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Cellulose nanofibers (CNFs) have exceptional mechanical and thermal properties, but the use of these materials to reinforce polyolefins is challenging. In the present study, ethanol, acetone, isopropyl alcohol (IPA) and water were used as dispersion media for alkenyl succinic anhydride-modified CNFs (ACNFs). Masterbatches were prepared from these ACNFs wetted in the various liquids and then melt-compounded with high-density polyethylene (HDPE) using a twin-screw extruder, followed by injection-molding. The morphologies of the resulting HDPE/ACNF composites were characterized using optical and electron microscopy, and the rheological and mechanical properties of these composites were also evaluated. The results showed that the storage and loss moduli as well as the tensile moduli and strength of the composites produced using the organic liquids were higher than those of the composite made using water, owing to the better dispersion of ACNFs in the HDPE matrix in the former. This improved dispersion would be expected to increase the contact area between the ACNFs and the matrix and to enhance the orientation of the HDPE molecules. IPA was found to give the highest tensile modulus and strength among the organic liquids used in this study. The tensile modulus and strength of the composite containing ACNFs produced from IPA were, respectively, four times and two times higher than those of the neat HDPE. IPA is a relatively non-toxic, inexpensive compound, and so could be readily adopted for industrial scale processing.

The use of a combination of calcium carbonate (CaCO3) and alkenyl-succinic-anhydride (ASA)-modified microfibrillated cellulose (AMFC) as a filler for high-density polyethylene (HDPE) has been investigated. AMFC and CaCO3 were mixed with HDPE using a twin-screw extruder, and the resulting composites were injection molded. Observations by X-ray computed tomography, phase-contrast microscopy, and energy dispersive X-ray spectrometry confirm that AMFC is homogenously dispersed in HDPE as a result of the alkenyl chains being incorporated on the surface of the microfibrillated cellulose. CaCO3 is also well dispersed in HDPE when mixed with AMFC. The combination of CaCO3 and AMFC results in high mechanical reinforcement of HDPE, and the composite has a tensile modulus that is almost 120% higher than that of neat HDPE. A melt rheological study revealed formation of a network consisting of AMFC and CaCO3 in HDPE. Microfibrillated cellulose treated with ASA acts not only as reinforcement for HDPE, but also as a dispersant of inorganic fillers, such as CaCO3.

Kraft pulp is the most common and economically advantageous raw material for making cellulose nanofibers (CNFs). However, when kraft pulp is subjected to mechanical fibrillation, unfibrillated pulp always remains, even though the pulp is undried. In this study, the effect of the kraft pulping process on the fibrillation of undried pulp was studied. The fibrillation ability was compared with that of undried pulp prepared using Wise method and alkaline treatment. Suspensions of undried pulps were mechanically fibrillated with a high-speed blender for different durations. The degree of fibrillation of pulps was evaluated using sedimentation, morphologies from field emission scanning electron microscopy, specific surface area, and water retention values. Every analysis showed that undried, kraft-based pulp was less fibrillated than undried, wise-based pulp. These results suggested that the kraft cooking process at high temperature hindered the fibrillation of pulp. This might be related to the aggregation occur in cellulose.

The dry-pulp direct-kneading method is an industrially viable, low-energy process to manufacture cellulose nanofiber (CNF) reinforced polymer composites, where chemically modified pulps can be nanofibrillated and dispersed uniformly in the polymer matrix during melt-compounding. In this study, cellulose fibers with different sizes, ranging from surface-fibrillated pulps with 20 µm in width to fine CNFs with 20 nm in width were prepared from softwood bleached kraft pulps (NBKPs) using a refiner and high-pressure homogenizer (HPH). These cellulose fibers were modified with alkenyl succinic anhydride (ASA), and then dried. The dried ASA-treated cellulose fibers were used as a feed material for melt-compounding in the dry-pulp direct kneading method to fabricate CNF reinforced high-density polyethylene (HDPE). When surface-fibrillated pulps were employed as a feed material, the pulps were nanofibrillated and dispersed uniformly in the HDPE matrix during the melt-compounding, and the composites had much better properties (i.e., much higher tensile modulus and strength and much lower coefficient of thermal expansion) than the composites produced using the pulps without pre-fibrillation. However, when CNFs were used as a feed material, the CNFs were shortened and agglomerated during the melt-compounding, thus deteriorating the properties of the composites. The study concludes that the pre-fibrillation of pulps had a significant impact on the morphology and properties of the composites. Unexpectedly, the surface-fibrillated pulp, which can be produced cost-effectively using a refiner at an industry scale, was a more suitable form than the CNF as a feed material for melt-compounding in the dry-pulp direct kneading method.

For ground pulp (GP) utilization in wood fiber composites as reinforced material, its thermal behavior is relevant. The contribution of lignin to thermal performance of GP from Pinus densiflora was the focus of the present study. Dimeric lignin model compounds and isolated milled wood lignins (MWLs) from three sources were submitted for thermogravimetric analysis (TGA). The temperatures leading to 1% weight loss (T per 1% WL) for the material were determined. The thermal stability of β-O-4 models was the lowest. Among the MWLs, the abaca MWL with its high β-O-4 content was the least thermostable. An acetylated nonphenolic β-O-4 lignin model compound showed that acetylation improves the thermal stability of this type of dimeric models. The acetylation of benzylic OH groups in β-O-4 linkages is especially relevant for the thermal resistance, which was also shown based on pre-acetylated benzylic OH groups in the GP before the total acetylation.

