不同初始结构间规聚丙烯纤维熔融过程中的结晶转变行为

通过熔融纺丝及随后的热处理制备了具有不同初始结构的间规聚丙烯纤维(sPP).采用差示扫描量热仪(DSC)和变温广角X-射线衍射仪详细研究了sPP纤维在升温过程中的结构转变和熔融行为.结果表明,不同初始结构sPP纤维的晶型不同,卷绕纤维和退火处理纤维以Ⅰ型和Ⅱ型晶型为主,牵伸纤维介晶相占优;升高温度导致Ⅰ型和Ⅱ型两种晶型直接熔融,没有出现Ⅱ型向Ⅰ型的晶型转变;初始结构为介晶相的纤维在升温过程中部分介晶相直接转变为Ⅱ型晶型,还有一部分介晶相直接熔融,并在随后的升温过程中,形成Ⅰ型晶型.sPP纤维的多重熔融行为与其初始结构和纤维制备条件密切相关.     

纤维素的高分子化学转化及其变性的研究——ⅩⅤ.纤维素在高铈盐溶液中的氧化动力学和氧化部位

从高铈盐水溶液分解动力学角度进一步确定了反应体系的光敏性质。 从水解纤维素、纤素二糖、二醛基纤维素、葡萄糖、葡萄糖甲甙等纤维素模型化合物在高铈盐溶液中的氧化动力学,确定了作为含有多种官能团的高聚物纤维素的氧化动力学方程式是: -(d[Ce~(4+)]/dt)=(k_Ⅰ[Ⅰ]_0+k_Ⅱ[Ⅱ]_0+k_Ⅲ[Ⅲ]_0+……)[Ce~(4+)]其中,[Ⅰ]_0、[Ⅱ]_0和[Ⅲ]_0分别为纤维素中第1、2和3官能团的初始浓度。k_Ⅰ、k_Ⅱ和k_Ⅲ分别为它们的反应速率常数。 不同模型化合物中相同官能团速率常数的对比,确定了速率常数的归属。k_Ⅰ、k_Ⅱ分别为巨分子端基环上的潜醛基和 5、6-乙二醇单元的反应速率常数。证明在纤维素巨分子中至少有三个氧化反应部位。 纤维素巨分子经高铈盐氧化时,每个潜醛基或5、6-乙二醇单元各消耗二个高铈离子,最后都转变为醛基。在消耗一个高铈离子时,可以生成中间络合物——巨分子自由基。自由基位于末端基环的第2位和第5位碳原子上。 第三反应部位位于中间基环上,其反应速率常数虽小,但由于含量很多,故其反应速率不容忽视。第三反应部位的精确位置现尚无法肯定。 用高铈引发所得共聚物主链没有明显的裂解,自由基的可能位置表明它可能是接枝-嵌段复合共聚物。     

不同结晶度的乙二醇及其水溶液玻璃化转变与焓松弛

为了考察晶体成分对无定形成分玻璃化转变和结构松弛行为的影响,利用差示扫描量热法(DSC),结合低温显微技术,研究了乙二醇(EG)及其50％水溶液在不同结晶度时的玻璃化转变和焓松弛行为.采用等温结晶方法控制骤冷的部分结晶玻璃体中的晶体份额.DSC结果表明,对于部分结晶的EG,只有单一的玻璃化转变过程,而对于50％EG,当结晶度不同时,不同程度地表现出两次玻璃化转变（无定形相Ⅰ和无定形相Ⅱ）.相Ⅰ的玻璃化转变温度和完全无定形态的含水EG的玻璃化转变温度相一致;相Ⅱ的玻璃化转变温度要比此温度约高6 ℃.低温显微观察结果印证了DSC实验结果.DSC等温退火的实验和KWW(Kohlrausch-Williams-Watts)衰变函数分析结果表明,EG无定形和50％EG中的两种无定形有不同的焓松弛行为.     

低共熔溶剂预处理木质纤维素生产生物丁醇

生物丁醇被认为是一种能够直接代替汽油的生物燃料,可满足经济发展对可持续液体燃料的需求。木质纤维素可再生,来源广泛且廉价,是生产生物丁醇的理想原料。但木质纤维素结构复杂,难以直接水解利用,高效的预处理方式是其商业化应用的关键。低共熔溶剂(DES)是一种环境友好的新型溶剂,具有成本低、绿色低毒、溶解能力强、良好的选择性和生物相容性等优点,有着较高的生物质预处理潜力。本文首先介绍了DES的种类和性质;其次,综述了木质纤维素中各组分在DES中的溶解效率,讨论了DES预处理木质纤维素对酶水解和丁醇发酵过程的影响;再次,通过对各种生物加工过程的梳理,对整合生物过程在生产生物丁醇领域的应用潜力进行了评述;最后,对DES预处理木质纤维素生产生物丁醇领域今后的工作做出了展望。     

