Preparation of Molded Fiber Products from Hydroxylated Lignin Compounded with Lewis Acid-Modified Fibers Its Analysis.

In this study, molded fiber products (MFPs) were prepared from lignin compounded with Lewis acid-modified fibers using enzymatic hydrolysis lignin (EHL) as a bio-phenol. The fibers were modified and compounded entirely through hot-pressing. To improve the reactivity of enzymatic lignin, hydroxylated enzymatic hydrolysis lignin (HEHL) was prepared by hydroxylation modification of purified EHL with hydrogen peroxide (H2O2) and ferrous hydroxide (Fe(OH)3). HEHL was mixed uniformly with Lewis acid-modified fibers on a pressure machine and modified during the molding process. The purpose of Lewis acid degradation of hemicellulose-converted furfural with HEHL was to generate a resin structure to improve the mechanical properties of a MFPs. The microstructure of the MFP was shown to be generated by resin structure, and it was demonstrated that HEHL was compounded on Lewis acid-modified fibers during the molding process. The thermal stability of the MFP with composite HEHL did not change significantly owing to the addition of lignin and had higher tensile strength (46.28 MPa) and flexural strength (65.26 MPa) compared to uncompounded and modified MFP. The results of this study are expected to promote the application of high lignin content fibers in molded fibers.

Hydrothermal synthesis of nitrogen-doped carbon quantum dots from lignin for formaldehyde determination.

This work assessed the fabrication of nitrogen-doped CQDs (NCQDs) from alkali lignin (AL) obtained from spruce, representing a green, low-cost biomass generated by the pulp and biorefinery industries. The AL was found to retain its original lignin skeleton and could be used to produce NCQDs with excellent photoluminescence properties by one-pot hydrothermal treatment of AL and m-phenylenediamine. These NCQDs exhibited blue-green fluorescence (FL) with excitation/emission of 390/490 nm under optimal conditions. The NCQDs showed pH and excitation wavelength-dependent FL emission behaviors. On the basis of the exceptional selective response of these NCQDs to specific solvents, we developed a FL probe for the detection of formaldehyde (FA). The FL intensity of NCQDs was found to be directly proportional to the concentration of FA in the range of 0.05 to 2 mM (R 2 = 0.993), with a detection limit of 4.64 µM (based on 3σ/K). A composite film comprising NCQDs with poly(vinyl alcohol) was found to act as a sensor with a good FL response to FA gas. When exposed to gaseous FA, this film exhibited increased FL intensity and transitioned from blue-green to blue. A mechanism is proposed in which the NCQDs react rapidly with FA to generate Schiff bases that result in enhanced FL emission and the observed blue shift in color.

Isolation and characterization of nanocellulose crystals via acid hydrolysis from agricultural waste-tea stalk.

Nanocellulose crystals (NCCs) were successfully prepared via acid hydrolysis from an abundant agricultural waste (tea stalk) in China. The effective factors for NCC yield were modeled by the response surface methodology (RSM). The RSM determined the reaction conditions (H2SO4 concentration, hydrolysis temperature, and reaction time) that optimized the yield of tea stalk NCCs (TNCCs). Under the optimized operating conditions, the fundamental properties of TNCCs were characterized via transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), laser diffraction particle-size analyzer, and scanning probe microscopy (SPM). Wood NCCs (WNCCs) and microcrystalline NCCs (MNCCs) were simultaneously prepared from common wood and microcrystalline cellulose under the same conditions. The results show that TNCCs not only shows similar physical and chemical properties with WNCCs and MNCCs, but also has better stability. Therefore, this study offers novel routes for high-valued utilization of tea stalk and provides some theoretical guidance for utilizing cellulose obtained from tea stalk.

Effect of lignin on the self-bonding of a natural fiber material in a hydrothermal environment: Lignin structure and characterization.

Self-bonding natural fiber materials (SNFMs) were prepared at different initial moisture contents (IMCs) through a molding pressing process. The self-bonding mechanism of the SNFMs was deduced from the chemical and structural changes of lignin and their mechanical strengths. The structural transformations of milled wood lignin (MWL) in the SNFMs were investigated by two-dimensional heteronuclear single quantum coherence, quantitative 31P-nuclear magnetic resonance spectra, gelpermeation chromatography, and thermogravimetric analysis. As IMC increased from 0% to 80%, the tensile strength increased from 23.0 to 70.0 MPa and the density increased from 0.99 to 1.05 g/cm3. IMC affected the distribution and abundance of the typical lignin linkages (ß-O-4', ß-ß, and ß-5') and the S-OH/G-OH ratios of lignin. Moreover, as IMC increased, the aliphatic hydroxyl groups proportionally decreased, while the condensed phenolic and non-condensed phenolic hydroxyl groups increased, the molecular weight of MWL became larger, and the thermal stability of lignin improved. These findings indicate the simultaneous occurrence of depolymerization and condensation reactions of lignin. The condensation reaction dominated, improving the mechanical strength of the material. Our results explain (at least partly) the self-bonding mechanism of SNFMs.

