LLDPE/EPDM复合材料高效阻燃体系的研究

以线性低密度聚乙烯(LLDPE)、(乙烯／丙烯／二烯)共聚物(EPDM)为基体,以经表面处理的氢氧化镁[Mg(OH)2]为主阻燃剂,微胶囊化红磷和自制阻燃剂S为核心的复合阻燃剂为阻燃增效剂,制备了阻燃性能优良的LLDPE／EPDM复合材料。重点探讨了Mg(OH)2与复合阻燃剂的阻燃效果及其对LLDPE／EPDM复合材料力学性能、加工性能的影响。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MS(OH)2用量为40份、复合阻燃剂用量为5-7份时,可获得较高的氧指数和垂直燃烧FV-0级的高阻燃性,且材料的加工性能和力学性能较好。     

复合阻燃体系阻燃电缆料的研究

通过氧指数、水平燃烧、力学性能、扫描电镜等方法的分析，研究了由超微细氢氧化镁[Mg(OH)]和Br-Sb卤素阻燃剂组成的复合阻燃体系的用量对HDPE阻燃性能、力学性能的影响。结果表明．Mg(OH)2和BrSb卤素阻燃剂最佳配比为4：1(质量比)时．综合效果较佳；通过与Mg(OH)2阻燃剂的对比试验．发现复合阻燃剂能保持复合材料较好的力学性能,而且显著提高了阻燃性能：熔体流动速率(MFR)的测定表明当复合阻燃剂的添加量为10份时，仍能满足加工工艺的要求。     

一种新型复合阻燃剂的制备及性能研究

ZnSiO3与Mg(OH)2复配成复合阻燃剂,研究了阻燃剂用量对PVC的阻燃性能及力学性能的影响。结果表明,最佳改性工艺配方为:PVC 100份,邻苯二甲酸二辛酯40份,有机锡稳定剂1份,偶联剂1份,硬脂酸钙1份,复合阻燃剂20份[ZnSiO3∶Mg(OH)2=1∶9],在此条件下,样品的氧指数可达31.8,且对PVC的物理力学性能影响很小。     

环保型无卤阻燃聚丙烯的研制

采用几种不同类型的无卤阻燃剂研制环保型阻燃聚丙烯(PP),讨论各阻燃剂的阻燃机理,对研制的阻燃PP进行了阻燃性能测试和燃烧热的测试。结果表明,Mg(OH)2复合阻燃体系和氮磷复合阻燃体系对PP均有良好的阻燃效果;研制的Mg(OH)2复合阻燃PP具有良好的阻燃性能和力学性能,并具有实际应用价值。     

环保阻燃聚丙烯的研究

采用新型环保阻燃剂十溴二苯乙烷(DBDPE)、三氧化二锑(Sb_2O_3)和氢氧化镁[Mg(OH)_2]复合对PP进行阻燃改性。研究了DBDPE与Sb_2O_3的协同效应,复合阻燃剂对PP阻燃性能、物理机械性能的影响。结果表明:当复合阻燃剂的质量分数为35%,DBDPE与Sb_2O_3的质量比为3:1,DBDPE与Mg(OH)_2的质量比为1:1时,改性阻燃PP的氧指数达到30%,阻燃等级达到V-0级,并保持良好的物理机械性能。     

HDPE/Br-Sb/Mg(OH)_2低卤阻燃电缆料的研制

研究了由超微细Mg(OH)2和Br Sb卤素阻燃剂组成的复合阻燃体系以及两组分之间最佳的配比关系,通过采用氢氧化镁阻燃剂和复合阻燃剂对HDPE阻燃的对比实验结果表明:复合阻燃剂对HDPE热解性能、阻燃性能、物理机械性能的影响都优于氢氧化镁阻燃剂。     

无卤阻燃聚烯烃电缆护套料的研制

以乙烯-乙酸乙烯酯塑料(EVAC)为基体,氢氧化镁[Mg(OH)2]为阻燃剂,红磷(RP)和氰尿酸三聚氰胺(MCA)为阻燃协效剂,制备了一种可应用于电缆护套料的无卤阻燃复合材料.探讨了Mg(OH)2、RP、MCA用量对复合材料性能的影响.结果表明,当Mg(OH)2为120份、RP为3.0份、MCA为3.O份、交联剂过氧...     

用锥形量热仪研究无卤阻燃HDPE体系的燃烧性

在35kW／m^2热辐照条件下,利用锥形量热仪研究了膨胀型阻燃剂／Mg(OH)2阻燃高密度聚乙烯(HDPE)体系的燃烧性。结果表明：膨胀型阻燃剂／Mg(OH)2能明显降低HDPE的热释放速率、总热释放量、最大生烟速率及总烟释放量。与膨胀型阻燃剂单独使用相比,Mg(OH)2与膨胀型阻燃剂复合使用的阻燃效果明显,总烟释放量减少了38％,总热释放量减少了10％,达到了低发炯、高效阻燃的目的。     

LDPE/LLDPE/纳米Mg(OH)2阻燃体系的研究

以LDPE/LLDPE(60:40)共混体系为基础,添加阻燃剂纳米Mg(OH)2,考察聚乙烯/纳米Mg(OH)2共混复合体系的阻燃性能、力学性能以及加工工艺条件.实验表明:随着Mg(OH):份量的增加,发烟量逐渐减少,纳米Mg(OH),添加量大于40%以后,发烟量逐渐趋近于零,说明纳米氢氧化镁在PE阻燃系统中具有优异的抑烟作用;随着阻燃剂纳米Mg(OH),的增加,燃烧级别最后升高至FV-O级.阻燃体系的力学性能随着纳米Mg(OH)2的增加而下降,当纳米氢氧化锾质量含量达到50%时,材料转为脆性.流动性随纳米Mg(OH)2含量的增加而下降.     

环保型无卤阻燃聚丙烯的研制

采用几种不同类型的无卤阻燃剂研制环保型阻燃聚丙烯（PP），讨论各阻燃剂的阻燃机理，对研制的阻燃PP进行了阻燃性能测试和燃烧热测试。结果表明，Mg（OH）2复合阻燃体系和氨磷复合阻燃体系对PP均有良好的阻燃效果；研制的Mg（OH）2复合阻燃PP具有良好的阻燃性能和力学性能，并具有实际应用价值。     

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 ).