HYDROGEN BONDING IN WOOD-BASED MATERIALS: AN UPDATE

The contribution of hydrogen bonding to wood science and technology has been well recognized over the past century. The hydrogen bond is an important chemical characteristic contributing to wood-based material behavior and it also provides an important contribution to processing features of wood. However, the current understanding of hydrogen bond strength as a contributor to wood-based material behavior has not been updated in the wood literature. Wood-based material literature typically report hydrogen bond strengths ranging from 12.6 to 25.2 kJ/mol (3 to 6 kcal/mol) while newer data from the general chemistry field report hydrogen bond strengths up to 189 kJ/mol (45 kcal/mol), which are characteristic of covalent bond strength. In light of these new data regarding hydrogen bond strengths, it provides impetus to discuss the new understanding of hydrogen bond strength relative to wood-based material behavior. Recent developments in nanotechnology of renewable materials leading to the production and applications of cellulose nanomaterials with much higher surface areas and hydrogen bonding capacity also mandate revisiting our knowledge of the hydrogen bonding mechanism and strength

Study on the effects of wood flour geometry on physical and mechanical properties of wood-plastic composites

The present study is focused on the effects of the shape and size of Fagus orientalis wood flour on physical and mechanical properties of HDPE based wood plastic composites (WPC). Variables included two mesh sizes (20 and 60), as well as five different contents of ground shavings (0, 25, 50,75, and 100%) mixed with sawdust; totally 10 treatments. HDPT content was 40% in all formulations. Panels were compression molded and physical and mechanical tests were carried out in accordance with ASTM D2240 standard specifications. Results showed that mesh size can only significantly affect the hardness in the studied wood-plastic composites. On the other hand, increasing the proportion of the ground shavings possessing higher aspect ratio (l/d) increased both flexural strength and hardness. This increasing effect however was not observed for ground shavings beyond 50%. It was also concluded that while the addition of ground shavings up to 50% could improve the mechanical properties, higher proportions would reduce some of the properties, particularly the impact strength. In was concluded that the panel made of 50% wood flour combined with 50% ground shavings exhibited overall suitableproperties for most applications

Cellulose nanofibrils as a bio-based binder for wood fiber composite insulation panels with enhanced thermo-mechanical properties for structural wall sheathing applications

A low-density wood fiber insulation panel (WIP) composite was developed with 100 % petrochemical-free, bio-based binder with high mechanical strength, water resistance and thermal insulation properties. This study investigated the manufacturing process of composite WIPs made with mechanical pulp fibers with cellulose nanofibrils (CNFs), lignin-containing CNFs (LCNFs), hybridized CNFs-LCNFs, and CNFs-starch as a binder on different scales and evaluated the effects of binder type and content on the panels’ physical, mechanical, and thermal properties. All panels had excellent thermal resistivity values, which increased with the decrease in density. The WIPs made with LCNFs as binder had lower mechanical properties, but it was possible to replace 20 % CNFs with LCNFs to obtain the same performance as neat CNFs as the binder. Untreated panels had poor water resistance but the water absorption properties were significantly improved with the addition wax. The WIPs made with 5 % and 7.5 % binder content and 2 % wax addition could fulfill the criteria of regular and structural wall sheathing applications, respectively. Overall, the results confirm the potential of CNFs and LCNFs to be used as 100 % bio-based adhesives to produce eco-friendly composite WIPs with excellent thermo-mechanical properties to be used for regular and structural wall sheathing applications

Investigation on the stress relaxation behavior of milled newsprint filled polyethylene composite

Stress relaxation behavior of milled newsprint/HDPE composite containing coupling agent was studied. Composites containing 25 and 50% filler in weight were produced, and were compared to neat polymer. Melt blending followed by injection molding was the manufacturing process. Results showed that incorporating filler to polymer increases the flexural strength and modulus. It was observed that higher stress is needed to maintain higher strain levels. Furthermore, comparing the stress ratio patterns revealed that the difference among relaxation of different samples develops over time. Power law computed parameters showed that higher strain level results in higher stress relaxation amplitude (A) and lower time exponent (t). It was also found that, almost complete linear relationship could be established between strain level and parameter A, and the effect of strain level on parameter A is more pronounced at higher filler contents

Effect of compatibilizer, MAPP, on physical and mechanical properties of reed stem flour- polypropylene composites

In order to investigate the effect of compatibilizer, (MAPP), on physical and mechanical properties of reed stem flour- polypropylene composites, 60 mesh size reed stem flour particles were compounded at 60% and 70% by weight with a polypropylene homopolymer with a melt flow index of 18 g/10min. Two compounds were prepared from which formulations with 60 mesh particle size and 60% and 70% filler loading were selected to evaluate the role of the compatibilizer. One of them was without MAPP and the other one had 3% MAPP by weight. Totally, 4 compounds were prepared. Composites were produced using a twin screw counter rotating extruder. Then, mechanical tests including static flexural test, tensile test, Izod impact test and hardness test were carried out. Physical tests including water absorption and thickness swelling were also performed. All testing was in accordance with ASTM D7031-04 specification. The results of physical tests have indicated that by the increase in reed flour content, maximum water absorption and maximum thickness swelling increased. Generally, by adding the coupling agent (MAPP), the physical and mechanical properties significantly improved

Vertical Density Profile and Internal Bond Strength of Wet-Formed Particleboard Bonded with Cellulose Nanofibrils

In this study, the effects of cellulose nanofibrils (CNFs) ratio, press program, particle size, and density on the vertical density profile (VDP) and internal bond (IB) strength of the wet-formed particleboard were investigated. Results revealed that the VDP was significantly influenced by the press program. Pressing using a constant pressure (CP) press program produced panels with flat-shaped profile. Panels made from a constant thickness (CT) press program produced U-shaped profile. The CNF ratio and density also influenced the VDP especially for the CT panels. As the CNF ratio increased, there were noticeable increases in face density, while the core density slowly increased. The CT panels had the lowest core density compared with the CP counterparts, thus significantly lowering the IB. The IB of CP panels increased with the increase of CNF ratio, but the trend for CT panels was different. For the 10% CNF ratio, the IB increased as the core density increased. For the 15% and 20% CNF ratios, the IB decreased as the core density increased. For CP panels, the minimum core densities were higher and thus the IB was significantly higher. None of the panels met the IB values for high-density standard particleboard. All CP panels met some of the medium-density standard IB values and all the low-density standard IB values. However, for the CT panels, only those with 15% and 20% CNF ratio marginally met the low- and medium-density particleboard standard. Trends show that increased CNF ratio and higher pressure could improve IB properties for the high-density particleboard