非离子型表面活性剂对木质纤维素酶催化水解的影响及机理

木质纤维素的酶解糖化过程是纤维素生物质转化中的关键步骤,也是限制纤维素生物转化生产燃料和化学品的主要瓶颈。大量的研究表明,非离子型表面活性剂能够强化木质纤维素酶解过程,显著提高纤维素的酶催化水解效率。本文综述了非离子型表面活性剂对纯纤维素和木质纤维素底物酶解的影响,分析了底物结构特性、水解条件、纤维素酶组成等诸多因素与表面活性剂作用效果之间的关联,并从纤维素酶的吸附特性、纤维素酶组分间的协同作用等方面对非离子表面活性剂的作用机理进行了总结。结合已有的研究进展和存在的问题,提出了今后表面活性剂对于木质纤维素酶催化水解影响的研究重点方向,即系统分析底物结构、水解条件等因素对表面活性剂作用的宏观影响,以及分析这种作用的热力学和动力学特性,而微观上需要从原子和分子层面上解析表面活性剂与底物和纤维素酶之间的相互作用特性。     

室温离子液体溶解和分离木质纤维素*

作为世界上最丰富的生物质资源,木质纤维素是生产清洁能源和精细化工品的天然原料。室温离子液体是近年来出现的一类绿色材料,对溶解和分离木质纤维素具有广阔的应用前景。本文在介绍木质素、纤维素、半纤维素和相关室温离子液体的组成与结构的基础上,综述了室温离子液体在溶解、分离木质纤维素方面的研究进展。根据目前所报道的研究结果,总结了不同离子液体对木质素、纤维素、半纤维素的溶解作用以及对木质纤维素的分离性能,分析了离子液体的结构与其溶解性能的关系,讨论了可能的溶解机理。最后提出了这一领域存在的问题,并对其未来的发展作了展望。     

双螺杆挤出机纺制的纤维素纤维

以离子液体氯化1-烯丙基-3-甲基咪唑([AMIM]Cl)为溶剂,采用双螺杆挤出机溶解并纺制了较高质量分数的纤维素纤维,测定了纤维素纤维的结构与性能以及纤维中[AMIMCl]残余质量分数,观察了纤维的微观形貌。结果表明:双螺杆挤出机能溶解并纺制较高质量分数的纤维素纤维,可达30%,纤维素纤维晶型由浆粕的Ⅰ型转变为Ⅱ型,纤维结晶度小于纤维素浆粕。成形过程中,纤维中的离子液体难于完全除去,导致纤维素纤维分解温度下降。实验范围内,纤维素质量分数为20%时,纤维断裂强度最高,为0.51cN/dtex。     

木质纤维素-蒙脱土纳米复合材料的制备

采用插层复合方法在碱性水溶液中制备了木质纤维素-蒙脱土纳米复合材料,并分析了反应温度、反应时间、木质纤维素与蒙脱土的质量比等因素对纳米复合材料有机化程度的影响,用FT-IR、XRD、TEM、SEM等方法对纳米复合材料的结构进行了表征。结果表明:蒙脱土片层结构在反应过程中被撑开,木质纤维素分散在其中,形成插层-剥离型纳米复合材料,其热稳定性较木质纤维素有了较大提高。     

生物质资源研究的新视野——木质纤维素全溶体系

木质纤维素全溶体系是指具有氢键破坏能力,从而导致木质纤维素溶解的一类特殊溶剂体系。包括有机溶剂全溶体系和离子液体全溶体系。前者主要是基于二甲基亚砜的全溶体系,具体可分为二甲基亚砜/四丁基氟化铵、二甲基亚砜/N-甲基咪唑和二甲基亚砜/氯化锂3种全溶体系。后者则主要是基于咪唑基离子液体的全溶体系,种类较多。这一全新概念的提出为更加便捷地对木质纤维素进行结构鉴定、化学改性和高效利用提供了一个可靠方法。本文对木质纤维素全溶体系的最新研究成果进行了综述。     

基于木质生物质分级利用的组分优先分离策略

木质生物质是地球上最丰富的一类生物质资源,主要由碳水化合物高分子(纤维素、半纤维素)和芳族聚合物(木质素)组成。木质纤维组分的清洁高效分离,是实现多元化、高值化生物精炼的重要基础。本文首先讨论了基于分级利用的组分分离技术与基于制备纤维素乙醇的预处理技术的不同之处;其次,梳理归纳了五种木质纤维组分优先分级分离策略:纤维素优先分离,木质素优先分离,半纤维素优先分离,木质素和半纤维素优先分离以及纤维素和半纤维素优先分离;再次,基于半纤维素优先分离策略,对国内相关的产业化应用进行了评述;最后,对木质生物质组分分离技术的当下定位和发展前景进行了总结与展望,以期对木质生物质的三大组分有较全面的价值观念和利用思路,并对木质生物质精炼技术的发展提供借鉴与参考。     

