Volume 10 Issue 3

This paper describes the preparation of poly(vinyl alcohol)/kenaf fiber (PVOH/KF) composites with entrapped urea. The major FTIR peaks of these composites could be identified. These composites are intended for agricultural applications as biodegradable mulches and could be potential carrier materials for fertilizer. The water solubility, release behavior, chemical properties, and thermal stability of the composites were evaluated. The composites lost 25% of their weight after 7 days in water. In a wet environment, urea was released from the composites through its dissolution in water, and around 57% of the urea was released from the composites in 24 h; Thermagravimetric analysis showed that these composites were stable up 150 °C. These composites would be able to withstand rain and protect seedlings from the sun when applied in the field as mulches. For around three to four weeks, these biobased mulches could slowly disintegrate as the PVOH binder was gradually dissolved by moisture, releasing the kenaf fibers to serve as soil fertilizer without leaving any undegradable waste for disposal. Hence, they would not pose any risks to the land or biological systems.

Wood chips from Norway spruce (Picea abies L.) and silver fir (Abies alba L.) were stored for a period of 15 months (experimental pile was 4.0 m high). Atmospheric temperature and the temperature inside the pile at heights of 1, 2, and 3 m were measured in regular intervals. Samples were taken from an assortment of heights at the beginning and the end of the experimental period. Subsequently, the samples were subjected to an analysis of moisture content and other properties such as calorific value (according to the standard STN ISO 1928:2003 and ÖNORM M 7132) and ash content (according to the standard STN ISO 1171). The most significant decrease in the chips’ moisture content, and increase in the calorific value from the beginning of storage, was at the height of 1.0 m. An increase in the moisture content and decrease in calorific value was recorded for samples taken from the height of 3.0 m. Samples taken from this height showed an increase in ash content after a 15-month storage period. The experiment described the influence of specific weather conditions on the development of temperature, calorific value, and ash content of coniferous wood chip piles with particle size up to 35.5 mm.

In this study, samples were subjected to the following surface treatment techniques: sawing with a circular saw, planing with a thickness machine, and sanding with a sanding machine (with No. 80 sandpaper). After samples were treated radially and tangentially with machines, their surface roughness values (Ra, Ry, and Rz) were measured according to ISO 4288. When statistics related to surface roughness values (for Ra, Ry, and Rz) were analyzed, it was found that surfaces processed with the thickness machine exhibited the smoothest surfaces. Also, according to the same statistical tables, the lowest surface roughness values were found for surfaces cut tangentially.

Combustion characteristics of leaves fallen off ornamental trees in city and forest parks were evaluated. The moisture content of the leaves at the time of falling was between Wr = 36.1 and 46.9%. The average contents of the individual elements in the combustible material were Cdaf = 48.1%, Hdaf = 6.1%, Ndaf = 1.2%, Sdaf = 0.1%, and Odaf = 44.6%. The resulting ash from the dry leaves varied between Ad = 4.8 and 13.1%. The heat of combustion of the dry leaves was between Qs = 16,046 and 20,247 kJ.kg-1, and the lower heating value was between Qn = 13,479 and 19,120 kJ.kg-1. The results were compared with dry firewood of hard deciduous trees. The higher heating value of the dry leaves was 11.7% lower and the lower heating value was also lower by 15.1%. The decline of these basic combustion characteristics is caused mostly by its high ash content and to a smaller extent by the increased nitrogen content.

The experimental production of gypsum-based products (cylindrical samples, solid bricks) using different fractions of wood chips and rubber particles was studied. Recovered rubber and wood materials were mixed with gypsum and water in various proportions to fabricate gypsum-wood and gypsum-rubber cylindrical samples and standard solid bricks with six holes using appropriate molds. It was shown that to manufacture gypsum-wood and gypsum-rubber products with good mechanical strength, coarse fractions of wood and rubber should be used, but the proportion of wood or rubber should not exceed 25%. No thermal conductivity differences were found between the wood- and rubber-type of gypsum products, and particle size and material proportion had no effect. Samples with fine wood and rubber particles present at a lower proportion (25%) exhibited similar sound absorption behavior. The solid bricks had slightly higher strength when loaded at the large surface of their lateral upper side than when loaded at the small surface. The bricks provided better thermal insulation than both the extruded and pressed house bricks but lower than that of insulating bricks. The emission of volatile organic compounds out of the bricks was at an acceptable level according to regulations for construction products.

