Pyrolysis is a promising method for converting biomass to biofuels. However, some of pyrolysis oil's physiochemical properties still limit its commercial applications. In this study, the autohydrolysis pretreatment at 175 ± 3 °C for 40 min was conducted to improve the resulting pine pyrolysis oil’s properties as a fuel. During autohydrolysis, deacetylation and decomposition of hemicellulose was observed by ion-exchange chromatography and Fourier transform infrared spectroscopy (FT-IR). In addition, the cleavage of lignin ether bonds was clearly determined by 13C cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR). Phosphitylation followed by 31P NMR analysis of the heavy oils gave detailed structural information of the hydroxyl groups; the results revealed that autohydrolysis pretreatment led to a reduction of carboxyl acids in the heavy oils generated at all three pyrolysis temperatures (400, 500, and 600 °C). The 31P NMR analysis also revealed that autohydrolysis pretreatment led to a reduction of condensed phenolic hydroxyl groups in the heavy oils produced at 600 °C. 1H-13C heteronuclear single-quantum correlation (HSQC) NMR analysis showed that at a pyrolysis temperature of 600 °C, the pretreated pine produced lower methoxy group constituents. Both 31P and HSQC NMR results indicated that autohydrolysis pretreatment increased levoglucosan yields in the bio-oils.

Novel bionanocomposite films have been prepared by depositing xylan onto cellulose nanowhiskers through a pH adjustment. Analysis of strength properties, water vapour transmission, transparency, surface morphology and thermal decomposition showed the enhancement of film performance. This provides a new green route to the utilization of biomass for sustainable biomaterials production.

Nanocomposite hydrogels were developed by cross-linking nanofibrillated cellulose with poly(methyl vinyl ether-co-maleic acid) and polyethylene glycol. The cross-linked hydrogels showed enhanced water absorption and gel content with the addition of nanocellulose. In addition, the thermal stability, mechanical strength, and modulus increased with an increase in the amount of nanocellulose in hydrogels, and this can be attributed to efficient cross-linking between the nanocellulose and the matrix. The addition of softwood nanocellulose showed much higher strength and strain properties in the hydrogels than with the addition of hardwood nanocellulose. The enhanced physical properties confirm that in situ cross-linking of nanofibrillated cellulose with the matrix polymer forms hydrogels that are not just blends of starting materials but are distinctively unique and formed by cross-linking interactions between the filler and matrix.Keywords: Gel content; Hydrogels; Nanofibrillated cellulose; Tensile property; Thermal stability; Water absorption;

•Sulfonated ECF bleached SW kraft pulp fibers were prepared.•SO3H content in fibers increased as the weight ratio of NaIO4: pulp was increased.•Fibers with SO3H of 371 to 501 μmol/g could be nanofibrillated easily.•Nanofibrillation was achieved in homogenizer at 70 MPa by one to four passes.•Nanofibrils are of website network structure, width of ∼20–50 nm and length of ˃1 μm.In this study, sulfonic acid groups were introduced to milled softwood (SW) bleached kraft fibers by oxidation and sulfonation with sodium periodate followed by sodium bisulfite under relatively mild conditions. The effect of variable amount of sulfonated groups on nanofibrillation of sulfonated cellulose samples was investigated. The cellulose samples, with contents of sulfonated groups of 371–501 μmol/g, were readily nanofibrillated by homogenization at relatively low pressure. These samples converted to viscous and transparent gels without clogging the homogenizer. By passing through the homogenizer one to four times, the transmittances of homogenized suspensions were up to 98%. SEM characterization of the homogenized and lyophilized fibril suspension indicates that the nanofibrillated fibrils are a network structure with lateral sizes of ∼15–45 nm and lengths ˃1 μm. The consecutive periodate oxidation and sulfonation with bisulfite was shown to be an effective pretreatment method to facilitate the nanofibrillation of softwood pulp cellulose and can be expectedly used with other cellulosic resources.

•Freeze–casting technique was used in the design of aligned porous nanochitin foams.•Chitin nanowhisker foams exhibited a thinner wall and more fine dendrites as compared to cellulose nanowhisker foams.•Continuous oriented lamellar with no apparent defects occurred at 0.8 wt% ChNs concentration.•The inter-lamellae spaces decreased with increasing content of the PVA binder.Structured biofoams with aligned porous structures were fabricated from nanosized chitin by employing a directional freeze–casting technique. The effects of the freezing conditions and slurry formulation on nanochitin foam morphology were investigated. The morphology of obtained foams was characterized using scanning electron microscopy (SEM). It was found that the pore structure of the obtained foams was a likewise of the ice crystals formed during the directional freezing. The results indicate that directional freeze–casting protocol can significantly influence the morphological features and microstructures of the obtained biofoams which could have numerous applications, including engineered carriers, scaffolds, filters and specifically as a template for potential multi-layered composites after infusion with a second phase.

The development of deuterated biomass is essential for effective neutron scattering studies on biomass, which can provide key insights into the complex biomass conversion processes. A method for optimized production of deuterated annual ryegrass (Lolium multiflorum) was developed by growing the plants in 50% D2O in perfused hydroponic chambers. Deuterium incorporation of 36.9% was found in the annual rye grown in 50% D2O. Further, deuterium incorporation of 60% was achieved by germinating the rye seedlings in H2O and growing in 50% D2O inside the perfusion chambers. The characteristics related to enzymatic hydrolysis such as biomass composition, degree of polymerization, and cellulose crystallinity were compared with its control protiated counterpart. The cellulose molecular weight indicated slight variation while hemicellulose molecular weights and cellulose crystallinity remain unaffected with the deuteration.

