Polyelectrolyte Titration Research Articles

Synthesis of Thermoresponsive Chitosan-graft-Poly(N-isopropylacrylamide) Hybrid Copolymer and Its Complexation with DNA.

A hybrid synthetic-natural, thermoresponsive graft copolymer composed of poly(N-isopropyl acrylamide) (PNIPAM) side chains, prepared via RAFT polymerization, and a chitosan (Chit) polysaccharide backbone, was synthesized via radical addition-fragmentation reactions using the "grafting to" technique, in aqueous solution. ATR-FTIR, TGA, polyelectrolyte titrations and 1H NMR spectroscopy were employed in order to validate the Chit-g-PNIPAM copolymer chemical structure. Additionally, 1H NMR spectra and back conductometric titration were utilized to quantify the content of grafted PNIPAM side chains. The resulting graft copolymer contains dual functionality, namely both pH responsive free amino groups, with electrostatic complexation/coordination properties, and thermoresponsive PNIPAM side chains. Particle size measurements via dynamic light scattering (DLS) were used to study the thermoresponsive behavior of the Chit-g-PNIPAM copolymer. Thermal properties examined by TGA showed that, by the grafting modification with PNIPAM, the Chit structure became more thermally stable. The lower critical solution temperature (LCST) of the copolymer solution was determined by DLS measurements at 25-45 °C. Furthermore, dynamic and electrophoretic light scattering measurements demonstrated that the Chit-g-PNIPAM thermoresponsive copolymer is suitable of binding DNA molecules and forms nanosized polyplexes at different amino to phosphate groups ratios, with potential application as gene delivery systems.

Cytotoxicity and Antibacterial Efficacy of Betaine- and Choline-Substituted Polymers.

Cationic charge has been widely used to increase polymer adsorption and flocculation of dispersions or to provide antimicrobial activity. In this work, cationization of hydroxyethyl cellulose (HEC) and polyvinyl alcohol (PVA) was achieved by covalently coupling betaine hydrochloride and choline chloride to the polymer backbones through carbonyl diimidazole (CDI) activation. Two approaches for activation were investigated. CDI in excess was used to activate the polymers' hydroxyls followed by carbonate formation with choline chloride, or CDI was used to activate betaine hydrochloride, followed by ester formation with the polymers' hydroxyls. The first approach led to a more significant cross-linking of PVA, but not of HEC, and the second approach successfully formed ester bonds. Cationic, nitrogen-bearing materials with varying degrees of substitution were obtained in moderate to high yields. These materials were analyzed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, polyelectrolyte titration, and kaolin flocculation. Their dose-dependent effect on the growth of Staphylococcus aureus and Pseudomonas aeruginosa, and L929 mouse fibroblasts, was investigated. Significant differences were found between the choline- and betaine-containing polymers, and especially, the choline carbonate esters of HEC strongly inhibited the growth of S. aureus in vitro but were also cytotoxic to fibroblasts. Fibroblast cytotoxicity was also observed for betaine esters of PVA but not for those of HEC. The materials could potentially be used as antimicrobial agents for instance by coating surfaces, but more investigations into the interaction between cells and polysaccharides are necessary to clarify why and how bacterial and human cells are inhibited or killed by these derivatives, especially those containing choline.

Layer-by-layer assembly of sustainable lignin-based coatings for food packaging applications

