Effects of vulcanization accelerator functionalized graphene on the co-vulcanization kinetics and mechanical strength of NR/SBR blends

Rubber blends are widely used for combining the advantages of individual 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 are still a challenge. Herein, high resolution pyrolysis gas chromatography-mass spectrometry (PyGC-MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene-butadiene rubber (SBR) in their blends filled with graphene. It is shown that the crosslinking rate of NR chains (k_NR) was much lower than that of SBR chains (k_SBR) in the unfilled blends and blends with untreated graphene. Interestingly, the gap between k_SBR and k_NR was narrowed effectively in the blends with vulcanization accelerator grafted graphene, showing a better co-vulcanization of NR and SBR. In addition, the vulcanization accelerator grafted graphene was uniformly dispersed in rubber matrix and endowed rubber blends with higher mechanical strength and thermal conductivity did the untreated graphene.     

Evaluation of the polymer-solvent interaction parameter χ for the system cured styrene butadiene rubber and toluene

One of the most popular cured rubbers used in industrial applications is styrene butadiene rubber (SBR) and frequently its network structure is studied by means of swelling techniques in solvent. Normally, toluene is used as solvent in this test. In order to estimate the crosslink density from the equilibrium volume fraction of rubber in the swollen state, the correct evaluation of the Flory-Huggins interaction parameter χ is necessary. This work covers the swelling behavior of cured SBR in toluene. The rubber was vulcanized with different amounts sulfur and accelerator at 433 K in order to obtain several network structures and crosslink densities. Network characterisations of the compounds were made by swelling measurements in the frame of the Flory-Rehner relationship using the molecular weight of the network chain between chemical crosslinks obtained previously by mechanical tests. A relationship between χ and v_r, the polymer volume fraction at equilibrium (maximum) degree of swelling, was established for the cured SBR/toluene system. It was found that χ is not a constant but depends on the crosslink density in the sample. The types of crosslinks in these samples where estimated applying this function to the swelling behavior of the compounds previously treated with the thiol probe method.     

Distorted-wave calculations for the three dimensional chemical reaction H + H2(v ⩽ 2, j = 0) → H2(v′ ⩽ 2, j′, mj) + H

Calculations of the vibrational—rotational product state population distributions and differential cross sections for the chemical reaction H + H₂(v ? 2, j = 0) → H₂(v′ ? 2, j′, m_j) + H have been carried out on the Porter—Karplus potential energy surface. The vibrationally-adiabatic-distorted-wave (VADW) method has been used. The relative rotational product distributions, differential cross sections and the helicity m_j, dependences of these quantities for the v = 0 reaction agree well with accurate close-coupling results. The absolute integral cross sections are considerably smaller than the accurate quantum values, however. The calculations for the v = 1 reaction agree with the findings of previous sudden quantum, limited close-coupling and quasiclassical theoretical studies and experiments that product H₂(v′ = 1) is more likely to be produced than H₂(v′ = 0). For the reaction with v = 2, it is found that at high translational energies product H₂(v′ = 2) is favoured over H₂(v′ = 1) or H₂(v′ = 0). The VADW differential cross sections for the v = 1 and v = 2 reactions have a similar shape to those of the v = 0 reaction, with backward peaking when summed over all m_j states. The relative rotational distributions for the v = 2, j = 0 → v′ = 2, j and v = 1, j = 0 → v′ = 1, j reactions are also similar to those obtained for the v = 0, j = 0 → v′ = 0, j reaction, with low rotational excitation.     

