Enzymatic saccharification of dissolution pretreated waste cellulosic fabrics for bacterial cellulose production by Gluconacetobacter xylinus

BACKGROUND: Waste textiles, such as dyed cellulosic and/or polyester blended fabrics have the potential to serve as an alternative feedstock for the production of biological products via microbial fermentation. Dissolution pretreatment was employed to enhance the enzymatic saccharification of dyed and synthetic fiber blended cellulosic fabrics. The fermentable reducing sugars obtained from waste cellulosic fabrics were used to culture Gluconobacter xylinus for value‐added bacterial cellulose (BC) production. RESULTS: Concentrated phosphoric acid was the ultimate cellulose solvent for dissolution pretreatment since 5% w/w cellulosic fabric can be completed dissolved at 50 °C. After regeneration in water, the cellulosic precipitate was subjected to cellulase hydrolysis, resulting in at least 4‐fold enhancement of saccharification rate and reducing sugars yield. The colored saccharification products can be utilized by G. xylinus to produce BC, approximately 1.8 g L^?1 BC pellicle was obtained after 7 days static cultivation. CONCLUSION: Dyed and blended waste fabric can be pretreated effectively by dissolution to produce fermentable sugars by cellulase hydrolysis. Dissolution pretreatment can expose the dyed or polyester fiber covered digestible cellulosic fibers to cellulase and leads to a significant enhancement of saccharification yield. The colored saccharification products have no significant inhibiting effect on the fermentation activity of G. xylinus for BC production. Copyright © 2010 Society of Chemical Industry     

Processing of Cellulose Using Ionic Liquids

The processing of cellulose dissolved in ionic liquids (ILs) enables the development of new materials. Besides the established production of cellulosic fiber products, interesting technical applications are developed like super micro filament fibers, cellulose/chitin blend fibers, precursors for carbon fibers, and all‐cellulose composites. This review provides a detailed summary of these new developments and describes how ILs are selected for the processing of cellulose with a particular emphasis on industrial realization. State‐of‐the‐art spinning processes are reviewed and it is illustrated how uniquely selected ILs can be used not only for established fiber spinning but for the development of new cellulose‐based materials.     

The quest for alternatives to microbial cellulase mix production: corn stover‐produced heterologous multi‐cellulases readily deconstruct lignocellulosic biomass into fermentable sugars

BACKGROUND: Production of cellulosic ethanol is still expensive compared with corn (maize) grain ethanol due to the high costs of bulk production of microbial cellulases. At least three cellulases including endo‐cellulase, exo‐cellulase and cellobiase are needed to convert cellulosic biomass into fermentable sugars. All these cellulases could be self‐produced within cells of transgenic bio‐energy crops. The production of heterologous Acidothermus cellulolyticus (E1) endo‐cellulase in endoplasmic reticulum and mitochondria of green tissues of transgenic corn plants was recently reported, and it was confirmed that the heterologous E1 converts cellulose into fermentable sugars. RESULTS: Biologically active A. cellulolyticus E1, Trichoderma reesei 1,4‐β‐cellobiohydrolases I (CBH I) exo‐cellulase and bovine rumen Butyrivibrio fibrisolvens cellobiase were expressed in corn plant endoplasmic reticulum (ER), apoplast (cell wall areas) and vacuole respectively. Results show that the ratio 1:4:1 (E1:CBH I:cellobiase) of crude heterologous cellulases is ideal for converting ammonia fiber explosion (AFEX) pretreated corn stover into fermentable sugars. CONCLUSIONS: Corn plants that express all three biologically active heterologous cellulases within their cellulosic biomass to facilitate conversion of pretreated corn stover into fermentable sugars is a step forward in the quest for alternatives to the present microbial cellulase mix production for cellulosic biofuels. Copyright © 2011 Society of Chemical Industry     

Green tissue‐specific production of a microbial endo‐cellulase in maize (Zea mays L.) endoplasmic‐reticulum and mitochondria converts cellulose into fermentable sugars

