温差共混法制备聚丙烯／热致液晶原位增强复合材料

采用温差共混法制备了聚丙烯／热致液晶（PP／TLCP）原位增强复合材料，研究了其共混物微观形貌以及力学性能。SEM分析表明，TLCP在体系中的成纤效果受到其含量的影响，当TLCP含量达到30％时，体系的表层和芯层均形成取向良好的TLCP纤维。力学性能分析表明，当TLCP含量低于20％时，PP／TLCP共混物的拉伸强度和拉伸模量均随着TLCP含量的增加而提高，断裂伸长率则有所下降。     

TLCP/GF混杂增强聚醚砜酮复合材料的研究

用热致性液晶聚合物(TLCP)和玻璃纤维(GF)对二氮杂萘酮联苯结构聚醚砜酮(PPESK)进行混杂增强改性,用双螺杆挤出机通过熔融共混的方式制备了改性PPESK复合材料。研究了PPESK/TLCP、PPESK/TLCP/GF复合材料的加工性能和力学性能,并对复合材料的拉伸断面形貌进行观察。结果表明,随着TLCP用量的增加,熔体的粘度逐渐降低,加工流动性得到改善;TLCP/GF的混杂增强使PPESK复合材料的拉伸强度得到一定提高,冲击强度有所降低;TLCP用量小于10份时,TLCP以球状粒子或棒状形式存在,当TLCP用量为20份时,TLCP在材料中形成直径为亚微米数量级的高长径比微纤。     

剑麻纤维/玻璃纤维混杂增强聚丙烯复合材料的结构与性能

采用熔融共混和模压成型方法将废剑麻纤维(SF)和玻璃纤维(GF)混杂增强聚丙烯(PP)制备SF/GF/PP木塑复合材料.研究复合材料力学性能、热性能、晶型结构和微观结构,探讨混杂纤维增强基体树脂的界面行为.结果表明:所制得复合材料的冲击强度、弯曲强度和弯曲模量都有不同程度的提高.同时,热稳定性、PP相的结晶速率及结晶度也有所提高,晶态结构无变化,仍是典型的α晶型.     

滑石粉-玻纤增强聚丙烯复合材料

采用熔融共混法制备了玻纤(GF)/聚丙烯(PP)复合材料,考察了GF含量对GF/PP复合材料力学性能的影响。实验结果表明,在玻纤含量较低时,拉伸强度、弯曲强度和冲击强度伴随着玻纤含量的增加而提高。当GF质量分数为30%时,复合材料的力学性能处于最佳状态。在GF增强的基础上,采用滑石粉(Talc)与GF复合增强体系,制备了系列增强聚丙烯复合材料。考察了Talc含量对PP/Talc/GF复合材料力学性能的影响,Talc含量为5%时,复合材料的力学性能最好,片层状Talc与纤维状GF发挥了良好的协同作用。同时GF的使用能降低聚丙烯复合材料的模塑收缩率,有望在汽车轻量化材料方面得到推广和应用。     

PP-g-Si对PP／GF的增容作用

制备了硅烷接枝聚丙烯(PP-g-Si)，研究了PP-g-Si作为聚丙烯／玻纤(PP／GF)复合体系的界面相容剂对界面结合和力学性能的影响，并与马来酸酐接枝聚丙烯(PP-g-MAH)的增容效果进行了比较。结果表明，PP-g-Si对PP／GF体系有增容作用，不仅可以改善PP／GF复合体系的拉伸强度，而且可以改善其韧性。硅烷接枝聚丙烯可以降低PP／GF复合体系的最大扭矩。玻纤的加入可以提高聚丙烯的热变形温度，硅烷接枝聚丙烯对PP／GF复合体系的热变形温度有稍微改善。扫描电镜观察表明，玻纤与基体间具有强有力的界面结合，硅烷接枝聚丙烯的增容效果优于马来酸酐接枝聚丙烯。     

