The chemical effects of photo-oxidation on isoprene rubber

There has been a detailed study of the non-volatile products of the photo-oxidation of two kinds of cis-1,4-polyisoprene, viz. natural and synthetic (98% cis), by irradiating films in the solid state under ambient conditions. I. R., ¹H- and ¹³C-NMR and chemical methods indicated the formation of the following functional groups: hydroperoxides, alcohols, ketones, aldehydes, epoxides and carboxylic acids. There is also evidence for the formation of esters and ethers. Viscometric measurements showed that chain-scission predominates over cross-linking for irradiation of toluene solutions of the rubbers. Photo-oxidation kinetic measurements for films containing singlet oxygen quenchers, such as 1,2-diazabicyclo[2,2,2]octane and diphenyl-p-isobenzofuran, showed that singlet oxygen is not responsible for the initiation of the environmental photo-oxidation of cis-1,4-polyisoprene. Increasing the number of successive coagulation steps, in the purification of natural rubber, decreased its stability, confirming the presence of an intrinsic natural stabilizer. Synthetic isoprene rubber showed less stability than natural rubber.     

The maximum superheating of butadiene rubber

The rates of thermal decomposition and maximum superheatings of butadiene rubber were measured by the contact thermal analysis method under the conditions of fast sample heating. The results are compared with the literature data on the products of the decomposition of butadiene rubbers of similar chemical compositions under flash pyrolysis conditions obtained by IR Fourier transform spectroscopy.     

Sensitized photo-oxidation of en-containing EPDM rubber

Terpolymers of ethylene, propylene and ethylidene norbornene (EN) rapidly react with singlet oxygen generated by dye sensitization. The singlet oxygen attacks the ethylidene double bond forming at least two different allylhydroperoxides. The instability of these hydroperoxides causes crosslinking of the photo-oxidized terpolymers at relatively low temperatures. Reduction of the hydroperoxide groups with triphenylphosphine yields a thermally stable hydroxylated polymer. Terpolymers of ethylene, propylene and dicyclopentadiene (DCPD) are inert towards singlet oxygen.     

Mechanistic studies on the photo-oxidation of commercial poly(butadiene)

Products from both the thermal and photo-oxidation of poly-butadiene have been studied using various analytical techniques such as infra-red and ultra-violet spectroscopy, gas-liquid chromatography and phosphorescence emission and phosphorescence excitation spectroscopy. Analyses have allowed a plausible mechanism to be formulated for the photo-oxidation of this polymer, consistent with all the observed physical and chemical changes. Both photo- and thermal oxidative polymer degradation initially result in the formation of α, β-unsaturated carbonyls which, under photo-degrading conditions, are subsequently photolysed to yield the observed final products.     

Preparation and properties of nanocomposites based on acrylonitrile–butadiene rubber,styrene–butadiene rubber,and polybutadiene rubber

Nanocomposites were prepared with different grades of nitrile rubber with acrylonitrile contents of 19, 34, and 50%, with styrene–butadiene rubber (23% styrene content), and with polybutadiene rubber with Na‐montmorillonite clay. The clay was modified with stearyl amine and was characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The XRD studies showed an increase in the gallery gap upon the modification of the filler by stearyl amine. The intercalation of the amine chains into the clay gallery gap was confirmed by the presence of some extra peaks (2928, 2846, and 1553 cm^?1) in the FTIR spectra. The clay–rubber nanocomposites were characterized by TEM and XRD. The mechanical properties were studied for all the compositions. An improvement in the mechanical properties with the degree of filler loading up to a certain level was observed. The changes in the mechanical properties, with changes in the nature and polarity of the rubbers, were explained with the help of XRD and TEM results. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1573–1585, 2004     

