Studies of tetrazoles as rubber chemicals. I. Preparation and characterization of reactive antioxidants based on tetrazoles

The novel reactive antioxidants based on tetrazoles that are stable at room temperature and convertible into the highly reactive nitrileimines by pyrolysis were prepared and the reactivity for carbon–carbon double bonds was evaluated. Antioxidants, i.e., 2-substituted phenyl-5-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)tetrazoles (PHPT) were prepared with the reaction of p-toluenesulfonylhydrazone of 3,5-di-tert-butyl-4-hydroxybenzaldehyde and substituted phenyl diazonium chloride in a mixed solvent of pyridine, ethanol, and water at ?10°C to ?20°C in 31-61% yields. To evaluate the reactivities of PHPT for carbon–carbon double bonds, m-chloro-substituted PHPT was pyrolyzed in an excess of styrene at 160–170°C for 0.5 h to give the 1-(3′-chlorophenyl)-3-(3″,5″-di-tert-butyl-4″-hydroxyphenyl)-5-phenyl-2-pyridazoline in a 44.1% yield by 1,3-dipolar addition reaction of the nitrileimine formed from the m-chloro-substituted PHPT. The thermogravimetric analysis of a mixture of proton isomer of PHPT and liquid polybutadiene showed that PHPT attached to liquid polybutadiene with an accompanying evolution of nitrogen.     

Oxidative aging of natural rubber vulcanizates. Part II. Effect of vulcanizate structure

The oxidation characteristics of protected and unprotected vulcanizates from natural rubber have been examined. With unpurified rubber (RSS1) in the presence or absence of added antioxidants the rate of oxidation of the vulcanizates is: unaccelerated sulfur > accelerated sulfur > TMTD sulfurless or EV > peroxide. This order is obtained because the sulfur compounds present in the sulfurated vulcanizates are antagonistic towards both natural and added antioxidants. The antagonism is greatest with polysulfides, and when they are present they dominate the aging behavior of vulcanizates.     

Influence of rubber composition on migration behaviors of antiozonants in carbon black‐filled rubber vulcanizates composed of NR,SBR, and BR

Migration behaviors of antiozonants in carbon black‐filled rubber vulcanizates with different rubber compositions of natural rubber (NR), styrene–butadiene rubber (SBR), and butadiene rubber (BR) were studied at constant temperatures of 40–100°C and outdoors. Three single rubber‐based vulcanizates, three biblends, and three triblends were used. N‐Phenyl‐N′‐isopropyl‐p‐phenylenediamine (IPPD) and N‐phenyl‐N′‐(1,3‐dimethylbutyl)‐p‐phenylenediamine (HPPD) were employed as antiozonants. Migration rates of the antiozonants became faster with increasing the temperature. The order of the migration rates in the single rubber‐based vulcanizates was BR > NR > SBR. The migration rates in the vulcanizates containing SBR, on the whole, increased with decreasing the SBR content, while those in the vulcanizates containing BR decreased with decreasing the BR content. Difference in the migration behaviors of the antiozonants depending on the rubber composition was explained both by the intermolecular interactions of the antiozonants with the matrix and by interface formed between dissimilar rubbers in the blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 237–242, 2001     

Constant Selectivity in Proton Exchange Reactions Between Aqueous Sulphuric Acid and Acetylenes

Linear Pfluger plots of unit slope are obtained from logarithmic rate constants for acid–catalysed hydration of phenylacetylene and its substituted derivatives p-OCH₃, p-CH₃, m-CH₃, p-Br, m-Cl, m-NO₂, p-NO₂ in aqueous sulphuric acid solution. This direct experimental observation of absence of any dependence on selectivity gives evidence for the applicability of the kinetic acidity function in these systems.     

