Ultrastrong and high gas-barrier nanocellulose/clay-layered composites

Nanocellulose/montmorillonite (MTM) composite films were prepared from 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibrils (TOCNs) with an aspect ratio of >200 dispersed in water with MTM nanoplatelets. The composite films were transparent and flexible and showed ultrahigh mechanical and oxygen barrier properties through the nanolayered structures, which were formed by compositing the anionic MTM nanoplatelet filler in anionic and highly crystalline TOCN matrix. A composite film with 5% MTM content had Young's modulus 18 GPa, tensile strength 509 MPa, work of fracture of 25.6 MJ m(-3), and oxygen permeability 0.006 mL μm m(-2) day(-1) kPa(-1) at 0% relative humidity, respectively, despite having a low density of 1.99 g cm(-3). As the MTM content in the TOCN/MTM composites was increased to 50%, light transmittance, tensile strength, and elongation at break decreased, while Young's modulus was almost unchanged and oxygen barrier property was further improved to 0.0008 mL μm m(-2) day(-1) kPa(-1).     

Pore size determination of TEMPO-oxidized cellulose nanofibril films by positron annihilation lifetime spectroscopy

Wood cellulose nanofibril films with sodium carboxylate groups prepared from a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized pulp exhibited an extremely low oxygen permeability of 0.0008 mL μm m(-2) day(-1) kPa(-1) at 0% relative humidity (RH). Positron annihilation lifetime spectroscopy (PALS) was used to determine the pore sizes in wood and tunicate TEMPO-oxidized cellulose nanofibril (TOCN-COONa) films in a vacuum (i.e., at 0% RH). PALS analysis revealed that the pore size of the wood TOCN-COONa films remained nearly at 0.47 nm from the film surface to the interior of the film. This is probably the cause of this high oxygen-barrier properties at 0% RH. The crystalline structure of TOCN-COONa also contributes to the high oxygen-barrier properties of the wood TOCN-COONa films. However, the oxygen permeability of the wood TOCN-COONa films increased to 0.17 mL μm m(-2) day(-1) kPa(-1) at 50% RH, which is one of the shortcomings of hydrophilic TOCN-COONa films.     

Characteristics of films prepared from native and modified branched β-1,3- -glucans

The properties of films prepared from a high molecular weight (mol. wt: 7·5 × 10⁶ g/mol) branched β-1,3- -glucan (schizophyllan) and a polyalcohol (mol. wt: 7·3 × 10⁶ g/mol) derived from schizophyllan by periodate oxidation and subsequent borohydride reduction are described. The films can only be prepared by casting from aqueous solutions, because the polymers are not thermoplastic. They have a low permeability to oxygen, but a high permeability to water vapour. The tensile strength of the films is 45–58 N/mm⁻² for schizophyllan and 12–18 N/mm² for the polyalcohol, and both, but especially the polyalcohol films, have a low elongation at break. Films prepared from both polymers, under conditions where the triple helices are disrupted (>0·01 NaOH), show lower tensile strength and elongations at break as well as higher oxygen permeabilities. A relationship exists between the water content of the films and the tensile strength.     

Effects of modified cellulose nanocrystals on the barrier and migration properties of PLA nano-biocomposites

The aim of this paper is to report the impact of the addition of cellulose nanocrystals on the barrier properties and on the migration behaviour of poly(lactic acid), PLA, based nano-biocomposites prepared by the solvent casting method. Their microstructure, crystallinity, barrier and overall migration properties were investigated. Pristine (CNC) and surfactant-modified cellulose nanocrystals (s-CNC) were used, and the effect of the cellulose modification and content in the nano-biocomposites was investigated. The presence of surfactant on the nanocrystal surface favours the dispersion of CNC in the PLA matrix. Electron microscopy analysis shows the good dispersion of s-CNC in the nanoscale with well-defined single crystals indicating that the surfactant allowed a better interaction between the cellulose structures and the PLA matrix. Reductions of 34% in water permeability were obtained for the cast films containing 1wt.% of s-CNC while good oxygen barrier properties were detected for nano-biocomposites with both 1wt.% and 5wt.% of modified and un-modified cellulose nanocrystals, underlining the improvement provided by cellulose on the PLA films. Moreover, the migration level of the studied nano-biocomposites was below the overall migration limits required by the current normative for food packaging materials in both non-polar and polar simulants.     

