乳胶／EVA／LDPE／PVC四元共混橡塑并用发泡的研究

采用模压发泡一次成型法研究了橡塑并用,乳胶/EVA/LDPE/PVC四元共混发泡材料的制备,着重讨论了配方和加工工艺、橡塑比、交联剂、发泡剂、填料等用量对发泡体性能的影响,交联与发泡的协调与配合,并用电镜扫描观察了四元动态硫化共混物材料和共混交联发泡体的断面结构。实验结果表明,当橡塑比R/P=20/80时,共混发泡体的密度0.10g/cm~3,扯断强度1.15MPa,断裂伸长率180％,硬度(邵氏A)36,挠曲>4万次,适合于制作轻质泡沫衬垫或包装材料;当橡塑比R/P=5/95时,发泡体密度(g/cm~3)0.23,扯断强度2.13MPa、断裂伸长率(％)243、硬度60(邵氏A)、挠曲>4万次,成品适合于制作大、中底等鞋用材料。     

LDPE／CPE／EVA三元共混发泡体系的研究

采用模压法研究了 LDPE/CPE/EVA 三元共混发泡体系的工艺技术,着重讨论了 LDPE/CPE/EVA 共混、交联剂和填充剂用量等因素对发泡材料物理机械性能的影响。     

EVA／EPDM／IR／IIR共混发泡材料的研制与应用

进行了ＥＶＡ／ＥＰＤＭ／ＩＲ三元共混和ＥＶＡ／ＥＰＤＭ／ＩＲ／ＩＩＲ四元共混发泡材料的研制,经物性对比表明：共混发泡材料的物性较非共混发泡普遍提高。ＥＰＤＭ的混入可以增加发泡材料的拉伸强度和撕裂强度,同时降低收缩率和永久压缩变形;ＩＩＲ的混入除具备ＥＰＤＭ的优点外尚对提高发泡材料的柔软度有帮助;ＩＲ的混入仅改善发泡材料二次热压成型制品表面的清晰度。     

EVA／EPDM／PVC三元塑料合金软质泡沫体的生产及其应用

采用物理共混及化学交联模压发泡工艺生产乙烯－醋酸乙烯酯共聚物（ＥＶＡ）／三元乙丙橡胶（ＥＰＤＭ）／聚氯乙烯（ＰＶＣ）三元塑料合金软质泡沫体。讨论了该体系的相容性、共交联与发泡的适配等问题，介绍了其复合衬垫的制造工艺及特点，生产实践证明，该材料的复合衬垫可完全替代国外同类产品。     

PVC／LDPE／EVA三元共混发泡体系的研究

本文研究了 PVC/LDPE/EVA 三元共混发泡体系的模压发泡工艺,主要讨论了工艺条件、组份及用量等因素对发泡体系性能的影响,并用扫描电镜(SEM)观察了泡孔结构的特点,所制泡沫塑料的容重为0.2～0.24kg/m~3性能良好,可用作鞋类和包装材料。     

CM与PVC共混发泡性能的研究

采用模压法进行发泡,研究了氯化聚乙烯(CM)与聚氯乙烯(PVC)的共混比和发泡剂用量对发泡体的泡体性能、泡孔结构的影响。结果表明,不同CM/PVC共混比的复合材料,随体系中CM的增加,发泡密度逐渐减小、泡孔体积和发泡倍率逐渐增大,当CM/PVC=50/50时,发泡材料具有较好的综合性能;改变共混体系中发泡剂AC的用量,测试泡体性能及观察泡孔结构得出,随AC发泡剂用量的增加,发泡材料的发泡密度减小,其相应的物理机械性能如拉伸强度、撕裂强度逐渐降低。     

PVC／LDPE／EVA三元共混物发泡体系的研究

采用模压发泡工艺研究了PVC/LDPE/EVA共混物的发泡体系,主要讨论了工艺条件、组分及用量等对发泡体性能的影响,并用扫描电镜(SEM)观察了泡孔结构的特点,制得泡沫微孔塑料的容重为0.2～0.24kg/m~3,性能良好,可用作鞋类和包装材料。     

EVA／EPDM／PVC三元聚合物合金软质泡沫体的制备及其在复合衬垫中的应用

采用物理共混以及化学交联模压发泡成型工艺制备聚乙烯－醋酸乙烯酯（ＥＶＡ）／乙丙橡胶（ＥＰＤＭ）／聚氯乙烯（ＰＶＣ）三元聚合物合金软泡沫体，并制成贴布复合衬垫。讨论了该体系的相容性，动态共交联与发泡的适配，以及贴布复合，造型等问题，结果表明，该衬垫可完合替代国外同类先进产品。     

