Research Articles

A series of metal chlorides with different valences were used during biomass pretreatment and enzymatic saccharification. After pretreatment, the solid substrate (SS), pretreatment liquor (PL), and conversion yield of cellulose (CYC) were characterized. The results showed that the monovalent salts, NaCl and KCl, as well as the divalent salts, MgCl2 and FeCl2, could promote the enzymatic saccharification to a certain extent, while CaCl2 had little influence on the enzymatic saccharification and cellulase activity, and ZnCl2 had an inhibitor effect on them. For a trivalent salt, FeCl3, the removal rate of hemicellulose and the CYC could come up to a high value. The hemicellulose degradation was mainly related to the valences of metal ions. The cellulose models, the enzymatic saccharification, and the enzyme activity assay results showed that most of the metal chlorides had promoter action toward the enzymatic hydrolysis and cellulase activity, with the exception of ZnCl2. Moreover, the metal ions, especially with high valences, had local effects, which could intensify the potentiation or inhibition impacts on the cellulase activities.

One of the most important aspects in the catalytic cracking of bio-oil is understanding the kinetics of the process.The aim of this paper was to study the kinetics of bio-oil cracking with a silica-alumina catalyst using a continuous fixed-bed reactor. The reaction was studied over the temperature range of 450 to 600 °C with a catalyst bed length of 1 to 4 cm. Three models, Models 1, 2, and 3, were proposed to represent the catalytic cracking kinetics of bio-oil. Model 1 was based on the cracking of bio-oil into the products, while Models 2 and 3 were based on the three-and four-lump models, respectively. The results showed that the rate constants of the catalytic cracking of bio-oil increased with an increasing temperature. The reaction rate constants of the catalytic cracking of bio-oil using Model 1 ranged from 0.221 to 0.416 cm³/g cat·min with an activation energy of  22.3 kJ/mol. It was found that the reaction rate constants from Model 2 can be employed to describe the cracking phenomenon of bio-oil, liquid hydrocarbons, and gas and coke, whereas Model 3 can illustrate the kinetics of bio-oil, kerosene, gasoline, and gas and coke cracking.

Differentiating and ecologizing of products have gained an increasing amount of importance, and green logistics has achieved an irreplaceable position as an important tool for competitiveness. Small and medium-sized enterprises (SMEs), in this case wood-processing enterprises, can achieve this position through the innovation of green products. Based on the results of research focused on finding out how customers perceive green wood products, the objective of this work is to propose possible ways to implement green products in wood-processing SMEs in Slovakia, while taking into account the requirements of customers related to green products. The research was evaluated by methods of testing the statistical hypothesis (binomial test, Chi-square test, Friedman test, and Wilcoxon test), descriptive statistics, and data visualization. The survey revealed that primary reasons why customers of wood-processing SMEs do not buy green wood products is their high price and an insufficient amount of available information about them. In addition to the price, respondents mainly take the quality and safety of the products into account when making purchases. Based on the analysis performed, three basic green strategies focused on product innovation are proposed for consideration by wood-processing SMEs in Slovakia and elsewhere.

The effect of weaving pattern and natural filler addition on the dynamic properties of composite structure was investigated. The reinforcement effect of plain, basket, and twill weave were compared with randomly oriented natural fiber in short form. An experimental modal analysis was used to determine the fundamental natural frequency and modal damping factor of composite structure. The results for a woven reinforced composite were compared with those of a randomly oriented short fiber composite. Reinforcement with woven form enhanced the fundamental natural frequency, while randomly oriented short fiber enhanced the damping factor of composite material. In addition, mechanical properties, such as tensile and flexural behavior, were examined to understand the effect of reinforcement on the composite material. The sisal bio fiber with woven form enhanced the properties of the composite material.

Hemp fiber’s origin has a large impact on the physical properties of degummed fibers. In this research, the effect of hemp fiber origin on the treated fibers was studied mainly by evaluation of chemical composition and microstructure, as well as by the evaluation of the degummed fiber’s properties under a biochemical process. The samples were chosen from the stem with two different growth periods (an early and a late harvest time) and three different sections along the hemp stem (top, middle, and bottom). The results showed a vast variety of chemical compositions and microstructures for raw hemp fibers in different growth periods. The results of the chemical composition analysis indicated that the cellulose content in raw fibers ranged from 41.9±2.3% to 44.8±0.8% and that the lignin content ranged between 12.0±1.5% and 16.5±0.9%. Both the Fourier transform infrared (FT-IR) and X-ray diffraction (XRD) results demonstrated the close relation of the raw fiber’s character to the growth period and sampling section. The physical properties of degummed fibers with different origins were also tested, and large variations in length and linear density were found, which ranged from 42 mm to 67 mm for length and from 11.36±0.37 dtex to 21.55±0.54 dtex for linear density.

