Comparison of nano- and microfibrillated cellulose films

Nanocellulose is an interesting building block for functional materials and has gained considerable interest due to its mechanical robustness, large surface area and biodegradability. It can be formed into various structures such as solids, films and gels such as hydrogels and aerogels and combined with polymers or other materials to form composites. Mechanical, optical and barrier properties of nanofibrillated cellulose (NFC) and microfibrillated cellulose (MFC) films were studied in order to understand their potential for packaging and functional printing applications. Impact of raw material choice and nanocellulose production process on these properties was evaluated. MFC and NFC were produced following two different routes. NFC was produced using a chemical pretreatment followed by a high pressure homogenization, whereas MFC was produced using a mechanical treatment only. TEMPO-mediated oxidation followed by one step of high pressure (2,000 bar) homogenization seems to produce a similar type of NFC from both hardwood and softwood. NFC films showed superior mechanical and optical properties compared with MFC films; however, MFC films demonstrated better barrier properties against oxygen and water vapor. Both the MFC and NFC films were excellent barriers against mineral oil used in ordinary printing inks and dichlorobenzene, a common solvent used in functional printing inks. Barrier properties against vegetable oil were also found to be exceptionally good for both the NFC and MFC films.     

Preparation and characterization of cationic nanofibrillated cellulose from etherification and high-shear disintegration processes

Oat straw cellulose pulp was cationized in an etherification reaction with chlorocholine chloride. The cationized cellulose pulp was then mechanically disintegrated in two process steps to obtain trimethylammonium-modified nanofibrillated cellulose (TMA-NFC). The materials thus obtained were analyzed by elemental analysis, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and other techniques. A higher nitrogen content of TMA-NFC samples was found by XPS analysis than by elemental analysis, which indicates that the modification occurred mainly on the surface of cellulose fibrils. XPS also confirmed the existence of ammonium groups in the samples. SEM provided images of very fine network structures of TMA-NFC, which affirmed the positive effect of ionic charge on mechanical disintegration process. According to XRD and SEM results, no severe degradation of the cellulose occurred, even at high reaction temperatures. Because of the different properties of the cationic NFC compared to negatively charged native cellulose fibers, TMA-NFC may find broad applications in technical areas, for instance in combination with anionic species, such as fillers or dyes. Indeed, TMA-NFC seems to improve the distribution of clay fillers in NFC matrix.     

Photopolymerized Cellulose Acetate/Poly(Acrylic Acid) Semi-IPN Films for Wound Dressing Applications

In this work, semi-IPN films, composed of cellulose acetate(CA) and crosslinked poly(acrylic acid), have been synthesized via benzophenone (BP) induced free radical photo-polymerization of acrylic acid (AAc) in the presence of dissolved cellulose acetate (CA) using N,N’ methylene bisacrylamise (MB) as the crosslinking agent. The mechanical properties were tested for the films having different compositions of MB, CA and AAc in the feed mixtures. The tensile strength (TS) and percent elongation (PE) were found to increase with a concentration of CA in the films, but showed decreasing trends with concentrations of CA in the films. However, with AAc content in the films, the TS increased and PE showed just the opposite trend. The film samples were also studied for water vapor and oxygen permeation studies. The water vapor transmission rate (WVTR) decreased with MB and CA contents, but showed an increasing trend with AAc contents in the films. Finally, a representative sample showed fair antibacterial and antifungal action against E. coli and Aspergillus flavus when studied using the ‘Zone of inhibition method’.     

Behavior of biodegradable composites based on starch reinforced with modified cellulosic fibers

The aims of this study were to develop composite films based on potato starch and cellulose modified with toluenediisocyanate, to investigate their morphology and structure, and to evaluate their behavior to enzymatic hydrolysis and their potential use to manufacture of biodegradable seedling pots. The effects of modified cellulosic fibers upon mechanical properties and biodegradability of composite materials based on starch matrix were investigated by tensile strength tests, Fourier infrared spectroscopy, X‐ray diffraction, and dynamic vapor sorption. The behavior of the films to enzymatic hydrolysis with amylase and cellulase was studied; the kinetic of enzymatic hydrolysis and characterization of materials are reported. Chemical modification of cellulose improves tensile strength with about 47%, and decreases the biodegradability of composites making them more resistant to microbial attack, thus prolonging their shelf life. Copyright © 2015 John Wiley & Sons, Ltd.     

