Effects of modified silica on the co-vulcanization kinetics and mechanical performances of natural rubber/styrene–butadiene rubber blends

Rubber blends are widely used for combining the advantages of each rubber component. However, to date, how to determine and distinguish the vulcanization kinetics for each single rubber phase in rubber blends during the co-vulcanization process is still a challenge. Herein, high-resolution pyrolysis gas chromatography–mass spectrometry (HR PyGC-MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene–butadiene rubber (SBR) in NR/SBR blends filled with modified silica (SiO₂). The reaction rates of crosslinking of each rubber phase in NR/SBR were calculated, which showed that the crosslinking rates of NR were much lower than those of SBR phase in the unfilled blends and blends filled with unmodified and silane modified silica. Interestingly, the vulcanization rates of NR and SBR phase were approximately same in the vulcanization accelerator modified silica filled blends, showing better co-vulcanization. In addition, the vulcanization accelerator modified silica was uniformly dispersed and endowed rubber blends with higher mechanical strength compared to the untreated silica. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48838.     

Bond characteristics,mechanical properties,and high-temperature thermal conductivity of (Hf1−xTax)C composites

Bond characteristics, mechanical properties, and high-temperature thermal conductivity of ultrahigh-temperature ceramics (UHTCs), hafnium carbide (HfC), tantalum carbide (TaC), and their solid solution composites, were investigated using first-principles calculations. Mulliken analyses revealed that Ta formed stronger covalent bonds with C than did Hf. Bond overlap analyses indicated that the Hf–C bond possessed mixed covalent and ionic bond characteristics, compared with the more covalent character of the Ta–C bond. Consequently, the overall elastic properties were enhanced with increasing number of Ta–C bonds in the composites. The overall metallicity of the composites also increased with increasing TaC content; thus, the mechanical properties did not improve monotonically. Our results indicate that adding a small amount of TaC to HfC or vice versa to produce a composite would create a new UHTC with greatly improved elastic and mechanical properties as well as high-temperature thermal conductivity.     

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.     

Synthesis,characterization, thermal constant and relaxation of gadolinium(III), iron(III) and manganese(II) chelates of diethylenetriamine-bis-inositol-N,N′,N″-triacetic acid

The reaction of the bicyclic anhydride of diethylenetraiamine-pentaacetic acid (DTPAA) with inositol gave diethylenetriamine-inositol-biester-N,N^′,N″-triacetic acid (DTPA-BI) (1). (1) was characterized by FAB-MS, ¹HNMR, IR and elemental analysis. Its chelates of Gd(III), Fe(III) and Mn(II) holding promise of magnetic resonance imaging (MRI) were synthesized. Gd(III) complex was obtained from Gd₂O₃ and the acid form of (1). Thermodynamic stability constant and relaxation of Gd(III) complex with DTPA-BI were determined. The spin–lattice relaxivity (R₁=5.6 l mmol⁻¹ s⁻¹) of chelate was slightly larger than that of [GdDTPA]²⁻. The results showed that the complex is a prospective MRI agent, although thermodynamic stability constant of DTPA-BI K_[GdDTPA-BI]⁻=10^18.2 was a little less than that of [GdDTPA]²⁻ (K_[GdDTPA]²⁻=10^20.73).     

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.     

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     

Chemical reactions,thermal and mechanical properties of epoxy — Polycarbonate blends cured with aromatic amines

Bisphenol-A polycarbonate (PC) has been incorporated into epoxy resin cured with 4,4-diaminodiphenyl sulphone (DDS) and 4,4'-diaminodiphenyl methane (DDM). IR spectra reveal that transesterification and transamidation occur between the carbonate group of PC and the hydroxyl group of cured epoxy resin for the DDM-cured system, and that only transesterification occurs for the DDS-cured system. Scanning electron micrographs (SEM) show no evidence of phase separation in these cured systems, which is an indication of full miscibility between the bisphenol-A monomers and PC-oligomers with the copolymer network. The mechanical strength and glass transition temperature (T_g) fluctuate with PC content, whereas the flexural modulus shows a steadily increasing tendency.     

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.     

The interplay between the fragility and mechanical properties of styrene–butadiene rubber composites with unmodified and modified sago seed shell powder