Isolation and Characterization of Nanocellulose with a Novel Shape from Walnut (Juglans Regia L.) Shell Agricultural Waste.

Herein, walnut shell (WS) was utilized as the raw material for the production of purified cellulose. The production technique involves multiple treatments, including alkaline treatment and bleaching. Furthermore, two nanocellulose materials were derived from WS by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) oxidation and sulfuric acid hydrolysis, demonstrating the broad applicability and value of walnuts. The micromorphologies, crystalline structures, chemical functional groups, and thermal stabilities of the nanocellulose obtained via TEMPO oxidation and sulfuric acid hydrolysis (TNC and SNC, respectively) were comprehensively characterized. The TNC exhibited an irregular block structure, whereas the SNC was rectangular in shape, with a length of 55-82 nm and a width of 49-81 nm. These observations are expected to provide insight into the potential of utilizing WSs as the raw material for preparing nanocellulose, which could address the problems of the low-valued utilization of walnuts and pollution because of unused WSs.

The Dispersion of Pulp-Fiber in High-Density Polyethylene via Different Fabrication Processes.

In this study, a pulp beating machine was used to premix the pulp fibers with high density polyethylene (HDPE) particles in water. The wet or pre-dried pulp fiber/HDPE mixture was then melt-compounded by a twin screw extruder. For further improving the dispersion of pulp fiber, some mixture was forced to pass through the twin-screw extruder twice. The resulting mixture was compression molded to the composite. The fiber distribution was observed by the aid of an optic and scanning electron microscope. The mechanical and rheological properties and creep resistance of the composites were characterized. Test results demonstrate that when the wet pulp fiber/HDPE mixture was subjected to pre-pressing and oven drying prior to extrusion compounding, the resulting composites exhibited homogeneous fiber distribution, superior flexural property, creep-resistance, and high storage modulus. Particularly, its flexural strength and modulus were 57% and 222% higher, respectively, than that of the neat HDPE, while the composites prepared without pre-dried were 19% and 100% higher, respectively. Drying the wet mixture in advance is more effective than re-passing through the extruder for improving the fiber dispersion and composite performance.

Ultrasound-assisted extraction of arabinogalactan and dihydroquercetin simultaneously from Larix gmelinii as a pretreatment for pulping and papermaking.

An ultrasound-assisted extraction (UAE) method using ethanol was applied for extracting arabinogalactan (AG) and dihydroquercetin (DHQ) simultaneously from larch wood, as a pretreatment for pulping and papermaking. The extraction parameters were optimized by a Box-Behnken experimental design with the yields of AG and DHQ as the response values. Under optimum conditions (three extractions, each using 40% ethanol, for 50 min, 200 W ultrasound power and 1∶18 solid-liquid ratio), the yields of AG and DHQ were 183.4 and 36.76 mg/g, respectively. After UAE pretreated, the wood chips were used for Kraft pulping (KP) and high boiling solvent pulping (HBSP). The pulping yield after pretreatment was higher than that of untreated (the pulping yields of untreated HBSP and KP were 42.37% and 39.60%, and the pulping yields of HBSP and KP after UAE-pretreated were 44.23% and 41.50% respectively), as indicated by a lower kappa number (77.91 and 27.30 for untreated HBSP and KP; 77.01 and 26.83 for UAE-pretreated HBSP and KP). Furthermore, the characteristics of paper produced from pretreated wood chips were superior to those from the untreated chips: the basis weight was lower (85.67 and 82.48 g·cm(-2) for paper from untreated KP and HBSP; 79.94 and 80.25 g·cm(-2) for paper from UAE-pretreated KP and HBSP), and the tensile strengths, tearing strengths, bursting strengths, and folding strengths were higher than these of paper after UAE-pretreated, respectively.

Preparation of nanocrystalline cellulose via ultrasound and its reinforcement capability for poly(vinyl alcohol) composites.

Rod-shaped nanocrystalline cellulose (NCC) was prepared from microcrystalline cellulose (MCC) using the purely physical method of high-intensity ultrasonication. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction was used for the characterization of the morphology and crystal structure of the material. The thermal properties were investigated using thermogravimetric analysis. The reinforcement capabilities of the obtained NCC were investigated by adding it to poly(vinyl alcohol) (PVA) via the solution casting method. The results revealed that the prepared NCC had a rod-shaped structure, with diameters between 10 and 20 nm and lengths between 50 and 250 nm. X-ray diffraction results indicated that the NCC had the cellulose I crystal structure similar to that of MCC. The crystallinity of the NCC decreased with increasing ultrasonication time. The ultrasonic effect was non-selective, which means it can remove amorphous cellulose and crystalline cellulose. Because of the nanoscale size and large number of free-end chains, the NCC degraded at a slightly lower temperature, which resulted in increased char residue (9.6-16.1%), compared with that of the MCC (6.2%). The storage modulus of the nanocomposite films were significantly improved compared with that of pure PVA films. The modulus of PVA with 8 wt.% NCC was 2.40× larger than that of pure PVA.