Fourier transform infrared study on the sorption of water to various kinds of polymer thin films

The state of sorbed water and the sorbing processes of water to various polymer thin films were studied with Fourier transform infrared (FTIR) spectroscopy. To prepare the polymer films, we used poly(ethylene glycol)s of different molecular weights and various kinds of vinyl polymers, such as poly(2‐methoxyethyl acrylate). The O? H stretching band of water sorbed in the films increased gradually on contact with water vapor at 50% relative humidity and leveled off. When O? H stretching bands of water sorbed to polymer films were compared, the peak positions and profiles of water sorbed to the polymeric materials with the same hydrogen‐bonding site were similar. A hybrid density‐functional method supported the assignment of the peaks. Furthermore, the diffusion coefficient (D) of water vapor in the polymer films was estimated by time‐resolved measurements of the sorbed water at the very initial stage (0–830 s). It was clearly shown that the D values of water vapor in the polymer materials with a strong hydrogen‐bonding site were smaller than those in hydrophobic polymers. The usefulness of the FTIR technique to investigate water sorption to polymer materials was definitely demonstrated. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2175–2182, 2001     

紫外光固化的聚氨酯－丙烯酸酯－纤维素复合膜

再生纤维素膜(甘蔗渣浆制)表面直接用紫外光固化聚氨酯-丙烯酸酯制备出防水性复合膜。由红外光谱和扫描电镜研究了复合膜的结构。同时,测定了膜的防水性、力学性能、水汽透过性和尺寸稳定性。实验结果表明,当聚氨酯：丙烯酸酯为40:55(质量比),在400W紫外光下固化5min制得的复合膜具有致密的表面结构和较好的性能,该膜经水浸泡后其断裂强度可达干膜的90%,浸水收缩率和膨胀率均小于2.5%,水汽渗透量仅为再生纤维素膜的1/4.由此表明复合膜的防水性和尺寸稳定性明显提高。此外,该复合膜在可见光区的透光率在80%～90%之间,而且对紫外光有屏蔽作用。     

Effect of surface‐grafted ionic groups on the performance of cellulose‐fiber‐reinforced thermoplastic composites

The influence of the surface chemistry of the cellulose fiber and polymer matrix on the mechanical and thermal dynamic mechanical properties of cellulose‐fiber‐reinforced polymer composites was investigated. The cellulose fiber was treated either with a coupling agent or with a coupling‐agent treatment followed by the introduction of quaternary ammonium groups onto the fiber surface, whereas the polymer matrix, with opposite polar groups such as polystyrene incorporated with sulfonated polystyrene and poly(ethylene‐co‐methacrylic acid), was compounded with the fiber. The grafting of the fiber surface was investigated with Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. Experimental results showed that an obvious improvement in the mechanical strength could be achieved for composites with an ionic interface between the fiber and the polymer matrix because of the adhesion enhancement of the fiber and the matrix. The improved adhesion could be ascribed to the grafted ionic groups at the cellulose‐fiber surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2022–2032, 2003     

Selective Water Sorbents for Multiple Applications. 11. CaCl2 Confined to Expanded Vermiculite

This paper presents the water sorption properties of a new selective water sorbent based on expanded vermiculite as a host matrix and calcium chloride as a hygroscopic salt. Sorption isobars, isosters and isotherms at T = 30–150°C and vapor partial pressure 8.2–42.0 mbar clearly show that at low water contents crystalline hydrates with 0.33, 1 and 2 molecules of water per 1 molecule of CaCl₂ are formed in the pores. These hydrates are stable over a temperature change of 20–30°C and exhibit kinetically slow transformations. At higher water uptake, the vapor absorption leads to the formation of a CaCl₂ aqueous solution inside the pores, which properties are close to those in the bulk. Isosteric sorption heat was found to depend on water sorption and change from 76.3 kJ/mol for solid hydrates to 39.1–46.6 kJ/mol.     

