Homogeneous and porous modified bacterial cellulose achieved by in situ modification with low amounts of carboxymethyl cellulose

To improve the rehydration ability of bacterial cellulose (BC), many macromolecules have been used as modifiers in previous reports. However, the aggregation of additives in the BC matrix appears to be inevitable. We investigated different parts of a BC pellicle, which was achieved by in situ modification with carboxymethyl cellulose (CMC) in culture with Gluconacetobacter xylinus ATCC53582 or Enterobacter sp. FY-07. We observed a concentration gradient of CMC in the BC pellicle from G. xylinus ATCC53582, but not with Enterobacter sp. FY-07. Low concentrations of CMC (0.01 %, m/v) are sufficient to modify BC in situ in culture with Enterobacter sp. FY-07, in which CMC could sufficiently contact with the newly formed BC. The crystallinity of the modified BC decreased by more than 39.8 %, and its rehydration ability and water holding capacity increased by 43.3 and 31.0 %, respectively. Unlike the pellicle of modified BC achieved from obligate aerobes, such as G. xylinus ATCC53582, that produced by Enterobacter sp. FY-07 exhibited better homogeneity and porosity.     

In situ modification of bacterial cellulose nanostructure by adding CMC during the growth of Gluconacetobacter xylinus

Many studies focus on bacterial cellulose (BC) functioning as multi-function bio-resource polymers, due to its fine fiber network, biocompatibility, high water holding capacity, and high mechanical strength. However, BC exhibits poor rehydration after drying due to its high crystallinity. This study added carboxymethylcellulose (CMC) to a BC producing culture medium, which interfered with the formation of BC structure in situ. This process created a modified BC called CBC, whose mechanical strength was found weaker than BC. Scanning electron microscope (SEM) images showed that the cellulose network in CBC became denser. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) analysis demonstrated that the addition of CMC reduced crystallinity. CBC also exhibited the highest rehydration ratio because of the lowest crystallinity at the 1.0% CMC addition level.     

Effect of cellulose crystallinity on bacterial cellulose assembly

Bacterial cellulose (BC) is a promising biomaterial as well as a model system useful for investigating cellulose biosynthesis. BC produced under static cultivation condition is a hydrous pellicle consisting of an interconnected network of fibrils assembled in numerous dense layers. The mechanisms responsible for this layered BC assembly remain unknown. This study used calcofluor as a fluorescent marker to examine BC layer formation at the air/liquid interface. Layers are found to move downward into the media after formation while new layers continue to form at the air/liquid interface. Calcoflour is also known to reduce the crystallinity of cellulose, changing the mechanical properties of the formed BC microfibrils. Consecutive addition and accumulation of calcofluor in the culture medium is found to disrupt the layered assembly of BC. BC crystalllinity decreased by 22 % in the presence of 12 % calcofluor (v/v) in the medium as compared to BC produced without calcofluor. This result suggests that cellulose crystallinity and the mechanical properties which crystallinity provides to cellulose are major factors influencing the layered BC structure formed during biosynthesis.     

Preparation and Characterization of Nanocomposites of Carboxymethyl Cellulose Reinforced with Cellulose Nanocrystals

Summary: Cellulose nanocrystals (CNC) were extracted from Kraft pulp of Eucalyptus urograndis. The CNC were isolated by acid hydrolysis with H₂SO₄ 64% (w/w) solution, for 20 minutes at 45 °C. The morphology and crystallinity of the CNC were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. The AFM image supports the evidence for the development of crystals of cellulose in nanometric scale. These nanoparticles were used as reinforcement material in carboxymethyl cellulose (CMC) matrix. Nanocomposites films were prepared by casting. The nanocomposites were characterized by thermal (TGA) and mechanical (DMA) analyses. A large reinforcing effect of the filler was observed. The tensile strength of nanocomposites was significantly improved by 107%, the elongation at break decreased by 48% and the thermal resistance increased slightly. The improvements in thermo-mechanical properties suggest a close association between filler and matrix.     

Structural Features and Properties of Bacterial Cellulose Produced in Agitated Culture

The structure and some properties of bacterial cellulose produced in agitated culture were studied. Scanning electron microscopy revealed that there was almost no difference between reticulated structures of bacterial cellulose fibrils produced in agitated culture and in static culture. Nevertheless, bacterial cellulose produced in agitated culture exhibited microstuctural changes, namely, a low degree of polymerization and a low crystallinity index. A CP/MAS ¹³C NMR analysis revealed that the cellulose I content of the cellulose produced in agitated culture was lower than that of the cellulose produced in static culture. The bacterial cellulose produced in agitated culture had a lower Young's modulus of sheet, a higher water holding capacity and a higher suspension viscosity in the disintegrated form than that produced in static culture.     

