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。     

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。     

纤维素浆粕和Lyocell纤维在LiCl/DMAc中溶解差异的研究

为了研究Lyocell工艺中纤维素相对分子质量分布的变化,分析了纤维素浆粕和相应的由浆粕生产出的Lyocell纤维在LiCl/DMAc中的溶解情况,发现两者存在很大差异,分别从纤维素的晶型、取向和形态结构等方面分析原因。结果表明:由于Lyocell纤维(纤维素II)比纤维素浆粕(纤维素I)在热力学上更稳定,分子间的氢键更多,且Lyocell纤维的取向较纤维素浆粕高,纤维结构较致密,使得溶剂的渗透和氢键的破坏更加困难,因此Lyocell纤维在LiCl/DMAc中的溶解比纤维素浆粕差。     

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。     

不同预处理条件下纤维素的结构变化及其在DMAc/LiCl中的溶解

介绍了乙二胺、氢氧化钠和高温等三种不同的纤维素预处理方法。研究预处理后纤维素的结构变化,讨论预处理过程中的转化机理,并通过X射线衍射对纤维素结晶度的变化进行表征,证明乙二胺预处理后纤维素的结晶度下降最大。纤维素经过预处理后可以溶解在DMAc/L iC l中,讨论其溶解机理,通过对比三种预处理纤维素的溶解性能,表明经过乙二胺预处理之后的纤维素在DMAc/L iC l中溶解性能最好,氢氧化钠预处理的纤维素次之,高温预处理的纤维素溶解性能相对较差。     

Recycling of waste cotton fabrics into regenerated cellulose films through three solvent systems: A comparison study

Large amounts of textile waste are generated every year and disposed of through landfill or incineration, leading to numerous environmental and social issues. In this work, the dissolution of three typical waste cotton fabrics (t-shirts, bed sheets and jeans) in NaOH/urea aqueous solution, H₂SO₄ aqueous solution, and LiCl/DMAc solution was investigated. Compared to different types of cotton fabrics, the effects of three solvents on the dissolution of fabrics were more obvious, leading to the significant changes in the structure and properties of regenerated cellulose films. Cotton fabrics (about 2%–5%) were rapidly dissolved (8 min) in H₂SO₄ and NaOH/urea solvents after acid pretreatment, while the dissolution in LiCl/DMAc solvent did not need any pretreatment, but a lower cellulose concentration (1%), higher dissolution temperature (80°C), and longer dissolution time (24 h) were required. The films produced from bed sheets in NaOH/urea solution exhibited the highest tensile strength, thermal stability, and water vapor barrier property. It was because of the stronger cellulose chain entanglement and hydrogen bonds induced by the higher cellulose concentration in NaOH/urea solution. Therefore, this work proves the feasibility to recycle waste cotton fabrics into biodegradable cellulose films, which can be potentially used in various food and agricultural applications.     

纤维素LiCl/DMAc溶液流变性能研究

本文研究了9％LICI／DMAC纤维素溶液的流变性能。在该体系中纤维素溶液是非牛顿流体，属于假塑性流体，具有典型的幂律性。通过幂律方程拟合计算，其稠度系数为60～135，流动特性指数为0.62～0．70。随着浓度增大，稠度系数增大和流动特性指数降低；温度的变化对流动特性指数的影响不大，温度升高，流动特性指数略有减小，而稠度系数相对增大。溶液的粘度随着剪切速率的增大，开始时粘度迅速降低，后趋于稳定，这可能与纤维素分子在溶液中的取向有关。在不同剪切速率下，其流动活化能为23～30kJ．     

Effect of solvent exchange on the pore structure and dissolution behavior of cellulose