Water Sorption Properties and Antimicrobial Action of Zinc Oxide Nanoparticles-Loaded Cellulose Acetate Films

In this work, ZnO nanoparticles loaded cellulose acetate (ZOLCA) films have been prepared and characterized by XRD, SPR and SEM analysis. The moisture permeation properties of the films have been investigated. The GAB isotherm model has been found to fit well on the moisture uptake data obtained at different temperatures. The monolayer sorption capacity χ_m was found to decrease from 0.059 to 0.0079 g water/g dry film with increase in temperature from 20 to 37°C. The isosteric heat of sorption, when studied in the lower water activity range of 0.04 to 0.10, was evaluated to be 46.55 to 87.29 kJ/mol. The water vapor permeability across the ZOLCA films was found to increase with temperature and activation energy of moisture sorption process was found to be 48.57 kJ/mol. These films have shown excellent antibacterial action against model bacteria E-Coli when investigated by qualitative and quantitative methods. Films exhibit great potential to be used as edible films to protect food stuff against microbial infections.     

Novel porous polyurethane films

Polyurethane films treated in a two-stage process with aqueous bromine and ammonia solutions underwent significant modifications in crystalline and surface structure as well as in mechanical and physical properties. Bromine was sorbed on the film, and formed several charge transfer complexes with the soft and hard segments of the polyurethane as well as bridges between adjacent chains. In the second stage, ammonia reacted with the sorbed bromine producing gaseous nitrogen and ammonium bromide. The expansion of the gas resulted in a repacking of the polymeric chains and the formation of a porous structure. The bromine concentrations used and the times of contact between the films and the bromine were 0.02–0.06 normal and 1–10 min, respectively. The contact angle of the films decreased, depending on treatment conditions, from 73 to 20. The water vapor permeability increased three-fold. The treatment appeared to bring about a crystallization in the hard as well as in the soft segments of the PU as shown by differential scanning calorimetry measurements. Possible applications of the treated films for wound dressing are discussed. © 1998 John Wiley & Sons, Ltd.     

Electrostatic assembly of Ag nanoparticles onto nanofibrillated cellulose for antibacterial paper products

Nanofibrillated cellulose offers new technological solutions for the development of paper products. Here, composites of nanofibrillated cellulose (NFC) and Ag nanoparticles (NP) were prepared for the first time via the electrostatic assembly of Ag NP (aqueous colloids) onto NFC. Distinct polyelectrolytes have been investigated as macromolecular linkers in order to evaluate their effects on the building-up of Ag modified NFC and also on the final properties of the NFC/Ag composite materials. The NFC/Ag nanocomposites were first investigated for their antibacterial properties towards S. aureus and K. pneumoniae microorganisms as compared to NFC modified by polyelectrolytes linkers without Ag. Subsequently, the antibacterial NFC/Ag nanocomposites were used as fillers in starch based coating formulations for Eucalyptus globulus-based paper sheets. The potential of this approach to produce antimicrobial paper products will be discussed on the basis of complementary optical, air barrier and mechanical data.     

Nanofibrillated cellulose originated from birch sawdust after sequential extractions: a promising polymeric material from waste to films

The residual cellulose of wood processing waste, sawdust, which was leftover after sequential hot-water extraction processes to isolate hemicelluloses and lignin in a novel forest biorefinery concept, was explored as the starting material for preparation of a highly value-added polymeric material, nanofibrillated cellulose (NFC) also widely termed as cellulose nanofiber, which has provided an alternative efficient way to upgrade sawdust waste. The residual cellulose in sawdust was converted to a transparent NFC suspension in water through the 2,2,6,6-tetramethylpiperidine-1-oxyl radical/NaClO/NaBr oxidization approach. The resultant NFC with a dimension of ca. 5 nm in width and hundreds of nanometers in length were further processed into NFC films. The morphological features of the NFC suspension and its films were assessed by transmission electron microscopy and scanning electron microscopy. Highly even dispersion of NFC fibrils in the films originated from sawdust feasibly contributes to the outstanding mechanical performance of the films. NFC suspension with higher carboxylate content and its resultant NFC films were found to show higher transmission of light.     