Studies on natural rubber bound para-phenylenediamine antioxidants in NBR

Para-phenylenediamine (PD) was chemically attached to depolymerized natural rubber by a photochemical reaction. The rubber bound PD was characterized by TLC, ¹H-NMR, IR, and TGA. The efficiency and permanence of the bound PD were compared with conventional antioxidants in NBR vulcanizates. The rubber bound PD was found to be less volatile and more resistant to water and oil extraction. The vulcanizates showed improved aging resistance in comparison to vulcanizates containing conventional antioxidants. The liquid rubber bound antioxidant reduces the amount of plasticizer required for compounding. © 1995 John Wiley & Sons, Inc.     

Specific heats of rubber compounds

The specific heats of rubber compounds are very important not only for the thermodynamic calculations in various rubber processings; mixing, extrusion, calendering, and vulcanization, etc., but also for the service life of the final products under repeated stressing conditions. In this study, the specific heats of various compounding ingredients and their compounds for tires were determined using a differential scanning calorimeter (DSC) in the temperature range from 45 to 95°C. The determined specific heats, C_p, were compared with the previous published results for natural rubber (NR), styrene–butadiene rubber (SBR), polybutadiene rubber (BR), and isoprene–isobutyl rubber (IIR). The effects of carbon black loading and vulcanization on the specific heats were investigated. The measured specific heats of the compounds were compared with the calculated values based on the fractional summation of the specific heat of each compounding ingredient. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1513–1522, 1999     

Synthesis and aging properties of reactive antioxidant NAPM in natural rubber vulcanizates

The rubber antioxidant N‐(4‐anilinophenyl) methacrylamide (NAPM) was synthesized by a two‐step reaction using thionyl chloride (SOCl₂) with methacrylic acid (MAA) and consequently 4‐aminodiphenylamine (ADPA) as precursors. NAPM was characterized by IR, ¹H NMR and elemental analysis. Thermal stability, aging property of NAPM and mechanical properties of natural rubber (NR) vulcanizates containing NAPM were investigated and compared with two other commercial antioxidants N‐isopropyl‐N′‐phenyl‐p‐phenylene diamide (4010NA) and N‐(1, 3‐dimethyl butyl)—N′‐phenyl‐p‐phenylene diamide (4020). It was found that NAPM was an effective antioxidant with a better thermal stability and higher antiaging resistance than unreactive antioxidants 4010NA and 4020. And unsaturation level of NR vulcanizates containing NAPM was lower than that of 4010NA and 4020. Moreover, an antiaging resistant mechanism of a surface reaction between NAPM and cis‐1, 4‐polyisoprene in NR was proposed to explain the better properties of NAPM based on the IR and SEM analyses. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Optimization of carbon black and nanoclay filler loading in chlorobutyl vulcanizates using response surface methodology

In this article, an attempt has been made to study the applicability of using organo nanoclay (Cloisite 30B) and carbon black (HAF, N330) in chlorinated isobutyl isoprene rubber vulcanizates. Statistical design of experimentation was adopted so that maximum information can be obtained from a minimum number of experiments. Response surface methodology was applied successfully to rubber compound design using a rotatable central compound design. Compounding trials were carried out at design points, and the rubber vulcanizates were characterized for modulus, tensile strength, elongation at break, tear strength, bound rubber, and free volume parameters τ₃ and I₃. The experimental data was used to generate mathematical models by multiple linear regression analysis using MATLAB (version 6) package. The variability of the postulated models was tested by analysis of variance (ANOVA) and R² tests and was found to be adequate. The accuracy of the models generated was tested by making an experimental trial. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Characterization of ethylene–propylene rubber and ethylene–propylene–diene rubber networks

The stress–strain (S/S) and the swelling equilibrium behavior in a series of ethylene propylene rubber (EPR) and ethylene propylene diene monomer (EPDM) networks were investigated and the results were employed to evaluate the effects of varying the cure conditions on the crosslinking efficiency in these networks. The S/S curve of completely swollen vulcanizates is in agreement with the predictions of rubber elasticity theory, while that of dry or partially swollen vulcanizates is fully described by the Mooney-Rivlin equation. ? values determined in benzene were found to vary linearly with v_r (v_r = equilibrium volume fraction of rubber in swollen sample). Crosslinking efficiency, moles of crosslinks produced per moles of crosslinking agent used, ranges from 3.7 in peroxide-cured EPDM (55% wt ethylene and 2.6% unsaturation) to 0.15 in similarly cured EPR (43% ethylene). Efficiency in the latter system improves to 0.6 by addition of a coagent (sulfur) to the cure formula. Crosslinking efficiency in EPDM (55% ethylene) was found to increase in the order: peroxide- > resin- > sulfur-cured. In the EPDM sulfur vulcanizates, changing the terpolymer in the cure formula resulted in significant changes in the crosslinking efficiency.     