Packaging plays a critical role in ensuring food safety and shelf life by protecting against e.g., moisture, gases, and light. Polyethylene (PE) is widely used in food packaging, but it is mainly produced from non-renewable resources and it is an inefficient oxygen and light barrier. In this study, the layer-by-layer (LbL) assembly of a sustainably produced lignin-based polymer (EH) with polyethylenimine (PEI) or chitosan (CH) was used to fabricate (partially or fully) bio-based coatings with the aim of improving barrier properties of PE films. The charge density of EH was calculated using a polyelectrolyte titration method and the hydrodynamic diameters of EH, PEI and CH were determined by Dynamic Light Scattering (DLS). LbL assembly was monitored in situ via Quartz Crystal Microbalance with Dissipation (QCM-D) and Stagnation Point Adsorption Reflectometry (SPAR). PE films were coated with a variable number of PEI/EH or CH/EH bilayers (BL) using an immersive LbL assembly method. Coated films were studied in terms of light-blocking ability, wettability, thermal behaviour, surface structure, as well as oxygen and water vapor barrier properties. QCM-D and SPAR data showed a stepwise multilayer formation and strong interactions between the oppositely charged polymers, with PEI/EH coating having a greater amount of deposited polymer compared to CH/EH coating at the same number of BL. Overall, light barrier properties and wettability of the coated films increased with the number of deposited bilayers. Coated PE films maintained the overall thermal behaviour of PE. A number of BL of 20 was found to be the most promising based on the studied properties. Selected samples showed improved oxygen and water vapor barrier properties, with PEI/EH coating performing better than CH/EH coating. Taken altogether, we demonstrated that a novel and sustainable lignin-based polymer can be combined with PEI or CH to fabricate (partially or fully) bio-based coatings for food packaging.

Specific ion effects in the adsorption of carboxymethyl cellulose on cellulose: The influence of industrially relevant divalent cations

The adsorption of carboxymethylcellulose (CMC) on cellulose surfaces is of relevance from both academic and industrial perspectives as it facilitates resource-efficient modification of cellulose fibres that allows them to carry negative charges. It is known that, compared to monovalent ions, Ca2+ ions are superior ions in facilitating CMC adsorption and the subsequent introduction of charge on cellulose fibres. However, the formation and deposition of calcium oxide involved in this process necessitates the search for alternative cations. Magnesium ions form one of the more promising candidates since they are already used in the pulping process to prevent cellulose degradation during peroxide bleaching. This work aims at elucidating the effects of the industrially relevant alkaline earth metal divalent cations Mg2+ and Ca2+ on the CMC adsorption process onto cellulose surfaces. Quartz Crystal Microbalance (QCM-D) technology was used to follow the adsorption in model systems in real time, whereas the adsorption of CMC on commercial fibres was studied using polyelectrolyte titrations, total organic carbon (TOC) analysis and conductometric titrations. This study shows that the presence of Ca2+ ions was more favourable for the adsorption of CMC to both types of cellulosic surfaces than Mg2+ ions. The distinction in the adsorption behaviour in the presence of Mg2+ and Ca2+ is suggested to be due to the differences in the polarizability of the ions. The findings are decisive in designing efficient industrial processes for the adsorption of polyelectrolytes to cellulose surfaces of similar charge.

Succinylation of Polyallylamine: Influence on Biological Efficacy and the Formation of Electrospun Fibers.

Succinylation of proteins is a commonly encountered reaction in biology and introduces negatively charged carboxylates on previously basic primary amine groups of amino acid residues. In analogy, this work investigates the succinylation of primary amines of the synthetic polyelectrolyte polyallylamine (PAA). It investigates the influence of the degree of succinylation on the cytotoxicity and antibacterial activity of the resulting polymers. Succinylation was performed in water with varying amounts of succinic anhydride and at different pH values. The PAA derivatives were analyzed in detail with respect to molecular structure using nuclear magnetic resonance and infrared absorbance spectroscopy. Polyelectrolyte and potentiometric charge titrations were used to elucidate charge ratios between primary amines and carboxylates in the polymers. The obtained materials were then evaluated with respect to their minimum inhibitory concentration against Staphylococcus aureus and Pseudomonas aeruginosa. The biocompatibility was assessed using mouse L929 fibroblasts. The degree of succinylation decreased cytotoxicity but more significantly reduced antibacterial efficacy, demonstrating the sensitivity of the fibroblast cells against this type of ampholytic polyelectrolytes. The obtained polymers were finally electrospun into microfiber webs in combination with neutral water-soluble polyvinyl alcohol. The resulting non-woven could have the potential to be used as wound dressing materials or coatings.

