Properties of poly(acrylamide)/TEMPO-oxidized cellulose nanofibril composite films

Self-standing composite films consisting of 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibril (TOCN) and anionic poly(acrylamide) (PAM) in various weight ratios were prepared by casting and drying of homogeneous mixtures of aqueous TOCN dispersion and PAM solution. PAM/TOCN composite films consisting of 25 % PAM and 75 % TOCN had clearly higher Young’s modulus (13.9 GPa) and tensile strength (266 MPa) than 100 % TOCN film (10.8 GPa and 223 MPa, respectively) or 100 % PAM film (4.9 GPa and 78 MPa, respectively), showing that PAM molecules have mechanical reinforcement ability in TOCN matrix. Some attractive interactions are likely formed between TOCN element surfaces and PAM molecules. In contrast, no such mechanical improvements were observed for poly(vinyl alcohol)/TOCN or oxidized starch/TOCN composite films prepared as references. Moreover, the mechanical properties of the PAM/TOCN composite films were further improved by controlling molecular mass and branching degree of the PAM. The high optical transparency and low coefficient of thermal expansion of the 100 % TOCN film were mostly maintained in the TOCN composite film containing 25 % PAM.     

Preparation of methylated TEMPO-oxidized cellulose nanofibril hydrogel with high-temperature sensitivity

Cellulose - TEMPO-oxidized cellulose nanofibril (TOCNF) hydrogel presents unique advantageous characteristics and has been envisioned as a building block to design novel biobased materials....     

Degradation of TEMPO-oxidized cellulose fibers and nanofibrils by crude cellulase

The biodegradation behavior of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose fibers (TOCs) suspended in water and TEMPO-oxidized cellulose nanofibrils (TOCNs) dispersed in water by a commercial crude cellulase was studied. Products crude cellulase-treated for 0–7 days were separated into water/ethanol-insoluble and -soluble fractions. Weight recovery ratios and viscosity-average degrees of polymerization of the water/ethanol-insoluble fractions clearly decreased with crude cellulase-treatment time, showing that both TOCs and TOCNs have biodegradability. Water/ethanol-soluble fractions were subjected to size-exclusion chromatography (SEC) with photodiode array (PDA) detection to obtain SEC elution patterns detected by reflective index and UV spectra of each SEC pattern elution slice. SEC–PDA and ¹³C-NMR analyses showed that glucuronosyl unit-containing molecules present on microfibril surfaces in TOCs and TOCNs were primarily cleaved by hydrolyzing enzymes present as contaminants in the crude cellulase to form glucuronic acid as one of the major water-soluble degradation compounds. After the glucuronosyl units in TOCs and TOCNs were degraded and removed from microfibril surfaces by the hydrolyzing enzymes, cellulose chains newly exposed on the microfibril surfaces were rapidly hydrolyzed by cellulases predominantly present in the crude cellulase to form cellobiose. Both TOCs and TOCNs having sodium carboxyl groups are thus biodegradable, but TOCN having free carboxyl groups had clearly low biodegradability by the crude cellulase. Thus, biodegradation behavior may be controllable by controlling the structure of carboxyl group counter ions in TOCs and TOCNs.     

Resin impregnation of cellulose nanofibril films facilitated by water swelling

Flexible composite films were produced by impregnating aqueous phenol formaldehyde (PF) resin into water-swollen cellulose nanofibril (CNF) films. CNF films were prepared using a pressurized filtration method in combination with freeze drying. The freeze-dried films were swollen with water then impregnated with PF resin by soaking in aqueous resin solutions of varying concentrations. Small amounts of PF slightly enhanced the tensile properties of CNF films. The formulation with the best mechanical properties was CNF/PF films with 8 wt % resin exhibiting tensile stress and toughness of 248 MPa and 26 MJ/m³, respectively. Resin concentrations higher than about 8 % resulted in composites with decreased tensile properties as compared to neat CNF films. The wet strength of the composite films was significantly higher than that of the neat CNF films. The resulting composites showed greater resistance to moisture absorption accompanied by reduced thickness swelling when soaked in water as compared to neat CNF films. The composites also showed decreased oxygen permeability at low humidity compared to neat films, but the composites did not show improved barrier properties at high humidity.     

TEMPO-oxidized cellulose nanofiber films: effect of surface morphology on water resistance

2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibers were prepared from two kraft pulps (Norway spruce and mixed eucalyptus) using the TEMPO/NaBr/NaClO system at pH 10 and 22?°C. After reaction and mechanical treatment, the TEMPO-oxidized celluloses were used for preparation of self-standing films and coatings of laminate films on 50-μm-thick polyethylene terephthalate films. Characterization of the films was performed based on water contact angle measurements, laser profilometry, scanning electron microscopy, and field-emission scanning electron microscopy. The purpose of this study is to understand how the measured contact angles are affected by the film’s physical properties (morphology, thickness, density, and roughness).     