Effects of ultrasonic treatment on unfilled butadiene rubber

The ultrasonic treatment of unfilled butadiene rubber (BR) gum with a grooved‐barrel ultrasonic reactor was carried out, leading to changes in the structure and physical properties. The ultrasonic treatment of BR gum led to gel formation, with the amount dependent on the amplitude. The rheological and mechanical properties of the ultrasonically treated samples and their vulcanizates were measured and compared with those of the virgin samples. Gel permeation chromatography measurements of the sol part of the virgin and the treated samples were carried out. Rheological property and molecular weight measurements indicated the creation of a branched structure and the occurrence of degradation in ultrasonically treated BR gum. Because of degradation, the tensile strength and Young's modulus of treated BR were lower than those of untreated BR, whereas the elongation at break was practically intact. Differential scanning calorimetry (DSC) curves at a high‐temperature range showed exothermic peaks with enthalpy reduction in the treated BR, indicating a decrease in the number of double bonds due to gel formation. DSC curves at a low‐temperature range indicated increased crystallinity in the treated samples. Competing reactions of gel formation, branching, and degradation occurred during the ultrasonic treatment. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2959–2968, 2003     

Rupture of swollen styrene butadiene rubber

Elastomers have recently been explored to make swellable packers in the oil industry, which have many advantages over traditional cement packers. In the applications, the elastomers absorb solvent and swell against the confinement, which can seal zones in the borehole. In addition, swollen elastomers are usually subjected to a large pressure difference, which can cause fracture of the elastomer. In this article, we conduct experimental studies of the rupture behavior of an oil-swellable elastomer, styrene butadiene rubber (SBR), swollen in hexadecane. This combination of elastomer and swelling agent can be considered representative of oilfield applications. Pure-shear tests are used to measure the stretch at rupture and fracture energy of swollen SBR with different swelling ratios. It is found that swelling can significantly reduce both the stretch at rupture and the fracture energy of the swollen elastomer. Using the measured fracture energy, we have also successfully predicted the stretches at rupture of SBR for a simple extension test with different volume swelling ratios.     

Investigate on mechanical and tribological properties of solution styrene butadiene and butadiene rubber composites

Solution styrene butadiene and butadiene rubber (SSBR‐BR) composites reinforced with different contents of SiO₂‐graphene have been fabricated firstly. The mechanical properties of the rubber composites were comparatively investigated using tensile tests; experimental results showed that, as an overall trend, the tensile and tear strength increased with increasing contents of SiO₂‐graphene. Most importantly, under the condition of simulating practical working condition, the tribological behavior of SSBR‐BR composites with different contents of SiO₂‐graphene was explored via a universal ring‐plate frictional tester in detail. Combined with the surface roughness of the counterparts, the wear mechanisms were discussed for SSBR‐BR composites under the cement and asphalt counterparts. Finally, several wear mechanisms under different actual working conditions were proposed.     

Thermal properties in cured natural rubber/styrene butadiene rubber blends

Blends of natural rubber (NR) and styrene butadiene rubber (SBR) were prepared with sulfur and n-t-butyl-2-benzothiazole sulfonamide (TBBS) as accelerator, varying the amount of each polymer in the blend. Samples were analysed by rheometer curing at 433 K until their maximum torque was reached. The miscibility among the constituent polymers of the cured compounds was studied in a broad range of temperatures by means of differential scanning calorimetry, analyzing the glass transition temperatures of the samples. The specific heat capacity of the compounds was also determined. Thermal diffusivity of the samples was measured in the temperature range from 130 to 400 K with a new device that performs measurements in vacuum. The thermal results are explained on the basis of the structure formed during the vulcanization of the samples considering the variation of the crosslink density of each phase. Finally, a serial thermal conduction model that takes into account the contribution of each phase to the thermal diffusivity was used to fit the experimental results.     

Copolymerization of modified oligoesteracrylates with oligomeric butadiene rubber

The kinetics of the low-temperature graft of three modified oligoesteracrylates with oligobutadiene rubber at 20–40°C in relation to the composition of starting mixtures was studied. Compositions of resulting copolymers in relation to process conditions, copolymerization constants, and also Q-e factors of the oligomers were determined by computational and graphical methods from the extraction data. The reactivity of oligoesteracrylates in binary graft copolymerization processes was estimated.     