Syndiospecific Polymerization of Styrene Using Half-Titanocene Catalyst Covalently Supported on MgCl<Subscript>2</Subscript>/AlEt<Subscript>n</Subscript>(OEt)<Subscript>3-n</Subscript>

The novel half-titanocene catalyst bearing reactive functional amino group, η⁵-pentamethylcyclopentadienyltri(p-amino-phenoxyl) titanium [Cp^∗Ti(p-OC₆H₄NH₂)₃], was easily synthesized by the reaction of η⁵-pentamethylcyclopentadienyltrichloride titanium (Cp^∗TiCl₃) with p-amino phenol in the presence of triethyl amine (NEt₃). Cp^∗Ti(p-OC₆H₄NH₂)₃ covalently anchored on MgCl₂/AlEt_n(OEt)_3-n support obtained from the reaction of triethylaluminium (AlEt₃) with the adduct of magnesium chloride (MgCl₂) and ethanol (EtOH), has been investigated and used to catalyze syndiospecific polymerization of styrene. Influences of the support structure, cocatalyst, and the molar ratio of Al in methylaluminoxane (MAO) and Ti (Al_MAO/Ti) on catalytic activity, syndiotacticity and molecular weight of the resultant polystyrene were investigated. Compared with the corresponding Cp^∗Ti(p-OC₆H₄NH₂)₃ homogeneous catalyst, a considerable increase in activity and molecular weight of syndiotactic polystyrene (sPS) was observed for the Cp^∗Ti(p-OC₆H₄NH₂)₃-MgCl₂/AlEt_n(OEt)_3-n supported catalyst even at a relatively low Al_MAO/Ti ratio of 50, and the kinetics of polymerization was stable during the reaction process.     

Effect of crosslink structures on dynamic mechanical properties of natural rubber vulcanizates under different aging conditions

The effects of crosslink structures on the dynamic mechanical properties (DMPs) of unfilled and carbon black N330‐filled natural rubber (NR) vulcanizates cured with conventional (CV), semiefficient (SEV), and efficient (EV) cure systems and having about the same total crosslink densities were investigated before and after aerobic and anaerobic aging at 100°C. The three unfilled NR vulcanizates cured with the CV, SEV, and EV systems had about the same mechanical loss factor (tan δ) values at about 0°C but showed some apparent differences in the tan δ values in the order EV > SEV > CV at relatively high temperatures of 40–80°C before aging. However, N330‐filled NR vulcanizates gave higher tan δ values than the unfilled vulcanizates and showed little effect of the crosslink types on the tan δ at different temperatures over the glass‐transition temperature (T_g) before aging. Aerobic heat aging increased the T_g and tan δ values of the vulcanizates over a wide range of temperatures from ?80 to 90°C that was mainly due to the changes in the total density and types of crosslinks. The unfilled vulcanizates cured with the CV system showed the greatest change in DMP because of their poor resistance to heat aging. Aerobic heat aging of NR vulcanizates caused a more significant change in the DMP than anaerobic heat aging because of the dominant effect of the oxidative degradation during aerobic heat aging on the main‐chain structure, crosslink structures, and DMPs of the vulcanizates. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 710–718, 2001     

Effect of liquid isoprene rubber on dynamic mechanical properties of emulsionpolymerized styrene/butadiene rubber vulcanizates

