Adsorption and viscoelastic properties of cationic xylan on cellulose film using QCM-D

The adsorption and viscoelastic properties of cationic xylan layers adsorbed from an aqueous electrolyte solution (NaCl 0, 1, 10, 100 mM) on a cellulose model surface were studied using quartz crystal microbalance with dissipation (QCM-D). Three cationic xylans with different charge densities were used (molecular weight, 9,600 g/mol with degrees of substitution, DS = 0.150, 0.191, and 0.259). The influences of the electrolyte concentration and charge density of cationic xylan on its adsorption onto a cellulose surface were investigated. Low charged cationic xylan was substantially more efficient in surface adsorption on cellulose compared to high charged cationic xylan at a low concentration of electrolytes. Adsorption of low charged cationic xylan decreased with increases in electrolyte concentration. However, adsorption of high cationic xylan increased with electrolyte concentration. The conformation and viscoelastic properties of the layers were interpreted by modeling the data under the assumption that the layers can be explained by the a Voigt model. Low charged cationic xylan adsorbed relatively weakly onto the cellulose surface, and formed a thicker, softer layer than high charged cationic xylan. On the other hand, high charged cationic xylan formed a thinner adsorption layer onto the cellulose surface.     

The effect of barley husk arabinoxylan adsorption on the properties of cellulose fibres

This study investigates the adsorption of (glucurono)arabinoxylan (GAX) on cellulose fibres and the properties thereof. A water-soluble GAX, from barley husks (Hordeum vulgare), was isolated using chlorite delignification and alkaline extraction followed by enzymatic purification. The isolated GAX fraction showed an arabinose to xylose ratio of 0.22 and a weight average molar mass of 20,200 g/mol, as determined by size exclusion chromatography (SEC) in DMSO:H₂O. The GAX was adsorbed on cellulose fibres under well controlled conditions, where temperature and initial concentration of GAX proved to be important parameters in controlling the level of adsorption. The adsorption process was also dependent on xylan molecular structure. Carbohydrate analysis on the modified fibres showed a preferential adsorption of low substituted xylans (arabinose to xylose ratio of ∼0.10). During the adsorption process the GAX solution was analyzed using SEC-RI-MALLS in aqueous solvent, which demonstrated a molecular xylan adsorption on cellulose fibres. Additionally, a decrease in light scattering responses, which corresponds to an adsorption of aggregated xylan and/or xylan with a great tendency towards self-association, could be observed during the adsorption process. This was demonstrated by adsorption of GAX on regenerated cellulose fibres (Lyocell), which compared to native fibres possesses a relatively smooth fibre surface. Atomic force microscopy analysis visualised a heterogeneous decoration of the Lyocell fibres with xylan agglomerates. The effect of GAX adsorption on paper strength was also investigated. A GAX modified kraft pulp showed an evident increase in tensile strength, which might be due to a retained fibre–fibre bonding ability for xylan coated fibrils after drying and rewetting.     

The effect of eucalypt pulp xylan content on its bleachability,refinability and drainability

Currently, bleached eucalypt pulps are largely used for printing and writing (P&W) and sanitary (tissue) paper grades. Among the many pulp quality requirements for P&W and tissue paper production the xylan content is one of the most significant. For P&W papers, increasing xylans improve pulp refinability and strength properties but negatively affect bulk and drainability. For tissue paper, xylans are purportedly advantageous during paper drying in the Yankee cylinder but negatively affect paper bulk and may increase dusting during paper manufacture. On the other hand, bleachability is a very important parameter for both P&W and tissue grade pulps since bleaching cost is the second most significant in eucalypt bleached kraft pulp production. The aim of this study was evaluating the influence of eucalyptus pulp xylan content on its bleachability, refinability and drainability. A sample of industrial unbleached eucalyptus kraft pulp containing 15.6?% xylans was treated with various alkali charges at room temperature in order to obtain materials with different xylan contents. The pulps were bleached to 90 % ISO brightness with the O–D_HT–(EP)–D sequence and evaluated for their refinability and drainability. By increasing the alkali concentration in the range of 10–70 g/L pulps of 14.5–5.9 % xylans were produced with no significant impact on cellulose crystallinity. The decrease of xylan content significantly decreased pulp bleaching chemical demand, water retention value and refinability and increased pulp drainability.     

