NR/环氧化天然橡胶共混物的动态力学性能*

研究了 Ｎ Ｒ／ 环氧化天然橡胶（ Ｅ Ｎ Ｒ） 共混物的动态力学性能。结果表明,在共混物中加入酚醛树脂后,仍只有两个动态力学损耗峰ｔａｎ δ（ 分别对应着 Ｔｇ１ 和 Ｔｇ２ ） 。随着树脂用量的增大（０ ～１５ 份） , Ｔｇ１ 基本不变, Ｔｇ２ 逐渐向高温方向移动; Ｔｇ１ 对应的ｔａｎδ峰值减小, Ｔｇ２ 对应的ｔａｎδ峰值则逐渐增大。因此,ｔａｎδ的大小和位置可以通过共混体系中树脂的并用量来调节,从而可获得湿抓着性能好、滚动阻力低的新型 Ｎ Ｒ／ Ｅ Ｎ Ｒ 胎面材料。     

氢化丁腈橡胶／超细全硫化粉末丁腈橡胶共混物的结构与性能研究

采用熔融共混工艺制备了氢化丁腈橡胶（HNBR）／超细全硫化粉末丁腈橡胶（UFPNBR）共混物,研究了共混物相态结构、动态力学性能、力学性能及老化性能,并与HNBR／NBR共混物作了对比。透射电镜观察表明：在HNBR／UFPNBR体系中,HNBR容易形成连续相,UFPNBR为分散相;在HNBR／NBR体系中容易形成双连续相结构。DMA动态力学性能分析表明：2种共混物都只有一个tanδ峰,且相容性较好。HNBR／UFPNBR共混物在玻璃化转变区的tanδ峰值逐渐降低,而HNBR／NBR体系的tanδ峰值先减小后增大。加入适量的UFPNBR能降低HNBR／UFPNBR共混物的压缩永久变形;与常规共混胶相比,HNBR／UFPNBR具有低脆性温度和良好的耐老化性能,但力学性能略低。     

IIR/CIIR共混胶的动态力学性能

研究了共混比、硫化体系、增强剂、软化剂和硅烷偶联剂对IIR/CIIR共混胶动态力学性能的影响。结果表明,随CIIR用量增加,共混胶的储能模量(E')和损耗模量(E″)逐渐增加,而阻尼因子(tanδ)峰值逐渐减小,共混胶的玻璃化转变温度(Tg)向高温方向偏移;采用叔丁基酚醛树脂硫化的共混胶的E″比硫黄硫化的高,但tanδ峰值和Tg均低于后者;细粒子高结构炭黑N220填充的共混胶的E'和E″较高,tanδ峰值较低,而粗粒子半增强炭黑N754填充的共混胶的E'和E″较低,tanδ峰值较高;软化剂凡士林的加入,使共混胶的E'和E″降低,tanδ峰值增加,而且Tg向低温方向偏移;γ-氨基丙基三乙氧基硅烷增加了共混胶的E'和E″值,但tanδ峰值降低,Tg基本不变。     

共混比对NR/NBR阻尼材料性能的影响

研究了天然橡胶/丁腈橡胶(NR/NBR)两相共混比对共混胶阻尼材料硫化特性、力学性能、压缩生热以及阻尼性能的影响。结果表明:随着NBR含量增加,共混胶M_L、M_H、M_H-M_L均增大,t_(s1)和t_(c90)先缩短后延长;共混胶拉伸强度、拉断伸长率、定伸应力和撕裂强度均减小,硬度有所增大,回弹性明显下降;压缩永久变形和温升明显增大;滞后能量损耗(HED)和阻尼系数增大。DMA曲线上表现出两个明显的损耗峰,随着NBR含量增加,NR相峰值tanδ_(max1)下降而NBR相损耗峰值tanδ_(max2)逐渐增大,损耗模量的变化趋势与之相似。NBR/NBR=70/30时,共混胶力学性能相比纯NR下降程度低,且室温附近的阻尼性能提高明显,综合性能相比其他更佳。     

ⅡR/CⅡR共混胶的动态力学性能

研究了共混比、硫化体系、增强剂、软化剂和硅烷偶联剂对ⅡR/CⅡR共混胶动态力学性能的影响。结果表明,随CⅡR用量增加,共混胶的储能模量(E′)和损耗模量(E″)逐渐增加,而阻尼因子(tanδ)峰值逐渐减小,共混胶的玻璃化转变温度(Tg)向高温方向偏移;采用叔丁基酚醛树脂硫化的共混胶的E″比硫黄硫化的高,但tanδ峰值和Tg均低于后者;细粒子高结构炭黑N220填充的共混胶的E′和E”较高,tanδ峰值较低,而粗粒子半增强炭黑N754填充的共混胶的E′和E″较低,tanδ峰值较高;软化剂凡士林的加入,使共混胶的E′和矿降低,tanδ峰值增加,而且乃向低温方向偏移;γ—氨基丙基三乙氧基硅烷增加了共混胶的E′和E″值,但tanδ峰值降低,Tg基本不变。     