The effect of liquid isoprene rubber (LIR) on the dynamic mechanical properties of emulsion‐polymerized styrene/butadiene rubber (ESBR) vulcanizates was investigated by temperature sweep using dynamic mechanical analysis. The introduction of LIR led to ESBR vulcanizates having higher loss factor (tan δ) in the temperature range ? 30 to 0 °C, and lower tan δ in the range 60 to 80 °C. A small amount of LIR‐403 (LIR with carboxyl groups) led to a significant change in tan δ: the addition of LIR‐403 (3 phr) led to a 7.5% increase in tan δ from ? 30 to 0 °C, and a 24.9% decrease in tan δ from 60 to 80 °C. It was found that the introduction of LIR increased the bound rubber content in the ESBR compound. Equilibrium swelling experiments showed that the crosslink density of the vulcanizates increased after the introduction of LIR‐403 or LIR‐50 (general purpose LIR). The change in tan δ from 60 to 80 °C was related to polymer–filler interactions. The characteristic constant of filler–ESBR matrix interaction (m) was calculated. At a given filler volume fraction, the increase in m in the presence of LIR could be well related to the decrease in tan δ from 60 to 80 °C. The influence of LIR on filler network in the ESBR compound was also investigated by strain and temperature sweeps using a rubber processing analyzer. Copyright © 2011 Society of Chemical Industry     

Curing Characteristics,Fatigue and Hysteresis Behaviour of Feldspar Filled Natural Rubber Vulcanizates

Curing characteristics, fatigue, and hysteresis behaviour of feldspar filled SMR L vulcanizates and feldspar filled ENR 50 vulcanizates were studied. Two different types of natural rubber, SMR L and ENR 50 having 0 and 50 mol% of epoxide groups were used. The feldspar filled natural rubber vulcanizates were compared at similar filler loading which were used at 0, 10, 20, and 30 phr of filler loading. The curing characteristics such as scorch time (t ₂) and cure time (t ₉₀) slightly increased with increasing feldspar loading for both rubber vulcanizates. Besides t ₂ and t ₉₀, maximum torque (M _HR) significantly increased for both rubbers with increasing feldspar loading. The fatigue test showed that fatigue life decreased with increasing extension ratio, strain energy and filler loading. As the filler loading increased, the poor wetting of the feldspar by the rubber matrix gave rise to poor interfacial adhesion between filler and rubber matrix. Results also indicate that the vulcanizates with the highest feldspar loading exhibited the highest hysteresis. The feldspar filled SMR L vulcanizates showed higher fatigue life and lower hysteresis compare to feldspar filled ENR 50 vulcanizates.     

Role of supercritical carbon dioxide for selective impregnation of decrosslinking reagent into isoprene rubber vulcanizate

The behavior of supercritical CO₂ (scCO₂)/low molar mass molecule/crosslinked rubber ternary system was investigated in relation to the impregnation of reagent into the isoprene rubber (IR) vulcanizates, which was the first step of new decrosslinking reaction. The diffusion coefficient of decrosslinking reagent, diphenyl disulfide (DD), into the IR network in scCO₂ was 3.2×10⁻¹¹ m²/s. The distribution coefficient (K_c) of DD between the solvent and IR matrix was also determined for scCO₂ and toluene. The K_c for scCO₂ was higher about four orders of magnitude than that for toluene. DD was uniformly dispersed in the crosslinked IR matrix under 10 MPa at 313 K in scCO₂. These phenomena are advantages of use of scCO₂ for the effective decrosslinking reaction of IR vulcanizate.     

Study on the life expectancy of storage and ageing for rubber vulcanizates

Summary In this paper the relationship of the ageing time to the tensile strength and the ultimate elongation of rubber vulcanizates was derived from the combination of ageing kinetics with the molecular theory of ultimate tensile strength of elastic networks, basing on the micro-structure model of rubber vulcanizates. According to this relation, a new simple method for determining the coefficients (α₄) of ageing time and the ageing rate constants (k ₄) of rubber vulcanizates from the data of the extension tests was proposed. The accelarated ageing experiments of Butadiene-acrylonitrile Rubber (BAR) vulcanizates were carried out at the range of temperature 70–110°C in a given period of 1–100 days, and the molecular parameters were determined by using this new method. It is shown that the experimental results are consistent to the theory.     