Molecular properties of hemicelluloses located in the surface and inner layers of hardwood and softwood pulps

The molecular properties of hemicelluloses located in the surface and inner layers of fibers present in hardwood and softwood pulps, together with the effects of different bleaching processes on these properties, have been investigated in this study. In order to separate the hemicelluloses located in these two layers, fibers were subjected to mechanical peeling and then separated by filtration into surface (filtrate) and inner layer materials. The materials thus obtained were characterized with respect to their polysaccharide compositions and uronic acid contents. The molar mass parameters of the hemicelluloses (extracted by alkali) were determined by employing size-exclusion chromatography in combination with off-line MALDI mass spectrometry. For all of the pulps examined, the relative content of xylan was found to be greater in the surface layer of the fiber than in the corresponding inner layer. The xylan polymers of the surface layer exhibited higher molar masses and lower frequencies of uronic acid side groups than did the xylans in the inner fiber layer. In connection with ozone treatment, hexenuronic acid residues in the surface layer xylan were removed to a greater extent than in the case of the inner layers, indicating a gradient for the reaction with ozone across the fiber wall. The xylan polymer remaining on the surface of the softwood pulps after completion of the chlorine dioxide bleaching process was predominantly uncharged.     

Carboxymethyl Xylan - Control of Properties by Synthesis

The hemicellulose xylan is a polysaccharide that occurs in nature in enormous amount in various one year- and perennial plants having different structures and molecular masses. Versatile ways to generate bio-based functional polymers result from the chemical modification of this biopolymer. In our research, xylans from various resources like birch-, beech-, and eucalyptus wood and from oat husk, rye bran, and corn cob were used to investigate the important method of carboxymethylation in detail. Different activation procedures were elaborated to synthesize carboxymethyl xylan. One step reactions lead to products with a degree of substitution (DS) from 0.13 to 1.22 in dependence on the molar ratio of anhydroxylose unit (AXU) to reagent. Two step syntheses yielded DS values up to 1.65. Carboxymethyl xylans are water soluble at a DS of 0.3. The solutions have different clearness depending on the provenience. NMR spectroscopy and HPL chromatography were applied to characterize the carboxymethyl xylans in detail.     

Hydrolytic Properties of a Hybrid Xylanase and Its Parents

The hydrolytic properties of a hybrid xylanase (ATx) and its parents (reAnxA and reTfxA) were studied using xylans and xylooligosaccharides as substrates. Analysis of reaction mixtures by high-performance liquid chromatograph revealed that xylotriose (X3) was the main product released from birchwood xylan and wheat bran insoluble xylan by ATx and reAnxA, respectively. Xylobiose (X2) was the main product separately released from birchwood xylan and wheat bran insoluble xylan by reTfxA. Xylotetraose (X4), xylopentaose (X5), and xylohexaose (X6) could be hydrolyzed by ATx, which showed no activity on X2 and X3. Therefore, X4 might be the minimum oligomer hydrolyzed by ATx. X2–X6 could be hydrolyzed by reAnxA and reTfxA, respectively. All of ATx, reAnxA, and reTfxA showed transglycosylation activity.     