纳米碳酸钙在环氧化天然橡胶中的应用

试验研究凝聚共沉法和机械共混法对纳米碳酸钙填充环氧化天然橡胶（ENR）性能的影响。结果表明，纳米碳酸钙用量为5份，凝聚共沉法和机械共混法胶料的储能剪切模量（G′）和损耗因子（tanδ）相近；纳米碳酸钙用量为40份，凝聚共沉法胶料的G′大于、tanδ值小于机械共混法胶料；采用机械共混法可增大胶料的MH，缩短ts1，纳米碳酸钙用量为5～20份时对ENR起补强作用;采用凝聚共沉法可使纳米碳酸钙较好地分散于ENR中，纳米碳酸钙用量为20～40份时对ENR起补强作用。     

NR/EPDM共混胶制备浅色胶料性能研究（轮胎会）

研究了天然橡胶（NR）和乙丙橡胶（EPDM）共混制备浅色胶料的力学性能、耐老化和耐臭氧性能,同时采用弹性体PNE增容NR/EPDM共混胶。结果表明：在NR中并用EPDM,随着EPDM用量的增加,NR/EPDM共混胶力学性能有所降低,耐臭氧老化性能和耐热空气老化性能提高;使用一定量增容剂PNE替代EPDM能明显改善NR/EPDM共混胶的力学性能和耐屈挠性能;通过对比不同PNE用量共混胶的SEM图像可以看出使用PNE后材料界面变得模糊,通过动态力学性能分析可知,在NR/EPDM共混胶中加入增容剂后损耗因子的两个tanδ峰值逐渐靠近,当PNE的份数为40时tanδ峰值由两个变为一个,界面的模糊和tanδ峰值的减少说明增容剂改善了两种橡胶的相容性。     

酚醛树脂对NBR性能的影响

针对酚醛树脂(PF)改性后的丁腈橡胶(NBR)胶料进行了FT-IR分析、物理性能分析和动态力学性能分析。结果表明,NBR和PF发生了化学反应,生成了-O-醚键;随着PF用量从0份增加到50份,NBR/PF的硬度逐渐增大,拉断伸长率、热空气老化后的硬度变化、拉伸强度变化率、拉断伸长率变化率逐渐降低,拉伸强度、撕裂强度、回弹性和低温脆性温度先增大后减小,压缩永久变形和相对体积磨耗量先减小后增大,NBR/PF损耗因子(tanδ)的峰值逐渐降低,玻璃化转变温度(Tg)呈现向高温方向移动的趋势;当PF用量为50份时,NBR/PF的Tg比PF用量为30份时NBR/PF的Tg稍低。     

短切碳纤维对NR/NBR阻尼材料性能的影响

为了探索天然橡胶/丁腈橡胶的阻尼性能,研究了短切碳纤维(CF)对天然橡胶/丁腈橡胶(NR/NBR)阻尼材料硫化特性、力学性能及阻尼性能的影响。结果表明:随着CF添加量增大,共混胶ML、MH和MH-ML增大,ts1缩短而tc90略有延长;拉伸强度和拉断伸长率下降,撕裂强度先增大后减小,当CF为10份时达到最大值,定伸应力明显增大,回弹性下降;滞后能量密度(HED)和阻尼系数增大;DMA测试表明:NR和NBR两相损耗因子(tanδ)峰值均略有下降,损耗模量E'显著增大,室温及较高温度下的tanδ随CF添加量增大而逐渐增大。可以看出,CF的加入能有效增强NR/NBR共混胶的阻尼性能。     

环氧化天然橡胶复合材料性能研究

采用新方法制备环氧化天然橡胶(ENR)/白炭黑和天然橡胶(NR)/ENR/白炭黑复合材料,并对其性能进行研究。结果表明:ENR/白炭黑复合材料的热稳定性优于ENR;在NR/ENR并用胶中加入白炭黑和硅烷偶联剂KH-550,NR/ENR/白炭黑复合材料0℃时的损耗因子(tanδ)增大,65℃时的tanδ值减小,复合材料的抗湿滑性能提高,滚动阻力减小。     

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 ).