Effects of rice-straw derived phytoliths on the surface charge properties of paddy soils

Straw of rice (Oryza sativa), a high Si-accumulating plant, is typically composed of amorphous silica bodies (namely phytoliths) that are deposited within the plant tissues. Recycling of rice straw is a traditional agricultural practice that introduces phytoliths into soil in many paddy regions. While the role of phytoliths as a carrier for nutrients, e.g., K, P, or terminal sink of Si, has been reported, it remains unclear to what extent phytolith can carry charges and act as a charge-interchange constituent in soils. Therefore, it was hypothesized that soil phytoliths can be involved in charge-related interactions e.g., pH buffering, multivalent cation exchange, polymerization, colloid stability or reactive transports. Based on a polyelectrolyte titration technique, our study evaluated surface charge (SC) dynamics of straw-derived phytoliths and paddy soils in the Mekong river and Red river deltas to characterize the possible contribution of phytoliths to soil SC properties. Phytoliths were extracted by both dry and wet ashing techniques and the SC of the obtained phytoliths were measured in the pH range from 3.5 to 8.0. The SC was detected to vary from slightly positive at low pH to –78.5 mmolc kg−1 at slightly alkaline pH, suggesting that these materials carry variable charges and could be a significant source of charge when they are returned to soil in relatively large quantities. Multiple regressions indicated that phytoliths, to some extents, can together with other soil constituents such as clay minerals, organic matter and iron oxides, regulate the SC of paddy soils. Despite phytoliths being more or less soluble, their SC properties suggest that the annual recycling of rice straw to paddy soils, particularly after burning, can contribute to the negative SC system. The phytolith-derived charge in turn might affect soil cation exchange capacity (CEC), dispersibility of clay particles and transport of solutes.

Differences and similarities between kraft and oxygen delignification of softwood fibers: effects on chemical and physical properties

The fiber properties after oxygen delignification and kraft pulping were studied by looking into the chemical characteristics and morphology. The effect of the two processes on the fibers was evaluated and compared over a wider kappa number range (from 62 down to15). Wide-angle X-ray scattering, nuclear magnetic resonance and fiber saturation point were used to characterize the fiber network structure. Fiber morphology and fiber dislocations were evaluated by an optical image analysis. The total and surface fiber charges were studied by conductometric and polyelectrolyte titrations. The fiber wall supramolecular structure, such as crystallinity, size of fibril aggregates, pore size and pore volume, were similar for the two processes. The selectivity, in terms of carbohydrate yield, was equal for kraft cooking and oxygen delignification, but the selectivity in terms of viscosity loss per amount of delignification is poorer for oxygen delignification. Clearly more fiber deformations (2–6% units in curl index) in the fibers after oxygen delignification were seen. Introduction of curl depended on the physical state of the fibers, i.e. liberated or in wood matrix. In the pulping stage, the fiber continue to be supported by neighboring fibers, as the delignified chips maintain their form. However, in the subsequent oxygen stage the fibers enter in the form of pulp (liberated fibers), which makes them more susceptible to changes in fiber form.Graphic abstract

Effects of solution chemistry on conformation of self-aggregated tannic acid revealed by laser light scattering