Upgrading of paper-grade pulps to dissolving pulps by nitren extraction: properties of nitren extracted xylans in comparison to NaOH and KOH extracted xylans

Different paper-grade pulps were extracted with nitren, NaOH and KOH in order to produce dissolving pulps and polymeric xylan. The yield and structure of the isolated nitren and alkali xylans were investigated by carbohydrate analysis, HPSEC and ¹H-NMR spectroscopy. In addition the effect of washing stages on the residual nickel content of the nitren xylans was investigated. By nitren extraction up to 98% of the xylan could be extracted out of the fully bleached eucalyptus and birch kraft pulps. The nitren extracted kraft xylans had DP values between 95 (birch) and 111 (eucalyptus). At most 5 mol% of the xylose units were substituted. In the case of pulps with low mannan content only marginally differences between the nitren and alkaline (KOH, NaOH) extractions occurred. The extraction of the relatively “mannnan rich” pulps of this study like softwood kraft and beech sulfite pulps revealed that the dissolution effect regarding mannans increased in the following order: nitren < KOH < NaOH. In general the nitren extractions required a lower chemical charge compared to the alkaline extractions, in order to yield similar amounts of xylans. On the other side the necessity of an effective nickel removal is a disadvantage of the nitren extractions.     

Extraction and characterization of native heteroxylans from delignified corn stover and aspen

Dimethylsulfoxide-solubilized polysaccharides from delignified corn stover and aspen were characterized. The biomass was delignified by two different techniques; a standard acid chlorite and a pulp and paper QPD technique comprising chelation (Q), peroxide (P), and acid-chlorite (D). Major polysaccharides in all fractions were diversely substituted xylan. Xylan acetylation was intact after chlorite delignification and, as expected, xylan from QPD-delignified fraction was de-acetylated by the alkaline peroxide step. The study of DMSO-extractable xylans from chlorite-delignified biomass revealed major differences in native acetylation patterns between corn stover and aspen xylan. Xylan from cell walls of corn stover contains 2-O- and 3-O-mono-acetylated xylan and [MeGlcA-α-(1 → 2)][3-OAc]-xylp units. In addition, aspen xylan also contains 2,3-di-O-acetylated xylose. 1,4-β-d-xylp residues substituted with MeGlcA at O-2 position are absent in chlorite-delignified aspen xylan. Sugar composition in accord with NMR-spectroscopic data indicated that corn stover xylan is arabinosylated while aspen xylan is not. We have shown that corn stover xylan has similar structure with xylans from other plants of Poales order. No evidence was found to indicate the presence of 1,4-β-d-[MeGlcA-α-(1 → 2)][Ara-α-(1 → 3)]-xylp in corn stover xylan fractions.     

Evaluation of microbial loads,physical characteristics,chemical constituents and biological properties of radiation processed Fagonia arabica

Whole plant of Fagonia arabica with 3 different particle sizes (30, 50 and 70 mesh) were exposed to gamma radiation doses of 1–10 kGy from a Cobalt 60 source. A series of tests was performed in order to check the feasibility of irradiation processing of the plant. The applied radiation doses did not affect (P<0.05) pH and antimicrobial activities of the plant. The total weight of the dry extracts in methanol as well as water was found increased with irradiation. The irradiated samples showed significant increase in phenolic content and free radical scavenging activity using DPPH. Shortly after irradiation (on the day of radiation treatment) high amounts of free radicals were detected in the irradiated plant samples and the chemiluminescence measurements were generally found to be dose dependent. Maximum luminescence intensity was observed in case of samples with mesh size of 30 for all the radiation doses applied. After a period of one month the chemiluminescence signals of the irradiated samples approximated those of the controls. The study suggests that gamma irradiation treatment is effective for quality improvement and enhances certain beneficial biological properties of the treated materials.     