The carbonyl groups in pyrolysis oil have been reported to be responsible for the two most challenging properties with regard to the usage of pyrolysis oil – corrosion and aging problems; indeed, the carbonyl groups also bring huge difficulties for any required upgrading process. Therefore, a comprehensive and quantitative understanding of the structural information on these carbonyl groups is a challenging but crucial topic. However, owing to the highly complex nature of pyrolysis oil, how to quantitatively determine carbonyl groups appears to be very important. To the best of our knowledge, this is the first study that has used the 4-(trifluoromethyl)phenylhydrazine derivatization 19F NMR spectroscopy method for the quantitative analysis of carbonyl groups in various bio-oils. Different pyrolysis oils produced from various sources were analyzed after treatment with 4-(trifluoromethyl)phenylhydrazine followed by 19F NMR spectroscopy, and semiquantitative FT-IR spectroscopy, and were also quantitatively determined by the wet chemistry oximation method. The results indicated that the 19F NMR method can be regarded as more efficient (24 h vs. 48 h; single step vs. multiple steps) while being as reliable as the traditional oximation method.

Pseudo-lignin is formed during dilute acid pretreatment (DAP), particularly under high-severity conditions, and has been shown to significantly inhibit enzymatic hydrolysis of cellulose. To suppress its formation, DAP was modified by performing it under O2 or N2; adding surfactant (Tween-80) to the reaction mixture; or using a water–dimethyl sulfoxide (DMSO) mixture as reaction medium. Pseudo-lignin analysis showed that only the addition of DMSO to DAP reaction medium can effectively suppress pseudo-lignin formation. This was attributed to DMSO preferentially solvating and stabilizing 5-hydroxymethyl furfural (HMF) which is the key intermediate to form pseudo-lignin, thereby reducing the overall yield of pseudo-lignin. Furthermore, the addition of DMSO was shown not to reduce pseudo-lignin molecular weight or change any of its structural features significantly. Therefore, pseudo-lignin generated from aqueous DMSO DAP had similar inhibition properties as compared to that acquired from routine DAP at equal mass dosages. This study is the first demonstration that the amount of pseudo-lignin formed during DAP can be reduced, which contributes to further optimization of DAP technology.

Structured Abstract

To evaluate the inhibition effects of pseudolignin to enzymatic hydrolysis of cellulose in comparison to lignin, enzymatic mild acidolysis lignin (EMAL) was isolated from poplar after an 8 min pretreatment at 170 °C using 0.5% H2SO4. Fourier transform infrared (FT-IR) and 13C NMR characterization revealed that the poplar lignin was partially degraded during the pretreatment and did not contain detectable amounts of pseudolignin. Holocellulose was treated with varying amounts of pseudolignin and/or EMAL dissolved in p-dioxane and then dried. The treated and control holocellulose was then treated to a standard cellulase treatment, and the results from enzymatic hydrolysis of these samples showed that the dilute acid-pretreated lignin inhibited hydrolysis in the initial stage but had a negligible impact on the overall cellulose-to-glucose conversion yield. In contrast, pseudolignin significantly reduced the overall enzymatic conversion yield of cellulose to glucose. This study suggests that pseudolignin formation needs to be avoided because it is more detrimental to enzymatic hydrolysis of cellulose than dilute acid-pretreated lignin.Keywords: Dilute acid pretreatment; Holocellulose; Lignin; Poplar; Pseudolignin

Lignocellulosic biomass is the most abundant renewable resource for the potential replacement of fossil fuels, though to fully realize this vision, an improved understanding of the chemical structures of its components within the biomass and after bioprocessing is critical. In this study, we investigated the fate of isolated poplar lignin during autohydrolysis pretreatment at different temperatures and subsequently analyzed the structural changes by gel permeation chromatography, 13C–1H HSQC and phosphorylation/31P NMR. Our results suggested that an increase in temperature and time of autohydrolysis of lignin resulted in an increase in phenolic hydroxyl groups coupled with a decrease in aliphatic hydroxyl groups. This may be attributed to the cleavage of β-O-4 linkages via acidolysis. Molecular weight determination revealed that lignin depolymerization predominates over condensation. Our results also highlight that the cleavage of lignin side-chain units is relatively fast in lignin autohydrolysis compared to the autohydrolysis of biomass. This study provides an enhanced understanding of the fundamental autohydrolysis pretreatment lignin chemistry and will facilitate improved methodology to reduce biomass recalcitrance.

Highlights•Deuterium incorporation in bacterial cellulose studied by solution NMR.•Acetylated bacterial cellulose exhibited partial deuteration at C-6.•No significant alterations in bacterial cellulose structure due to deuteration.•The findings support possible use of deuterated bacterial cellulose in SANS.In vivo generated deuterated bacterial cellulose, cultivated from 100% deuterated glycerol in D2O medium, was analyzed for deuterium incorporation by ionic liquid dissolution and 2H and 1H nuclear magnetic resonance (NMR). A solution NMR method of the dissolved cellulose was used to determine that this bacterial cellulose had 85% deuterium incorporation. Acetylation and 1H and 2H NMR of deuterated bacterial cellulose indicated near equal deuteration at all sites of the glucopyranosyl ring except C-6 which was partly deuterated. Despite the high level of deuterium incorporation no significant differences in the molecular and morphological properties were observed for the deuterated and protio bacterial cellulose samples. The highly deuterated bacterial cellulose presented here can be used as a model substrate for studying cellulose biopolymer properties via future small angle neutron scattering (SANS) studies.Graphical abstract

Two potential biofuel resources, Douglas-fir and Loblolly pine bark, were subjected to extensive chemical and compositional analysis. The barks were initially extracted with dichloromethane, and the resulting extracted compounds were characterized by gas chromatography coupled with mass spectrometric analysis. Characterization of the major bark biocomponents indicated that Douglas-fir and Loblolly pine bark contained 22.5 and 13.2 % tannins, 44.2 and 43.5 % lignin, 16.5 and 23.1 % cellulose, and 7.6 and 14.1 % hemicellulose, respectively. Of particular interest is the high content of tannins and lignin, which make these barks excellent potential precursors for bio-oils and/or other value-added chemicals. 13C nuclear magnetic resonance (NMR) was used to characterize the chemical structure of the lignin and tannins. These samples were also analyzed by 31P NMR after phosphitylation of the hydroxyl groups in lignin and tannins. The NMR spectral data indicated that the lignin in both barks contained p-hydroxyphenyl (h) and guaiacyl (g) of lignin monomers with an h/g ratio of 10:90 and 22:78 for Douglas-fir and Loblolly pine bark, respectively. Gel permeation chromatography was used to analyze the molecular weight distributions of extracted tannins, isolated cellulose, and ball-milled lignin. The pyrolysis of Douglas-fir and pine bark at 500°C in a tubular reactor generated 48.2 and 45.2 % of total oil, of which the light oil contents are 14.1 and 20.7 % and heavy oil are 34.1 and 24.4 %. Similarly, fast pyrolysis at 375°C yielded 56.1 and 49.8 % of total oil for Douglas-fir and pine bark, respectively.

