The surface embrittlement of a ductile blend due to a brittle paint layer

The surface embrittlement phenomenon has been studied on a coated polymer by means of instrumented falling weight impact tests. The specimens are made of a ductile blend, used in the car industry, coated with a double layer paint system composed of a primer and a top coat. The energy absorbed during the impact test is correlated with the viscoelastic spectra and tensile properties of both the blend and paint system components. The viscoelasticity of the coating system is found to be the crucial parameter of the embrittlement. In the case of a brittle coating its thickness must exceed a critical value to embrittle the substrate.     

加氢反应器回火脆化动力学模型

基于晶界偏析理论,以广泛应用于加氢反应器的材料2 25Cr 1Mo钢为研究对象,以2 25Cr 1Mo钢中杂质元素P的晶界偏析为基础,研究加氢反应器回火脆化动力学,建立加氢反应器长期使用过程中产生回火脆化动力学模型(混合模型),为在役加氢反应器材料损伤的研究以及寿命预测提供理论基础。     

Mechanism of the thermal decomposition of bisphenol C polycarbonate: nature of its fire resistance

Quantum chemical methods have been used to identify reaction pathways of the thermal decomposition of bisphenol C polycarbonate, one of the most fire-resistant polymers known to the scientific community. Despite substantial interest in its unusual high-temperature behavior, the mechanism of its thermal decomposition has been unknown. On the basis of computational results, a mechanism is proposed where the main feature is a shift of Cl atom from the β-styrene position to the adjacent aromatic ring, which leads to crosslinking and cyclization of the polymer. The proposed mechanism is consistent with experimental observations of char, HCl, and CO₂ as the main pyrolysis products.     

Physical aging of bisphenol A polycarbonate

The physical aging of bisphenol A polycarbonate was studied using the differential scanning calorimetry technique. Cowie and Ferguson's model and Williams‐Watts function were used to analyze the data. It is confirmed that the relation ΔH_∞(T_a) = ΔC_p(T_g − T_a), where ΔH_∞(T_a) is the value of the aging enthalpy for t = ∞, T_a the aging temperature, and ΔC_p the difference in the specific heat above and below the glass transition temperature (T_g), can be used to study quantitatively the physical aging of bisphenol A polycarbonate. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1646–1648, 1999     

弹性零件镀锡氢脆的预防及消除

探讨了弹性零件碱性镀锡产生氢脆的原因并提出了预防及消除措施。     

含能材料冲击波引发判据的分析

分析含能材料的五种典型冲击波引发的判据和有关数据,认为目前的判据局限于没有考虑装药微结构的影响。据此,提出了用局部化因子修正原判据的新思想。     

A novel approach to predict the recovery time of shape memory polymers

In this paper a novel approach is presented for prediction of the recovery time for a shape memory polymer. The Transient Stress Dip Tests of Fotheringham and Cherry are used to determine the two parameters of a Kelvin-Voigt element. The characteristic retardation time of this element can then be calculated to predict the recovery time. It is shown that this approach is successful in predicting the recovery times for a shape memory polymer drawn and recovered under a range of temperatures. Furthermore it is shown that the ratio of the recovery stress to the draw stress is independent of the drawing conditions to a very good approximation.     

Molecular simulations of the solubility of gases in polyethylene below its melting temperature

We have employed Monte Carlo simulations in the osmotic ensemble to study the solubility of three different gases (N₂, CH₄, CO₂) in polyethylene. The simulations are performed at temperatures below the polymer melting point. Although under such conditions, polyethylene is in a semicrystalline state, we have used simulation boxes containing only a purely amorphous material. We show that under such circumstances, computed solubilities are 4-5 times larger than experimental data. We therefore introduce an original use of the osmotic ensemble to implicitly account for the effects of the complex morphology of semicrystalline materials on gas solubility. We have made the assumption that i) the network formed by polymer chains trapped between different crystallites and ii) the changes in local density from crystalline regions to purely amorphous regions, may be both represented by an ad-hoc constraint exerted on the amorphous phase. A single constraint value emerges, independent of the gas nature, characteristic of the crystalline degree of the polymer. It is concluded that the role of this constraint is mostly to reproduce the effective density of the permeable phase of the real material, indirectly giving insights into the morphology of a semicrystalline polymer.     