BACKGROUND: Commercial conversion of lignocellulosic biomass to fermentable sugars for biofuels and chemical byproducts uses relatively expensive bulk production of biologically active cellulase enzymes, which could alternatively be achieved by using solar energy for direct production of these enzymes within feedstock crop cellulosic biomass. RESULTS: The Acidothermus cellulolyticus endo‐cellulase E1 has been produced in transgenic maize plants. This heterologous enzyme was specifically targeted for accumulation into two sub‐cellular compartments, endoplasmic reticulum (ER) or mitochondria of plant leaves and stalks. Furthermore, successful use of this maize‐produced heterologous cellulase in converting cellulose into fermentable sugars for biofuels, has been confirmed. CONCLUSIONS: Green‐specific expression of cellulases in maize plants can avoid public controversies associated with production of transgene products in maize seeds and/or pollen. Sub‐cellular targeting of cellulases may result in better expression of transgene products because these compartments, specially ER, normally contain molecular chaperones that enhance protein folding and there the biological activity. Also, using solar energy to produce cellulases within crop cellulosic biomass can replace the costly process of cellulase production in microbial bioreactors, and therefore, save costs. Copyright © 2008 Society of Chemical Industry     

Effect of fiber structure on yield stress during enzymatic conversion of cellulose

Enzymatic hydrolysis of cellulose for conversion to chemicals or fuels presents engineering challenges due to the large changes in suspension viscosity and yield stress that occur. A flow reactor with an in‐line rheometer was used to investigate the role of changes in fiber structure on rheology. The evolution of the suspension yield stress was compared to amount of soluble sugars released and changes in fiber length and width. A model was constructed that links the yield stress, conversion, and fiber shape. These results provide insights into the relationship between fiber structure and transport properties during the early stages of hydrolysis of cellulosic biomass. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1582–1590, 2014     

Rheograms of cellulosic polymers from the melt flow index

Data on the variation of melt viscosity over a wide range of shear rates and temperatures are necessary in the processing of cellulosic polymers. An effective method has been proposed to estimate the viscosity vs. shear rate flow curves of a cellulosic resin at temperatures relevant to the processing conditions, from its melt flow index and glass transition temperature. The method involves the use of a master curve obtained by coalescing the rheograms of various grades in terms of a modified viscosity, η˙MFI, and a modified shear rate, γ˙/MFI. Master curves have been reported for cellulose esters and ethers.     

Dilute acid depolymerization of cellulose in aqueous phase: Experimental evidence of the significant presence of soluble oligomeric intermediates

The objective of this investigation is to show that rapid hydrolysis can be achieved by passage of aqueous cellulosic suspensions (2–10% solids) through capillaries followed by sudden decompression and post-treatment under dilutes acid conditions. Through detailed experimentation within the 200–240°C temperature range and at low sulfuric acid concentrations (0.2–1.0% w/w) it was found that liquefaction of the cellulose proceeds via extensive formation of soluble oligomeric intermediates. A simple kinetic model has been developed to explain the liquefaction-saccharification patterns of the cellulose. The sequence considered is: Cellulose → Oligo-derivatives → Glucose → Decomposition products Quantitative values of the rate constants have been determined and a discussion on the selectivity of the overall reaction sequence is presented.     

Horizontal Dip‐Spin Casting of aqueous alumina‐polyvinylpyrrolidone suspensions with chopped fiber

A novel ceramic processing method, called Horizontal Dip Spin Casting (HDSC), enabled fabrication of tubular ceramic parts with an aligned chopped fiber phase. HDSC was demonstrated using highly loaded aqueous alumina suspensions with >50 vol.% solids loading and ≤5 vol.% water‐soluble polymer employed as a rheological modifier. Chopped carbon fibers were added to the suspensions to attain maximum loadings of 30 vol.%. During forming, cylindrical foam molds were dipped into the suspension while being rotated radially about the long axis. Simultaneously, a doctor blade was placed at a specified distance from the foam surface to facilitate the flow of the suspension to align the fiber and control the thickness of the material that accrued on the mold. Rheological study of alumina‐PVP suspensions with and without chopped carbon fiber showed that the suspensions exhibited a yield‐pseudoplastic flow behavior. The degree of alignment of the carbon fiber phase in the green bodies was characterized for various suspension formulations, carbon fiber contents and forming speeds. Stereological characterization of green body specimens confirmed the effectiveness of HDSC to attain the desired tubular geometry with considerable fiber alignment for a suspension composition containing ≤20 vol.% chopped fibers.     

