the silica) and without. The addition of TESPT to the ENR-51 compatibilized silica-filled NR compound had no effect on Mooney viscosity but lowered the Payne effect to the same level as that of the silica/TESPT compound, and significantly decreased both scorch and optimum cure times. The silica-filled NR with ENR and the small amount of TESPT combination showed a further increase in tensile strength to match that of the optimized silica/TESPT system, while maintained the elongation at break. This work demonstrates that the use of ENR as compatibilizer clearly enhances the properties of silica-filled NR compounds, and that such properties can be further improved by adding TESPT at a half or less amount of TESPT normally needed for silica-filled compounds.

Influence of Benzyl Ester Oil on Processability of Silica Filled NR Compound

Modified benzyl esters from coconut, palm, and soybean oil were used as alternative rubber processing oil to replace distillate aromatic extract oil (DAE). The effect of benzyl esters on mixing, curing properties, polymerfiller interaction and Mooney viscosity was investigated in silica filled natural rubber compound. Benzyl ester oil was found to be effective processing oil with decreasing of mixing energy and Mooney viscosity. Furthermore, it was found that coconut and palm benzyl esters showed higher torque difference than the aromatic oil filled compound. Also, benzyl ester oil gave similar level of cure time and dynamic properties compared with the rubber compound with aromatic oils.

The Effect of Excess Silane-69 Used for Surface Modification on Cure Characteristic and Mechanical Properties of Precipitated Silica Filled Natural Rubber (PSi/NR)

This research is concentrated on the effect of concentration of silane-69 used for surface modification on precipitated silica (PSi), on cure characteristic and mechanical properties of PSi filled NR. The PSi content in this study was fixed at 20 phr in order to reveal the effect of silane used to modify PSi, on NR compound and vulcanizate. Moving Die Rheometer (MDR) was used to characterize cure characteristic of rubber compounds. Generally, scorch and cure time of NR would increase with the addition of PSi due to the absorption of accelerator on its surface whereas the addition of Si-69 modified PSi would reduce both scorch and cure time. It was found in this research that the excess amount of Si-69 used increased scorch and cure time of rubber compounds. This was thought to be that the excess of Si-69 led to the formation of polysiloxane clusters which could absorb accelerator in rubber compound and resulted in a prolonged scorch and cure time. In term of vulcanized rubber, it was found that maximum torque increased with the concentration of Si-69 up to 6 %. The polysiloxane formed during the cure characterization test was responsible for the slightly decreased torque after 6% of Si-69 treatment. Nonetheless, even with high concentration of Si-69 used, torque was still higher than that of untreated PSi filled NR. This is widely understood that sulfur atoms in Si-69 molecule are able to participate in the bonding between rubber and silane molecules resulted in the enhancement of crosslink density of the vulcanizate rubber. The increased of modulus at 200 % elongation, tensile strength under tension, with the silane concentration, was evidence of the crosslink enhancement. Tear strength and hardness of the vulcanizates exhibiting the increment, with the silane used, also clearly confirmed the bonding between Si-69 and rubber molecules. It was elucidated from the research that excess of Si-69 would lead to polysiloxane formation, cluster form of silane and crosslinking density. Scanning Electron Microscope (SEM) micrographs and swelling test are also presented to confirm the phenomena.

Mechanistic Investigations into the Adhesion between RFL-Treated Cords and Rubber. Part II: The Influence of the Vinyl-Pyridine Content of the RFL-Latex

Abstract The adhesion between virgin textile cords and rubber is always weak, because of significant differences between fiber and rubber in modulus, elongation, polarity as well as reactivity. In order to improve the adhesion, it is common to use adhesive systems, which act as bridges between elastomer and reinforcement. These are commonly based on Resorcinol/Formaldehyde/Latex (RFL) dips. Despite the fact that this technique was invented in 1938 and no major improvements have been achieved since then, the mechanism by which the adhesion is obtained is still unclear. This paper contributes more fundamental understanding of RFL to rubber bonding. In previous work an enrichment of curatives at the RFL-rubber interface was observed by use of a Scanning Electron Microscope coupled to an Energy Dispersive X-ray spectrometer. In the present paper, the same method is used to determine the degree of enrichment for several RFL formulations, based on latices with varying vinyl-pyridine (VP) contents. The vinyl-pyridine content is varied by copolymerization of various VP terpolymers. Adhesion decreases with increasing vinyl-pyridine content for most rubber compounds. For aN NR compound with low accelerator content and a NR/SBR blend, an optimum vinyl-pyridine content of 10% is observed.