Xylo-Oligosaccharide (XOS) Formation through Hydrothermolysis of Xylan Derived from Viscose Process

Xylo-oligosaccharides (XOS) have gained growing interest during the past decade owing to their beneficial influence on health. At the same time, a trend to a more effective utilization of biomass and biomass degradation products can be observed. As a consequence, also the steeping-lye of the viscose process is discussed as a potential source of new products based on xylans, xylooligosaccharides, xylose, and different xylose degradation products, thus being a driving force for the development of appropriate production processes. Therefore, xylan isolated from the steeping-lye was subjected to hydrothermal degradation for production of xylo-oligosaccharides (XOS). The experiments were carried out at 120, 150, and 180 °C, respectively. This hydrothermal treatment led to a soluble fraction, consisting of neutral and acidic XOS, and an insoluble residue predominantly made up of highly crystalline cellulose. A mass balance was established to calculate the activation energy for hydrothermal xylan degradation from weight loss kinetics. The degree of polymerization (DP) of the neutral product fraction could be influenced in a wide range by the reaction conditions applied. Acidic XOS were further characterized using mass spectrometry (MS). A 4-O-methylglucuronic acid residue α-(1,3)-linked to the xylose backbone was detected as a new structural element in alkaline degradation products derived from beech wood xylan.     

Influence of structural and morphological factors on the mechanical properties of the polyethylenes

Force-length relations at ambient temperature have been determined for a set of polyethylenes which represent a wide range in molecular weight and molecular constitution. Taking advantage of previous work from this laboratory, samples have been prepared in such a manner that the important independent structural variables can be identified and isolated and their influence on the different aspects of the deformation process assessed. Partial melting-recrystallization processes appear to play an important role. For the linear polymers there is a direct influence of molecular weight. The influence of molecular weight manifests itself in the structure of the interlamellar zone which has a major influence on the initial modulus as well as the ultimate properties. Copolymers and branched copolymers display quite different behavior. The most striking difference is the invariance of the ultimate properties with molecular weight, branching, and level of crystallinity. From the set of experimental results that are presented the molecular factors involved in the deformation process can be sorted out. It becomes quite evident that all of the basic structural regions, characteristic of semicrystalline polymers, contribute to the observations. Focus solely on the changes in the crystallite, in analogy to the deformation of small-molecule crystalline systems, is inadequate in the case of crystalline polymers.     

Styrene-terminated polysulfone reactive oligomers: Cure and properties

Oligomers end-capped by groups capable of thermally induced polymerization have found wide applications in advanced structural composites and adhesives. The styrene-terminated polysulfone reactive oligomers described in this paper represent an example of such thermosetting systems. The advantage of these compounds, over high molecular weight polysulfone resin, lies in their easier processing and improved solvent resistance. This paper addresses the properties of the neat oligomer as a function of initial molecular weight and those of the resulting cured resin as well as a complete characterization of the curing reaction. Furthermore, a comparison will be made between these oligomers and the better known acetylene-terminated sulfone oligomers.     

Comprehensive review in moisture retention mechanism of polysaccharides from algae,plants, bacteria and fungus

Polysaccharides have attracted much attention due to their significant bio-activities. This review aims to summarize the main polysaccharides sources of related polysaccharides from algae, plants, fungus, and bacteria, and give insights into the structure–activity relationship between the moisture retention and structural characteristics of polysaccharides. The molecular weight, functional groups, polysaccharide modifications and apparent structure of polysaccharides are closely related to the moisturizing properties of polysaccharides in terms of moisturizing conformation. Based on recent moisturizing pieces of evidence, we propose a new framework focusing on the moisturizing intrinsic and extrinsic mechanisms. Polysaccharides molecular weight has different effects on moisturizing property. The extrinsic moisturization is mainly via the formation of hydrogen bonds between polysaccharides, the intrinsic moisturizing is mainly by regulating the production of some tight junction proteins. Accordingly, this review could further open the door for the production and application of polysaccharides as novel moisturizing agents in the cosmetic field.     

