Surface modification of natural rubber film by polymerisation of methyl methacrylate in water-based system

Polymerisation of methyl methacrylate (MMA) on the surface of natural rubber (NR) film was studied in order to increase the surface hardness, roughness and, hence, to decrease the friction coefficient of rubber. We used the two-step process: (i) swelling of MMA and tert-butyl hydroperoxide, emulsified in an aqueous solution of sodium dodecyl sulphate, onto the NR film surface, and (ii) subsequently immersing the swollen rubber strip into an alkaline aqueous solution of ferrous ion/fructose for redox initiation. The presence of PMMA on the NR surface was examined by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Increasing the concentration of ferrous ion caused an increase in MMA conversion. The surface morphology observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) in tapping mode revealed the aggregation of micronmetre-scale nodules on the modified surface. The surface hardness and roughness increased with increasing PMMA content.     

Ionic strength effect on the liquid–liquid extraction of zinc(II) and cadmium(II) from sulphate medium by 1-phenyl-3-methyl-4-benzoylpyrazol-5-one in chloroform

The liquid–liquid extraction of zinc(II) and cadmium(II) from sulphate medium by 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (HPMBP) in chloroform is studied. The ionic strength effect of the aqueous phase shows that the extraction of the metal increases with decreasing concentration of sulphate. At initially of about 10^?4?M with three different sulphate concentrations 0.033, 0.16 and 0.33?M in the aqueous phase, Zn(II) and Cd(II) are extracted as the complexes Zn(PMBP)₂ and Cd(PMBP)₂. Sulphate complexes of Zn(II) and Cd(II) are formed in the aqueous phase. The metal–sulphate interaction has been made in evidence by using the Debye–Huckel extended limiting law of ionic activity coefficient.     

Surface characterization of polybutadiene and natural rubbers oxidized by silver(II)

Silver (II) ion is a powerful oxidizing mediator that was used for surface modification of vulcanized polybutadiene rubber (BR) and natural rubber (NR) through mediated electrochemical oxidation (MEO). Scanning electron microscopy (SEM) pictures showed that surface morphology of the oxidized rubbers was changed so that some cracks and holes appeared on the surface in macroscopic scale. This is possibly due to chain scission caused by alkane group formation which is in turn in accordance with the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra. The amounts of hydroxyl and carbonyl type surface functional groups were also increased in both oxidized rubbers. The results obtained by atomic force microscopy (AFM) showed that the surface roughness for both rubbers was changed significantly from nano- to micro-scale. Energy dispersive X-ray analysis (EDXA) expresses that surface concentration of atomic oxygen for both BR and NR was increased significantly. Also surface polarity of the treated rubbers was enhanced based on contact angle measurements leading to a higher hydrophilicity. Finally it was found that silver(II) has a somewhat greater oxidation impact on the surface of natural rubber than polybutadiene rubber.     

Study and Control of the Distribution of Elastomer in High Impact Polypropylene

In an initial step, different techniques were used to investigate the distribution and properties of the rubbery domains inside individual high impact polypropylene particles. Both Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were used to visualise the local of rubber nodules as a function of the quantity of ethylene propylene rubber (EPR) in the final product. It was demonstrated that the EPR forms first as nodules near the centre of the homopolymer particles, and then accumulates as the rubber quantity increases.     

配位体SO2-4对激发态铀(VI)去活化的影响

The dependence of the luminescence decay of electronically excited uranyl ions on the concentrations of uranium and sulphate in aqueous solution has been investigated with a pulsed nitrogen laser as a light source and a programmable transient recorder for lifetime measurements. Single exponential decay of the Luminescence is observed. The deactivation process of the excited uranyl ions should include radiative, nonradiative, water quenching and uranium self quenching and the measured lumine-scenec lifetime inidcates the result of all these processes. The Luminescence lifetime of uranyl ions increases with increasing concentration of sulphate and becomes constant when the equilibrium concentration of sulphate reaches 3.0 mol·L~(-1). The dependence of the Luminesence lifetime is similar to that of the UO_2(SO_4)_3~(4-) formation. This phenomenon can be interpreted in terms of the fact that in aqueous solution uranyl ions exist as aquo-uranyl ions. As the concentration of sulphte increaes the water molecule of hydrated uranyl ions will be replaced by sulphate ions via complex formation, and the quenching of excited uranyl ions by water is reduced. The self quenccing and the water quenching rate constants of UO_2(H_2O)_6~(2+) and UO_2(SO_4)_3~(4-) are estimated. Based on the experimental results a model for the deactivation mechanism of excited uranyl ions in sulphate solution is proposed.     

