Migration of low molecular weight moiety at rubber-polyurethane interface: An ATR-IR spectroscopy study

In this study, a novel approach based on ATR-IR spectroscopy consisting in the combined use of two prisms of different nature and refraction index (germanium—about 1 μm depth and zinc selenide—about 3 μm depth) was proposed to study the polyurethane-rubber interface. More precisely, the migration of paraffin wax additive in as-received and MEK cleaned vulcanized styrene-butadiene rubber (SBR)-polyurethane coating interface was monitored. Polyurethane coating with thickness of about 2 μm was applied on the SBR rubber surface and the ATR-IR spectra were recorded in the polyurethane coating. Thus, the ATR-IR spectrum obtained with Ge prism analyzed only the polyurethane coating whereas the ATR-IR spectrum obtained with ZnSe analyzed both the polyurethane coating and the near surface SBR. The results obtained showed that the paraffin wax migrated from the SBR rubber bulk to the rubber-polyurethane interface, then diffused into the polyurethane and finally migrated to the polyurethane surface.     

低相对分子质量反式-1，4-聚异戊二烯蜡在橡胶配方中的应用

研究了低相对分子质量反式—1，4—聚异戊二烯蜡(LMTPIW)在橡胶配方中的应用。用LMTPIW替代芳烃油用于SBR或SSB／TPI配方中，可改善混练胶的加工性能；硫化胶的拉伸强度略有下降，回弹性、屈挠性能、热老化性能及抗湿滑性能都有所提高。当LMTPIW用量为20份时，胶料的综合性能最佳。     

Effect of molecular weight of epoxidized natural rubber on shear strength of adhesives

The dependence of shear strength of epoxidized natural rubber (ENR)‐based adhesives on molecular weight of the rubber is studied using coumarone–indene resin, gum rosin, and petro resin as tackifiers. The adhesive was coated on polyethylene terephthalate (PET) film substrate using a SHEEN hand coater at various coating thickness. The shear strength of adhesives was determined by a Texture Analyzer. Results show a maximum at 6.63 × 10⁴ and 4.14 × 10⁴ for ENR 25 and ENR 50, respectively, after which the shear strength decreases with further increases in molecular weight for all the coating thickness. This observation is attributed to varying degree of cohesiveness which culminates at the respective optimum molecular weight of ENR. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal aging properties and chemical resistance of blends of natural rubber and epoxidized low molecular weight natural rubber

Studies into solvent resistance and aging properties of blends of natural rubber and epoxidized low molecular weight natural rubber were carried out. Vulcanization of the blends using the semi‐efficient vulcanization (semi‐EV) system was found to have curing advantages over conventional vulcanization (CV) and efficient vulcanization (EV) systems. The rheological properties (cure time, t₉₀, and scorch time, t₂), solvent resistances, and aging properties of the vulcanizates were found to improve as the level of epoxidized low molecular weight natural rubber in the blends increases. The mechanical properties of the blends were also found to be within the accepted level for NR vulcanizates. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1733–1739, 2005     

辐射对纤维素结晶度的影响

以Co-60γ射线为辐射源，辐射预处理精制棉纤维素。用IR研究了经射线辐射的精制棉纤维素的相对结晶度的变化，结果表明随辐射剂量的加大，棉纤维素的相对结晶度逐渐减小。     

Effects of surface flaws on the wettability of solids

Wetting hysteresis, or the variability of contact angle, is recognized to be caused by several phenomena. In particular, we consider it to be due to heterogeneity of the solid surface in contact with the liquid. Results describing the deformation of an initially straight triple line in the proximity of an isolated, small, energetic inhomogeneity are summarized. The theory is extended to describe the behaviour of a wetting front near a circular, high-energy (i.e. corresponding to zero intrinsic contact angle) flaw of dimensions comparable to those of the triple line distortion. A simple model is proposed to explain the breakaway of the isthmus of liquid connecting the flaw to the bulk liquid. Separation time is found to be proportional to ^-5, where 0 is the intrinsic contact angle of the solid/ liquid system. The behaviour of a triple line on a solid possessing a randomly distributed population of identical, small, circular flaws is considered. Contact angle hysteresis can thus be explained, as can the noise often observed in a (dynamic) Wilhelmy plate experiment. A simple statistical model is proposed in which random force fluctuations related to a moving triple line are shown to correspond to the Poisson process of probability theory.     

