Research Articles

Crude cellulose prepared from alkali-extracted sugarcane bagasse was subjected to a rapid purification treatment with a mixture of 80% acetic acid-68% nitric acid (10/1, v/v) at 120 °C for 15 min. The yields of the preparations decreased slightly from 57.3%-58.6% in the crude cellulose preparations to 50.3%-51.9% in the purified cellulose samples. The purification treatment removed large amounts of resistant hemicelluloses strongly associated to the cellulose. XRD analysis revealed that the structure of both the crude and purified cellulose was cellulose I. Compared to the crude cellulose, a slight increase in the crystallinity index of the purified cellulose was observed by FTIR, XRD, and CP/MAS 13C NMR analyses. In addition, SEM showed that the macrofibril surface of the crude cellulose was almost free of trenches, but many terraces, steps, and kinks formed in the preparations after the purification.

The effects of partial replacement of rattan powder (RP) by carbon black (CB), mica, and calcium carbonate (CaCO3) on the curing characteristics, tensile properties, rubber-filler interaction, and morphological studies of natural rubber (NR) composites were investigated. Rattan powder with an average particle size of less than 180 µm was used in this study. NR/RP/CB, NR/RP/mica, and NR/RP/CaCO3 composites with five different RP/commercial fillers loadings (i.e. 30/0, 20/10, 15/15, 10/20, 0/30 phr) were prepared using a laboratory size two-roll mill. Results showed that the maximum torque (MH) of the NR/RP/CB, NR/RP/mica, and NR/RP/CaCO3 composites increased with increasing the commercial filler-loading ratio. The scorch time (ts2) and cure time (t90) of NR/RP/CB composites decreased as the ratio of CB loading was increased, whereas, ts2 and t90 of NR/RP/mica and NR/RP/CaCO3 composites increased as mica and CaCO3 loading ratio were raised, respectively. The tensile strength, elongation at break (Eb), stress at 100% elongation (M100), and stress at 300% elongation (M300) of all the composites increased as the commercial filler-loading ratio increased. This is due to the presence of the commercial filler, which brought a better rubber-filler interaction, as confirmed by the rubber-filler interaction and scanning electron microscopy (SEM) studies.

The durability of thermally modified (TM) and untreated (UT) mini-stakes exposed to in-ground contact was compared by modulus of elasticity (MOE) and mass loss with decay type using microscopy. Results showed a strong correlation between MOE and soft rot decay for UT stakes over a 30 month exposure period. For TM stakes, the correlation between MOE and decay rate (soft rot/bacteria) was not as strong. Loss of MOE of the TM stakes is suggested to be accentuated by the extensive micro-checking produced in the TM wood tracheids during the original heat treatment. The micro-checks are thought to expand during the winter season due to water expansion during freezing, thereby leading to weakening of the wood in addition to the decay caused by soft rot and bacteria. Using molecular methods, Phialophora hoffmannii was identified as the main fungus causing soft rot decay.

The effect of biomass loading from 50 to 200 g/L on enzymatic hydrolysis was studied using switchgrass samples pretreated by dilute acid and hypochlorite-alkaline methods. It was confirmed that an increase of initial loading of the pretreated biomass leads to a decrease of enzymatic digestibility, probably due to difficulty of mass transfer of cellulolytic enzymes in the high-viscous substrate slurry and also because of an inhibiting effect of the formed sugars. An additional sharp problem connected with enzymatic hydrolysis at the high-solids loading is absorption and retention of liquid hydrolysate by residual non-hydrolyzed biomass that causes diminution of the available volume (Va) of the sugar solution and decreases productivity of the saccharification process. To optimize the high-solids enzymatic hydrolysis, the maximal amount of the formed sugars was determined Am = Cm x Va,m , where Cm is maximal concentration of the sugar solution and Va,m is maximal available volume. Such an approach makes it possible to find the optimal conditions for the hydrolysis: optimal biomass loading and hydrolysis time. After enzymatic hydrolysis at these optimal conditions, the low-lignified biomass pretreated by hypochlorite-alkaline method displayed much more available volume of sugar solution and higher digestibility characteristics than the cellolignin obtained by acidic pretreatment of the initial biomass sample.

Microfibrillated celluloses, liberated from macroscopic lignocellulosic fibers by mechanical means, are sub-fiber elements with lengths in the micron scale and diameters ranging from 10 to a few hundred nanometers. These materials have shown strong water interactions. This article describes an investigation and quantification of the ‘hard-to-remove (HR) water content’ in cellulose fibers and microfibrillated structures prepared from fully bleached softwood pulp (BSW). The fiber/fibril structure was altered by using an extended beating process (up to 300 minutes), and water interactions were determined with isothermal thermogravimetric analysis (TGA). Isothermal TGA is shown to be a convenient and insightful characterization method for fiber-water interactions for fibers and microfibrils at small sample size. In addition, scanning electron microscopic (SEM) images depict the differences between fibers and microfibrils with respect to beating time in the dried consolidated structures. Highly refined pulps with microfibrils were determined to have two critical drying points, i.e., two minima in the second derivative of weight versus time, not before reported in the literature. Also in this study, hard-to-remove (HR) water content is related to the area above the first derivative curve in the constant rate and falling rate drying zones. This measure of HR water correlates with a previous measurement method of HR water but is less ambiguous for materials that lack a constant drying rate zone. Blends of unbeaten fibers and microfibril containing samples were prepared and show potential as composite materials.