(Series Editor) Transform Techniques in Chemistry,P.R. Griffiths,D. Hercules (Eds.), in: Modern Analytical Chemistry Series,Plenum, New York,NY (1978), 385 pp. $47.40

Concentration potentials in zinc sulphate, copper sulphate, nickel sulphate and cobalt sulphate solutions across liquid membranes based on myristates and laurates of zinc, copper, nickel and cobalt and caprate and caprylate of copper have been studied in concentration cells in which the liquid membrane separates the two solutions of the same electrolyte. The behaviour of the cell with heavy metal soap liquid ion-exchange membranes becomes more and more nernstian as the number of carbon atoms in the hydrocarbon chain of the fatty acid soap increases. Concentration potential values with copper, zinc, nickel or cobalt soap follow the order of their insolubility in water. The failure to record the theoretical potentials as calculated by Nernst's equation has been explained by considering the transport of water across organic phase by hydrated ions and the dissolution of heavy metal soaps in aqueous solutions. Liquid membranes based on heavy metal myristate soaps when used in concentration cells could measure the activities of zinc, copper, nickel and cobalt ions in the concentration range of 10^?4–10^?1M.     

Adapting the Accelerated Solvent Extraction Method for Resin and Rubber Determination in Guayule Using the BÜCHI Speed Extractor

Guayule (Parthenium argentatum Gray) is a promising alternative source to Hevea brasiliensis for the production of natural rubber, which can reach levels of 8–9% under industrialized farming conditions. The most common method for determining rubber concentration is by accelerated solvent extraction (ASE), a technique developed by the Dionex Corporation and almost exclusively performed with the Dionex ASE-200 or 350 systems. Herein, it is sought to apply and adapt the most common methods used in the literature for the Dionex system to another extraction platform, the BÜCHI Speed Extractor E-914. Results showed that using a sand sandwich method to confine the sample in the center and exploiting a larger cell volume (80 mL) for extraction prevents the occurrence of overpressure and problems with clogging. Under optimized conditions, the coefficient of variation was <15% for both resin quantification for samples containing 5.0–15.8% of resin and for rubber quantification for samples with 1.7–10.3% rubber content. The extraction time for resin (2 cycles of 5 min each) was smaller than for rubber (2 cycles of 20 min each). It would be interesting to carry out interlaboratory comparisons to standardize the method at an international level.     

乙二胺硅胶材料对铜和锌离子的动态吸附

合成了胺基含量为1.35 mmol/g的乙二胺硅胶材料(EDA/SiO2),研究了EDA/SiO2对Cu2+和Zn2+的动态吸附及动态竞争吸附。结果表明,铜溶液流量和初始浓度对材料动态吸附性能有显著影响,随着溶液初始浓度的增大、流速的加快,穿透时间明显缩短。动态吸附实验结果符合Thomas模型,计算结果显示,铜溶液初始浓度由1.99 mmol/L增大至10.00 mmol/L时,模型平衡吸附容量q0从0.272 mmol/g增大至0.476 mmol/g,影响显著;流量对q0影响不显著。溶液流量和初始浓度对吸附速率常数kTh均有影响,随溶液流量增大、初始浓度的降低,速率常数值增大。在单一体系中,EDA/SiO2对Cu2+和Zn2+的工作吸附量分别为0.340和0.127 mmol/g,混合体系的吸附量均小于单一体系中的吸附量,并且对Zn2+的吸附量下降显著,表明EDA/SiO2对Cu2+的吸附能力强于Zn2+。6次循环实验表明,盐酸和氨水可对EDA/SiO2材料实现再生,再生后材料对铜的吸附容量和穿透时间的下降幅度不大,可重复使用。     

Effects of epoxidized natural rubber as a compatibilizer in melt compounded natural rubber-organoclay nanocomposites

Nanocomposites containing natural rubber (NR) as matrix, epoxidized natural rubber (ENR) as compatibilizer and organophilic layered clay (organoclay) as filler were produced in an internal mixer and cured using a conventional sulphuric system. The effects of ENR with 25 (ENR 25) and 50 mol% epoxidation (ENR 50), respectively, were compared at 5 and 10 parts per hundred rubber (phr) concentrations. The organoclay content was fixed at 2 phr. Cure characteristics, clay dispersion, (thermo)mechanical properties of the nanocomposites were determined and discussed. Incorporation of ENR and organoclay strongly affected the parameters which could be derived from Monsanto MDR measurements. Faster cure and increased crosslink density were attributed to changes in the activation/crosslinking pathway which was, however, not studied in detail. The organoclay was mostly intercalated according to X-ray diffraction (XRD) and transmission electron microscopic (TEM) results. The best clay dispersion was achieved by adding ENR 50. This was reflected in the stiffness of the nanocomposites derived from both dynamic mechanical thermal analysis (DMTA) and tensile tests. The tensile and tear strengths of the ENR 50 containing nanocomposites were also superior to the ENR 25 compatibilized and uncompatibilized stocks.     

