Interactions of Ionic Liquids with Polysaccharides – 2: Cellulose

Some general comments about ionic liquids (ILs) and carbohydrates are given. The main scope of the review is to discuss the present state of the art of chemical modification of cellulose applying IL as reaction media considering own research results. ILs, namely 1-butyl-3-methylimidazolium chloride (BMIMCl), 1-ethyl- 3-methylimidazolium chloride (EMIMCl), 1-butyl-2,3-dimethylimidazolium chloride (BDMIMCl), 1-allyl-2,3-dimethylimidazolium bromide (ADMIMBr) and 1-ethyl-3- methylimidazolium acetate (EMIMAc) are solvents for cellulose (even for high molecular bacterial synthesized cellulose) and can easily be applied as reaction media for cellulose modification. We investigated the homogeneous acylation, carbanilation and silylation of the biopolymer cellulose. Under mild conditions and within short reaction time at low temperature (65 °C to 80 °C) and low excess of reagent, various cellulose esters and carbanilates, dendronized cellulose and trimethylsilyl cellulose were obtained. The DS of the cellulose derivatives can be controlled by varying the reaction time, reaction temperature and the IL used as reaction medium.     

Synthesis of cellulose benzoates under homogeneous conditions in an ionic liquid

The ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl) as a reaction medium was studied for the synthesis of cellulose benzoates by homogeneous acylation of dissolved cellulose with benzoyl chlorides in the absence of any catalysts. Cellulose benzoates with a degree of substitution (DS) in the range from about 1 to 3.0 were accessible under mild conditions. The DS of cellulose derivatives increased with the increase of the molar ratio of benzoyl chloride/anhydroglucose unit (AGU) in cellulose, reaction time, and reaction temperature. Benzoylation of cellulose with some 4-substituted benzoyl chlorides including 4-toluoyl chloride, 4-chlorobenzoyl chloride and 4-nitrobenzoyl chloride was also readily carried out under mild conditions. Furthermore, regioselectively substituted mixed cellulose esters were synthesized in this work. All products were characterized by means of FT-IR, ¹H-NMR, and ¹³C-NMR spectroscopy. In addition, at the end of benzoylation of cellulose, the ionic liquid AmimCl was easily recycled. When the recycled AmimCl was used as the reaction media, the cellulose benzoate with a similar DS was obtained under comparable reaction conditions.     

LiCl／DMAc溶剂体系中长链脂肪酸纤维素酯的制备及其药物释放性能

在ＬｉＣｌ／ＤＭＡｃ溶剂体系中由纤维素与长链脂肪酸氯反应制备长链脂肪酸纤维素酯，并研究了反应条件对酯化反应取代度的影响。结果表明在适当的反应条件下，酯化聚代度可达到２．８５（９５％）。还研究了纤维酯作为药物控制释放载体对ＬＮＧ、Ａｓｐｉｒｉｎ、ＢＡＳ的释放性能。     

Cellulose Peroxides with Structures of Peracid and α-Hydroxyhydroperoxide Types

Cellulose peroxides derived from various cellulose derivatives with hydrogen peroxide were investigated. Fibrous carboxy-methyl cellulose, periodic acid-oxidized cellulose, and methyl vinyl ketone-treated cellulose were employed as cellulose derivatives. Carboxyl and carbonyl groups in the cellulose derivatives were believed to react with hydrogen peroxide to form peroxides with structures of peracid and α-hydroxyhydroperoxide types, respectively. The decomposition of the cellulose peroxides and their abilities to initiate grafting reaction were examined.     