Characterization of Two New <Emphasis Type="Italic">Endo</Emphasis>-β-1,4-xylanases from <Emphasis Type="Italic">Eupenicillium parvum</Emphasis> 4–14 and Their Applications for Production of Feruloylated Oligosaccharides

Two new endo-1,4-beta-xylanases encoding genes EpXyn1 and EpXyn3 were isolated from mesophilic fungus Eupenicillium parvum 4–14. Based on analysis of catalytic domain and phylogenetic trees, the xylanases EpXYN1 (404 aa) and EpXYN3 (220 aa) belong to glycoside hydrolase (GH) family 10 and 11, respectively. Both EpXYN1 and EpXYN3 were successfully expressed in Pichia pastoris and the recombinant enzymes were characterized using beechwood xylan, birchwood xylan, or oat spelt xylan as substrates, respectively. The optimum temperatures and pH values were 75 °C and 5.5 for EpXYN1, and 55 °C and 5.0 for EpXYN3. EpXYN1 exhibited a high stability at high temperature (65 °C) or at pH values from 8 to 10. EpXYN3 kept over 80% enzymatic activity after treatment at pH values from 3 to 10. The specific activities of EpXYN1 and EpXYN3 were 384.42 and 214.20 U/mg using beechwood xylan as substrate, respectively. EpXYN1 showed lower K_m values and higher specific activities toward different xylans compared to EpXYN3. Thin-layer chromatography analysis indicated that the hydrolysis profiles of xylans or xylo-oligosacharides were different by EpXYN1and EpXYN3. EpXYN3 had a higher efficiency than EpXYN1 in production of feruloylated oligosaccharides (FOs) from de-starched wheat bran. The maximum levels of FOs released by EpXYN1 and EpXYN3 were 11.1 and 14.4 μmol/g, respectively. In conclusion, the two xylanases are potential candidates for various industrial applications.     

Comparison of potential energy maps and molecular shape invariance maps for two-dimensional conformational problems

Summary It is well known that many molecular properties are strongly dependent on internal nuclear arrangements. Two possible, independent approaches can be followed while studying changes in molecular characteristics as functions of the nuclear geometry. These are the analysis of potential energy surfaces and the analysis of molecular shape. In this work, we seek to establish relationships between potential energy maps and shape invariance region maps, where each point of these maps represents a nuclear configuration. The study is performed by analyzing the occurrence and lack of certain symmetries in both types of maps. As illustrative examples, we consider the three structural isomers of the dihydroxybenzene molecule. Potential energy is computed at the STO-3G ab initio level, while the shape is described by the shape group method as applied to fused-sphere van der Waals surfaces. It is shown that the symmetry of the shape invariance maps follows closely, but not exactly, the symmetry of potential energy surfaces. The molecular surface is thus blind to some small changes of the potential (a feature to be expected to hold also for molecular surfaces defined in terms of electronic charge density). Our findings suggest that a crude fused-sphere model may suffice to describe some of the structural changes in molecular surfaces, as well as their relationships to the electronic energy.     

Protective,Biostimulating, and Eliciting Effects of Chitosan and Its Derivatives on Crop Plants

Chitosan is a biodegradable and biocompatible polysaccharide obtained by partial deacetylation of chitin. This polymer has been gaining increasing popularity due to its natural origin, favorable physicochemical properties, and multidirectional bioactivity. In agriculture, the greatest hopes are raised by the possibility of using chitosan as a biostimulant, a plant protection product, an elicitor, or an agent to increase the storage stability of plant raw materials. The most important properties of chitosan include induction of plant defense mechanisms and regulation of metabolic processes. Additionally, it has antifungal, antibacterial, antiviral, and antioxidant activity. The effectiveness of chitosan interactions is determined by its origin, deacetylation degree and acetylation pattern, molecular weight, type of chemical modifications, pH, concentration, and solubility. There is a need to conduct research on alternative sources of chitosan, extraction methods, optimization of physicochemical properties, and commercial implementation of scientific progress outcomes in this field. Moreover, studies are necessary to assess the bioactivity and toxicity of chitosan nanoparticles and chitosan conjugates with other substances and to evaluate the consequences of the large-scale use thereof. This review presents the unique properties of chitosan and its derivatives that have the greatest importance for plant production and yield quality as well as the benefits and limitations of their application.     