Effect of solvent exchange, i.e., the sequential immersion in water, acetone, and DMAc on the pore structure of cellulose and its dissolution behavior in lithium chloride/N,N‐dimethylacetamide (LiCl/DMAc) was investigated by using size exclusion liquid chromatography (SEC), dynamic light scattering (DLS), and small‐angle X‐ray scattering (SAXS). In the SEC experiment, poly(styrene)s, diethyl phthalate, and acetone were used as probe solutes and 2‐butanone was used as an eluent. Capacity factor of these solutes in the solvent‐exchanged cellulose were larger than those in the untreated one. This was remarkable when diethyl phthalate and acetone were used as solutes. Since the molecular radii of these solutes were estimated to be less than 1 nm, it was shown that the solvent exchange increases the amount of pores within cellulose with the radii of less than 1 nm. In the SAXS experiment, structural difference between the solvent exchanged and the untreated celluloses was observed when the celluloses were immersed in acetone. Values of specific inner surface and average chord length calculated from SAXS profile showed that the amount of small pores was increased in the solvent exchanged cellulose. Considering the results from SEC, DLS, and SAXS measurements, facilitated dissolution of the solvent exchanged cellulose in LiCl/DMAc was attributed to the increase in the pores with the radii of less than 1 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3976–3984, 2007     

The role of rheological premonitory of hydrogels based on cellulose nanofibers and polymethylsilsesquioxane on the physical properties of corresponding aerogels

Cellulose nanofibers (CNFs) and polymethylsilsesquioxane (PMSQ)-based aerogels (CNF/PMSQ aerogels) have been prepared by the sol–gel method. The extraction of CNFs from pine wood and formation of composite aerogel with PMSQ were confirmed by Fourier transform infrared spectroscopic and field emission scanning electron microscopic analyses. The rheological premonitory of hydrogel has been performed to predict the physical properties (i.e., density, mechanical properties) of aerogels. The variation in the precursor (methyltrimethoxysilane [MTMS]) and urea content has shown a considerable effect on the storage modulus and phase angle of the hydrogel. The variation in urea content showed a 4–8% increment in the density with a pronounced difference in aerogel's morphology. The increment in the MTMS concentration demonstrated a 10–20% enhancement in density with a minor change in morphology. The van Gurp–Palmen plot of hydrogel has represented a relationship between complex modulus and phase angle. This study establishes that hydrogel's premonitory analysis could compare aerogel's physical properties without going through drying and further analysis.     

Effects of microstructures on the viscoelastic and rheological properties of metallocene‐catalyzed cyclo‐olefin copolymers: A preliminary study

We characterized metallocene‐catalyzed cyclo‐olefin copolymers (mCOCs) with similar heat distortion temperatures but dramatic differences in melt‐flow indices to understand how the molecular conformation affected their rheological and viscoelastic properties. The mCOC conformations were identified with ¹³C‐NMR, whereas the viscoelastic and rheological properties were measured with cone‐and‐plate and high‐pressure capillary rheometers. Our preliminary results showed that the mCOC rheological and viscoelastic properties might depend strongly on the conformation rather than the norbornene content, molecular weight, and molecular weight distribution. mCOCs containing ‐NNN‐ locks (where N represents norbornene) exhibited stronger molecular entanglements than those having no ‐NNN‐ blocks, as reflected in lower crossover frequencies and higher crossover torque. Furthermore, the existence of larger rigid ‐NNN‐ blocks resulted in higher molten viscosities and flow activation energies. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3695–3701, 2002     

基于离子液体的聚丙烯腈/纤维素溶液的动态流变性能研究

采用旋转流变仪分别对以离子液体1-烯丙基-3-甲基咪唑氯盐[AMIM]Cl,1-丁基-3-甲基咪唑氯盐[BMIM]Cl,1-乙基-3-甲基咪唑醋酸盐[EMIM]Ac为溶剂的聚丙烯腈/纤维素共混溶液(分别标记为溶液A,B,E)的动态流变性能进行了研究,讨论了溶液的储能模量(G′)、损耗因子(tanδ)及角频率(ω)之间的关系。结果表明:A、B溶液lgG′-lgω曲线分别在70,90℃开始呈现"第二平台",且随温度升高,平台宽度变大;A,B溶液时温叠加主曲线分别在70,100℃下的低频区域发生偏离,表明时温等效原理在低频下对于G′失效,E溶液不符合时温等效原理;A,B溶液tanδ随ω增大而降低,E溶液则升高;A,B溶液lgG′～lgG″曲线分别在80,110℃时发生偏离,在测试温度范围内对温度具有依赖性,E溶液lgG′-lgG″呈非线性关系;A,B溶液的Cole-Cole曲线出现拖尾现象。     