The photo-oxidation of EPDM rubber: Part III—Mechanistic aspects and stabilization

The kinetics of the photo-oxidation of crude EPDM rubber has been studied in order to propose a mechanism for the sequence of reactions which occurs during the photo-degradation process. The presence of the unsaturation markedly affects the kinetics of the photo-oxidation of EPDM in comparison with that of EPM. We have also studied the stabilization effect of a hindered amine and a hindered phenol on EPDM and compared this with crude EPM rubber. These stabilizers showed poor efficiency, which is explained by the presence of impurities which act as sensitizers for the degradation of the crude rubber.     

Thermal properties of compatibilized and filled natural rubber/acrylonitrile butadiene rubber blends

The thermal behaviour of natural rubber/acrylonitrile butadiene rubber (NR/NBR) was studied using thermogravimetry (TG) and differential scanning calorimetry (DSC) in terms of blend ratio, crosslinking systems, fillers and compatibilizer (neoprene) were analyzed. The presence of NBR markedly increases the thermal stability of their blends and it lies in between NR and NBR. DSC studies revealed the thermodynamic immiscibility of the NR/NBR blends by the presence of two distinct glass transition temperatures and the immiscibility was prominent even in the presence of a compatibilizer.     

Mathematical modeling of butadiene rubber synthesis process on neodymium-containing catalyst system

The synthesis of butadiene rubber mediated by a lanthanide catalyst system based on neodymium(III) chloride in a batch reactor was mathematically modeled. The mechanism of the process was identified and the rate constants of various reaction steps were determined. It was found that chain transfer reactions with different rate constants have an effect on the molecular-mass characteristics of butadiene rubber.     

Sugar cane bagasse-lignin as photo-stabilizer for butadiene rubber

In this work we have studied the stabilizing effect of a natural antioxidant, sugar cane bagasse-lignin, on the photo-oxidation of a commercial sample of butadiene rubber. This stabilizer was investigated in various concentrations, in the pure form, and associated with a diamine or a phosphite stabilizer. Stabilization of butadiene rubber with this lignin associated with the diamine produced a material with a photo-chemical stability comparable to that of a stabilized commercial sample.     

Conductivity of carbon black-loaded styrene–butadiene rubber

Styrene–butadiene rubber (SBR) charged with 50 phr of HAF carbon black has been found to show a positive temperature coefficient of resistivity close to 0.07/°C at 27°C. Beyond a point (75°C) of minimum conductivity, however, it behaves as a normal noncrystalline semiconductor with a resistivity which decreases with rise of temperature with an activation energy of 0.56 eV. Blending the composition with poly(vinyl chloride) (PVC) shifts the minimum towards lower temperatures. The descending branch of the conductivity versus reciprocal absolute temperature characteristic is probably associated with thermal expansion of tunnelling paths separating the conducting carbon particles.     

Vulcanization kinetics of graphene/styrene butadiene rubber nanocomposites

This paper presents the influence of graphene on the vulcanization kinetics of styrene butadiene rubber （SBR） with dicumyl peroxide. A curemeter and a differential scanning calorimeter were used to investigate the cure kinetics, from which the kinetic parameters and apparent activation energy were obtained. It turns out that with increasing graphene loading, the induction period of the vulcanization process of SBR is remarkably reduced at low graphene loading and then levels off; on the other hand, the optimum cure time shows a monotonous decrease. As a result, the vulcanization rate is suppressed at first and then accelerated, and the corresponding activation energy increases slightly at first and then decreases. Upon adding graphene, the crosslinking density of the nanocomposites increases, because graphene takes part in the vulcanization process.     

