Preparation of carbon nanotubes/hydrogenated nitrile rubber composite by ultrasonic technique

将低相对分子质量的液体氢化丁腈橡胶(HNBR)溶于丙酮溶剂中,加入碳纳米管,用超声波技术制备了液体HNBR与碳纳米管的复合母料,然后再与HNBR混炼、硫化,获得碳纳米管/HNBR复合材料.结果表明,碳纳米管在HNBR中分散性好,对HNBR有较好的增强性,但在后期机械加工中产生了断裂.     

Soybean oil induced efficient thermal–oxidative degradation of covalently crosslinked styrene butadiene rubber

It has been a technical challenge of recycling tire rubbers due to the covalently crosslinked polymer network structure. Unlike conventional recombination of crosslinked SBR under thermal oxidation, SBR vulcanizate was efficiently degraded by thermal oxidation at 150 °C in presence of soybean oil, resulting in 47.3% sol fraction by weight. The structural evolution of SBR vulcanizates during thermal oxidation was characterized by sol–gel ratio, chemical structure, molecular weight, and oxidative erosion on the rubber surface. It was found that the continuous oxidation process facilitated main chain scission of SBR vulcanizates, resulting in a decrease of molecular weight of the sol fraction. The concentration of carbonyl groups, sol fraction, and surface erosion continually increased with reaction time. The large amounts of soybean oil significantly affect the thermal stability of SBR vulcanizates. Moreover, soybean oil is more efficient in decomposition of the SBR vulcanizates and results in more homogeneous and efficient oxidation reactions than paraffin oil. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48935.     

Mechanistic insights into the thermal–mechanical aging of the interface of cross-linked polyethylene/silicone rubber

Cable accessory has the interface formed by cross-linked polyethylene (XLPE)/silicone rubber (SiR), which is prone to surface discharge and thus causes the failure of cable system. This article conducts the simulated experiment of thermal–mechanical aging on the interface of XLPE/SiR. The interfacial breakdown and dielectric properties under different aging states are analyzed. It is found the interfacial aging process of XLPE can be divided into the recrystallization stage and the oxidation reaction stage. The former contributes to the interfacial roughness and thus the better insulating performance, whereas the latter leads to degradation of interface, and thus the worse insulating performance. In addition, combined with the established electric field model for the interface, the differences between thermal–mechanical aging and individual thermal aging on the interface are discussed. The sample under thermal–mechanical aging reaches the maximum interfacial breakdown voltage later than that under individual thermal aging, but their performance tends to be consistent in the later stage of aging.     

Studies on thermal–oxidative degradation behaviours of raw natural rubber: PRI and thermogravimetry analysis

Abstract

Thermal–oxidative degradation behaviours of raw natural rubber (NR) have been investigated by using thermogravimetry analysis in inert and oxidative atmospheres and the plasticity retention index (PRI). The activation energy E_a, was calculated using Horowitz–Metzger and Coats–Redfern methods and compared with PRI. The E_a values obtained by each method were in good agreement with each other. The June samples are the least stable rubbers among the studied ones, whereas February samples exhibited the highest values of activation energy, therefore in agreement with the PRI behaviour, which indicates that the thermo-oxidative stability of the June samples are the poorest during the thermo-oxidative degradation reaction. Natural rubber is a product of biological origin, and thus these variations in the values of thermal behaviour and PRI might be related to the genetic differences and alterations of climatic conditions that act directly on the synthesis of non-rubber constituents, which are generally reflected in latex and rubber properties.     

Correlation of the morphology and thermooxidative degradation behavior of poly(ethylene terephthalate)–nitrile butadiene rubber–polycarbonate ternary blends

In this study, we prepared ternary poly(ethylene terephthalate) (PET)–nitrile butadiene rubber (NBR)–polycarbonate (PC) blends through a molten mixing procedure, and with a corotating extruder, we studied the morphology and thermodynamic properties of each purified polymer and the binary and ternary blends with different compositions. Dynamic mechanical analysis of both the PET–PC and PET–NBR samples showed individual loss peaks for each component, but in different ternary samples, the effects of different percentages of components (PC–PC and PET–NBR) were observed; this revealed changes in the loss peak locations. Individual loss peaks of PET and PC in the ternary PET–NBR–PC blends (81/9/10 and 63/30/7)—proof of the miscibility of the samples—were also observed in this study. The thermal properties of the samples were measured and examined with the thermogravimetric analysis and differential thermogravimetry testing methods. The activation energy and order of reaction values for the samples under an air atmosphere with single-rate methods of heating were studied. Finally, the relation between the type of morphology and the thermal degradation behavior was investigated. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47171.     