The torrefaction of Loblolly pine (Pinus taeda) was examined at 250 and 300 °C, to determine the effects of treatment temperatures on the chemical structure of the torrefied Loblolly pine. Solid-state cross-polarization/magic angle spinning (CP/MAS) 13C nuclear magnetic resonance (NMR) spectroscopy was used to characterize the torrefied and native Loblolly pine. The NMR results indicate that aryl-ether bonds in lignin were cleaved during the torrefaction. The methyl carbons in hemicellulose acetyl groups were no longer present after the torrefaction at 250 °C for 4 h, which is consistent with HPLC carbohydrate analysis of the torrefied wood which indicated that the hemicellulose fraction of pine was completely absent, whereas the cellulose and lignin remained largely intact. Under these conditions the torrefied wood has a relatively high energy yield of 81.29% and a HHV of 24.06 MJ kg−1. After torrefaction at 300 °C for 4 h, the cellulose and hemicellulose in the wood were completely eliminated, the residue contains enriched amounts of carbonyl groups, aromatic carbons and methoxyl groups, which represent complex condensed aromatics, these aromatics units were linked with aliphatic C–O and C–C bonds and the product has a very high HHV of 32.34 MJ kg−1.

A commercially available deuterated kale sample was analyzed for deuterium incorporation by ionic liquid solution 2H and 1H nuclear magnetic resonance (NMR). This protocol was found to effectively measure the percent deuterium incorporation at 33%, comparable to the 31% value determined by combustion. The solution NMR technique also suggested by a qualitative analysis that deuterium is preferentially incorporated into the carbohydrate components of the kale sample.

The ability to accurately and rapidly measure plant cell wall composition, relative monolignol content and lignin–hemicellulose inter-unit linkage distributions has become essential to efforts centered on reducing the recalcitrance of biomass by genetic engineering. Growing 13C enriched transgenic plants is a viable route to achieve the high-throughput, detailed chemical analysis of whole plant cell wall before and after pretreatment and microbial or enzymatic utilization by 13C nuclear magnetic resonance (NMR) in a perdeuterated ionic liquid solvent system not requiring component isolation. 1D 13C whole cell wall ionic liquid NMR of natural abundant and 13C enriched corn stover stem samples suggest that a high level of uniform labeling (>97%) can significantly reduce the total NMR experiment times up to ∼220 times. Similarly, significant reduction in total NMR experiment time (∼39 times) of the 13C enriched corn stover stem samples for 2D 13C–1H heteronuclear single quantum coherence NMR was found.

In this work, milled softwood (SW) bleached kraft fibers were crosslinked by esterification with poly(vinyl methyl ether-co-maleic acid) (PVMEMA) and polyethylene glycol (PEG). The effects of fiber length, crosslinking reaction time, and dosage of PVMEMA on water absorption and retention value (WAARV) for the crosslinked fibers were determined. The results show that as the softwood fiber length is mechanically decreased from 2.41 to 0.50 mm and employing a weight ratio of fiber to polymers equivalent to 1.00:1.28 the WAARV increased from 86.50 to 189.20 g/g. Analysis of the crosslinked fibers by SEM and light microscope indicated that the polymers and fibers form a crosslinked fibrous matrix. FT-IR spectroscopy was employed to detect the ester linkage between PVMEMA and PEG/SW kraft pulp fibers. The results suggested that the ester crosslinked pulps exhibit excellent water absorbent properties and have the potential of utilizing milled bleached SW kraft fibers, such as refiner dust or pulp fines, for novel water absorbent applications.Highlights► Cellulosics were crosslinked with poly(vinyl methyl ether-co-maleic acid) and PEG. ► As the cellulose fiber was decreased in length water absorption properties increased. ► Refined softwood and hardwood bleached kraft fiber showed similar hydrogel properties.

In this study, Populus trichocarpa was subjected to dilute acid pretreatment at varying pretreatment times. The three major components of lignocellulosic biomass, namely cellulose, hemicellulose and lignin, were isolated from the starting and dilute acid pretreated poplar. Gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) techniques were utilized to elucidate structural transformations of poplar during dilute acid pretreatment. The results demonstrated that the pretreatment dissolved hemicelluloses and disrupted structural features of lignin and polysaccharides. As revealed by NMR, the aryl-O-ether linkage (β-O-4) of lignin was extensively cleaved and lignin repolymerization occurred during pretreatment. The lignin was also observed to have a decrease in S/G ratio and methoxyl group content and these changes were accompanied with an increase in condensed lignin. The dilute acid pretreatment resulted in a reduction in molecular weight of cellulose and hemicellulose, while no prominent change of molecular weight was observed for lignin. The polydispersity index of cellulose appeared to increase initially within a short time of pretreatment (0.3–1 min) and start to decrease with longer pretreatment time during the bulk phase of chain scission (5.4–26.8 min). The DA pretreatment demonstrated no significant impact on the crystalline index (CrI) of cellulose particularly within the short time range of pretreatments examined in this study, with CrI remaining almost unchanged during the pretreatment time of 0.3–5.4 min and a slight increase observed as the pretreatment time extended to 8.5 and 26.8 min.

The formation of pseudo-lignin by the combination of carbohydrate and lignin degradation products has been proposed to be responsible for the increased Klason lignin content in biomass pretreated under acidic conditions. Direct evidence for the presence of pseudo-lignin has never been presented. The formation of additional lignin-like material may be detrimental to enzymatic hydrolysis due to the non-productive binding of enzymes with lignin. To investigate the chemistry of pseudo-lignin formation, dilute acid pretreatments were performed on delignified hybrid poplar biomass under conditions of varying severity. The results show a progressive increase in the Klason lignin content of the acid pretreated material with increasing pretreatment severity. NMR and FT-IR spectroscopic characterization shows the development of aliphatic, unsaturated and carbonyl carbon functionalities in the samples pretreated at higher severities. Given the very low Klason lignin content of the starting material, acid catalyzed dehydration of carbohydrates is responsible for the formation of pseudo-lignin.

The last decade has seen tremendous growth and interest in renewable energy and fuels aimed primarily at addressing issues of climate change, energy security, and rising energy costs. These efforts coupled with the demand for efficient utilization of biomass place a premium on the detailed analysis of the fundamental chemical structures of biomass, especially in light of the ever-increasing efforts to generate transgenic plants with reduced recalcitrance and altered lignin structure. This review examines the growing application of phosphitylation followed by 31P NMR to quantitatively analyze biomass lignin structures including guaiacyl, syringyl, guaiacyl with carbon substituents at the C5 position, catechol, p–hydroxyphenyl, aliphatic and carboxylic hydroxyl groups. The application of this methodology to provide a rapid analytical tool for lignin/biomass derived bio-oils and biodiesel precursors is also discussed. Utilizing lignin isolated from native and transgenic plants as well as from pretreatment and biological/thermal deconstruction processes, researchers have demonstrated that this technique has unique characterization capabilities which have broad applicability in the biofuels research community.

In this work the potential of organosolv treated Kanlow switchgrass for ethanol production was determined and the changes imparted to cellulose crystallinity and degree of polymerization (DP) along the course of enzymatic hydrolysis were assessed. The organosolv pretreatment yielded a substrate that was readily hydrolyzed by cellulases allowing 92.0% recovery of the glucan present in untreated switchgrass after 72 h of enzymatic hydrolysis. Cellulose crystallinity remained approximately constant after organosolv pretreatment and additionally during the course of enzymatic hydrolysis (8 h of enzymatic hydrolysis). The degree of polymerization decreased upon organosolv pretreatment. During enzymatic hydrolysis the DP decreased for the first two hours and thereafter remained approximately constant (4–8 hours). The polydispersity index showed a small increase along the course of enzymatic hydrolysis (0–8 hours). The obtained results indicated the occurrence of a “peeling off” type mechanism.

L-Leucine amino acid functionalized cellulose whiskers were synthesized via esterification reaction which comprised the reaction between Fmoc–L-leucine and cellulose whiskers and removal of Fmoc-protecting group. This strategy provides a direct, facile way to merge the properties of these biocompatible materials and offers the possibility to introduce biologically active building blocks in cellulose whiskers.

Comparative studies between the leaf and internode portions of switchgrass, Panicum virgatum L., were performed by compositional analysis and structural determination. GC-MS, ICP, and HPAEC-PAD were employed to analyze the chemical compositions of the fractionated switchgrass samples. Quantitative 13C NMR and CP/MAS 13C NMR techniques were employed to determine the structures of lignin and cellulose, respectively. These results indicated that the leaves and internodes differed chemically in the amounts of inorganic elements, hot-water extractives, benzene/ethanol extractives, carbohydrates, and lignin content. However, the ultrastructure of isolated cellulose was comparable between leaves and internodes. Ball-milled lignins isolated from leaves and internodes were found to have H/G/S ratios of 12.4/53.9/33.7 and 8.6/54.8/36.6, respectively.

Milled wood lignin samples from Loblolly pine stem wood, forest residue, and bark were isolated and characterized by quantitative 13C and 31P nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC) for molecular weight determination. Results from 13C NMR show the stem wood and forest residue samples have similar functional group contents. However, the bark has fewer methoxyl groups, β-O-4 structures, dibenzodioxocin, and side chains than the other two lignins. The bark lignin has the highest amounts of p-hydroxyphenyl (h) and C-5 condensed lignin, stem wood has the lowest, and the residue lies between. 31P NMR analysis indicates that bark lignin contains more C-5 substituted phenolics and fewer aliphatic hydroxyl groups than the lignin isolated from stem wood or residue. The molecular weight distribution analysis indicates the bark lignin has higher weight-average molecular weight (Mw) and polydispersity index than the lignin recovered from stem wood or residue.

Samples Alamo, Kanlow, GA993, and GA992 switchgrass, Panicum virgatum L., were partitioned into two morphological portions, leaves and internodes, and analyzed for chemical compositions in the previous study. These samples underwent a hydrothermal pretreatment, followed by cellulase and cellobiase treatment. Hydrothermal pretreatment was found to provide comparable gravimetric yields ranging from 48.1 to 51.4%. However, cellulose digestibility of the pretreated leaf portion of the switchgrass exhibited 32.5% greater glucose yield (77.4%) than that of the internode portion (44.9%). The carbohydrate profiles, cellulose crystal structure, and degree of polymerization (DP) of the cellulose were analyzed for native and pretreated leaves and internodes. The results demonstrated that pretreated leaves and internodes had similar chemical constituent profiles and chemical structure for cellulose and lignin but significant differences for the DP of α-cellulose. The lower DP of cellulose for the pretreated leaf portion of the switchgrass was attributed to be a factor for the enhanced cellulose digestibility in comparison with the internode portion.

To improve the bondability between clay filler and lignocellulosic fiber, Kaolin clay particles were modified using a starch−fatty acid complex method. The coating efficiency of starch on clay particle surfaces was investigated by measuring the dissolved starch in the supernatant. The experimental results indicated that more than 98% of the applied starch was precipitated onto the surface of the filler, and the resulting starch−fatty acid−clay composites had relatively good resistance against moderate shear force. The morphology, particle size, and ζ potential of the starch modified filler were also determined with scanning electron microscopy, Malvern particle size analyzer, and Malvern Zetasizer, respectively. An aqueous slurry of linerboard pulp containing 5−15 wt % modified fillers was used for handsheet preparation, and the effects of the addition of modified filler on the paper properties were studied. At a dosage of 10% of the modified filler (based on filler), the retention of the filler was higher than 75%. The strength properties of paper with starch modified fillers were improved by approximately 15% when compared against those of paper with unmodified fillers.

Diminishing fossil fuel resources as well as growing environmental and energy security concerns, in parallel with growing demands on raw materials and energy, have intensified global efforts to utilize wood biopolymers as a renewable resource to produce biofuels and biomaterials. Wood is one of the most abundant biopolymer composites on earth that can be converted into biofuels as well as used as a platform to produce bio-based materials. The major biopolymers in wood are cellulose, hemicelluloses, and lignin which account for >90% of dry weight. These polymers are generally associated with each other in wood cell walls resulting in an intricate and dynamic cell wall structure. This mini-review provides an overview of major wood biopolymers, their structure, and recent developments in their utilization to develop biofuels. Advances in genetic modifications to overcome the recalcitrance of woody biomass for biofuels are discussed and point to a promising future.

Over the past two decades, the use of biomass as a resource for biofuels and bioenergy has garnered much interest. The reduction in green house gas emissions of renewable fuels as compared to conventional fossil fuels, coupled with the sustainability of these technological approaches, has fostered increased research into this field. Switchgrass is a perennial grass native to North America, and as a feedstock for biofuels it has garnered much interest because of its high productivity, adaptability and potential ease of integration into existing agricultural operations. In order to maximize the use of switchgrass as an energy crop, the chemical constituents as well as the chemical processes involved in its conversion to biofuels need to be understood. The goal of this paper is to review the published work on the chemistry of switchgrass as it pertains to biofuel production including elemental composition, chemical composition, biopolymer constituents and their structure. In addition, the impacts of these chemical constituents on the biological conversion to ethanol and pyrolysis oils are summarized.

Milled wood lignin samples from untreated Loblolly pine, post-ethanol organosolv pretreatment, and ethanol organosolv dissolved lignin were isolated and characterized by quantitative 13C and 31P nuclear magnetic resonance (NMR) spectroscopy. β-O-4 linkages are the predominant substructures present in lignin from the starting material, as well as after the pretreatment. During organosolv treatment of Loblolly pine, acid-catalyzed cleavage of β-O-4 linkages and ester bonds were the major mechanisms of lignin cleavage. This degradative pathway results in the formation of a dissolved ethanol organosolv lignin, which is more condensed and has a lower molecular weight than the starting lignin. The residual lignin isolated from the solid pretreated residue was also more condensed. Results from quantitative 13C and 31P NMR show that the residual and dissolved lignin fractions after pretreatment have a higher abundance of phenols and carboxylic acids and lower aliphatic carbon content and may be suitable as antioxidants or other value-added lignin products.

Detailed chemical structural elucidation of ethanol organosolv lignin (EOL) of Buddleja davidii was performed to determine the fundamental structure released from an ethanol organosolv pretreatment (EOP). Several nuclear magnetic resonance (NMR) techniques were used to analyze the structure of EOL, including quantitative 13C, 31P NMR, and qualitative DEPT-135 13C, 2D 1H−13C correlation NMR. As revealed by NMR, the aryl-O-ether linkage (β-O-4′) of lignin was extensively cleaved via homolysis during pretreatment and led to the formation of stilbene structures. Other linkages, such as resinol (β-β′) and phenylcoumaran (β-5′), were resistant to degradation. The high degree of condensation of EOL indicated that condensation reactions occurred but did not impede the delignification efficiency of EOP. Both guaiacyl and syringyl lignin were found to be reactive toward condensation during pretreatment. The results from gel-permeation chromatography showed that the degree of polymerization (DP) of lignin significantly decreased by ∼85%, facilitating lignin solubilization in ethanol.

Ethanol organosolv pretreatment was performed on Buddleja davidii to evaluate this bioresource as a potential feedstock for bioethanol production. B. davidii was pretreated and delignified, while 85% of the glucose content of the untreated material was retained in the pretreated solid fraction. The enzymatic hydrolysis showed that organosolv pretreatment produced solid substrates that were readily digestible by cellulases. Gel-permeation chromatography was used to determine the degree of polymerization (DP) of cellulose, and solid-state cross polarization/magic angle spinning 13C NMR experiments were conducted to study the changes in crystallinity and ultrastructure of cellulose. The results showed a decrease in DP along with an increase in the relative proportions of para-crystalline and amorphous cellulose and a decrease in cellulose Iα and Iβ. Removal of lignin and hemicellulose, reduction in DP, and decrease in the crystalline allomorphs (Iα and Iβ) increased the amenability of the biomass to enzymatic degradation.

Water-soluble sulfonated cellulose (SC) samples were synthesized by oxidizing hardwood kraft pulp with sodium periodate followed by the sulfonation reaction with sodium bisulfite. Six levels of oxidation/sulfonation were obtained by using different mmols (0.93–4.67) of periodate per gram of pulp. The aldehyde and sulfonic acid contents, surface morphology, and water solubility property of these treated fibers were characterized. It was found that carbonyl group content increased with the periodate charge and so did the sulfonic acid content in subsequent sulfonation step. Scanning electron microscopy images showed a significant change in surface morphology of the sulfonated samples. Solubility of sulfonated cellulose in water was determined from 1H NMR spectra and a solubility of 28.57 g/L was found when cellulose was oxidized with 4.67 mmol periodate per gram cellulose followed by the sulfonation reaction.The initial amount of sodium periodate used for cellulose periodation significantly affects the solubility of the final sulfonated cellulose, determined by NMR analysis.

Copper(II) acetate proves to be an active catalyst for ultrasound-promoted conversion of aldoximes into nitriles. This dehydration reaction was carried out in acetonitrile under ambient conditions to provide nitriles with moderate tolerance toward water, which allows one-pot synthesis of a nitrile from an aldehyde with minimal purification.Ultrasound-promoted copper(II)-catalyzed dehydration of aldoximes in acetonitrile to give nitriles under ambient conditions.

Ethanol organosolv pretreatment was performed on Loblolly pine to enhance the efficiency of enzymatic hydrolysis of cellulose to glucose. Solid-state 13C NMR spectroscopy coupled with line shape analysis was used to determine the structure and crystallinity of cellulose isolated from pretreated and enzyme-hydrolyzed Loblolly pine. The results indicate reduced crystallinity of the cellulose following the organosolv pretreatment, which renders the substrate easily hydrolyzable by cellulase. The degree of crystallinity increases and the relative proportion of para-crystalline and amorphous cellulose decreases after enzymatic hydrolysis, indicating preferential hydrolysis of these regions by cellulase. The structural and compositional changes in this material resulting from the organosolv pretreatment and cellulase enzyme hydrolysis of the pretreated wood were studied with solid-state CP/MAS 13C NMR spectroscopy. NMR spectra of the solid material before and after the treatments show that hemicelluloses and lignin are degraded during the organosolv pretreatment.Changes in the ordering of cellulose in Loblolly pine with organosolv pretreatment and enzymatic hydrolysis.

Nanocomposites were developed by cross-linking cellulose nanowhiskers with poly(methyl vinyl ether-co-maleic acid) and polyethylene glycol. Nuclear magnetic resonance (NMR) studies showed cross-linking occurs between the matrix and cellulose nanowhiskers via an esterification reaction. Proton NMR T2 relaxation experiments provided information on the mobility of the polymer chains within the matrix, which can be related to the structure of the cross-linked nanocomposite. The nanocomposite was found to consist of mobile chain portions between cross-linked junction points and immobilized chain segments near or at those junction points, whose relative fraction increased upon further incorporation of cellulose nanowhiskers. Atomic force microscopy images showed a homogeneous dispersion of nanowhiskers in the matrix even at high nanowhisker content, which can be attributed to cross-linking of the nanowhiskers in the matrix. Relative humidity conditions were found to affect the mechanical properties of the composites negatively while the nanowhiskers content had a positive effect. It is expected that the cross-links between the matrix and the cellulose nanowhiskers trap the nanowhiskers in the cross-linked network, preventing nanowhisker aggregation subsequently producing cellulose nanocomposites with unique mechanical behaviors. The results show that in situ cross-linking of cellulose nanowhiskers with a matrix polymer is a promising route to obtain nanocomposites with well dispersed nanowhiskers, tailored nanostructure, and mechanical performance.

A novel qualitative method has been developed for the determination of the various types of hydroxyl groups present in biodiesel production streams. The use of 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane as a phosphitylation reagent for quantitative 31P NMR analysis of the hydroxyl groups in biodiesel process samples has been fully developed. This experimental protocol allows for rapid analysis of biodiesel mixtures of alcohols, fatty acids, glycerol, and mono- and disubstituted glycerides. Characteristic chemical shift ranges were developed with model compounds and used to fully characterize the conversion of triglyceride samples to biodiesel for two commercial production processes.

The goal of this work is to produce nanocomposite film with low oxygen permeability by casting an aqueous solution containing xylan, sorbitol and nanocrystalline cellulose. The morphology of the resulting nanocomposite films was examined by scanning electron microscopy and atomic force microscopy which showed that control films containing xylan and sorbitol had a more open structure as compared to xylan-sorbitol films containing sulfonated nanocrystalline cellulose. The average pore diameter, bulk density, porosity and tortuosity factor measurements of control xylan films and nanocomposite xylan films were examined by mercury intrusion porosimetry techniques. Xylan films reinforced with nanocrystalline cellulose were denser and exhibited higher tortuosity factor than the control xylan films. Control xylan films had average pore diameter, bulk density, porosity and tortuosity factor of 0.1730 µm, 0.6165 g/ml, 53.0161% and 1.258, respectively as compared to xylan films reinforced with 50% nanocrystalline cellulose with average pore diameter of 0.0581 µm, bulk density of 1.1513 g/ml, porosity of 22.8906% and tortuosity factor of 2.005. Oxygen transmission rate tests demonstrated that films prepared with xylan, sorbitol and 5%, 10%, 25% and 50% sulfonated nanocrystalline cellulose exhibited a significantly reduced oxygen permeability of 1.1387, 1.0933, 0.8986 and 0.1799 cm3·µm/m2·d·kPa respectively with respect to films prepared solely from xylan and sorbitol with a oxygen permeability of 189.1665 cm3·µm/m2·d·kPa. These properties suggested these nanocomposite films have promising barrier properties.

A novel nanocomposite of rigid polyurethane foam was prepared by the polymerization of a sucrose-based polyol, a glycerol-based polyol and polymeric methylene diphenyl diisocyanate in the presence of cellulose whiskers. The cell morphology of the resulting foams was examined by scanning electron microscopy which showed both the pure foam and the nanocomposite foam had homogeneous cell dispersion and uniform cell size of approximately 200 μm. Analysis of the foams by Fourier transform infrared (FT-IR) spectroscopy indicated that both samples exhibited signals attributed to the polyurethane including the NH stretching and bending vibrations at 3320 cm−1 and 1530 cm−1, the OC=O vibration at 1730 cm−1 and the CO-NH vibration at 1600 cm−1. FT-IR analysis of the nanocomposite indicated that cellulose whiskers were crosslinked with the polyurethane matrix as the signal intensity of the OH stretch at 3500 cm−1 was significantly reduced in comparison to the spectral data acquired for a control sample prepared from the pure polyurethane foam mixed with cellulose whiskers. According to ASTM standard testing procedures, the tensile modulus, tensile strength and yield strength of the nanocomposite foam were found to be improved by 36.8%, 13.8% and 15.2%, and the compressive modulus and strength were enhanced by 179.9% and 143.4%, respectively. Dynamic mechanical analysis results testified the improvements of mechanical properties and showed a better thermal stability of the nanocomposite foam.

A bi-solvent system consisting of perdeuterated pyridinium molten salt and DMSO-d6 (dimethyl sulfoxide-d6) has been developed for direct dissolution and nuclear magnetic resonance (NMR) analysis of plant cell walls, which will shed a new light on efficient detailed structure of the plant cell walls and benefit lignin engineering for biofuel and biomaterial research.