Controlling the water content of never dried and reswollen bacterial cellulose by the addition of water-soluble polymers to the culture medium

For the modification of medically useful biomaterials from bacterially synthesized cellulose, fleeces of Acetobacter xylinum have been produced in the presence of 0.5, 1.0, and 2.0% (m/v) carboxymethylcellulose (CMC), methylcellulose (MC), and poly(vinyl alcohol) (PVA), respectively, in the Hestrin-Schramm culture medium. The incorporation of the water-soluble polymers into cellulose and their influence on the structure, crystal modifications, and material properties are described. With IR and solid-state ¹³C NMR spectroscopy of the fleeces, the presence of the cellulose ethers and an increase in the amorphous parts of the cellulose modifications (NMR results) have been detected. The incorporation is represented by a higher product yield, too. As demonstrated by scanning electron microscopy, a porelike cellulose network structure forms in the presence of CMC and MC. This modified structure increases the water retention ability (expressed as the water content), the ion absorption capacity, and the remaining nitrogen-containing residues from the culture medium or bacteria cells. The water content of bacterial cellulose (BC) in the never dried state and the freeze-dried, reswollen state can be controlled by the CMC concentration in the culture solution. The freeze-dried, reswollen BC-CMC (2.0%) contains 96% water after centrifugation, whereas standard BC has only 73%. About 98% water is included in a BC-MC composite in the wet state, and about 93% is included in the reswollen state synthesized in the presence of 0.5, 1.0, or 2.0% MC. These biomaterial composites can be stored in the dried state and reswollen before use, reaching a higher water absorption than pure, never dried BC. The copper ion capacity of BC-CMC composites increases proportionally with the added amount of CMC. BC-CMC (0.5%) can absorb 3 times more copper ions than original BC. In the case of 0.5 and 1.0% PVA additions to the culture solution, this polymer cannot be detected in the cellulose fleeces after they are washed. Nevertheless the presence of PVA in the culture medium effects a decreased product yield, a retention of nitrogen-containing residues in the material during purification, a reduced water absorption ability, and a slightly higher copper ion capacity in comparison with original BC. The water content of freeze-dried, reswollen BC-PVA (0.5%) is only 62%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 463–470, 2004     

Bacterial cellulose/poly(ethylene glycol) composite: characterization and first evaluation of biocompatibility

Bacterial cellulose (BC)/poly(ethylene glycol) (PEG) composite was prepared by immersing wet BC pellicle in PEG aqueous solution followed by freeze-drying process. The product looks like a foam structure. The morphology of BC/PEG composite was examined by scanning electron microscope (SEM) and compared with pristine BC. SEM images showed that PEG molecules was not only coated on the BC fibrils surface but also penetrated into BC fiber networks. It has very well interconnected porous network structure and large aspect surface. The composite was also characterized by Fourier transform infrared spectrum, X-ray diffraction, thermogravimetric analysis (TGA) and tensile test. It was found that the presence of PEG affected the preferential orientation of the (1[`1]0 1\bar{1}0 ) plane during the drying process of BC pellicle, which in turn decrease the crystallinity of dried BC. The TGA result showed that the thermal stability was improved from 263 to 293 °C, which might be associated with strong interaction between BC and PEG. Tensile test results indicate that the Young’s modulus and tensile strength tend to decrease. Biocompatibility of composite was preliminarily evaluated by cell adhesion studies using 3T3 fibroblast cells. The cells incubated with BC/PEG scaffolds for 48 h were capable of forming cell adhesion and proliferation, which showed much better biocompatibility than the pure BC. The prepared BC/PEG scaffolds can be used for wound dressing or tissue-engineering scaffolds.     

More Than Meets the Eye in Bacterial Cellulose: Biosynthesis,Bioprocessing, and Applications in Advanced Fiber Composites

Bacterial cellulose (BC) nanofibers are one of the stiffest organic materials produced by nature. It consists of pure cellulose without the impurities that are commonly found in plant‐based cellulose. This review discusses the metabolic pathways of cellulose‐producing bacteria and the genetic pathways of Acetobacter xylinum. The fermentative production of BC and the bioprocess parameters for the cultivation of bacteria are also discussed. The influence of the composition of the culture medium, pH, temperature, and oxygen content on the morphology and yield of BC are reviewed. In addition, the progress made to date on the genetic modification of bacteria to increase the yield of BC and the large‐scale production of BC using various bioreactors, namely static and agitated cultures, stirred tank, airlift, aerosol, rotary, and membrane reactors, is reviewed. The challenges in commercial scale production of BC are thoroughly discussed and the efficiency of various bioreactors is compared. In terms of the application of BC, particular emphasis is placed on the utilization of BC in advanced fiber composites to manufacture the next generation truly green, sustainable and renewable hierarchical composites.     