用分子动力学模拟研究丁腈橡胶/顺丁橡胶共混胶的相容性及耐低温性能

为提高丁腈橡胶(NBR)的耐低温性能,选择耐寒性能较好的顺丁橡胶(BR)按不同比例与其共混,采用分子动力学模拟的方法对NBR/BR共混胶的相容性和玻璃化转变温度进行了仿真计算。结果表明,NBR与BR在一定配比范围内可以相容。通过对比BR用量不同共混胶的Flory-Huggins相互作用参数和分子间径向分布函数关系图,可知当共混胶中BR的质量分数低于20%时两种橡胶的相容性较好,高于30%后二者相容性较差,甚至不相容。随着BR用量的增加,共混胶的玻璃化转变温度逐渐降低,BR质量分数为20%时共混胶的玻璃化转变温度为213 K,较纯NBR降低了18 K,有效提高了共混胶的耐低温性能。     

Effect of low molecular weight polybutadiene as processing aid on properties of silica‐filled styrene–butadiene rubber compounds

Because silica has strong filler–filler interactions, a silica‐filled rubber compound shows a poor filler dispersion compared to a carbon black‐filled one. Improvement of the filler dispersion in silica‐filled styrene–butadiene rubber (SBR) compounds was studied using low molecular weight polybutadiene (liquid PBD) with the high content of 1,2‐unit. By adding the liquid PBD to the silica‐filled SBR compound, the filler dispersion and flow property are improved. The cure time and cure rate become faster as the 1,2‐unit content of the liquid PBD increases for the compounds containing the liquid PBD. The crosslink density increases linearly with increase in the 1,2‐unit content of the liquid PBD. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3135–3140, 2003     

Thermal decomposition of alkyl ammonium ions and its effects on surface polarity of organically treated nanoclay

The surface free energy and surface polarity of organically modified montmorillonite clay change when exposed to elevated temperatures. This was verified in this study using contact angle measurements and Wu's harmonic-mean equation. It was observed that the surface polarity of organically modified clay measured from the values of contact angle of water and diiodomethane reduced significantly owing to thermal degradation of the organic modifier of clay, the latter was confirmed by Fourier transform infra-red spectroscopy. As a consequence, nonpolar polymer, polypropylene (PP), was found to spread more on heat treated surface of organically modified clay than a polar polymer, polyamide 6 (PA6). The ramification of these phenomena on blending of PP, PA6, and organically modified clay is discussed.     

Effect of fluid velocity and temperature on the corrosion mechanism of low carbon steel in industrial water in the absence and presence of 2-hydrazino benzothiazole

This work was carried out to study the inhibition mechanism of volatile corrosion inhibitors (VCIs) such as 2-hydrazinobenzothiazole (2-HBTA) on the corrosion of low carbon steel in industrial water by using polarization and mass loss measurement. It was found that 2-HBTA revealed good performance as inhibitor for low carbon steel corrosion in industrial water. After some time, the performance decreased due to the volatility of these kinds of inhibitors away from the open system unlike the closed system. The experimental data indicated that the inhibitive performance of 2-HBTA for low carbon steel was improved with increasing of concentration up to the critical concentration (4.24×10⁻³M). The adsorption behavior of 2-HBTA was found to obey Langmuir’s adsorption isotherm. The thermodynamic parameters of adsorption process and activation energy were obtained from polarization technique. Scanning electron microscopy (SEM) was performed to characterize the film formed on the surface. Box-Wilson statistical method was employed to correlate the results obtained, and the optimization of fluid velocity, temperature and concentration of inhibitor by using Box-Wilson statistical method was evaluated.     

Influence of gel and molecular weight on the properties of natural rubber

The influence of gel and molecular weight on the properties of natural rubber has been described. Crystallization, stress relaxation and orientation properties of different samples have been studied. Samples having different gel contents but similar molecular weights and samples having the same gel content with varying molecular weights have been prepared by extracting whole natural rubber. The gel content was varied from 1.5 to 29% and molecular weight from 1 × 10⁵ to 9.9 × 10⁵ g mol⁻¹. The gels reduce the overall crystallinity measured by differential scanning calorimetric experiments after freezing the samples for different time periods at −15°C. They also have a stiffening effect on the tensile relaxation modulus and decrease the rate of relaxation significantly. Birefringence, which measures the orientation and stress-induced crystallization, increases with time at high elongation for samples containing gels. At lower elongation, however, the birefringence of unvulcanized samples decreases with time. This decrease is less for gel samples. Natural rubbers of high molecular weight behave similarly in the above properties when compared to low molecular weight samples. The effect of gel is more predominant than that of molecular weight.     