Understanding hydrophobicity variations in dense medium ferrosilicon from different production routes

Dense medium ferrosilicon (FeSi) powders produced via submerged arc furnace smelting, granulation, and milling route show varying hydrophobicity, sometimes totally nonwetting, amounting to production losses. This does not occur in powders produced via induction furnace smelting and atomization. Although wetting is fundamentally a surface phenomenon, bulk property can dictate surface behavior. Hence, for detailed insight into the cause of the variation, particles of powders from different production routes were studied from surface to the core. Particle shapes differ clearly for the two production routes, but this was found inconsequential to the wetting behavior. Rather, size distribution, proportion of ultra-fine particles in the powder, was seen to have effect, being more in the nonwetting sample. From the optical microscopy: in the granular particles (that is, before milling), it is visible that different phases formed from the Fe-Si-C system, and this will impact milling differently; particles from nonwetting milled powders show a notable surface layer, and in contrast, the atomized particles show more homogeneous equiaxed grains. From X-ray photoelectron spectroscopy, argon ions sputtering, and depth composition profiling, graphitic carbon (C1s at 284.5 eV binding energy) was found on the surface for all samples at levels above bulk alloy composition but highest (65%) for the totally nonwetting sample. From these pointers, graphite coating on particles is responsible for varying hydrophobicity. Carbon affects solid FeSi microstructure, milling, and powder properties. Controlling carbon content from the smelting stands out for avoiding milled FeSi hydrophobicity. This is however not a straight forward minimization problem.     

Effect of mechanical activation of reagents’ mixture on the high-temperature synthesis of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiB<Subscript>2</Subscript> composite powder

A powder mixture of Al/TiO₂/H₃BO₃ = 10/3/6 in molar ratio was used in this study to form the Al₂O₃–TiB₂ ceramic composite via thermite reactions (combustion synthesis). As no combustion synthesis occurred for an unmilled sample in a furnace, the mixture was milled in a planetary ball-mill for various milling times, and the as-milled samples were in situ synthesized in the furnace at a heating rate of 10 °C/min. The differential scanning calorimetry (DSC) measurements were performed with the same heating rate on the unmilled and the as-milled samples to evaluate the influences of the milling on the mechanisms and efficiencies of reactions. Although no combustion synthesis occurred for the unmilled sample in the furnace, two exothermic peaks were detected in its DSC curve after the melting of the Al. For the as-milled samples, significant changes revealed in the DSC curves, suggest that the milling process before the combustion synthesis changed the mechanisms and efficiencies of reactions. In addition, the intensity and the temperature of the exothermic peaks in the DSC curves changed by increasing the milling time. According to the XRD analyses, by enhancing the milling time, the purity of the final products would increase, confirming that the efficiency of the reactions increased. Finally, the microstructures of the as-milled and as-synthesized samples were examined by a SEM, and it was shown that the morphology of the reactant powders was altered by increasing the milling time.     

Size Effects of Nano-crystalline Cellulose

Natural cellulose with the crystal form of cellulose I, when treated with condensed lye(e.g. 18% NaOH), can change into new crystal form of cellulose II. But the nano-crystaUinecellulose (NCC) can do it when only treated with dilute lye (e.e. 4%NaOH) at room temperature and even can dissolve into slightly concentrated lye (e.g.4%NaOH).     

A study on the inhibition of cellulolytic activities by lignin

It is well known that cellulolytic enzymes hardly attack lignocellulose. Hitherto knowledge, however, has not yet fully elucidated the mechanisms of the inhibition; whether it depends on a steric hindrance or protein-binding inhibition. For the purpose of acceleration of enzymatic digestion of lignocellulose biomass, the study was carried out using partially purified cellulase of Meicelase and milled wood lignin from soft or hard wood. Milled wood lignin was prepared from soft wood,Picea jezoensis, or from hard wood,Quercus serrata, by the method of Björkman. Lignin was dissolved in methyl cellosolve, since the solvent has little effect on cellulolytic activities, and enzymic activities were followed with partially purified Meicelase. The results show that cellobiose activities of enzymes fromTrichoderma viride are markedly depressed by both lignin of soft and hard wood, and the former lignin inhibits the reaction stronger than the latter. Lignins show no inhibition in the reaction with CMC and debris of filter paper. Liberation of glucose from filter paper by the enzyme in the presence of lignin is also depressed, and addition of cellobiase instead of lignin in the above enzyme reaction shows the delay of time for breakdown of filter paper. This phenomenon indicates that lignin inhibits enzymic decomposition of cellobiose in the degradation pathway of cellulose and accumulated cellobiose gives a feedback function to digestion of fibers of paper.     