Thermal stabilization of TEMPO-oxidized cellulose

A partially C6-carboxylated cellulose with carboxylate content of 1.68 mmol/g was prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation of a softwood bleached kraft pulp. Thermogravimetric analyses of the TEMPO-oxidized cellulose (TOC) and its related materials were studied to improve thermal stability of the TOC. Thermal decomposition (T_d) points of the TOC with sodium carboxylate groups, alkali-treated TOC with free carboxyl groups of 0.23 mmol/g and the original cellulose were 222 °C, 264 °C and 275 °C, respectively. Thus, the anhydroglucuronic acid units formed by TEMPO-mediated oxidation of the native wood cellulose and present in the TOC cause the decrease in T_d point by decarbonation during heating process. When carboxyl groups in the TOC were methylated with trimethylsilyl diazomethane (TMSCHN₂), the T_d point increased from 222 °C to 249 °C, and the peak temperature in its derivative thermogravimetric (DTG) curve increased from 273 °C to 313 °C, which was almost equal to that of the original cellulose. Thus, the methyl esterification of carboxyl groups in the TOC is effective in improving thermal stability. When sodium ions present in the TOC as counter ions of carboxylate groups were exchanged to some other metal ions, thermal stability was improved to some extent. Especially, when CaCl₂, Ca(OAc)₂, Ca(NO₃)₂ and CaI₂ solutions were used in the ion-exchange treatments, the peak temperatures in the DTG curves increased to approximately 300 °C. MgCl₂, NiCl₂, SrCl₂ and Sr(OAc)₂ solutions were also effective to some extent in increasing the peak temperatures of DTG curves. Thus, thermal stability of the fibrous TOC can be improved to some extent by methyl esterification of the sodium carboxylate groups present in the original TOC with TMSCHN₂ or ion-exchange treatments with some metal salt solutions.     

Multifunctional silk fibroin/PVA bio-nanocomposite films containing TEMPO-oxidized bacterial cellulose nanofibers and silver nanoparticles

Cellulose - Silk fibroin (SF) has been intensively studied as a biobased renewable material for biomedical and other applications. However, its relatively low mechanical properties have limited its...     

Mechanical enhancement of cellulose nanofibril (CNF) films through the addition of water-soluble polymers

Cellulose - In this work, water-soluble polymers were screened through solution casting and polyvinyl alcohol (PVA) and poly(2-ethyl-2-oxazoline) (PEOX) were found as reinforcement agents for...     

Magnetic cellulosic materials based on TEMPO-oxidized viscose fibers

A simple method for preparation of magnetic cellulose fibers by coating (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized viscose with oleic-acid-coated or uncoated, freshly prepared magnetic nanoparticles (MNp) is presented. MNp attachment was facilitated by chemical activation of the cellulose fibers through introduction of negatively charged carboxylic groups using the well-established TEMPO-mediated oxidation protocol. The resulting composite materials preserved the intrinsic properties of the cellulose fibers, but gained notable specific features due to the presence of magnetic nanoparticles. The obtained composite materials were characterized using spectral (Fourier-transform infrared spectroscopy) and microscopic (scanning electron microscopy) methods. Thermogravimetric analyses were carried out to evaluate the thermal stability of the magnetic fibers. The magnetic properties were evaluated using vibrating-sample magnetometry.     

Transparent montmorillonite/cellulose nanofibril nanocomposite films: the influence of exfoliation degree and interfacial interaction

To obtain high performance of nanocomposite films made of cellulose nanofibrils (CNFs) and montmorillonites (MMTs), highly ordered nanostructures and abundant interfacial interactions are of extreme importance, especially for CNF film with high MMT content. Here, we tend to unveil the influence of exfoliation degree of MMTs and their interfacial interactions with CNFs on the properties of ensuing nanocomposite films. Monolayer MMTs (ML-MMTs) prefer to form highly ordered nanostructure during water evaporation induced self-assembly. The obtained nanocomposite film with 30 wt% ML-MMTs exhibits a tensile strength of 132 MPa, a total light transmittance of 90.2% (550 nm), and water vapor transmission rate (WVTR) of 41.5 g mm/m² day, better than the film made of original MMTs (O-MMTs) and CNFs (30 MPa strength, 60% transparency, and 78.7 g mm/m² day WVTR). Moreover, the physical properties (153 MPa strength and 20.9 g mm/m² day WVTR) of nanocomposite film can be further enhanced by constructing ionic interactions between the ML-MMT and CNF using 0.5 wt% cationic polyethylenimine (PEI). However, as the amount of PEI continues to increase, its performance will be deteriorated dramatically because of the disordered orientation of ML-MMTs. This work could provide an insight into the fabrication of high performance MMT/CNF nanocomposite film for advanced applications.

