Acid-Catalyzed Solvolysis of Softwood in Caprylyl Glycol to Produce Lignin Derivatives.

Glycol lignin (GL) is produced via the acid-catalyzed solvolysis of softwood meal using glycols such as polyethylene glycol. The physicochemical and thermal properties of GL are expected to be controllable by varying the glycol type. In this study, caprylyl glycol (CG), which is a biobased glycol derived from the caprylic acid component of coconut and palm oils, was used to investigate the effects on the acid-catalyzed solvolysis of softwood. The reactions were performed at 140, 150, and 160 °C for 30-120 min to obtain lignin derivatives (CG-lignin: CGL). The chemical and physical properties of CGLs were investigated. Two-dimensional heteronuclear single-quantum coherence nuclear magnetic resonance analysis suggested that CGL possesses an α-CG-ß-O-4 structure as CG is grafted onto the lignin structure. CGLs prepared at higher reaction temperatures exhibited lower molecular weights. The thermomechanical analysis of CGL revealed a glass transition temperature of 89-96 °C and a viscous thermal flow temperature of 134-155 °C.

Hydrogen Peroxide Treatment of Softwood-Derived Poly(Ethylene Glycol)-Modified Glycol Lignin at Room Temperature.

Recently, a large-scale production system of softwood-derived poly(ethylene glycol) (PEG)-modified glycol lignin (GL) was developed to produce high-quality lignin derivatives with substantially controlled chemical structures and attractive thermal properties. In this study, the further upgrading of GL properties with carboxy functionalization was demonstrated through the room-temperature hydrogen peroxide (H2O2) treatment with the mass ratio of H2O2 to GL, 1:1 and 1:3, for 7 d. The changes in the chemical structure, carboxy group content, molecular weight, and thermal properties of the insoluble portions of partially oxidized glycol lignins (OGLs) were then investigated. Nuclear magnetic resonance and thioacidolysis data revealed that the oxidative functionalization involved the cleavage of ß-O-4 linkages and the oxidative cleavage of guaiacyl aromatic rings into muconic acid-type structures. This was validated by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and potentiometric titration. Overall, the results suggested that the varying outcomes of carboxy group content (0.81-2.04 mmol/g OGL) after 7-d treatment depended on the type of the GL origin having varying amounts of the retained native lignin structure (e.g., ß-O-4 linkages), which were prepared from different source-wood-meal sizes and PEG molecular masses.

Effect of Heat Treatment on the Chemical Structure and Thermal Properties of Softwood-Derived Glycol Lignin.

A large-scale glycol lignin (GL) production process (50 kg wood meal per batch) based on acid-catalyzed polyethylene glycol (PEG) solvolysis of Japanese cedar (JC) was developed at the Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Japan. JC wood meal with various particle size distributions (JC-S < JC-M < JC-L) (average meal size, JC-S (0.4 mm) < JC-M (0.8 mm) < JC-L (1.6 mm)) and liquid PEG with various molecular masses are used as starting materials to produce PEG-modified lignin derivatives, namely, GLs, with various physicochemical and thermal properties. Because GLs are considered a potential feedstock for industrial applications, the effect of heat treatment on GL properties is an important issue for GL-based material production. In this study, GLs obtained from PEG400 solvolysis of JC-S, JC-M, and JC-L were subjected to heating in a constant-temperature drying oven at temperatures ranging from 100 to 220 °C for 1 h. All heat-treated GL series were thermally stable, as determined from the Klason lignin content, TMA, and TGA analyses. SEC analysis suggests the possibility of condensation among lignin fragments during heat treatment. ATR-FTIR spectroscopy, thioacidolysis, and 2D HSQC NMR demonstrated that a structural rearrangement occurs in the heat-treated GL400 samples, in which the content of α-PEG-ß-O-4 linkages decreases along with the proportional enrichments of ß-5 and ß-ß linkages, particularly at treatment temperatures above 160 °C.

Solvent-Free Fabrication of an Elastomeric Epoxy Resin Using Glycol Lignin from Japanese Cedar.

In this study, a simple formulation of softwood-derived glycol lignin (GL)-based epoxy resin with a high GL content of greater than 50 wt % was demonstrated by direct mixing with poly(ethylene glycol) diglycidyl ether (PEGDGE), an aliphatic epoxide, without using any solvent. Because the GL powder produced from poly(ethylene glycol) (PEG400) solvolysis of Japanese cedar softwood meal was a PEG400-modified lignin (GL400), a strong affinity between PEG counterparts facilitates the uniform mixing of GL400 with PEGDGE, and one component uncured GL400/PEGDGE epoxy resin was prepared at a relatively lower temperature (100 °C) than the curing temperature (130 °C). The epoxy curing reaction was monitored by 1H NMR and Fourier transform infrared spectroscopies. The physical and mechanical properties of the epoxy resins with different GL400 contents were then evaluated. The developed resins exhibited good flexibility and elasticity depending on the GL400 content.