性能可调的PVC／NBR发泡弹性体

研究了具有良好综合性能的HPVC/NBR共混体系的发泡 ,通过调节配方和工艺参数 ,制得了密度和硬度可大范围调节的发泡弹性体。考察了发泡剂、增塑剂、交联剂用量等配方参数对发泡弹性体密度、硬度及其他物理力学性能的影响。通过改变工艺参数 ,制得了泡孔大小不同的发泡体 ,并考察了泡孔大小对性能的影响。制得的发泡弹性体性能可以在如下范围调节 :密度 45～110 0kg/m3,邵氏硬度 (A) 0～ 2 7或更高。泡孔结构为闭孔 ,吸水率小于 0 0 5kg/m2 ,泡孔直径 3 0～ 60 0 μm。     

BA／VAc／AN／AA共聚乳液胶粘剂的研制

介绍了一种丙烯酸丁酯／醋酸乙烯酯／丙烯腈／丙烯酸四元共聚乳液胶粘剂的制备方法,该胶具有良好的耐黄变性,可替代天然橡胶胶乳应用于EVA低发泡体与腈纶绒面布的复合。     

Compact Swelling in Bi1.4Pb0.6Sr2Ca2Cu3.6Oy During the Formation of High-Tc Superconducting Phase

Compact swelling in Pb-doped Bi-Sr-Ca-Cu-O superconductor has been studied by observing the effects of the size of calcined powders, volatilization of materials, and sintering of high- T _c (2223) powders. The bulk density increases at the early stage of sintering, for about 20 h, and then decreases. Densification occurs when the low- T _c (2212) phase and a liquid phase exist, whereas dedensification occurs with the formation of the 2223 phase regardless of the presence of the liquid. Gas evolution from specimens does not appear to be responsible for compact swelling. Compact swelling is explained by anisotropic growth of thin, platelike 2223 grains in random orientation. When 2223 grains grow in a preferred direction, compact swelling is suppressed.     

Synthetic routes to nanoscale BxCyNz architectures

B_xC_yN_z nanoscale materials, hybrids of h-BN and graphite, have been recently synthesised using various techniques. Here, we present the latest advances in the synthesis and characterisation of B-C-N nanotubes and nanofibres. In particular, we focus on layered BC₂N, BN, BC and CN_x systems, reviewing their production methods as well as their structural and electronic properties. These materials may find important applications in the fabrication of nanotransistors, robust nanocomposites, conducting polymers, storage components and field emission sources.     

Microwave Dielectric Properties of CaTiO3-CaAl1/2Nb1/2O3 Ceramics Doped with Li3NbO4

The microwave dielectric properties of CaTi_{1− x} (Al_1/2Nb_1/2) _x O₃ solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO₃. The substitution of Ti⁴⁺ by Al³⁺/Nb⁵⁺ improved the quality factor Q of the sintered specimens. A small addition of Li₃NbO₄ (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛ_r) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τ_f) of −2 ppm/K. Li₃NbO₄ as a sintering additive had no harmful influence on τ_f of ceramics.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.     

Structure Evolution from Pb(Mg1/3Nb2/3)O3 to La(Mg2/3Nb1/3)O3

The crystal structure of lanthanum-modified lead magnesium niobates having composition (Pb_{1− x} La _x ) (Mg_{(1+ x )/3}-Nb_{(2− x )/3})O₃ with X = 0 to 1 was investigated by X-ray powder diffraction. It was found that the fundamental reflections from perovskite structure remain in the whole range of composition. The superlattice reflections from the A(B'_1/2-B"_1/2)O₃ ordered structure are also well preserved for La content greater than 50 at.%; however, a series of extra peaks of mixing indices appears, with intensities gradually enhanced with the increase of La content. For the complete substitution of Pb by La, a splitting of some reflections can be observed in the diffraction pattern. The results indicate that the crystal structure evolves continuously with the La content, from disordered cubic perovskite of space group Pm 3 m for X = 0, to ordered cubic perovskite of space group Fm 3 m for X = 0.5, distorted cubic perovskite of space group Pa 3 for 0.5 < X < 0.9, and finally to a rhombohedral perovskite, possibly belonging to the space group R 3 , for X ≥ 0.9. In the evolution of structure, a linear reduction of the lattice constant of the perovskite cell from 4.048 to 3.964 Å was observed.     

Dielectric-State Analysis in Solid-Solution Pb(Yb1/2Ta1/2)O3–Pb(Lu1/2Nb1/2)O3

The structure and temperature dependence of complex lead perovskite dielectrics were investigated for the system (1 − x )Pb(Yb_1/2Ta_1/2)O₃– x Pb(Lu_1/2Nb_1/2)O₃. Superlattice reflections for the compositions 0.8 < x < 1.0 were observed by X-ray diffractometry, and the temperature-composition dielectric-state diagram was determined. In the present study, the disordered middle composition, with 0.2 < x < 0.8, showed a diffuse paraelectric–ferroelectric phase transition, whereas the ordered end compositions, with 0 ≤ x < 0.2 and 0.8 < x ≤ 1.0, revealed successive sharp paraelectric–antiferroelectric and weak antiferroelectric–ferroelectric phase transitions. The dielectric state was confirmed by examining the variation of polarization ( P ) with electric field ( E ).