Graphical abstract

     

Surface modification of TEMPO-oxidized cellulose nanofibers,and properties of their acrylate and epoxy resin composite films

Cellulose - The carboxy groups abundantly and densely present on 2,2,6,6-tetramehylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibers (TEMPO-CNFs) have been chemically modified to...     

Atomic layer deposition of metal-oxide thin films on cellulose fibers

Abstract

Atomic layer deposition (ALD) is a vapor-phase technique capable of producing inorganic thin films with precise control over the thickness of the film. The ALD method offers high precision in the design of advanced 3D nanostructures. In this article, silica and alumina thin films have been grown over fibers of cellulose by the ALD process. The morphology and the chemical composition of the fabricated thin films are characterized, as well as their thermal durability through elevated temperatures. Moreover, XPS is used to confirm the phases of the alumina nanofilms and to further understand the deposition process on the cellulose microfibers.     

Oriented cellulose films and fibers from a mesophase system

Cellulose mesophases were obtained by preparing concentrated solutions of cellulose (20–55%) in a mixture of N-methyl-morpholine N-oxide (MMNO) and water. The anisotropy depends on four interconnected parameters: the temperature of the solution which, in general, must be lower than 90°C; the concentration of cellulose which must exceed 20%; a water content such that the mole ratio water/anhydrous MMNO is smaller than unity; and the degree of polymerization of the dissolved cellulose. The anisotropic cellulose solutions can readily be oriented during extrusion or casting thus giving fibers or films which upon regeneration exhibit high orientation.     

Structures and cyclization behaviors of gel-spun cellulose/polyacrylonitrile composite fibers

Polyacrylonitrile (PAN)/cellulose composite fibers have been produced by dry-jet gel spinning through their co-solution. The rheological properties of PAN/cellulose/dimethylacetamide/LiCl solutions containing different cellulose contents from 0 to 10 wt% were characterized, and 5 wt% PAN/cellulose composite solution shows the best solution homogeneity. During gel spinning, the cellulose forms elongated particles inside the gelation bath, and the particle diameters depend on the as-spun draw ratio. It was found that the glass transition of PAN fibers shifts to higher temperatures along with the increase of cellulose content, and the glass transition activation energy of PAN chains becomes higher when cellulose particles become smaller. Regardless the changes of cellulose amount (2–10 wt%) and particle diameter (7.1–1.4 μm), the cyclization activation energy of PAN/cellulose composite fibers is 13–17% lower than that of neat PAN fibers. Our experiments suggest that the addition of cellulose in PAN fibers has no direct effect on the cyclization reaction of PAN chains. Instead, the released by-products during the pyrolysis of cellulose at high temperature degradation affect the cyclization reaction of PAN chains.     

Formation of <Emphasis Type="Italic">N</Emphasis>-acylureas on the surface of TEMPO-oxidized cellulose nanofibril with carbodiimide in DMF

A method for conversion of carboxyl groups present on the surface of TEMPO-oxidized cellulose nanofibrils to N-acylureas using carbodiimide was developed. A TEMPO-oxidized cellulose nanofibril with free carboxyl groups (TOCN–COOH) dispersed in N,N-dimethylformamide (DMF) is prepared from a bleached kraft pulp, and then the TOCN–COOH is reacted with either N,N′-diisopropylcarbodiimide (DIC) or N,N′-dicyclohexylcarbodiimide (DCC) under apparently homogeneous conditions. FT-IR and solid-state ¹³C NMR analyses showed that the reaction products contained N-acylurea groups, and yields were >80%. Conversion ratios of carboxyl groups to N-acylureas are approximately 80 and 60%, when DIC and DCC, respectively, of 5 mol per mole of carboxyl groups are used as the reagents. X-ray diffraction analysis demonstrated that neither crystallinity nor crystal width of the original wood cellulose I structure was changed by the N-acylurea formation. The isolated and never-dried TOCN-N-acylureas are nano-dispersed in DMF but not in i-PrOH or dioxane. Pellets of the TOCN-N-acylureas had water-contact angles of >70°.     

Synthesis of a novel antimicrobial-modified starch and its adsorption on cellulose fibers: part II––adsorption behaviors of cationic starch on cellulose fibers

The adsorption of guanidine polymer modified starches on cellulose fibers was investigated along with the systematic studies on various influencing factors including temperature, pH, ionic strength and charge density of the starches. The AFM results revealed the relationship between the adhesion force and adsorption capacity. The adsorption capacity is not necessarily proportional to the adhesion force. The conditions for achieving the maximum adsorption were: temperature, 40 °C; pH, 6; C_NaCl, 0 mM and charge density, 0.4 meq/g. The corresponding the normalized adhesion force is approximate 1 mN/m. In terms of the surface roughness determined by AFM, it has been proved that adsorbed starches of high charge density tend to form train structure, whereas those of low charge density tend to form tails and loops. Due the comb molecular structure, the adsorption capacity of the novel cationic starch reaches 124.3 mg/g, which is much greater than those reported previously.