UHMWPE/HDPE/PA1012复合材料的制备及性能研究

以高密度聚乙烯接枝马来酸酐(HDPE-g-MAH)为相容剂,在双螺杆挤出机上通过原位增容反应制备了超高摩尔质量聚乙烯(UHMWPE)/HDPE/尼龙1012(PA1012)复合材料。固定配比PE(HDPE∶UHMWPE)∶PA1012∶HDPE-g-MAH=50∶50∶7,考察HDPE与UHMWPE的比例对复合材料性能的影响。研究发现随着UHMWPE含量的增加,共混物的拉伸强度逐渐增加,断裂伸长率逐渐减小。维卡软化温度在HDPE∶UHMWPE=60∶40时达到最小值,仅为141℃,高于或低于此配比,维卡软化温度有所提高。复合材料的耐磨性则呈现出先减小后增加的趋势;通过SEM对复合材料的微观形态、结构进行表征,发现随着HDPE与UHMWPE配比的变化,复合材料的基体与分散相发生了反转,从而引起了复合材料性能的改变。     

高温热处理对HDPE/CB导电复合材料性能的影响

在高密度聚乙烯(HDPE)中加入适量的炭黑(CB)制备了HDPE/CB导电复合材料。通过对HDPE/CB导电复合材料热处理前后性能的研究,发现高温热处理可以消除成型加工对导电复合材料导电性的不利影响,显著改善未交联HDPE导电复合材料的导电性;并发现在热处理的温度上可以突破传统的将热处理温度限制在HDPE熔点之下的做法。而使材料的热处理温度超过熔点。     

隔离结构CB/HDPE复合材料结构及温敏性研究

以炭黑(CB)为导电填料,高密度聚乙烯(HDPE)为基体,通过机械研磨-超声分散-热压成型法成功制备出具有隔离结构的CB/HDPE导电高分子复合材料。结果表明,CB粒子选择性地分布于HDPE粒子界面,体系形成良好的隔离结构导电网络;与普通CB/HDPE复合材料相比,隔离结构CB/HDPE导电材料具有较低的逾渗值;温敏行为研究发现,隔离结构的CB/HDPE复合材料的温度-电阻曲线呈现出特殊的双峰现象。     

CB填充HDPE/POE复合材料阻-温特性的研究

以乙炔碳黑(ACET)为导电填料,高密度聚乙烯/乙烯-辛烯共聚物(HDPE/POE)为基体,制备了碳黑(CB)填充HDPE/POE复合材料,并研究了该材料的电阻率-温度变化规律。     

PP/POE/CB半导电屏蔽复合材料的制备和性能

研究了导电炭黑含量和聚乙烯-辛烯弹性体接枝马来酸酐(POE-g-MAH)的加入对热塑性半导电屏蔽材料,即聚丙烯烯/聚乙烯-辛烯弹性体/炭黑(PP/POE/CB)复合体系的体积电阻率和力学性能的影响,并通过扫描电镜(SEM)分析了POE-g-MAH的加入对PP基热塑性半导电屏蔽复合材料断面形貌的影响。利用转矩流变仪对复合材料的流变性能进行了研究。结果表明,PP/POE/CB热塑性半导电屏蔽复合材料的逾渗现象与炭黑粒子在聚合物基体中的分布状态有关,POE-g-MAH的加入可以进一步降低复合材料的体积电阻率;随着导电炭黑含量的增加,复合材料的拉伸强度均呈现先增加,后降低的趋势,当炭黑用量为30%时,拉伸强度达到最大值。PP/POE/CB热塑性半导电屏蔽复合材料具有较高的导电性能、力学性能、较高的熔体流动速率及良好的加工流动性。     

隔离-双逾渗结构GNS/HDPE/UHMWPE导电复合材料研究

通过溶液和机械搅拌混合的方法,成功制备出具有隔离-双逾渗结构的GNS/HDPE/UHMWPE复合材料,使用低含量的高密度聚乙烯(HDPE)作为石墨烯(GNS)载体,分布于超高摩尔质量聚乙烯(UHMWPE)粒子界面。形貌观察显示:在复合材料中形成一种特殊的二维隔离-双逾渗结构导电网络,在极低GNS含量下(体积分数0.05%)达到导电逾渗值。GNS/HDPE/UHMWPE复合材料的拉伸强度随着GNS含量的增加,呈现先增后减的趋势,而其拉伸模量则随GNS增加而提高。     

HDPE/CB/PA6复合材料的导电与力学性能研究

为了改善尼龙6低温与干态存在着冲击强度低、纤维状易于电荷富集的缺陷,制备了高密度聚乙烯(HDPE)/导电炭黑(CB)/尼龙6(PA6)复合材料。首先制备了HDPE/CB共混物作为功能改性剂,再以马来酸酐接枝乙烯-辛烯共聚物(POE-g-MAH)为增容剂,通过双螺杆挤出机熔融共混制备了HDPE/CB/PA6复合材料。通过扫描电子显微镜(SEM)、万能试验机、高阻计等方法,研究了添加增容剂和HDPE与PA6配比以及导电炭黑粒子含量对复合材料力学性能和导电性能的影响。结果表明,加入5 phr的增容剂POE-g-MAH,明显提高了HDPE与PA6的界面黏附力,复合材料相容性较好;当HDPE与PA6的质量比为35/65时,复合材料的断裂伸长率从纯PA6的88%增加到251%,缺口冲击强度从12.5 kJ/m~2增加到53.7 kJ/m~2;当导电炭黑的含量增加到2.5 phr时,复合材料的室温体积电阻率降低了7~10个数量级,约为10~8Ω·cm。     