Ni-WO3/SBA-15催化剂上纤维素的水解加氢

采用等体积浸渍法制备了Ni-WO₃/SBA-15催化剂,将其应用于纤维素的水相氢解.考察了温度对纤维素水解和其形貌的影响及Ni、WO₃含量等对纤维素转化行为的影响.XRD表征结果表明,随着温度的升高纤维素颗粒粒径逐渐变小并趋于均一,结晶状态逐渐由晶型变为无定型态.H₂-TPR结果表明,Ni和WO₃间存在较强的相互作用,这种相互作用提高了W物种对C-C键的解离性能,同时,提高了Ni物种的加氢活性,促进了纤维素向乙二醇的转化.在3%Ni-15%WO₃/SBA-15催化剂上,反应条件为230 ℃、6.0 MPa、6.0 h时,纤维素完全转化,乙二醇的产率达到70.7%.     

Synthesis,characterization and properties of novel cellulose derivatives containing phosphorus: cellulose diphenyl phosphate and its mixed esters

Using ionic liquid 1-allyl-3-methylimidazolium chloride as reaction medium, a series of novel cellulose esters containing phosphorus including cellulose diphenyl phosphate (C-Dp) and cellulose acetate (CA)–diphenyl phosphate mixed esters was synthesized homogeneously. The degree of substitution was well controlled by altering reaction conditions, such as the molar ratio of the acylating reagents/anhydroglucose unit and reaction time. The structure and thermal properties of cellulose esters were characterized by FTIR, NMR, wide-angle X-ray powder diffraction and differential scanning calorimetry. All the products possessed excellent solubility in some common organic solvents, and transparent films of cellulose esters were obtained by solution casting. In contrast to C-Dp, CA–diphenyl phosphate mixed esters showed clear glass transitions. More interestingly, these cellulose mixed esters exhibited thermoplastic behavior and could be processed by traditional melt processing methods.     

过渡金属基催化剂降解纤维素应用研究进展

使用廉价过渡金属替代强酸和贵金属催化剂实现纤维素的高效转化是绿色化工的发展方向,一直是众多研究者关注的焦点。本文分别从纤维素热解(包括热解液化和热解气化)、纤维素水解、纤维素氢解和纤维素降解转化为5-羟甲基糠醛(5-HMF)等方面综述了过渡金属基催化剂在纤维素转化过程中的应用,从催化剂类型、反应条件和反应机理等方面介绍了过渡金属基催化剂催化的纤维素转化应用研究进展;最后,指出了催化过程中存在的问题,并对未来的研究方向进行展望。     

Green and combinational method towards clickable alkynylated cellulose fibers (ACFs)

This paper presents an environmentally friendly strategy to obtain alkynylated cellulose fibers (ACFs), a versatile platform for tailoring cellulose by robust click reaction. This strategy is based on the integration of two efficient reactions: selective oxidation of cellulose fibers by sodium periodate (NaIO₄) generating dialdehyde cellulose fibers and subsequent Schiff base reaction with 3-ethynylaniline yielding alkynylated cellulose fibers (ACFs). The alkynyl moieties introduced into ACFs were simply transferred with azido compounds under Cu(I) catalysis and mild conditions. The content of alkynyl groups of ACFs was found to be as high as 3.0 mmol/g. Fourier transform infrared spectroscopy (FTIR) showed that the selective oxidation of cellulose fibers generated aldehyde groups and the Schiff base reaction resulted in the incorporation of ethynyl groups and benzene rings into cellulose fibers. FTIR and X-ray photoelectron spectroscopy results confirmed the successful click reaction between ACFs and 4-azidobenzoic acid. This clickable platform would serve as a versatile starting precursor for finely tuning cellulose fibers for advanced applications.     

Structural and thermal characterization of sugarcane bagasse cellulose succinates prepared in ionic liquid

The chemical modification of SCB cellulose with succinic anhydride using 1-butyl-3-methylimidazolium chloride ionic liquid/DMSO system as reaction medium was studied. The parameters including the molar ratio of succinic anhydride/anhydroglucose units in cellulose from 1:1 to 12:1, reaction time 5-120 min, and reaction temperature 85-105 °C were investigated. The results showed that the degree substitution of succinylated cellulosic preparations ranged from 0.037 to 0.53. It was found that the treatment of the native cellulose in the ionic liquid/DMSO system under the conditions given significantly degraded the cellulose and completely destroyed the cellulose crystals. FT-IR and solid-state CP/MAS ¹³C NMR spectra produced evidence for succinoylation reaction and the results showed that succinoylation occurred at positions C-6, C-2 and C-3. The thermal stability of the succinylated cellulose decreased upon chemical modification.     