We report an integrated production process that simultaneously nanofibrillates dried pulp and uniformly disperses cellulose nanofibers (CNFs) in resins. Refiner-treated pulp were modified using alkenyl succinic anhydride (ASA) in N-Methyl-2-pyrrolidone (NMP). The ASA treated pulp with DS 0, 0.22, 0.43 and 0.57 was mixed with maleic anhydride-grafted polypropylene (MAPP) powder, CaCO3 and high density polyethylene (HDPE) powder (pulp content: 10 wt%). The mixture was melt-extruded at 140 °C with HDPE. The dumbbell-shaped specimens were prepared using injection molding. The SEM images of refiner-treated pulp (DS 0.43) and previously nanofibrillated CNFs (DS 0.44) using a bead mill as a comparison, both of which were extracted from the melt compounded composites, showed comparable degrees of nanofibrillation. The highest mechanical reinforcing efficiency was obtained at DS 0.43, which was shown to exhibit the most fibrillated morphology. The tensile modulus increased from 1.08 GPa for neat HDPE, to 3.46 GPa. The tensile strength also increased from 23 MPa (neat HDPE) to 56 MPa. The mechanical properties were very similar to the bead mill-fibrillated CNF-reinforced composite. This is the first report of nanofibrillation of dried pulp with uniform CNF dispersion into hydrophobic HDPE. We have termed the process the Pulp Direct-Kneading Method.

The acetylation behavior of xylan and cellulose in kraft pulp (KP) was investigated. Heteronuclear single quantum coherence-nuclear magnetic resonance (HSQC-NMR) spectroscopy was used to identify the positions at which the hydroxyl groups of polysaccharides were acetylated. X-ray diffraction analysis was used to determine the acetylation of cellulose in the crystal region. It was found that only xylan was obviously acetylated in the initial stages of the reaction. In the next stage of the acetylation, however, both the xylan and surface of the cellulose crystals reacted. Then, acetylation of the inner crystal region of the cellulose started before the completion of the xylan modification. To improve the reactivity of xylan in KP, the effect of drying or the dehydration of never-dried KP prior to acetylation was also investigated. The use of supercritical CO2 (scCO2) drying produced a KP with a higher specific surface area. This caused the xylan to exhibit a higher reactivity than that resulting from freeze drying and vacuum drying after solvent exchange. Furthermore, never-dry dehydration pretreatment produced xylan with the highest reactivity. This suggests that the cellulose–cellulose and/or cellulose–hemicellulose adhesion in the cell wall that arises as a result of drying reduces the reactivity of the xylan.

Because of their high mechanical performance, high specific surface area, and high aspect ratio, there is a strong interest in cellulose nanofibers (CNFs) as a reinforcing material for plastics. Although three hydroxyl groups per repeating unit exposed on the surface is a unique characteristic of CNFs, an effective chemical treatment to improve the reinforcing efficiency of CNFs for hydrophobic thermoplastic resin has not yet been reported. In this study, six systematically designed aliphatic ester groups with linear, cyclic and branched structures, were incorporated on the surface of CNFs using the hydroxyl groups with a degree of substitution of 0.4. The melt compounding of the esterified CNFs and HDPE was performed at 140 °C using a twin screw extruder followed by injection molding at 160 °C and investigated the CNF dispersibility in HDPE and the CNF reinforcing efficiency in injection-molded HDPE samples. Incorporation of linear long chains results in the best dispersion of CNFs in HDPE compared with cyclic and branched chains, but the latter chains give higher reinforcing efficiencies in Young’s modulus and tensile strength. Especially, the bulky t-butyl group gave the highest reinforcing efficiency. Thus, the structure of ester groups incorporated on the CNFs very much affects on the dispersibility in HDPE, Young’s modulus and tensile strength, and coefficient of thermal expansion (CTE) of the esterified CNFs-reinforced HDPE composites. Addition of pivaloylated CNFs increases the Young’s modulus of HDPE from 1.20 to 3.32 GPa, and the tensile strength from 23.4 to 51.2 MPa. The CTE is 72.5 ppm/K, which is less than one-third that of the HDPE. The high reinforcing efficiency of these composites is partly explained by the formation of the double shish–kebab crystal structure during injection molding identified by the TEM observation.

The study demonstrated the improvement in the resistance of nanocellulose against thermally-induced depolymerization by esterification with benzoyl (BNZ) and pivaloyl (PIV). The change in the degree of polymerization (DP) and molecular weight distribution (MWD) after thermal treatment in nitrogen and in air was investigated using viscometry and gel permeation chromatography. BNZ and PIV nanocellulose esters without α-hydrogens gave higher DP and narrower MWD than pure bacterial cellulose; and the acetyl and myristoyl esters, which possess α-hydrogens. Results also showed that when depolymerization is suppressed, thermal discoloration is also reduced. Resistance against depolymerization inhibits the formation of reducing ends which can be active sites for thermal discoloration. Finally, the findings suggest that benzoylation and pivaloylation can be an excellent modification technique to improve the thermal stability of nanocellulose.

It is a challenging task to reinforce polyamide 6 (PA6) using nanofibrillated cellulose because the melting temperature of PA6 is high and nanofibrillated cellulose degrade at high temperatures. First, soft wood kraft pulps were acetylated (Ac) to improve the heat resistance. The weight loss temperature of the pulps increased by 31 °C through acetylation (DS = 0.64). It was evident that the melt compounding process using a twin-screw extruder allowed for nanofibrillation of the Ac-pulps. Ac-nanofibrillated cellulose reinforced PA6 showed a high storage modulus, which suggests that the Ac-nanofibrillated cellulose formed a network in the PA6 matrix. The Ac-nanofibrillated cellulose improved the bending modulus from 2.22 GPa (neat PA6) to 5.43 GPa, the strength from 91.2 MPa to 154 MPa, the coefficient of thermal expansion from 110.9 ppm/K to 24.3 ppm/K, and the heat-deflection temperature from 85.7 °C to 166.6 °C. The melt compounding of Ac-pulps with PA6 using a twin-screw extruder facilitates the commercial production of nanofibrillated cellulose reinforced PA6.

The acetylation of ground pulp (GP) was followed by heteronuclear single quantum coherence-nuclear magnetic resonance (HSQC-NMR) spectroscopy to investigate the relationship between the degree of acetylation and the introduction positions of acetyl groups during this acetylation. We also examined the effect of acetylation on thermal stability. Seven acetyl GPs (AcGPs) with degree of substitution (DS) values of 0.19, 0.29, 0.59, 0.74, 1.04, 1.11, and 1.19 were prepared and analyzed using HSQC-NMR spectroscopy. Acetylation was found to occur first on the primary hydroxyl groups of polysaccharides and lignin, followed by the secondary hydroxyl groups of polysaccharides, and finally the hydroxyl groups at the α-position of lignin. The thermal stabilities of the AcGPs were analyzed using thermogravimetric analysis (TGA). The 1% weight loss temperatures of the AcGPs were higher than that of the GP. The acetylation of the primary hydroxyl groups in polysaccharides and lignin and the hydroxyl groups at the α-posi...

