Cationic wood cellulose films with high strength and bacterial anti-adhesive properties

In this work, periodate oxidized birch wood pulp and microfibrillated cellulose (MFC) were cationized using Girard’s reagent T or aminoguanidine. Cationic celluloses were used to obtain films via solvent-casting method, and the effects of the cationization route and the cellulose fiber source on the properties of the films were studied. Thermal and optical properties of the films were measured using differential scanning calorimetry and UV–Vis spectrometry, and the morphology of the films was examined using an optical microscope and a field emission scanning electron microscope. Bacterial anti-adhesive properties of the films were also studied using a modified leaf print method and against Staphylococcus aureus and Escherichia coli. Both cationizing agents exhibited similar reactivity with periodate oxidized celluloses, however, MFC had significantly higher reactivity compared to birch pulp. The films with high tensile strength (39.1–45.3 MPa) and modulus (3.5–7.3 GPa) were obtained from cationized birch pulp, aminoguanidine modification producing a film with slightly better mechanical properties. Modulus of the films was significantly increased (up to 14.0 GPa) when MFC was used as a cellulose fiber source. Compared to the unmodified MFC films, the cationic MFC films were less porous and significantly more transparent; however, they had slightly lower tensile strength values. It was found that aminoguanidine modified celluloses had no culturable bacteria on its surface and also exhibited resistance to microbial degradation, whereas there were culturable bacteria on the surface of Girard’s reagent modified films and they were partially degraded by the bacteria.     

Improved thermal and mechanical properties of bacterial cellulose with the introduction of collagen

Composite films comprised of bacterial cellulose (BC) and collagen (COL) were developed using BC hydrogel membranes as the base material and COL as the reinforcing material. Glutaraldehyde (GT) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC·HCl) were then used as cross-linking agents to prepare cross-linked BC/COL composite films by a wet chemical method. The effects of chemical cross-linking on the thermal and mechanical properties of composite films were investigated in detail. The COL molecules were adsorbed and deposited inside of 3D nanofiber networks of BC, coated on the surface of BC fibers. Chemical bonds formed between BC molecules, and between BC and COL molecules after cross-linking. Compared with BC, the obtained composite films showed 57.9 and 70.8% improvement in tensile strength after being cross-linked by GT and EDC·HCl, respectively. Cross-linking also enhanced the thermal stability of the specimens.     

Roles of xyloglucan and pectin on the mechanical properties of bacterial cellulose composite films

Xyloglucan and pectin are major non-cellulosic components of most primary plant cell walls. It is believed that xyloglucan and perhaps pectin are functioning as tethers between cellulose microfibrils in the cell walls. In order to understand the role of xyloglucan and pectin in cell wall mechanical properties, model cell wall composites created using Gluconacetobacter xylinus cellulose or cellulose nanowhiskers (CNWs) derived there from with different amounts of xyloglucan and/or pectin have been prepared and measured under extension conditions. Compared with pure CNW films, CNW composites with lower amounts of xyloglucan or pectin did not show significant differences in mechanical behavior. Only when the additives were as high as 60 %, the films exhibited a slightly lower Young’s modulus. However, when cultured with xyloglucan or pectin, the bacterial cellulose (BC) composites produced by G. xylinus showed much lower modulus compared with that of the pure BC films. Xyloglucan was able to further reduce the modulus and extensibility of the film compared to that of pectin. It is proposed that surface coating or tethering of xyloglucan or pectin of cellulose microfibrils does not alone affect the mechanical properties of cell wall materials. The implication from this work is that xyloglucan or pectin alters the mechanical properties of cellulose networks during rather than after the cellulose biosynthesis process, which impacts the nature of the connection between these compounds.     

On thermal crystallization in cellulose triacetate films

Thermomechanical analysis by extension under static and periodic impulse loads as well as the plotting of isometric heating diagrams are used for the investigation of thermally stimulated crystallization of cellulose triacetate (CTA) in unplasticized and plasticized films, the latter being known as the film base of photo and cinema materials. By introducing appropriate additives, it appeared possible to affect the crystallization process in various directions; the mechanism'of the process is discussed. The curves obtained by the techniques of thermal analysis give an individual characteristic of CTA film, reflecting the peculiarities of its production.

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Zusammenfassung Zur Untersuchung der thermisch stimulierten Kristallisierung von Cellulose-triacetat (CTA) in unplastifizierten und plastifizierten (letztere bekannt als Filmgrundlage für Foto- und Kinomaterial) Filmen wurden thermomechanische Analyse durch Ausdehnung unter statischen und periodisch-impulsförmigen Belastungen sowie die Aufnahme von isometrischen Aufheizdiagrammen verwendet. Durch Einbringung entsprechender Zusatzstoffe erschien es möglich, den Kristallisationsprozeß in verschiedenen Richtungen zu beeinflussen; der Mechanismus dieses Vorganges wird besprochen. Die bei den verschiedenen Thermoanalysetechniken erhaltenen Diagramme stellen eine individuelle Charakteristik der CTA-Filme dar, in der sich die Besonderheiten ihrer Produktion wiederspiegeln.

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Bacterial cellulose films: influence of bacterial strain and drying route on film properties

Structural properties of bacterial cellulose (BC) depend on the microstructure of the material, which in turn is influenced by the bacterial strain. This paper reports the production of BC thin films from two bacterial strains, gluconacetobacter xylinus (GX) and gluconacetobacter europaeus (GE), and three methods of drying the films; at room temperature, freeze drying and supercritical drying. The porosity, transparency, water absorption capacity (WAC) and mechanical properties of the obtained films are further investigated. We conclude that materials with different properties can be fabricated by selecting the bacterial strain or the drying method. Supercritical drying of films of GE achieved mechanically robust and extremely light films, 0.05 g/mL, with up to 96 % of porosity, and with a WAC up 110 times their dried weight. We determined that materials resulting from GE strain are not much affected by the drying method. On the other hand, GX produced BC films more sensitive to the drying method used. Films are denser, 0.6–0.2 g/mL, with tunable porosity from 60 to 90 % and their maximum WAC is 66 times their dried weight.     

Bio and soft-imprinting lithography on bacterial cellulose films

Bacterial cellulose (BC) is a biocompatible polysaccharide produced by bacteria currently used in packaging, cosmetics, or health care. A highly attractive feature of BC is the possibility of patterning the BC pellicle during its biosynthesis, a concept coined as bio-lithography. BC-patterned films have demonstrated improved properties for cellular-guided growth, implant protection, or wound dressing. However, aspects such as the diversity and size of the features patterned, how those features withstand postprocessing steps, or if large areas can be patterned remain unanswered. Gathering knowledge on these characteristics could extend the use of patterned cellulose-based materials in emerging fields such as transient devices, nanogenerators, or microfluidics. Here, we show that bio-lithographed BC films present good-quality micropatterned features for various motifs (wells, pillars, and channels) in a wide range of sizes (from 200 to 5 μm) and areas as large as 70 cm². Besides, we have studied the fidelity of the motifs and the fiber organization for wet, supercritical, and oven-dried films. When wells and pillars were patterned, the x and y dimensions were faithfully replicated in the wet and dried samples, but only wet and supercritically dried films afforded mold accuracy in the z-direction. In addition, x/z ratio should be carefully considered for obtaining self-standing pillars. Finally, we compared bio-lithography and soft-imprint lithography. In the latter case, fiber alignment was not observed and the depth of the resulting features dramatically decreased; however, this technique allowed us to produce submicron features that remain after the rewetting of the BC films.     

Sustainable nanocomposite films based on bacterial cellulose and pullulan

Bionanocomposites with improved properties based on two microbial polysaccharides, pullulan and bacterial cellulose, were prepared and characterized. The novel materials were obtained through a simple green approach by casting water-based suspensions of pullulan and bacterial cellulose and characterized by TGA, RDX, tensile assays, SEM and AFM. The effect of the addition of glycerol, as a plasticizer, on the properties of the materials was also evaluated. All bionanocomposites showed considerable improvement in thermal stability and mechanical properties, compared to the unfilled pullulan films, evidenced by the significant increase in the degradation temperature (up to 40 °C) and on both Young’s modulus and tensile strength (increments of up to 100 and 50%, for films without glycerol and up to 8,000 and 7,000% for those plasticized with glycerol). Moreover, these bionanocomposite films are highly translucent and could be labelled as sustainable materials since they were prepared entirely from renewable resources and could find applications in areas as organic electronics, dry food packaging and in the biomedical field.     

Morphology and thermal stability of bacterial cellulose/collagen composites

The aim of this paper was to prepare composites of bacterial cellulose (BC) and collagen to evaluate both the effect of collagen on the morphological, mechanical and thermal properties of BC and the effect of BC on the thermal stability of collagen for designing composites with increased potential biomedical applications. Two series of composites were prepared, the first series by immersing BC pellicle in solutions of collagen obtained in three forms, collagen gel (CG), collagen solution (CS) and hydrolysed collagen (HC), followed by freeze drying; and the second series of composites by mixing BC powder in solutions of collagen (CG, CS and HC), also followed by freeze drying. The properties of obtained composites were evaluated by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), mechanical tests, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results revealed that BC acts as a thermal stabilizer for CS matrix, while with CG matrix it interacts synergistically leading to composites with improved properties. On the other hand, the BC sheet impregnated with collagen has a significantly improved thermal stability. Collagen (as HC, CS or CG) has also a positive influence on the mechanical properties of lyophilized BC sheet. A four times increase of modulus was observed in BC/HC and BC/CG composites. and an increase of 60 times for BC/CS. The spectacular increase of elastic modulus and tensile strength in the case of BC/CS composite was explained by the easier penetration of collagen solution in the BC network and impregnation of BC fibrils as revealed by SEM and AFM analyzes.

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Raman characterization of thermal conduction in transparent carbon nanotube films

Using materials with high thermal conductivity is a matter of great concern in the field of thermal management. In this study, we present our experimental results on two-dimensional thermal conductivity of carbon nanotube (CNT) films obtained by using an optical method based on Raman spectroscopy. We use four kinds of CNTs in film preparation to investigate the effect of CNT type on heat spreading performance of CNT films. This first comparative study using the optical method shows that the arc-discharge single-walled carbon nanotubes yield the best heat spreading film. We also show that the Raman method renders reasonable thermal conductivity value as long as the sample is a transparent film by testing CNT films with various transmittance. This study provides useful information on characterization of thermal conduction in transparent CNT films and could be an important step toward high-performance carbon-based heat spreading films.     

Self-supported bacterial cellulose/boehmite organic–inorganic hybrid films

Self-supported organic-inorganic hybrid transparent films have been prepared from bacterial cellulose and boehmite. SEM results indicate that the BC membranes are covered by Boehmite and XRD patterns suggest structural changes on cellulose due to Boehmite addition. Thermal stability is accessed through TG curves and is dependent on Boehmite content. Transparency, as evaluated by UV?CVis absorption, increases with increasing content of boehmite suggesting application of these materials as transparent substrates for opto-electronic devices.     

Nanocomposite films based on TEMPO-mediated oxidized bacterial cellulose and chitosan

Nanobacterial cellulose (BC) and chitosan (CH) have similar molecular structures. In the present work, nanocomposite films based on BC and CH were prepared by stepwise modification instead of by conventional physical blending. First, surface C6-carboxylated BC was prepared in a bromide-free system using 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO) as a catalyst. The carboxylate groups of oxidised BC could couple to the amine groups of CH. The composite films were characterised by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Carbon-13 solid nuclear magnetic resonance ¹³C NMR. The results showed that a cross-linking reaction occurred between TEMPO-mediated oxidised BC and CH. Even in the absence of cross-linkers, these two biopolymers could interact with each other because of their structural similarity. SEM images and tensile tests showed that the TEMPO-oxidized BC and CH composite film prepared at a 0.5:1 ratio was an exception. The mechanical properties of the composite films decreased with increasing CH content, passed through a minimum, and then increased. To explain this phenomenon, we propose that the hydrogen bonding in the original BC microstructure plays a decisive role in the modified nanocomposites. However, BC/CH composites with excellent properties could be synthesised at appropriate reactant ratios.     

Preparation and properties of photochromic bacterial cellulose nanofibrous membranes

The photochromic bacterial cellulose (BC) nanofibrous membranes containing 1′,3′,3′-trimethyl-6-nitrospiro(2H-1-benzopyran-2,2′-indoline) (NO₂SP) were successfully prepared by surface modification of BC nanofibers with spiropyran photochromes, and their physical and photochromic properties were characterized. The FTIR spectra indicated the interaction between BC and NO₂SP which leads to the uniform dispersion of NO₂SP in the nanofibrous membrane. SEM results demonstrated that the introduction of NO₂SP maintains the nanofibrous network structure of BC. UV/vis spectrometry of the resulting BC-NO₂SP revealed that the membranes show reversible photochromic property by changing their color from colorless to pink forming a merocyanine structure upon UV irradiation, and returning back again to colorless spiropyran structure by visible light. The contact angle of the BC-NO₂SP with water was found to be reversibly regulated due to the reversible isomerization of the spiropyran moieties in BC-NO₂SP. The result indicates that the surface modification with spiropyran photochromes expands new applications of BC nanofibers and such photochromic nanofibers with excellent photosensitivity have great potentials for sensitive displays, biosensors and other optical devices.     

Layer-by-layer assembled films of cellulose nanowires with antireflective properties

Natural nanowires (NWs) of cellulose obtained from a marine animal tunicate display surprisingly high uniformity and aspect ratio comparable with synthetic NWs. Their layer-by-layer assembled (LBL) films show strong antireflection (AR) properties having an origin in a novel highly porous architecture reminiscent of a "flattened matchsticks pile", with film-thickness-dependent porosity and optical properties created by randomly oriented and overlapping NWs. At an optimum number of LBL deposition cycles, light transmittance reaches nearly 100% (lambda approximately 400 nm) when deposited on a microscope glass slide and the refractive index is approximately 1.28 at lambda = 532 nm. In accordance with AR theory, the transmittance maximum red-shifts and begins to decrease after reaching the maximum with increasing film thickness as a result of increased light scattering. This first example of LBL layers of cellulose NWs can be seen as an exemplary structure for any rigid axial nanocolloids, for which, given the refractive index match, AR properties are expected to be a common property. Unique mechanical properties of the tunicate NWs are also a great asset for optical coatings.     

Conductive properties of TiO2/bacterial cellulose hybrid fibres

In this article, we report the first micellization study of amphiphilic copolymers composed of bacterial medium chain length poly(3-hydroxyalkanoates) (mcl-PHAs). A series of diblock copolymers based on fixed poly(ethylene glycol) (PEG) block (5000 g mol(-1)) and a varying poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHHx) segment (1500-7700 g mol(-1)) have been synthesized using "click" chemistry. These copolymers self-assembled to form micelles in aqueous media. The influence of PHOHHx block molar mass on the hydrodynamic size and on the critical micelle concentration (CMC) has been studied using dynamic light scattering and fluorescence spectroscopy, respectively. With increasing PHOHHx length, narrowly distributed micelles with diameters ranging from 44 to 90 nm were obtained, with extremely low CMC (up to 0.85 mg/L). Cryogenic transmission electron microscopy (Cryo-TEM) showed that micelles took on a spherical shape and exhibited narrow polydispersity. Finally, the colloidal stability of the micelles against physiological NaCl concentration has been demonstrated, suggesting they are promising candidates for drug delivery applications.     

Preparation,thermal characterization,and DFT study of the bacterial cellulose

A bifunctional comonomer 3-aminocarbonyl-3-butenoic acid methyl ester (ABM) was designed and synthesized to prepare poly(acrylonitrile-co-3-aminocarbonyl-3-butenoic acid methyl ester) [P(AN-co-ABM)] copolymer which can be used as carbon fiber precursor instead of poly(acrylonitrile–acrylamide–methyl acrylate) [P(AN–AM–MA)] terpolymer. The stabilization mechanism and structural evolution of P(AN-co-ABM) and P(AN–AM–MA) during stabilization were studied by Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and thermogravimetry. The activation energy (E _a) of the cyclization reactions was calculated by Kissinger method and Ozawa method. The results show that the stabilization of P(AN-co-ABM) has been remarkably improved by ABM compared with P(AN–AM–MA) terpolymer, such as lower initiation temperature, broadened exothermic peak, larger extent of stabilization, and smaller E _a of cyclization, which is attributed to the initiation of ABM through ionic mechanism. Moreover, the spinnability of P(AN-co-ABM) is also improved by ABM due to the lubrication of ester groups in ABM. This study clearly shows that P(AN-co-ABM) copolymer is a better material used as carbon fiber precursor than P(AN–AM–MA) terpolymer.     