Bacterial cellulose/gelatin composites: in situ preparation and glutaraldehyde treatment

Bacterial cellulose (BC)/GEL composites were prepared in situ by adding gelatin into BC-producing culture medium. The addition of gelatin interfered with the formation of the BC pellicle structure and thus made the BC yield and growth rate quite different from that of pure BC. Scanning electron microscope images showed that the width of cellulose ribbons became narrower than that of pure BC and the gelatin filled in the pores of BC to form a dense structure. The addition level of gelatin significantly influences the yield of BC/GEL composites. An optimum value of 0.5 wt/v% gelatin was attained, with which the highest yield of 0.0541 g/100 mL was achieved. Under this condition, the weight percentage of gelatin in BC/GEL composite was 65 wt%. BC/GEL composites were treated with glutaraldehyde to crosslink BC fibrils and gelatin. The crosslinking degree, determined by the concentration of glutaraldehyde and crosslinking time, could affect the swelling behavior, thermal stability and mechanical properties of composites. With increasing of the crosslinking degree, the crystallinity index and swelling behavior of the composites decreased. The increase in the crosslinking degree also descreased the composite’s strain at break in elongation but increased the compressive and tensile strength. Covalent bonding between BC and gelatin provides good strength retention to the glutaraldehyde-treated composites with a high crosslinking degree. Considering the cytocompatibility and properties of composites, the most appropriate concentration of glutaraldehyde and crosslinking time were 1.0 wt/v% and 24 h, respectively.     

Production and Characterization of Cellulose by <Emphasis Type="Italic">Acetobacter</Emphasis> sp. V6 Using a Cost-Effective Molasses–Corn Steep Liquor Medium

In order to reduce of the manufacturing cost of bacterial cellulose (BC), BC production by Acetobacter sp. V6 was investigated in shaking culture using molasses and corn steep liquor (CSL) as the sole carbon and nitrogen sources, respectively. The highest BC production was obtained with Ca₃(PO₄)₂-treated molasses. Maximum BC yield (2.21 ± 0.04 g/l) was obtained at 5% (w/v) total sugar in molasses. In improved medium containing molasses and CSL, BC production was observed in the medium after 1 day of incubation and increased rapidly thereafter with maximum yield (3.12 ± 0.03 g/l) at 8 days. This value was approximately twofold higher than the yield in the complex medium. Physical properties of BC from the complex and molasses media were studied using Fourier-transform infrared (FT-IR) spectroscopy and X-ray diffractometer. By FT-IR, all the BC were found to be of cellulose type І, the same as typical native cellulose. The relative crystallinity of BC produced in the complex and molasses media were 83.02 and 67.27%, respectively. These results suggest that molasses and CSL can be useful low-cost substrates for BC production by Acetobacter sp. V6 without supplementation with expensive nitrogen complexes such as yeast extract and polypeptone, leading to the reduction in the production costs.     

Synthesis and characterization of microcrystalline cellulose produced from bacterial cellulose

In this study, microcrystalline cellulose (MCC) was prepared from the acid hydrolysis of bacterial cellulose (BC) produced in culture medium of static Acetobacter xylinum. The MCC-BC produced an average particle size between 70 and 90 μm and a degree of polymerization (DP) of 250. The characterization of samples was performed by thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy (SEM). The MCC shows a lower thermal stability than the pristine cellulose, which was expected due to the decrease in the DP during the hydrolysis process. In addition, from X-ray diffractograms, we observed a change in the crystalline structure. The images of SEM for the BC and MCC show clear differences with modifications of BC fiber structure and production of particles with characteristics similar to commercial MCC.     

牵伸倍率对联苯型聚酰亚胺纤维形貌、取向及性能的影响

均苯四甲酸二酐(PMDA)和联苯二酐(BPDA)与3,3′-二甲基联苯二胺(OTOL)共聚得到聚酰亚胺(PI)溶液,通过干喷-湿法纺制成纤维.利用扫描电镜(SEM)、广角X射线衍射(WAXD)、纤维力学性能测试仪、动态力学分析仪(DMA)和热失重分析仪(TGA)等表征手段,研究不同牵伸倍率对联苯型聚酰亚胺纤维形貌结构、...     