Insight into vulcanization mechanism of novel binary accelerators for natural rubber

A novel TU derivative, N-phenyl-N′-(у-triethoxysilane)-propyl thiourea(STU), is prepared and its binary accelerator system is investigated in detail. Compared to the control references, the optimum curing time of NR compounds with STU is the shortest, indicating a more nucleophilic reaction occurs. The Py-GC/MS results present that the phenyl isothiocyanate fragment still remains in the NR/STU compounds with or without extracting treatment, but no silane segment can be found in the vulcanizate with extracting treatment. Vibrations of C=S, NH and aromatic ring in FTIR experiments and a new methyne carbon peak, as well as the peaks of phenyl group of STU, in the solid state 13C-NMR experiments are found in the NR/STU vulcanizate with extracting treatment. Moreover, the crosslinking density of vulcanizates with STU evolves to lower level, indicating the sulfur atom of STU does not contribute to the sulfur crosslinking. Therefore, a new vulcanization kinetic mechanism of STU is propounded that the thiourea groups can graft to the rubber main chains as pendant groups by chemical bonds during the vulcanization process, which is in accordance with the experimental observations quite well.     

Extraction of Phenolic Compounds from Fresh Apple Pomace by Different Non-Conventional Techniques

Red Delicious apple pomace was produced at laboratory scale with a domestic blender and different non-conventional extraction techniques were performed to isolate phenolic compounds, such as ultrasound-assisted extraction (UAE), ultraturrax extraction (UTE), accelerated solvent extraction (ASE) and pulsed electric field (PEF) extraction pre-treatment. Total phenolic content (TPC) was determined by Folin–Ciocalteu assay. Phloridzin, the main phenolic compound in apples, was determined by chromatographic analysis Q-TOF-LC/MS. The results obtained with these techniques were compared in order to identify the most efficient method to recover polyphenols. The highest value of TPC (1062.92 ± 59.80 µg GAE/g fresh apple pomace) was obtained when UAE was performed with EtOH:H₂O (50:50, v/v), while ASE with EtOH:H₂O (30:70, v/v) at 40 °C and 50% of flush was the most efficient technique in the recovery of phloridzin. The concentration of the main phenolic compounds ranged from 385.84 to 650.56 µg/g fresh apple pomace. The obtained results confirm that apple pomace represents an interesti-ng by-product, due to the presence of phenolic compounds. In particular, phloridzin could be considered a biomarker to determine the quality of numerous apple products. Therefore, this research could be a good starting point to develop a value-added product such as a functional food or nutraceutical.     

Organophosphorus chemistry: Part IV. Vibrational spectroscopic study of the PO,PS and PSe bonds in triarylphosphorous chalcogenides

The infrared and Raman spectra of the series (4-XC₆H₄)_3-n(C₆H₅)_nPY, (3-XC₆H₄)_3-n (C₆H₅)_nPY (X = Cl or F, n = 0,1,2) and (4-FC₆H₄)_3-n (3-FC₆H₄)_nPY (n = 1,2) (Y = O, S and Se) compounds have been studied and assignments for the v(P=O), v(P=S) and v(P=Se) stretching frequencies are proposed. The results indicate that the frequency shifts caused by the substituents bonded to phosphorus are more important in the PS and PSe bond than in the PO bond. Mechanisms for the changes in PY bond order as a result of changing the aromatic substituent are discussed.     

Vibrational spectra in cyclopropane series: II. Symmetry and conformation in the gas phase of the monomer and dimer of cyclopropanecarboxylic acid

Infrared and Raman spectra of gaseous cyclopropanecarboxylic acid (C₃H₅COOH and C₃H₅COOD) were measured from 250 to 4000 cm^?1. The bands were assigned respectively to the monomer and to an associate. The depolarization ratio measurement, the vib—rot envelope study and the detailed analysis of the v(CO) and v(CH) regions enabled the symmetry and the conformation of the molecular entities in equilibrium to be determined. The monomer belongs to the C_s symmetry group and the conformation of its predominant fraction is trans/trans. The associate is a centrosymmetrical dimer (C_i symmetry) having (trans/cis)₂ conformation. Some features of the geometry of the pseudocycle are discussed.     