Solvent impact on esterification and film formation ability of nanofibrillated cellulose

In this study we have manufactured nanofibrillar cellulose and modified the fibre surface with ester groups in order to hydrophobise the surface. Nanofibrillated cellulose was chosen to demonstrate the phenomena, since due to its high surface area the effects at issue are pronounced. The prepared NFC ester derivatives were butyrate, hexanoate, benzoate, naphtoate, diphenyl acetate, stearate and palmitate. X-ray photoelectron spectroscopy, solid state NMR and contact angle measurements were used to demonstrate the chemical changes taking place on the cellulose surface. NFC ester derivatives can be prepared after a careful solvent exchange to a water-free solvent medium has been carried out. Butyl and palmitoyl esters were chosen for film forming tests due to the difference in their carbon chain lengths, and their contact angles and water vapour and oxygen permeation rates were studied. The prepared nanocellulose esters show increased hydrophobicity even at very low levels of substitution and readily form films when the films are prepared from acetone dispersions. The permeation rates suggest a potential use as barrier materials.     

医用多孔壳聚糖膜的制备及性能研究

以邻苯二甲酸二丁酯为致孔剂,制备了多孔壳聚糖膜,并用扫描电镜对其表面和断面形貌进行了分析,同时对膜的吸水性、水蒸气透过性、比表面积、力学性能及生物相容性等进行了考察。分析结果表明:以邻苯二甲酸二丁酯为致孔剂,制备的多孔壳聚糖膜孔径均匀,吸水性好,孔隙率高,比表面积大,膜的最大吸水率、孔隙率和比表面积分别为196%、71.5%和1.0472 m2.g-1;膜的力学性能好,最大抗拉强度为273.17MN/m2。     

Acid Leaching Vermiculite: A Multi-Functional Solid Catalyst with a Strongly Electrostatic Field and Brönsted Acid for Depolymerization of Cellulose in Water

Vermiculite is a natural mineral. In this study, vermiculite and acid-activated vermiculite was used as a solid acid catalyst for the hydrolysis of cellulose in water. The catalysts were characterized by XRD, FT-IR, and BET. The effects of time, temperature, mass ratio and water amount on the reaction were investigated in the batch reactor. The results showed that the highest total reducing sugars (TRS) yield of 40.1% could be obtained on the vermiculite activated by 35 (wt)% H₂SO₄ with the mass ratio of catalyst to cellulose of 0.18 and water to cellulose of 16 at 478 K for 3.5 h. The acid-activated vermiculite was a stable catalyst through calcination at 628 K and the yield of TRS decreased to 36.2% after three times reuse. The results showed that the crystal structure of vermiculite was destroyed and the surface -OH groups increased after the acid treatment. However, the synergistic effect of a strongly electrostatic polarization and Brönsted acid was responsible for the efficient conversion of cellulose. The mechanism of cellulose hydrolysis on the acid-activated vermiculite was suggested. This work provides a promising strategy to design an efficient solid catalyst for the cellulose hydrolysis, and expands the use of vermiculite in a new field.     

Permeation of nitrogen and water vapor through sulfonated polyetherethersulfone membrane

The novel polyetherethersulfone (PES-C) prepared from phenol-phthalein in our institute is an amorphous, rigid, tough material with good mechanical properties over a wide temperature range. To improve its water vapor permeability for the application of gas drying, the PES-C was sulfonated with concentrated sulfuric acid and transferred in sodium, cupric, and ferric salt forms. The sulfonation degree can be regulated by controlling the temperature and reaction time. Characterization of sulfonated PES-C in sodium form was made by IR. Some properties of the sulfonated PES-C, such as solubility, glass transition temperature, thermal stability, mechanical properties, and transport properties to nitrogen and water vapor have also been discussed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2133–2140, 1997     

Preparation and Barrier Properties of Chitosan-Layered Silicate Nanocomposite Films

Summary: In this study, chitosan nanocomposite films were prepared using a solvent-casting method by incorporation of an organically modified montmorillonite (Cloisite 10A). The effect of filler concentration on the water vapor permeability, oxygen permeability, mechanical and thermal properties of the composite films was evaluated. The structure of nanocomposites and the state of intercalation of the clay were characterized by XRD. The water vapor permeability of pure chitosan films was measured as a function of relative humidity (RH). It was found that the permeability value increased with an increase in RH. The water vapor and gas permeability values of the composite films decreased significantly with increasing filler concentration. Permeation data was fitted to various phenomenological models predicting the permeability of polymer systems filled with nanoclays as a function of clay concentration and aspect ratio of nanoplatelets. According to the XRD results, an increase in basal spacing was obtained with respect to pure clay for chitosan/clay nanocomposites. This demonstrated the formation of intercalated structure of clay in the polymer matrix. Tensile strength and elongation at break of the composites increased significantly with the addition of clay, however the thermal and color properties of the films were not much affected by the intercalation of clay into polymer matrix.     