EVA对HDPE/EVA/CB导电复合材料性能的影响

分别研究了HDPE/CB、EVA/CB两种复合材料的导电性能,并研究了不同含量EVA对HDPE/EVA/CB复合材料性能的影响,包括体系结晶度的变化和微观形态。根据TEM图片发现,CB在HDPE/EVA/CB复合材料中主要存在于HDPE相中,EVA的加入增加了复合材料的室温电阻率,同时,提高了材料的熔体指数。当EVA含量在37.5%～50.0%之间时,可以得到较理想的加工性与导电性能的平衡点。     

钒电池集流板用导电塑料的研制

采用高速搅拌混合的方式制备了高密度聚乙烯/超高分子量聚乙烯/石墨/碳纤维(HDPE/UHMwPE/GP/CF)复合材料,分析了复合材料的导电性能及微观相态结构,并对复合材料的物理机械性能及加工成型性能进行了研究.结果表明:HDPE和UHMWPE发生相分离,UHMWPE占据非导电相,使得导电相HDPE中的导电填料的浓度相对提高,从而有效提高了复合材料的导电性能;HDPE与UHMWPE的质量比为1/3时,复合材料的导电性能最佳;导电填料质量分数为65%时,复合材料的体积电阻达到0.1 Ω·cm,缺口冲击强度为5.2 kJ/m2,材料的成型性良好,具有最优的综合性能,符合钒电池(VRB)集流板的使用要求.     

LDPE/HDPE/炭黑PTC复合材料的制备与性能研究

采用流变仪对不同比例的低密度聚乙烯/高密度聚乙烯(LDPE/HDPE)进行了共混,研究了共混温度、转速和时间对LDPE/HDPE复合材料流变性能的影响。对不同比例的LDPE/HDPE进行了X射线衍射(XRD)测试,分析其结晶性能。制备了LDPE/炭黑(CB)复合材料和LDPE/HDPE/CB复合材料,并对其正温度系数(PTC)性能进行了测试。结果表明,制备LDPE/HDPE复合材料的最佳工艺条件为:转速50 r/min、温度170℃、共混时间10 min;LDPE∶HDPE质量比为1∶3时的复合材料结晶度最大;LDPE/HDPE/CB复合材料与LDPE/CB复合材料相比具有较高的PTC转变温度及更高的PTC强度。     

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.     

Wet Milling of Fe/Al/Al2O3 and Fe2O3/Al/Al2O3 Powder Mixtures

Wet milling of Al₂O₃-aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al₂O₃ and Fe₂O₃/Al/Al₂O₃ powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe₂O₃/Al/Al₂O₃ powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al₂O₃ powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8.     

Sintering of Si3N4-Y2O3-Al2O3

Sintering kinetics of the system Si₃N4-Y2O₃-Al₂O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si₃N₄ were studied with additions of 4 to 17 wt% Y₂O₃ and 4 wt% A1₂O₃. Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si₃N₄ and glass or β '-Si₃N₄, α '-Si₃N₄, and glass. The compositions and amounts of the residual glassy phases are estimated.     

Participation of lewis base on vinyl chloride polymerization with Al(C2H5)3CCl4 catalyst system

The polymerization of vinyl chloride has been investigated using an $\text{Al}\text{(}\text{C}{}_2\text{H}{}_5\text{)}{}_3\text{CCl}{}_4$ catalyst system in the presence of various Lewis bases. Effective Lewis bases are γ-butyrolactone, diglyme and diethylenetriamine which are multidentate. The rate of polymerization is dependent not only on the basicity of the Lewis base used but also on a coordination number of one. The latter is the predominant factor. For the effect of polymeric amines, a tentative hypothesis is discussed.     

Synthesis and Characterization of Ti0.33Ta0.33Nb0.33C and Ti0.33Ta0.33Nb0.33CxN1-x Whiskers

Ta_0.33Ti_0.33Nb_0.33C and Ta_0.33Ti_0.33Nb_0.33C _x N_{1− x} whiskers were synthesized via a carbothermal vapor-liquid-solid growth mechanism in the temperature range 900°-1450°C in Ar or N₂. The optimum temperature was 1250°C. Whiskers were obtained in a yield of 70-90 vol%. The whiskers were 0.5–1 µm in diameter and 10–30 µm in length. The starting materials that produced the highest whisker yield were: TiO₂, Ta₂O₅, Nb₂O₅, C, Ni, and NaCl. C was added to reduce the oxides, and Ni to catalyze whisker growth. NaCl was used as a source of Cl for vapor-phase transportation of Ta and Nb oxochlorides and Ti chlorides to the catalyst. The catalyst metal was recycled several times during the synthesis and was transported as NiCl₂( g ) according to thermodynamic calculations. The rate of formation and the chemical composition of the whiskers depended on the synthesis temperature, the choice of catalyst, and the atmosphere. At low temperatures, the whiskers were enriched in Nb and Ta, whereas the Ti content increased with increased synthesis temperature.