Densification of biomass feedstocks, such as pelletizing, can increase bulk density, improve storability, reduce transportation costs, and ease the handling of biomass using existing handling and storage equipment for grains. In order to study the pelletizing process, compost pellets were produced under controlled conditions. The aim of the work was to investigate the effect of raw material properties and the die geometry on the true density of formed pellets and also find the optimal conditions of the densification process for producing pellets with high density. Compost was extruded into cylindrical pellets utilizing open-end dies under axial stress from a vertical piston applied by a hydraulic press. The effects of independent variables, including the raw material moisture content (35 to 45% (wet basis)), hammer mill screen size (0.3 to 1.5 mm), speed of piston (2 to 10 mm/s), and die length (8 to 12 mm) on pellet density, were determined using response surface methodology. A quadratic model was proposed to predict the pellet density, which had high F and R2 values along with a low p value, indicating the predictability of the model. Moisture content, speed of piston, and particle size significantly affected (P < 0.01) the density of pellets, while the influence of die length was negligible (P > 0.05).

For many wood cutting processes, the interest of high-speed tool steels and tungsten carbides remains very important because of their good tool edge accuracy and easy grinding. The wear of high-speed steel and tungsten carbide is an important economic parameter. Wood extractives and silica have a potential adverse effect on tool wear. Rapid chemical wearing due to corrosion and mechanical wearing has been attributed to the presence of extractives and silica in wood and wood composites. This paper presents the wear characteristics of SKH51 high-speed steel and K10 tungsten carbide caused by extractive and abrasive materials present in the lesser-known Tapi-Tapi wood and wood composites of wood cement board, particleboard, MDF, and oriented strand board (OSB). Experimental results showed that wearing of the cutting tools tested was determined by extractives and silica contained in the wood and wood composites. Wood cement board, which is high in silica content, caused severe damage to the cutting edge of the high-speed steel. A corrosion/oxidation mechanism was found to contribute to the wear of SKH51 and K10 when cutting the Tapi-Tapi wood, MDF, particleboard, wood cement board, and OSB. The silica and extractives determined the abrasion and corrosion wear mechanism to a varying degree.

Modulus of elasticity (MOE) in the tangential direction for Norway spruce, Picea abies (L.) H. Karst, was measured. Test samples were tested in three-point bending, and moisture content (MC) and temperature were varied between the green condition and 7% MC and between 20 °C and 80 °C, respectively. Using correction factors calculated from finite element simulations, an adjustment of measured MOE was made to the ideally tangential direction. The results show MOE and the gradients with respect to MC and temperature and how they vary with MC and temperature. The gradients are factors in gradient terms in the incremental stress-strain relation for linear elastic behaviour during load cycles where there are mechanical loads and at the same time, varying MC and temperature. The gradient terms add to the temperature and MC expansion coefficients and may be of significant size for cases with high stress, high temperature, and high MC.

Six hemicellulosic samples were isolated from cell wall material of dewaxed sweet sorghum (Sorghum bicolor (L.) Moench) leaves by sequential extractions with distilled water, alkali, and organic alkali solvent. The samples were treated with water, 1% NaOH, and 60% ethanol. The organic alkali samples were treated with 1%, 3%, 5%, and 8% NaOH, which yielded 8.3%, 5.4%, 1.0%, 5.6%, 2.5%, and 4.9% hemicelluloses based on the dry initial sweet sorghum leaves, respectively, and resulted in a total release of 81% of all hemicelluloses originally present in the cell wall. The results indicated that water-soluble hemicelluloses contained noticeable amounts of glucose, arabinose, galactose, and xylose, and had a relatively lower molecular weight (17300 g/mol). The four alkali-soluble hemicellulosic fractions, rich in xylose, were more linear, and had higher molecular weights (48500-128000 g/mol) than those of the alkali organic-soluble hemicellulosic fraction. With an increase of NaOH concentration from 1% to 8%, the ratio of arabinose to xylose decreased from 0.29 to 0.01, which implied that the hemicelluloses obtained by the higher concentration of alkali appeared to be more linear. Based on the sugar analysis, Fourier transform infrared (FT-IR), and nuclear magnetic resonance (NMR) results, 4-O-methylglucuronoarabinoxylans were the major constituents of the hemicellulosic polymers.

Agarose films were formed with the addition of 30 to 70 wt% choline chloride/urea eutectic-based ionic liquid (ChCl/Urea). The ChCl/Urea was prepared through complexation at a 1:2 mole ratio. The films were prepared by dissolving ChCl/Urea in distilled water followed by dispersion of the agarose at 95 °C. The solution was gelled at room temperature, and the formed gel was dried in an oven overnight at 70 °C. Mechanical testing indicated that the agarose film containing 60 wt% ChCl/Urea had higher tensile extension and tensile strain at break compared to the pristine agarose film. The addition of ChCl/Urea also reduced the glass transition temperature (Tg) of agarose films. Cross-section SEM images of the agarose films showed that surface roughness disappeared with the incorporation of ChCl/Urea. FTIR spectra confirmed the presence of intermolecular hydrogen bonding between agarose and ChCl/Urea. XRD patterns demonstrated that an amorphous phase was obtained when ChCl/Urea was added. Agarose films containing more ChCl/Urea exhibited higher transparency, as measured by a UV-Vis spectrometer. In summary, the physicochemical properties of agarose films were evidently affected by the incorporation of the ChCl/Urea as a plasticizing agent.