Kinetics of the effect of ageing on tensile properties of a natural rubber compound

AbstractNatural rubber (NR) undergoes chemical changes on heat and air ageing. These changes affect its physical properties and as such, affect the service life of the rubber compound. In this study, a vulcanized NR compound of a typical engine mount composition was subjected to thermo‐oxidative ageing at temperatures from 70 to 110°C, to assess the effect on the tensile properties. The kinetics of degradation of the rubber compound, in terms of changes in these properties, was investigated. A fractional rate law was used to describe the kinetics of ageing in terms of its effect on modulus. Rates of ageing, in terms of effect on modulus, passed through a minimum at about 80°C, indicating the danger of trying to extrapolate in‐service ageing behavior from high temperature ageing data. The activation energy of ageing in terms of its effect on modulus, determined for temperatures of 90–110°C, was 151 kJ mol−1. A second order rate law was used to describe the kinetics of ageing in terms of its effect on tensile strength and elongation at break, with activation energies of 88.32 and 74.3 kJ mol−1, respectively. According to Ahagon's (Ahagon et al., Rubber Chem Technol, 1990, 63, 683) classification of ageing mechanisms, Type I and Type III ageing mechanisms were predominant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3732–3740, 2006

A test method to measure fatigue crack growth rate of rubbery materials

Crack growth characteristics of rubbery materials are an important factor determining the strength and durability of the materials. It is necessary to define the means of measuring the fatigue crack growth rate of rubbery materials. In this paper, a test method is introduced using a newly designed test machine. Measurements were made in order to characterize the fatigue crack growth behavior under repeated load expressed as a crack growth rate, i.e. crack length per cycle, as a function of the tearing energy, determined by a broad range of the strain energy density in a test piece of pure shear geometry. Measurements were also made to observe the effects of test temperature and loading frequency. A high speed CCD camera is utilized to allow in situ measurements following the path of the crack growth simultaneously. The power law dependency between crack growth rate and tearing energy was confirmed by the new test methodology. Comparison of the fatigue crack growth behavior between NR and SBR rubber compounds was made, and the exponent α values of the NR compound were found to be, in general, lower than those of the SBR compound, indicating that the NR compound is more resistant to fatigue crack growth than the SBR compound.

A study on the material properties and fatigue life of natural rubber with different carbon blacks

Natural rubber compounds filled with N330, N650 or N990 were experimentally investigated in order to examine the effects of carbon black on the fatigue life, the hysteresis, the fracture surface morphology and the critical J-value. The fatigue life was obtained by conducting a displacement-controlled fatigue test on an hourglass-shaped specimen, and the hysteresis was calculated from the loading and unloading curves obtained during the fatigue test. The fracture surface obtained after the fracture test was examined by a microscope, and its roughness was calculated for the surface profile obtained by using a stylus-type roughness tester. In addition, the critical J-value was obtained by conducting a tensile test for pre-cracked dumbbell specimens. Based on the test data, it was noticed that the fatigue life, the hysteresis, the small-scale roughness and the critical J-value were ranked in the following order for the NR compound filled with N330, N990 or N650. It was also noticed that the logarithmic value of the fatigue life was linearly proportional to the square root of the product of the critical J-value and the hysteresis.

Use of Marble Waste in Rubber Industry: Part I (in NR Compound)

In this study an attempt has been made to utilise marble powder derived from the marble slurry produced by gangsaw machines while cutting marble blocks in the north-west of India. The marble powder has been used; 1) as a cheap filler, 2) as a semi reinforcing filler, by doing chemical treatment of the slurry and 3) as partial replacement of carbon black filler to reduce the cost of the compounds, subsequently for products and also to find suitable disposal of the powder, which is creating a serious threat to the local environment. The methodology in this study is as follows: collection of marble powder and characterisation, evaluation of rubber compound including partial replacement of carbon black filler, treatment of the marble powder to enhance the reinforcing characteristics and evaluation of the product. It was found in this study that the marble powder can be used as a cheap filler, in place of other commercial fillers like whiting. However, no significant improvement was obtained by chemical treatment of the marble powder. Marble powder can also be used as a partial replacement of carbon black (up to 10 phr) in various rubber products, which operate under static conditions.