Flexible Electronic Substrate Film Fabricated Using Natural Clay and Wood Components with Cross-Linking Polymer.

Requirements for flexible electronic substrate are successfully accomplished by green nanocomposite film fabricated with two natural components: glycol-modified biomass lignin and Li+ montmorillonite clay. In addition to these major components, a cross-linking polymer between the lignin is incorporated into montmorillonite. Multilayer-assembled structure is formed due to stacking nature of high aspect montmorillonite, resulting in thermal durability up to 573 K, low thermal expansion, and oxygen barrier property below measurable limit. Preannealing for montmorillonite and the cross-linking formation enhance moisture barrier property superior to that of industrial engineering plastics, polyimide. As a result, the film has advantages for electronic film substrate. Furthermore, these properties can be achieved at the drying temperature up to 503 K, while the polyimide films are difficult to fabricate by this temperature. In order to examine its applicability for substrate film, flexible electrodes are finely printed on it and touch sensor device can be constructed with rigid elements on the electrode. In consequence, this nanocomposite film is expected to contribute to production of functional materials, progresses in expansion of biomass usage with low energy consumption, and construction of environmental friendly flexible electronic devices.

Transparent Conductive Nanofiber Paper for Foldable Solar Cells.

Optically transparent nanofiber paper containing silver nanowires showed high electrical conductivity and maintained the high transparency, and low weight of the original transparent nanofiber paper. We demonstrated some procedures of optically transparent and electrically conductive cellulose nanofiber paper for lightweight and portable electronic devices. The nanofiber paper enhanced high conductivity without any post treatments such as heating or mechanical pressing, when cellulose nanofiber dispersions were dropped on a silver nanowire thin layer. The transparent conductive nanofiber paper showed high electrical durability in repeated folding tests, due to dual advantages of the hydrophilic affinity between cellulose and silver nanowires, and the entanglement between cellulose nanofibers and silver nanowires. Their optical transparency and electrical conductivity were as high as those of ITO glass. Therefore, using this conductive transparent paper, organic solar cells were produced that achieved a power conversion of 3.2%, which was as high as that of ITO-based solar cells.

Surface functional group dependent apatite formation on bacterial cellulose microfibrils network in a simulated body fluid.

The apatite forming ability of biopolymer bacterial cellulose (BC) has been investigated by soaking different BC specimens in a simulated body fluid (1.5 SBF) under physiological conditions, at 37 degrees C and pH 7.4, mimicking the natural process of apatite formation. From ATR-FTIR spectra and ICP-AES analysis, the crystalline phase nucleated on the BC microfibrils surface was calcium deficient carbonated apatite through initial formation of octacalcium phosphate (OCP) or OCP like calcium phosphate phase regardless of the substrates. Morphology of the deposits from SEM, FE-SEM, and TEM observations revealed the fine structure of thin film plates uniting together to form apatite globules of various size (from <1 mum to 3 mum) with respect to the substrates. Surface modification by TEMPO (2,2,6,6-tetramethylpyperidine-1-oxyl)-mediated oxidation, which can readily form active carboxyl functional groups upon selective oxidation of primary hydroxyl groups on the surface of BC microfibrils, enhanced the rate of apatite nucleation. Ion exchanged treatment with calcium chloride solution after TEMPO-mediated oxidation was found to be remarkably different from other BC substrates with the highest deposit weight and the smallest apatite globules size. The role of BC substrates to induce mineralization rate differs according to the nature of the BC substrates, which strongly influences the growth behavior of the apatite crystals.

Characterization of uniaxially aligned chitin film by 2D FT-IR spectroscopy.

Two-dimensional FT-IR spectroscopy (2D FT-IR) was applied to the investigations of crystalline chitin structure. From this study, new information about spectral bands which are not observed in conventional 1D FT-IR was obtained. In 2D spectra, three specific bands were differentiated at 3482, 3421, and 3380 cm(-1) in the OH region. They could be assigned as C(6)OH groups which are hydrogen-bonded to the next C(6)OH; C(3)OH groups hydrogen-bonded to O(5); and C(6)OH groups bifurcated hydrogen-bonded to C(6)OH as well as C=O, respectively. Two pairs of bands appeared in the amide region, indicating the two types of hydrogen-bonded states of C=O groups. This is in good agreement with the results in the OH region; half of the C(6)OH groups are hydrogen-bonded to C=O as well as the next C(6)OH. The results accurately confirmed the Blackwell model which was established by an X-ray diffraction study. The temperature-dependency of hydrogen-bonds was also revealed by 2D FT-IR. Interchain hydrogen-bonds [C(6)OH...O(6)] first respond to a temperature followed by intrachain [C(6)OH...O=C] and [C(3)OH...O(5)] with increasing temperature. Interchain hydrogen-bonds [NH...O=C] are relatively stable in the temperature range of 40-180 degrees C.