Controlling the characteristics of butadiene rubber on the basis of molecular weight distribution

Mathematical modeling of the synthesis of diene rubber on a neodymium-based catalytic system is performed for a cascade of continuous reactors. The influence of operating parameters on molecular weight distribution and, as a consequence, on molecular weight characteristics and physicomechanical properties of the synthesized polymer is studied. The averaging of molecular weight characteristics obtained by mixing the polymers from the cascades of reactors with various process modes is simulated.     

Synthesis and characterization of maleinized‐silylated low molecular weight guayule rubber (MASiGR)

Maleinization followed by silylation of low molecular weight guayule rubber was accomplished for the first time via a two‐step process. Maleinization was first effected by grafting maleic anhydride onto guayule rubber under the influence of benzoyl peroxide catalyst to give maleinized guayule rubber (MAGR). The maleinized rubber was then further derivatized via hydrosilylation with dichloromethyl silane and chloroplatinic acid (Speier's catalyst) to give maleinized‐silylated guayule rubber (MASiGR). The silylated polymer (MASiGR) was further functionalized by reaction with ethanol or aqueous ammonia to produce ethoxysilane and silanol moieties, respectively. The products were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H‐, ¹³C‐, and ²⁹Si‐ nuclear magnetic resonance spectroscopy (NMR). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 754–761, 2001     

相对分子质量及其分布对高反式1，4-丁二烯-异戊二烯共聚橡胶性能的影响

研究相对分子质量(门尼粘度)及其分布对反式1,4-丁二烯-异戊二烯共聚橡胶(TBIR)性能的影响。结果表明,TBIR的塑炼、混炼性能随着门尼粘度的减小逐渐改善,门尼粘度大于60的TBIR混炼难度增大、加工性能变差;TBIR的综合物理性能随着门尼粘度的增大而提高,但当门尼粘度大于55之后胶料物理性能和动态性能改善效果不显著,TBIR胶料综合性能在门尼粘度为50～60时达到最佳。相对分子质量分布呈双峰的TBIR生胶和硫化胶的强伸性能、磨耗性能和生热性能较优;相对分子质量分布呈单峰的TBIR硫化胶耐屈挠性能得到很大提高。     

Synthesis and microstructural characterization of low to high molecular weight poly(vinylphosphonic acid)s: effect of molecular weight and temperature on acidity and polyelectrolyte behavior

Poly(vinylphosphonic acid) (PVPA) was synthesized by free radical polymerization of vinylphosphonic acid (VPA) in different solvents. Bromotrichloromethane as a chain transfer agent (CTA) was used in some experiments to control molecular weight of the PVPA. The effects of solvent type and initiator and CTA concentrations on the microstructure, molecular weight and stereoregularity of the resulting PVPA was extensively investigated by FTIR, ¹HNMR, ³¹PNMR and elemental analysis. Polymers with a number-average molecular weight (M_n) in the range of 1550 to 42,190 gmol^?1 were prepared. High molecular weight PVPA with M_n of 42,190 gmol^?1 was obtained from aqueous solution polymerization of VPA with initiator/monomer molar ratio of 0.16/100 at 80°C. Molecular weight decreased with increasing the concentration of initiator and CTA. ¹HNMR spectra were used to investigate tetrad sequences for the methylene protons of PVPA, from which stereochemical information of the polymer chain was obtained. Tetrad sequences were also calculated by Bernoullian probabilities. Moreover, the percent of head-to-head and tail-to-tail irregularities of the resulting PVPA were obtained to be in the range of 16.6–58% depending on the reaction conditions. The PVPA synthesized in acetic anhydride as a solvent had highest amount of the irregularities due to the high reaction rate, which does not allow controlling the structure. Furthermore, due to the importance of PVPA in the proton exchange membranes (PEMs), the effects of molecular weight and temperature on the acidity and titration behavior of PVPA polyelectrolyte were investigated. It was found that molecular weight has no significant effect on the acidity and dissociation of protons at operational conditions of degree of dissociation lower than 0.5. It was also found that by increasing the temperature, pH values were decreased, meaning that dissociation of protons and consequently the proton conductivity of PVPA membranes can be affected by temperature. Titration behavior of PVPA also showed that the PVPA has a behavior similar to a monoprotic acid.     