Competitive adsorption of water-soluble polymers on attapulgite clay

The individual, competitive, and displacement adsorption of polyvinyl alcohol (PVOH), hydroxyethyl cellulose (HEC), and hydroxypropylmethyl cellulose (HPMC) in aqueous solution onto an attapulgite clay has been systematically studied. For the individual adsorption experiments, the amount of polymer adsorbed at equilibrium decreased in the order PVOH, HEC, HPMC. In the competitive adsorption experiments, the adsorption level of each polymer is diminished by the presence of a competing polymeric species. Binary mixtures of a cellulosic polymer (HEC or HPMC) with PVOH result in a substantial reduction in the amount of cellulosic polymer adsorbed. In the displacement adsorption studies, the sequential addition of HEC or HPMC is not able to displace previously adsorbed PVOH molecules to any appreciable extent. However, the addition of PVOH to previously equilibrated HEC/clay or HPMC/clay suspensions results in a large amount of the adsorbed cellulosic polymer being displaced by PVOH, especially under conditions of high surface coverage. These results indicate that PVOH is preferentially adsorbed on the clay surface and the strength of attachment to the surface is greater for PVOH than for either cellulosic polymer.     

Dynamics of semi-flexible and breakable fibers under Poiseuille flow

In the processing of fiber-reinforced polymer composites, especially in injection molding, the fiber's orientation, length, and distribution vary depending on the location of the channel flow and its properties, which affects the performance of final products. To investigate the intricate behavior of fiber suspensions under Poiseuille flow, we used the hybrid simulation approach, multiparticle collision dynamics–molecular dynamics (MPC-MD), which takes hydrodynamic interactions and fiber properties (strength, flexibility) into account. For non-breakable and rodlike fibers, fibers align well along the flow direction while showing more alignment near the wall. As fiber becomes breakable and/or flexible, the length and orientation of fibers strongly depend on their properties. The interesting phenomenon is specifically seen for breakable and semiflexible fibers, where the orientation of the fiber exhibits non-monotonic behavior depending on the flow rate. This complex behavior highlights the importance of comprehending the dynamics of many types of fibers and necessitates research into the best conditions for injection molding.     

Influence of process parameters on the structure formation of man‐made cellulosic fibers from ionic liquid solution

The influence of dry‐jet wet spinning parameters on the production of man‐made cellulosic fibers from 13 wt % cellulose/1,5‐diazabicyclo[4.3.0]non‐5‐ene acetate solutions was investigated. The spinneret nozzle diameter, extrusion velocity, draw ratio, and coagulation bath temperature were the studied parameters. The production of highly oriented fibers was favored by selecting higher extrusion velocity and lower spinneret diameter. A spinneret size of 100 µm and a draw ratio of 6 were sufficient to highly orient the cellulose macromolecules and achieve tenacities above 40 cN/tex (600 MPa). Total orientation assessed via birefringence measurement, tenacity, and Young's modulus values reached a plateau at a draw of 6 and no further development in properties was observed. A temperature of the aqueous coagulation bath of 15 °C slightly promoted greater orientation of the fibers by hampering structural changes of the cellulose macromolecules in the nascent solid fibers. Furthermore, the determination of the elongational viscosity of the liquid thread via the measurement of radial force tensor was tested and showed promising results. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43718.     

Comparison of catalytic hydrolysis of bagasse cellulose under heterogeneous and homogeneous systems

The conversion of cellulose into valuable chemicals has attracted a great deal of interest. In this study, heterogeneous and homogeneous systems in the conversion of bagasse cellulose into the total reducing sugars were investigated. In the heterogeneous system, the effects of several critical factors including types and concentrations of ionic liquid, temperature, and time were all investigated for cellulosic conversion. Parameters considered included temperature, dosage of catalyst, and water in the homogeneous system. It was found that the hydrolysis capacity for cellulose in homogeneous system was better than that in heterogeneous system. In addition, the structure and physicochemical properties of the treated cellulose were characterized by Fourier transform infrared spectroscopy, thermogravimetry, and scanning electron microscopy, and then compared with the native fibers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42228.     