Wettability and surface composition of partly and fully regenerated cellulose thin films from trimethylsilyl cellulose

The wettability and surface free energy (SFE) of partly and fully regenerated cellulose model surfaces from spin coated trimethylsilyl cellulose were determined by static contact angle (SCA) measurements. In order to gain detailed insight into the desilylation reaction of the surfaces the results from SCA measurements were compared with data from other surface analytical methods, namely thickness measurements, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-IR). Additionally, the influence of ultra high vacuum treatment (UHV) during XPS measurements on the water wettability and surface morphology of regenerated cellulose thin films was investigated. The wetting of polar and non-polar liquids increased with prolonged regeneration time, which is reflected in the higher SFE values and polarities of the films. After UHV treatment the water SCA of partly regenerated films decreases, whereas fully regenerated cellulose shows a higher water SCA. Therefore it is assumed that volatile desilylation products tend to adsorb on partly regenerated films, which strongly influences their wettability.     

Studies on the effect of milling on reduction of niobium pentaoxide with aluminium

The effect of milling on the aluminothermic reduction of niobium pentaoxide was investigated. Charges of Nb₂O₅ and Al (containing 5 % excess Al) were milled for different time (2, 5 and 10 h). XRD profile of milled samples indicated no phase formations during milling; only peak broadening were seen. Milled and unmilled charges were heated in a thermal analyser up to 1,400 °C. Products of milled charges showed formation of Nb, NbO and Al₂O₃; whereas unmilled hand mixed charges showed formations of Nb₃Al along with Nb and Al₂O₃. The tendency of milled charges towards Nb formations without the presence of aluminides was explained from the increase in surface area of charges caused by particle reduction.     

Aqueous pretreatment for reactive ball milling of cellulose

Aqueous swelling pretreatment of cellulose was found highly effective for reactive ball milling to prepare surface-esterified cellulose nanofibers. Compared with starting from dry cellulose, water- or 2 % NaOH-pre-swollen materials were esterified and dispersed in significantly shorter milling time. Especially commercial kraft pulp was difficult to disperse even with water pretreatment, but 2 % NaOH treatment gave full surface esterification with a bulk degree of substitution of 0.69 by 12-h ball milling, presumably because of removal of non-cellulosic components.     

Crystalline transformation of native cellulose from cellulose I to cellulose ID polymorph by a ball-milling method with a specific amount of water

We have demonstrated for the first time that a mechano-chemical treatment of native cellulose with a specific amount of water (30 wt%) present ID the cellulose solid state caused the crystalline transformation from cellulose I into cellulose ID polymorph. X-ray diffractometry was used to show that the extent of transformation into cellulose ID increased with milling time. This specific phenomenon can be explained by considering the chain mobility ID the cellulose–water system, because ₁ ^1H measurement shows that cellulose molecules are most mobile when the water content ID around 30 wt%, and thus are favorable for molecular rearrangement under external forces.     

Electron paramagnetic resonance spectroscopy of γ-irradiated cellulose and related compounds

EPR studies were carried out on different irradiated cellulosic materials. The shape of the EPR spectrum was found to depend upon the fine structure of cellulose. The peak-to-peak distances of the large peaks on the differential curves were found to be 23.3 and 24.8 gauss, respectively, for the amorphous and recrystallized cellulose. The number of free radicals present per unit weight in the recrystallized cellulose and in the amorphous cellulose were found to be in the ratio of 2.1:1. The EPR spectrum of a sample of irradiated cotton crystallites which was soaked in acetone before being dried was markedly symmetrical, in contrast to the EPR spectra of samples of cotton linters and of cotton crystallites dried from water, and was considered to be a reflection of the lower intermolecular bonding in the former. For corresponding doses, the free radicals on cotton crystallites have the highest g value, followed by cotton linters, followed by regenerated cellulose I. The g value decreased as the irradiation dose was increased.     

1-烯丙基,3-甲基咪唑室温离子液体的合成及其对纤维素溶解性能的初步研究

随着不可再生资源 (如石油、天然气、煤矿和金属矿藏等 )的急剧耗竭 ,天然高分子的开发与利用日益引起世人的关注 .纤维素作为自然界中最丰富的天然高分子材料 ,其开发与利用一直备受关注[1] .但由于天然纤维素较高的结晶度和分子间和分子内存在大量的氢键 ,使其具有不熔化、在大多数溶剂中不溶解的特点 ,这成为纤维素在应用开发中的最大障碍 .开发有效的纤维素溶剂体系是解决这一难题的关键 .研究较多的纤维素溶剂主要有铜氨溶液、Ｎ 甲基吗啉 Ｎ 氧化物(ＮＭＭＯ)溶剂体系 ,氯化锂 二甲基乙酰胺 (ＬｉＣｌ ＤＭＡＣ)溶剂体系等[2 ] ,而这…