The effect of nature of raw coal on the adhesion of bacteria to coal surface

The surface properties of coal and solution pH play a major role in determining the adhesion of microorganisms. In this study, three Indian coal samples with different compositions have been used and the adhesion of the bacterium Bacillus polymyxa to these coals has been investigated. It was found that due to the high ash content of coal, the zeta-potential was negative over most of the pH range which is close to the values exhibited by pure quartz as well as B. polymyxa. Similarly, the surface free energy components of coal (derived from contact angle measurements) showed that the electron-donor component increased with ash content. Adhesion experiments revealed that maximum adhesion of the bacterium B. polymyxa occurred on to the coal samples around the point-of-zero-charge of the coal and the bacterium i.e. about pH 2. Further, adhesion was found to be dependent on the ash content and the surface free energy of the coals.     

Influence of temperature,molecular weight,and molecular weight dispersity on the surface tension of PS,PP, and PE. I. Experimental

In this work, the influence of temperature, molecular weight (M?_n), and molecular weight dispersity (MWD) on the surface tension of polystyrene (PS) was evaluated using the pendant drop method. The influence of temperature on the surface tension of isotatic polypropylene (i‐PP) and of linear low‐density polyethylene (LLDPE) was also studied here. It was shown that surface tension decreases linearly with increasing temperature for all the polymers studied. The temperature coefficient ?dγ/dT (where γ is the surface tension, and T, the temperature) was shown to decrease with increasing molecular weight and to increase with increasing MWD. The surface tension of PS increased when the molecular weight was varied from 3400 to 41,200 g/mol. When the molecular weight of PS was further increased, the surface tension was shown to level off. The surface tension was shown to decrease with increasing molecular weight distribution. Contact angles formed by drops of diiomethane and water on films of PS with different molecular weights were measured at 20°C. The surface energies of those polymers were then evaluated using the values of the different pairs of contact angles obtained here using two different models: the harmonic mean equation and the geometric mean equation. It was shown that the values of the surface energy obtained are slightly less than are the ones extrapolated from surface‐tension measurements in the rubbery state. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1907–1920, 2001     

Influence of temperature,molecular weight,and molecular weight dispersity on the surface tension of polystyrene,polypropylene, and polyethylene. II. Theoretical

Experimental data for the surface tension of polystyrenes of different molecular weights (3400–200,000) and different molecular weight dispersities (1–3) and of different polyolefins are compared with the predictions of the Patterson–Rastogi and Dee–Sauer cell theories, which infer the surface tension from pressure–volume–temperature (PVT) data. PVT data for these polymers were obtained from the literature and experimentally and are fitted to the Flory–Orwoll–Vrij equation of state. Both theories predict that the surface tension will decrease linearly with increasing temperature and increase with molecular weight, thereby corroborating the experimental data. However, both theories underestimate the entropy change in the surface formation per unit area at a constant volume for low molecular weight and polydisperse systems and underestimate the effect of molecular weight dispersity on surface tension. Both theories feature two parameters, m and b, that quantify the enthalpic and entropic contributions to surface tension. The theoretical predictions are fitted to the experimental data for monodisperse polystyrene (with a molecular weight above the molecular weight of entanglement), polypropylene, and linear low‐density polyethylene to quantify the enthalpic contribution to surface tension. b is then evaluated as a function of molecular weight and molecular weight dispersity and is found to decrease with increasing molecular weight and to increase with increasing molecular weight dispersity, showing that end‐group excess at the surface has some effect on surface tension. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2201–2212, 2002     

Effect of molecular weight on the surface morphology of crosslinked polymer particles in the RITP-dispersion polymerization

The RITP (reverse iodine transfer polymerization)-dispersion polymerization of methyl methacrylate (MMA) was conducted and the molecular weight and SEM images of them were investigated to propose the mechanism of the formation of surface morphology in crosslinked polymers. The morphology of the crosslinked particles varied depending on the sorts and contents of the crosslinking agents and iodine. As the iodine content increased under the same content of the crosslinking agent, the average molecular weight of the polymers [uncrosslinked portion of the polymers] decreased and the surface roughness simultaneously reduced. On the other hand, as the contents of the crosslinking agent increased, the molecular weight of polymers reduced and the surface morphology changed from smooth to rough in the absence of iodine. On the other hand, was the molecular weight was barely changed and the solubility increased upon iodine. Thus the mechanism of the formation of crosslinked polymers in the RITP-dispersion polymerization was proposed as the following; when crosslinking agent and iodine were simultaneously involved, the low molecular weight of polymers were first formed due to the effect of iodine and then the crosslinking was taking place, resulting in that iodine was a critical factor in controlling the molecular weight, particle size, solubility and the surface morphology in the crosslinked polymer particles.