Miscibility study of polycarbonate and SBS triblock copolymer blends

Polymer blends of Polycarbonate (PC) and Styrene-Butadiene-Styrene triblock (SBS) have been investigated. SBS copolymers have four different styrenic contents, three of which are linear SBS. PC and PS blends are partially miscible as revealed by dynamic mechanical analysis with two clear Tgs near 100–150°C. On the contrary, PC/SBS blends have only one Tg with a left shoulder. Based on the PS domain model of pure SBS, we suggest a micelle model based on the structure when the micelle and absorb PC in the PC/SBS blends. The micelle plays an important role in improving the miscibility. The proposed micelle model has been empolyed to interpret the testing results, such as toughness, impact strength, dynamic mechanical property and SEM morphologies. This proposed micelle model seems a worth-while method to explain the properties of partialtly miscible blends of PC and SBS.     

聚碳酸酯老化行为研究进展

双酚A型聚碳酸酯性能优异,应用广泛。但在户外使用时,由于光、一氧和湿度等环境因素的作用,导致聚碳酸酯力学强度和外观发生变化。为提高PC的抗老化性能,必须通过研究。充分认识聚碳酸酯的老化反应和老化进程。综述了近年来聚碳酸酯老化行为的研究,并提出存在的问题和今后研究的方向。     

Boiling water aging of polycarbonate and polycarbonate/acrylonitrile–butadiene–styrene resin and polycarbonate/low‐density polyester blends

The effects of boiling water on the mechanical and thermal properties and morphologies of polycarbonate (PC), PC/acrylonitrile–butadiene–styrene resin (PC/ABS), and PC/low‐density polyester (PC/LDPE) blends (compositions of PC/ABS and PC/LDPE blends were 80/20) were studied. PC and the PC/ABS blend had a transition from ductile to brittle materials after boiling water aging. The PC/LDPE blend was more resistant to boiling water aging than PC and the PC/ABS blend. The thermal properties of glass‐transition temperature (T_g) and melting temperature (T_m) in PC and the blends were measured by DSC. The T_g of PC and PC in the PC/ABS and PC/LDPE blends decreased after aging. The T_g of the ABS component in the PC/ABS blend did not change after aging. The supersaturated water in PC clustered around impurities or air bubbles leading to the formation of microcracks, which was the primary reason for the ductile–brittle transition in PC, and the microcracks could not recover after PC was treated at 160°C for 6 h. The PC/ABS blend showed slightly higher resistance to boiling water than did PC. The highest resistance to boiling water of the PC/LDPE blend may be attributed to its special structural morphology. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 589–595, 2003     

AV铜套(面板)脆裂原因分析及解决方案

介绍了AV铜套(面板)制作工艺及其传统的电镀工艺。对AV铜套(面板)电镀后产生的脆裂现象进行了描述。从材质及电镀工艺2个方面对脆裂原因进行了分析。结果发现,产品不经过酸洗就不会引起氢脆。从而提出了解决方法:产品除油后用酸盐活化替代酸洗。     

Non-linear, rate-dependent strain-hardening behavior of polymer glasses

This study is concerned with the finite, large strain deformation behavior of polymeric glasses. True stress-strain curves in uniaxial compression obtained for five different polymeric glasses: polycarbonate, polystyrene, poly(2,6-dimethyl-1,4-phenylene oxide), and linear and cross-linked poly(methylmethacrylate), revealed a strain-hardening response during plastic deformation that is strain-rate dependent and deviates from neo-Hookean behavior. An empirical modification of the so-called compressible Leonov model by a strain dependent activation volume is suggested, which describes the strain-rate dependent large strain behavior of these glassy polymers in good agreement with experimental data.     

缓冷玻璃态ABS在拉伸应变状态下的老化行为

用万能拉伸实验机和差示扫描量热仪(DSC)对物理老化和应变老化的ABS试样进行研究。力学性能测试结果表明:在相同老化时间内,应变老化试样的屈服应力和弹性模量高于物理老化试样,而断裂伸长率却小于物理老化试样。DSC测试表明:在相同老化时间内,应变老化试样比物理老化试样的热流吸收峰面积更大,说明应变老化试样形成了与物理老化试样不同的结构。     

Analysis of agglomerate dispersion mechanisms of multiwalled carbon nanotubes during melt mixing in polycarbonate

Dispersion of primary nanotube agglomerates in polymer melts is one of the difficult tasks when applying melt mixing for nanocomposite preparation. Hence, there is a need for a better understanding of the ongoing processes. Filler agglomerates generally undergo dispersion by rupture and erosion mechanisms, which usually occur simultaneously. To analyse these mechanisms and their corresponding dispersion kinetics 1 wt% multiwalled carbon nanotubes (MWNT) were incorporated into polycarbonate using a microcompounder. Different mixing speeds at constant melt temperature were applied thereby changing the applied stress. The states of MWNT agglomerate dispersion at different mixing times were assessed by quantifying the agglomerate area ratio and particle size distribution using image analysis of optical transmission micrographs. A model is proposed to estimate the fractions of rupture and erosion mechanisms during agglomerate dispersion. At low mixing speeds, the dispersion was found to be governed by both mechanisms, whereas rupture dominance increases with increasing mixing speed. Further, the relationship between electrical resistivity and dispersion was studied indicating a critical behaviour. A dependency on the amount of dispersed nanotubes was found only in a certain range of state of dispersion.     

