Shaobo Pan

High Shear Homogenization of Lignin to Nanolignin and Thermal Stability of Nanolignin‐Polyvinyl Alcohol Blends

A new method to prepare nanolignin using a simple high shear homogenizer is presented. The kraft lignin particles with a broad distribution ranging from large micron- to nano-sized particles were completely homogenized to nanolignin particles with sizes less than 100 nm after 4 h of mechanical shearing. The (13) C nuclear magnetic resonance (NMR) and (31) P NMR analysis showed that there were no major changes in the chemical composition between the starting kraft lignin particles and the nanolignin obtained after 4 h of mechanical treatment. The nanolignin particles did not show any change in molecular weight distribution and polydispersity compared to the original lignin particles. The nanolignin particles when used with polyvinyl alcohol (PVA) increased the thermal stability of nanolignin/PVA blends more effectively compared to the original lignin/PVA blends.

Preparation of aligned porous chitin nanowhisker foams by directional freeze–casting technique

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.

Thermo-responsive and fluorescent cellulose nanocrystals grafted with polymer brushes

Cellulose nanocrystals (CNCs) grafted with fluorescent and thermo-responsive poly(N-isopropylacrylamide) (PNIPAAM) brushes were prepared via surface-initiated activators generated by electron transfer for atom transfer radical polymerization (SI-AGET-ATRP) in the CH3OH–H2O mixing solvent with different volume ratios. The successful grafting was supported by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) measurements. Gravimetric analysis plus 1H NMR and gel permeation chromatography (GPC) measurements showed that there was an increase in the monomer conversion and molecular weight of polymer brushes with increasing H2O proportion of the solvent system. The variation trend of graft length was further evidenced by the gradual change of decomposition and glass transition temperatures of the surface-grafted CNCs. A large scale of chain transfer occurred on the surface of CNCs in view of the minute quantity of free polymers generated by a sacrificial initiator. Free polymers cannot be used as a substitute to characterize grafted polymers in terms of the big difference between their molecular weights. The obtained surface-grafted CNCs showed thermo-enhanced fluorescence owing to the thermal-driven chain dehydration of the grafted PNIPAAM brushes.

Freeze-casting of cellulose nanowhisker foams prepared from a water-dimethylsulfoxide (DMSO) binary mixture at low DMSO concentrations

Porous cellulose nanowhisker-based foams with a lamellae-like channel structure were fabricated by a novel freeze-casting technique using a water-dimethyl sulfoxide (DMSO) binary solvent mixture. With the incorporation of a 0.5–1.5% of DMSO the pore morphology of the materials can be controlled and the foams show strongly improved mechanical properties as determined by compression tests.

Preparation and characteristics of cellulose nanowhisker reinforced acrylic foams synthesized by freeze-casting

Directional freeze-casting of acrylic latex with a cellulose nanowhisker (CNW) suspension was investigated as a novel technique for preparing an acrylic-based nanocomposite foam. Compared with the control acrylic foam, the nanocomposites showed significantly improved mechanical and thermal properties, which were mainly due to the oriented and continuous channel architectures and high functionality of CNWs.

Enhancement of nanofibrillation of softwood cellulosic fibers by oxidation and sulfonation.

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.

19 F NMR spectroscopy for the quantitative analysis of carbonyl groups in bio-oils

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.

The use of combination of zeolites to pursue integrated refined pyrolysis oil from kraft lignin

A mixture of Y and M type zeolites were applied to pyrolyze kraft softwood (SW) lignin with the objective of studying the combination effect of different types of zeolite on pyrolysis. The chemical structures of the subsequent pyrolysis oils were examined. Nuclear Magnetic Resonance (NMR) spectroscopy including 13C, 31P of phosphitylated bio-oils, Heteronuclear Single-Quantum Correlation (HSQC)-NMR, and Gel Permeation Chromatography (GPC) were used to characterize the pyrolysis oils. The yields of pyrolysis products (light oil, heavy oil and char) from the zeolites combination ‘Y + M’ catalyzed pyrolysis ranged between the pyrolysis oil yields from zeolite Y or M catalyzed pyrolysis. 31P NMR analysis of the phosphitylated bio-oils revealed that the mixture of ‘Y + M’ during pyrolysis could decrease the carboxyl groups by 84%, which is close to the effect of the M zeolite. The yields of hydroxyl groups and other functional groups in the ‘Y + M’ generated bio-oil was between the individual Y and M generated oils. The molecular weight of the pyrolysis oil using a zeolite mixture of ‘Y + M’ was similar to the individual zeolite Y assisted pyrolysis. These results show that the zeolite mixture of ‘Y + M’ manifests additive characteristics for pyrolysis.