Fiber-forming properties of polymer mixture melts and properties of fibers on their basis

The fiber-forming properties of the following polymer mixture melts have been investigated: polypropylene-copolyamide (PP/CPA), polyoxymethylene-copolyamide (POM/CPA), POM-copolymer of ethylene and vinyl acetate (POM/EVAC), PP/EVAC, EVAC/CPA, and polypropylene-polyvinylalcohol (PP/PVA). The capability of the polymer mixture melts to fiber-form was estimated by degree of the polymer melt longitudinal deformation. It has been determined that the fiber-forming properties of polymer mixture melts can be regulated by changing the chemical nature of the mixture components, structure-formation processes and by introducing various additives of polymer and non-polymer nature into binary mixture. The mechanism of action of additives is connected with changing microrheology processes during mixture melt flowing under the influence of the specific interaction between polymer macromolecules and additives at the interphase. The complex threads from PP, POM or EVAC microfibers have been produced and the features of their structure and properties have been investigated. There are the following distinctive properties of the complex threads consisting of microfibers: high strength and initial modulus, high elasticity, exclusive softness, pleasant feel, coupling, capaciousness, and wool-likeness without special textural procedures, high sorption of moisture, dyes and other substances.     

Measurement of the elastic properties of polymer melts

A method and apparatus for measuring the elastic and other properties of polymers in the melt state is presented. The recoverable strain magnitude and the rate of strain recovery have been measured as a function of: applied shear rate, applied shear magnitude, temperature and molecular weight. The elastic properties indicate that there is an abrupt change or “transition” in the response of polystyrene melts at temperatures well above the glass transition. This abrupt change is found to be molecular weight dependent. The results are interpreted qualitatively in terms of molecular structure and practical processing operations. The possible relationship of this “transition” to T_u, is briefly discussed.     

Comparative evaluation of acoustical properties of heat-bonded and needle-punched fibrous materials prepared from polymer melts

Conclusions The acoustical properties of heat-bonded and needle-punched fibrous materials have been studied by the steady-state method.The basic structural and technological parameters which affect the sound-absorption coefficient of these materials have been established.It has been shown that heat-bonded fibrous materials have advantages over the needle-punched ones, since they ensure an equal sound-absorption coefficient at a lower thickness.Translated from Khimicheskie Volokna, No. 6, pp. 27–28, November–December, 1989.     

The extensional and failure properties of polymer melts

The extensional and failure properties of polystyrene melts were studied by pulling sample rods in a special “weight dropping” extensiometer. This apparatus allows pulling to long final lengths and at relatively high rates; except for the highest rates, the experiment is one of constant applied force. Various commercial (broad molecular weight distribution) and special (narrow molecular weight distribution) samples were studied at various temperatures and applied forces. The striking result was that the former (BMWD) samples stretched reasonably uniformly and displayed what has been described as “viscoelastic failure”; the latter (NMWD) samples necked in the final stages and showed what might be called “viscous” failure. In the case of the BMWD material, the stress–time behavior was analyzed theoretically by independently determining the parameters in a nonlinear constitutive equation from GPC and rheogoniometer (shear) data. The theoretical tensile stresses compared quite well with the experimental values. An interesting result came from comparing the complete viscoelastic theory with a viscous (Trouton viscosity) asymptote. These two theoretical curves closely approximated the experimental data until just short of the failure point; at this incipient point, the stresses from the complete theory grew to very large values compared with the viscous stresses. That is, the material could not relax fast enough to allow steady stresses to develop, and the sample failed shortly thereafter.     

The effect of temperature on the elastic properties of polymer melts

A correlation is developed between the melt elasticity and temperature, the melt elasticity being defined by the normal stress difference. The correlation follows the form of the Arrhenius equation, for the temperature range tested, for high density polyethylene and polypropylene melts. Measurements were taken using the capillary rheometer which is described in detail in the author's earlier publications. The author further presents a correlation between the pressure drop at the entrance of a capillary and the residual pressure at the exit of the capillary (exit pressure). The correlations presented in the paper support the author's earlier contention that the exit pressure is indeed a manifestation of elastic behavior.     