A study of rheological properties of cellulose diacetate in acetone solution at low and high shear rates

The rheological properties of cellulose diacetate (CDA) with different intrinsic viscosity (IV) and different concentration in acetone solutions were studied at low and high shear rates. The zero-shear viscosity increased and the structural index increased, when the IV of CDA was increased or the acetone solution concentration was increased. Evidence suggested that a sulfate structure may be forming. It is shown that the increase of hemicellulose and sulfur content is associated with an increase of chain entanglements between CDA molecules and the abnormal increase of solution zero-shear viscosity. At a high shear rate, the correlation curve between inlet pressure drop and solution concentration obtained by Bagley method analysis shows an inflection point, which appears to be the critical concentration at which the cellulose diacetate molecular chains in the solution form a long range entangled elastic network. After the concentration exceeds a certain range of above critical points, the entanglement of the molecular chains in the solution is significantly enhanced. The zero shear viscosity inflection point concentration calculated by the rheological curve with low shear velocity and the inlet pressure drop inflection point concentration calculated by the capillary rheological calculation have good consistency.     

A comparative study of the effect of some paraffinic oils on rheological and dynamic properties and behavior at low temperature in EPDM rubber compounds

The influence of some paraffinic oils on rheological properties, dynamic properties, and behavior at low temperature of various ethylene–propylene–diene monomer rubber (EPDM) compounds was studied. Three different types of EPDM, Dutral TER 4049, Dutral Ter 4038, and Nordel IP 4770 R, and five different paraffinic oils were used. The properties of the compounds were evaluated with reference to the oil characteristics: viscosity, composition, glass transition temperature, and solubility parameter. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1825–1834, 2005     

Influence of water content,time, and temperature on the rheological behavior of polyethylene terephtalate

In this work, the main factors affecting the rheological behavior of polyethylene terephtalate (PET) in the linear viscoelastic regime (water content, time delay before test, duration of experiment, and temperature) were accessed. Small amplitude oscillatory shear tests were performed after different time delays ranging from 300 to 5000 s for samples with water contents ranging from 0.02 to 0.45 wt %. Time sweep tests were carried out for different durations to explain the changes undergone by PET before and during small amplitude oscillatory shear measurements. Immediately after the time sweep tests, the PET samples were removed from the rheometer, analyzed by differential scanning calorimetry and their molar mass was obtained by viscometry analysis. It was shown that for all the samples, the delay before test and residence time within the rheometer (i.e. duration of experiment) result in structural changes of the PET samples, such as increase or decrease of molar mass, broadening of molar mass distribution, and branching phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of the vinyl concentration on the structural and rheological characteristics of peroxide‐modified high‐density polyethylenes

The effect of the hydrogenation of the terminal vinyl groups on the peroxide modification and rheological properties of high‐density polyethylene (HDPE) was investigated. The aim of the study was to determine exclusively the effect of the terminal vinyl groups on the peroxide crosslinking and rheological properties of HDPE with one polymer type. This was achieved by hydrogenation of the terminal vinyl groups of a commercial HDPE to obtain an identical material from a structural point of view, which differed only in the nature of the terminal unsaturations, and the comparison of its level of peroxide crosslinking with that of the original polymer. Hydrogenated and unhydrogenated polymer samples were modified at 170°C with different amounts of organic peroxide ranging from 125 to 5000 ppm. Changes in the molecular structure were determined by Fourier transform infrared spectroscopy, size exclusion chromatography, and rheological measurements. Hydrogenation of the terminal groups of the original polymer significantly reduced the rate of modification or crosslinking. The dynamic viscosity and elasticity increased with the level of peroxide modification. Unhydrogenated samples exhibited rapid increases in viscosity and elastic modulus, whereas their hydrogenated counterparts required about 500% of the amount of peroxide needed for the unhydrogenated sample to attain similar structural changes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of cellulose nanofibers and acetylated cellulose nanofibers on the properties of low‐density polyethylene/thermoplastic starch blends