Various Langmuir–Blodgett (LB) films of tetraphenylporphyrin (TPP)-bound acyl celluloses with different degrees of substitution of the TPP groups (DSTPP) and different acyl groups were prepared. TPP-bound acyl celluloses with DSTPP values less than 0.38 and myristoyl groups as the O-2 and O-3 substituents were suitable for obtaining LB mono-layer films with high quantum yields. The horizontal lifting method was better than the vertical dipping method for the deposition of LB films. The number of layers in LB multi-layer films of TPP-bound myristoyl cellulose with a DSTPP of 0.36 also influenced the quantum yield, and the quantum yield of the LB di-layer film was higher than those of the LB mono- and tri-layer films. This information will be useful in the improvement of the photocurrent generation performances of LB films of TPP-bound acyl celluloses.

Hydrophobic cellulose nanofibers (CNFs) were prepared by surface modification using alkenyl succinic anhydride (ASA). The hydrophobicity of CNFs was varied by changing the degree of substitution (DS) from 0 to 0.83. Modified CNFs were mixed with high-density polyethylene (HDPE) using a twin-screw extruder and the resulting composites were injection molded. The tensile properties initially improved with increasing DS up to ∼0.3–0.5, and then decreased with further substitution. The tensile strength and modulus of 10 wt.% HDPE/CNF composites containing 8.8 wt.% ASA (DS: 0.44) were 43.4 MPa and 1.97 GPa, respectively. These values were both almost 70% higher than those of composites containing unmodified CNF, and 100% and 86% higher, respectively, than those for pure HDPE. X-ray computed tomography measurements showed that CNFs modified with a DS of 0.44 were dispersed uniformly within the resin matrix, whilst unmodified CNFs and those modified with a DS of 0.77 agglomerated within the composites.

The reinforcement effect of microfibrillated cellulose (MFC) in high-density polyethylene (HDPE) was investigated by mechanical, thermal, and rheological analysis. The reinforcement effect using both maleic-anhydride-grafted polypropylene (MAPP) and cationic polymer using primary amine (CPPA) as coupling agents in MFC-reinforced polypropylene (PP) has been reported in our previous study (Suzuki et al. in Cellulose 21:507–518, 2014. doi: 10.1007/s10570-013-0143-9 ). The combined use of MAPP and CPPA showed a greater reinforcement effect in the MFC-reinforced HDPE composite than in MFC-reinforced PP. The tensile modulus of MFC-reinforced HDPE was about 22 % higher than that of MFC-reinforced PP. Rheological analysis showed that there was a drastic improvement in the interaction between MFC and HDPE using CPPA and MAPP. The storage modulus of the MFC/HDPE composite in the melt state using MAPP and CPPA as coupling reagents was about three times higher than that without the coupling reagents. Furthermore, differential scanning calorimetry analysis suggested that a chemical reaction occurred between MAPP and CPPA. In addition, the thermal properties of MFC-reinforced HDPE were remarkably improved using MAPP and CPPA: the coefficient of thermal expansion of the composite decreased from 237.2 (HDPE) to 57.1 ppm/K (MFC/HDPE/MAPP/CPPA) and the heat distortion temperature under 0.45 MPa load improved from 67.4 (HDPE) to 116.7 °C (MFC/HDPE/MAPP/CPPA).

The selective lignin degradation in a LCC was proceeded with the γ-TTSA method, which is a selective cleavage method for β-O-4 linkages in lignins, in order to obtain more precise information concerning LCC bonding sites. To this purpose, crude MWL from Eucalyptus globulus, containing lignin and xylan, was treated by the γ-TTSA method. This approach consists of four steps: (1) γ-tosylation, (2) thioetherification, (3) sulfonylation, and (4) mild alkali treatment. The degradation products were extracted consecutively with Et2O, EtOAc, and THF for the lignin removal, and thus the residue was enriched in LCCs. The residue was characterized by HSQC-NMR. Results indicated that the residue contained xylan and β-β substructures, although lignin was degraded. It can be concluded that the β-β substructures play an important role in the bonding sites between lignin and xylan of Eucalyptus globulus.

Improvement in the thermal stability of wood-based cellulose; the needle-leaf, bleached, krafp pulp (NBKP) and the wood cellulose nanofibers (WCNF) obtained from the NBKP, was achieved by esterification. Initially, four different types of NBKP esters (acetyl, C2; myristoyl, C14; benzoyl, BNZ; and pivaloyl, PIV) with different degree of substitution (DS) values were prepared to evaluate the effect of esterifying the hemicellulose. The findings revealed that an optimum DS, which possibly completely esterifies the hemicellulose and amorphous cellulose, is needed to achieve significant improvement in thermal stability. Moreover, BNZ and PIV gave higher thermal stability than that of the C2 and C14. BNZ was selected over PIV to modify the WCNF. Benzoylation increased the 1% weight loss temperature (WLT) of WCNF by 25 °C and improved its resistance against thermal weight loss at the early stage of degradation and discoloration. Unlike the results of NBKP, changing the DS from 0.4–1.1 did not show variation in the thermal behavior of WCNF esters. The effect of esterifying the hemicellulose in WCNF was not clearly observed possibly due to the formation of reducing ends brought by mechanical fibrillation during WCNF preparation. Finally, the thermal stability of wood-based celluloses can be comparable to that of highly crystalline and pure bacterial cellulose after benzoylation at an optimum DS.