文丘里管结构对高浓度煤粉流动特征及压差特性的影响

研究粉煤密相气力输送系统高压、高浓度煤粉通过不同节流比(0.44、0.55、0.7)、收缩角(2.5°、5°、9°)、扩张角(2.5°、8°、13°)、喉段长度(23d、43d、80d)的文丘里管的流动特征和压差特性。结果表明,不同结构参数的文丘里管的量纲1化压力分布趋势一致,但程度不一。其中节流比影响最为显著,并最直接地影响煤粉流经文丘里管的压差。节流比越小,总压差越大,扩张段压差显著增大。其他结构参数在各自的结构序列下主要改变文丘里管内压力分布,而对总压差改变不大。2.5°收缩角的收缩段压差最大,高浓度体系下5°和9°收缩角的收缩段压差差别不大。80d喉段长度的喉段压差最大。8°扩张角的扩张段压差最小。引入固相动量通量,获得本系统内煤粉流经文丘里管的压降经验方程,大部分实验点的计算偏差在30%以内,方程计算效果较好。     

机械致荧光变色材料的分子结构特点及其对性能的影响

从荧光分子的结构设计及对性能的影响出发,综述了近年机械致荧光变色材料(MFC)的国内外最新进展,主要包括荧光分子骨架上引入脂肪链、荧光分子骨架上引入芳香环(或杂环)、荧光分子骨架上引入卤素原子、荧光分子骨架上引入氰基以及荧光分子结构的其他改变等。同时对该材料今后的发展趋势进行了分析与展望。研发固态下具有高荧光量子产率的智能发光体以及具有较好水溶性、成膜性和快速恢复性的MFC荧光材料将是今后该领域的主要目标。     

机械致荧光变色材料的分子结构特点及其对性能的影响

从荧光分子的结构设计及对性能的影响出发,综述了近年机械致荧光变色材料(MFC)的国内外最新进展,主要包括荧光分子骨架上引入脂肪链、荧光分子骨架上引入芳香环(或杂环)、荧光分子骨架上引入卤素原子、荧光分子骨架上引入氰基以及荧光分子结构的其他改变等。同时对该材料今后的发展趋势进行了分析与展望。研发固态下具有高荧光量子产率的智能发光体以及具有较好水溶性、成膜性和快速恢复性的MFC荧光材料将是今后该领域的主要目标。     

Dynamic characteristics of the high-speed process of spinning polymer melts

Conclusions A procedure has been given for calculating the instability in fibre diameter under the action of technological perturbations, which is based on the use of the dynamic characteristics of high-speed process of spinning polymer melts.It has been shown that the reaction of the high-speed spinning system to stepwise perturbations is less than the reaction to harmonic perturbations at the inherent frequency of the spinning system. The range of perturbation frequencies which adjoins the inherent frequency of the spinning system is very dangerous from the point of view of instabiity in the diameter of the spun fibres.The possibility of using dynamic characteristics to base requirements on accuracy in stabilization of technological parameters in the high-speed spinning process has been examined.Translated from Khimicheskie Volokna, No. 5, pp. 13–15, September–October, 1989.     

Influence of chitosan characteristics on polymer properties: II. Platinum sorption properties

The sorption of platinum on glutaraldehyde cross‐linked chitosan was investigated at pH 2, using several chitosan samples prepared from different origins and characterized by different mol fractions of N‐acetylation (F_A). The influence of material conditioning was also tested: chitosan was dissolved and then re‐precipitated and/or dried (using either oven‐drying or freeze‐drying). The influence of the different characteristics and treatments on both sorption isotherms and uptake kinetics was checked. Part I has studied the effect of preparation and source on sample crystallinity. Shrimp chitosan has a greater sorption affinity for platinum than fungal chitosan and squid chitosan respectively. Sorption kinetics were found comparable for fungal chitosan and shrimp chitosan, while diffusion was more restricted in squid chitosan due to the higher crystallinity. Decreasing the F_A increased sorption capacity for shrimp chitosan but decreased sorption levels for squid material. While F_A did not influence sorption kinetics for shrimp material it strongly decreased kinetics for squid chitosan. The type of drying procedure hardly affected sorption kinetics and isotherms but when a re‐precipitation step was included in the preparation procedure, the material had to be freeze‐dried to maintain high sorption properties. The freeze‐drying did not control sorption performance, except in the case of re‐precipitated material. © 2003 Society of Chemical Industry     