Pyrolysis chemistry of alkaline-treated loblolly pine is investigated in this study. The pyrolysis experiments were accomplished under an argon atmosphere at 200−400 °C, to determine the effect of alkaline treatment on the char formation. Solid-state cross-polarization/magic angle spinning (CP/MAS) 13C nuclear magnetic resonance (NMR) spectroscopy was used to characterize the chars of the treated and untreated loblolly pine. These studies showed that, in the samples treated with NaOH, there is a shift in the chemical composition of the thermally modified char from cellulosic/hemicellulosic structures to more aryl C structures. At 300 °C, carbohydrate peaks were still present in the char of untreated wood but not in the char of the alkaline-treated wood. This indicated that the addition of NaOH enhanced the thermal degradation of the sugars in the pine sawdust. Our studies also showed that there was an emergence of an aliphatic peak around 12 ppm in the treated pine, which is absent in the spectra of the untreated pine. In addition to the relative increase in aryl and aliphatic C species, there is also an increase in the signals seen for the carbonyl species centered around 210 ppm at the higher end of the temperature range in this study for the treated samples. This investigation showed that solid-state NMR provided a facile methodology to investigate the types of changes that occur to wood chars during pyrolysis.

A compositional analysis was performed on Buddleja davidii to determine its general biomass characteristics and provide detailed analysis of the chemical structures of its cellulose and lignin using NMR. B. davidii is a new potential lignocellulosic bioresource for producing bioethanol because it has several attractive agroenergy features. The biomass composition of B. davidii is 30% lignin, 35% cellulose, and 34% hemicellulose. Solid-state CP/MAS 13C NMR showed that 33% of the cellulose is para-crystalline and 41% is at inaccessible surfaces. Both quantitative 13C and 31P NMR were used to examine the structure of lignin. The lignin was determined to be guaiacyl and syringyl with an h:g:s ratio of 0:81:19.

Independent down-regulation of genes encoding p-coumarate 3-hydroxylase (C3H) and hydroxycinnamoyl CoA:shikimate/quinate hydroxycinnamoyl transferase (HCT) has been previously shown to reduce the recalcitrance of alfalfa and thereby improve the release of fermentable sugars during enzymatic hydrolysis. In this study, ball-milled lignins were isolated from wild-type control, C3H, and HCT gene down-regulated alfalfa plants. One- and two-dimensional nuclear magnetic resonance (NMR) techniques were utilized to determine structural changes in the ball-milled alfalfa lignins resulting from this genetic engineering. After C3H and HCT gene down-regulation, significant structural changes had occurred to the alfalfa ball-milled lignins compared to the wild-type control. A substantial increase in p-hydroxyphenyl units was observed in the transgenic alfalfa ball-milled lignins as well as a concomitant decrease in guaiacyl and syringyl units. Two-dimensional 13C–1H heteronuclear single quantum coherence correlation NMR, one-dimensional distortionless enhancement by polarization transfer-135, and 13C NMR measurement showed a noteworthy decrease in methoxyl group and β-O-4 linkage contents in these transgenic alfalfa lignins. 13C NMR analysis estimated that C3H gene down-regulation reduced the methoxyl content by ~55–58% in the ball-milled lignin, while HCT down-regulation decreased methoxyl content by ~73%. The gene down-regulated C3H and HCT transgenic alfalfa lignin was largely a p-hydroxyphenyl (H) rich type lignin. Compared to the wild-type plant, the C3H and HCT transgenic lines had an increase in relative abundance of phenylcoumaran and resinol in the ball-milled lignins.

A standard two-step dilute sulfuric acid pretreatment was performed on Loblolly pine to enhance the overall efficiency of enzymatic deconstruction of woody biomass to monomeric sugars. The structure of milled wood lignin and cellulose isolated from the untreated and acid-treated biomass was studied in detail. Solid-state 13C NMR spectroscopy coupled with line shape analyses has been employed to elucidate cellulose crystallinity and ultrastructure. The results indicate an increase in the degree of crystallinity and reduced relative proportion of less ordered cellulose allomorphs following the acid pretreatment. This increase was attributed to a preferential degradation of amorphous cellulose and less ordered crystalline forms during the high temperature pretreatment. Milled wood lignin structural elucidation by quantitative 13C and 31P NMR reveals an increase in the degree of condensation of lignin due to the pretreatment. The increase in degree of condensation is accompanied by a decrease in β-O-4 linkages which were fragmented and recondensed during the high temperature acid-catalyzed reactions.

The one-pot synthesis of 1,4-naphthoquinones by the Diels–Alder reaction of dienes with para-quinones generated in situ with laccase (EC 1.10.3.2, p-diphenol:dioxygen oxidoreductase) in an aqueous medium was developed in this study. The para-quinones were generated in situ by the laccase oxidation of the corresponding 1,4-hydroquinones and subsequently underwent the Diels–Alder reaction with dienes, and further oxidation to finally generate 1,4-naphthoquinones, in good yields. This reaction methodology provides unique green chemistry synthesis for isolation of the naphthoquinones, and without relying on organic solvents or hazardous heavy metal reagents. In this paper, the effects of laccase dose, temperature, and substrate sensitivity on the overall reaction were investigated.

A practical procedure for synthesizing cellulose nanospheres with sizes ranging from 60 to over 570 nm was developed. This methodology provides a near linear relationship between cellulose nanoparticle size and treatment time. The hydrolyzed nanocelluloses are predominantly cellulose II polymorphic crystalline structure and relatively uniform in particle size.

Future developments in cellulosic materials are predicated by the need to understand the fundamental interactions that occur at cellulose fibre interfaces. These interfaces strongly influence the material properties of fibre networks and fibre reinforced composites. This study takes advantage of fluorescence resonance energy transfer (FRET) and fluorescence microscopy to image cellulose interfaces. Steady-state epi-fluorescence microscopy suggests that energy transfer from coumarin dyed fibres to fluorescein dyed fibres is occurring at the fibre–fibre interface. The FRET response for natural spruce fibre interfaces is distinctly different from that observed in synthetic viscose fibres. This approach constitutes a novel methodology for the characterization of soft material interfaces on the molecular scale, and represents a major opportunity for advancing the understanding of fibrous network structures.