Influence of Polymer Coated CaCO3 on Vulcanization Kinetics of Natural Rubber/Sulfur/N-Oxydiethyl Benzthiazyl Sulfenamide (BSM) System

The effect of polymethyl methacrylate (PMMA)-encapsulated calcium carbonate on the kinetics of the vulcanization of natural rubber (NR) with a vulcanizing agent (sulfur) accelerated by N-oxydiethyl benzthiazyl sulfenamide (BSM) has been studied. The PMMA coating (4% by weight of CaCO₃) was prepared by dispersion polymerization, and compositions of five NR composites were 10, 15, 20 phr of treated CaCO₃ and 20 and 40 phr of untreated CaCO₃. The vulcanization kinetics was determined by oscillating disc rheometry (ODR) and the kinetic parameters were determined by the model equations. The kinetic analysis suggests that the two-parameter auto catalytic model is the more appropriate one to elucidate the kinetics of the vulcanizing reaction of the present system. These parameters support the nature of the experimental ODR curves (degree of conversion–time plots). The encapsulated CaCO₃ leads to a change in vulcanization reaction and has an effect on the kinetic parameters E, ln K₀, m and n, and consequently on the overall reactivity.     

The infrared spectra (500-150 CM−1) of the complexes cis- and trans-[Pt(pyridine)2X2] (X = Cl,Br, I,SCN)

The IR spectra of cis- and trans-[Pt(pyridine)₂X₂] (X = Cl, Br, I, SCN) are discussed. Distinction between the vPt—N and vPt—X bands is based on their relative sensitivities to ¹⁵N-labelling and deuteration of the pyridine ring, to halogen substitution and to ¹⁵NCS-labelling. Two vPt—N and two vPt—X bands are observed in the cis-complexes as required for C_2v symmetry. The D_2h symmetry of the trans-complexes requires one vPt-N and one vPt—X band but additional bands are observed and are ascribed to coupling between vPt—N and vPt—X.     

Studies of conventional sulfur vulcanization of SBR rubber: Analysing the reaction products from thermal degradation of the accelerator by means of MCC-IMS technique

A combination of knowledge on curing process of rubber mixes with novel methods of chemical analysis, a new unconventional approach to analysis of rubber vulcanization is presented in this study. Six SBR samples containing various N-tert-butyl-2-benzothiazole sulfenamide (TBBS) accelerator: sulfur ratios (within) the range of conventional (CV) sulfur vulcanization system were studied using multi-capillary column ion mobility spectrometry (MCC-IMS) technique. For these analysis, calibration/dilution curves were established. Moreover, data from MCC-IMS were correlated with other parameters of the rubber vulcanizates – their crosslink density and structure as well as their tensile strength and modulus at elongation. For such comparison, one of the reaction products from thermal decomposition of TBBS, benzothiazole was selected. Furthermore, the concentration of benzothiazole released during the vulcanization process corresponded well with the crosslink density of the rubber vulcanizates studied. It was even possible to calculate the crosslink density from the concentration of benzothiazole determined by MCC-IMS, using Boltzmann fitting curve. The presented results could be an important contribution in understanding the mechanisms occurring during rubber vulcanization, demonstrating a new approach to testing and evaluation of the process.     

The physical and mechanical properties and cure characteristics of NBR/silica/MWCNT hybrid composites

The main objective of the present study was to investigate the synergistic effect of simultaneous use of two reinforcing fillers in rubber compounds based on acrylonitrile-butadiene copolymer (NBR). Silica was used as reinforcing filler in all samples and the loading content was 25 phr. 3 and 5 phr of multiwall carbon nanotubes (MWCNT) were used as second reinforcing filler in NBR/silica compounds. Melt mixing method was employed for compound preparation. The effects of carbon nanotube/silica hybrid filler on mechanical and vulcanization characteristics of the rubber compounds were investigated. These results revealed that addition of the reinforcing filler, either carbon nanotube or silica, shortened the optimum cure time (t₉₀) and also scorch time (t_s1) of samples compared to that of pure NBR compound. In hybrid compounds, the reduction in optimum cure time and scorch time was higher than that of for silica-filled NBR or CNT-filled NBR compounds. This can be attributed to the synergistic effect between CNT and silica as two reinforcing agents in NBR compounds. Regardless the composition of the reinforcing filler, an increase of the relaxed storage modulus is observed, while the tan δ value is decreased steadily. The dynamic modulus reinforcement of nanocomposites was examined by the Guth Gold and Modified Guth Gold equations. For hybrid samples, the experimental values show a significant positive deviation from model predictions. According to the Barlow’s formula, hybrid compounds show higher burst strength compared to silica or CNT filled NBR compounds.     