Analysis of thermal parameters and factors acting on thermal conduction of low‐k films

The thermal properties of a silicon oxide‐based low‐k film and a thermally oxidized silicon film were investigated using the 3‐omega and laser thermo‐reflectance (LTR) methods. Thermal conductivity and effusivity were successfully estimated by the 3‐omega and LTR methods, respectively. It was confirmed that the combination of thermal effusivity and conductivity can successfully provide the heat capacity and thermal diffusivity of the films. The thermal parameters thus obtained suggested that the lower thermal conductivity of the examined low‐k film comes mainly from the rather low level of thermal diffusivity. Based on an analysis of the X‐ray diffraction profiles of the films, it was found that the low thermal diffusivity of the low‐k film can be attributed to the discontinuity of the network structure of their clusters. The heat resistance at the interface between the film and Si substrate was also evaluated. We found that the low‐k film exhibited, interestingly, negative interfacial heat resistance, although interfacial heat resistance should have a positive value in general. In order to determine the origin of the negative interfacial heat resistance, the interface state of the films was analyzed in detail on the basis of X‐ray reflectivity (XRR) measurements. The XRR results showed clearly that a thin, high‐density layer was present at the interface of the low‐k films. This high‐density layer presumably promoted heat flow to the substrate, resulting in the apparent negative interfacial heat resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

Molecular optimization of multiply-functionalized mesoporous films with ion conduction properties

Sequential processing of multiply functionalized mesoporous films is shown to yield materials that are compositionally and structurally heterogeneous on mesoscopic and molecular length scales, both of which must be controlled to optimize macroscopic ion-conduction properties. Cubic mesoporous silica films prepared from strongly acidic solutions were subsequently functionalized under highly alkaline conditions to incorporate hydrophilic aluminosilica surface moieties, followed by nonaqueous conditions to introduce perfluorosulfonic-acid surface groups. Such sequential combination of individually incompatible steps yielded stable mesoporous films with high surface hydrophilicities and strong acid functionalities that exhibited high proton conductivities (ca. 9 × 10(-2) S/cm) at elevated temperatures (120 °C). Molecular, mesoscopic, and macroscopic properties of the multiply functionalized films were monitored and correlated at each stage of the syntheses by nuclear magnetic resonance (NMR) spectroscopy, small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), elemental analysis, adsorption, and ion conductivity measurements. In particular, variable-temperature solid-state two-dimensional (2D) (27)Al{(1)H}, (29)Si{(1)H}, (27)Al{(19)F}, and (29)Si{(19)F} HETeronuclear chemical-shift CORrelation (HETCOR) NMR spectra reveal separate surface adsorption and grafting sites for the different functional surface species within the mesopore channels. The hydrophilic aluminosilica and acidic fluoro-group loadings and interaction sites are demonstrated to be strongly affected by the different synthesis and functionalization treatments, which must be separately and collectively optimized to maximize the proton conductivities.     

Supramolecular structure and properties of high strength regenerated cellulose films

Water-swollen cellulose films prepared from LiOH/urea solution were uniaxially drawn to investigate the effect of orientation on their supramolecular structure and properties. Their structures and properties were investigated with X-ray diffraction, atomic force microscopy and tensile testing. The results revealed that the drawing process led to substantial reorientation of the cellulose molecular chains, resulting in a significant improvement of their mechanical properties and water-resistance. With an increase of the drawn ratios from 1 to 1.22, the tensile strength of the films at dry and wet states increased from 89 to 213 MPa and 2.9 to 33.9 MPa, respectively. Furthermore, the drawn cellulose films also exhibited good biocompatibility with the capability of supporting cell adhesion and proliferation.     

Rheological and thermal properties of stereocomplexed polylactide films

Poly(l-lactide) (PLLA) and Poly(d-lactide) (PDLA) blended films (PLLA/PDLA) were prepared (5/95; 25/75; 50/50, and 75/25) by solvent casting method. Blend of PLLA and PDLA of medium molecular mass led to the formation of stereocomplex which was evidenced by differential scanning calorimetry, rheological measurement and Fourier transform infrared spectroscopy. The stereocomplex had a higher melting temperature (T _m) (more than 50 °C) and crystallized at higher temperature (T _c) (more than 25 °C) from the melt compared to neat PLLA and PDLA. The T _m and T _c gradually decreased with increasing the number of thermal scans. The enthalpy of fusion (?H_m) for stereocomplex crystallites in 50/50 blend films was the highest than that of homo-crystallites. Rheological measurement at a temperature of 180–195 °C revealed that the neat PLA was predominantly liquid-like behavior (G″ > G′) which transformed to extreme solid-like behavior by incorporation of PDLA into PLLA. Among blends, 50/50 PDLA/PLLA showed the maximum mechanical strength (G′) followed by 25/75, 75/25, and 5/95 blends. The significant increase in mechanical strength is believed to be attributed by stereocomplex formation by blends. Thermal and rheological data supported higher mechanical strength and an increase in melting and crystallization temperature adequately.