配合剂和共混工艺对PVC／POM／NBR三元共混弹性体性能的影响

在制备PVC／POM／NBR三元共混弱性体的研究基础上,进一步探讨了防老剂品种及用量、炭黑品种及用量、增塑剂品种、共混工艺等因素对共混物力学性能的影响。结果表明：选择PVC／POM／NBR（20／10／70）100,半补强炭黑30－45,防老剂MB1.0－1.5,硫黄硫化体系及适量DOP,并选择共混温度175－180℃,共混时间4－5min以及采用先将PCV与NBR制成二元共混物再与已塑化的POM共混制成三元共混物为共混工艺,可制得综合性能较佳的PVC／POM／NBR三元共混弹性体。     

三元共聚尼龙/聚氯乙烯/丁腈橡胶三元共混弹性体研究

选择三元共聚尼龙（PA），聚氯乙烯（PVC）和丁腈橡胶（NBR）为主体材料，采用高温机械共混，化学交联工艺制得了PA／PVC／NBR三元共混弹性体，探讨了PA／NBR，POM／NBR，PVC／NBR，HMWPVC／NBR三元共混体系性能，重点讨论了PA／PVC／NBR共混比，不同硫化体系，有机过氧物DCP用量等因素对PA／PVC／NBR三元共混弹性体性能的影响，实验结果表明：选择适宜配方制得力学性能和耐油耐溶剂性能较好的PA／PVC／NBR三元共混弹性体，扫描电镜的实验结果证实m(PA):m(PVC):m(NBR)=10:30:60和m(PA):m(PVC):m(NBR)=30:10:60两个体系的三元共混弹性体均具有较好的相容性，且前者的相容性更好。     

高聚合度聚氯乙烯/聚甲醛/丁腈橡胶三元共混弹性体的研究

采用机械共混、化学交联工艺制备高聚合度聚氯乙烯 (HMWPVC) /聚甲醛 (POM) /丁腈橡胶 (NBR)三元共混弹性体合金。重点讨论了 HMWPVC/ POM/ N BR共混比、PVC树脂的相对分子质量、NBR橡胶的丙烯腈含量、硫化体系等因素对弹性体性能的影响。 HMWPVC/ POM/ NBR共混弹性体的力学性能、耐油耐溶剂性能优于PVC/ POM/ NBR共混弹性体。采用动态粘弹谱仪、扫描电子显微镜等现代分析技术研究了 HMWPV C/ POM/ NBR三元共混弹性体的微观结构 ,结果显示 H MWPVC/ POM/ NBR(10 / 10 / 80 )三元共混弹性体的 tgδ- T谱上只出现一个峰值 ,其对应的玻璃化转变温度为 - 0 .8℃ ,三元共混弹性体具有较好的相容性     

补强剂和共混工艺对PA/PVC/NBR三元共混弹性体性能的影响

在选择三元共聚尼龙（PA）、聚氯乙烯（PVC）、丁腈橡胶（NBR）为主体材料，制备PA／PVC／NBR（10／30／60）三元共混弹性体的工作基础上，进一步探讨了填料品种和用量，共混温度，加料顺序等因素PA／PVC／NBR三元共混弹性体的影响。试验结果表明：在PA／PVC／NBR（10／30／60）共混体系中，补强型填料的补强效果优于非补强型的填料，6种填料补强效果依次是：快压出炭黑＞半补强炭黑＞白炭黑＞活性重质，CaCO3＞陶土＞滑石粉，快压出炭黑的适宜用量是20－50份。在制备PA／PVC／NBR三元共混物时，适宜的共混温度是122－140℃，并且采用二段法混工艺制得的共混物性能优于采用一段法共混工艺。     

PVC／NBR／BR三元共混弹性体的制备与研究

本文重点叙述了聚氯乙烯(PVC)、丁腈橡胶(NBR)、顺丁橡胶(BR)三元共混弹性体的制备与研究,通过添加顺丁胶后,三元共混体的冲击回弹性、耐磨性及耐寒性均比二元PVC/NBR共混物得以改善,但拉仲强度、断裂伸长率及耐油性降低。获得最佳综合性能的共混比为PVC:NBR:BR=30:60:10(重量比)。实验表明,PVC/NBR/BR三元共混弹性体是复相体系,有较好的相容性。     

共混工艺对HMWPVC/POM/NBR弹性体性能的影响

在制备高聚合度聚氯乙烯 (HMWPVC) /聚甲醛 (POM) /丁腈橡胶三元共混弹性体的工作基础上 ,进一步探讨了防老剂品种和用量、炭黑品种和用量、增塑剂品种、共混温度、共混时间、加料顺序等因素对三元共混弹性体力学性能的影响。结果表明 :1.0～ 1.5份防老剂MB对HMWPVC/POM/NBR三元共混弹性体的防护效果最好 ;加入 15～ 6 0份半补强炭黑时 ,拉伸强度提高 4 0 %～ 5 6 % ,撕裂强度提高 4 6 %～ 89% ,耐溶剂性能显著改善 ;HMWPVC/POM/NBR三元共混弹性体适宜的共混温度 175～ 180℃ ,共混时间 5～ 7min。     

PVC／NBR共混胶在汽车密封条中的应用研究

以NBR-26为改性剂,用熔融共混的方式对PVC的共混体系进行了研究．对NBR／PVC共混体系的老化前后力学性能进行了测试及分析．实验结果表明,当NBR达到30份（重量份）时,共混体系综合性能最好．用改性后的PVC做汽车门窗密封条,替代进口PVC热塑性弹性体。     

影响NBR/PVC共混硫化胶性能因素的研究

系统研究了影响丁腈橡胶/聚氯乙烯(NBR/PVC)共混胶性能的主要因素,包括PVC塑化温度、增塑剂用量、橡塑比、PVC的聚合度、NBR的丙烯腈质量分数。研究结果表明,塑化温度在160℃、增塑剂用量为20份、橡塑比为60/40~70/30时,NBR/PVC共混硫化胶综合性能较好。随着PVC聚合度的提高,NBR/PVC共混硫化胶力学性能得到提高;NBR中丙烯腈含量的增大有利于NBR/PVC共混硫化胶性能的提高。     

热塑性聚氨酯弹性体与塑料的共混体系

本文简述了热塑性聚氨酯弹性体(TPU)与聚氯乙烯(PVC)、聚甲醛(POM)和聚碳酸酯(PC)的共混工艺以及共混物的物理机械性能。结果表明,TPU/PVC、TPU/POM、TPU/PC共混物的性能优异,极具发展潜力。     

PVC／NBR共混汽车门窗密封条研究

研究了不同共混工艺对PVC/NBR性能影响，讨论了PVC/NBR在不同共混工艺条件下耐油性能，结果表明共混工艺对材料综合性能影响很大，PVC/NBR=60/40时，共混材料综合性能较好。     

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.     

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.     

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.     

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 ).