Synthesis and characterization of chlorinated paraffin wax-bound paraphenylenediamine antioxidant and its application in natural rubber

p-Phenylenediamine was chemically attached to low molecular weight chlorinated paraffin wax. The polymer-bound p-phenylenediamine was characterized by vapor-phase osmometry (VPO), proton magnetic resonance spectroscopy (¹H-NMR), infrared spectroscopy (IR), and thermogravimetric analysis (TGA). The efficiency and permanence of the polymer-bound p-phenylenediamine as an antioxidant was compared with a conventional amine-type antioxidant in natural rubber vulcanizates. The vulcanizates showed improved aging resistance in comparison to vulcanizates containing a conventional antioxidant. The presence of liquid polymer-bound p-phenylenediamine also reduces the amount of the plasticizer required for compounding. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2183–2189, 2001     

The influence of anilino-substituted salicylanilide on the physicomechanical properties of ultraviolet-aged natural rubber

The effect of nine derivatives of salicylanilides on the elastic properties of ultraviolet-aged natural rubber have been investigated. The results are compared with similar blends without additives and also with reference samples containing phenyl salicylate. The compounds showed variable effects, but both o-Cl and p-OCH₃ derivatives showed remarkable effects. They both help in the thermal crosslinking. Also, natural rubber samples containing these derivatives showed remarkable stability in tensile stress, elongation, and swelling.     

Bond reactivity and antioxidant effect on the autoxidation of soybean oil

Soybean oil (SBO) contains many unsaturated fatty acids, so that it can be easily oxidized by air/oxygen. Therefore the autoxidation of soybean oil was performed to investigate the bond reactivities of allylic, bisallylic CH₂, α-CH₂, β-CH₂, chain CH₂ and CH₂O of backbone in the presence and absence of phenolic and aniline antioxidants by means of iodometry and 500 MHz ¹H NMR spectroscopy. From the active oxygen concentration, the inhibiting effect and by application of proton integration of each bond of pure and oxidized soybean oil to the first order rate equation, got firstly the orders of the reactivity of each C–H bond and inhibiting effect of antioxidants. In the presence of 2,6-di-t-butyl-4-cresol, three phenol adducts from oxidation product also firstly were identified by means of GC–MS spectroscopy.     

Structural characterization of vulcanizates. Part V. Determination of degree of chemical crosslinking of natural rubber gum vulcanizate networks

A general treatment is given of the methods to be used in other parts of this series for calculating the degree of chemical crosslinking in natural rubber vulcanizates from stress–strain measurements in extension and from equilibrium volume swelling measurements. Corrections are required for the presence in the vulcanizate of appreciable quantities of particulate solids or soluble diluents and for the introduction of foreign atoms into the rubber network. For this purpose distinction is made between the rubber vulcanizate, the rubber matrix, the rubber network, and the rubber hydrocarbon component of the network. Expressions are derived, in terms of these concepts, for the Money-Rivlin parameter, C₁, measured on vulcanizates which have undergone various treatments.     

Blend rules for homogenous and heterogenous systems

Blend rules for (a) homogeneous and (b) heterogeneous systems are proposed in a form of P = (?^m₁P₁ + ?^m₂P₂)/(?^m₁ + ?^m₂), where P is the property, and ?, the volume fraction of component 1 or 2. For (a) m>1 and for P₂>P₁, an S-shaped relation occurs between P or ?₁. On the contrary, for (b) m<1, an anti-S-shaped relation occurs. When the hard component forms particles in continuous soft media, P is larger than the arithmetic mean P?. When the interface slips, a mean of harmonic function holds so that 1/P = ?₁/P₁ + ?₂/P₂ and P < P?. For special cases, i.e., the filler in the rubber and the rubber particles in the resin, the strength at break attains a maximum at 20 and 13% of particles, respectively. For rubber blended with a small amount of polypropylene by dynamic vulcanization, the latter forms a continuous phase, reinforcing rubber domains by the plastic force when the size of rubber particles becomes very small. © 1994 John Wiley & Sons, Inc.