Acetylation Of Cellulose Research Articles

Lipase-catalyzed transesterification in aqueous medium under thermodynamic and kinetic control using carboxymethyl cellulose acetylation as the model reaction

Enzymatic acetylation of carboxymethyl cellulose (CMC) with vinyl acetate by lipase A12 from Aspergillus niger ( A. niger) in buffer was used as a model reaction for investigating lipase-catalyzed ester synthesis in aqueous solution. An increase in CMC concentration (1–15 wt.%) enhanced the reaction yield via thermodynamically favoring the CMC ester synthetic reaction in aqueous medium. The use of vinyl acetate as activated acetyl donor kinetically drove the forward transesterification over product hydrolysis, but partially inhibited enzyme activity when used at large amounts (>5 mL/g CMC). The increase in enzyme amount initially improved the reaction markedly, but less efficiently at larger enzyme amounts (>1000 lipase activity units/g CMC) due to the substrate diffusion limitation. The difference in reaction course demonstrated that the lipase-catalyzed transesterification was under kinetic control, while the non-enzymatic reaction under thermodynamic control. The acetylation yield of the lipase-catalyzed reaction was 5.6 times higher than that of the non-enzymatic reaction. This increase in reaction yield was attributed partly (by 19%) to the side cellulase activity of the lipase due to its substrate degradation role, but largely (81%) to the lipase activity by virtue of its transesterification catalysis function. The A. niger lipase was identified as a hydrolase capable of catalyzing ester synthesis in aqueous solution.

3. Acetate manufacturing, process and technology 3.1 Chemistry of cellulose acetylation

AbstractNowadays Celluloseacetate is mainly produced with the acetic acid process. After an activation with acetic acid and sulfuric acid the acetylation of the cellulose starts by adding acetic anhydride. The temperature and the catalyst concentration play an important role for the reaction. Beneath acetylation also degradation of the cellulose chains occurs. In the first step of the process cellulosetriacetate is formed. In a second step, the hydrolysis, several acetyl groups are removed to achieve an average degree of substitution of 2,5. The water content in this step influences the acetyl distribution.

Homogeneous acetylation of cellulose in a new ionic liquid.

Acetylation of cellulose has been accomplished in a new room-temperature ionic liquid, 1-allyl-3-methylimidazolium chloride, in the absence of any catalysts, and cellulose acetates with a wide range of degree of substitution have been obtained directly under homogeneous reaction conditions.

Biofilm formation at the air-liquid interface by the Pseudomonas fluorescens SBW25 wrinkly spreader requires an acetylated form of cellulose.

The wrinkly spreader (WS) genotype of Pseudomonas fluorescens SBW25 colonizes the air-liquid interface of spatially structured microcosms resulting in formation of a thick biofilm. Its ability to colonize this niche is largely due to overproduction of a cellulosic polymer, the product of the wss operon. Chemical analysis of the biofilm matrix shows that the cellulosic polymer is partially acetylated cellulose, which is consistent with predictions of gene function based on in silico analysis of wss. Both polar and non-polar mutations in the sixth gene of the wss operon (wssF ) or adjacent downstream genes (wssGHIJ ) generated mutants that overproduce non-acetylated cellulose, thus implicating WssFGHIJ in acetylation of cellulose. WssGHI are homologues of AlgFIJ from P. aeruginosa, which together are necessary and sufficient to acetylate alginate polymer. WssF belongs to a newly established Pfam family and is predicted to provide acyl groups to WssGHI. The role of WssJ is unclear, but its similarity to MinD-like proteins suggests a role in polar localization of the acetylation complex. Fluorescent microscopy of Calcofluor-stained biofilms revealed a matrix structure composed of networks of cellulose fibres, sheets and clumped material. Quantitative analyses of biofilm structure showed that acetylation of cellulose is important for effective colonization of the air-liquid interface: mutants identical to WS, but defective in enzymes required for acetylation produced biofilms with altered physical properties. In addition, mutants producing non-acetylated cellulose were unable to spread rapidly across solid surfaces. Inclusion in these assays of a WS mutant with a defect in the GGDEF regulator (WspR) confirmed the requirement for this protein in expression of both acetylated cellulose polymer and bacterial attachment. These results suggest a model in which WspR regulation of cellulose expression and attachment plays a role in the co-ordination of surface colonization.