Photoprocesses in sodium decyl sulphate micellar media

The absorption and fluorescence behaviour of thionine dye in sodium decyl sulphate (sds) medium has been studied in detail. The transient spectra and kinetics of decay of semithionine species produced by photoreduction of thionine by ferrous ions has-been studied using flash photolysis technique. The results have been compared with those in neat aqueous medium and in sodium lauryl sulphate (sls) media published earlier. It was found that the decay of semithionine which is kinetically second order in neat aqueous medium becomes pseudo first order as in thesls medium; however unlike in the latter case, the pseudo first order rate decreases with increasing surfactant concentration at all concentrations of ferric ion. The effect of electrolyte concentration on transient semithionine spectra and decay kinetics has also been studied. It was found that with increasing NaCl concentration the transient absorbance decreases and the decay slowly reverts back to second order as in aqueous medium. Insds medium as compared tosls a much higher concentration of NaCl is needed for the reaction to become second order which is attributed to stronger binding of ferric ions to thesds micelles.     

Comparative study of natural rubber and acrylonitrile rubber reinforced with aligned short aramid fiber

The aims of this paper are three-fold. The first is to determine the reinforcement of high performance short aramid fiber in two representative rubber matrices, namely natural rubber and acrylonitrile rubber. The second is to ascertain the effect of rubber polarity on the reinforcement. The third is to establish a pattern of reinforcement for use with less studied fibers. The rubbers were reinforced either with only aramid fiber or with a hybrid of aramid fiber and carbon black. The fiber contents were varied at 0, 2, 5 and 10 parts (by weight) per hundred rubber (phr) while those of carbon black were 0, 10, 20 and 30 phr. Conventional sulfur vulcanization was used. It was found that aramid fiber can reinforce both rubbers in the low strain region effectively, although to a significantly different degree. The hybrid carbon black provides additional reinforcement at low to medium strains and allows high strain stress upturn to occur in both rubber matrices. The findings enable the preparation of rubber composites having a wide, controllable range of mechanical behavior for specific high-performance engineering applications. Significantly, they also serve as a benchmark for developing reinforced systems from alternative fibers, particularly those from natural sources.     

Improvement of properties of silica-filled styrene-butadiene rubber (SBR) compounds using acrylonitrile-styrene-butadiene rubber (NSBR)

Since silica has strong filler–filler interactions and adsorbs polar materials, a silica-filled rubber compound wil have poor dispersion of the filler and a poor cure characteristic. Improvement of properties of silica-filled styrene-butadiene rubber (SBR) compounds has been studied using emulsion SBR-based acrylonitrile-styrene-butadiene rubber (NSBR). The silica dispersion is improved by adding NSBR to the compound. The bound rubber content increases with increase in the NSBR content. The scorch time and cure rate become faster as the NSBR content increases. The crosslink density also increases by increasing the NSBR content. The wear property is improved by adding the NSBR. Copyright © 2003 John Wiley & Sons, Ltd.     

HEAT-SENSITISATION OF AnnONIA-PRESERVED CENTRIFUBED NATURAL RUBBER LATEX CONCENTRATE BY POLYVINYLMETHYL ETHER. I. EFFECTS DF MATURATION,FORMER TEMPERATURE,OWELL TIME,LATEX pH,LEVEL DF ZINC OXIDE,DILUTION. AND CONCENTRATION AND MOLECULAR WEIGHT OF POLYVINYLMETHYL ETHER

This and a subsequent paper report the results of a systematic investigation of the factors which affect the heat-sensitisation of natural rubber (NR) latex by polyvinylmethyl ether (PUME). Possible mechanisms for the heat-sensitisation of aqueous latices by uateisoluble polymers such as PUME are outlined, and observations concerning the behaviour PUME in aqueous solution and the effects of maturation, former temperature, dwell time, latex pH, level of zinc oxide, dilution, and level and molecular weight of PUME upon heat-sensitisation are reported and discussed. The cloud-point temperature of PUME in aqueous solution is insensitive to polymer concentration, ionic strength, pH, polymer molecular weight, concentration of fatty-alcohol ethoxylate, and concentration of a hydrogen-bond breaker such as urea. Results for the effects of the variables listed above upon the heat- sensitisation being a consequence of PVME adsorbed at the surface of the rubber particles. rather than of PVME dissolved in the aqueous phase of the latex.     