The present study was conducted to determine the influence of the chemically modified kenaf bast fiber (KBF) on the mechanical, morphological, and thermal properties of fiber-reinforced polypropylene composites. The KBF was modified via the in situ sol-gel silica process through soaking the KBF in tetraethyl orthosilicate (TEOS) at a pH of 11, room temperature (25 °C ± 1 °C), and a KBF to TEOS ratio of 1:10 for 24 h. Silica successfully formed on the surface of the KBF. Subsequently, the sol-gel silica-modified KBF was utilized to produce sol-gel silica-modified KBF-reinforced polypropylene (PP-KBF-S) composites. Several analytical methods were utilized to determine the mechanical, morphological, and thermal properties of the PP-KBF-S composites, which were then compared with those of the untreated KBF-reinforced polypropylene composite. The findings revealed that sol-gel silica modification of the KBF reduced the void content and enhanced the mechanical properties and thermal stability of the PP-KBF-S.

As the world’s leading civil construction materials, concrete and mortar are the focus of ongoing studies aimed at improving their properties.  These materials are highly versatile; hence, some of their aspects, such as their interaction with toxic materials, should be examined in greater depth. An investigation was therefore undertaken to ascertain how these products react to phorbol ester (PE), a toxin found in Jatropha seed cake (JSC). The mechanical behavior of mortar and concrete containing JSC waste from the manufacture of biofuel was examined based on the analysis of axial compressive strength. The interaction between mortar and PE molecules was examined by means of high performance liquid chromatography. A study of the mechanical behavior of the materials indicated that the inclusion of JSC greatly reduced their mechanical properties, and that this inclusion had a stronger impact on mortar than on concrete, while liquid chromatography showed that the toxic material inserted into the mortar remained inert, indicating the promising potential of this material to store toxic products.

The mean arithmetic deviation of the roughness profile was investigated during cylindrical milling of the board edges. The machined materials were a medium-density fiberboard, medium-density fiberboard with single-sided lamination, and edge-glued spruce panel. Contactless and contact profilometers were used to measure the roughness. Both methods were evaluated and compared. Tungsten carbide blades with three different compositions and treatments were used. The effect of the cutting speed (20 m/s, 30 m/s, 40 m/s, and 60 m/s) and feed rate (4 m/min, 8 m/min, and 11 m/min) on the surface roughness was also monitored. The results of this study compared two different methods for determining the surface roughness. The measurements were more accurate with a contactless profilometer, but the price is higher than that of the contact method. The operation was also more complicated, and the measurement itself took longer with a contactless profilometer. The evaluation of individual surface quality variables was faster with a contact device. The best results in terms of the surface quality were achieved by lowering the feed rate and increasing the cutting speed.

Mechanical properties are among the properties to be considered in designing and fabricating any composite to be used as a firewall blanket in the designated fire zone of an aircraft engine. The main focus of this work was to study the tensile, compression, and flexural strengths of the combination of natural/synthetic fibres with metal laminates as reinforcement in a polymer matrix. The materials included flax fibres, kenaf fibres, carbon fibres, aluminium alloy 2024, and epoxy. The two-hybrid fibre metal laminate composites were made from different layers of natural/synthetic fibres with aluminium alloy of the same thickness. The composites were made from carbon and flax fibre-reinforced aluminium alloy (CAFRALL) and carbon and kenaf fibre-reinforced aluminium alloy (CAKRALL). Based on the results obtained from the mechanical tests, the CAFRALL produced better mechanical properties, where it had the highest modulus of elasticity of 4.4 GPa. Furthermore, the CAFRALL was 14.8% and 20.4% greater than the CAKRALL in terms of the tensile and compressive strengths, respectively, and it had a 33.7% lower flexural strength. The results obtained in the study shows that both composites met the minimum characteristics required for use in the fire-designated zone of an aircraft engine due to their suitable mechanical properties.

The water repellency, elastic modulus, and hardness of hydrophobic-treated and untreated wood cell walls were investigated. Chinese fir (CF; Cunninghamia lanceolata (Lamb.) Hook) wood was modified using polydimethylsiloxane (PDMS) and dimethyldichlorosilane (DMDCS) dissolved in n-hexane at 2%, 5%, and 8% (w/w) for 5 min, 30 min, and 2 h, respectively. A hydrophobic property was observed in the modified wood. The water contact angle value of the untreated wood surface was 85°, but after treatment this value increased to 147° and 143° for the PDMS- and DMDCS-treated wood, respectively. Increases in the elastic modulus and hardness of the wood cell wall were observed after PDMS treatment. These treatments also improved the water repellency of the wood surface, as verified by the reduction of the hydroxyl group O-H stretching vibrations at 3328   cm^-1. Compared to DMDCS, the PDMS treatment improved the hydrophobicity of wood surfaces and increased the nanomechanical properties of the wood cell wall. When an 8% concentration of PDMS and a 2 h treatment time were used, the treated wood showed the best mechanical properties.