Rapid conversion of cellulose to 5-hydroxymethylfurfural using single and combined metal chloride catalysts in ionic liquid

Direct conversion of cellulose into 5-hydroxymethylfurfural(HMF) was performed by using single or combined metal chloride catalysts in 1-ethyl-3-methylimidazolium chloride(Cl) ionic liquid.Our study demonstrated formation of 2-furyl hydroxymethyl ketone(FHMK),and furfural(FF) simultaneously with the formation of HMF.Various reaction parameters were addressed to optimize yields of furan derivatives produced from cellulose by varying reaction temperature,time,and the type of metal chloride catalyst.Catalytic reaction by using FeCl3 resulted in 59.9% total yield of furan derivatives(HMF,FHMK,and FF) from cellulose.CrCl3 was the most effective catalyst for selective conversion of cellulose into HMF(35.6%) with less concentrations of FHMK,and FF.Improving the yields of furans produced from cellulose could be achieved via reactions catalyzed by different combinations of two metal chlorides.Further optimization was carried out to produce total furans yield 75.9% by using FeCl3/CuCl2 combination.CrCl3/CuCl2 was the most selective combination to convert cellulose into HMF(39.9%) with total yield(63.8%) of furans produced from the reaction.The temperature and time of the catalytic reaction played an important role in cellulose conversion,and the yields of products.Increasing the reaction temperature could enhance the cellulose conversion and HMF yield for short reaction time intervals(5~20 min).     

The swelling and dissolution of cellulose crystallites in subcritical and supercritical water

The swelling and dissolution phenomena of microcrystalline cellulose (MCC) were investigated in subcritical and supercritical water. Commercial MCC was treated in water at temperatures of 250–380 °C and a pressure of 250 bar for 0.25–0.75 s. As reaction products, undissolved but depolymerised cellulose residue, short-chain cellulose precipitate, water-soluble cello-oligosaccharides and monosaccharides, as well as their degradation products, were detected. The highest yield of the cellulose II precipitate was obtained after a reaction time of 0.25 s at 360 °C. Our hypothesis was that if the crystallites were swollen, the depolymerization pattern would be that of homogeneous reaction and the cellulose Iβ to cellulose II transformation would be observed. The changes in the structure of the undissolved cellulose residue were characterised by size exclusion chromatography, wide-angle X-ray scattering and ¹³C solid-state NMR techniques. In many cases, the cellulose residue samples contained cellulose II; however, due to experimental limitations, it remains unclear whether it was formed through the swelling of crystallites or the partial readsorption of the dissolved cellulose fraction. The molar mass distributions of untreated MCC and after low intensity treatments showed a bimodal shape. After high intensity treatments the high molar mass chains disappeared which indicated a complete swelling or dissolution of the crystallites.     

ZnCl_2溶液中微波辅助SnCl_4催化纤维素制备5-HMF

将纤维素溶解在ZnCl_2溶液中,以SnCl_4为催化剂,微波下使纤维素降解成5-羟甲基糠醛(5-HMF)。实验考察了微波功率、纤维素的质量、ZnCl_2溶液浓度、反应时间及催化剂与纤维素物质的量比等对5-HMF产率的影响。结果表明,以SnCl_4为催化剂,在优化条件:1.0 g纤维素溶解在100 m L 70%ZnCl_2溶液中,微波功率为420 W,降解反应9 min,SnCl_4与纤维素物质的量比2∶1下,5-HMF的产率达到39.4%。     

Mn/ZSM-5 participation in the degradation of cellulose under phosphoric acid media