Thermal and thermomechanical properties of biocomposites made from modified recycled cellulose and recycled polypropylene

AbstractResidual cellulose fibers from the paper industry have been used as reinforcements in recycled polypropylene (PP) composites. The main obstacle to obtaining good properties with this biocomposite is deficiencies in the compatibility between the nonpolar matrices and the polar cellulose fibers used as reinforcements. The aim of this work was to improve the compatibilization between these cellulose fibers and the PP matrix with four different methods: modification by the addition of polypropylene–maleic anhydride copolymer (PPgMA) during the process of blending, preblending modification of the cellulose with a solution of PPgMA, modification of cellulose by silanes (vinyltrimethoxysilane), and acetylation of cellulose. Blends with all of the differently modified celluloses were prepared with the cellulose content varied up to 40%, and then all of the blends were subjected to thermal (differential scanning calorimetry and thermogravimetric analysis) and thermomechanical (dynamic mechanical thermal analysis) analyses. The results showed that the addition of cellulose fibers improved the thermomechanical behavior of the PP, increasing the value of the log of the dynamic modulus, and affected the thermal and thermooxidative behavior. Moreover, an advantage of the use of a recycled PP containing a small quantity of ethyl vinyl acetate (EVA) as a prime material in the composition was the enhancement of mechanical properties. The use of these methods for the modification of cellulose led to more desirable thermal and thermooxidative stabilities. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2353–2360, 2003

Location of sulfate groups on sulfoacetate derivatives of cellulose

A water-soluble cellulose acetate sulfate (CAS) with a degree of acetylation (DS Ac) 2.4 and a degree of sulfation (DS Sulf) of 0.3 was obtained by direct acetylation of cellulose using sulfuric acid as catalyst. Using methylation analysis, IR and NMR spectroscopy, sulfate groups have been located on primary alcohol function of glucose residues. The distribution of the sulfate groups along the cellulose chain has been investigated using enzymatic hydrolysis. CAS was first de-acetylated under mild hydrolysis conditions (NaOH 0.25 mol/L at room temperature), and then cellulose sulfate was hydrolyzed by a cellulolytic complex (Celluclast 1.5L). Reaction products were separated by ion exchange chromatography on a DEAE Sepharose CL6B column into five fractions F 1, F 2, F 3, F 4 and F 5, which were analyzed for their chemical composition. F 1 was glucose and represented the main product of reaction (∼50% of the initial glucose), F 2 was a dimer (∼30%) with a ratio Sulfates–Glucose of 0.41 (about one sulfate group for two glucose units), F 3 a trimer (∼10%) with a ratio Sulfates–Glucose of 0.62 (about two sulfate groups for three glucose units), and F 4 a tetramer (∼5%) with a ratio Sulfates–Glucose of 0.69. The structure of the oligomers was established using 1H and 13C NMR. The observed proportion of the different blocks of sulfate groups was in good agreement with computed random distribution.

CP/MAS (13)C NMR study of cellulose and cellulose derivatives. 2. Complete assignment of the (13)C resonance for the ring carbons of cellulose triacetate polymorphs.

Complex ring (13)C resonance lines of the cross-polarization/magic angle spinning (CP/MAS) (13)C NMR spectra of cellulose triacetate (CTA) I and CTA II were completely assigned, for the first time, by (13)C-enriched CTA allomorphs. The (13)C-enriched CTA I was prepared by heterogeneous acetylation of bacterial cellulose which was biosynthesized by Acetobacter xylinum (A. xylinum) ATCC10245 from culture medium containing D-(2-(13)C)-, D-(3-(13)C)-, or D-(5-(13)C)glucose as a carbon source, while CTA II samples were obtained by solution acetylation of the (13)C-enriched bacterial celluloses. From comparison of the spectra of normal CTA prepared from ramie with those of the enriched CTA samples, it was revealed that all carbons composed of CTA I appeared as a singlet, while those of CTA II except for C1 were shown as equal-intensity doublets in the CP/MAS (13)C NMR spectrum. This finding suggests that CTA I is made up of one kind of glucopyranose residue while there are two magnetically inequivalent sites in the unit cell of CTA II in the same population.