Effect of corona modification on the mechanical properties of polypropylene/cellulose composites

The effect of various corona treatment conditions on the mechanical properties of cellulose fibers/polypropylene composites was studied. The cellulose fibers and polypropylene were modified using a wide range of corona treatment levels and concentrations of oxygen. The treatment level of the fibers was evaluated using the electrical conductance of their aqueous suspensions. The mechanical properties of composites obtained from different combinations of treated or untreated cellulose fibers and polypropylene were characterized by tensile stress–strain measurements; they improved substantially when either the cellulose fibers alone or both components were treated, although composites made from untreated cellulose fibers and treated polypropylene showed a relatively small improvement. The results obtained indicate that dispersive forces are mostly responsible for the enhanced adhesion. The relationship between the electrical conductance of the fibers, the mechanical properties, and the mechanism of improved adhesion is discussed. © 1994 John Wiley & Sons, Inc.     

Flammability of natural plant and animal fibers: a heat release survey

With increased interest in sustainable materials for use in building materials and clothing, there is a renewal in the use of natural fibers (plant or animal‐based) versus synthetic fibers in a variety of applications. However, there is not as much information available on the flammability of these natural fibers especially when they are used in products where purification techniques used in conventional textile processing are not required. The literature to date suggests that all of the fibers can be grouped into two categories: cellulosic and animal, with the assumption that regardless of original species, the flammability is similar for fibers within each category. In this report, we have conducted a survey via microcombustion calorimetry to determine if all cellulose‐based and all protein‐based fibers are the same from a heat release perspective. Our findings show that this is not the case, and there are notable differences in fiber types within each genus. Further, how the natural fiber has been treated prior to use can have some dramatic effects on heat release caused by residual impurity content. The results in this paper suggest that there is more to be learned about these natural fiber types in regards to their inherent flammability. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of bamboo-derived porous carbon: exploring structure change,pore formation and supercapacitor application

Biomass porous carbon possessing hierarchical pores and abundant heteroatoms has emerged as a sustainable and cost-effective functional material. Herein, a green cellulose solvent was employed as the activation agent and nitrogen source to obtain this distinctive structure from bamboo cellulose fibers. With the assistance of thermal treatment, the solvent could fully infiltrate into cellulose structure of raw material and result in the cellulosic structure damage, forming ultimately the three-dimensional conductive network, hierarchical pores, as well as high heteroatom doping (8.43 at%). Benefited from the unique structure, the obtained porous carbon as the supercapacitor electrode showed excellent capacitive performance (280 F/g at 0.3 A/g), good rate capability and cyclic stability. Moreover, influences of hydrothermal temperature on cellulose structure, pore formation, and the resultant supercapacitor performance were demonstrated. This green strategy shows potential for producing hierarchical porous carbon with high heteroatoms from biomass resources.

     

Grafting of poly(acrylic acid) onto cellulosic microfibers and continuous cellulose filaments and characterization

Results from the grafting of poly(acrylic acid) (PAA) onto cellulosic microfibers and continuous cellulose filaments are presented. The grafting of PAA onto cellulosic fibers offers the possibility of developing enhanced ion exchange and fluid absorbency on the fibers. The grafting of PAA was carried out with a two‐step procedure. First, vinyl‐terminated ethoxy silane was deposited on the surface of the fiber. This was followed by a grafting polymerization reaction in aqueous media of acrylic acid with different concentrations of potassium persulfate (KPS), which acted as the initiator. The percentage of grafting increased with increasing KPS concentration and reached a maximum value at a concentration of about 0.4 wt % with respect to the weight of the fiber. The grafted copolymer was characterized by Fourier transform infrared spectroscopy. Strong evidence that the grafting reaction was successful was given by the presence of a band, with a maximum at 1732 cm^?1, that was characteristic of carbonyl group absorption and was not initially present in the cellulosic fibers. The water absorption of the cellulosic microfibers grafted with PAA was three times greater than the water absorption of the nongrafted microfibers. The mechanical properties of continuous cellulose filaments did not change drastically with PAA grafting. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 386–393, 2002     

The non-trivial role of native xylans on the preparation of TEMPO-oxidized cellulose nanofibrils

Cellulose nanofibrils have become increasingly prized as a raw material toward the preparation of composites due to their specific surface character and biocompatibility. TEMPO-mediated oxidation with post-mechanical treatment has been proposed as a promising method for the preparation of cellulose nanofibrils from cellulosic raw materials. In the current study it was found that the native hemicellulosic components in the raw material played a pivotal chemical role on the kinetics of generation of TEMPO-oxidized cellulose nanofibrils (TOCNs), as well as on thermal stability, and transmittance. The removal of xylans from the original feedstock facilitated not only an increase in both the carboxylate content and water retention value of the TEMPO-oxidized fibers, but also improved the transmittance of subsequently obtained TOCNs suspensions. It was also determined that the presence of xylans in the cellulosic feedstock hindered chemical accessibility through a barrier mechanism in which the TEMPO-mediated oxidation reaction rate was reduced.     