Mechanical,Optical, Thermal,and Barrier Properties of Poly (Lactic Acid)/Curcumin Composite Films Prepared Using Twin-Screw Extruder

In this present work, we synthesized poly (lactic acid) (PLA)/curcumin composite films using a twin-screw extruder and evaluated their mechanical, optical, thermal, and barrier properties. The composite films were characterized using Fourier transform infrared spectroscopy (FTIR), Universal testing machine (UTM), thermogravimetric analysis (TGA), ultraviolet-visible spectrometry (UV-visible), colorimetry, goniometry, and oxygen permeation analysis. The results confirmed that, the composite films exhibited better ultraviolet radiation-blocking properties and hydrophobicities than did the reference PLA film. The oxygen and water vapor permeabilities of the composite films were also lower than those of the reference PLA film.

     

Design of mucoadhesive polymeric films based on blends of poly(acrylic acid) and (hydroxypropyl)cellulose

Mixing of aqueous solutions of poly(acrylic acid) and (hydroxypropyl)cellulose results in formation of hydrogen-bonded interpolymer complexes, which precipitate and do not allow preparation of homogeneous polymeric films by casting. In the present work the effect of pH on the complexation between poly(acrylic acid) and (hydroxypropyl)cellulose in solutions and miscibility of these polymers in solid state has been studied. The pH-induced complexation-miscibility-immiscibility transitions in the polymer mixtures have been observed. The optimal conditions for preparation of homogeneous polymeric films based on blends of these polymers have been found, and the possibility of radiation cross-linking of these materials has been demonstrated. Although the gamma-radiation treatment of solid polymeric blends was found to be inefficient, successful cross-linking was achieved by addition of N,N'-methylenebis(acrylamide). The mucoadhesive potential of both soluble and cross-linked films toward porcine buccal mucosa is evaluated. Soluble films adhered to mucosal tissues undergo dissolution within 30-110 min depending on the polymer ratio in the blend. Cross-linked films are retained on the mucosal surface for 10-40 min and then detach.     

Aerocellulose: new highly porous cellulose prepared from cellulose-NaOH aqueous solutions

New highly porous pure cellulose aerogel-like material called "aerocellulose" was prepared from aqueous cellulose/NaOH solutions. Solutions were gelled to obtain shaped three-dimensional objects, then cellulose was regenerated and dried in supercritical conditions using CO2. The porosity of aerocellulose is higher than 95% with pore sizes distribution from a few tens of nanometers to a few tens of micrometers. The internal specific surface area is around 200-300 m2/g, and density ranges from 0.06 to 0.3 g/cm3, depending on the preparation conditions. The influence of cellulose DP and concentration, of the addition of a surfactant leading to solution foaming, of gelation conditions and the temperature and acidity of regenerating bath on the morphology of aerocellulose has been studied. The results are compared with another type of aerocellulose that was prepared from cellulose/NMMO solutions.     

Characterization of films made with chayote tuber and potato starches blending with cellulose nanoparticles

The aim of this study was to characterize chayotextle starch films reinforced with cellulose (C) and cellulose nanoparticle (CN) (at concentrations of 0.3%, 0.5%, 0.8% and 1.2%), using thermal, mechanical, physicochemical, permeability, and water solubility tests. C was acid-treated to obtain CN. The films were prepared by casting; potato starch and C were used as the control. The solubility of the starch films decreased with the addition of C and CN compared with its respective film without C and CN. No statistical difference (α = 0.05) was found in the films added with different concentrations of C and CN. In general, the mechanical properties were improved with the addition of C and CN, and higher values of tensile strength and elastic modulus were determined in the films reinforced with CN. The melting temperature and enthalpy increased with the addition of C and CN, and the values of both thermal parameters were higher in the films with CN than with C; the enthalpy value of the film decreased when the concentration of C or CN increased in the composite. Low concentration of C and CN is better distributed in the matrix film. The addition of C and CN in the starch films improved some mechanical, barrier, and functional properties.     