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.

Relative susceptibility of the Iα and Iβ phases of cellulose towards acetylation

The relative reactivity of the Iα and Iβ phases of Valonia cellulose toward partial homogeneous acetylation was investigated by FT-IR and CP/MAS 13C-NMR spectroscopy. At the beginning of the acetylation and when only partial reaction was achieved, it was found that the reactivity of the Iα phase was substantially higher than that of the corresponding Iβ component. At a later stage of acetylation, the difference in reactivity between the two phases was less pronounced. In correlation with previous ultrastructural observations (Sassi and Chanzy, 1995), it can be concluded that at equivalent accessibility, the Iα phase of cellulose is indeed more reactive toward acetylation than the Iβ phase. The homogeneous acetylation of cellulose is essentially a surface reaction that affects only the accessible parts located at the surface of the microfibrils. The decrease in the rate of Iα phase disappearance with acetylation time confirms therefore that the microstructure of Valonia is made of domains that are distributed throughout the thickness of its microfibrils.

Thermoplastics Reinforced with Wood Fillers: A Literature Review

Problems concerning the processing of thermoplastics reinforced with wood fillers are discussed. The high level of moisture absorption by the filler, its poor wettability, as well as the insufficient adhesion between untreated filler and the polymer matrix are reasons for the low tensile strength and high moisture sorption of composites. These shortcomings of composites can be prevented by the modification of the interface. The fiber-matrix compatibility and the composites properties can be improved by using some physical (e.g., steam explosion, corona, cold plasma) and chemical (cross-linking and acetylation of cellulose, grafting, use of coupling agents) methods. Modified wood-polymer interaction mechanisms are complex and specific for each definite system and processing conditions. Cellulose cross-linking and acetylation reduce hygroscopicity and swelling of wood and wood composites. Grafting of styrene to wood is effective for wood-polystyrene systems. The best coupling agent for wood-thermoplastics is polymethylenepolyphenyl isocyanate. Silanes coupling effect can be increased with additives to the polymer matrix. Optimizing of technological parameters of wood-thermoplastics processing is necessary.

Acetylation of Bacterial Cellulose: Preparation of Cellulose Acetate Having a High Degree of Polymerization.

Cellulose triacetate prepared from bacterial cellulose of Acetobacter xylinum subsp. sucrofermentans BPR3001A showed a higher degree of polymerization and higher mechanical strength than that from the cotton linter. The fine fibrils of bacterial cellulose required only a short time for acetylation which preserved the high degree of polymerization.

An investigation in solution acetylation of cellulose by microscopic techniques

The solution acetylation process of cellulose has been investigated by means of scanning electron and transmission microscopic techniques. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the different morphologies of cellulose acetates, which were prepared at different temperatures. Simply, for the high-temperature acetylation (90°C), the reagents progressed in a linear manner, consisting of the formation of continuous micropores, from the surface into the interior of the supermolecular structure. In contrast, for the low-temperature acetylation (45°C), the reaction took place only through the segregated micropores on the surface of cellulose. As a result, the successive layers and, subsequently, fragmented platelets of the acetylated surface were solubilized in the reaction medium, and a viscous solution was eventually obtained. The experimental conformity between the SEM and TEM results provided valuable information in support of different solution acetylation mechanisms at low and high temperatures. © 1997 John Wiley & Sons, Inc. J. Appl Polym Sci 64: 1953–1960, 1997