Enhanced bacterial cellulose production from <Emphasis Type="Italic">Gluconobacter xylinus</Emphasis> using super optimal broth

The bacterial cellulose (BC) produced by Gluconobacter xylinus due to its versatile properties, is used in healthcare and industrial applications. However, its use is restricted owing to the limited yield from the existing culture protocols. In the current study, BC production is studied in the presence of Super Optimal Broth with catabolite repression (SOC) medium which is used to revive Escherichia coli cells after electroporation or chemoporation. In SOC medium, Gluconobacter xylinus produces cellulose pellicles within 5 days of incubation with an enhanced conversion of the carbon source to cellulose compared to traditional Hestrin–Schramm (HS) medium. SOC medium also maintains the pH close to 7.0 in static cultures unlike in HS medium where the pH is acidic. The physico-chemical and morphological characteristics of the BC produced in SOC are determined using powder X-ray diffraction (pXRD), thermo gravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH), and scanning electron microscopy (SEM) analyses. Our results indicate that SOC enhance the yield of bacterial cellulose and allows conversion of 50% of the carbon source to bacterial cellulose, compared to only 7% conversion in the case of traditional HS medium after 7 days of interaction. We also observe an increase in hydration capacity of BC produced using SOC as compared to HS media.     

Studies on anticancerious and photocatalytic activity of carboxymethyl cellulose-cl-poly(lactic acid-co-itaconic acid)/ZnO-Ag nanocomposite

In this paper, the microwave-assisted synthesis of carboxymethyl cellulose-cl-poly(lactic acid–co-itaconic acid)/ZnO-Ag nanocomposite [CMC-cl-p(LA-co-IA)/ZnO-Ag] has been discussed. Lactic acid (LA) and itaconic acid (IA) monomers were grafted onto carboxymethyl cellulose (CMC) using potassium persulphate and N, N^'-methylene-bis-acrylamide (MBA) as initiator and crosslinker, respectively at optimized conditions of temperature and pressure. The nanocomposite was characterized using different techniques such as Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and energy dispersive X-ray (EDX). XRD, TEM and FTIR spectral analysis confirmed the formation of the nanocomposite. The release of amoxicillin drug-using nanocomposite as a function of pH and time has been investigated. The maximum drug release of 94.64% was pragmatic at pH 2.2 after 6 h. The degradation of congo red using nanocomposite followed the pseudo-first-order reaction model with the regression coefficient (R²) values of 0.99312. The nanocomposite was also explored for anticancer behavior against yeast cells.     

Thermal behavior of poly(vinylbenzyl chloride)‐grafted poly(ethylene‐co‐tetrafluoroethylene) films

The effect of the degree of grafting (DOG) on the thermal behavior of poly(vinylbenzyl chloride)‐grafted poly(ethylene‐co‐tetrafluoroethylene) (ETFE‐g‐PVBC) films was investigated by differential scanning calorimetry (DSC), X‐ray diffraction (XRD), dynamic mechanical analysis ( DMA), FT‐IR, and thermogravimetric analysis (TGA) instruments. Several ETFE‐g‐PVBC films with various degrees of grafting, including 10, 24, 41, 60, and 94%, were prepared using a radiation grafting technique. The DSC and XRD results of the ETFE‐g‐PVBC films revealed that the crystallinity of the films decreased as the DOG increased. The DMA and FT‐IR results of the films indicated that a crosslinking reaction occurred at temperatures above 250 °C. In the thermal properties of the grafted films, an increase in the DOG led to an increase in the decomposition temperature. The activation energy (E_a) of the thermal decomposition was calculated using Kissinger's equation from TGA results. The E_a value of the PVBC graft chain was found to increase as the DOG increased, indicating that the crosslinking reaction of ETFE‐g‐PVBC films increased with an increase in the DOG during the thermal degradation process. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 517–525     

Production of bacterial cellulose by Gluconacetobacter sp. RKY5 isolated from persimmon vinegar

The optimum fermentation medium for the production of bacterial cellulose (BC) by a newly isolated Gluconacetobacter sp. RKY5 was investigated. The optimized medium composition for cellulose production was determined to be 15 g/L glycerol, 8 g/L yeast extract, 3 g/L K₂HPO₄, and 3 g/L acetic acid. Under these optimized culture medium, Gluconacetobacter sp. RKY5 produced 5.63 g/L of BC after 144 h of shaken culture, although 4.59 g/L of BC was produced after 144 h of static culture. The amount of BC produced by Gluconacetobacter sp. RKY5 was more than 2 times in the optimized medium found in this study than in a standard Hestrin and Shramm medium, which was generally used for the cultivation of BC-producing organisms.     