Reinforcing rubber with natural fillers from agrarian wastes is a new area of interest in developing rubber composite technologies. Lignocellulosic material from sago seed shell is one of the important promising natural fillers having 37% cellulose used to reinforce styrene–butadiene rubber (SBR) for enhancing its mechanical properties. Moreover, chemically or physically modified natural fillers play a significant role in enhancing the properties of SBR like morphological, thermal, and electrical characteristics. In this investigation, the changes encountered in molecular mobility, glassy dynamics, thermal stability, flexibility, and tensile strength of SBR on reinforcing with unmodified and modified sago seed shell powder were studied using broadband dielectric spectroscopy (BDS) in conjunction with thermogravimetric analysis, and mechanical properties. BDS has been successfully employed to investigate the relaxation phenomena and glass/rubbery transition in SBR, as well as its composites with unmodified and modified sago seed shell powder over the frequency (10⁻¹ to 10⁷ Hz) and wide temperature range (−100 to 150°C). Experimental data were analyzed in terms of electric modulus formalism and were suited well with the Havriliak Nigami equation. The incorporation of filler and its nature (unmodified or modified it with polyaniline, PANI) greatly influenced the morphological pattern, miscibility, and mode of interaction with the rubber matrix of SBR, which owed a path to diverse charge transport mechanism in the composites. The mechanical properties of all the composites were in good correlation with the steepness index obtained from BDS. The tensile strength, tear strength, and hardness of SBR increased slightly on loading with unmodified cellulose, whereas with modified cellulose causes substantial enhancement in its tensile strength.     

Synthesis and characterization of iron(II) and iron(III) complexes with a tridentate O,N,O′-ligand

The coordination chemistry of the ligand precursor 1-benzoyl-4,5-dihydro-3,5-bis(trifluoromethyl)-1H-pyrazol-5-ol (1a) to iron(II) acetate was studied. In dependence of the added co-ligand different complex geometries were observed. In case of 4-dimethylaminopyridine (DMAP) as co-ligand an octahedral iron(II) complex was found with an O,N,O′-coordination of the tridentate ligand (1a-2H), in which the ligand is planar, the oxygen donors are trans to each other, and the nitrogen donor is in a cis position. The other coordination sites on the iron center are occupied by DMAP ligands. In contrast to that, with triphenylphosphane as the co-ligand an oxidation process took place, which revealed an octahedral iron(III) complex with a comparable geometry for the tridentate ligand (O,N,O′-coordination, 1a-2H) demonstrating the usefulness of 1a-2H to stabilize different oxidation states. The additional coordination sites are occupied by one triphenylphosphane oxide and ethoxide ligands. Interestingly, the ethoxide ligands act as bridging ligands to form a bimetallic complex.     

Thermorheological studies of novel thermoplastic elastomeric blends of nitrile rubber (NBR) and scrap computer plastics (SCP) based on acrylonitrile–butadiene–styrene terpolymer (ABS)

Abstract

Thermorheological properties of thermoplastic elastomeric 60/40, 70/30 and 80/20 nitrile rubber (NBR)/scrap computer plastics (SCP) blends were studied by using parallel plate rheometer. The blends exhibit pseudoplasticity and obey power law model. The dynamically vulcanised blends have higher dynamic viscosities than their unvulcanised counterparts. Surface finish and die swell of the extrudates are improved upon dynamic vulcanisation. The thermoplastic elastomeric blends of NBR/SCP exhibit 'thermorheological complexity'.     

Morphological characteristics and thermal,rheological, and mechanical properties of cellulose nanocrystals-containing biodegradable poly(lactic acid)/poly(ε-caprolactone) blend composites

This work investigates the effect of cellulose nanocrystal (CN) loading on the properties of polylactide / poly(ε-caprolactone) (PLA/PCL) (70/30) blend processed in a twin-screw extruder as a potential material that can be utilized in various applications where biodegradation is highly desired. The morphological analysis revealed a reduction in droplet size of dispersed PCL phase upon addition of CN at low concentrations (1 and 2 wt %) with maximum reduction at 2 wt % which led to maximum improvement in mechanical properties. The reinforcing effect of CN in increasing the DMA storage modulus of the prepared systems was noticed when CN concentration was increased. Further, CN enhanced the crystallization of PCL, whereas the cold crystallization of PLA remained the same with CN addition. Both melt strength and viscosity of PLA improved with the incorporation of PCL and CN. In general, a green composite material with improved properties was successfully prepared using an environmentally friendly filler material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48665.     

A spin-crossover catecholato–iron(III) system: Synthesis,crystal structure and magnetic properties

A new mononuclear Fe(III)–catecholate complex, which exhibits an incomplete spin transition without hysteresis, had been synthesized and structurally characterized. Analyzed from the structural characteristics, the tripodal ligand must play the important role in affecting the spin crossover (SCO) behavior. The larger steric strain effect and weak cooperativity existed in the crystal lattice are inclined to favor the incomplete transition.     

Effect of modified rubber powder on the morphology and thermal and mechanical properties of blown poly(lactic acid)–hydroxyl epoxidized natural rubber films for flexible film packaging

In this study, we prepared and used modified natural rubber powder to increase the toughness of poly(lactic acid) (PLA) films. We blended PLA and hydroxyl epoxidized natural rubber (HENR) via a melt-mixing process with twin-screw extruder and a blowing machine. We investigated the influence of the HENR content in the blend films on the microstructure, thermal, mechanical, and optical properties. The morphology of the blend showed a coarse surface and elongated fibrils of HENR in the PLA matrix. After blowing, the dispersion of small particles of HENR in the substrate was seen. The size of the remaining HENR particles was smaller than that of the starting powder. The compatibility of HENR and the remaining rubber particles may have synergistically contributed to improvements in the elongation at break, impact strength, and ultraviolet–visible transition protection of the PLA films. The elongation at break drastically increased from 3 to 228% after PLA was blended with 20 wt % HENR. On the other hand, all of the blends exhibited lower glass-transition temperatures and cold crystallization temperatures than the pure PLA films. We concluded that the blend was partially compatible and may have increased the flexibility of the PLA films. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47503.     

