Surface acetylation of bacterial cellulose

Bacterial cellulose was partially acetylated by the fibrous acetylationmethod to modify its physical properties, while preserving the microfibrillarmorphology. The overall degree of substitution was varied from 0.04 to 2.77 bychanging the amount of acetic anhydride added. X-ray diffraction of thepartially acetylated samples showed the crystalline pattern of unmodified celluloseI up to moderate degrees of acetylation, and the change in peak widthsindicatedthat acetylation proceeded from the surface of microfibrils, leaving the coreportion unreacted. Scanning electron microscopy revealed that even low levelsofacetylation were effective to maintain the original microfibrillar morphologyofbacterial cellulose on direct drying from water.     

Partial cellulose acetylation in 1-ethyl-3-methylimidazolium acetate induced by dichloromethane

Cellulose acetate (CA) is one on the most important cellulose derivatives. The use of ionic liquids in cellulose processing was recently discovered to not exclusively act as a solvent but also as a reagent. Recent studies showed that bulky chlorides as well as acetyl chloride mixed with ionic liquids can facilitate cellulose acetylation. This work focused on a simple chloro-organic cosolvent, dichloromethane (DCM), and showed the ability of this relatively small molecule, mixed with the ionic liquid, to facilitate homogenous acetylation by displacement of the acetate ion of the ionic liquid with a chloride ion. Maximal acetylation achieved by this method was a degree of substitution (DS) of 1.9, were only a small fraction of DCM was utilized for acetylation, well below even that expected for equimolar reaction. The degree of substitution was controlled by the dichloromethane content, thus controlling its solubility in water. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2458–2462     

纤维素醋酸酯的均相合成

纤维素的非均相反应取代不均匀、产率低。本文用纤维素在LiCl／DMAc溶液中的均相反应。制得了纤维素三醋酸酯(CTA)、纤维素二醋酸酯(CDA)、纤维素—醋酸酯(CMA),并对产品结构性能进行了表征。     

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.     

热致液晶性羟乙基纤维素醋酸酯/聚乙烯共混物的热行为

本文用DSC方法研究了热致液晶性羟乙基纤维素醋酸酯（HECA）与聚乙烯（PE）共混物的相转变过程．结果表明，HECA与PE不相容，但当HECA含量＞50％时，则明显影响PE的结晶过程，使其在冷却过程中出现多重结晶。将共况物在393K退火，可改善PE结晶缺陷；在425K退火，可提高HECA液晶相的取向度。     

New coupling reagents for homogeneous esterification of cellulose

A group of known, but in cellulose chemistry new coupling reagents for homogeneous esterification has been investigated: 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride, N-methyl-2-bromopyridinium iodide, N-methyl-2-chloropyridinium iodide, and N-methyl-2-bromopyridinium tosylate. In order to study their ability to activate carboxylic acids in esterifications of cellulose they have been employed in synthesis of cellulose adamantate esters. Their effectiveness has been estimated in terms of degree of substitution of resulting esters and compared to that obtained with the commonly used N,N′-carbonyldiimidazole.     

Thermal properties of oxidized cellulose

Three series of oxidized celluloses – 2,3-dialdehyde celluloses (DACs), 2,3-dicarboxycelluloses (DCCs) and sodium 2,3-dicarboxycelluloses (NaDCCs) — were prepared, having incremental changes in their degrees of oxidation. Their thermogravimetric analysis (TG) and differential thermal analysis (DTA) were studied. It was found that oxidation generally destabilized cellulose at lower temperatures (below 250 °C), but at higher temperatures the oxidized products were found to be more stable. Cellulose, DACs, and DCCs all showed final weight losses in the region of 80–85%. However, 80% NaDCC and 98% NaDCC showed weight losses of only 30 and 37%, respectively.NCL Communication No. 6051.     

