PP/石墨/CaCO3导热复合材料制备及性能

采用熔融共混法制备聚丙烯(PP)/石墨/CaCO3导热复合材料,分别研究了CaCO3增韧母料、石墨的添加量对复合材料导热性能及力学性能的影响。结果表明:500A的CaCO3增韧母料对改善复合材料的综合性能最为有效;将石墨和500A共混复合时,可以同时提高复合材料的刚性和韧性;随着500A及石墨用量的增加,复合材料的热导率及热稳定性相应提高,熔融温度略微下降;复合材料中PP的结晶度随500A用量的增加而下降,随石墨用量的增加而增加;PP/石墨/500A(质量比45/30/25)复合材料的热导率为纯PP的3倍,缺口冲击强度与纯PP相近,拉伸强度有所下降,弯曲强度和弯曲模量增加了28%。     

苯并噁嗪/磷酸三苯酯/ABS无卤阻燃体系的增韧研究

选用丙烯腈-丁二烯-苯乙烯(ABS)高胶粉(ABSHR)和丁腈橡胶(NBR)对苯并噁嗪(BOZ)/磷酸三苯酯(TPP)/ABS无卤阻燃体系进行增韧改性;探讨了增韧剂对ABS无卤阻燃体系的阻燃性能和力学性能的影响;同时采用扫描电镜(SEM)对其断面形态进行表征。结果表明:ABSHR添加量为10份时,体系的冲击强度提高了35%,其拉伸强度和氧指数影响较小;NBR添加量为10份时,体系的冲击强度从4.62 kJ/m2提高到26.3 kJ/m2,提高了469%。体系的拉伸强度和氧指数有所下降。DMA显示在丁腈橡胶增韧的体系中,苯并噁嗪树脂的Tg与ABS高胶粉增韧体系相比向低温方向移动了4.6℃。     

ABS/PA6复合材料的力学性能影响研究

制备了一系列ABS/PA6复合材料,并探讨了不同增容剂、不同种类ABS以及不同增韧剂对ABS/PA6复合材料力学性能的影响。结果表明,马来酰亚胺(MS-NB)对ABS/PA6的增容效果最佳,当添加量为5%时,缺口冲击强度由4.4 k J/m~2提高到7.8 k J/m~2,提升幅度为77%。在缺口冲击强度表现上,具有核壳结构的MBS增韧剂明显优于高胶粉;不同ABS种类的ABS在该体系中力学性能差异很大,高胶含量的ABS树脂能显著提高复合材料的缺口冲击强度,但弯曲强度,弯曲模量等性能有一定程度下降。     

PP/EG/MWNTs导热复合材料试验对比

利用高温膨胀插层工艺制备PP/EG/MWNTs导热复合材料,对比置于室温、800℃、900℃3种条件下制备的导热复合材料的热性能和力学性能,试验结果表明,经900℃高温膨胀后,PP/EG/MWNTs热导率可达1.51 W/(m·K),比纯PP的热导率提高了487.5%,与室温和800℃条件下制备的PP/EG/MWNTs相比,热稳定性和拉伸强度均得到有效增强,但缺口冲击强度没有明显变化。结合微观形貌可知,高温可使MWNTs进入膨胀后的EG层间,将复合材料结构空间填实后,有利于形成导热网络,从而提高了复合材料的热性能和力学性能。     

PE-HD复合材料导热性能及力学性能的研究

通过双螺杆挤出机制备了高密度聚乙烯（PE-HD）/石墨/CaCO3增韧母料复合材料,并研究了石墨的表面处理、粒径、含量以及CaCO3增韧母料含量对复合材料导热性能及力学性能的影响。结果表明,偶联剂NDZ201对石墨表面具有较好的处理效果。石墨颗粒直径越小,复合材料的热导率及综合力学性能越高。CaCO3增韧母料能明显提高复合材料的热导率及缺口冲击强度。PE-HD/石墨/增韧母料250B的质量比为45/30/25时,复合材料的热导率可达1.72 W/(m·K),其缺口冲击强度与纯PE-HD相近,拉伸强度和弯曲强度分别比PE-HD提高了52 %和88 %。     

高剪切应力下不同弹性体对ABS材料力学性能影响

采用材料在熔融挤出共混过程中提高双螺杆挤出机螺杆转速的方法,研究了较高螺杆转速条件下双螺杆挤出机的高剪切应力、不同弹性体(SEBS、POE、EVA、NBR)等对ABS材料力学性能的影响.结果表明:双螺杆挤出机的高剪切应力可促进弹性体颗粒的分散和界面结合力的增强,引起共混材料力学性能的改善;NBR、EVA等弹性体有利于ABS材料韧性的提高,POE、EVA等弹性体有利于ABS材料加工流动性的改善.在220℃的挤出温度下,当螺杆转速由240 r/min提高至1200 r/min时,其中ABS/NBR(质量比90/10)共混材料的缺口冲击强度由22.1 kJ/m2提高至28.8 kJ/m2,提高了30%,比纯ABS树脂提高一倍.     

