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.     

Bacterial cellulose/triethanolamine based ion-conducting membranes

New bacterial cellulose (BC)–triethanolamine (TEA) ion-conducting membranes have been prepared and characterized. The samples were obtained by soaking BC membranes in triethanolamine aqueous solutions and drying. The scanning electron microscopy pictures revealed that the incorporation of TEA in BC membranes covers the cellulose microfibrils. Raman spectra exhibited BC and TEA characteristic group frequencies and thermal analysis evidenced an influence of TEA content on the sample thermal stability. The ion-conductivity as a function of the temperature showed an Arrhenius behavior increasing from 1.8 × 10^?5 S/cm at room temperature to 7.0 × 10^?4 S/cm at 80 °C for the BC–TEA 1 M sample.     

The Effect of Drying Temperature on the Composition of Biomass

The compositional quality of different lignocellulosic feedstocks influences their performance and potential demand at a biorefinery. Many analytical protocols for determining the composition or performance characteristics of biomass involve a drying step, where the drying temperature can vary depending on the specific protocol. To get reliable data, it is important to determine the correct drying temperature to vaporize the water without negatively impacting the compositional quality of the biomass. A comparison of drying temperatures between 45 °C and 100 °C was performed using wheat straw and corn stover. Near-infrared (NIR) spectra were taken of the dried samples and compared using principal component analysis (PCA). Carbohydrates were analyzed using quantitative saccharification to determine sugar degradation. Analysis of variance was used to determine if there was a significant difference between drying at different temperatures. PCA showed an obvious separation in samples dried at different temperatures due to sample water content. However, quantitative saccharification data shows, within a 95% confidence interval, that there is no significant difference in sugar content for drying temperatures up to 100 °C for wheat straw and corn stover.     

Effect of fiber drying on properties of lignin containing cellulose nanocrystals and nanofibrils produced through maleic acid hydrolysis

The effect of fiber drying on the properties of lignin containing cellulose nanocrystals (LCNC) and nanofibrils (LCNF) produced using concentrated maleic acid hydrolysis of a never dried unbleached mixed hardwood kraft pulp was evaluated. Two drying conditions, i.e., air drying and heat drying at 105 °C were employed. It was found that drying (both air and heat) enhanced acid hydrolysis to result in slightly improved LCNC yields and less entangled LCNF. This is perhaps due to the fact that drying modified the cellulose supermolecular structure to become more susceptible to acid hydrolysis and the enhanced hydrolysis severity at the fiber surface when using dried fibers. Drying substantially improved LCNC crystallinity and LCNF suspension viscoelastic behavior. The present study quantitatively elucidated the effect of pulp drying (either air or heat) on producing cellulose nanomaterials and has practical importance because commercial market pulp (heat dried) is most likely to be used commercially.     

Thermal analysis of the powder and the bran of algaroba

The powder and the bran of algaroba pods, submitted to drying temperatures of 55, 65, 75, 85, 95 and 105°C, were studied by conventional and thermogravimetric methods. The dynamic thermogravimetric curves of the samples indicated the following thermal stability order: 105>55>65>95>85>75°C. The powder and the bran of algaroba pods, dried at 55°C, presented protein content higher and isothermal thermogravimetric profiles comparable. The calorimetric curves of samples, dried at 55°C, indicated the gelatinization of starch. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structure characterization of native cellulose during dehydration and rehydration

The goal of this study is to investigate the hydration and dehydration induced structural changes of native cellulose. Never dried cotton, and never dried bacterial cellulose with and without added matrix polymer xyloglucan, are examined under the influence of dehydration and rehydration. Significant crystal structure changes were observed in the later stage of drying for both cotton and bacterial cellulose (BC). The 1 % lateral expansion in glucan chain spacing and 17 % decrease of calculated Scherrer dimension were detected for cotton due to the distortion of the structure possibly caused by mechanical stresses associated with drying. No detectable changes on average glucan chain spacings were observed for large BC crystals. However, an average width decrease by 4.4 nm was discovered in the (010) direction, which was more significant than that observed in the (100) and (110) directions. It is hypothesized that co-crystallized elementary fibrils preferentially disassociate along the (010) plane resulting in a significant reduction of crystal width. In the BC-xyloglucan model composite, the presence of xyloglucan does not interfere with the dehydration behavior. Rehydration leads to some structural changes but to a lesser extent than the initial drying. High temperature dehydration induced deformation and crystal size changes are found to be non-reversible due to the removal of the last hydration layer on the cellulose surface.     

Water redispersible cellulose nanofibrils adsorbed with carboxymethyl cellulose

Cellulose nanofibrils (CNFs) are difficult to redisperse in water after they have been completely dried due to the irreversible agglomeration of cellulose during drying. Here, we have developed a simple process to prepare water-redispersible dried CNFs by the adsorption of small amounts of carboxymethyl cellulose (CMC) and oven drying. The adsorption of CMC onto CNFs in water suspensions at 22 and 121 °C was studied, and the adsorbed amount of CMC was measured via conductimetric titration. The water-redispersibility of dried CNFs adsorbed with different amounts of CMC was characterized by sedimentation test. Above a critical threshold of CMC adsorption, i.e. 2.3 wt%, the oven dried CNF–CMC sample was fully redispersible in water. The morphology, rheological, and mechanical properties of water-redispersed CNF–CMC samples were investigated by field emission scanning electron microscopy, viscosity measurement, and tensile test, respectively. The water-redispersed CNFs preserved the original properties of never dried CNFs. This new method will facilitate the production, transportation and storage, and large-scale industrial applications of CNFs.     

Physicochemical Properties and Storage Stability of Microencapsulated DHA-Rich Oil with Different Wall Materials

This study aimed to evaluate the physicochemical properties and storage stability of microencapsulated DHA-rich oil spray dried with different wall materials: model 1 (modified starch, gum arabic, and maltodextrin), model 2 (soy protein isolate, gum arabic, and maltodextrin), and model 3 (casein, glucose, and lactose). The results indicated that model 3 exhibited the highest microencapsulation efficiency (98.66 %) and emulsion stability (>99 %), with a moisture content and mean particle size of 1.663 % and 14.173 μm, respectively. Differential scanning calorimetry analysis indicated that the Tm of DHA-rich oil microcapsules was high, suggesting that the entire structure of the microcapsules remained stable during thermal processing. A thermogravimetric analysis curve showed that the product lost 5 % of its weight at 172 °C and the wall material started to degrade at 236 °C. The peroxide value of microencapsulated DHA-rich oil remained at one ninth after accelerated oxidation at 45 °C for 8 weeks to that of the unencapsulated DHA-rich oil, thus revealing the promising oxidation stability of DHA-rich oil in microcapsules.     

The nanostructure of kraft pulp 1: evaluation of various mild drying methods using field emission scanning electron microscopy

Wood pulp fiber consists of carbohydrate fibrils containing crystalline cellulose microfibrils of a few nanometer width. The structure of the fibril in water is currently unclear due to the difficulty of imaging pulp fiber in water at nanometer resolution. An alternative method is to observe the sample dried with a mild drying method to preserve the structure of the wet sample. In this study, we studied softwood kraft pulp fibers which were dried with various mild drying methods and then imaged by field emission scanning electron microscopy at nanometer resolution. Both mild dried samples, as well as air dried samples, showed 10–20 nm wide fibrils, the width of which corresponded to a crystalline cellulose microfibril or bundles of them. The mild dried sample, which was critical point dried with liquid CO₂ (CPD), mainly showed 20–40 nm thick fibrils, in addition to the 10–20 nm fibrils. The existence of the thick fibril implies that the fibril itself has a swelling nature in water, although the possibility that the thick fibril was an artifact of the CPD process could not be excluded. Further investigation as to the extent that the thick fibrils found in the CPD samples reflect the nanostructure of pulp fiber in water is warranted.     

Influence of drying method on the material properties of nanocellulose I: thermostability and crystallinity

The effect of drying method on selected material properties of nanocellulose was investigated. Samples of nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNC) were each subjected to four separate drying methods: air-drying, freeze-drying, spray-drying, and supercritical-drying. The thermal stability and crystallinity of the dried nanocellulose were evaluated using thermogravimetric analysis (TGA) and X-ray diffraction. Supercritical-drying produced NFCs with the least thermal stability and the lowest crystallinity index. Air-drying or spray-drying produced NFCs which were more thermally stable compared with freeze-dried NFCs. The CNCs dried by the three methods (air-drying, freeze-drying, and spray-drying) have similar onset temperature of thermal degradation. The different drying methods resulted in various char weight percentages at 600 °C for the dried NFCs or CNCs from TGA measurements. The dried NFCs are pure cellulose I while the dried CNCs consist of cellulose I and II. The calculated crystallinity indices differ with each drying method. The cellulose II content in CNCs changes as a function of drying method. For the application of nanocellulose in non polar thermoplastics, spray-dried products are recommended according to their higher thermal stability and higher crystallinity index.     

Influence of supercritical drying fluids on structures and properties of low-density Cu-doped SiO2 composite aerogels

The Cu-doped SiO₂ composite aerogels were successfully prepared by sol–gel process and subsequently supercritical drying with ethanol and CO₂. The Cu-doped SiO₂ composite aerogels had porous texture, low density (<100 mg cm^?3) and high specific surface area (>800 m² g^?1), which were investigated by FESEM and nitrogen adsorption desorption porosimetry. The FTIR spectra of the aerogels showed that the ethanol-dried aerogels had been modified by ethyl while the corresponding CO₂-dried aerogels had more Si–OH groups. The phase structure and thermal stability were investigated by XRD and TGA, respectively. Due to the reducibility of ethanol, the copper was crystalline in ethanol-dried sample. The Cu-doped SiO₂ composite aerogels dried with supercritical ethanol had larger pore diameter and better thermal stability under 400 °C in comparison with CO₂-dried composite aerogels. The structures and properties of Cu-doped SiO₂ composite aerogels are obviously affected by supercritical drying conditions. The effect research could instruct the synthesis of different state of Cu in composite aerogels.     

Thermoplasticity of sol–gel-derived titanoxanes chemically modified with benzoylacetone

Titanium tetra-n-butoxide was hydrolyzed in the presence of benzoylacetone (BzAc), and the solution obtained was concentrated and served for spin-coating or dropping on substrates, followed by successive drying at 120, 200 and 250 °C. The dried products were transparent and amorphous, and the infrared absorption and Raman spectroscopic studies showed that BzAc forms chelate rings. Thermomechanical analysis showed that the 120 and 200 °C-dried products showed steep, thermoplastic shrinkage at around 30 and 70–85 °C, respectively, whereas the 250 °C-dried product did not show thermoplasticity. Thus as the drying temperature was increased, the thermoplasticity appeared at a higher temperature and finally disappeared. These changes in thermoplasticity with drying temperature were concluded to result from the progress of condensation between titanoxane polymers and/or clusters, which was evidenced in gel permeation chromatographic analysis.     

High performance poly (vinyl alcohol)/cellulose nanocrystals nanocomposites manufactured by injection molding

Polyvinyl alcohol (PVA)/cellulose nanocrystals (CNCs) compounds were successfully melt-processed by injection molding. During the processing, water was involved in the system as both the dispersion medium for CNCs and the plasticizer for PVA. Meanwhile, formamide was added to prevent the evaporation of water and to co-plasticize PVA. Thermal gravimetric analysis and differential scanning calorimetry indicated the melt processing window of PVA was expanded by 40 °C. Tensile tests showed that the mechanical properties of injection-molded samples were significantly improved with the addition of CNCs. The tensile strength of the composites increased from 32 to 58 MPa, and modulus increased from 175 to 1,252 MPa when 7 wt% CNCs was added. Moreover, the volume shrinkage of PVA nanocomposites upon drying as well as their water leaching rate could be remarkably reduced in the presence of CNCs.     

Effect of multivalent cations,temperature, and aging on SOM thermal properties

Multivalent cations are suggested to influence the supramolecular structure of soil organic matter (SOM) via inter- and intra-molecular interactions with SOM functional groups. In this study, we tested the combined effect of cations, temperature treatment, and isothermal aging on SOM matrix properties. Samples from a peat and a mineral soil were either enriched with Na, Ca, and Al or desalinated in batch experiments. After treatment at 25, 40, 60, and 105 °C and after different periods of aging at 19 °C and 31 % relative humidity, we investigated the physicochemical matrix stability and the thermal stability against combustion. We hypothesized that multivalent cations stabilize the SOM matrix, that these structures disrupt at elevated temperatures, and that aging leads to an increase in matrix stability. The results show that cation-specific effects on matrix rigidity started to evolve in the peat only after 8 weeks of aging and were significantly lower than the temperature effects. Temperature treatment above 40 °C caused a non (or not immediately) reversible loss of water molecule bridges (WaMB) and above 60 °C a partly reversible melting process probably of semi-crystalline poly(methylene). Thermal stability increased with increasing cation valence and degree of protonation and was much less affected by temperature. Generally, Na-treated and control samples revealed lower thermal stability and lower increase in matrix rigidity with aging than those treated with Ca, Al, and H. We conclude that drying at elevated temperatures (>40 °C) may irreversibly change SOM structure via disruption of labile cross-links and melting of semi-crystalline domains.     

Influence of recycling and temperature on the swelling ability of paper

Hornification is the loss of fiber wall swelling which is detrimental to subsequent recycling resulting from drying. It is known that dried fibers lose their conformability and swelling capacity. The effect of recycling treatment on the swelling ability of hardwood bleached kraft pulp fibers was determined. Modelling paper recycling, sheets were recycled using heat treatment (23°C, 60°C, 100°C). The results were compared with those for natural fibers from bleached kraft pulp. Swelling kinetics of sheets was measured by a modified method monitoring interactions of pulp with water. Swelling ability decreased during the recycling in comparison with never-recycled pulp at all temperatures. Recycling of sheets caused only small changes in the cupri-ethylene-diamine viscosity, however, the water retention value decreased considerably.     

Metabolomics method based on ultra high performance liquid chromatography with time‐of‐flight mass spectrometry to analyze toxins in fresh and dried toad venom

Drying is a critical step to prolong the storage time in natural medicine processing but it changes the chemical characteristics of the product. In this study, research was performed to characterize the metabolomic changes in toad venom induced by vacuum‐drying at 60°C and air‐drying at room temperature by ultra high performance liquid chromatography coupled with pattern recognition approaches. In total 52 metabolites, down‐regulated or up‐regulated, were identified as potential chemical markers. Compared with fresh toad venom, vacuum‐drying at 60°C succeeded in raising the conjugated‐type bufadienolide content significantly, while the content of free‐type bufadienolides were slightly reduced. On the other hand, toad venom air‐dried at room temperature presented a relatively low amount of bufadienolides compared with fresh venom. For example, the content of several known anti‐tumor components (gamabufotalin, bufotalin, cinobufagin, etc.) were significantly reduced. The 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide bioassay further showed that venom air‐dried at room temperature had weaker anti‐tumor activity on human hepatocellular carcinoma SMMC‐7721 proliferation in vitro than samples vacuum‐dried at 60°C. These results showed that the great metabolomic changes of toad venom occurred during the drying process, suggesting that a proper drying procedure is important for sustaining the chemical quality of natural medicines.     

BTATz–HNIW–CMDB propellants

The high nitrogen compound 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine and the high energy density material hexanitrohexaazaisowurtzitane (HNIW), were used as substitute of hexogen (RDX) in the composite modified double base (CMDB) propellant formulations, the propellant samples were prepared, the thermal behaviors, nonisothermal reaction kinetics, and thermal safety were carried out, and the eight important parameters were calculated and obtained as the self-accelerating decomposition temperature (T _SADT), thermal ignition temperature (T _TIT), critical temperatures of thermal explosion (T _b), critical temperature of hot-spot initiation (T _cr,hot-spot), characteristic drop height of impact sensitivity (H ₅₀), critical thermal explosion ambient temperature (T _acr), safety degree (S _d), and thermal explosion probability (P _TE). It shows that the content of HNIW has a large effect on the decomposition reaction mechanism of the CMDB propellant, when the content of HNIW is 10 %, the decomposition reaction are controlled by the random nucleation and subsequent growth (n = l), and the reaction mechanism obeys Mampel law; but when the content of HNIW is 20 %, the decomposition reaction are controlled by the chemical reaction (n = 1/4). The mechanism can not be changed by the catalysts, and they just make the apparent activation energy change slightly. For the sample, from BC01 to BC04, the values of T _SADT and T _TIT making an upward tendency, show the resistivity to heat: BC04 > BC03 > BC02 > BC01; the values of T _acr and S _d, BC01 are the maximum and BC02 are the minimum, show the heat sensitivity: BC01 > BC03 > BC04 > BC02. For the same radius, the thermal safety of the sphere sample is greater than that of the infinite cylinder one.     