Rheological,mechanical and morphological properties of thermoplastic vulcanizates based on NR‐g‐PMMA/PMMA blends

Graft copolymer of natural rubber and poly(methyl methacrylate) (NR‐g‐PMMA) was prepared using semi‐batch emulsion polymerization technique via bipolar redox initiation system. It was found that the grafted PMMA increased with the increase of methyl methacrylate (MMA) concentration used in the graft copolymerization. The NR‐g‐PMMA was later used to prepare thermoplastic vulcanizates (TPVs) by blending with PMMA through dynamic vulcanization technique. Conventional vulcanization (CV) and efficient sulphur vulcanization (EV) systems were studied. It was found that the CV system provided polymer melt with lower shear stress and viscosity at a given shear rate. This causes ease of processability of the TPVs via extrusion and injection molding processes. Furthermore, the TPVs with the CV system showed higher ultimate tensile strength and elongation. The results correspond to the morphological properties of the TPVs. That is, finer dispersion of the small vulcanized rubber particles were observed in the PMMA matrix. Various blend ratios of the NR‐g‐PMMA/PMMA blends using various types of NR‐g‐PMMA (i.e. prepared using various percentage molar ratios of NR and MMA) were later studied via dynamic vulcanization by a conventional sulphur vulcanization system. It was found that increasing the level of PMMA caused increasing trend of the tensile strength and hardness properties but decreasing level of elongation properties. Increasing level of the grafted PMMA in NR molecules showed the same trend of mechanical properties as in the case of increasing concentration of PMMA used as a blend component. From morphological studies, two phase morphologies were observed with a continuous PMMA phase and dispersed elastomeric phase. It was also found that more finely dispersed elastomeric phase was obtained with increasing the grafted PMMA in the NR molecules. Copyright © 2005 John Wiley & Sons, Ltd.     

hGH release from directly compressed hGH-PLGA biodegradable implantable tablets: Influence of physicomechanical factors

The incidence of compression conditions, porosity and polymer degradation on human growth hormone (hGH) release from PLGA implantable tablets was evaluated with the aim of gaining insight in the mechanism involved in drug delivery from biodegradable matrices. Tablets elaborated by direct compression of hGH with PLGA, applying various compression forces for different times, kept the integrity and the stability of the hormone. Tablet dimensions, viscoelastic properties, glass to rubber transition temperature (T_g), PLGA degradation rate and water uptake were analyzed in the freshly prepared implantable tablets as well as at several times during release test in phosphate buffer pH 7.4. Placebo tablets were also prepared to evaluate the incidence of hGH on the physicomechanical properties of the device and PLGA degradation rate. Porosity remarkably determined the amount of hGH released, through an effect on the easiness of water penetration in the tablet and on the beginning of PLGA degradation. The decrease in PLGA molecular weight during the first days in the release medium, despite of being minor, significantly conditioned hGH release rate. The more dramatic changes in PLGA molecular weight observed after 20 days in the release medium notably reduced the T_g and the viscous and elastic moduli of the tablets. The overall analysis of the events underwent by the tablets in contact with the aqueous medium was used to explain the drug release profile and may help to optimize the design of the PLGA-based implantable tablets as peptidic drug delivery systems.     

Finite Element Analysis and Structure Optimization for Improving the Fatigue Life of Rubber Mounts

The fatigue crack problem of a rubber mount on the crankshaft of a wheel in an automobile was investigated by theoretical calculation and experimental analysis. A finite element analysis (FEA) model of the rubber mount was developed and analyzed using the software MSC.MARC. FEA results imply that stress concentration may arise on the interfaces of the rubber layer and metal layer. Modifications were made to the structure parameters and rubber material of the rubber mount based on the analysis of FEA results. The stress concentration of the rubber mount at the rubber and metal interfaces was improved and the fatigue life of the improved rubber mount was increased. Finally, experiments were made to validate the accuracy of the FEA process and the reliability of the improved method. The proposed FEA and improved method can shorten the product design cycle, decrease the design and trial‐product cost and remarkably improve the product quality.     