POSS nanoparticles as a potential compatibilizer for natural rubber/butadiene rubber blends

In this study, it was aimed to investigate octavinyl‐polyhedral oligomeric silsesquioxane (OV‐POSS) incorporation into natural rubber (NR)/butadiene rubber (BR) elastomer blends as a potential compatibilizer. The effects of OV‐POSS loading levels on the thermal, mechanical, morphological, and dynamic‐mechanical properties of elastomer blends were explored. Fourier‐Transform Infrared Spectrometer (FTIR), Temperature Scanning Stress Relaxation (TSSR), and Differential Scanning Calorimetry (DSC) results revealed the conceivable effect of OV‐POSS nanoparticles in the vulcanization through reacting with sulfur and/or elastomers. Scanning Electron Microscope (SEM), X‐Ray Diffraction (XRD), and tensile test measurements supported the improvement of mechanical properties due to homogeneous dispersion at low loading levels. On the other hand, high amount of OV‐POSS incorporation (7 and 10 phr) resulted in a decrease in mechanical properties, owing to the agglomeration of nanoparticles. According to contact angle and Dynamic mechanical analysis (DMA) results, it could be concluded that OV‐POSS nanoparticles were localized at the interface of the elastomers and enabled the compatibilization of immiscible NR/BR blends.     

Media effects on the kinetics of anthracene photo-oxidation in polymers

An improved quantitative analysis of the photochemical reaction of diphenylanthracene (DPA) in thin films of poly(ethyl methacrylate) (PEMA) is reported. This analysis confirms the previous suggestion (J.R. Sheats, J. Phys. Chem., 94 (1990) 7194) that the rate of reaction between singlet oxygen and DPA decreases as the reaction proceeds, consistent with the hypothesis that the free volume is decreased by endoperoxide formation. For [DPA]≈30 wt.%, the rate constant decreases by approximately 50% for complete conversion. The initial value is 25-fold smaller than in fluid solution, and decreases slightly as [DPA] is increased.     

Styrene‐butadiene rubber synthesized by anionic polymerization

In this paper we report on the copolymerization of styrene with butadiene in cyclohexane as solvent. Some experiments were also done using toluene as a solvent in order to check the influence of this solvent on the polydispersity index of the copolymers obtained, n‐ Butyllithium (BuLi) was used as initiator, while methyl‐tert‐butyl ether (MTBE) was used as an active center modifier. Reaction parameters such as polymerization temperature, the [MTBE]/[BuLi] molar ratio and the nature of solvent were studied in relation to their effects on the copolymerization rate, the randomness of the polymer and the microstructure of the butadiene units incorporated.     

The photo-oxidation of propionaldehyde

C₂H₅CHO vapor was photolyzed with 313 nm radiation at 22 °C in the presence of O₂ and O₂He, O₂N₂, O₂NO and O₂cis-2-C₄H₈ mixtures. The contents of the reaction mixture were allowed to bleed through a pinhole into a quadrupole mass spectrometer providing for continous monitoring of the C₂H₅OH and C₂H₅C(O)O₂H produced. CO, CO₂, C₂H₄ and CH₃CHO concentrations were determined by gas chromatography. From CO quantum yield determinations we found that the only photolytic process of importance is the following:

The CO quantum yields also indicate that the reactive state of C₂H₅CHO is pressure quenched, and the half-quenching pressures for the various reactant gases were measured. The primary quantum yield in 1 atm of air is 0.30 ± 0.05. The data suggest that the reacting state is a vibrationally excited triplet state which consists of levels which are quenched with different efficiencies by any quenching gas. The more rapidly quenched leves account for about 40% of the total, while the less rapidly quenched levels account for about 60% of the total. Large quantum yields were measured for CO₂, C₂H₅OH and C₂H₅C(O)O₂H indicating a chain reaction initiated by abstraction of the aldehydic hydrogen of C₂H₅CHO by C₂H₅O radicals. The C₂H₄ quantum yields are dependent on the total pressure, and we believe that C₂H₄ is produced from the decomposition of vibrationally excited C₂H₅CO₃ radicals:

The deactivated C₂H₅CO₃ radicals will either react with HO₂ or C₂H₅CHO or at the walls to produce C₂H₅CO₃H, or ultimately decompose to CO₂ + C₂H₅. We found that the following reactions are unimportant at 22 °C: