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By adding poly(ethylene oxide) (PEO) to the growth medium of Acetobacter xylinum, finely dispersed bacterial cellulose (BC)/PEO nanocomposites were produced in a wide range of compositions and morphologies. As the BC/PEO w/w ratio increased from 15:85 to 59:41, the cellulose nanofibers aggregated in larger bundles, indicating that PEO mixed with the cellulose on the nanometer scale [corrected]. Fourier transform infrared spectroscopy suggested intermolecular hydrogen bonding and also preferred crystallization into cellulose Ibeta in the BC/PEO nanocomposites. The fine dispersion of cellulose nanofibers hindered the crystallization of PEO, lowering its melting point and crystallinity in the nanocomposites although remaining bacterial cell debris also contributed to the melting point depression. The decomposition temperature of PEO also increased by approximately 15 degrees C, and the tensile storage modulus of PEO improved significantly especially above 50 degrees C in the nanocomposites. It is argued that this integrated manufacturing approach to fiber-reinforced thermoplastic nanocomposites affords a good flexibility for tailoring morphology and properties. These results further pose the question of the necessity to remove bacterial cells to achieve desirable materials properties in biologically derived products.

Imidazole is reported to be an effective reactant for the production of nanocellulose from hardwood pulp. The morphologies and surface properties of the nanocellulose can be simply tailored according to the water content in the imidazole system: with pure imidazole, cellulose nanofibrils (CNFs) in a yield of 10 wt % can be produced. With 25 wt % of water in imidazole, cellulose nanocrystals (CNCs) are obtained in 20 wt % yield. Both nanocelluloses exhibit crystallinity indices in the order of 70%. Interestingly, they retain the original xylan from the pulp with ca. 9-10 wt % of residual xylan content. [ABSTRACT FROM AUTHOR]

Key message: Hot pressing leads to changes in wood water sorption properties, linear viscoelastic behavior, and chemistry. In hot-pressed hybrid poplar, storage modulus linearly correlates with cellulose apparent crystallinity index and degree of polymerization, revealing the impact of cellulose hydrolysis on wood viscoelasticity during hot pressing. Context: Heat treatment and densification during hot pressing are known to alter wood chemical, physical, and viscoelastic properties. Interrelationships between these properties and their changes during hot pressing are, however, unknown. They are expected to play a significant role on mat consolidation during the manufacture of wood-based composites. Aims: This study aims (1) to characterize the impact of hot pressing on the physical, viscoelastic, and chemical properties of hybrid-poplar wood and (2) to assess possible relationships between these properties. Methods: Dry and moist wood samples were hot-pressed under various conditions of temperature. Specific gravity, water sorption isotherms, and dynamic viscoelastic properties of hot-pressed wood were measured together with cellulose apparent crystallinity and molecular weight. Possible relationships between these properties were assessed with statistical analyses. Results: Wood specific gravity, sorption isotherm, dynamic moduli, and cellulose crystallinity were all affected by the hot-pressing conditions. The viscoelastic response of hot-pressed wood was found to relate not only to the extent of densification but also to in situ molecular properties of cellulose. Cellulose apparent crystallinity index and degree of polymerization in hot-pressed wood linearly correlated with storage modulus, revealing the importance of cellulose hydrolysis during hot pressing on wood viscoelastic response. Conclusion: During hot pressing, wood cellulose hydrolysis appears to govern the viscoelastic response, in addition to wood densification. [ABSTRACT FROM AUTHOR]

Bacterial cellulose/fibrin composites were treated with glutaraldehyde in order to crosslink the polymers and allow better match of the mechanical properties with those of native small-diameter blood vessels. Tensile and viscoelastic properties of the glutaraldehyde treated composites were determined from tensile static tests and cyclic creep tests, respectively. Glutaraldehyde-treated (bacterial cellulose) BC/fibrin composites exhibited tensile strength and modulus comparable to a reference small-diameter blood vessel; namely a bovine coronary artery. However, the breaking strain of the glutaraldehyde-treated composites was still well below that of the native blood vessel. Yet a long strain hardening plateau was induced by glutaraldehyde treatment which resembled the stress-strain response of the native blood vessel. Tensile cyclic creep test indicated that the time-dependent viscoelastic behavior of glutaraldehyde-treated BC/fibrin composites was comparable to that of the native blood vessel. Covalent bonding between BC and fibrin occurred via glutaraldehyde, affording mechanical properties comparable to that of the native small blood vessel. [ABSTRACT FROM AUTHOR]