Effect of filler on rheologic and thermodynamic characteristics of binary polymeric mixture melts

Rheologic, thermodynamic, and mechanical loss tangent properties of a binary polymeric mixture were studied. The system was a mixture of poly(vinyl acetate) (PVA) with ethylenevinyl acetate copolymer (EVC) with varying concentrations of the polymer components and filler. A correlation between the above characteristics of the PVA/EVC two-phase mixture was found. This mixture was thermodynamically unstable (positive values of the interaction parameter, χ) practically over the entire range of compositions at temperatures of rehologic studies. The presence of a disperse filler raised the thermodynamic stability, that is, parameter χ decreased. Reversal of the sign of the temperature dependence of χ of a mixture with increasing concentration of filler was found. The variations of viscosity with the composition, temperature, and shear for the PVA/EVC mixture are ascribed to different levels of heterogeneity occurring in the process of the shear straining in the working unit of the rheometer. © 1993 John Wiley & Sons, Inc.     

Influence of ultrasound on the basic parameters of the extrusion of polymer melts

The process of imposing ultrasound and its influence on the rheological properties of polymers, the high-elasticity properties of extrudates, the changes in the power of ultrasonic vibrations absorbed by a polymer in the course of extrusion, and also on the strength properties of extrudates are considered.     

Effect of composition and processing on rheological properties of multicomponent polymer melts

Polyamide and polyether maleic anhydride were blended with carbon black at various compositions and processing conditions. The compositions were varied from 0/92/8 percent, 23/69/8 percent, 46/46/8 percent, 69/23/8 percent to 92/0/8 percent of polyamide/polyether maleic anhydride/carbon black. The polymer blends were processed by a Banbury roll mill and an extruder under various conditions and were spray dried. The effects of composition and processing conditions on steady state and dynamic viscoelastilc properties were determined. These effects were compared with the thermal and morphological properties of the blends.     

Influence of the structure characteristics of ordered mesoporous silica materials on their properties as supports for Ni-modified hydrogenation catalysts

The structure characteristics of Ni-modified (7 wt% Ni) mesoporous materials with cubic (Ia3d and Fm3m space groups) structure have been compared to that of the hexagonal MCM-41 material with uni- dimentional channel arrangement by X-ray diffraction and N₂ adsorption–desorption measurements. Thermal gravimetric analysis and toluene hydrogenation have been used for characterization of the reducibility of the supported Ni phase and its catalytic activity in this test reaction, respectively. The results from N₂ physisorption suggest that substantially higher pore blockage with Ni occurs when it is deposited on the 1D channel structure of MCM-41 compared to the cage-like pores of Fm3m and the interconnected pores of Ia3d material. It is proposed that the pore architecture determines the distribution of the oxide metal phase and its reducibility and strongly influences the hydrogenation activity of the catalysts.     

The influence of titanium dioxide on the rheological and extrusion properties of polymer melts

An experimental study of the influence of titanium dioxide (TiO₂) on the rheological and extrusion properties of five polymer melts (two low-density polyethylenes, two high-density polyethylenes, and a polystyrene) has been carried out. Increasing TiO₂ loading increases the shear viscosity η, with the extent of increase being greater at lower shear rates. At moderate and high TiO₂ loadings, the filled melts may possess yield values. Empirical equations relating viscosity to filler loading have been developed. The first normal stress difference was measured for the melts and found to increase with increasing TiO₂ loading. However, the extent of increase was less than found for the viscosity function and interpretation in terms of the theory of viscoelasticity suggests that the characteristic relaxation time of the melts decreases with increasing TiO₂ level. Empirical equations relating the first normal stress difference coefficient to volume fraction of the filler have been developed. Addition of TiO₂ is found to decrease extrudate swell and retard the occurrence of extrudate distortion.