Mechanical, thermal and transport properties of nitrile rubber (NBR)—nanoclay composites

The article describes the properties of nitrile rubber (NBR)—nanoclay composites prepared by a two-step method. viz. preparation of a 3:1 [by weight] masterbatch of NBR and nanoclay followed by compounding on a two roll mill and molding at 150 °C and 20 MPa pressure. The tensile strength, elongation at break, modulus, storage modulus (E’) and loss modulus (E”) increased with the nanofiller content, reached the maximum value at 5 phr and decreased thereafter. The solvent uptake, diffusion, sorption and permeation constants decreased with nanoclay content with the minimum value at 5 phr nanoclay. The mechanism of solvent diffusion through the nanocomposites was found to be Fickian. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on nanoclay content was correlated to the morphology of the nanocomposites. supported by morphological analysis.     

Mechanical, thermal and transport properties of nitrile rubber (NBR)—nanoclay composites

The article describes the properties of nitrile rubber (NBR)??nanoclay composites prepared by a two-step method. viz. preparation of a 3:1 [by weight] masterbatch of NBR and nanoclay followed by compounding on a two roll mill and molding at 150?°C and 20?MPa pressure. The tensile strength, elongation at break, modulus, storage modulus (E??) and loss modulus (E??) increased with the nanofiller content, reached the maximum value at 5 phr and decreased thereafter. The solvent uptake, diffusion, sorption and permeation constants decreased with nanoclay content with the minimum value at 5 phr nanoclay. The mechanism of solvent diffusion through the nanocomposites was found to be Fickian. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on nanoclay content was correlated to the morphology of the nanocomposites. supported by morphological analysis.     

Study on aging of clay–rubber masterbatch from modified clay

Clay was modified by using a polymeric coating agent, a silicane coupling agent, and a titanate coupling agent together with the antioxidant for preparing the clay–rubber masterbatch. After the thermooxidative, photooxidative, and ozone aging, the properties of the masterbatch were also determined. The results indicate that, under the synergistic actions of the polymeric coating agent, antioxidant, and coupling agent, the thermooxidative and photooxidative aging resistances of the masterbatch were greatly improved. The properties of ozone aging resistance of the masterbatch can be increased by 50% under the combined action of a new kind of amine antioxidant with a titanate coupling agent. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 338–342, 2001     

Synthesis and characterization of polymeric plasticizer from PET waste and its applications in nitrile rubber and nitrile–PVC blend

Polyethylene terephthalate (PET) waste is not biodegradable; thus, it will create environmental hazards if disposed in landfills. Therefore, the only way of addressing the problem of disposal of post-industrial and post-consumer PET wastes is through recycling. The polyester plasticizer for polyacrylonitrile butadiene rubber (NBR) and polyacrylonitrile butadiene–polyvinylchloride rubber blend (NBR–PVC) was obtained by the depolymerization of PET waste with 2-ethyl-1-hexanol. The PET waste was depolymerized until a polymeric plasticizer with the average molecular weight in the range of 450–900 g/mol was obtained. The polymeric plasticizer was characterized for acid and hydroxyl numbers, viscosity, density, FTIR, NMR and TGA/DTA thermogram. The prepared polymeric plasticizer was used in the preparation of nitrile rubber and nitrile–PVC rubber blend rubber sheets, where these sheets were tested for compatibility, tensile strength, elongation-at-break, hardness and ageing properties. Nitrile rubber and nitrile–PVC blend sheets were also prepared using DOP as a plasticizer and a comparative study with the synthesized polymeric plasticizer was made. It was observed that synthesized polymeric plasticizer provides excellent tensile properties and ageing resistance for high-performance applications as compared to that obtained from DOP. The end uses for nitrile rubber and nitrile–PVC rubber blend compounds are quite diverse, but they can be loosely categorized as being either general performances or higher performance applications. Each of these performance categories requires a different set of considerations in terms of compounding with plasticizers.     