The sulfur reversion process in natural rubber in terms of crosslink density and crosslink density distribution

Unfilled natural rubber compounds composed of conventional (CV), semi-efficient (SEV), efficient (EV) and sulfur donor (SD) vulcanization systems were heat aged to promote sulfur reversion. Rheometry, hardness, strain-strain characteristics including Mooney-Rivlin analysis, equilibrium solvent swell and Double Quantum (DQ) Nuclear Magnetic Resonance (NMR) were used to monitor crosslink density changes. A loss of crosslink density was observed by rheometry, C₁, equilibrium swelling and by DQ NMR as a function of cure extent. No chain scission reactions were operating in the time/temperature conditions used. All crosslink distributions were unimodal and the network homogeneity followed the order of EV > SD > SEV > CV. The crosslink distribution narrowed during the curing process for the CV and SEV systems. Non-oxidative maturation reactions were advantageous in promoting a more random distribution of crosslinks in the polymer matrix.     

Effect of nanocrystalline cellulose on the curing characteristics and aging resistance properties of carbon black reinforced natural rubber

This work focused on the effect of nanocrystalline cellulose (NCC) on the curing characteristics, aging resistance and thermal stability of natural rubber (NR) reinforced with carbon black (CB). Sharing the same fillers loading of 45 parts per hundred rubber (phr), NR/NCC/CB composites with different NCC/CB ratios (i.e. 0/45, 5/40, 10/35, 15/30, 20/25 phr) were prepared and analyzed. Resorcinol and hexamethylene tetramine (RH), acting as the modifier in NR/NCC interface, was also discussed for its influence. The result showed that an relatively higher ratio of NCC/CB led to a lower torque, a shorter cure time (T ₉₀), a slightly longer scorch time (T ₁₀) and a bigger vulcanization rate constant (K). This tendency suggested that the existence of NCC accelerated the vulcanization process. Additionally, modified by RH, NR/NCC/CB compounds exhibited a short T ₁₀ and a elevated torque. And a moderate RH content would lower the E _a of vulcanization. A 10 phr substitute of CB by NCC can help to improve aging resistance in terms of mechanical properties. In a high temperature aging condition, composites with 10 phr NCC also performed the highest storage modulus (G′) among composites tested. A moderate NCC content contributed to the best retention of G′ after high temperature aging, so did the incorporation of RH. With the partial replacement of CB by NCC, the temperature of 5% weight-lose had a slight drop and the apparent crosslink density showed a decrease. Thanks to the interaction of RH with both NR and NCC, composites showed an improvement in apparent crosslink density after modified by RH.     

Crystal field aspects of vibrational spectra: VII. Derivation of a spectrochemical series of ligands from infrared spectra

The infrared spectra (700-200 cm^?1) of 52 complexes of general formula Na[ML₃] or [ML₂B] (where M = a divalent metal ion of the first transition series; L = α-thenoyltrifluoroacetonate or benzoyltrifluoroacetonate anion; B = 2H₂O, 2NH₃, 2pyridine, 2,2'-bipyridine or 1,10-phenanthroline) are discussed. Within each series of complexes with common L and B, the IR band near 400 cm^?1 which exhibits maximum sensitivity to the coordinated metal ion (the sensitivity being in the sequence of crystal field stabilization energies) and which generally occurs in a region free from ligand absorption, is assigned to the metal—oxygen stretching frequency (v(M—O)). For each series of complexes with common M and L, the magnitude of v(M—O) decreases progressively with increasing ligand field strength of B. This relationship enables the coordinated bases, B, to be arranged in a spectrochemical series which is practically identical with that obtained from electronic spectra.     