Modeling of hydration reactions using neural networks to predict the average properties of cement paste

This paper presents a hydration model that describes the evolution of cement paste microstructure as a function of the changing composition of the hydration products. The hydration model extends an earlier version by considering the reduction in the hydration rate that occurs due to the reduction of free water and the reduction of the interfacial area of contact between the free water and the hydration products. The BP Neural Network method is used to determine the coefficients of the model. Using the proposed model, this paper predicts the following properties of hardening cement paste: the degree of hydration, the rate of heat evolution, the relative humidity and the total porosity. The agreement between simulation and experimental results proves that the new model is quite effective and potentially useful as a component within larger-scale models designed to predict the performance of concrete structures.     

Inhibition of corrosion and hydrogen embrittlement of a HSLA steel in 0.5m H2SO4 by nitrile compounds

The inhibitive action of valeronitrile, benzonitrile and derivatives of benzonitrile on the corrosion and hydrogen embrittlement behaviour of HSLA steel in 0.5m H2SO4 was investigated. All these inhibitors reduced the corrosion rate of the steel with naphthonitrile showing the highest inhibitive efficiency and valeronitrile the lowest. All the inhibitors adsorbed on the steel as per the Temkin adsorption isotherm. The steel become less active on the addition of benzonitrile, 3-chlorobenzonitrile, 4-chlorobenzonitrile, 4-methylbenzonitrile and naphthonitrile to the acid while valeronitrile and 2-chlorobenzonitrile made the steel more active. Naphthonitrile reduced the rate of the hydrogen evolution reaction most efficiently. Derivatives of benzonitrile inhibited hydrogen absorption most effectively.     

Dispersion, agglomeration, and network formation of multiwalled carbon nanotubes in polycarbonate melts

Three different industrially available multiwalled carbon nanotube (MWNT) materials were directly incorporated into polycarbonate by melt mixing using a small-scale compounder. Despite of similar aspect ratios the electrical percolation behaviour was different. TEM investigations reveal significant differences in the nanotube dispersion which can be attributed to different dispersability of the raw MWNT materials. It is shown that the investigation of the sedimentation behaviour of aqueous MWNT dispersions is a simple method to estimate the nanotube dispersability.The relationships between melt processing conditions and MWNT dispersion and distribution were studied on polycarbonate samples containing 0.875 wt% MWNT prepared by masterbatch dilution. During melt mixing only high shear forces can provide suitable MWNT dispersion because firstly the MWNT disentanglement is facilitated and secondly secondary agglomeration is prevented. At low shear agglomeration of formerly well dispersed MWNT could be observed. During hot pressing the network or MWNT arrangement and the resulting electrical conductivity can be manipulated by the processing conditions like melt temperature and pressing speed. A certain nanotube agglomeration can enhance the development of an electrical percolated network as shown by dielectric spectroscopy.     

Evaporation and Diffusion Transport Properties and Mechanical Properties of Alginate Dried Film

The effects of alginate concentration and drying temperature on drying kinetics/characteristics of alginate solution and mechanical property of formed solid films were examined. Solid films were fabricated through thin-layer drying of 1 to 4%w/w sodium alginate solution at 40, 60, and 80°C using the solvent-evaporation method. The water weight loss profile of alginate solution undergoing drying was recorded with time. The polymer weight of all solid films was kept constant. The plasticity of films was evaluated using thermomechanical analyzer. The findings indicated that both constant rate and falling rate periods existed during drying of dilute alginate solution or at low drying temperature since both surface and core waters were available for drying. The falling rate period dominated in drying of an alginate solution of high polymer concentration and at high drying temperatures with internal diffusion being the governing transport phenomenon for water. In the latter, an exponential relationship between water content and drying time was obtained. The drying process of 4%w/w alginate solution at 60 and 80°C was relatively simple as there was only a single drying stage, viz. the falling rate period requiring no consideration of critical moisture content. The drying rate was faster than those obtained from the dilute alginate solution or conducted at low temperature, such as 40°C. The plasticity attributes of films prepared from 4%w/w alginate solution can be modulated to a degree similar to films prepared from dilute alginate solution or dried at low temperature via changing the drying temperature between 60 and 80°C.