An investigation in solution acetylation of cellulose by microscopic techniques

The solution acetylation process of cellulose has been investigated by means of scanning electron and transmission microscopic techniques. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the different morphologies of cellulose acetates, which were prepared at different temperatures. Simply, for the high-temperature acetylation (90°C),the reagents progressed in a linear manner, consisting of the formation of continuous micropores, from the surface into the interior of the supermolecular structure. In contrast, for the low-temperature acetylation (45°C), the reaction took place only through the segregated micropores on the surface of cellulose. As a result, the successive layers and, subsequently, fragmented platelets of the acetylated surface were solubilized in the reaction medium, and a viscous solution was eventually obtained. The experimental conformity between the SEM and TEM results provided valuable information in support of different solution acetylation mechanisms at low and high temperatures.

Hydroxybutenyl cellulose acetates

The effect of the conditions of acetylation of hydroxybutenyl cellulose and vulcanization of the acetates obtained on the physicomechanical properties and structure of films and cloth was investigated. X-ray structural analysis and electron microscopy revealed the structural characteristics of the products of HBC — HBCA chemical transformations and the corresponding derivatives and composites based on them.

A kinetic study of the acetylation of cellulose, hemicellulose and lignin components in wood

A kinetic study of the acetylation of cellulose, hemicellulose and lignin components in wood

A kinetic study of the acetylation of cellulose, hemicellulose and lignin components in wood

The rates of acetylation of Deal, Larch, Southern Yellow Pine and Sitka Spruce using acetic anhydride in xylene have been measured and compared with the composition of the woods. Although these woods have similar macroscopic characteristics, the correlation between rate of acetylation and composition remains unclear, although the holocellulose may play a role in converting the hydrophilic hydroxyl groups to hydrophobic acetyl groups. The rate of acetylation of Larch at 373 K was insignificant but the other wood samples showed significant acetylation at this temperature. The activation energies for the acetylation process suggest that several routes may be involved.

A Laboratory Model for Studying Environmently Dependent Chemical Modifications in Textile Cellulose

We have developed a laboratory model to evaluate possible microbial impact on cellulose during long-term contact with air microorganisms. This model is based on the capillary zone electrophoretic /mass spectrometric estimation of modified glucose residues in cellulose enzymatic hydrolysates isolated from linen samples. We subjected these samples to a pump-directed air flow line for 8 days and 10 weeks. Simultaneously, we measured protein contamination of the samples followed by AMS-determination of the associated 14C and 13C values. All measurements were done in non-aseptic environments in two different geographical/ecological regions. We pre-impregnated all experimental samples with deionized water and pretreated the control samples with urea and sodium azide in order to prevent both enzymatic activity and microbial growth. Our results show that the filtration of atmospheric air through the linen samples leads to a statistically significant methylation and acetylation of textile cellulose, de pending on air volume (and therefore the amount of air bacteria cells), ecological conditions, and the presence of bacteriostatic (sodium azide) and protein denaturing ( urea ) agents. We found that the amount of alkylation in the cellulose samples correlates with the measured 14C and 13C values and protein contamination levels. A biochemical mechanism of the phenomenon and its possible application for forensic and archae ological chemistry are under discussion.

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.

Procedure for the polarographic determination of bound formaldehyde content in cellulose acetates

-- A procedure has been developed for the polarographic determination of the bound formaldehyde content of cellulose acetates prepared by the high-temperature homogeneous cellulose acetylation method involving the use of a cross-linking agent.

Partiell acetylierte cellulose — synthese und bestimmung der substituentenverteilung mit hilfe der 1H NMR‐spektroskopie

AbstractPartially acetylated cellulose was synthesized by homogeneous acidic and basic saponification of cellulose triacetate (fully acetylated cellulose) and by homogeneous acetylation of cellulose dissolved in molten N‐ethyl‐pyridinium chloride. The result of 1H NMR spectroscopic investigations was that acetylation and acid saponification lead to products with different esterification of the hydroxy groups at C2, C3 and C6 whilst basic saponification leads to uniform acetylation. Furthermore, the solubility of the cellulose acetates depends on the method of preparation.