高剪切应力对ABS/NBR共混物力学性能的影响

研究了较高螺杆转速条件下双螺杆挤出机的机械剪切应力和挤出温度对丙烯腈-丁二烯-苯乙烯共聚物/丁腈橡胶（ABS/NBR）共混物力学性能的影响。结果表明,双螺杆挤出机的高剪切应力可促进NBR颗粒的分散,提高界面结合力,提高共混物的力学性能。在220 ℃的挤出温度下,当螺杆转速由240 r/min提高至1200 r/min时,ABS/NBR（90/10）共混物的缺口冲击强度由22.1 kJ/m2提高至28.8 kJ/m2,,提高了30 %。双螺杆挤出机的熔融挤出温度对ABS/NBR共混物力学性能的影响存在最佳值。     

不同改性剂对ABS复合材料力学性能的影响

通过在丙烯腈-丁二烯-苯乙烯共聚物(ABS)中添加不同的改性剂制备ABS复合材料。采用动态力学分析仪,扫描电子显微镜等分析了不同改性剂对ABS复合材料力学性能的影响。结果表明:与未改性的ABS相比,ABS/苯乙烯-马来酸酐共聚物(SMA)复合材料的拉伸强度为51.5 MPa,提高了6.8%;SMA作为相容剂提高了热塑性聚氨酯弹性体(TPU)粒子与ABS树脂之间的界面黏结强度,使得ABS/SMA/TPU复合材料的力学性能得以提高,其拉伸强度达到52.2 MPa,ABS/SMA/ABS高胶粉复合材料的冲击强度为29.3 kJ/m~2,提高了34.4%,综合力学性能较为理想。     

3D打印PC/ABS合金的性能

以马来酸酐接枝ABS树脂(ABS-g-MAH)为增容剂,制备聚碳酸酯(PC)/丙烯腈–丁二烯–苯乙烯塑料(ABS)合金,对其力学性能、热性能及熔体流动性等进行了研究,结果表明,当该合金质量比PC∶ABS∶ABS-gMAH=70∶30∶6时,PC/ABS合金的缺口冲击强度为33.92kJ/m~2,远高于纯PC与其它配方合金的缺口冲击强度,且其它性能较好。采用3D打印耗材挤出机将纯PC及PC/ABS合金制成丝材,PC丝材直径为(1.75±0.27)mm,PC/ABS合金丝材直径为(1.75±0.05)mm,PC/ABS合金的尺寸稳定性得到很好地改善。研究两种丝材的熔融沉积成型(FDM)性能以及打印方向对试样力学性能的影响。结果表明,当采用FDM工艺水平向和侧向打印时,试样的力学性能超过注塑工艺成型试样,但是竖向打印试样力学性能较差。与纯PC打印试样相比,PC/ABS合金试样的缺口冲击强度得到大幅提高,侧向打印PC/ABS合金的缺口冲击强度为40.13kJ/m~2,而侧向打印纯PC的缺口冲击强度仅5.73kJ/m~2。     

ABS高胶粉增韧PMMA的研究

研究了不同丙烯腈-丁二烯-苯乙烯共聚物(ABS)高胶粉含量对聚甲基丙烯酸甲酯(PMMA)结构与性能的影响,并以一种核-壳型共聚物硅/丙烯酸复合橡胶接枝(SAN)作为增容增韧的第三组分助剂,研究了其含量对ABS高胶粉/PMMA体系结构与性能的影响。结果表明,ABS高胶粉明显改善了PMMA的冲击强度和断裂伸长率,但降低了拉伸强度和弹性模量。随着ABS高胶粉含量增加,体系的复数黏度和储能模量均增加。加入硅/丙烯酸复合橡胶接枝SAN,ABS高胶粉/PMMA体系的拉伸强度稍有降低,缺口冲击强度有所增加,当硅/丙烯酸复合橡胶接枝SAN含量为4份时,体系缺口冲击强度为7.57 kJ/m²,比纯PMMA的缺口冲击强度(1.38 kJ/m²)提高了450%,从SEM照片也表征,此配方体系下的共混物有较好的相容性。     

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 ).