Application of hygrothermally decomposed polyurethane in rubber recipes Part 2–Influence of hygrothermally decomposed polyester–urethane on cure characteristics and viscoelastic behaviour of styrene/butadiene rubber

Abstract

Hygrothermally decomposed polyester–urethane (HD PUR) was mixed at concentrations up to 20 pphr with a styrene/butadiene rubber (SBR), using an efficient vulcanisation system. Changes in the cure behaviour were followed by vulcametry, plate–plate rheometry, and differential scanning calorimetry. It was found that the degree of crosslinking was increased by the incorporation of HD PUR, which acts as an accelerator in SBR stocks. Increasing crosslinking resulted in higher stiffness and strength and was accompanied by a reduction in elongation at break and swelling index.     

Synthesis,mechanical property,and thermal stability of reduced graphene oxide–zinc oxide/cyanate ester/bismaleimide resin composites

Reduced graphene oxide–zinc oxide/cyanate ester/bismaleimide resin (RGO–ZnO/CE/BMI) composites were synthesized via a blending method. The RGO–ZnO composite was incorporated into the CE/BMI copolymer to improve the properties of RGO–ZnO/CE/BMI composites. The structure, elements, and morphology of the RGO–ZnO composite were studied with XPS, FTIR, XRD, and SEM analyses. It indicated that the ZnO micro-sphere was attached to RGO by electrostatic attraction and the RGO–ZnO composite was prepared successfully. The mechanical properties and thermal stability of RGO–ZnO/CE/BMI composites were investigated. When RGO–ZnO composite was 1 wt.%, the flexural and impact strengths of RGO–ZnO/CE/BMI composites were 1.07 and 1.35 times of the CE/BMI copolymer, respectively. However, the RGO–ZnO composite tended to aggregate in the CE/BMI matrix with high loading. According to the SEM analysis, appropriate RGO–ZnO composite was evenly dispersed in the CE/BMI copolymer. Compared to the CE/BMI copolymer, the thermal stability of the RGO–ZnO/CE/BMI composites was good. Thus, the RGO–ZnO composite was successfully filled in the CE/BMI matrix; the mechanical properties and thermal stability of the RGO–ZnO/CE/BMI composites were enhanced.     

Preparation of dispersible nanosilica surface-capped by hexamethyl disilazane via an in situ surface-modification method and investigation of its effects on the mechanical properties of styrene–butadiene/butadiene rubber

Silica has been established as one of the most promising materials in green tires. The filler–rubber interactions can increase the comprehensive performance of rubber composites. In this study, sodium silicate was used as the silicon source and hexamethyl disilazane (HMDS; molecular formula: C₆H₁₉NSi₂) was used as a modifier to synthesize dispersible silica (DNS) via an in situ surface-modification method. The effects of the HMDS-capped silica on the properties of rubber–matrix composites made of styrene–butadiene rubber (SBR) and high-cis-polybutadiene rubber (BR9000 or BR) were investigated with Zeosil 1165MP (Z1165-MP; a commercial highly dispersible silica produced by Rhodia for the production of green tires in the rubber industry) as a reference. The results show that the SBR–BR–DNS composite was before the SBR–BR–Z1165-MP composite in increasing the tear strength and elongation at break and reducing the compression heat buildup. On the basis of the resulting properties, the reinforcing behaviors in the rubber–matrix composites were analyzed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47763.     

Mechanical,morphological and thermal properties of short carbon and aramid fibres-filled bromo-isobutylene-isoprene rubber vulcanised with 4, 4’ bis(maleimido)diphenylmethane

ABSTRACT

This paper describes the use of a combination of 4, 4’ bis(maleimido)diphenylmethane and ZnO as a high-temperature processable vulcanising agent for the short aramid and carbon fibre-filled bromo-isobutylene-isoprene rubber. The fibre breakage analysis, cure characteristics, mechanical, thermal and morphological properties of the composites were evaluated with different fibre loading. The fibre breakage analyses revealed that the aramid fibres have good length retention property compared to carbon fibres. The morphological analysis of the extracted aramid fibres showed severe surface roughness primarily due to fibrillation after shear mixing. The fibrillated aramid fibres lead to aggregation and poor dispersion of the fibres in the rubber matrix. However, fibrillation imparted surface roughness and increased surface area on the aramid fibres which improved the fibre–matrix interaction via mechanical anchoring. On the other hand, the carbon fibre-filled composite showed poor fibre–matrix interaction and inferior strength and modulus.