The reinforcement of sulfur-vulcanized natural rubber using cellulose nanofibers (CNFs) was investigated. Natural rubber consists mainly of cis-1,4-polyisoprene, and becomes stretchable after vulcanization. Vulcanization was performed via crosslinking with the polyisoprene double bonds, using sulfur and unsaturated fatty acids (oleic acid) incorporated on the CNF surfaces, resulting in highly efficient reinforcement of the CNFs. The Young's modulus of rubber reinforced with 5 wt% oleoyl was 27.7 MPa, i.e., 15 times higher than that of neat rubber, while retaining a strain to failure rate of 300%. The coefficient of thermal expansion of 226.1 ppm K−1 for natural rubber was reduced to 18.6 ppm K−1 after the addition of 5 wt% oleoyl CNFs.

The α-TSA method has been developed for the cleavage of β-O-4 linkages in lignin. It consists of three steps: (1) thioetherification at α-position of β-O-4 substructures, (2) sulfonylation, and (3) mild alkali treatment of the α-sulfone derivative. The method was tested on a nonphenolic dimeric β-O-4 lignin model compound, namely on 4-benzyloxy-3-methoxyphenylglycerol-β-guaiacyl ether. It demonstrated that the mild alkali degradation of the α-sulfone derivative proceeds efficiently, i.e., the electron-withdrawing sulfone group at α-position contributes to the cleavage of the β-O-4 linkage in the same mechanism as that in the γ-TTSA method.

Milled wood lignin (MWL) of Eucalyptus globulus has been treated by a selective degradation method for β-O-4 linkages, which lets the lignin carbohydrate complexes (LCC) intact. The method consists of four reaction steps: (1) γ-tosylation, (2) thioetherification, (3) sulfonylation and (4) mild alkali treatment (γ-TTSA method). Each step was followed by spectroscopies for chemical structural analysis; especially, the HSQC-NMR analysis was in focus. It was demonstrated that β-O-4 linkages were selectively and quantitatively cleaved by the γ-TTSA method while the β-β linkages in the MWL remained intact. The method leads to an enrichment of LCCs.

A selective cleavage method for β-O-4 linkages (the γ-TTSA method) was introduced in previous works, which consists of four reaction steps: (1) γ-tosylation, (2) thioetherification, (3) sulfonylation, and (4) mild alkali degradation. This method was applied to the degradation of a lignin polymer model (dehydrogenation polymer, DHP) consisting of guaiacyl units. Each reaction step was followed by Fourier transform infrared (FT-IR) spectroscopy and heteronuclear single quantum coherence nuclear magnetic resonance (HSQC-NMR) spectroscopy. It was demonstrated that only the β-O-4 linkage was selectively cleaved by the γ-TTSA method, although other linkages, such as β-5 and β-β linkages, were also present in the DHP. Consequently, the γ-TTSA method is expected to be also useful for the degradation of native lignins.

6-Azafulleroid-6-deoxy-2,3-di- O -myristoylcellulose ( 3 ) was synthesized from 6-azido-6-deoxycellulose ( 1 ) by two reaction steps. The myristoylation of compound 1 with myristoyl chloride/pyridine proceeded smoothly to give 6-azido-6-deoxy-2,3-di- O -myristoylcellulose ( 2 ) in 97.0% yield. The reaction of compound 2 with fullerene (C 60 ) was carried out by microwave heating to afford compound 3 in high yield. It was found from FT-IR, 13 C NMR, UV–vis, differential pulse voltammetry (DPV), SEC analyses that compound 3 was the expected C 60 -containing polymer. Consequently, maximum degree of substitution of C 60 (DS C60 ) of compound 3 was 0.33.

In order to elucidate the characteristic features of commercial methylcellulose precisely, O-methylcellulose model copolymers consisting of 2,3,6-tri-O-methylanhydroglucose unit (236MeAGU) and 2-O-methylanhydroglucose unit (2MeAGU) with various composition ratios were synthesized via cationic ring-opening copolymerization of the corresponding glucose orthoester derivatives, subsequent removal of pivaloyl and allyl groups, and methylation. The structure of the obtained copolymers was confirmed by 1H-, 13C-NMR, and FT-IR. Temperature-dependent turbidity measurement verified their thermoresponsive behavior in aqueous solution. The lower critical solution temperature was tuned from 63 to 45 °C above 47 mol-% 236MeAGU content. The hydrophobicity along the cellulose chain was dominant to determine their physical properties. However, the aqueous properties of the MC model copolymers were strongly affected by the slight difference of the composition ratio. The present method would provide further details of the structure–property relationship of O-methylcellulose.

Role-sharing functionalized cellulose derivatives having Mg, Zn, Cu, and Pd porphyrins are used for photocurrent generation system fabricated by the LB technique, mimicking the array of natural photosynthetic light-harvesting systems. These polymers exhibited different absorption and redox properties in solution depending on the central metal ions. On visible light illumination, the LB film generated anodic photocurrent in the order of Pd > free base > Zn > Cu > Mg. By inserting Pd ion, using myristoyl group, and adjusting the DS, the photocurrent quantum yield was 6.9 times as great as that of conventional porphyrin cellulose. These findings may provide opportunities for the design of a new class of organic solar cells, based on cellulose molecular characteristics.

Regioselectively ethylated celluloses, 2-O- (1), 3-O- (2), and 6-O-ethyl- (3) celluloses were synthesized via ring-opening polymerization of glucopyranose orthopivalate derivatives. The number-average degrees of polymerization (DP(n)s) of compounds 1 and 2 were calculated to be 10.6 and 49.4, respectively. Three kinds of compound 3 with different DP(n)s were prepared: DP(n)s = 12.9 (3-1), 60.3 (3-2), and 36.1 (3-3). The 2-O-, 3-O-, and 6-O-ethylcelluloses were soluble in water, confirmed by NMR analysis. Furthermore, the 3-O- (2), and 6-O-ethyl- (3-2) celluloses showed thermo-responsive aggregation behavior and had a lower critical solution temperature (LCST) at about 40 degrees C and 70 degrees C, respectively, based on the results from turbidity tests and DSC measurements. The 6-O-ethyl-cellulose (3-3) with DP(n) = 36.1 and DP(w) = 54.6 showed gelation behavior over approx 70 degrees C, whereas the 6-O-ethyl-celluloses 3-1 and 3-2 with lower and higher molecular weight, such as DP(n)s 12.9 and 60.3, did not show gelation behavior at this temperature. It was revealed that the position of ethyl group affected the phase transition temperature. According to our experiments, the 3-O-ethyl and 6-O-ethyl groups along the cellulose chains caused the thermo-responsive property of their aqueous solutions. The appropriate DP of the regioselective 6-O-ethyl-cellulose existed for gelation of the aqueous solution.