4.2 Chemical characteristics of cellulose acetate

The chemical structure of cellulose acetates (CA), different synthesis paths, analysis strategies and the correlation of these structural features with properties, especially with the solubility are summarized. Alternative paths, in particular homogeneous procedures, for the synthesis of CA are described focusing on the application of new media and the in situ activation of acetic acid. The preparation of selectively substituted CA is reviewed including the defined hydrolysis under acidic or basic conditions. Strategies for the structure analysis by means of ¹H- and ¹³C-NMR spectroscopy and by means of chromatographic methods are discussed. In addition, the preparation and the application of a variety of mixed CA ethers and esters are described.     

Sisal cellulose whiskers reinforced polyvinyl acetate nanocomposites

Sisal nanowhiskers were used as novel reinforcement to obtain nanocomposites with polyvinyl acetate (PVAc) as matrix phase. They are seen as attractive materials due to the widespread availability and low cost of the sisal source material. Statistical analysis of the sisal whisker length and diameter resulted in average values of 250 nm and 4 nm, respectively, resulting in an average aspect ratio in the upper range of reported cellulose nanowhisker values. The high aspect ratio ensures percolation, with resulting mechanical improvements and thermal stability, at lower fiber loads. Water uptake and thermal behaviour of the sisal whisker–PAVc composites were studied. Whisker addition was found to stabilize the nanocomposites with no benefit seen when increasing the whisker content beyond the percolation threshold: For all whisker contents studied above percolation, the water uptake stays constant, and the Tg does not vary with whisker content at a given relative humidity. The water diffusion rate however increases due to water accumulation at the whisker–PVAc interface. Below whisker percolation, stabilization is only noticed at low relative humidity, whereas high humidity results in disruption of whisker–PVAc interactions. This work shows the potential of cellulose nanowhiskers to stabilize polar polymers even at high humidity conditions with minimal reinforcement addition.     

Thermal analysis of cellulose acetate modified with caprolactone

Cellulose acetate (CA) was modified with caprolactone (CL) under various reaction conditions in an internal mixer. The thermal behavior and relaxation transitions of the samples were determined by dynamic mechanical analysis and differential scanning calorimetry. Various relaxation transitions were detected in externally and internally modified cellulose acetate by DMTA. These were assigned to the glass transition of the main chain, to the movement of single glucose units and to hydroxymethyl groups. The β′ transition must belong to structural units larger than a single glucose ring and their formation must depend on sample preparation conditions. No transition could be assigned to grafted polycaprolactone (PCL) chains by DMTA. Contrary to other groups, we could not detect even the transitions of modified CA by DSC. Only the crystallization of oligomeric PCL homopolymer was observed mostly when it diffused to the surface of the sample.     

Reactivities of cellulases from fungi towards ribbon-type bacterial cellulose and band-shaped bacterial cellulose

We have investigated the reactivities of various cellulases onribbon-type bacterial cellulose (BC I) and band-shaped bacterial cellulose (BCII) so as to clarify the properties of different cellulases. BC I waseffectively hydrolyzed by exo-type cellulases from different fungi from twicetofour times as much as BC II, but endo-type cellulases showed little differencein reactivity on those substrates. One of the endo-type cellulases, EG II fromTrichoderma reesei, degraded BC II more rapidly thanexo-type cellulases even in the production of reducing sugars. The degree ofpolymerization (DP) of BC II was rapidly decreased by endo-type cellulases atanearly stage, while exo-type cellulases did not cause the decrease of DP atthe initial stage, though the decrease of DP was observed after an incubation of24 h. All exo-type cellulases adsorbed on BC I and BC II,whileendo-type cellulases except for EG II adsorbed slightly on both substrates. Itwas interesting to observe EG II adsorbed on BC I but not on BC II. It issuggested that the adsorption of enzyme on cellulose is important for thedegradation of BC I, but not for BC II. It is proposed that the ratio of aspecific activity of each enzyme between BC I and BC II represents thedifference in the mode of action of cellulase. Furthermore, the K _RW value, which we can calculate from thedecrease of DP/reducing sugar produced, is effective for discriminating themode of action of cellulase, especially the evaluation of randomness in thehydrolysis of cellulose by endo- and exo-type cellulases.     

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.     