Inorganic soil solution constituents can alter the charge, size, and conformation of dissolved organic molecules, thus affecting their environmental behavior. Here, we investigated how pH, cation valence and activities induce conformational changes and aggregation-sedimentation reactions of organic polyelectrolytes. For that we determined the hydrodynamic diameter of the model compound tannic acid by laser light scattering at concentrations of 1–30 g L−1 in the pH range from 3 to 10 and with electrolyte additions of CaCl2 and hydroxyl-Al cations. Charge properties were quantified by polyelectrolyte titration and zeta potential measurements. After dispersion by sonication, aggregation was determined in time sequences up to 60 min and suspension stability was traced in sedimentation experiments. Tannic acid was present in ultrapure water in a self-aggregated state. At pH <3 as well as >7.5, its hydrodynamic diameter increased. Whereas at high pH this behavior could be assigned to unfolding of molecular conformations, at low pH it is likely that charge neutralization decreased repulsive forces and facilitated aggregation. At pH 5 and ionic strengths of up to 5 mM, CaCl2 did not affect aggregation state of tannic acid and results resembled those obtained in ultrapure water. Addition of hydroxyl-Al cations broke-up the self-aggregated tannic acid structures under formation of Al-organic coprecipitates. Strong aggregation only occurred at mixing ratios where opposite surface charges were completely balanced. Under natural conditions, self-aggregation of tannic acid can be expected only at higher solution concentrations. However, at acidic pH, hydroxyl-Al cations and tannic acid may form discrete colloidal particles already at low tannic acid concentrations, resulting in the destabilization of suspensions. Our data emphasize that the soil solution composition strongly modifies the physical state of tannic acid, and likely also of other biopolymers, and thus their interactions within environmental matrices.

Functionalized Wool as an Efficient and Sustainable Adsorbent for Removal of Zn(II) from an Aqueous Solution.

In this paper, the aim of the research was to obtain a highly efficient wool-based sorbent for the removal of zinc Zn(II) from wastewater. To increase the functional groups for metal binding, the wool was functionalized with chitosan. Chitosan has amino groups through which metals can be complexed easily to chelates. The physical and chemical modification of chitosan on wool was performed to analyze the influence of the coating bond on the final ability of the wool to remove metals. The presence of functional chitosan groups onto wool after adsorption was verified by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FT-IR) spectra. The effective binding of chitosan to wool was also determined by potentiometric and polyelectrolyte titration methods. The latter titration was used to analyze the chitosan desorption. The main part of the study was the sorption of Zn(II) on natural and functionalized wool. The influence was investigated as a function of contact time, pH, metal ion concentration and temperature on the sorption process. The absorbent with the highest concentration of protonated amino groups (607.7 mmol/kg) and responding sorption capacity of 1.52 mg/g was obtained with wool physically modified by a macromolecular chitosan solution (1%) at pH = 7. Adsorption of Zn(II) onto pristine and modified wool corresponded to pseudo-second order kinetics (R2 > 0.9884). The Langmuir model was found to be more suitable (R2 > 0.9866) in comparison to the Freundlich model. The Zn(II) sorption process was spontaneous (∆G < 0) and exothermic (∆H < 0). The results found in this study are significant for escalating the possible use of wool modified with polysaccharide coatings as a sustainable source to improve or increase the metal sorption activity of wool.

Copolymeric nano/microgels of N-isopropylacrylamide and carboxyalkyl methacrylamides: Effect of methylene chains and the ionization state of the weak acids on size and sensitivity to pH and temperature

ABSTRACT We prepared nano/microgels by precipitation copolymerization of N-isopropylacrylamide (NIPAAm), and one of three different carboxyalkyl methacrylamides [methacryloylamido hexanoic acid (M5), 8-methacryloylamido octanoic acid (M7), and 11-methacryloylamido undecanoic acid (M10)], either in the acid forms or as carboxylates (potassium salts). The hydrodynamic diameter (Dh) of the nano/microgels prepared with the carboxylates was smaller (≈100 nm for M10 copolymers), compared to the size of homopolymeric NIPAAm microgels prepared by dispersion polymerization (around 600 nm), indicating that the carboxylates act as surfactants reducing the size of the seeds during the polymerization process. These materials presented a swollen-shrunken transition temperature (T tr) similar to the T tr of the homopolymeric NIPAAm microgels, without pH sensitivity. On the other hand, the copolymeric microgels prepared from the acid form of the comonomers have a similar or bigger size than NIPAAm microgels. For these copolymers, the T tr can be tuned by the type and proportion of acid comonomer used and present pH sensitivity. This is important for biomedical applications such as positive temperature control release. Polyelectrolyte titration demonstrates that the nano/microgels prepared with the carboxylates behave as hard spheres, while the microgels prepared with the weak acid behave as porous materials.