Persimmon (Diospyros kaki Thunb.) accumulates soluble condensed tannin (CT) in fruit which is responsible for its astringency trait. In this study, we analyzed the CT composition in persimmon fruit with phloroglucinol, and identified and characterized novel epigallocatechin-3-O-gallate-phloroglucinol (EGCG-P) adducts as one of the main CT components of persimmon fruit. Analysis with phloroglucinol in persimmon cultivars revealed the different tendencies of the CT composition and component ratio among the four astringency types (PCNA, PVNA, PVA, and PCA), which are categorized by their patterns of astringency loss. The concentration of the main CT component in persimmon fruit, epigallocatechin-3-O-gallate (EGCG), was particularly different among astringency types. Further analysis of the fruit at various maturation stages will help in understanding the different mechanisms of CT accumulation among astringent types. Our results demonstrated that the phloroglucinol methodology is useful for CT composition analysis in persimmon fruit and will contribute to future studies on the astringency trait in this fruit.

It is known that the conventional dehydrogenative polymerization of sinapyl alcohol (S-alc) gave syringyl synthetic lignins (S-DHPs), but in extremely low yields. In this article, to examine the contribution of syringyl quinone methide intermediates (S-QM) on S-DHP production, horseradish peroxidase (HRP)-catalyzed dehydrogenative polymerization of S-alc was carried out in the presence of nucleophilic reagents that promote the rearomatization of S-QM. First, the HRP-catalyzed polymerization of sinapyl alcohol γ-O-β-D-glucopyranoside (isosyringin, iso-S), which allows us to monitor the polymerization process in a homogeneous aqueous phase, was utilized for screening of a nucleophile used as an S-QM scavenger. Monitoring of iso-S polymerization in the presence of various nucleophilic reagents by UV spectroscopy and gel permeation chromatography with photodiode array detection (GPC-PDA) revealed a high ability of azide ion to convert oligomeric S-QM efficiently to S-DHP. Accordingly, azide ion was utilized as an S-QM scavenger in HRP-catalyzed polymerization of S-alc, which resulted in high-yield production of S-DHPs (∼83%), as expected. The 1H-, 13C-, and 2D-HSQC NMR investigations on the resulting S-DHPs clearly demonstrated that azide ion efficiently performed nucleophilic additions to the C-α of S-QM during the polymerization. These results provide experimental proof that the low reactivity of S-QM with nucleophiles (such as water, phenolic, and aliphatic hydroxyl groups) in the conventional polymerization system critically impedes the production of S-DHPs from S-alc.

6-O-Alkyl-celluloses with well-defined ratio of ethyl and methyl groups at position 6 were prepared by ring-opening copolymerization of 6-O-ethyl and 6-O-methyl glucose 1,2,4-orthopivalate derivatives. An aqueous solution of 6-O-ethyl-cellulose having no methyl group was found to be thermo-responsive to be turbid at ~70 °C. An aqueous solution of 6-O-ethyl-cellulose with higher molecular weight showed endothermic and exothermic peaks in the heating and cooling curves of DSC measurements, respectively. However, 6-O-alkyl-cellulose having 10% methyl group lost its thermo-responsive character. 6-O-Alkyl-celluloses having more than ten percent of ethyl group at position 6 became water-soluble, though 6-O-methyl-cellulose is insoluble in water. Thus, 6-O-ethyl group was found to be of importance for the water solubility of regioselective 6-O-alkyl-celluloses. Furthermore, a small amount of methyl group introduced at C6 position was found to affect some of physical properties of 6-O-alkyl-celluloses such as thermo responsive property.

2,6-Di-O-ethyl (2E6E) (1), 2-O-ethyl-6-O-methyl (2E6M) (2), and 6-O-ethyl-2-O-methyl (6E2M) (3) celluloses were synthesized via ring-opening polymerization of glucose orthopivalate derivatives. 2,6-Di-O-methyl cellulose (2M6M) was insoluble in any common solvents, though it was not expected. On the other hand, cellulose derivative 1 (2E6E) was soluble in chloroform. Introduced positions of alkyl groups on cellulose affected solubilities of cellulose derivatives. Their solubility in chloroform decreased in the order: polymer 1 (2E6E) > polymer 2 (2E6M) > polymer 3 (6E2M) ≫ 2M6M.

The incompatibility between cellulose fibers and hydrophobic polymers has presented a major obstacle for the fabrication of composites and nanocomposites. In this study, we applied a one-time grinder treatment to disintegrate chemi-thermomechanical pulp (CTMP) and obtained micro- to nano-meter-sized lamellar or fibrous fragments. The CTMP fragments were composed of cellulose microfibrils with high aspect ratios encased in matrix substances including hydrophobic lignin. Furthermore, we produced compression-molded products from the CTMP fragments by thermally plasticizing lignin without any adhesives or resins. The molded products pressed at 180 °C exhibited a plastic-like gloss on the surface and a high bending strength, 221 MPa, which greatly exceeded that of the conventional plant-based binderless boards. The molded products produced here are a novel form of ideal cellulose nanocomposite, which exploited the inherent compatibility between cellulose microfibrils and matrix substances present in CTMP fragments.

(13)C-Perlabeled cellulose was obtained in a seven-step approach from (13)C(6)-labeled d-glucose with a cationic ring-opening polymerization as the key step. Isopropylidene protection, benzylation of the remaining free 3-O-position and subsequent deprotection afforded 3-O-benzyl-(13)C(6)-glucose (2). Regioselective bis-pivaloylation followed by subsequent ortho-esterification provided the precursor for the cationic ring-opening polymerization, 3-O-benzyl-(13)C(6)-glucopyranose 1,2,4-orthopivalate (4). The actual polymerization step gave a stereo- and regioregular (13)C-perlabeled (1--4)-beta-glucopyranan derivative, which was deprotected into fully labeled (13)C-cellulose, as the cellulose II allomorph with a DP of 40, in an overall 28% yield. All reaction steps were optimized beforehand with nonlabeled compounds toward high yields and high reproducibility and the final compound was comprehensively analytically characterized.

Triblock cooligomers consisting of tri-O-methyl-glucopyranosyl and unmodified glucopyranosyl residues, methyl 2,3,4,6-tetra-O-methyl-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1 → 4)-β-d-glucopyranosyl-(1 → 4)-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-α-d-glucopyranoside (1: ABA triblock cooligomer; DS = 2.1) and β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1 → 4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1 → 4)-d-glucopyranose (2: BAB triblock cooligomer; DS = 1.8) were prepared. Compound 1 dissolved both in distilled water and chloroform but compound 2 dissolved in distilled water not in chloroform, though compounds 1 and 2 consist of 4 tri-O-methyl-glucopyranosyl and 2 unmodified anhydro glucopyranosyl units.

A cellulose macromonomer, N-(15-methacryloyloxypentadecanoyl)-tri-O-acetyl-beta-cellulosylamine (CTA-C15-MA (2); M(2)) with number averaged degree of polymerization (DP(n)) = 13), was copolymerized with methyl methacrylate (MMA; M(1)) to give cellulosic copolymer with CTA side chains, PMMA-g-(CTA-C15) (3-A). An absolute molecular weight determined by multiangle laser light scattering (MALS; M(w,LS)), degree of polymerization of MMA (X) and CTA-C15-MA (Y) of PMMA-g-(CTA-C15) (3-A) were determined to be M(w,LS) = 6.30 x 10(4), X = 4.14 x 10(2), and Y = 3.86. Cellulose graft copolymer with cellulose side chains, PMMA-g-(cellulose-C15) (3-H) was successfully obtained after deacetylation of the copolymer 3-A. Thermal analysis of copolymers 3-A and 3-H by means of differential scanning calorimetry (DSC) measurements revealed that a small amount of CTA and cellulose side chains affected thermal properties of the PMMA main chain.

Model experiments for synthesis of a comb-shaped copolymer with cellulose side-chains were performed with cellobiose derivatives. A novel cellobiose monomer, N-(15-methacryloyloxypentadecanoyl)-2,3,6-tri-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)-β-d-glucopyranosylamine (2) was prepared from heptaacetylcellobiosyl- amine. Homopolymerization of cellobiose monomer 2 and copolymerization of monomer 2 with methyl methacrylate (MMA) were performed using 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator to obtain homopolymers 3-i (i = 1–4) and copolymers 3-i (i = 5–7), poly(methyl methacrylate)-graft-(heptaacetylcellobiosylamine-C15). The size exclusion chromatography—multi-angle laser light scattering (SEC-MALS) measurements revealed that comb-shaped homopolymers 3-i (i = 1–4) had more compact structures compared to copolymers 3-i (i = 5–7) at the same elution volume. Selective deacetylation of polymers 3-i (i = 1–7) gave novel cellobiose polymers 4-i (i = 1–7), poly(methyl methacrylate)-graft-(cellobiosylamine-C15). The amide linkages between cellobiose moiety and long-chain alkyl group, and the ester linkages between PMMA main-chain and long-chain alkyl group remained after deprotection. The differential scanning calorimetry (DSC) measurements revealed that the T gs of the polymers 4-i (i = 1, 5, 6, 7) increased with increasing cellobiose composition in the polymers. It was indicated that cellobiose moieties of polymers 4-i (i = 1, 5, 6, 7) reduced the mobility of PMMA main-chain.

Three methyl celluloses with completely uniform substitution pattern, 2-O-methyl cellulose (1), 3-O-methyl cellulose (2) and 6-O-methyl cellulose (3), were prepared according to the cationic ring opening polymerization approaches starting from substituted 1,2,4-orthopivalate derivatives of d-glucose. These samples allowed for the first time to sort out the methyl substitution effects on solid-state NMR chemical shifts and relaxation. Dipolar dephasing experiments allowed the detection and assignment (1H, 13C) of the methyl groups. In 1 and 2, these resonances overlapped with those of C-6, whereas in 3, the methyl signal experienced a low-field shift into the region of C-2,3,5. 13C T1 experiments were used to verify different relaxation behavior of the carbon sites, particularly the short relaxation time of at the carbon substitution site next to the methyl groups. This effect was used to unambiguously identify the 13C chemical shifts of the carbons carrying the methoxyl substituent, although they overlap with all resonances in the C-2,3,5 region. The data obtained for the standard samples with uniform substitution will now be used as the basis for determining methylation patterns and substitution degree in commercial methyl celluloses.

The syntheses of several perdeuterated substances—some of them isotopically labeled (15N) in addition—are described, which act as direct solvents of cellulose either on their own, such as N-methylmorpholine N-oxide (NMMO), 1-butyl-3-methylimidazolium acetate (BMIM-OAc), or 1-ethyl-3-methylimidazolium acetate (EMIM-OAc), or in combination with auxiliaries, such as N,N-dimethylacetamide (DMAc—for the cellulose solvent DMAc/LiCl). NMMO-d11 (9) was obtained in an eight-step approach from non-labeled diglycolic acid (1) via diethylene glycol-d8 (4) and its bis-tosylate (5), which underwent ring closure with benzylamine to N-benzylmorpholine-d8 (6). Debenzylation, methylation and oxidation completed the synthetic sequence, which was also able to provide the 15N-labeled product (9a) by usage of 15N-benzylamine. DMAc-d9 (14) was obtained from deuterated acetic acid (10) and dimethylamine-d6–carbon dioxide complex (13) in a solvent-free gas-solid reaction with acidic alumina as the catalyst. Employing the CO2-complex of 15N-dimethylamine-d6 afforded the 15N-labeled product 15N-DMAc-d9 (14a) in a similar way. The two ionic liquids EMIM-OAc (21) and BMIM-OAc (22) were obtained from imidazole in three-step sequences starting with butylation and ethylation, respectively. The resulting 1-alkyl imidazoles were purified, and subsequently methylated according to a novel protocol using dimethylcarbonate-d6. Addition of acetic acid-d4 caused traceless degradation of the methylcarbonate anions and exchange for acetate. In all syntheses, the reaction steps were optimized with non-labeled compounds towards high yields and high reproducibility before entering the “hot runs” with deuterated and otherwise isotopically labeled material.