series of resole-type phenolic resin-based nanocomposites, uniformly filled with cellulose nanowhiskers (CNWs), was successfully fabricated via direct solution mixing, then solvent-exchange with DMF and finally stepwise thermal curing. Dynamic mechanical analysis evidenced a moderate reinforcing effect with a minimum CNWs weight content of 5.0 wt% especially above the resin glass transition temperature ( T). The Halpin-Kardos model provided a good description of the CNWs reinforcing effect, suggesting perhaps the contribution of whiskers/matrix interactions rather than that of whiskers/whiskers interactions. Differential scanning calorimetry (DSC) further indicated that the nanowhiskers enhanced the resin cure, resulting in a more extensive degree of cure. Finally, the CNWs were found to only slightly lower the thermal stability of PF resins. In spite of a modest reinforcing effect, it is proposed that CNWs are also interesting fillers for high modulus and high T thermosetting resins that require high temperature cure. [ABSTRACT FROM AUTHOR]

BC/fibrin composites having fibrin/BC weight percent ratios ranging from 2/98 to 64/36 were produced by immersing never-dried-BC into varying compositions of fibrin/ionic liquid/DMSO solutions and for increasing time periods. The composite compositions were predicted from an FTIR/Beer's law calibration method based on calibration samples which exhibited an RMSEP of 2.5 weight percent. Observations of the composite surface with atomic force microscopy and of the internal pore structure with scanning electron microscopy showed that increasing immersion times resulted into smoother surface composites and allowed further infiltration of fibrin into the microporous structure of BC. Tensile strength and cyclic creep tests demonstrated that the composition had significant impact on the ultimate tensile stress and cyclic creep strain level of BC/fibrin composites. It is proposed that these composites have potential for artificial blood vessel applications. [ABSTRACT FROM AUTHOR]

We report for the first time the direct extraction of cellulose nanocrystals (CNCs) from wood by means of a 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) treatment. A native cellulosic product could be recovered in 44% yield with respect to wood cellulose content. The product was analyzed for morphological (TEM, AFM, XRD), chemical (FTIR, 13 C CP/MAS NMR), thermal (DSC, TGA) and surface properties (Zeta potential, contact angle). These analyses evidenced the presence of partially acetylated (surface DS = 0.28) nanocrystals of native cellulose I microstructure, with a crystallinity index of about 75% and aspect ratio of 65. Direct production of CNCs from wood is ascribed to the simultaneous capability of [EMIM][OAc] to (1) dissolve lignin in situ while only swelling cellulose, (2) decrease intermolecular cohesion in wood via acetylation, and (3) to catalyze cellulose hydrolysis. [ABSTRACT FROM AUTHOR]

1Butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO 4 ) is efficient at extracting cellulose nanocrystals from pulp fibers. To shed some light on the respective contributions of swelling and hydrolysis of pulp fibers by [Bmim]HSO 4 , the physical, structural and morphological characteristics of hardwood Kraft pulp fibers were monitored under various conditions of temperature, water content and time. Swelling was largely compounded by hydrolysis at the highest temperatures (120 °C) as evidenced by mass loss and reduced degree of polymerization (DP n ) at this temperature. At 120 °C only, water content appeared to play a significant role on the extent of hydrolysis. At this temperature, a heterogeneous kinetic model involving weak links and amorphous regions best described the experimental data. Hydrolysis rates were maximum at 25% water content in the aqueous ionic liquid. [ABSTRACT FROM AUTHOR]

Abstract: Thermochemical conversion of biomass has been studied extensively over the last decades. For the design, optimization and modeling of thermochemical conversion processes, such as fixed bed pyrolysis, a sound understanding of pyrolysis is essential. However, the decomposition mechanism of most biomass types into gaseous, liquid, and solid fractions is still unknown because of the complexity of pyrolysis and differences in biomass composition. The aim of this study was to find characteristic differences in the pyrolysis behavior of three widely used biomass feedstocks to optimize the performance of industrial fixed bed pyrolysis. This aim was achieved in three steps. First, devolatilization kinetics during pyrolysis of three biomass types was investigated in a thermogravimetric analyzer (TGA). Then, a one-step multi-component pyrolysis model with three independent parallel reactions for hemicellulose, cellulose and lignin was derived to correlate the kinetics with single component decomposition and to identify their amount in the biomass sample. In a final step, the findings were tested in a fixed bed reactor at laboratory scale to prove applicability in industrial processes. Three types of biomass were chosen for this investigation: wheat straw, rape straw and spruce wood with bark. They represent biomass with a high cellulose, hemicellulose and lignin content, respectively. Since lignin is the most stable and complex of these three biomass components, its amount is assumed to be the main controlling factor in the thermochemical decomposition process. The thermogravimetric (TG) curve of spruce wood with bark was found to shift to about 20K higher temperatures compared to the TG curves of straw and rape straw. This result indicates that a higher activation energy is needed to decompose woody biomass, which contains a higher amount and a different type of lignin than straw. Three wood decomposition phases were distinguished from the negative first derivatives curves (DTG): a shoulder during hemicellulose decomposition, a peak during cellulose decomposition and a smaller rise during lignin decomposition. By comparison both herbaceous biomass types decomposed in only two phases at lower temperatures. The decomposition of the herbaceous, and woody biomass samples was completed at about 830K and 900K, respectively, leaving only a solid residue of ash. The derived pyrolysis model estimated the composition and described the devolatilization curves of each biomass with sufficient accuracy for industrial processes, although the same activation energy set, taken from the literature, was used for each biomass. In the fixed bed pyrolysis experiments similar characteristics were found to those in the TGA experiments. Herbaceous biomass with a higher cellulose and hemicellulose content decomposed faster and produced a larger fraction of gaseous products than woody biomass with a higher lignin content. According to the assessment of the product distribution, performed after each experiment, woody biomass pyrolysis led to a larger fraction of solid products than herbaceous biomass pyrolysis. We conclude that industrial fixed bed pyrolysis can be optimized for different biomass feedstocks with a specific composition of cellulose, hemicellulose and lignin. [Copyright &y& Elsevier]

Abstract: All-cellulose composites (ACCs) were prepared by partial dissolution in ionic liquid and compared to composites with epoxy matrix. Wide-angle X-ray diffraction and scanning electron microscopy were used to reveal differences in the structure of the composites. In tensile tests, lyocell-fibre based ACCs showed similar strength and stiffness, yet superior extensibility compared to lyocell-epoxy composites. However, when flax fibres were used, tensile properties clearly inferior to flax-epoxy were observed. Dynamic-mechanical and thermogravimetric analysis revealed a favourable behaviour for ACC in terms of more diffuse thermal softening and increased resistance to thermal degradation. [Copyright &y& Elsevier]

Abstract: Polycaprolactone (PCL)/cellulose nanocomposites were prepared by mixing PCL with surface modified sisal nanowhiskers (CNW) and microfibrillated cellulose (MFC) extracted from sisal fibers. The influence of cellulosic nanoparticles on the crystallization behavior of PCL was investigated by differential scanning calorimetry. Isothermal crystallization data were modeled with Avrami’s kinetics, Lauritzen–Hoffman secondary nucleation theory and equilibrium melting points were determined with the Hoffman–Weeks method. The cellulose nanoparticles, acting as nucleating agents, drastically accelerate the crystallization of PCL while depressing its equilibrium melting by 9–10°C. The crystallization of MFC-nanocomposites is slightly faster than that of CNW-nanocomposites, in agreement with the slightly lower bulk activation energy for crystallization and nucleation parameter in the former. The results are discussed based on the differences of specific surface area and surface chemistry of nanoparticles, as well as the confinement phenomenon. [Copyright &y& Elsevier]