Preparation of Encapsulated Polymer Adhesion Beads and Adhesion with Porous Fibers

Adhesion beads of 10–130 μm, prepared by suspension polymerization, were encapsulated by melamine–formaldehyde. The capsule-type adhesives prepared consist of core and shell structure where the core region is sticky and viscous and the shell region consists of a hard shell at room temperature. The air permeable pads are made by hot pressing the mixture of capsule-type adhesives and porous materials including charcoal chips and Camellia sinensis fibers, which have a porous structure. The interfacial adhesion between polymer adhesion bead and porous fibers after processing shows a good porous sheet structure, which can penetrate air.     

Effect of viscosity ratio of the components of thermoplastic and liquid-crystalline polymer blends on the properties

The effects of viscosity ratio on the rheological and mechanical properties of the blends of four thermoplastics of low viscosity and a liquid crystalline polymer (LCP) were studied. A polyamide of reduced crystallinity (amorphous PA), a polycarbonate (PC), a polyethylene-terephthalate (PET), and a cyclic polyolefin (COC) were investigated with the copolymer of 2-hydroxy-6-naphthoic acid (HNA) and 4-hydroxybenzoic acid (HBA) (Vectra A type LCP). The LCP content changed in the range of 0–50 w/w%. The mechanical properties were determined by tensile tests on injection molded test bars in parallel and perpendicular directions to the flow. Except for the PC/LCP blends, the viscosity decreased with increasing LCP content, the tensile strength increased significantly in the parallel and decreased in the perpendicular direction indicating formation of fibrillar phase morphology. In the case of PC/LCP blends, a reinforcing effect was observed at low LCP contents, but above 20 w/w% the viscosity increased and the parallel tensile strength dropped to the value measured in the perpendicular direction. The loss of the reinforcing effect might originate from chemical reactions of the two polymers.     

倒导数计时电位法研究

本文推导出倒导数计时电位法理论,实验结果与理论基本相符。本工作结果使计时电位法的信号灵敏度提高约一个数量级。     

Optimizing the accuracy and precision of the single‐pulse Laue technique for synchrotron photo‐crystallography

The accuracy that can be achieved in single‐pulse pump‐probe Laue experiments is discussed. It is shown that with careful tuning of the experimental conditions a reproducibility of the intensity ratios of equivalent intensities obtained in different measurements of 3–4% can be achieved. The single‐pulse experiments maximize the time resolution that can be achieved and, unlike stroboscopic techniques in which the pump‐probe cycle is rapidly repeated, minimize the temperature increase due to the laser exposure of the sample.     

Relationship between the flexural properties and specimen aspect ratio in unidirectional composites

It is well known that the bending test provides a simple and convenient way of measuring the strength of unidirectional composite materials and gives very repeatable results. The aim of this research work was to study and analyze the flexural properties of unidirectional reinforced carbon fiber/epoxy (UD) specimens subjected to three-point loading. The effect of span-to-thickness ratio (L/h) and width-to-thickness ratio (b/h) on the three-point bending of UD composites has been investigated. Results have shown that unidirectional composites exhibit a transition in the failure mode from shear delamination to fiber yield with the span-tothickness ratio (L/h) is increased. The observed experimental data are confirmed by theoretical considerations presented here. Using the classical beam theory the conclusions of the tests could be extended by applying some reasonable requirements and simple rational fractional functions identified. This made it possible to express the asymptotic values of the flexural strength, the flexural modulus and apparent shear stress in a form that is independent from the values of the span-to-thickness ratio applied, and characterize the bending behavior of the composite materials at a more exact level.     

OBTAINING THE CRITICAL DRAW RATIO OF DRAW RESONANCE IN MELT SPINNING FOR POWER LAW POLYMER FLUIDS

A direct difference method has been developed for Non-Newtonian power law fluids to solve the simultaneous non-linear partial differential equations of melt spinning,and to determine the critical draw ratio for draw resonance.The results show that for shear thin fluids,the logarithm of the critical draw ratio has a well defined linear relationship with the power index for isothermal and uniform tension melt spinning.When the power index approaches zero,the critical draw ratio points at unity,indicating no melt spinning can be processed stably for such fluids.For shear thick fluids,the critical draw ratio increases in a more rapid way with increasing the power index.     

Polypropylene-natural fibre composites. Analysis of fibre structure modification during compounding and its influence on the final properties

The final properties of composite materials are highly dependent on the residual geometrical parameters (length, diameter, aspect ratio), orientation and distribution of the fibres in the matrix, which in turn are related to the processing conditions. This study analysed the fibre structure variation during the processing of a polypropylene matrix reinforced with cellulose flax pulp for different reinforcement concentrations. The fibre's geometrical parameters, length, diameter and aspect ratio have been measured and their statistical distributions have been assessed for each concentration. Furthermore, the effect of the microstructure variation on the final mechanical properties was analysed. In particular, changes in the interfacial area were evaluated based on the hypothesis that the fibres were cylindrical in shape and considering the average values of the diameters and the lengths calculated using a statistical distribution approach. The fibre interfacial area after the process decreases as the fibre concentration increases and this evaluation explains how the adhesion methods that are used for fibre surface modification fail because of the decrement in the modifier interfacial density. The Halpin–Tsai approach was used to model the experimental data obtained from tensile tests for different composites, so as to confirm the effect of fibre parameters, such as aspect ratio and interfacial area values, in the PP/cellulose blends final properties.     

Synthesis of poly(butylene succinate) nanocomposites via in-situ interlayer polymerization: thermo-mechanical properties and morphology of the hybrid fibers

A series of poly(butylene succinate) (PBS) nanocomposites with the organoclay C₁₂PPh-Mica were synthesized by using the in-situ interlayer polycondensation of 1,4-butanediol with succinic acid. The PBS nanocomposites were melt-spun to produce monofilaments with various organoclay contents and draw ratios (DRs). The thermo-mechanical properties and morphologies of the PBS nanocomposites were determined using differential scanning calorimetry, thermogravimetric analysis, wide angle X-ray diffraction, transmission electron microscopy, and a universal tensile machine. Some of the clay particles were found to be well dispersed in the PBS matrix, with some agglomerated at a size level greater than approximately 20 nm. The thermal degradation properties of undrawn PBS hybrid fibers were found to improve with increasing clay content. The ultimate tensile strengths and initial moduli of the hybrid fibers increased with increasing clay content at DR = 1. However, the ultimate strengths were found to decrease markedly with increases in DR from 1 to 6. In contrast to the trend for the tensile strengths, the initial moduli of the hybrid fibers increased only slightly with increases in DR up to 6.