Volume 74, Issue 5

Fast-growing wood is an abundant and low-cost material and is widely used for structural building and furniture construction. However, inferior mechanical properties and dimensional instability limit its application in advanced engineering structures. Herein, we developed a simple, effective and “green” method to transform bulk poplar into a high-performance wood composite. The wood composite was prepared by the impregnation of the itaconic acid (IA) solution acting as a grafting anchor into the wood matrix, followed by in situ polymerization of styrene upon heating to form a hydrophobic polymer within the wood scaffold. Scanning electron microscope (SEM) analysis revealed that hydrophobic polystyrene (PS) was deposited in wood cell walls and lumens, leading to a reduced water uptake and remarkably enhanced dimensional stability, as well as generally improved mechanical properties. In addition, the PS generated improvement in the thermal stability of the wood composite in comparison with that of natural wood (W).

Changes in relative humidity of the ambient air, RH (%), cause wetting and drying of wood material, which results in non-uniform moisture contents or moisture gradients, and consequently in moisture-induced stresses and strains in the glued-laminated timber (glulam) members. The aim of the present paper is to perform a hygro-mechanical analysis to predict the mechanical behavior of glulam specimens exposed to two RH regimes, causing wetting from 50% to 90% RH and drying from 90% to 50% RH, and compare the numerical to the experimental results. The aims are also to quantitatively analyze the influence of characteristic material parameters required in the multi-Fickian moisture transport model and the mechanical model on moisture-induced strains and stresses in glulam specimens and to determine the possibility of cracking of the material by analyzing the maximum tensile stresses perpendicular to the grain. Accurate numerical predictions of moisture contents and moisture-induced strains are obtained in the glulam specimens during wetting and drying as compared to the experimental results. The influence of a particular characteristic material parameter on moisture-induced strains and stresses is characterized as significant, but not crucial when a rough numerical estimation of the mechanical behavior of the glulam beam exposed to RH changes is required.

To achieve efficient utilization of compression wood (CW), a deeper insight into the molecular interactions is necessary. In particular, the role of lignin in the wood needs to be better understood, especially concerning how lignin contributes to its mechanical properties. For this reason, the properties of CW and normal wood (NW) from Chinese fir ( Cunninghamia lanceolata ) have been studied on a molecular scale by means of polarized Fourier transform infrared (FTIR) spectroscopy, under both static and dynamic loading conditions. Under static tensile loading, only molecular deformations of cellulose were observed in both CW and NW. No participation of lignin could be detected. In relation to the macroscopic strain, the molecular deformation of the cellulose C-O-C bond was greater in NW than in CW as a reflection of the higher microfibril angle and the lower load taken up by CW. Under dynamic deformation, a larger contribution of the lignin to stress transfer was detected in CW; the molecular deformation of the lignin being highly related to the amplitude of the applied stress. Correlation analysis indicated that there was a direct coupling between lignin and cellulose in CW, but there was no evidence of such a direct coupling in NW.

In this study, poplar chemi-mechanical pulp was used as a raw material to investigate the effect of enzymatic hydrolysis lignin (EHL) content on the tensile strength and hydrophobicity of molded fiber materials (MFMs). The tensile strength and hydrophobic properties of the fabricated MFMs with different EHL contents were evaluated, and changes in their microstructure, chemical structure, and thermal stability were characterized via scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric (TG) analysis, respectively. Results show that under the experimental conditions used herein, the addition of EHL could increase the tensile strength and surface water contact angle of MFMs up to 20.3 MPa and 95.0°, respectively. The SEM observations indicate that the addition of EHL expanded the contact area between the EHL and fibers, thereby reducing the holes between fibers. The FTIR and TG analyses indicated that hot-pressing degraded EHL to form small molecular substances and improved the reaction with aldehydes produced via carbohydrate degradation, improving both the inter-fiber bonding strength and hydrophobicity of the MFM surface.

With industrial groundwood pulping processes relying on carefully designed grit surfaces being developed for commercial use, it is increasingly important to understand the mechanisms occurring in the contact between wood and tool. We present a methodology to experimentally and numerically analyse the effect of different tool geometries on the groundwood pulping defibration process. Using a combination of high-resolution experimental and numerical methods, including finite element (FE) models, digital volume correlation (DVC) of synchrotron radiation-based X-ray computed tomography (CT) of initial grinding and lab-scale grinding experiments, this paper aims to study such mechanisms. Three different asperity geometries were studied in FE simulations and in grinding of wood from Norway spruce. We found a good correlation between strains obtained from FE models and strains calculated using DVC from stacks of CT images of initial grinding. We also correlate the strains obtained from numerical models to the integrity of the separated fibres in lab-scale grinding experiments. In conclusion, we found that, by modifying the asperity geometries, it is, to some extent, possible to control the underlying mechanisms, enabling development of better tools in terms of efficiency, quality of the fibres and stability of the groundwood pulping process.