Formaldehyde adsorption and release tests of karamatsu (Larix leptolepis) bark and bark ingredients were performed. Karamatsu bark had good formaldehyde adsorption ability that was better than microcrystalline cellulose. An acetone-soluble fraction from karamatsu bark, which might contain bark tannin, had excellent formaldehyde adsorption ability, and was found to release a trace amount of the adsorbed formaldehyde, suggesting that its formaldehyde adsorption was predominantly due to chemical adsorption. It was confi rmed that the acetone-soluble fraction played an important part in formaldehyde adsorption by karamatsu bark. An acetone-insoluble fraction from karamatsu bark had good formaldehyde adsorption ability as well as the bark, in spite of the residue after the removal of the acetone-soluble fraction.

2,6-Di-O-methylcellulose was prepared from natural and synthetic celluloses. Natural cellulose was converted to 2,6-di-O-thexyldimethylsilylcellulose, then to 3-mono-O-allyl-2,6-di-O-methylcellulose, and finally into 2,6-di-O-methylcellulose. Alternatively, 2,6 di-O-methyl-cellulose was synthesized trom the synthetic cellulose derivative 3-mono-O-benzyl-2,6-di-O-pivaloylcellulose by depivaloylation and methylation to give 3-mono-O-benzyl-2,6-di-O-methyl-cellulose, which was debenzylated to yield the dimethyl ether. Both types of 2,6-di-O-methyl-cellulose are insoluble in water and common organic solvents. The structures of all cellulose derivatives were determined by NMR.

Horseradish peroxidase (HRP)-initiated dehydrogenative polymerizations of guaiacyl (G) and syringyl (S)-type monolignol γ-O-glucosides, isoconiferin (iso-G) and isosyringin (iso-S), which contain a hydrophilic glucosyl unit on γ-position of coniferyl alcohol (G-alc) and sinapyl alcohol (S-alc), respectively, were monitored by UV spectroscopy to study the formation of dehydrogenation polymer (DHP, lignin polymer model) in a homogeneous aqueous phase. During homopolymerization of iso-S, a new absorbance band at 325 nm (A 325) rapidly increased in intensity and then gradually disappeared, whereas such stable changes in absorbance were not observed during homopolymerization of iso-G. During polymerization of iso-S, A 325 rapidly disappeared when an acid, nucleophile or reductant was added to the reaction mixture, indicating that A 325 can be attributed to S-type quinone methide intermediates (QMs). Similar to iso-S polymerization, temporary absorbance at 328 nm was observed during conventional polymerization of S-alc. We interpret this observation as follows: S-type QMs accumulated in the reaction mixture and the progress of subsequent DHP formation during oxidative polymerization of iso-S or S-alc was hindered. UV monitoring of iso-G and iso-S copolymerization revealed that the presence of iso-G promoted the disappearance of A 325. Furthermore, S-type QMs generated in situ by iso-S polymerization disappeared more rapidly after guaiacol addition than after 2,6-dimethoxyphenol addition. The following mechanism for copolymerization of iso-G and iso-S can be proposed: G-type precursors with phenolic hydroxyl groups react readily by nucleophilic addition with the α-C of S-type QMs, and the molecular chains of DHPs increase via non-cyclic α-aryl ether bonds.

In the present paper we suggest a new concept to overcome some of the so far unsolved problems of the structure–property relationship of methylcellulose, the most important nonionic cellulose ether industrially produced in large scale. Not only from the viewpoint of scientific understanding, but also from that of the peculiar and application-determining behavior, the aggregation in aqueous solution and phase separation on heating are the most important questions. As a part of the concept, we had prepared amphiphilic block co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides as structural models of typical sequences in methylcellulose chains. Now static and dynamic light scattering measurements and transmission electron microscopy (TEM) were carried out using solutions of the oligomers in water. Ellipsoidal particles with dimensions of about 50 nm for the semi-major axis and of circa 25 nm for the semi-minor one could be detected. These findings agree with the radii of gyration and the hydrodynamic radii, determined by static and dynamic light scattering. The data preliminary obtained demonstrate the strong aggregation tendency of block-like methylated cello-oligosaccharides.

Thin films consisting of 6-O-porphyrin-2,3-di-O-stearoylcellulose (H 2 PCS) and fullerene (C 60 ) were fabricated for anodic photocurrent generation systems by the Langmuir-Blodgett (LB) technique. The π-complexation between the porphyrin moiety and C 60 in the LB films was investigated by means of the surface pressure (π)-area (A) isotherms, UV-vis, and fluorescence spectroscopy. The photocurrent density generated from the H 2 PCS-C 60 LB monolayer films exhibited an increase with increasing the C 60 proportion and reached a maximum at a mixing ratio of 1:2, yielding a quantum yield of 12.5% and an IPCE (incident photon-to-current efficiency) of 0.50% at a bias potential of +100 mV vs. SCE. Furthermore, the LB five-layer films could give rise to the IPCE value of 1.5% at +100 mV without significant decline of the quantum yields, which was due to the function of C 60 as an electron carrier to improve the interlayer electron transfer through each layer. These results have demonstrated a promising method for preparing the donor-acceptor systems using cellulose as a scaffold in the LB films.

Langmuir-Blodgett (LB) films containing porphyrin molecules were fabricated by use of 6-O-dihydrophytylcellulose (DHPC) toward anodic photocurrent generation systems. To suppress the porphyrin aggregation, two different approaches were applied: (1) mixing a low-molecular-weight porphyrin having a diterpenoid carbon skeleton (DPor) with DHPC as a matrix (matrix fabrication) and (2) bonding porphyrin molecules to the hydroxyl groups of DHPC covalently, converting into 6-O-dihydrophytyl-2,3-di-O-[p-(10,15,20-triphenyl-5-porphyrinyl)-benzoyl]cellulose as a scaffold (scaffold fabrication). The structure and film properties of the monolayers and the LB films were investigated by the surface pressure (π)–area (A) isotherm measurements, atomic force microscopy, UV–Vis spectroscopy, and absorption dichroism measurements. The porphyrin aggregation in the LB film could be well suppressed only by the scaffold fabrication, leading to the improvement of the photocurrent quantum yields. The efficient photocurrent performance can be demonstrated by the isolation and the parallel orientation of porphyrin moieties due to the cellulose rigid scaffold.

