LiCl/DMAc体系对蔗渣的溶解性

LiCl/DMAc体系是近年来日益受到重视的纤维素非水溶剂,但其溶解植物生物质,如蔗渣的情况却鲜有报道。本文从活化时间、固液比、LiCl浓度、加热时间及加热温度5个方面对LiCl/DMAc体系溶解蔗渣的行为进行研究。结果表明最佳溶解条件为:蔗渣160℃活化1h,烘干后取400mg与10%LiCl/DMAc溶液20mL按固液比1:50g/mL混合,160℃加热3h后,蔗渣溶解率可达81.8%。这为均相条件下利用蔗渣进行高效衍生化提供了有前景的发展方向。     

在线红外跟踪碱活化纤维素在LiCl/DMAc中的溶解

LiCl/DMAc可作为纤维素的溶剂。笔者利用在线红外技术实时跟踪碱活化纤维素在LiCl/DMAc中的溶解过程。结果表明,LiCl/DMAc可以在一定程度上破坏纤维素中氢键,实现对纤维素的溶解,无中间衍生物产生,最终溶液中纤维素主要以多聚体形式存在。同时,检测出LiCl/DMAc对纤维素的高温预溶解与室温溶解过程,且此过程可逆。     

LiCl/DMAc非水溶液中纤维素均相接枝制备絮凝剂材料

为了使纤维素改性制备表面活性剂,采用LiCl/DMAc溶剂体系,以丙烯酰胺和木材纤维素为原料,进行接枝共聚及阳离子化,合成阳离子型天然高分子改性絮凝剂。讨论了LiCl用量、纤维素用量、单体浓度等因素对接枝产物絮凝性能的影响。通过正交实验确定最佳合成条件为:LiCl用量为6g/50mL,纤维素用量为0·50g/50mL,丙烯酰胺量为2·0g/50mL。产物接枝产率可达到62·74%。     

棉纤维在LiCl/DMAc极性溶液中的溶解性能研究

采用不同方法将棉纤维活化并溶解在LiCl/DMAc极性溶液中,研究了活化方法、溶解温度、时间及LiCl浓度对棉纤维素溶解性的影响。结果表明:DMAc热活化法为较好的活化方法;提高溶解温度,延长溶解时间及提高LiCl浓度均有利于棉纤维溶解;棉纤维在LiCl质量分数为12%的LiCl/DMAc溶液中,150℃下搅拌4h,溶解度可达3%。碱活化法使棉纤维素聚合度大幅度降低,可提高棉纤维溶解度至8%。通过扫描电镜和X射线衍射方法研究了棉纤维在前处理和溶解过程中的形态和结构变化,初步揭示了纤维素高温处理后在低温下发生溶解的机理。     

细菌纤维素在LiCl/DMAc溶剂体系中的溶解性能研究

纤维素经过活化后可以溶解在LiCl/DMAc溶剂体系中,研究了乙二胺活化对细菌纤维素溶解性能的影响,得到最佳活化条件;研究了LiCl的浓度、溶解温度和搅拌时间对溶解性能的影响,得到最佳溶解条件;研究了细菌纤维素在LiCl/DMAc极性溶剂体系中的溶解机理。     

阳离子絮凝剂在纤维素/离子液体中的均相合成

纤维素在离子液体中有良好的溶解性能形成均相体系,文中制备了1-烯丙基-3-甲基氯代咪唑[Amim]Cl离子液体,与丙烯酰胺进行接枝共聚合及阳离子化,合成不同聚合度的纤维素阳离子絮凝剂,并与LiCl/DMAc体系进行比较,探讨其絮凝性能.结果显示:纤维素在[Amim]Cl中溶解性能良好、接枝共聚反应活性较好;纤维素聚合度...     

醋酸长链酸纤维素酯合成技术探索研究

以纤维素、醋酸酐和十二酰氯为原料在N,N-二甲基乙酰胺/氯化锂(DMAc/LiCl)溶剂体系中制备了醋酸月桂酸纤维素酯。考察了在不使用缚酸剂的条件下,反应物的加入顺序及加入量、纤维素溶液浓度、反应温度和反应时间对接枝率的影响,试验结果表明,在较优的工艺条件下,产物接枝率可达230%以上。     

细菌纤维素在LiCI/DMAc溶剂体系中的溶解性能研究

纤维素经过活化后可以溶解在Lic1/DMAc溶剂体系中,研究了乙二胺活化对细菌纤维素溶解性能的影响,得到最佳活化条件;研究了LICl的浓度、溶解温度和搅拌时间对溶解性能的影响,得到最佳溶解条件;研究了细菌纤维素在LiCl/DMAc极性溶剂体系中的溶解机理。     

均相制备纤维素/丙烯酰胺/甲基丙烯酸丁酯接枝共聚物的研究

以氢氧化钠/硫脲/尿素新型溶液溶解纤维素,在均相条件下以丙烯酰胺(AM)、甲基丙烯酸丁酯(BMA)为接枝单体,过硫酸铵为引发剂,N,N′-亚甲基双丙烯酰胺(MBA)为交联剂,通过自由基聚合法制备出了纤维素/AM/BMA接枝共聚物。考察了聚合温度、时间以及(NH4)2S2O8、AM、BMA、MBA的用量对接枝效果的影响。利用红外光谱(FT-IR)、X射线衍射(XRD)和扫描电镜(SEM)对接枝产物进行了结构表征。实验结果表明,纤维素/AM/BMA接枝共聚物的最佳合成条件为:m(纤维素)∶m(AM)∶m(BMA)∶m[(NH4)2S2O8]∶m(MBA)=1∶4∶2∶0.05∶0.006,反应温度为65℃,反应时间为2h,在此条件下接枝率可达87%,接枝效率为36%。制备的纤维素/AM/BMA接枝共聚物的吸水倍率为583g/g。     

纤维素LiCl/DMAc体系的溶液特征

本文研究了纤维素LiCl／DMAc体系的溶液特征。实验结果证明该体系具有良好的时间稳定性和热稳定性，能在常温下近30天内没有明显的粘度降低；在100℃高温下，4h不降解。同时测定了溶液的特性粘数和Huggins常数，Huggins常数在0．4～0．6之间，对比纤维素的铜乙二胺（Cuen）溶液，发现特性粘数[η]LICI/DMAc＞[η]Cuen，无扰尺寸ALiCi／DMAc＞ACuen，可见在LiCl／DMAc体系中，溶剂与纤维素分子表现出更强的相互作用力，分子链充分伸展。该体系的特性粘数、粘度常数不仅与温度、溶剂有关，而且是LiCl浓度的函数，具有与聚电解质溶液相类似的性质。这可能是因为纤维素分子链上的H质子和溶液中的Cl-离子相互作用，而使纤维素分子带上部分电荷，相互排斥而引起的。因此利用M－H方程测分子量，粘度常数的确立必须考虑诸多因素的影响，否则会导致分子量的高估。     

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.