Defoliating insects damage forest plantations, but the estimation of their losses does not take into account wood quality changes. The objective was to evaluate the wood quality and pulp production of two clones of Eucalyptus grandis  ×  Eucalyptus urophylla (clone A) and Eucalyptus saligna (clone B) damaged or not by defoliating insects. Five healthy trees and five attacked by Gonipterus platensis Marelli (Coleoptera: Curculionidae) were selected per clone. The wood volume per hectare in the affected settlements was at least 9% lower and damaged trees showed lower wood basic density, with at least 4.6%. The lignin and extractive content in the wood increased by at least 5.6 and 45%, respectively, while the syringyl/guaiacyl (S/G) ratio remained constant for clone A and increased 10% for clone B. For pulps, an increased effective alkali and decreased pulp yield were experienced for both clones while bleaching or pulp quality was not affected. In the stands affected by defoliating insects, productivity was 9 and 19% lower considering the wood volume per hectare and 15 and 24% considering the cellulose pulp production per hectare, respectively.

This study analyzed the effect that pulp fibers have on the surface softness component of hygiene paper. The surface softness component has more of an influence on the evaluation of subjective softness results than the bulk softness component. Using the surface softness measurement technique, this study aimed to evaluate the effect that fibers have on the softness of hygiene paper substrate via objective numerical values to measure the surface softness component of hand sheets composed of various pulp species. The results indicate that coarseness effects had the largest effect on softness among the various fiber characteristics, such as average fiber length, width and coarseness. As fiber coarseness increased, a rough surface formed, which resulted in an increase in the mean deviation from the average friction (MMD). Nonwood fibers had long fiber length and low coarseness, which enables the production of hygiene paper with high strength and softness. This study hopefully could lead to the development of various process technologies that may improve the softness of hygiene paper products.

Modification techniques have been widely employed to improve cellulose properties, thus increasing the diversity of industrial applications. While wood pulp cellulose is the most common source for industrial production, little has been studied about the effects of the cellulose source and its purity on modification. Therefore, this article investigates the influence of cellulose source (e.g. wood or cotton) on its modification (acetylation), by estimating the obtained degree of substitution (DS) through Fourier-transform infrared (FT-IR), proton nuclear magnetic resonance ( 1 H NMR) and back titration. The intense reduction in samples’ crystallinity after acetylation was a result of breakage of inter- and intra-molecular hydrogen bonds, thus confirming acetylation. Although Avicel showed the highest cellulose content and was virtually free of hemicellulose and lignin, this did not affect the acetylation degree, as all samples were successfully triacetylated. The techniques used in this study were ideal for detecting acetylation and estimating the DS, which makes them good tools for modification studies of cellulose derivatives.

Aiming to improve the poor miscibility between lignin and non-polar materials, alkali lignin (AL) was self-assembled into lignin reverse micelles (LRM) and blended with high-density polyethylene (HDPE) to fabricate composite films. The particle size of AL increased from 3.5 nm to 130 nm after forming LRM, showing a uniform spherical morphology. The water droplet contact angle increased from 54° to 89°. Optimal and rheological analysis revealed that composite films exhibited good transparency, ultraviolet (UV)-blocking performance and low viscoelasticity after adding the nano LRM. Under the optimal dosage of 5 wt% LRM, the composite film can screen 93% UV rays, and the apparent viscosities, complex viscosities, storage and loss modulus of the mixture were the lowest. Atomic force microscopy (AFM) was used to investigate the molecular interactions between lignin and HDPE. The average adhesion force between LRM and HDPE in dry air was 1.07 mN m −1 , while that between AL and HDPE was 0.77 mN m −1 . AFM experiments fundamentally demonstrated better compatibility between LRM and HDPE, which was beneficial for the improvement of UV-blocking, rheological properties, as well as their processability of LRM/HDPE films.

With the increasing application of polyvinyl alcohol (PVA) films in the field of food packaging, it is important to improve its mechanical and antibacterial properties. This paper focuses on the preparation of PVA nanocomposite films and how their properties are affected by a silver-loaded nanocellulose solution. Cellulose nanocrystals (CNCs) were used as both the carrier and the dispersant of silver nanoparticles (AgNPs) prepared using glucose as the reducing agent. Ag + was stabilized by the many hydroxyl groups located in the CNCs, and then the Ag + was reduced to AgNPs in situ . After addition of silver-loaded nanocellulose, the tensile strength of the CNC-PVA-AgNP films increased from 47 MPa to 73 MPa, and the nanocomposite films displayed reduced moisture absorption and good antibacterial properties.

Echinus-like nitrogen-doped carbon with a hierarchical porous structure was synthesized from green larch waste and urea via liquid in situ doping and high-temperature carbonization. Benefitting from a large specific surface area (649 m 2 g −1 ) and hierarchical porous structure, the nitrogen-doped carbon exhibited excellent electrochemical performance for supercapacitors. Remarkably, the echinus-like nitrogen-doped carbon achieved a high specific capacitance of 340 F g −1 at a current density of 1 A g −1 in 6 M KOH electrolyte as well as a good performance rate and stability (with a capacitance retention of 98% after 5000 cycles). This capacitance was almost 1.5 times higher than that of undoped carbon due to the contribution of the pseudocapacitance from the nitrogen doping. Larch sawdust is a promising carbon source for fabricating inexpensive, sustainable and high-performance supercapacitor materials.