The aim of this study was to evaluate the effect of cellulose nanofibers (CNFs) and acetylated cellulose nanofibers (ACNFs) on the properties of low‐density polyethylene/thermoplastic starch/polyethylene‐grafted maleic anhydride (LDPE/TPS/PE‐g‐MA) blends. For this purpose, CNFs, isolated from wheat straw fibers, were first acetylated using acetic anhydride in order to modify their hydrophilicity. Afterwards, LDPE/TPS/PE‐g‐MA blends were reinforced using either CNFs or ACNFs at various concentrations (1–5 wt%) with a twin‐screw extruder. The mechanical results demonstrated that addition of ACNFs more significantly improved the ultimate tensile strength and Young's modulus of blends than addition of CNFs, albeit elongation at break of both reinforced blends decreased compared with the neat sample. Additionally, biodegradability and water absorption capacity of blends improved due to the incorporation of both nanofibers, these effects being more pronounced for CNF‐assisted blends than ACNF‐reinforced counterparts. © 2018 Society of Chemical Industry     

溶剂含量对变燃速发射药的流变性影响研究

用MLW-90防爆流变仪测试不同溶剂含量下变燃速发射药内、外层的流变性能.得出结论,随着溶剂含量的增加,其表观黏度降低,流动性增强;乙基硝化纤维素(EC)、黑索今(RDX)的加入降低了变燃速发射药的表观黏度.     

不同预处理条件下纤维素的结构变化及其在DMAc／LiCI中的溶解

介绍了乙二胺、氢氧化钠和高温等三种不同的纤维素预处理方法。研究预处理后纤维素的结构变化，讨论预处理过程中的转化机理，并通过X射线衍射对纤维素结晶度的变化进行表征，证明乙二胺预处理后纤维素的结晶度下降最大。纤维素经过预处理后可以溶解在DMAc／LiCI中，讨论其溶解机理，通过对比三种预处理纤维素的溶解性能，表明经过乙二胺预处理之后的纤维素在DMAc／LiCI中溶解性能最好，氢氧化钠预处理的纤维素次之，高温预处理的纤维素溶解性能相对较差。     

Influence of water on phase transition and rheological behavior of cellulose/ionic liquid/water ternary systems

The influence of water content on liquid crystalline (LC) gel formation and the rheological behavior of a ternary microcrystalline cellulose (MCC)/1‐ehtyl‐3‐methylimidazolium acetate (EmimAc)/water system was investigated using polarized optical microscopy (POM) and rheometry. POM indicated that the distinct water content range for forming a fully anisotropic LC gel with 14 wt % MCC was 4–10 wt %. Adding water to the MCC/EmimAc system resulted in enhanced complex viscosity and storage and loss moduli, and ultimately LC gel formation. Comparison of creep compliance vs. time revealed that the system without water showed representative viscoelastic behavior, while the time dependence of creep compliance disappeared as the water content increased, suggesting elastic‐solid behavior. Additionally, hydrogen bonding between cellulose and EmimAc weakened as water content increased, whereas the intra‐ and intermolecular hydrogen bonds of cellulose became stronger because of strong self‐association. This strong bonding caused aggregation, chain entanglement, and self‐supporting LC gel network formation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44658.     

Using multiple‐mode models for fitting and predicting the rheological properties of polymeric melts. II. Single and double step‐strain flows

Several classes of multiple‐mode rheological constitutive equations are examined for predicting the viscoelastic flow properties of a typical polymer melt in single and double step‐strain flows. The phenomenological parameters appearing in these models have been obtained by the fitting of experimental data taken in small‐amplitude oscillatory shear and steady shear flows. The performance of the models for predicting the experimental data in the step‐strain experiments is examined in detail. Specifically, we examine whether or not mode coupling is necessary to describe the experimental behavior under step‐strain flows. Furthermore, it is demonstrated that the reversing double step‐strain experiment is a very powerful tool for testing viscoelastic constitutive equations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007