How alkaline solvents in viscosity measurements affect data for oxidatively damaged celluloses. Cuoxam and Cadoxen.

The effect of the degradation induced by the solvents for cellulose cuoxam and cadoxen and its dependency on the nature of the carbonyls in oxidatively-damaged cellulosics was investigated by combining a novel approach of sample regeneration and gel permeation chromatography coupled with carbonyl-selective labelling for reliable molecular characterization. The type of cellulosic pulp, degree and mode of oxidation and dissolution time were considered. Results show that the main discriminating factors in determining the degradation of oxidatively-damaged celluloses in alkaline dissolving media are: (1) the type of pulp, i.e. hemicellulose-containing pulps are more severely compromised; (2) of particular relevance, the prior oxidation mechanism, meaning not only the amount of oxidized moieties (greater oxidation, greater solvent-induced damage) but also their position on the chains (i.e. peroxide-oxidized cellulose is more unstable than hypochlorite-oxidized cellulose).

The disastrous copper. Comparing extraction and chelation treatments to face the threat of copper-containing inks on cellulose.

Iron gall inks are known to be detrimental to the permanence of historic documents. Among the transition metals present, copper is the greatest threat and an open challenge due to the lack of Cu-specific treatments. In this study, we address the inhibition of copper by comparing extraction (a newly proposed glucose-based treatment) vs. chelation (phytate-based) approaches in terms of performances in scavenging copper and slowing the degradation rate, and of possibly induced side effects. Results show that the glucose treatment partially extracts copper, but it causes long-term damages to paper, i.e. increased fragility and discoloration. The phytate protocol was found beneficial in inhibiting the catalytic activity of copper-rich inks. It limits both long-term oxidation and hydrolytic breakdown of samples without compromising the visual appearance.

Phenolic compounds and antioxidant properties of arabinoxylan hydrolysates from defatted rice bran.

BACKGROUND: The water unextractable arabinoxylans (WUAX) contain beneficial phenolic compounds that can be used for food rather than for animal feed. The antioxidant activities of defatted rice bran obtained by xylanase-aided extraction is reported herein. The chemical and molecular characteristics of extracted fractions were investigated. RESULTS: The WUAX hydrolysate precipitated by 0-60% ethanol (F60), 60-90% ethanol (F6090), and more than 90% ethanol (F90) had decreased molar masses with increasing ethanol concentration. The fractions of interest, F60 and F6090, contained 75% arabinoxylans with ferulic acid as the major bound phenolic acid, followed by p-coumaric acid. According to chemical-based antioxidant assays F60 and F6090 exhibited higher diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric iron reducing ability than F90 which contained minor contents of small sugars and free phenolic acids. In cell-based antioxidant assays, using the fluorescent 2',7'-dichlorofluorescein diacetate probe, all three fractions were potent intracellular scavengers. CONCLUSION: The high molar mass of WUAX hydrolysates with high amount of bound phenolics contributes to the chemical-based antioxidant activity. All fractions of WUAX hydrolysates showed high potent intracellular scavenging activity regardless of molar mass, content and the component of bound phenolics. © 2017 Society of Chemical Industry.

Degradation of the Cellulosic Key Chromophore 5,8-Dihydroxy-[1,4]-naphthoquinone by Hydrogen Peroxide under Alkaline Conditions.

5,8-Dihydroxy-[1,4]-naphthoquinone (DHNQ) is one of the key chromophores in cellulosic materials. Its almost ubiquitous presence in cellulosic materials makes it a target molecule of the pulp and paper industry's bleaching efforts. In the presented study, DHNQ was treated with hydrogen peroxide under alkaline conditions at pH 10, resembling the conditions of industrial hydrogen peroxide bleaching (P stage). The reaction mechanism, reaction intermediates, and final degradation products were analyzed by UV/vis, NMR, GC-MS, and EPR. The degradation reaction yielded C1-C4 carboxylic acids as the final products. Highly relevant for pulp bleaching are the findings on intermediates of the reaction, as two of them, 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) and 1,4,5,8-naphthalenetetrone, are potent chromophores themselves. While DHBQ is one of the three key cellulosic chromophores and its degradation by H2O2 is well-established, the second intermediate, 1,4,5,8-naphthalenetetrone, is reported for the first time in the context of cellulose discoloration.

Submicron hierarchy of cellulose nanofibril films with etherified hemicelluloses.

The lack of simple differentiation of all-polysaccharide-film components in nanoscale hinders unveiling their structure-property dependency. Submicron hierarchy of films of cellulose nanofibrils (CNFs) and carbohydrate-based additives was revealed via visualization of the components by their differentiating adhesion to an Atomic Force Microscope (AFM) tip. The differentiation of the film components revealed that distribution of hydroxypropylated hemicellulose in the CNF matrix could be tuned by addition of a plasticizer. The hemicellulose hydroxypropylation degree of substitution (DS) was detected to be another parameter affecting the film structure due to the water-solubility depending on the DS. This was further verified via Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D). The translucent, self-standing films comprising CNFs, sorbitol and hydroxypropylated hemicellulose were tested for mechanical, optical and oxygen diffusion performance. The performance was linked to their structural evenness, which confirmed that the oxygen diffusion through the film is tremendously affected by the film nano hierarchy.

Synthesis and Characterization of Periodate-Oxidized Polysaccharides: Dialdehyde Xylan (DAX).

The cleavage of the C2-C3 bond in the building units of 1 → 4-linked polysaccharides by periodate formally results in two aldehyde units, which are present in several masked forms. The structural elucidation of such polysaccharide dialdehydes remains a big challenge. Since polysaccharide derivatives are increasingly applied in materials technology, unveiling the exact structure is of utmost importance. To address this issue for xylan, dialdehyde xylan (DAX, oxidation degree of 91.5%) has been synthesized as water-soluble polymer. The ATR-FTIR spectrum of DAX showed free aldehyde to be absent and exhibited a characteristic absorption at 858 cm(-1) related to hemiacetal groups. By a combination of 1D and 2D NMR techniques, it was confirmed that oxidized xylan is present as poly(2,6-dihydroxy-3-methoxy-5-methyl-3,5-diyl-1,4-dioxane). Based on GPC analysis, the DAX polymer shows a slightly lower molar mass (6.6 kDa) compared to the starting material (7.7 kDa) right after oxidation, and degraded further after one month of storage in 0.1 M NaCl solution (4.3 kDa). The oxidized xylan demonstrated lower thermal stability upon TGA analysis and a greater amount of residual char (20.6%) compared to the unmodified xylan (13.7%).

Etherification of Wood-Based Hemicelluloses for Interfacial Activity.

We present wetting, hygroscopicity, and interfacial activity of hemicellulose with respect to etherification and contrast it to their potential as interfacial modifiers, which is demonstrated by oil-in-water emulsification containing up to 60 vol% of the oil phase. Tunable amphiphilicity of hardwood and softwood hemicelluloses, xylans, and galactoglucomannans, respectively, was accomplished via controlled etherification. A series of degree of substitution (DS) of hydroxypropylated and 3-butoxy-2-hydroxypropylated ("butylated") grades was synthesized. The hemicellulose ethers were characterized by gel permeation chromatography, spectroscopic techniques, such as NMR, and contact angle measurements. An attenuated total reflectance infrared method was developed for fast identification of the DS. Near infrared analysis was utilized to explore the hygroscopicity of the material and to perform principle component analysis. The modification to butylated grades decreased the hygroscopicity, whereas the hydroxypropylated grades bound moisture. All of the hemicellulose ethers were water-soluble. The interfacial tension of the aqueous hemicellulose solutions was determined by pendant-drop tensiometer, and it was demonstrated to be dependent on the degree of modification.

Detection of Cellulose-Derived Chromophores by Ambient Ionization-MS.

The detection of individual chromophores that contribute to the overall discoloration of paper ("yellowing") is a challenge because those substances are only present in very small amounts. In this research, two analytical approaches based on ambient ionization techniques, namely, desorption electrospray ionization and paper spray, both coupled to mass spectrometry, are compared to each other with regard to their suitability for detecting acetylated cellulosic key chromophores. The paper spray approach proved to be the more sensitive and versatile method. Subsequently, paper spray (PS)-mass spectrometry was applied to model papers and historical papers in which the acetylated chromophores were detected successfully. Independent accurate mass measurements confirmed the results obtained from reference compounds, model samples, and real-world specimens.

Bacterial cellulose as a material for wound treatment: Properties and modifications. A review.

Advanced approaches to wound healing have attracted much attention in the last decades due to the use of novel types of dressings that provide a moist environment and take an active part in wound protection and tissue regeneration processes. The materials for novel wound dressings should have a set of features that will contribute to efficient skin recovery. The use of bacterial cellulose (BC) is attractive for advanced wound management because of the favorable characteristics of BC, such as its biocompatibility, non-toxicity, mechanical stability, and high moisture content. Numerous approaches can be taken to modify BC to address the shortcomings of the native material and to optimize its biocompatibility, water uptake and release, and antimicrobial activity. This review highlights possible pathways for functionalization of BC, affecting all levels of its structural organization. The focus is on post-production treatment of BC, although selected studies concerning in situ modifications during the biosynthesis process are also emphasized.

Nano-cellulosic materials: the impact of water on their dissolution in DMAc/LiCl.

The dissolution behaviour of disassociated cellulosic materials in N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) was investigated. The parameters monitored were chromatographic elution profiles and recovered mass by means of gel permeation chromatography (GPC) with RI detection. In order to elucidate the impact of the disassembly on cellulosic fibres, comparative studies were performed with the non-disassociated cellulose counterparts. The importance of the presence of water was addressed by Karl Fischer titration and solvent exchange experiments. Morphological changes during the dissolution process were studied by scanning electron microscopy (SEM). Dissolution of fibrillated cellulosic materials is impeded compared to the non-fibrillated material. This is a consequence of the high-surface-area fibrils prone to retain high amounts of water. Dissolution behaviour of nano-crystalline cellulosic materials appeared to be source-dependent. Due to the absence of entangled networks, these materials retain only water bound at the surface of the nano-crystallites, indicative of both the exposed surface area and solubility. The small cellulose nano-particles extracted from dissolving pulp show lower solubility compared to the large NCC particles from cotton.

Electron Beam Irradiation of Cellulosic Materials-Opportunities and Limitations.

The irradiation of pulp is of interest from different perspectives. Mainly it is required when a modification of cellulose is needed. Irradiation could bring many advantages, such as chemical savings and, therefore, cost savings and a reduction in environmental pollutants. In this account, pulp and dissociated celluloses were analyzed before and after irradiation by electron beaming. The focus of the analysis was the oxidation of hydroxyl groups to carbonyl and carboxyl groups in pulp and the degradation of cellulose causing a decrease in molar mass. For that purpose, the samples were labeled with a selective fluorescence marker and analyzed by gel permeation chromatography (GPC) coupled with multi-angle laser light scattering (MALLS), refractive index (RI), and fluorescence detectors. Degradation of the analyzed substrates was the predominant result of the irradiation; however, in the microcrystalline samples, oxidized cellulose functionalities were introduced along the cellulose chain, making this substrate suitable for further chemical modification.

Irradiation of cellulosic pulps: understanding its impact on cellulose oxidation.

Different pulp samples were irradiated by three energy sources: plasma, electron beaming, and γ radiation. The effect of increased exposure to irradiation was studied by multidetector gel permeation chromatography with fluorescence labeling of carbonyl groups to quantify changes of the cellulose. Whereas plasma treatment had no effect, for gamma and electron beam the degradation primarily affects the high molar mass area. Kinetic calculations based on DPw were performed. They show close-to-linear relations with slopes in the same order of magnitude, suggesting that wood-derived pulps degrade slower than pulps from annual plants. The rise in carbonyl group content is linear with increasing dose. In particular, in pulps from annual plants, most detected carbonyl structures originate from the new reducing end groups. Therefore, oxidative modification of cellulose molecules by means of radiation appears to be viable for pulps produced from wood. Here the increase in oxidized functionalities is partially disconnected from chain scission.

Dissolution behavior of different celluloses.

Celluloses from different origins were dissolved stepwise in N,N-dimethylacetamide/lithium chloride (9% v/w; DMAc/LiCl) with the aim to study the time course of the dissolution process, completeness of dissolution in the dissolved fractions, possible discrimination effects, and differences between the celluloses. Cellulosic pulps from both annual plants and different wood species were analyzed. The obtained fractions were subject to gel permeation chromatography (GPC) with multiple detection to monitor the development of molecular mass distribution (MMD), molecular mass, and recovered mass. The dissolution behavior of accompanying xylans was followed by quantitative analysis of the uronic acids by fluorescence labeling--GPC. The morphological changes at the remaining fibers in the stepwise dissolution were addressed by SEM. The time needed to dissolve completely the cellulosic pulp differed from species to species, mainly between pulps from annual plants and pulps from wood. Annual plants generally needed much longer to dissolve completely. In the beginning of the dissolution, the dissolved fractions of annual plants showed a distinct discrimination effect because they were enriched in hemicellulose. By contrast, wood pulps dissolve fast and without distinct changes in the MMD of the dissolved fractions over time. Bagasse pulp is an exception to the observation for annual plants and rather resembled the behavior of wood celluloses. Prolonged dissolution times, as often practiced in cellulose GPC, do not lead to any improvements regarding the determination of molecular mass, MMD, and recovered mass of injected sample, so that the dissolution times required for reliable GPC analysis can be significantly shortened, which will be important for biorefinery analytics with high numbers of samples.