High shape-memory effect of hindered phenol/nitrile–butadiene rubber composites by forming hydrogen bonding

To widen the type and scope of use of shape memory polymers (SMPs), we added hindered phenol (AO-80) to nitrile–butadiene rubber (NBR) to gain a group of AO-80/NBR rubber composites. The glass transition temperature (T_g), structure, mechanical properties, and shape memory properties of the AO-80/NBR rubber composites were characterized. It was concluded that the dispersion of AO-80 in the NBR matrix was homogeneous and intra-molecular hydrogen bonds were formed between the hydroxyl groups ( OH) of AO-80 and the cyano groups ( CN) of NBR molecular chain. The dosage of AO-80 added could be changed to tune the T_g. AO-80/NBR rubber composites revealed outstanding shape fixity and shape recovery. The method for tuning the T_g of AO-80/NBR rubber composites will provide an idea for the fabrication and design of new SMPs. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48911.     

Mechanical and thermal behavior of modified epoxy–novolak film adhesives

Modified epoxy-based film adhesives were developed for bonding structural joints. Film adhesives with different compositions were prepared by hot pressing the molten resins. Peel and shear tests were carried out to evaluate the adhesion properties. Dynamic mechanical thermal analyses were conducted to follow the changes in the adhesive structure and also the trend of impact strength. Incorporation of thermoplastic poly(vinyl butyral) (PVB) into an epoxy- novolak combination resulted in higher cohesive strength, better film-forming ability, enhanced adhesive shear and peel strengths, but decreased thermostability. However, due to the lower chemical functionality of PVB, a lower crosslink density was achieved. Incorporation of a small amount of ethylene glycol dimethacrylate (EGDM) as a flexibilizer led to improved mechanical properties, easy handling and facile application. Finally, good shear strength retention up to 200 °C for 1 h was observed in the case of EGDM-modified adhesives.     

Nitrile rubber–bentonite composites: a thermal degradation study

The aim of the present work was to study the kinetics of the thermal degradation mechanisms of NBR–bentonite composites by means of three methods: E2 Function, Coast-Redfern, and Invariant Kinetics Parameters (IKP). Composites with 10, 20, and 30 phr of pristine bentonite and of treated bentonite with octadecylamine were prepared. Thermogravimetric analysis was followed at different heating rates (5, 7, 10, and 13 °C/min) under N₂ atmosphere. The kinetic parameters values calculated according to the E₂ Function reflect a decrease in the activation energy with the increase in the filler content, being this effect more pronounced for the treated filler, as an indicative of a lower thermal stability. With respect to the IKP method, the activation energy of the different composites lies between 262 and 293 kJ/mol. The distribution of probabilities associated to the 18 kinetic functions indicate that all the studied systems present the kinetic model of nucleation and nuclei growth as the most probable degradation mechanism, S3 with 24% of probability and S1, S2, and S4 with 12%; followed by the interphase reaction model with the S6, S7, and S8 functions with a probability ranging between 13 and 10%. In addition, we can conclude that both types of bentonites employed in this study promote an increase in the probability of the diffusion mechanism, being this fact an indicative of the formation of small molecules that diffuse in the interphase and give rise to degradation mechanisms corresponding to the reaction order kinetic model. Finally, we can say that the results of the thermal study can be corroborated by the rheological behavior and the morphology of the NBR–bentonite composites.     

Effects of overhalogenation of a synthetic vulcanized styrene–butadiene rubber sole on its adhesion behavior