Isolation and identification of residual chromophores in cellulosic materials

A general procedure was developed for the isolation of residual chromophores in or on cellulosic material, which were hitherto inaccessible to structure elucidation due to their extremely low content in the ppb concentration scale. It is applicable to cellulosic pulp, cellulosic fibers (viscose, Lyocell) and cellulose derivatives (acetate, carbonyl-labeled cellulose) as well. The chromophore identification comprises treatment of the cellulosic material with boron trifluoride-acetic acid complex (BF₃·2HOAc) containing sulfite, chromatographic separation of the resulting chromophore-containing mixture, and structure determination of the main constituents by NMR/MS and comparison to authentic samples. Both adsorbed and covalently bound aromatic and quinoid compounds are selectively released by the treatment. Covalent ester, ether and secondary alkyl links between chromophore and cellulose are broken.Four cellulosic example substrates have been analyzed for their chromophore content: Lyocell fibers, cellulose triacetate, pulp after thermal treatment in N,N-dimethylacetamide, and pulp containing carbonyl-selective labels, and up to 11 chromophores per sample have been identified.     

Fundamental understanding and modeling of diffuse interphase properties and its role in interfacial flow stability of multilayer polymers

This work aims to investigate the growth and structural evolution of a diffuse interphase generated in a flow field and to highlight its importance on controlling the final properties of compatible multilayer materials. The model polymers chosen are poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). Interdiffusion kinetics, geometrical, and rheological properties of the interphase decoupled and coupled to flow have been probed and quantified under fundamental conditions of rheological measurement and under real practical conditions of processing, respectively. Polymer chain orientation is shown to decelerate the interdiffusion coefficient. This phenomenon is demonstrated to be balanced by intermixing (i.e. flow effect) at the vicinity of the interface triggered from excess interfacial shear stress, thus favors development of the interphase. The diffuse interphase generated therein during the processing has been well characterized via scanning electron microscopy coupled with energy dispersive X‐ray analysis (SEM‐EDX) and transmission electron microscopy (TEM). Results indicate that the interphase is robust with a geometrical property of tens microns depending on processing conditions and the interfacial structure is shown to be smooth with continuous amorphous‐crystallization transition between neighboring layers without causing any interfacial disturbances. Finally, experimental studies concerning the interfacial flow instability and encapsulation in coextrusion process have been performed, taking into account some key classical decisive parameters such as viscosity ratio, thickness ratio and elasticity ratio, etc. Different from severe flow instability observed in incompatible multilayer systems, presence of the interphase at PMMA/PVDF multilayers plays a vital role in weakening (or even eliminating) the viscous instabilities and elastic instabilities despite of the very high rheological contrast. POLYM. ENG. SCI., 55:771–791, 2015. © 2014 Society of Plastics Engineers     

Fractionation of woodmeal by prehydrolysis and thermal organosolv. Process strategy,recovery of constituents,and solvent fractionation of lignins so produced

A prototype hardwood Populus deltoids has been fractionated in kg quantities into its primary constitutive polymers, namely, cellulose, hemicelluloses, and lignin, under optimal recovery conditions for each fraction. Our approach is targeted at processing sawdust or finally divided wood (d_p ≤ 0.5 mm) and involves a thermomechano-solvolytic treatment of medium consistency suspensions in two process development units operated sequentially. Firstly, the hemicellulose fraction is removed from the initial wood by a aqueous-steam pretreatment (auto-hydrolysis) at conditions where nearly 90% of the hemicelluloses are solubilized. Secondly, the treated wood (lignocellulose) is separated into cellulose and lignin rich fractions by subjecting it to an organosolvolytic treatment using ethylene glycol as solvent. An experimental unit which can be operated in semi-continuous or continuous modes is described and was employed for this step. The recovery of each fraction via appropriate mass balances is presented. Also, a comparative characterization of the lignins isolated via (a) the direct solvolysis route and (b) the sequential aqueous-steam pretreatment followed by solvolysis approach is made using solvent fractionation, molar mass distribution, and ¹³C NMR spectroscopy methods.