Application of three-variables Doehlert matrix for optimisation of an on-line pre-concentration system for zinc determination in natural water samples by flame atomic absorption spectrometry

This article describes an on-line pre-concentration system for zinc determination in environmental samples by flame atomic absorption spectrometry (FAAS). It was based on the sorption of zinc(II) ions in a minicolumn of polyurethane foam loaded with 4-(2-pyridylazo)-resorcinol (PAR). The optimisation step was carried out using two-level full factorial and a Doehlert design. Three variables (sampling flow rate, buffer concentration and pH) were regarded as factors in the optimisation. Results of the two-level full factorial design 2³ for 8 runs (in duplicate) based on the Analysis of Variance (ANOVA) demonstrated that all the factors in the tested levels are statistically significant. Besides, the interaction (sampling flow rate×buffer concentration) was also statistically significant. A three-variables Doehlert design was applied in order to determine the best condition for pre-concentration and determination of zinc. The validation process was assessed as: parameters of the analytical curve, precision, effect of other ions in the proposed system, robustness test and accuracy. The proposed system allowed determination of zinc with detection limit (3σ/S) of 0.28 μg l⁻¹, and a precision (reproducibility), calculated as relative standard deviation (R.S.D.) of 10.0 and 3.7% for zinc concentration of 1.0 and 5.0 μg l⁻¹, respectively. The achieved pre-concentration factor was 91.23 and the sampling frequency was 48 samples per hour. The achieved recovery for zinc determination in presence of several cations demonstrated that this procedure could be applied for analysis of water samples. The accuracy was confirmed by analysis of three certified reference materials. This procedure was applied for zinc determination in several kinds of water samples including saline aqueous waste from oil Refinery.     

Finite Element Analysis and Structure Optimization for Improving the Fatigue Life of Rubber Mounts

The fatigue crack problem of a rubber mount on the crankshaft of a wheel in an automobile was investigated by theoretical calculation and experimental analysis. A finite element analysis (FEA) model of the rubber mount was developed and analyzed using the software MSC.MARC. FEA results imply that stress concentration may arise on the interfaces of the rubber layer and metal layer. Modifications were made to the structure parameters and rubber material of the rubber mount based on the analysis of FEA results. The stress concentration of the rubber mount at the rubber and metal interfaces was improved and the fatigue life of the improved rubber mount was increased. Finally, experiments were made to validate the accuracy of the FEA process and the reliability of the improved method. The proposed FEA and improved method can shorten the product design cycle, decrease the design and trial‐product cost and remarkably improve the product quality.     

Release mechanism of electrodeposited polypyrrole doped with corrosion inhibitor anions

Scanning Kelvin probe and electrochemical impedance spectroscopy were used to study the release behaviour of inhibitor anions doped in polypyrrole film (e.g. molybdate, 3-nitro salicylate). The polypyrrole coatings were formed on mild steel and zinc substrates in aqueous solution. It was shown that the release behaviour of the molybdate and 3-nitro salicylate anions depends on the size of cations in the electrolyte. The delamination is determined with the migration and incorporation of small cations.     

Thermo and pH Dual-Responsive Micelles of N-phthaloylchitosan-g-Poly(N-isopropylacrylamide) and Poly(acrylic acid-co-tert-butyl acrylate) for Drug Delivery

A novel amphiphilic copolymer N-phthaloylchitosan graft poly(N-isopropylacrylamide) and poly(acrylic acid-co-tert-butyl acrylate) (PHCS-g-PNIPAAm&P(AA-co-tBA)) was synthesized. The graft copolymer could form micelles in aqueous medium, and the critical micelle concentration (CMC) of the copolymer was 7.5 × 10^{? 3}mg/mL. The lower critical solution temperature (LCST) of the micelles was measured to be 30°C. Transmission electron microscopy (TEM) image showed that the micelles exhibited a regular spherical shape, and the mean diameter of the micelles was 94.1 ± 0.8 nm as determined by dynamic light scattering (DLS). The potential usefulness of the micelles as drug delivery systems was investigated using anti-inflammation drug prednisone acetate as the model. The drug loading capacity of the micelles was measured to be 22.86 wt%, and the DLS results showed that the mean diameter of the drug-loaded micelles was 133.3 ± 2.4 nm. In vitro drug release studies indicated that the micelles exhibited thermo and pH dual-responsive release profiles.