The effects of halogenating the same synthetic vulcanized styrene–butadiene rubber (R2) (used as a sole material in the shoe industry) twice (double halogenation) using solutions of trichloroisocyanuric acid (TCI) in MEK were studied. The R2 rubber was treated with 0.5 and 2 wt% TCI/MEK solutions and after 1 h re-treated with additional 0.5 (0.5 + 0.5 wt% TCI/MEK) and 2 wt% TCI/MEK (2 + 2 wt% TCI/MEK) solutions. The results obtained were compared with those obtained by treating the R2 rubber once with 1 and 4 wt% TCI/MEK solutions. The surface modifications produced by the double halogenation of the R2 rubber were analyzed using advancing and receding contact angles (variations in wettability), XPS and ATR-IR spectroscopy (characterization of chemical modifications) and SEM (morphological modifications). T-peel tests on doubly halogenated R2 rubber/polyurethane adhesive joints were carried out to quantify the adhesion properties of the treated R2 rubber. The degree of chlorination was higher with increasing amount of chlorinating agent. Furthermore, the most efficient removal of hydrocarbon substances from the R2 rubber surface was obtained by double halogenation and by increasing the TCI concentration. Similar trends in surface chemistry of the R2 rubber were obtained using 0.5–2 wt% TCI/MEK, with or without double halogenation. On the other hand, by comparing the effects of treatments with 0.5 + 0.5 wt% TCI/MEK and 1 wt% TCI/MEK or with 2 + 2 wt% TCI/MEK and 4 wt% TCI/MEK, less effective removal of zinc stearate and less degree of chlorination were obtained by double halogenation although similar outermost surface modifications were produced. The second application of the TCI/MEK solution on the already halogenated R2 rubber dissolved the unreacted TCI and/or the isocyanuric acid crystals on its surface. The mechanical properties of the treated R2 rubber decreased because it became stiffer. Higher and relatively similar peel strength values were obtained in all adhesive joints prepared using treated R2 rubber. A cohesive failure in the rubber close to the chlorinated layer was always obtained.     

Effect of the sheet size on the thermal stability of silicone rubber–reduced graphene oxide nanocomposites

The structures of differently sized reduced graphene oxides (rGOs), the dispersion state, and the compatibility of rGO with silicone rubber (SR) are important impact factors on the properties of SR–rGO nanocomposites. To analyze the influence of the size of rGO on the properties of SR-based nanocomposites, three differently sized rGO sheets were introduced into SR to fabricate a series of SR-based nanocomposites. The SR–middle-sized reduced graphene oxide (MrGO) nanocomposites showed the best mechanical and thermal properties. Compared with the blank sample, the SR–MrGO nanocomposites presented remarkable two-fold and three-fold increases in the tensile modulus and strength values. The initial degradation temperature increased nearly 40 °C. In this study, we investigated the size effect of graphene on the thermal stability by examining the thermal degradation mechanism of the different SR–rGO nanocomposites in detail. Ultimately, this research may suggest a facile approach for improving the thermal stability of SR. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47034.     

Stress–strain behavior of cold-drawn isotactic polypropylene subjected to various drawn histories

Uniaxial tensile properties of cold-drawn isotactic polypropylenes (iPP) subjected to various drawn histories were investigated to elucidate the molecular origin of strain-hardening in the uniaxial stress–strain behavior of semicrystalline polymers. Two series of Ziegler–Natta catalyzed iPP with a wide range of crystallinities and metallocene catalyzed iPP with a wide range of molecular weights were used in this study. We propose a tie molecular model which assumes that tie-chains anchored in adjacent crystalline lamellae are expanded into tautness, and the taut tie-chains are pulled out from the crystalline lamellae within the lamellar units. On the basis of this model, we derive a universal constitutive equation for various cold-drawn iPPs subjected to various drawn histories.     

Sintering and thermal expansion behaviors of glass and glass–YSZ composites as self-repairable seals for SOFC

Glass and glass–ceramics are used as sealants in solid oxide fuel cell (SOFC) because their thermophysical properties can be tailored to meet the stringent requirements of the SOFC stack. The processing, sintering, and thermal expansion behaviors of self-healing and non-crystallizing glass and glass containing 10%–30 wt.% non-reacting yttria-stabilized zirconia (YSZ) are studied. The addition of inert YSZ to glass significantly retarded the sintering behavior. Thermal expansion behaviors of glass and glass–YSZ are also measured to study the role of YSZ addition on the glass transition, softening point, and coefficient of thermal expansion (CTE). It is shown that the densification is controlled by the viscous sintering mechanism, in which the addition of YSZ increased the effective viscosity of the glass–YSZ as evident from higher glass transition and softening temperatures and decreased CTE. These results demonstrated that the addition of YSZ to glass is promising for achieving optimum thermophysical properties useful as seals for SOFC.     

