Nanocomposites based on polyethylene and Mg-Al layered double hydroxide. I. Synthesis and characterization

Low density polyethylene (LDPE)/Mg-Al layered double hydroxide (LDH) nanocomposites have been synthesized with different compositions by melt-mixing technique using maleic anhydride grafted polyethylene as compatibilizer. LDH has been modified by sodium dodecylbenzene sulfonate using reconstruction method and characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The nanocomposites are characterized by different techniques such as, transmission electron microscopy (TEM), XRD and rheology. The TEM analysis shows a complex nature of particle dispersion in the polymer matrix with wide distribution of particles sizes and shapes. The rheological analysis showed significant changes in linear viscoelastic responses of the composites, even at very low concentration (2 phr) of LDH materials, in comparison to the pure polymer in low frequency regime in dynamic frequency sweep experiments. These changes are related to the LDHs-polymer chains interactions resulting in network-like structure.     

Stiffer and super-tough poly(butylene terephthalate) based blends by modification with phenoxy and maleated poly(ethylene-octene) copolymers

New super-tough poly(butylene terephthalate) (PBT) materials were obtained by melt blending PBT with both 20 wt% phenoxy (Ph) and 0-30 wt% maleic anhydride grafted poly(ethylene-octene) (mPEO) copolymers with different grafting levels. Ph was completely miscible in the PBT matrix. The presence of mPEO did not influence either the nature of the PBT-Ph matrix or the crystallization of PBT. The overall decrease in particle size and in interfacial tension upon grafting indicated that compatibilization had taken place. Super-tough (impact strength 23-fold that of the PBT) and stiffer PBT based blends were obtained at mPEO contents equal to or higher than 15%. The dependence of the critical inter-particle distance (τ_c), on both adhesion measured by means of the interfacial tension, and on the relation between the modulus of the matrix and that of the rubbery dispersed phase (E_m/E_d), is proposed.     

Time dependences of conduction and self‐heating in acetylene carbon black‐filled high‐density polyethylene composites

The time dependences of electrical conduction and self‐heating behaviors in high‐density polyethylene filled with acetylene carbon black of 0.082 in volume fraction are studied in relation to voltage and ambient temperature. The characteristic decay current constant τ_i, and the exponential growth time constant for self‐heating τ_g are determined for the samples under voltages U above the critical value U_c for the onset of self‐heating. The influences of voltage and ambient temperature on τ_i and τ_g as well as the amplitude of the low‐resistance to high‐resistance switching are discussed on the basis of the random resistor network (RRN) model and the relationship between U_c and the intrinsic resistivity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1124–1131, 2006     

振动剪切作用下聚合物熔体的非仿射网络结构模型——振动参数对聚合物熔体黏性的影响

利用非仿射网络结构本构模型分析了正弦脉动流场中振动参数对聚合物熔体黏性的影响作用，并从缠结密度的概念上来解释其影响规律。     

Pickup (critical) velocity of particles

This work presents experimental results on pickup velocity (critical velocity) measurements for a variety of particulate solids. The present experiments together with previously published experiments of a number of researchers encompass about 100 measurements of 24 materials for a wide range of particle sizes, shapes and densities. Based on the experimental results, three zones are defined by establishing simple relationships between the Reynolds and Archimedes numbers. The empirical relationships were further modified by taking into account the pipe diameter and particle shape (sphericity). The three-zone model was shown to reasonably correlate to Geldart's classification groups.     

PE-LLD／EVA／Mg（OH）2／复合阻燃剂高效无卤阻燃体系的研究

采用线形低密度聚乙烯/乙烯-醋酸乙烯共聚物作为复合材料主体,表面处理过的氢氧化镁(Mg(OH)2)为主阻燃剂,以微胶囊化红磷和自制硅类阻燃剂为核心的复合阻燃剂为阻燃增效剂,重点探讨了Mg(OH)2和复合阻燃剂的阻燃效果。结果表明,Mg(OH)2与复合阻燃剂并用具有良好的协同效应,当Mg(OH)2用量40份,复合阻燃剂5～7份时,可获得较高的氧指数,垂直燃烧试验通过FV0级,且材料抗静电能力提高,力学性能、加工性能较好。     

规整填料在铜洗塔中的应用研究

本文研究了铜洗液脱除合成气中少量ＣＯ、ＣＯ２的反应和传质吸收机理。分析了铜洗塔中应用高效规整填料所具有的技术优势，以及在设计改造中应注意的关键问题。模拟结果和应用效果表明，采用高效填料塔技术是合成氨装置扩大生产能力、提高合成气质量、降低成本的重要措施。     

印刷哈萨克斯拉夫粘连字符的切分方法

哈萨克斯拉夫图像文本经过行切分和列切分后,存在水平方向接触和垂直方向重叠的粘连字符。为提高字符识别率,依据字符连通域的最小外接矩形切分开垂直方向重叠的粘连字符图像块;利用判决条件:字符宽度概率密度分布图、字符图像块垂直投影的波峰数目和字符图像块垂直投影波峰的对称性,分离初始粘连字符图像块中正确的单个字符图像块和实际接触的粘连字符图像块;在允许的字符宽度范围内,寻找粘连字符图像垂直投影图的极小值点,以切分实际接触的粘连字符。实验结果表明,该方法泛化能力较好且识别率有明显提高。     

LDPE/石墨导电复合材料的研究

为了制备具有低渗滤阈值的导电复合材料，通过溶液插层法，选用三种不同的导电填料（石墨，膨胀石墨，膨化石墨），引入马来酸酐接枝聚乙烯。制备低密度聚乙烯/石墨导电复合材料，导电填料的结构对复合材料的电性能和力学性能有很大的影响，其中膨化石墨可使复合体系具有较低的导电渗滤阈值，但复合材料的力学性能较差。     

Development of a bio‐based composite material from soybean oil and keratin fibers

A novel bio‐based composite material, suitable for electronic as well as automotive and aeronautical applications, was developed from soybean oils and keratin feather fibers (KF). This environmentally friendly, low‐cost composite can be a substitute for petroleum‐based composite materials. Keratin fibers are a hollow, light, and tough material and are compatible with several soybean (S) resins, such as acrylated epoxidized soybean oil (AESO). The new KFS lightweight composites have a density ρ ≈ 1 g/cm³, when the KF volume fraction is 30%. The hollow keratin fibers were not filled by resin infusion and the composite retained a significant volume of air in the hollow structure of the fibers. Due to the retained air, the dielectric constant, k, of the composite material was in the range of 1.7–2.7, depending on the fiber volume fraction, and these values are significantly lower than the conventional silicon dioxide or epoxy, or polymer dielectric insulators. The coefficient of thermal expansion (CTE) of the 30 wt % composite was 67.4 ppm/°C; this value is low enough for electronic application and similar to the value of silicon materials or polyimides used in printed circuit boards. The water absorption of the AESO polymer was 0.5 wt % at equilibrium and the diffusion coefficient in the KFS composites was dependent on the keratin fiber content. The incorporation of keratin fibers in the soy oil polymer enhanced the mechanical properties such as storage modulus, fracture toughness, and flexural properties, ca. 100% increase at 30 vol %. The fracture energy of a single keratin fiber in the composite was determined to be about 3 kJ/m² with a fracture stress of about 100–200 MPa. Considerable improvements in the KFS composite properties should be possible by optimization of the resin structure and fiber selection. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1524–1538, 2005