Morphology and properties of low-density (branched) polyethylene

The different types of morphology that can be developed in a large number of low-density (branched) polyethylene whole polymers, as well as in a series of fractions, have been studied for two different extreme crystallization modes. Concomitantly, thermodynamic properties of the same samples have also been determined. After isothermal crystallization at elevated temperatures, spherulitic structures are found in all the whole polymer samples. On the other hand, after rapid crystallization a variety of different types of supermolecular structures are observed which are shown to depend systematically on the concentration of side-chain branches and the relative proportion of high molecular weight species in the sample. This temperature dependence of the morphological forms is opposite to that previously reported for linear polyethylene. The studies with the fractions show that the individual species are not the cause of this behavior; rather, the total composition is the important factor. The thermodynamic properties are also quite different from those of linear polyethylene in showing virtually no molecular weight dependence and being governed primarily by the concentration of short-chain branches. The degrees of crystallinity as determined from density and enthalpy of fusion measurements do not vary much with the two extreme crystallization conditions employed, are not sensitive to the morphology, and differ from one another, even when well-developed spherulites are formed. A major influence of the branching concentration on these properties is clearly indicated.     

Structural properties and antioxidant activities of polysaccharides isolated from sunflower meal after oil extraction

Making full use of sunflower seeds, including oil and the polysaccharides extracted from the meals which oil has been extracted, is one way to enhance their industrial value. Such meals contain abundant polysaccharides; however, the application of polysaccharides isolated from sunflower remaining meals after oil extraction has not been investigated. In this study, polysaccharides were isolated by alkali from sunflower meals after different oil extraction processes, and their structural properties and antioxidant activities were compared. The results indicated that these polysaccharides displayed significant variability in monosaccharide composition and molecular weight. Differences in structural properties could result in differences in functional antioxidant properties. The polysaccharide (SPHE-1) obtained from the meals after traditional hexane extraction exhibited the best antioxidant activities, including DPPH free radical-scavenging assay and hydroxyl radical scavenging activity among all the polysaccharide fractions. The research provides valuable information for making efficient use of sunflower seeds in the food industry.     

The rheological,thermal, and mechanical properties for polypropylene and amorphous poly alpha olefin blends

Rheological, thermal, and mechanical properties of polypropylene homo polymer (PPH)/amorphous poly alpha olefin (APAO) blends as a function of molecular weight, comonomer type and content, and blend composition have been investigated. Homo APAO grade showed better compatibility than copolymerized ones in terms of rheological and thermal properties. The mechanical strength showed strong dependence on APAO content and type, and the impact strength and melt index rapidly increased for certain types of APAO at and above 30 wt%. On comparison with commercially used PPH/ethylene–propylene rubber (EPR) blend system, it is supposed that PPH/APAO blend can be successfully used in thermoplastic polyolefin applications. Copyright © 2007 John Wiley & Sons, Ltd.     

Polyarylsulfones,synthesis and properties,

A new class of high molecular weight polyarylsulfones is described. Polymer synthesis and structure–property relationships are discussed. The polymers are prepared by Friedel-Crafts type polycondensation of aromatic sulfonyl chlorides with aromatic hydrocarbons. A number of Lewis acids in small quantities are useful as catalysts for the polymerization. The polymerization reaction is carried out at elevated temperatures in the melt or in solution. Inert, nonbasic solvents which are compatible with the Lewis acid catalysts such as nitrobenzene and dimethyl sulfone are useful for conducting the polymerization. Many of the polyarylsulfones are amorphous, rigid thermoplastics with unusually high softening points, having glass transition temperatures in the range of 200–350°C. Outstanding resistance to air oxidation at high temperatures is derived from incorporation of the deactivating sulfone groups in the aromatic polymer backbone. Melt stability and solubility in selected solvents are emphasized as basis for processibility by conventional solution casting and molding techniques. The combination of properties, which in addition to thermal stability includes a high level of mechanical and electrical properties, chemical inertness, and hydrolysis resistance makes these new arylsulfone polymers useful over a wide temperature range and in severe and corrosive environments.