The structure and dynamic properties of nitrile–butadiene rubber/poly(vinyl chloride)/hindered phenol crosslinked composites

In this article, a new nitrile–butadiene rubber (NBR) crosslinked composites containing poly(viny chloride) (PVC) and hindered phenol (AO-80 and AO-60) was successfully prepared by melt-blending procedure. Microstruture and dynamic mechanical properties of the composites were investigated using SEM, DSC, XRD, and DMTA. Most of hindered phenol was dissolved in the NBR/PVC matrix and formed a much fine dispersion. The results of DSC and DMTA showed that strong intermolecular interaction was formed between the hindered phenol and NBR/PVC matrix. The NBR/PVC/AO-80 crosslinked composites showed only one transition with higher glass transition temperature and higher tan δ value than the neat matrix, whereas for the NBR/PVC/AO-60 crosslinked composites, a new transition appeared above the glass transition temperature of matrix, which was associated with the intermolecular interaction between AO-60 and PVC component of the matrix. Both AO-80 and AO-60 in the crosslinked composites existed in amorphous form. Furthermore, the chemical crosslinking of composites resulted in better properties of the materials, e.g., considerable tensile strength and applied elastic reversion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study on friction behavior of fabric–silicone rubber composites under dry/wet sliding environment

The dry/wet environment's effects on the sliding friction properties of fabric–silicone rubber composites are studied, and the wear resistance of polyester fabric is evaluated. The yarn directions of the fabrics (inner and outer) have significant influence on the coefficient of friction (COF) of fabric–silicone rubber composites during sliding friction due to the difference in fabric texture and yarn modulus. The COF's variation laws of fabric–silicone rubber composites under different vertical loads and sliding rates are observed, respectively. Additionally, the outer fabric is more sensitive to the changes of vertical loads than those of the sliding rates under the wet environment, which can be attributed to the destruction of the fabric original structure by high load, resulting in the fabric fibers' pulling and breaking during the steel ball's sliding. This study provides new ideas for the design of fabric–silicone rubber composites applied in friction conditions and complex environments.     

Effects of SiC content on thermal shock behavior and elastic modulus of cordierite–mullite composites

Cordierite (Mg₂Al₄Si₅O₁₈) is a commercially available ceramic with low fracture toughness that hampers its broad industrial applications. Although several studies have reported the mechanical improvement of cordierite using various reinforcements, modulating its mechanical and thermal shock characteristics is not explored precisely. In the present research, we investigated the manufacturing of cordierite–mullite ceramics and the role of SiC on their thermomechanical properties. The in-situ formed mullite particles were obtained by mixing andalusite-talc-alumina and addition of SiC. It was found that thermal shock behavior and elastic moduli are dependent on SiC content and retained porosity. Furthermore, the addition of SiC to cordierite-based ceramics could enhance the thermal shock resistance via proper activation of the crack bridging mechanism in the matrix of the prepared composite.     

Structure–property relationships of silica/silane formulations in natural rubber,isoprene rubber and styrene–butadiene rubber composites

The mechanical performance of natural rubber (NR), synthetic poly-isoprene rubber (IR), and styrene–butadiene rubber (SBR) composites filled with various silica/silane systems is investigated. The results are analyzed by referring to micro-mechanical material parameters, which quantify the morphological and structural properties of the polymer and filler network. These are obtained from fits with the dynamic flocculation model (DFM) describing the strongly nonlinear quasi-static stress–strain response of filler-reinforced elastomers as found from multihysteresis measurements of the investigated compounds. We focus on the reinforcement mechanisms of silica compounds with coupling and covering silane, respectively. The fitted material parameters give hints that the coupling silane provides a strong chemical polymer–filler coupling, which is accompanied by improved strength of filler–filler bonds for all three rubbers types. This may result also from the chemical coupling of short chains bridging adjacent silica particles. It implies larger stress values for the coupling silane and, in the case of NR and IR, a more pronounced “Payne effect” compared to the covering silane. In contrast, for SBR, the coupling silane delivers a lower Payne effect, which is explained by differences in the compatibility between rubber type and silane-grafted silica surface. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48435.