Alkali-peroxide extraction of xylan from sugar cane bagasse. Characteristics and film forming capacity

ABSTRACT This work analyzes the main characteristics of hemicellulose alkali and peroxide/alkali extracted from sugar cane bagasse and precipitated by 1:1 ethanol/liquor ratio and studies the influence of the chemical charge on these characteristics. It also evaluates the film forming capacity of these hemicelluloses when they are combined in a polyelectrolyte complex with chitosan. Extraction conditions were determinant of the glucuronic acid to xylose ratio and arabinose to xylose ratio. The charge density of xylan, determined by polyelectrolyte titration at pH 7.0, showed a linear relation with the glucuronic acid content. Xylans with low polydispersity and acceptable molecular weight were obtained in all cases. Hemicellulose-based films (70% of xylan) without the addition of plasticizer or crosslinking agent, obtained through the controlled formation of the polyelectrolyte complexes, were flexible with acceptable mechanical properties. The film with the highest stress and strain at break (19.1 MPa and 10.7%, respectively) corresponded to hemicellulose with the highest molecular weight, extracted with the highest alkali charge and no peroxide addition.

Recyclable Polymer-Supported N-Hydroxyphthalimide Catalysts for Selective Oxidation of Pullulan.

This paper proposes a convenient route to oxidize the –CH2–OH groups in the water-soluble pullulan, using a new catalytic polymer-supported N-hydroxyphthalimide (NHPI) immobilized on polystyrene. The protocol involves the presence of sodium hypochlorite and sodium bromide. The conversion is possible at room temperature, atmospheric pressure, and pH = 10. The characterization of both the catalysts and oxidized pullulan was done using NMR and FTIR methods. Using polyelectrolyte titration with end-point indication by means of a particle-charge detector (PCD), we were able to assess the degree of electrokinetic charge in all oxidized samples as a consequence of the conversion of the –CH2–OH group into –COOH moieties. The possibility of recovery and recycling of the polymer-supported NHPI catalyst was tested for up to four cycles, since the morphological analyses performed on the catalysts using SEM revealed no significant changes.

Protonation behavior of dextran amino acid esters

Dextran esters of different amino acids (glycine, -alanine, L-ornithine, L-lysine) are investigated regarding their pKa values by potentiometric titration. The pKa values of the dextran derivatives are generally dependent on the position of the amino group in relation to the ester group, i.e. the nearer they are located in the molecule, the lower the resulting pKa values are, L-ornithine ester being the exception. An influence of the polymer backbone is ruled out. Stability against hydrolysis at different pH values and over longer periods at constant pH value is measured by potentiometric and polyelectrolyte titration. The -alanine ester shows slowest hydrolysis at alkaline pH values, starting at a pH value of 8. The esters investigated are polycations at physiological pH values; thus, the charging properties are essential for using these esters as nonviral vectors in gene delivery.

Explicit Ion Effects on the Charge and Conformation of Weak Polyelectrolytes.

The titration behavior of weak polyelectrolytes is of high importance, due to their uses in new technologies including nanofiltration and drug delivery applications. A comprehensive picture of polyelectrolyte titration under relevant conditions is currently lacking, due to the complexity of systems involved in the process. One must contend with the inherent structural and solvation properties of the polymer, the presence of counterions, and local chemical equilibria enforced by background salt concentration and solution acidity. Moreover, for these cases, the systems of interest have locally high concentrations of monomers, induced by polymer connectivity or confinement, and thus deviate from ideal titration behavior. This work furthers knowledge in this limit utilizing hybrid Monte Carlo–Molecular Dynamics simulations to investigate the influence of salt concentration, , pH, and counterion valence in determining the coil-to-globule transition of poorly solvated weak polyelectrolytes. We characterize this transition at a range of experimentally relevant salt concentrations and explicitly examine the role multivalent salts play in determining polyelectrolyte ionization behavior and conformations. These simulations serve as an essential starting point in understanding the complexation between weak polyelectrolytes and ion rejection of self-assembled copolymer membranes.