Modifying bacterial cellulose with gelatin peptides for improved rehydration

Bacterial cellulose (BC) is a nanoscale and useful biomaterial with a fine fiber network and high water holding capacity. However, dried BC exhibits poor rehydration ability. The present study investigated the rehydration ability of composites of hydrolyzed gelatin peptides (HGP) and hydroxypropylmethyl cellulose-modified BC (HBC). The HGP with molecular weights <9 kDa were obtained by hydrolyzing gelatin with a combination of 1 % alcalase and 1.5 % pronase E at 50 °C for 2 h. The HGP/HBC nanocomposites exhibited higher rehydration ratios than composites prepared with gelatin. According to SEM images, gelatin and HGP successfully penetrated the cellulose network in composite films prepared using both immersion and adsorption (DA) methods. The high hydrophilic property of HGP resulted in a rehydration ratio of approximately 180 % at a HGP/HBC ratio of 4.5:1 (W/W) in DA composites. The 1 min rehydrated HGP/HBC composites possessed similar mechanical properties to the original wet type composites. Overall, results indicated that the HGP/HBC composites prepared using the DA method demonstrated the highest rehydration ability among the composite films evaluated.     

Carbonization and graphitization of pitch applied for anode materials of high power lithium ion batteries

The artificial graphite materials were prepared by carbonizing coal tar pitch using two methods, namely, one- and two-step processes, and all sintered samples were graphitized at 2800 °C. Effects of different heat treatments on the performance of the samples were characterized by scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction, Brunauer–Emmett–Teller, electrochemical impedance spectroscopy (EIS), particle size analysis, polarized light microscopy, and charge–discharge measurements. All samples show a typical graphite crystalline structure; moreover, the degree of graphitization (g factor) and crystallite size along the c-axis (L _c ) were calculated from (002) peak. The polarized light microscopy indicates that the coke with carbonization at 700 °C has an obvious wide domain (D) optical structure, while that with two-step sintering at 400 and 700 °C has a mixed optical structures of wide D, flow domains, and mosaics. TEM analysis revealed a number of irregular graphene layer images which are caused by the defects of graphite. EIS shows that the sample carbonized by two-step has a larger diffusion coefficient than the sample carbonized at 700 °C by one step. Higher carbonization temperature leads to better cycle performance as the temperature increasing from 500 to 700 °C in the one-step route. Specifically, the charge (Li⁺ extraction) capacity at the 50th cycle increases from 318 mA?h?g^?1 to 357 mA?h?g^?1. The results show that the rate performance of the artificial graphite is improved with the addition of the presintering at 400 °C.     

Adsorption mechanism of Chromium(III) from water solution on bone char: effect of operating conditions

The adsorption capacity of bone char (BC) towards Cr(III) from an aqueous solution was studied in this work. The characterization of the BC showed that the BC is mainly composed of hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂, and its point of zero charge was 7.7. The infrared spectroscopic analysis of the BC loaded with Cr(III) revealed that the Cr(III) adsorbed on BC interacted with the phosphate of the hydroxyapatite. The adsorption capacity increased 2.6 times by raising the solution pH from 3 to 5. This tendency was due to the interactions between the surface charge and the cationic species of Cr(III) in aqueous solution. The adsorption capacity was enhanced 2.5 and reduced 1.3 times when the temperature was increased from 15 to 25 °C and from 25 to 35 °C, respectively. The effect of temperature on the adsorption capacity of BC showed an anomalous behavior since the adsorption capacity exhibited a maximum at T = 25 °C. It was demonstrated that the main adsorption mechanism of the Cr(III) species was coordination to the phosphate ions and the Ca(II) in the BC was substituted or replaced by the Cr(III) species from the solution. This latter result was further corroborated by XPS analysis.