A series of one-stage oxygen delignification treatments with a softwood (SW) kraft pulp were studied employing 0.0–0.5% of a bismuth ruthenium pyrochlore oxide catalyst. The results demonstrated that a 0.09–0.18% charge of catalyst in an oxygen stage provided a 52.2–116.0% increase of carboxylic acid groups in the cellulosic component of kraft pulps without a significant decrease in fiber viscosity. A 3-factor at 3-level (L933) orthogonal experimental design was used to identify the main factors influencing acid group formation in pulp carbohydrates. The relative significance of experimental parameters for polysaccharide acid group formation was the molar equivalent NaOH, oxygen pressure, and finally, reaction temperature under the experimental conditions studied. The optimized reaction parameters for fiber charge development were shown to be 85–100 °C, 2.5% NaOH, and 800–960 kPa oxygen pressure. Pulps with higher fiber carboxylic acid content introduced by catalytic oxidation during oxygen delignification yielded a 10.9–33.7% increase in fiber charge after elemental chlorine free (ECF) pulp bleaching. The enhanced fiber charge resulted in 6.7–17.1% increase in paper sheet tensile index at comparable pulp viscosity.A 0.09–0.18% of bismuth ruthenium pyrochlore oxide employed during an oxygen stage resulted in 52.2–116.0% increase of carboxylic groups in the polysaccharides of oxygen delignified kraft pulps without significantly decreasing pulp viscosity.

Three closely related cellulosic acrylic latex films were prepared employing acacia pulp fibers, cellulose whiskers and nanocellulose balls and their respective strength properties were determined. Cellulose whisker reinforced composites had enhanced strength properties compared to the acacia pulp and nanoball composites. AFM analysis indicated that the cellulose whisker reinforced composite exhibited decreased surface roughness.

Abstract

Biomass represents an abundant carbon-neutral renewable resource for the production of bioenergy and biomaterials, and its enhanced use would address several societal needs. Advances in genetics, biotechnology, process chemistry, and engineering are leading to a new manufacturing concept for converting renewable biomass to valuable fuels and products, generally referred to as the biorefinery. The integration of agroenergy crops and biorefinery manufacturing technologies offers the potential for the development of sustainable biopower and biomaterials that will lead to a new manufacturing paradigm.

The relationship between the surface chemistry of cellulosic fibers treated with an atmospheric cold plasma generated by dielectric-barrier discharge and recently discovered improvements in wet-strength and wet-stiffness was evaluated. ESCA characterization of cellulosic fibers indicates that treated fiber surfaces undergo selective oxidation, degradation, and removal of extractives and other contaminants. Fiber wettability in water increases with low dielectric-barrier discharge treatment (1.0 kW m−2 min), but diminishes with increased treatment intensity (5.0 kW m−2 min). This is related to changes in the polar and dispersive components of surface energy as determined by dynamic contact angle analysis. ESCA, combined with analysis of wettability and wet-strength properties, reveals that reductions in surface energy at increased treatment levels occur due to oxidative reactions.

Fully bleached softwood kraft pulps were hydrolyzed with cellulase (1,4-(1,3:1,4)-β-d-glucan 4-glucano-hydrolase, EC 3.2.1.4) from Trichoderma reesei. Supra-molecular structural features of cellulose during enzymatic hydrolysis were examined by using CP/MAS 13C NMR spectra in combination with line-fitting analysis. Different types of cellulose allomorphs (cellulose Iα, cellulose Iβ, para-crystalline) and amorphous regions were hydrolyzed to a different extent by the enzyme used. Also observed was a rapid initial phase for hydrolysis of regions followed by a slow hydrolysis phase. Cellulose Iα, para-crystalline, and non-crystalline regions of cellulose are more susceptible to enzymatic hydrolysis than cellulose Iβ during the initial phase. After the initial phase, all the regions are then similarly susceptible to enzymatic hydrolysis.

•Access to cellulose by cellulase limits the efficiency of enzymatic hydrolysis.•Access to cellulose is mainly through the pores in the cell wall rather than external surface area.•Different pretreatment effects cellulose accessibility to different extent through different mechanisms.•Lignin and hemicellulose plays important role in effecting cellulose accessibility.•Accurate assess cellulose accessibility needs multiple analytical techniques.Cellulose accessibility has been proposed as a key factor in the efficient bio-conversion of lignocellulosic biomass to fermentable sugars. Factors affecting cellulose accessibility can be divided into direct factors that refer to accessible surface area of cellulose, and indirect factors referring to chemical composition such as lignin/hemicellulose content, and biomass structure-relevant factors (i.e. particle size, porosity). An overview of the current pretreatment technologies special focus on the major mode of action to increase cellulose accessibility as well as multiple techniques that could be used to assess the cellulose accessibility are presented in this review. The appropriate determination of cellulose accessibility before and after pretreatment can assist to understand the effectiveness of a particular pretreatment in overcoming lignocellulosic recalcitrance to improve substrate enzymatic digestibility.Download high-res image (371KB)Download full-size image

This study demonstrates the potential of laccase-facilitated grafting of amino acids to high-lignin content pulps to improve their physical properties in paper products. Research studies have recently reported that increases in anionic fiber charge can improve strength properties of paper. In an effort to increase carboxylic acid groups, we developed a unique two-stage laccase grafting protocol in which fibers were initially treated with laccase followed by grafting reactions with amino acids. The bulk acid group content was measured, and a variety of amino acids including glycine (Gly), phenylalanine (Phe), serine (Ser), arginine (Arg), histidine (His), alanine (Ala), and aspartic acid (Asp) were examined. The effects of optimizing laccase dose, and amino acid structures, on fiber modification chemistry were studied. Histidine provided the best yield of acid groups on pulp fiber, and was used for the preparation of handsheets for physical strength testing. Laccase-histidine treated pulp showed an increase in strength properties of the resulting paper.