Green composite films prepared from cellulose,starch and lignin in room-temperature ionic liquid

A series of novel biobased composite films derived from cellulose, starch and lignin were prepared from an ionic liquid (IL), 1-allyl-3-methylimidazolium chloride (AmimCl) by coagulating in a nonsolvent condition. The ionic liquid can be recycled with a high yield and purity after the green film was prepared. The uniform design method was applied to investigate mechanical properties of the biobased composite films. The effect of each component and their associated interactive effects were investigated. The experimental results showed that contents of cellulose, lignin and starch had a significant influence on the mechanical properties of composite films. The composite films showed relatively excellent mechanical properties in dry and wet states owing to the mutual property supplement of different components. The composite films were characterized via FT-IR, X-ray diffraction (XRD) and scanning electron microscope (SEM). Their thermal stability and gas permeability were also investigated, and the results showed that the composite films had good thermal stability and high gas barrier capacity and give a CO₂:O₂ permeability ratio close to 1.     

Bacterial cellulose reinforced polyurethane-based resin nanocomposite: A study of how ethanol and processing pressure affect physical, mechanical and dielectric properties

Nanocomposite films of bacterial cellulose (10-50 wt%) and polyurethane-based resin were prepared and characterized for physical, mechanical and dielectric properties. It was observed that the bacterial cellulose swelled in ethanol, and that bacterial cellulose sheets prepared from fibre suspension in ethanol exhibited a relatively less dense structure in comparison to those processed from aqueous fibre suspension. Nanocomposites fabricated from ethanol suspension also showed inferior mechanical properties but superior dielectric properties. Higher amounts of free proton generated from ethanol can induce more dipole mechanism; therefore, there is higher mobility of proton localized along cellulose chain, indicating that higher dielectric constants can be obtained.     

Preparation and characterization of poly(acrylic acid)-hydroxyethyl cellulose graft copolymer

Poly(acrylic acid) hydroxyethyl cellulose [poly(AA)-HEC] graft copolymer was prepared by polymerizing acrylic acid (AA) with hydroxyethyl cellulose (HEC) using potassium bromate/thiourea dioxide (KBrO(3)/TUD) as redox initiation system. The polymerization reaction was carried out under a variety of conditions including concentrations of AA, KBrO(3) and TUD, material to liquor ratio and polymerization temperature. The polymerization reaction was monitored by withdrawing samples from the reaction medium and measuring the total conversion. The rheological properties of the poly(AA)-HEC graft copolymer were investigated. The total conversion and rheological properties of the graft copolymer depended on the ratio of KBrO(3) to TUD and on acrylic acid concentration as well as temperature and material to liquor ratio. Optimum conditions of the graft copolymer preparation were 30mmol KBrO(3) and 30mmol TUD/100g HEC, 100% AA (based on weight of HEC), duration 2h at temperature 50°C using a material to liquor ratio of 1:10.     

Carboxymethylcellulose-montmorillonite nanocomposite films activated with murta (Ugni molinae Turcz) leaves extract

The functionality of nanocomposite films based on carboxymethylcellulose (CMC) and montmorillonite (MMT) activated with murta (Ugni molinae Turcz) leaves extract was studied. Films were prepared by casting from film-forming dispersions containing CMC, glycerol (used as plasticizer) and different concentrations of MMT, using water or murta extract as solvent. The addition of MMT increased the tensile strength and the elasticity modulus of the films, and decreased their permeabilities to water vapor, oxygen and carbon dioxide. Besides the antioxidants properties provided to the films, the addition of murta leaves extract changed the gas permeability in different forms according to the MMT content, and plasticized the nanocomposite matrix.     