A green and regioselective acetylation of thioglycoside with ethyl acetate

Treatment of saccharidic polyols in ethyl acetate with catalytic sulfuric acid leads to the corresponding primary monoacetate derivatives in good yields. The transesterification was realized by simple stirring without rigorous exclusion of moisture or oxygen. Our protocol is applicable to the regioselective monoacetylation of amino sugars having different substituents at the 2-positions.     

Synthesis and characterization of hydroxypropyl cellulose from bacterial cellulose

Bacterial cellulose produced by Acetobacter xylinum has been reacted with propyleneoxide to synthesize hydroxypropyl cellulose(HPC) under different reaction conditions while diluted by toluene. The effects of mass ratio of bacterial cellulose to propyleneoxide, dilutability of toluene, reaction temperature(T) and time(t) were investigated by series of experiments. The degree of substitution(DS), hydroxypropyl content(A) and yield(η) were compared. The optimized product exhibited cold-water solubility and hot-water gelatinization in aqueous medium. Further study was carried out with FTIR, TGA, XRD, SEM and 13C-NMR for characterization. The water/air contact angle measurement reveals that it is a good hydrophobic material with good mechanical properties.     

Synthesis, characterization and thermal studies on cellulose acetate membranes with additive

Cellulose acetate (CA) membranes are used in ultrafiltration applications, although they show low chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with polyethelene glycol (PEG 600) has been attempted. In this study, CA has been mixed with PEG 600 as an additive in a polar solvent. The effects of CA composition and additive concentration given by a mixture design of experiments on membrane compaction, pure water flux, water content and membrane hydraulic resistance have been studied and discussed. The efficiency of protein separation by the developed CA membranes have been quantified using model proteins such as pepsin, egg albumin (EA) and bovine serum albumin (BSA). The thermal stability of the developed membranes prepared with PEG 600 additive has also been investigated using thermogravimetric analysis and differential scanning calorimetry.     

Transparent polymer blends composed of cellulose acetate propionate and poly(epichlorohydrin)

Structure and properties for binary blends composed of biomass-based cellulose acetate propionate (CAP) and poly(epichlorohydrin) (PECH) have been studied. It is found from the dynamic mechanical measurements that mutual dissolution takes place to some degree with remaining CAP-rich and PECH-rich regions in the blends. As a result of the interdiffusion, leading to fine morphology, the blends exhibit high level of optical transparency although the individual pure components have different refractive index. Furthermore, the mechanical toughness of CAP, which is one of the most serious problems for CAP, is considerably improved by blending PECH. This will have a great impact on industries because the blend technique widens the application of CAP.     

Ultrafine fibrous cellulose membranes from electrospinning of cellulose acetate

Three solvents, that is, acetone, acetic acid, and dimethylacetamide (DMAc), with a range of solubility parameter δ, surface tension γ, viscosity η and boiling temperature were used to generate mixtures for electrospinning cellulose acetate (CA) (degree of substitution, DS = 2.45). Although none of these solvents alone enables continuous formation of fibers, mixing DMAc with either acetone or acetic acid produced suitable solvent systems. The 2:1 acetone:DMAc mixture is the most versatile mixture because it allows CA in the 12.5–20% concentration range to be continuously electrospun into fibrous membranes. These CA solutions have η between 1.2 and 10.2 poise and γ around 26 dyne/cm and produce smooth fibers with diameters from 100 nm to ～1 μm. Fiber sizes generally decrease with decreasing CA concentrations. The nature of the collectors affects the morphology as well as packing of fibers. Fibers collected on paper have more uniform sizes, smooth surfaces, and fewer defects, whereas fibers collected on water are more varied in size. Electrically conductive solid collectors, such as Al foil and water, favor more tightly packed and less porous membranes. Porous collectors, like paper and copper mesh, produce highly porous membranes. The pores in membranes collected on the Al foil and paper are much better interconnected in the planar directions than those in membranes collected on water. There is evidence that electrospinning induces order in the fibers. Deacetylation of CA membranes is more efficient and complete in NaOH/ethanol than in aqueous NaOH, producing DS values between 0.15 and 2.33 without altering fiber surfaces, packing, or organization. The fully regenerated cellulose membranes are similarly hydrophilic as commodity cellulose fibrous matrices but absorb nearly 10 times as much water. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2119–2129, 2002     