Enhanced Xylose Recovery from Oil Palm Empty Fruit Bunch by Efficient Acid Hydrolysis

Oil palm empty fruit bunch (EFB) is abundantly available in Malaysia and it is a potential source of xylose for the production of high-value added products. This study aimed to optimize the hydrolysis of EFB using dilute sulfuric acid (H₂SO₄) and phosphoric acid (H₃PO₄) via response surface methodology for maximum xylose recovery. Hydrolysis was carried out in an autoclave. An optimum xylose yield of 91.2 % was obtained at 116 °C using 2.0 % (v/v) H₂SO₄, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. A lower optimum xylose yield of 24.0 % was observed for dilute H₃PO₄ hydrolysis at 116 °C using 2.4 % (v/v) H₃PO₄, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. The optimized hydrolysis conditions suggested that EFB hydrolysis by H₂SO₄ resulted in a higher xylose yield at a lower acid concentration as compared to H₃PO₄.     

Interaction of zinc oxide clusters with molecules related to the sulfur vulcanization of polyolefins ("rubber")

The vulcanization of rubber by sulfur is a large‐scale industrial process that is only poorly understood, especially the role of zinc oxide, which is added as an activator. We used the highly symmetrical cluster Zn₄O₄ (T_d) as a model species to study the thermodynamics of the initial interaction of various vulcanization‐related molecules with ZnO by DFT methods, mostly at the B3LYP/6‐31+G* level. The interaction energy of Lewis bases with Zn₄O₄ increases in the following order: CO62H₄3H₆2S₂<1,4‐C₅H₈2O2S3N?CH₃COO^?. The corresponding binding energies range from ?57 to ?262 kJ mol^?1. However, Brønsted acids react with the Zn₄O₄ cluster with proton transfer from the ligand molecule to one of the oxygen atoms of Zn₄O₄, and these reactions are all strongly exothermic [binding energies [kJ mol^?1] in parentheses: H₂O (?183), MeOH (?171), H₂S (?245), MeSH (?230), C₃H₆ (?121), and CH₃COOH (?255)]. The important vulcanization accelerator mercaptobenzothiazole (C₇H₅NS₂, MBT) containing several donor sites reacts with the Zn₄O₄ cluster with proton transfer from the NH group to one of the oxygen atoms of ZnO, and in addition the exocyclic thiono sulfur atom and the nitrogen atom coordinate to one and the same zinc atom, resulting in a binding energy of ?247 kJ mol^?1. A second isomer of [(MBT)Zn₄O₄] with a strong O? H???N hydrogen bond rather than a Zn? N bond is only slightly less stable (binding energy ?243 kJ mol^?1). The NH form of free MBT is 36 kJ mol^?1 more stable than the tautomeric SH form, while the sulfurized MBT derivative benzothiazolyl hydrodisulfide C₇H₅NS₃ (BtSSH) is most stable with the connectivity >CSSH.     

Interactions entre les seringues non réutilisables et les médicaments: Migration d'un Accélérateur de Vulcanisation Benzothiazolique et de Composés Apparentés

Interactions between disposable syringes and drugs. Leaching of a benzothiazole vulcanization accelerator and related compounds)Disposable syringes (three brands) filled with water very quickly yielded one or more compounds with u.v. absorption peaks. The rubber plunger seals were identified as the source of contaminant. Their analysis by t.l.c. showed the presence of 2-mercaptobenzothiazole, used as vulcanization accelerator. The compounds extracted into water were identified by mass spectrometry (electron impact and methane chemical ionization) as 2-mercaptobenzothiazole, 2-methylthiobenzothiazole, 2-hydroxybenzothiazole, 2-(2-hydroxyethylthio)benzothiazole and 2-(2-hydroxyethoxy)benzothiazole. The last three compounds were formed during sterilization of the syringes with ethylene oxide. The role of the precise nature of the vulcanization accelerator in this reaction is briefly described (zinc ions seem to be necessary), as are the analytical interferences resulting from the observed phenomena.     