Novel regenerated cellulose films prepared by coagulating with water: Structure and properties

Regenerated films were successfully prepared from cellulose/NaOH/urea solution by coagulating with water at temperature from 25 to 45 °C. The results of solid ¹³C NMR, wide angle X-ray diffraction, scanning electron microscopy (SEM) and tensile testing revealed that the cellulose films possessed homogeneous structure and cellulose II crystalline, similar to that prepared previously by coagulating with 5 wt% H₂SO₄. By changing the coagulation temperature from 25 to 45 °C, tensile strength of the films was in the range of 85-139 MPa. Interestingly, the RC35 film coagulated at 35 °C exhibited the highest tensile strength (σ_b = 139 MPa). The inclusion complex associated with cellulose, NaOH and urea hydrates in the cellulose solution were broken by adding water (non-solvent), leading to the self-association of cellulose to regenerate through rearrangement of the hydrogen bonds. This work provided low-cost and “green” pathway to prepare cellulose films, which is important in industry.     

Influence of interactions on water and aroma permeabilities of ι-carrageenan–oleic acid–beeswax films used for flavour encapsulation

The objective of this work is to investigate the water and aroma barrier properties of films obtained from ι-carrageenan containing glycerol and lipids mixtures of oleic acid (OA) and beeswax (BW) used for encapsulation of active compounds. Water vapor permeability (WVP) is greatly influenced by lipid composition, encapsulated aroma compound and also relative humidity. WVP decreases when films contain encapsulated aroma compound but increases when the moisture content in the films increases. When oleic acid was the main compound of lipid phase, the plasticizing effect of water revealed through water permeability is less marked. The results of ethyl acetate, ethyl butyrate, ethyl hexanoate, 2-hexanone, 1-hexanol and cis-3-hexenol permeabilities reveal that physicochemical interactions between aroma compounds-hydrocolloid and aroma compound-lipid induce structural changes and modify their permeability. This work gives evidence of the ability of ι-carrageenan–OA–BW films to protect encapsulated aroma compound and its influence in barrier properties.     

Multifunctional coating films by layer-by-layer deposition of cellulose and chitin nanofibrils

An environmentally benign surface modification process for plastic films was demonstrated by fabricating composite coatings through layer-by-layer assembly with green solid materials: aqueous dispersions of two kinds of crystalline polysaccharide nanofibrils. Anionic cellulose nanofibrils were obtained by the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation of native cellulose, while cationic β-chitin nanofibrils were prepared by the protonation of squid pen chitin. Uniform layer depositions, driven by electrostatic attraction and enhanced by hydrogen bonding, were observed on silicon wafers and then reproduced onto poly(ethylene terephthalate) films. Contact angle measurements and dyeing tests on the resulting films revealed their hydrophilic nature and the sorption of both charged and uncharged substances. Antireflection properties were also confirmed via the light transmittance measurements. As might be presumed from all these properties, this composite coating exhibited its unique behavior largely due to its structure, which was distinct from both those of nanofibril cast films and polymer films.     

Mechanical and water barrier properties of starch/PVA composite films by adding nano-sized poly(methyl methacrylate-co-acrylamide) particles

The aim of this work is to prepare starch/PVA composite films added nano-sized poly(methyl methacrylate-co-acrylamide) (PMMA-co-AAm) particles and to investigate the mechanical properties, water barrier properties, and soil burial degradation for the films. Composite films were prepared by using corn starch, polyvinyl alcohol (PVA), nano-sized PMMA-co-AAm particles, and additives, i.e., glycerol (GL), xylitol (XL), and citric acid (CA). Nano-sized PMMA-co-AAm particles were synthesized by emulsion polymerization. The results of the evaluation of properties for prepared films indicated that compared with films without PMMA-co-AAm particles, the mechanical properties and water resistance were improved up to 70-400% by the addition of nano-sized PMMA-co-AAm. In addition, the results of the soil burial biodegradation revealed that films added PMMA-co-AAm particles were degraded by about 45-65% after 165 days.     