The waste of medium density fiberboards was carbonized at a temperature of 500 °C. The activated carbons were obtained after 16 h of impregnation and 1 h of activation by KOH at 800 °C with KOH/coke mass ratios of 2.5, 3.0, 3.5, and 4.0. The activated carbons were investigated for determination of porosity and elemental analysis. The results showed that the surface area of the activated carbons varied from 1456 to 1647 m2/g and the total pore volume ranged from 0.701 to 1.106 cm3/g, which was affected by different KOH/coke mass ratios . The pore size distribution indicated that waste medium density fiberboard activated carbons included both micropores and mesopores, and the elemental analysis implied that the contents of nitrogen varied from 0.97% to 2.60%. Electric double layer capacitors were made using the activated carbons and their electrochemical properties were studied. The specific capacitances of the activated carbon electrodes ranged from 212 to 223 F/g. The results suggest that activated carbon from waste medium density fiberboard can be a candidate material for electric double layer capacitor electrodes because of its good electrochemical capacities.

Lignin-based membrane material was prepared from lignosulfonate extracted from sulfite pulping. The effects of formaldehyde, polyvinyl alcohol (PVA), urea, borax, glutaraldehyde (GD), and dimethyl phthalate (DMP) on tensile strength and water absorption were investigated. The experimental results showed that the optimum conditions were as follows: a reaction temperature of 85 °C, 22.22 wt.% lignosulfonate, 1.59 wt.% borax, 22.22 wt.% urea, 31.75 wt.% formaldehyde, 22.22 wt.% PVA, 32.32 wt.% GD (to PVA glue), and 32.32 wt.% DMP (to PVA glue). Under these conditions, the tensile strength reached 2.2 ×104 Pa and the water absorption was 35.2%. The products were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results showed that the product components were compatible in this system, and the introduction of cross-linking agents may have resulted in a decrease in pore size.

To investigate the effect of bleach pretreatment on the surface photo-discoloration of dyed wood, two kinds of bleached and unbleached dyed wood veneers were irradiated in a xenon light source accelerated aging tester. The exposed surfaces’ color, spectral reflectivity, chemical functional groups, and microstructure were characterized. Bleach pretreatment improved the dyeing effect of the wood veneers. However, it decreased the light fastness of the samples, and as adsorption between the dyes and wood components was reduced, some chromophoric chemical structures of the wood lignin and dyes were degraded, and some extractives (which can function as antioxidants to protect wood surfaces from discoloration) were removed. After light irradiation, the reflectance curves of dyed wood veneers was shifted toward longer wavelengths and noticeable yellowing was observed. Some parenchyma tissue, such as pit membranes in wood cell walls, suffered serious deterioration, as indicated by SEM.

Pulp fibers were treated in aqueous NaOH/urea/thiourea solution at low temperatures (from -14 °C to 8 °C) to prepare high-permeability filter papers. The effects of treatment temperature and time were investigated to control the permeability of the filter paper. SEM images were taken to observe the physical configuration of fibers, and fiber quality analysis was used to characterize the properties of the fibers. The main parameters of the filter papers (permeability and bulk) were increased markedly. The permeability was increased from 150.1 L/(m2·s) for the untreated paper to 1136 L/(m2·s) for the treated paper, and from 4.3 cm3/g for the untreated paper to over 5.5 cm3/g for the treated paper. The zero-span tensile strength changed only slightly. Moreover, the characteristics of the pulp fibers underwent some positive changes. These results demonstrate that the permeability of paper sheets can be preferably improved by treating fibers in NaOH/urea/thiourea solution at -2 °C for 30 min.

Fiber-reinforced thermosetting composites have been of interest since the 1940s due to their ease of use in processing, fast curing times, and high specific stiffness and strength. While the use of plant fibers in a polyester matrix has been thoroughly studied, only limited information is available regarding using wood as reinforcement. In this study, composites of thin wood veneer and a polyester matrix were made and the difficulties in the lamination and curing processes were investigated. Sheets of Douglas fir, maple, and oak veneers using a catalyzed polyester resin were assembled as unidirectional, balanced, and unbalanced cross-ply laminates. These were compared to control specimens using glass fiber as reinforcement. The impact properties of the samples, with respect to the laminate thicknesses, were characterized using a drop-weight impact tester. The wettability and surface roughness of unsanded and sanded wood veneers were also investigated. Results showed that Douglas fir cross-ply laminates had an impact energy equivalent to glass fiber laminates, making them an interesting alternative to synthetic fiber composites. Wood/polyester laminates absorbed a considerable amount of energy through a higher number of fracture modes. The balanced lay-up limited twisting of the wood/polyester composites. The lowest contact angle and highest wettability were observed in unsanded Douglas fir veneers.