PP基纳米SiO2复合材料性能的研究

利用纳米SiO2、马来酸酐接枝聚乙烯（PE-g-MAH）和聚丙烯（PP）通过熔融共混的加工工艺制备了PP基纳米SiO2复合材料，考察了不同处理方法及用量的纳米SiO2对PP基体的影响。结果表明：经表面处理，用量4％（质量分数，下同）的纳米SiO2和4％PEgMAH协同作用，可以使复合材料的冲击强度提高40％，拉仲强度提高10％，耐热性较PP基体提高22℃。采用偏光显微镜（POM）、扫描电镜（SEM）对PP基纳米SiO2复合材料的微观结构进行了表征和分析，证明经表面改性的纳米SiO2（TS530）均匀地分散于PP基体中，从而起到良好的改性作用。     

PPB/SiO2填充改性复合材料的研究

考察了二氧化硅(SiO2)、聚乙烯接枝马来酸酐(PE-g-MAH)对嵌段共聚聚丙烯(PPB)基体性能的影响.结果表明,用六甲基二硅氮烷表面处理的SiO2填充PPB,使PPB各项性能均得到了提高,PE-g-MAH的加入又进一步提高复合材料的冲击性能.红外分析表明,表面处理后的SiO2表面羟基减少,极性明显减弱,增加了与PP基体的相容性;POM照片和DSC曲线分析表明,SiO2填充起到了异相成核作用,增加了与PPB基体的相容性,加入PE-g-MAH作为增容剂后,复合材料的晶粒更加细化,结晶温度有所提高;SEM断口分析表明,加入SiO2及PE-g-MAH的PPB复合材料呈现明显的韧性断裂特征.     

反应性增容对PP/纳米SiO_2界面作用的影响

通过动态力学分析和拉伸性能的测试,采用不同模型研究了反应性增容对聚丙烯(PP),纳米SiO2复合材料界面作用的影响.研究表明,反应性增容使纳米SiO2粒子与PP基体的界面作用明显增强,使PP分子链的松弛活化能增大.在环氧功能化改性纳米SiO2粒子和反应性增容剂(氨基化PP)的质量分数分别为3%和10%时,复合材料的冲击强度从1.85 kJ/m2提高到3.46 kJ/m2,体现了明显的增韧作用.     

PP/纳米SiO2复合材料的研究

采用傅立叶红外光谱仪(FT-IR)表征了改性前后纳米SiO2粉体的性能特征;通过熔融共混法制备了PP/纳米SiO2复合材料。研究了纳米SiO2用量对PP基体性能的影响。通过力学性能测试、DSC热分析和SEM照片观测,对PP/纳米SiO2复合材料的结构和性能进行了系统的研究。结果表明:当纳米SiO2含量为2%时,PP/纳米SiO2复合材料的综合力学性能最好。DSC表明,纳米SiO2对PP基体有异相成核作用。SEM电镜分析得出,经表面改性的纳米SiO2均匀地分散于PP基体中,从而起到良好的改性作用。     

PP/纳米SiO2/PP-g-MAH复合材料的研究

通过熔融共混法制备了PP/纳米SiO2/PP-g-MAH复合材料。研究了纳米SiO2和PP-g-MAH用量对PP基体性能的影响。通过力学性能测试、DSC热分析和SEM照片观测对PP/纳米SiO2和PP/纳米SiO2/PP-g-MAH复合材料的结构和性能进行了系统的研究。结果表明:2%的纳米SiO2和10%PP-g-MAH有较好的协同效应。可以使复合材料的缺口冲击强度提高80%,拉伸强度提高12.5%。DSC表明,纳米SiO2对PP基体有异相成核作用。SEM电镜分析得出,经表面改性的纳米SiO2均匀地分散于PP基体中,从而起到良好的改性作用。     

聚氨酯弹性体/纳米SiO2复合材料的力学性能研究

采用预聚体的方法制备了聚氨酯弹性体(PUE)/纳米SiO2复合材料,通过AJ(OH)3对纳米SiO2表面改性以及超声波分散的方法来提高纳米SiO2在PUE基体中的分散性,并考查了表面处理前后的纳米SiO2对PUE/纳米SiO2复合材料力学性能的影响.结果表明:改性后的纳米SiO2能均匀分散于PUE基体中,复合材料的力学性能明显提高;纳米SiO2的用量对PUE/纳米SiO2复合材料的力学性能影响较大,并且当纳米SiO2的质量分数为2%和3%时,复合材料的拉伸强度和撕裂强度分别达到最大.     

聚丙烯／纳米二氧化硅复合材料性能研究

通过熔融共混法制备了聚丙烯(PP)/纳米二氧化硅(nano-SiO2)复合材料,研究了nano-SiO2用量和第3组分聚丙烯接枝马来酸酐(PP-g-MAH)对材料力学性能的影响.结果表明,nano-SiO2用量为4份时,材料的力学性能最佳.对PP,PP/nano-SiO2,PP/nano-SiO2/PP-g-MAH复合材料进行DSC热分析和SEM照片观察发现,nano-SiO2对PP基体有异相成核作用,PP-g-MAH可以提高nano-SiO2在PP基体中的相容性.     

SiO2粒径对PP发泡行为和力学性能的影响

通过把改性过的不同粒径SiO2以不同用量加入到聚丙烯(PP)中,制备PP/SiO2复合材料母粒,在二次开模条件下制备微发泡PP/SiO2复合材料.通过对不同粒径的SiO2粒子对PP纳米复合材料发泡行为的影响研究,讨论了超细SiO2在聚合物微孔发泡中的作用机理,分析了超细SiO2对PP的力学性能及泡孔结构的影响规律.结果表明,不同粒径的SiO2粒子的加入都能够显著降低PP的泡孔直径和增加泡孔密度;SiO2粒子使PP的缺口冲击强度升高,发泡材料的拉伸强度低于未发泡材料的拉伸强度.     

聚丙烯/聚烯烃弹性体/纳米SO2复合材料的制备与性能研究

通过熔融挤出法制备了一系列聚丙烯(PP)/聚烯烃弹性体(POE)/纳米SiO2复合材料,利用差热扫描量热仪(DSC)、电子拉伸机、悬臂梁冲击试验机等对复合材料进行了表征,分析了聚烯烃弹性体和纳米SiO2对聚丙烯的热性能和力学性能的影响.结果表明:当纳米SiO2的用量为3%时,PP/POE/纳米SiO2复合材料的拉伸强度...     

NBR／PP／蒙脱土纳米复合体系的制备和性能研究

以丙烯酸接枝聚丙烯为增容剂,采用熔融复合方法制备出NBR/PP/蒙脱土纳米复合体系。对丙烯酸熔触接枝PP的增容体系进行了深入得研究,其次还对未处理的MMT和处理过的纳米MMT对共混物结构和性能得影响进行了讨论。研究表明,在使用丙烯酸接枝PP对NBR/PP体系得增容性较好,通过熔融共混得方法制备了NBR/PP/蒙脱土纳米复合材料。对复合材料的介电性能,力学性能和相容性进行了研究,用红外光谱和扫描电镜表征该复合材料的结构。结果表明:丙烯酸接枝聚丙烯能够很好的改善PP和NBR、MMT的相容性,当十六烷基三甲基溴化铵(CTAB)改性的蒙脱土用量为5Wt%、PP-g-AA用量为10Wt%时,NBR/PP/蒙脱土纳米复合材料的断裂伸长率提高20%,拉伸强度提高10%,撕裂强度提高80%。     

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 ).