Horseradish peroxidase–catalyzed dehydrogenative polymerizations of the p-hydroxyphenyl monolignol glucoside (triandrin (1P)) and the syringyl monolignol glucoside (isosyringin (1S)) resulted in the formation of water-soluble lignin-like polymers (DHPs). The polymerization of 1P gave highly polymerized DHPs in high yields as did previously reported polymerization of the guaiacyl monolignol glucoside (isoconiferin (1G)). It was shown that the hydrophilic D-glucose units of 1G and 1P contribute to a marked increase in the molecular weights of the resulting DHPs. On the other hand, the homogeneous phase polymerization of 1S, similar to the polymerization of sinapyl alcohol, gave DHPs with extremely low molecular masses in poor yields. Structural characterization indicated that the DHPs from 1P and 1S were lignin-like polymers containing glucosidic units on their sidechains. It was also confirmed that D-glucosyl units introduced onto the γ-position of monolignols do not significantly affect the elect...

The synthesis of the perdeuterated cellulose solvents NMMO-d11 (9) and N,N-dimethylacetamide-d9 (14) is described. NMMO-d11 was obtained according to a five-step approach from non-labeled diglycolic acid (1) via diethylene glycole-d8 (4) and its bis-tosylate (5), which underwent cyclization with benzylamine to N-benzylmorpholine (6). The removal of the benzyl protecting group, methylation and N-oxidation completed the synthesis. DMAc-d9 (14) was obtained from deuterated acetic acid (10) and dimethylamine–carbon dioxide complex (17) with acidic alumina as the catalyst according to a solvent-free gas–solid reaction. Copyright © 2008 John Wiley & Sons, Ltd.

The mechanism of a novel reaction type, the “furan endwise peeling” reaction, has been studied. Making extensive use of experiments on model compounds, the structural prerequisites to the reaction were found to be a 2-hydroxpyran β-glycosidically linked to a 2-(2-furyl)ethyl moiety. Proceeding from the reducing end of the celluloses, the reaction causes the one-by-one loss of anhydroglucose units (AGUs) which are concomitantly converted into 2-(tetrahydroxybutyl)furans (4) by co-reacting with 1,3-dicarbonyl compounds such as ethyl acetoacetate (1). The key step of the reaction is the formation of a furan at the reducing end followed by the attack of the 2-OH group of the last-but-one AGU at this terminal furan. The intermediate, unstable dioxepane fragments by cleavage of the glycosidic bond. The terminal AGU is released as a substituted furan, the “new” reducing end reacting immediately with the 1,3-dicarbonyl component to form a new terminal furan which, in turn, undergoes the same cycle. The “furan endwise peeling” reaction represents an interesting way to convert cellulosic biomass by an easy procedure into substituted furans that are valuable fine chemicals with multiple uses.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Geared towards reinforcing thermoplastics of high melting points with nanocellulose, this study evaluated the factors affecting the thermal properties of and the thermal stabilizing effect of acetylation on nanocellulose with different average degree of polymerization (DPv) from bacterial cellulose (BC). Cellulose nanocrystals with DPv values of 300 and 500 were prepared by hydrolyzing BC nanofibers with a DPv of 1100 using hydrochloric acid. The thermal stability decreased after acid hydrolysis and showed a decreasing trend with decreasing DPv. The decrease in thermal stability is attributed to the increase in the number of reducing ends (REs) with decreasing DPv. Heterogeneous acetylation to an average degree of substitution of 0.38 improved the thermal stability, and the degree of improvement increased with decreasing DPv. The dependence of the degree of improvement on the DPv is attributed to possible protection of the REs by more stable acetyl groups. The influence of protecting the REs on the degree of improvement in thermal stability was further confirmed by sodium borohydride (NaBH4) reduction. The findings suggest that the thermal stabilization caused by acetylation to nanocellulose with small DPv is a combined effect of protecting both the surface OH and the REs; while for nanocellulose with high DPv, the thermal stabilization caused by acetylation is mainly due to protection of the surface OH.

Esterification was used to improve the thermal stability of nanocellulose to extend its application as reinforcing filler to polymer matrices with high melting point. The effect of the structure of ester groups on thermal stability was studied in detail. Various types of nanocellulose esters (straight-chain, C2–C14; cyclic adamantoyl, ADM; aromatic benzoyl, BNZ; and branched pivaloyl, PIV) with degree of substitution values in the range of 0.40–0.47 were prepared from bacterial cellulose nanofibers and nanocrystals. The reaction conditions used to prepare the esters maintained the viscosity-average degree of polymerization (DPv) and crystallinity of the starting materials. Thermogravimetric analysis showed that the temperature at maximum weight loss rate (Tmax) increased after esterification. The structure of the ester groups and the DPv, however, showed no varying effect on Tmax. The 5 % weight loss temperature (WLT) which was used to assess the thermal stability at the onset of thermal degradation varied with the type of ester. Lower 5 % WLT was observed in straight-chain esters than those of the bulky esters of ADM, BNZ and PIV; which also showed high resistance to weight loss when subjected to isothermal heating. To understand the event at the onset of thermal degradation, low temperature pyrolysis was conducted. The evolved gases were separated and identified by gas chromatography–mass spectrometry technique. Results showed that at the onset of thermal degradation, levoglucosan (LG) is produced from the untreated BC nanocrystals. After esterification, LG formation was inhibited. The removal of the ester groups or deprotection is the main event at the onset of thermal degradation of nanocellulose esters. From the structure of the pyrolysis products, the mechanism of thermal deprotection of nanocellulose esters is proposed for the first time.