Comparison of two distinct phenolic antioxidants in γ‐sterilized NR compounds used as rubber pistons in syringes for single use

AbstractThe effects of γ‐irradiation and aging on pharmaceutical NR compounds have been studied mainly by DSC. The extent of aging was measured quantitatively by enthalpy changes and peak temperature shifts of the primary oxidation exotherm. Quantitative thermal evaluations were supplemented by extraction tests and mechanical testing. The NR compound formula has been kept constant and only the type and concentration of antioxidant was varied. Two distinct phenolic antioxidants, BHT and Wingstay‐L at four different concentration levels, have been employed for this purpose. The most effective antioxidant package for a given elastomeric compound, subjected to γ‐irradiation and aging, giving the lowest changes in physical properties, is evaluated. © 1992 John Wiley &amp; Sons, Inc.

The Resolution of Elastomer Blend Properties by Stress-Strain Modelling. An Extension of the Model to Carbon-Black-Loaded Elastomers

Abstract The unique stress-strain behavior of a carbon-black-loaded elastomer is due to the presence of a rigid, particulate phase, but also to the interaction of the elastomer chains with the filler. It is postulated that this interaction takes the form of adsorption on the filler-particle surface, which results in trapped entanglements. Upon deformation, the trapped chains are aligned parallel to the axis of stress. Thus, a practical stress-strain relationship could be developed which is capable to model the stress-strain behavior of compounds over the full range of extensions up to break. The analysis of a highly prestrained carbon-black-loaded NR compound in which the entanglement effect had been mechanically destroyed, demonstrated that the “sea-island” (SIP) coupling arrangement is most suitable for accounting for the interaction effect of the elastomer and carbon black. For moderately prestrained carbon-black-loaded NR and BR compounds a good fit of theory to experiment is obtained for a combination of the SIP coupling arrangement and the specially derived stress-strain relationship. Thus, a practical method is available for describing the deformation of carbon-black-loaded elastomers and for the modelling of carbon-black-loaded elastomer blends.

Studies on Cure Synergism. II, Effect of Diisopropyl Thiophosphoryl-N-Oxydiethylene Sulfenamide and Dibenzothiazyl Disulfide in the Vulcanization of NR

Abstract Thiazole sulfenamides as well as thiocarbamyl sulfenamides in the presence of dibenzothiazyl disulfide (MBTS) form synergistic combinations of rubber accelerators that provide technologically important rubber vulcanizates. The present investigation explores the feasibility of using thiophosphoryl sulfenamide with MBTS as a binary system of mutually activated accelerators in the vulcanization of rubber. The cure characteristics of the NR compound containing various proportions of diisopropyl thiophosphoryl-N-oxydiethylene sulfenamide (DIPTOS) and MBTS have been investigated keeping the total concentrations of the accelerators at 6 mmol per 100 rubber. The results indicated mutual activity of the mixed accelerators and significant enhancement of torque, modulus, and tensile strength of the resulting vulcanizates. The general character of the reaction of thiophosphoryl sulfenamide and MBTS has been established by replacing DIPTOS by diisopropylthiophosphoryl-N-cyclopentamethylene sulfenamide (DIPTCS), in the investigation. The mutual activity consequent upon the interaction of the accelerators can be demonstrated through isolation and identification of the reaction products formed in the early part of cure using the HPLC technique, which is also extremely helpful in explaining the cure behavior of the different stocks used in the investigation. The study reveals that diisopropylthiophosphoryl-2-benzothiazole disulfide (DIBDS), formed (in situ) as a result of interaction of DIPTOS and MBTS, plays an active part in improving the physical properties of NR vulcanizates. From the chemical analyses of the vulcanizates it is evident that the network structure obtained with the binary system of accelerators is highly rich in monosulfidic linkages that render the vulcanizates resistant to aging at 100°C.

Effect of air change rate on rubber accelerated ageing tests in hot air. Part 1. Preliminary study

Using a multi-cell ageing oven an NR compound was aged for 168 h at 70 °C in air with 3, 8, 10 and 15 air changes per hour. Ageing was evaluated by values of stress at 300% elongation ( M 300), tensile strength ( TS), elongation at break ( EB) and hardness ( IRHD). Simultaneously, a similar ageing treatment but in a normal oven at much lower air change rate was carried out. The statistical analysis of results showed that there are significant differences in M300 and TS after ageing among the various air-flows and also in M300 and EB between the results obtained in the normal oven and in the block oven at 3 air changes per hour. There were no significant differences among the cells in the oven nor (except in hardness test prices) in the material subjected to ageing, although it was prepared in several curing operations.