Cellulose Nano Whiskers (CNWs) Loaded-Poly(sodium acrylate) Hydrogels. Part-I. Effect of Low Concentration of CNWs on Water Uptake

In this work, de-watered cellulose pulp(DCP), obtained from a paper mill, have been acid-hydrolyzed to yield cellulose nano-whiskers (CNWs). As revealed from FESEM measurements, these CNW were found to possess a median length of 258.5 nm, diameter of 35.2 nm, and an aspect ratio of 7.3. The CNWs were also characterized by TGA, XRD and FTIR analysis. The CNWs were found to possess a fairly high Crystallinity Index (CI) of 0.925. The addition of cellulose at low concentration range, i.e., from 25 to 125 mg (nearly 1.25 to 6.25 weight percent of polymer sodium acrylate) caused an enhancement in water uptake of resulting hydrogels .The CNWs-loaded poly(SA) hydrogels showed chain relaxation controlled swelling in the medium of pH 7.4 as was confirmed from the swelling exponent ‘n’ values obtained using power function law‥ The second order kinetic model was found to fit well to the kinetic water uptake data. However, all the samples, when prepared in the form of films, did not show any remarkable increase in their mechanical strength.     

Semi-continuous bacterial cellulose production in a rotating disk bioreactor and its materials properties analysis

A rotating disk bioreactor with plastic composite support (PCS) as the solid support was evaluated for bacterial cellulose (BCel) production. Results demonstrated that BCel can be produced in a semi-continuous manner. The BCel productivity reached around 0.24 g/L/day and can be sustained for at least five consecutive runs. Scanning electron microscopy results confirmed that Gluconacetobacter can attach on the PCS surface, which eliminates the need of reinoculation. X-ray diffraction patterns and mechanical analysis of BCel produced from this semi-continuous process exhibited lower crystallinity (66.9 %) and mechanical property (Young's modulus of 372.5 MPa) when compared with the BCel obtained from static culture (crystallinity = 88.7 %, Young's modulus of 3,955.6 MPa). Both BCel samples possessed similar water content (98.66 vs. 99.04 %) and thermostability (around 346 °C). In conclusion, the PCS rotating disk bioreactor system can be used to produce BCel in pellicle form with enhanced productivity and, meanwhile, can be scaled up easily to meet commercial need.     

Using a fully recyclable dicarboxylic acid for producing dispersible and thermally stable cellulose nanomaterials from different cellulosic sources

We fabricated cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) from different cellulose materials (bleached eucalyptus pulp (BEP), spruce dissolving pulp (SDP) and cotton based qualitative filter paper (QFP) using concentrated oxalic acid hydrolysis and subsequent mechanical fibrillation (for CNFs). The process was green as acid can be easily recovered, and the prepared cellulose nanomaterials were carboxylated and thermally stable. In detail, the CNC yield from the different materials was similar. After hydrolysis, the DP of the cellulose materials decreased substantially, whereas the mechanical fibrillation of the cellulosic solid residues (CSRs) did not dramatically reduce the DP of cellulose. CNCs with different aspect ratios were produced from different starting materials by oxalic acid hydrolysis. The CNCs and CNFs obtained from BEP and QFP possessed more uniform dimensions than those from SDP. On the other hand, CNFs derived from SDP presented the best suspension stability. FTIR analyses verified esterification of cellulose by oxalic acid hydrolysis. The results from both XRD and Raman spectroscopy indicated that whereas XRD crystallinity of CNCs from BEP and QFP did not change significantly, there was some change in Raman crystallinity of these samples. Raman spectra of SDP CNCs indicated that the acid hydrolysis preferably removed cellulose I portion of the samples and therefore the CNCs became cellulose II enriched. TGA revealed that the CNCs obtained from QFP exhibited higher thermal stability compared to those from BEP and SDP, and all the CNCs possessed better thermal stability than that of CNCs from sulfuric acid hydrolysis. The excellent properties of prepared cellulose nanomaterials will be conducive to their application in different fields.     

细菌纤维素/聚丙烯酰胺水凝胶的制备及性能表征

通过自由基聚合在细菌纤维素(BC)网络中引入聚丙烯酰胺(PAM),制备了细菌纤维素/聚丙烯酰胺(BC/PAM)复合水凝胶,并采用扫描电子显微镜(SEM)、红外光谱(IR)、热失重分析(TGA)、X射线衍射(XRD)和力学测试等手段对复合凝胶的结构和性能进行了研究.研究结果显示在复合水凝胶中,虽然PAM自身没有交联,但由...