One-pot preparation of bi-functional cellulose nanofibrils

Herein, we present a route to obtain bi-functional cellulose nanofibrils (CNF) by a one-pot approach using an already established functionalisation route, carboxymethylation, to which a subsequent functionalisation step, allylation or alkynation, has been added in the same reaction pot, eliminating the need of solvent exchange procedures. The total charge of the fibres and the total surface charge of the nanofibrils were determined by conductometric and polyelectrolyte titration, respectively. Furthermore, the allyl and alkyne functionalised cellulose were reacted with methyl 3-mercaptopropionate and azide-functionalised disperse red, respectively, to estimate the degree of functionalisation. The samples were further assessed by XPS and FT-IR. Physical characteristics were evaluated by CP/MAS 13C-NMR, XRD, AFM and DLS. This new approach of obtaining bi-functionalised CNF allows for a facile and rapid functionalisation of CNF where chemical handles can easily be attached and used for further modification of the fibrils.Graphical abstract

Hydrolysis of cationic polyacrylamide and its effect on flocculation of ground calcium carbonate

Cationic polyacrylamides (C-PAMs) have been widely used as flocculating agents to aggregate particles carrying negatively charged surfaces. This study examined the effects of hydrolysis of C-PAM on its adsorption behaviour and flocculation of negatively charged particles, specifically ground calcium carbonate (GCC). C-PAM hydrolysis was examined using polyelectrolyte titration and ion chromatography, while the adsorption behaviour of the polymer was monitored using a quartz crystal microbalance with dissipation (QCM-D). Laser diffraction spectroscopy was used to measure the size of the GCC aggregates under neutral and alkaline conditions. The charge density measurements and ion chromatograms indicated that the hydrolysis of C-PAM was accelerated with increased pH and temperature. The QCM-D measurements of hydrolysed C-PAMs, adsorbed on a substrate with a flat and rigid structure, indicated that hydrolysis of C-PAM suppressed its ability to cause inter-particle bridging flocculation, which reduced the aggregate size of GCC.

Active Ester Containing Surfmer for One-Stage Polymer Nanoparticle Surface Functionalization in Mini-Emulsion Polymerization.

Functional surface active monomers (surfmers) are molecules that combine the functionalities of surface activity, polymerizability, and reactive groups. This study presents an improved pathway for the synthesis of the active ester containing surfmer p-(11-acrylamido)undecanoyloxyphenyl dimethylsulfonium methyl sulfate (AUPDS). Further, the preparation of poly(methyl methacrylate) and polystyrene nanoparticles (NPs) by mini-emulsion polymerization using AUPDS is investigated, leading to NPs with active ester groups on their surface. By systematically varying reaction parameters and reagent concentrations, it was found that AUPDS feed concentrations between 2–4 mol% yielded narrowly distributed and stable spherical particles with average sizes between 83 and 134 nm for non-cross-linked NPs, and up to 163 nm for cross-linked NPs. By basic hydrolysis of the active ester groups in aqueous dispersion, the positive ζ-potential (ZP) was converted into a negative ZP and charge quantities determined by polyelectrolyte titrations before and after hydrolysis were in the same range, indicating that the active ester groups were indeed accessible in aqueous suspension. Increasing cross-linker amounts over 10 mol% also led to a decrease of ZP of NPs, probably due to internalization of the AUPDS during polymerization. In conclusion, by using optimized reaction conditions, it is possible to prepare active ester functionalized NPs in one stage using AUPDS as a surfmer in mini-emulsion polymerization.