Highly flexible, transparent cellulose composite films used in UV imprint lithography

Highly flexible, optically transparent epoxy resin/cellulose composites were prepared by using the solution impregnation method firstly and then thermal cured. The composite contained 60 wt% resin was still mechanically stable and flexible, and it integrated the merits of cellulose and resin, but the highly hydrophilic behavior of cellulose has been reduced. Contact angle measurements with water demonstrated that the composite films had obvious hydrophobic properties, and a decrease in the water uptake and the permeability towards water vapor gas was also observed. The transmittance of the composite films at 550 nm was about 85–88 %. The thermal and mechanical properties of the composite films were improved. Moreover, the composite films could be used in UV imprint lithography for circuit, and the definition could be compared with that of widely used glass plate.     

The role of nanocellulose fibers, starch and chitosan on multipolysaccharide based films

Thin nanocomposite films of thermoplastic starch, chitosan and cellulose nanofibers (bacterial cellulose or nanofibrillated cellulose) were prepared for the first time by solvent casting of water based suspensions of the three polysaccharides. The role of the different bioploymers on the final properties (thermal stability, transparency, mechanical performance and antimicrobial activity) of the films was related with their intrinsic features, contents and synergic effects resulting from the establishment of interactions between them. Thermoplastic starch displays an important role on the thermal stability of the films because it is the most stable polysaccharide; however it has a negative impact on the mechanical performance and transparency of the films. The addition of chitosan improves considerably the transparency (up to 50 % transmittance for 50 % of chitosan, in respect to the amount of starch), mechanical performance and antimicrobial properties (at least 25 % of chitosan and no more than 10 % of cellulose nanofibers are required to observe bacteriostatic or bactericidal activity) but decrease their thermal stability. The incorporation of cellulose nanofibers had the strongest positive impact on the mechanical properties of the materials (increments of up to 15 and 30 MPa on the Young′s modulus and Tensile strength, respectively, for films with 20 % of BC or NFC). Nonetheless, the impact in thermal stability and mechanical performance of the films, promoted by the addition of chitosan and cellulose nanofibres, respectively, was higher than the expected considering their percentage contents certainly because of the establishment of strong and complex interactions between the three polysaccharides.     

Dissolution and regeneration of cellulose in NaOH/thiourea aqueous solution

A novel cellulose solvent, 1.5 M NaOH/0.65 M thiourea aqueous solution, was used to dissolve cotton linters having a molecular weight of 10.1 × 10⁴ to prepare cellulose solution. Regenerated cellulose (RC) films were obtained from the cellulose solution by coagulating with sulfuric acid (H₂SO₄) aqueous solution with a concentration from 2 to 30 wt %. Solubility of cellulose, structure, and mechanical properties of the RC films were examined by infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, ¹³C NMR, and tensile tests. ¹³C NMR analysis indicated that the novel solvent of cellulose is a nonderivative aqueous solution system. The presence of thiourea enhanced significantly the solubility of cellulose in NaOH aqueous solution and reduced the formation of cellulose gel; as a result, thiourea prevented the association between cellulose molecules, leading to the solvation of cellulose. The RC film obtained by coagulating with 5 wt % H₂SO₄ aqueous solution for 5 min exhibited higher mechanical properties than that with other H₂SO₄ concentrations and a homogenous porous structure with a mean pore size of 186 nm for free surface in the wet state. The RC film plasticized with 10% glycerin for 5 min had a tensile strength of 107 MPa and breaking elongation of 10%, and about 1% glycerin in the RC film plays an important role in the enhancement of the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1521–1529, 2002