The degradation reactions of cellulose under a combination of heterogeneous Fenton-like reagent with catalyst Mn/ZSM-5 and phosphoric acid media have been investigated. Phosphoric acid solution was selected as the reactive medium for the degradation of cellulose due to its good ability to destroy inter- and intra-molecular hydrogen bond so as to promote cellulose activation. The Fenton-like system, composing of H₂O₂ and Mn/ZSM-5 in combination with phosphoric acid, can effectively depolymerize cellulose to soluble sugars and partly degraded cellulose with much lower degree of polymerization. Small molecular products, 5-hydroxymethyl furfural and levulinic acid were extracted from the reaction solution. The performance of the catalyst Mn/ZSM-5 and the effect of reaction factors on the molar yield of 5-hydroxymethyl furfural were investigated. A three-step degradation scheme reflecting the main pathways of cellulose degradation in the reaction is proposed.     

纤维素在超临界水中的反应

纤维素是一种非常有价值的可再生资源,通过其反应可以获得多种有用的物质。对纤维素在超临界水中的反应进行了综述。在没有催化剂的情况下,纤维素在超临界水中水解生成葡萄糖、果糖、低聚物等;对纤维素水解的设备、产物分布以及纤维素水解反应机理进行了阐述。采用Ni,Pt,Ru,KOH等作催化剂,纤维素在超临界水中发生气化反应,生成的气体产物主要为H2,CO2和CH4;介绍了纤维素及其主要水解产物葡萄糖的制氢反应过程。对纤维素超临界水反应技术的发展前景进行了展望.     

二醋酸纤维素 -聚乙二醇接枝共聚物的核磁共振表征

用^1H NMR和^13C NMR核磁共振技术研究了二醋酸纤维素和聚乙二醇的接枝反应,并确定了^1H NMR和^13C NMR谱中各谱峰的归属,为证明二醋酸纤维素和聚乙二醇的接枝反应提供了依据。     

纤维素超临界水预处理与水解研究

利用超临界水解工艺进行生物质废弃物(秸秆)能源转化, 使其主要成分纤维素在超临界水中快速水解为低聚糖, 为其进一步葡萄糖转化和乙醇发酵解决技术瓶颈. 其中纤维素在超临界水中的溶解是预处理与水解过程的限速步骤. 研究表明, 反应温度达到380 ℃及以上时, 纤维素可迅速溶解并进行水解, 液化比例可达100%; 在374～386 ℃范围内反应温度对纤维素的转化率有明显作用, 低聚糖和六碳糖的总产率在临界点附近出现最大值. 超临界条件下, 低聚糖和六碳糖转化率在较短反应时间内出现峰值, 而后随反应时间的延长快速下降, 固液比对于纤维素的低聚糖和六碳糖转化也有显著影响. 最优水解条件研究显示, 在380 ℃, 40 mg纤维素/2.5 mL水条件下反应16 s可获得最大的低聚糖产率, 为29.3%, 在380 ℃, 80 mg纤维素/2.5 mL水条件下反应18 s可获得最大的六碳糖产率, 为39.2%.     

Ultrastructural aspects of the acetylation of cellulose

An ultrastructural study of the acetylation of cellulose was achieved by subjecting well characterized cellulose samples fromValonia cell wall and tunicin tests to homogeneous and heterogeneous acetylation. The study involved transmission electron microscopy observations on negatively stained microcrystals as well as diffraction contrast images of the cross sections of wall fragments at various stages of the reaction. These observations showed that the acetylation of crystalline cellulose proceeds by a reduction of the diameters of the crystals while their lengths are reduced to a lower extent. These results were corroborated by electron and X-ray diffraction experiments that showed that during the reaction there was a rapid decrease in the intensities of the equatorial diffraction spots of cellulose, whereas those located on the meridian or close to the meridian stayed constant. A model of acetylation of the cellulose crystal is presented. It is based on a non swelling reaction mechanism that affects only the cellulose chains located at the crystal surface. In the case of homogeneous acetylation, the partially acetylated molecules are sucked into the acetylating medium as soon as they are sufficiently soluble. In heterogeneous conditions the cellulose acetate remains insoluble and surrounds the crystalline core of unreacted cellulose.     