高强高韧GF／PP复合材料的研究

通过在短玻(GF)增强聚丙烯(PP)中添加聚烯烃弹性体(POE),并用马来酸酐对PP进行接枝交联的方法, 制备了高冲击韧性GF／PP复合材料。在该材料中,短切玻璃纤维的加入大幅度提高了材料的拉伸、弯曲强度,而POE 则通过产生形变等方式,提高了材料的冲击韧性;在其中加入马来酸酐接枝聚丙烯增加界面结合力,可使GF／PP／POE 复合体系表现出良好的综合力学性能,其拉伸强度为51．9 MPa,弯曲强度为68．1MPa,冲击韧性为44．2 kJ／m2。     

聚丙烯／BA原佐聚合改性MMT纳米复合材料的DSC分析与力学性能

通过原位聚合制备了聚丙烯酸丁酯(PBA)改性蒙脱土(MMT)，与聚丙烯(PP)熔融复合制成P／MMT纳米复合材料，系统地研究了复合材料的熔融、结品行为和力学性能。结果表明：随着处理MMT的BA用量的增加，PP／MMT纳米复合材料中PP相的结晶度、熔点和结晶温度明显提高，结晶速度加快；复合材料的拉伸强度变化不大，但拉伸横量和冲击强度有显著提高。当BA／0MMT质量比为1／12左右时，复合材料的韧性趋于平衡值，而拉伸横量出现最大值。     

混杂增强PP/g-PP/GF复合材料的性能研究

目前玻纤增强PP复合材料在电子、汽车领域已得到广泛应用,但其性能仍无法达到AS/玻纤(GF)复合材料水平而应用于制造空调风轮叶片。在前期接枝PP改善聚丙烯(PP)/玻纤(GF)复合材料研究的基础上,引入4种粉末增强材料,研究了增强材料的种类、用量、成核剂等因素对复合材料力学性能、耐热变形温度及熔融指数的影响。结果表明所选用的四种粉末增强材料均能有效的提高复合材料的力学性能,对其他性能的影响不大,其中CaSO4晶须的增强效果最好,当CaSO4晶须与PP的重量比为1∶4时,复合材料的力学性能已完全到达AS/GF复合材料水平。向滑石粉及BaSO4增强体系加入少量成核剂能使复合材料的力学性能进一步提高。该新型混杂增强复合材料有望替代AS/玻纤增强复合材料,应用于制造空调风轮叶片。     

排水管道中玻纤增强聚丙烯防腐材料性能研究

本研究制备了玻璃纤维增强聚丙烯(PP/GF)复合材料,并研究了玻璃纤维(GF)添加的用量对PP/GF复合材料的力学性能和耐腐蚀性的影响。采用SEM、热失重和强度测试对PP/GF复合材料的形貌和力学性能进行分析。结果表明:GF作为增强体可以在PP材料中呈现出良好的分散状态,GF在PP材料的均匀分散能够提高其作为工程塑料的力学性能、阻燃特性和耐腐蚀性。通过拉伸强度和弯曲强度测试发现,当GF在PP/GF复合材料中的加入量为15%时,复合材料具有最佳的力学性能。     

玻纤增强聚丙烯软触感材料的制备及性能

采用聚丙烯(PP)、玻璃纤维(GF)和弹性体(POE)作为原料,利用熔融共混方法制备了玻纤增强聚丙烯软触感材料.分别研究了 GF含量及POE/PP比例对复合材料力学性能的影响.研究结果表明,玻纤能够显著提高复合材料的力学性能和硬度,随着GF含量的增加,复合材料的拉伸性能呈先增加后减弱的趋势,而其弯曲性能、冲击性能及硬度...     

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.     

Characteristic Spherulitic Microstructure in Partial-Melt-Processed YBa2Cu3Ox/HfO2

The microstructure of partial-melt-processed YBa₂Cu₃O _x /HfO₂ has been studied by transmission electron microscopy. A characteristic spherulitic microstructure is formed in the system. A model for the growth mechanism has been proposed. The critical heterogeneous nucleation of the YBa₂Cu₃O _x phase appears to occur from the melt in an epitaxially controlled manner on CuO particles. Subsequent growth of YBa₂Cu₃O _x platelets from the nucleus region is repeatedly interrupted by the nucleation of hafnium-rich phases in the liquid at the solid/liquid interface in a manner that again appears to be epitaxially controlled and that promotes the splay of the c orientation of the YBaCuO grain.