Molecular structure and properties of cellulose acetate chemically modified with caprolactone

Cellulose acetate (CA) with a degree of substitution of 1.7 was modified with caprolactone (CL) under various reaction conditions in an internal mixer. Processing temperature changed from 120 to 220 °C, while reaction time varied between 5 and 45 min. The composition and structure of the polymer was analyzed by various methods including FTIR, MALDI-TOF and NMR spectroscopy and its mechanical characteristics were determined by dynamic mechanical analysis and tensile testing. The results indicate that homopolymerization occurs under relatively mild conditions, while grafting requires higher temperatures and longer times. Grafted polycaprolactone (gPCL) chains are attached mainly to positions 2 and 6 of the glucose ring and their length increases with increasing reaction time and temperature, but the chains are always much shorter than those obtained in solution polymerization. Changes in the degree of substitution during grafting are small indicating that homopolymerization proceeds easier than grafting. Grafting seems to be easier in cellulose acetate with a larger degree of substitution in spite of the smaller number of active -OH groups present. Internal plasticization is more efficient than the external plasticizing effect of monomeric caprolactone. Plasticization results in a decrease of stiffness and strength, but deformability increases only slightly.     

Efficient alternative of antimicrobial nanocomposites based on cellulose acetate/Cu-NPs

The current research presents an efficient, cheap, and safe antimicrobial material for widespread use based on copper nanoparticles (Cu-NPs) loaded on cellulose acetate (CA) matrix. A reduction process of CuSO₄·5H₂O has been performed to prepare Cu-NPs. The nanosized copper particles included oxidized Cu (15–20 nm). Two different loads of Cu-NPs were used in this study, 2% and 6% mol.%. The presence of Cu-NPs incorporated with CA films slightly affected the tensile index of the films, where low and high-loaded Cu-NPs enhanced the tensile index by small values ranged from 0.640 to 0.650 and 0.667, respectively. A study on the antibacterial activity of these nanocomposites was carried out for Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. It has been found that CA containing Cu-NPs (2%) exhibited the highest antimicrobial activity against all test microbes including S. aeureus (21 mm), P. aeruginosa (18 mm), C. albicans (19 mm), and Aspergillus niger (15 mm). Results also revealed that CA film with 6% exhibited lower activity than film with 2% Cu-NPs. The morphological properties of CA/Cu-NPs films were characterized by scanning electron microscopy and transmission electron microscope in addition to X-ray diffraction. Low-loaded Cu-NPs showed homogenous distribution through CA matrix while, the high-loaded Cu-NPs were agglomerated through CA matrix. Thermal properties illustrated the enhancement of thermal stability of the film with increasing the loaded Cu-NPs.     

Some aspects of acylation of cellulose under homogeneous solution conditions

Commercially available cellulose (Avicell PH101) was successfully acylated under homogeneous solution conditions by the following procedure: 2.0 g of cellulose were stirred with 75 mL of N,N‐dimethylacetamide for 1 h at 150°C, 3.5 g of LiCl were added, the temperature was raised to 170°C, ca. 18.5 mL of the solvent were distilled and the suspension was cooled to room temperature and stirred overnight. The temperature of the clear cellulose solution was raised to 110°C, kept at that temperature for 1 h, an acid anhydride was added and the solution stirred at 110°C for additional 4 h. Acetates, propionates, butyrates, and acetate/propionate mixed ester were prepared with excellent control of the degree of substitution, DS, 1 to 3 for acetates, 2 and 3 for propionates and butyrates, and 3 for acetate/propionate. The degree of polymerization of cellulose is negligibly affected under these reaction conditions. The distribution of the acetyl moiety among the three OH groups of the anhydroglucose unit shows a preference for the C₆ position. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1357–1363, 1999