Graft copolymerization of cellulose initiated by ceric salts: Effect of reaction conditions on the consumption of ceric ion

A soluble monomer [methyl acrylate (MA)] and an insoluble monomer [butyl methacrylate (BMA)] were grafted onto cellulose by three types of ceric salts under both oxygen-free conditions and in the presence of oxygen. For comparison, Ce(IV) consumption during cellulose oxidation was also determined under similar reaction conditions. Slightly more Ce(IV) was consumed during cellulose oxidation in the presence of oxygen. During graft copolymerization of MA under oxygen-free conditions, the consumption of Ce(IV) was much lower than during cellulose oxidation regardless of the type of ceric salt employed. The opposite was observed in the presence of oxygen: much more Ce(IV) was consumed during grafting than during cellulose oxidation. The consumption of Ce(IV) in the graft copolymerization of BMA by ceric sulfate was nearly independent of reaction conditions and it was approximately the same as in cellulose oxidation. In the reaction initiated by ceric ammonium nitrate under oxygen-free conditions, less Ce(IV) was once again used up during grafting than during cellulose oxidation. However, the difference was much smaller than in the case of MA.     

Studies on the synthesis of 2,3-o-hydroxyalkyl ethers of cellulose

Novel 2,3-O-hydroxyethyl- and 2,3-O-hydroxypropyl cellulose products were synthesized by heterogeneous etherification of 6-O-(4-monomethoxytrityl) cellulose (MMTC). Due to the very hydrophobic character of MMTC, the reaction was successful in the presence of anionic and non-ionic detergent in the reaction mixture yielding the 2,3-O-cellulose ethers with a molar degree of substitution (MS) varying between 0.25 and 2.00 after detritylation. The products were characterized by means of (1)H and (13)C NMR spectroscopy including two-dimensional methods. The 2,3-O-hydroxypropyl cellulose samples are soluble in water at a MS as low as 0.8. The spectroscopic studies showed that the unusual solubility results from a preferred substitution of hydroxy groups of the anhydroglucose unit while the newly formed hydroxy moieties are included in the reaction to a minor extent only. In contrast, conventionally synthesized hydroxypropyl cellulose is soluble in water starting at a MS of about 4.0 because of the formation of oxyethylene side chains. (13)C DEPT 135 NMR spectrum of 2,3-O-hydroxypropyl cellulose.     

纤维素纳米纤维接枝聚(N-异丙基丙烯酰胺)水凝胶的制备与表征

将具有温度响应的聚N-异丙基丙烯酰胺(PNIPAm)接枝到电纺纤维素纳米纤维膜上,制备温度响应型纤维素接枝聚N-异丙基丙烯酰胺(PNIPAm-g-Cell)纳米纤维水凝胶。 研究接枝单体(N)与纤维素(c)的质量比、反应温度、反应时间和引发剂浓度对产物接枝率、溶胀性和形貌的影响。 结果表明,最佳聚合反应条件为m(N):m(c)=15:1、反应温度40 ℃、反应时间3 h、引发剂浓度为10 mmol/L,得到PNIPAm-g-Cell接枝率和溶胀率分别为35%和31%。 与PNIPAm相比,PNIPAm-g-Cell水凝胶的低临界相转变温度(LCST)显著升高,说明亲水性纤维素的引入改变了体系的亲疏水平衡。 去溶胀动力学测试表明,0.5 min内接枝率为25%和35%的水凝胶保水率分别降低至93%和61%。 说明接枝率越高PNIPAm-g-Cell水凝胶对温度的响应速度越快,对温度越敏感。