Morphological and optical characterization of polyelectrolyte multilayers incorporating nanocrystalline cellulose

Aqueous layer-by-layer (LbL) processing was used to create polyelectrolyte multilayer (PEM) nanocomposites containing cellulose nanocrystals and poly(allylamine hydrochloride). Solution-dipping and spin-coating assembly methods gave smooth, stable, thin films. Morphology was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and film growth was characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry, and optical reflectometry. Relatively few deposition cycles were needed to give full surface coverage, with film thicknesses ranging from 10 to 500 nm. Films prepared by spin-coating were substantially thicker than solution-dipped films and displayed radial orientation of the rod-shaped cellulose nanocrystals. The relationship between film color and thickness is discussed according to the principles of thin film interference and indicates that the iridescent properties of the films can be easily tailored in this system.     

Citric acid and maleic anhydride as compatibilizers in starch/poly(butylene adipate-co-terephthalate) blends by one-step reactive extrusion

Starch/poly(butylene adipate-co-terephthalate) films were obtained by one-step reactive extrusion using maleic anhydride (MA) and citric acid (CA) as compatibilizers. The mechanical, structural, optical and barrier properties of the films were analyzed when glycerol (GLY), CA and MA were added to the starch/PBAT (55:45, w/w) according to mixture design. FTIR analysis showed that CA and MA were able to promote esterification/transesterification reactions and that CA induced them more efficiently. When a greater proportion of compatibilizer (1.5 wt%) was used, the resulting films were more opaque and had a greater tensile strength. A greater proportion of GLY (10.0%, w/w) improved the elongation at the break of the films. The barrier properties to water vapor of the films were improved by high levels of CA (1.5 wt%) and intermediate levels of GLY (9.25 wt%). The inclusion of compatibilizers resulted in blends with improved properties, representing a potential replacement for non-biodegradable films.     

New nanocomposite materials reinforced with flax cellulose nanocrystals in waterborne polyurethane

New nanocomposite films were prepared from a suspension of cellulose nanocrystals as the filler and a polycaprolactone-based waterborne polyurethane (WPU) as the matrix. The cellulose nanocrystals, prepared by acid hydrolysis of flax fiber, consisted of slender rods with an average length of 327 +/- 108 nm and diameter of 21 +/- 7 nm, respectively. After the two aqueous suspensions were mixed homogeneously, the nanocomposite films were obtained by casting and evaporating. The morphology, thermal behavior, and mechanical properties of the films were investigated by means of attenuated total reflection Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and tensile testing. The results indicated that the cellulose nanocrystals could disperse in the WPU uniformly and resulted in an improvement of microphase separation between the soft and hard segments of the WPU matrix. The films showed a significant increase in Young's modulus and tensile strength from 0.51 to 344 MPa and 4.27 to 14.86 MPa, respectively, with increasing filler content from 0 to 30 wt %. Of note is that the Young's modulus increased exponentially with the filler up to a content of 10 wt %. The synergistic interaction between fillers and between the filler and WPU matrix played an important role in reinforcing the nanocomposites. The superior properties of the new nanocomposite materials could have great potential applications.     

Factors influencing the regeneration of cellulose I from phosphoric acid

The regeneration of cellulose I from phosphoric acid solution was studied, with emphasis both on the conditions required for the regeneration of cellulose I and characterization of the resulting cellulose by X-ray diffraction. Raman spectroscopy and SS¹³C n.m.r. As the conditions of regeneration were varied with respect to temperature and time a variety of polymorphs were produced. As previously reported, the cellulose I polymorph dominated at high temperature and long regeneration time. The question of the authenticity of the regenerated cellulose I was addressed, with several tests confirming that it was not an insoluble residue. Further analysis of the various regenerated celluloses revealed that they all had a small cellulose I component that could be isolated by acid hydrolysis. It is suggested that during regeneration, nuclei of different cellulose polymorphs are formed simultaneously, the proportion of each dependent upon the relative rates of nucleation. Under degradative regeneration conditions the polymorphs more susceptible to hydrolysis are attacked preferentially, leaving behind resistant cellulose I