Tailoring flame-retardancy and strength of papers via layer-by-layer treatment of cellulose fibers

The layer-by-layer (LbL) technology was used to adsorb polyelectrolyte multilayers consisting of cationic polyethylenimine (PEI) and anionic sodium hexametaphosphate (SHMP) onto cellulose fibers in order to enhance the flame-retardancy and tensile strength of paper sheets made from these fibers. The fundamental effect of PEI molecular mass on the build-up of the multilayer film was investigated using model cellulose surfaces and a quartz crystal microbalance technique. The adsorption of a low (LMw) and a high molecular weight (HMw) PEI onto cellulose fibers and carboxymethylated (CM) cellulose fibers was investigated using polyelectrolyte titration. The fibers were consecutively treated with PEI and SHMP to deposit 3.5 bilayers (BL) on the fiber surfaces, and the treated fibers were then used to prepare sheets. In addition, a wet-strength paper sheet was prepared and treated with the same LbL coatings. Thermal gravimetric analysis of LbL-treated fibers showed that the onset temperature for cellulose degradation was lowered and that the amount of residue at 800 °C increased. A horizontal flame test and a vertical flame test were used to evaluate the combustion behavior of the paper sheets. Papers prepared from both cellulose fibers and CM-cellulose fibers treated with HMw-PEI/SHMP LbL-combination self-extinguished in a horizontal configuration despite the rather low amounts of adsorbed polymer which form very thin films (wet thickness of ca. 17 nm). The tensile properties of handsheets showed that 3.5 BL of HMw-PEI and SHMP increased the stress at break by 100% compared to sheets prepared from untreated cellulose fibers.

Adsorption of cationized xylans onto polyethylene terephthalate fabrics for antimicrobial medical textiles

The main aim of this research was development of thin functional xylan layers on polyethylene terephthalate (PET) fabric surfaces. Xylans, derived from hard wood and oat spelt, were modified chemically in order to introduce cationic functional groups. Cationization of xylans was proved by elemental analysis, total bound nitrogen determination, and Raman techniques, as well as by polyelectrolyte titrations. The antimicrobial activity of xylans was investigated by the determination of Minimal Inhibitory Concentration against bacteria S. aureus and E. coli, and fungi C. albicans. Xylan solutions were then applied onto PET fabric using the spray coating technique. Charging behavior of the treated PET fabric samples was evaluated by potentiometric titration supported by X-ray electron spectroscopy. Hydrophilicity was examined by the water contact angle determination. The morphology of coated fabrics was analyzed using Scanning Electron Microscopy. The results of microbial testing showed that PET fabrics functionalized by cationic xylans act antimicrobially against S. aureus and E. coli. The presented work suggests that cationized xylans, originally derived from hard wood and/or oat spelt, could be applied successfully as a coating material for PET fabrics in order to introduce hydrophilicity and antimicrobial properties.

Superior Flame-Resistant Cellulose Nanofibril Aerogels Modified with Hybrid Layer-by-Layer Coatings.

Nanometer thin films consisting of cationic chitosan (Ch), anionic poly(vinylphosphonic acid) (PVPA), and anionic montmorillonite clay (MMT) are deposited on highly porous, wet-stabilized cellulose nanofibril (CNF) aerogels via the layer-by-layer (LbL) technique. Model experiments with silicon oxide surfaces are used to study the details of LbL formation and the multilayer structure. Formation of layers on the aerogels is also investigated as a function of solution concentration by use of polyelectrolyte titration. Thermogravimetric analysis indicates that the LbL coating significantly improves thermal stability of the CNF aerogel. Horizontal flame test shows that aerogels coated with five quadlayers of Ch/PVPA/Ch/MMT, using solutions/dispersion of high concentration, are able to self-extinguish immediately after removal of flame, and LbL-coated aerogels do not ignite under heat flux (35 kW/m2) in cone calorimetry. The LbL-coated aerogel can prevent flame penetration from a torch focused on the surface, achieving temperature drops up to 650 °C across the 10 mm thick specimen for several minutes. LbL treatment is hence a rapid and highly effective way to specifically tailor the surface properties of CNF aerogels in order to confer unprecedented flame-retardant characteristics.