A Comparative Study of Various Pretreatment Approaches for Bio-Ethanol Production from Willow Sawdust,Using Co-Cultures and Mono-Cultures of Different Yeast Strains

The effect of different pretreatment approaches based on alkali (NaOH)/hydrogen peroxide (H₂O₂) on willow sawdust (WS) biomass, in terms of delignification efficiency, structural changes of lignocellulose and subsequent fermentation toward ethanol, was investigated. Bioethanol production was carried out using the conventional yeast Saccharomyces cerevisiae, as well as three non-conventional yeasts strains, i.e., Pichia stipitis, Pachysolen tannophilus, Wickerhamomyces anomalus X19, separately and in co-cultures. The experimental results showed that a two-stage pretreatment approach (NaOH (0.5% w/v) for 24 h and H₂O₂ (0.5% v/v) for 24 h) led to higher delignification (38.3 ± 0.1%) and saccharification efficiency (31.7 ± 0.3%) and higher ethanol concentration and yield. Monocultures of S. cerevisiae or W. anomalus X19 and co-cultures with P. stipitis exhibited ethanol yields in the range of 11.67 ± 0.21 to 13.81 ± 0.20 g/100 g total solids (TS). When WS was subjected to H₂O₂ (0.5% v/v) alone for 24 h, the lowest ethanol yields were observed for all yeast strains, due to the minor impact of this treatment on the main chemical and structural WS characteristics. In order to decide which is the best pretreatment approach, a detailed techno-economical assessment is needed, which will take into account the ethanol yields and the minimum processing cost.     

A SAXS and swelling study of cured natural rubber/styrene–butadiene rubber blends

A small‐angle X‐ray scattering (SAXS) and swelling study of natural rubber and styrene–butadiene rubber blends (NR/SBR) is presented. To this aim, specimens of NR and SBR and blends with 75/25, 50/50, and 25/75 NR/SBR ratios (in phr) were prepared at a cure temperature of 433 K and the optimum cure time (t₁₀₀). This time was obtained from rheometer torque curves. The system of cure used in the samples was sulfur/n‐t‐butyl‐2‐benzothiazole sulfenamide. From swelling tests of the cured samples, information about the molecular weight of the network chain between chemical crosslinks was obtained. For all cured compounds, in the Lorentz plots built from SAXS scattering curves, a maximum of the scattering vector q around 0.14 Å^?1 was observed. However, the q position shows a linear‐like shift toward lower values when the SBR content in the SBR/NR blend increases. In pure NR or SBR the q values show a different tendency. The results obtained are discussed in terms of the existence of different levels of vulcanization for each single phase forming the blend and the existence of a third level of vulcanization located in the interfacial NR/SBR layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2320–2327, 2009     

The far infrared spectra of metal chloride complexes of pyridine in relation to their structures

The infrared spectra of the complexes [M(py)₂Cl₂] (py = pyridine; M = Mn, Fe, Co, Ni, Cu, Zn) have been determined within the range 650–150 cm^?1. Assignments of the metal—nitrogen and metal—halogen stretching frequencies (vM—N and vM—Cl) are made on the basis of the band shifts induced by deuteration of the pyridine ring and by varying the coordinated metal ion. If the band of lowest frequency is assigned to a bending mode, the number of vM—N and vM—Cl bands observed agrees with the number required by symmetry considerations based on the known structures of the complexes. On the basis of this work, some earlier assignments have been revised.