Research Articles

Glycolaldehyde, produced from cracking of glucose, was tested as a substitute for formaldehyde in urea-based wood adhesives. Initially, different parameters (water content, aldehyde/urea-ratio, curing temperature, and time) were screened to identify the optimal curing conditions providing the highest bond strength. Afterwards, the system was reformulated as a 2-component system and compared to a urea-formaldehyde 2-component system, which showed a comparatively low strength of the resulting resin. Different hardeners were tested, and AlCl3 showed an 80% increase in bond strength for the resin compared to NH4Cl. Infrared and nuclear magnetic resonance analyses were performed to ensure formation of the desired aminal bond network, which showed that the hardener was essential for proper curing of the resin. Finally, a urea-glycolaldehyde-formaldehyde resin was tested that further indicated major differences between the reactivity of formaldehyde and glycolaldehyde.

A carboxymethyl cellulose (CMC)/polyethyleneimine (PEI) hybrid hydrogel was successfully prepared under green processing conditions. The CMC and PEI formed a polyelectrolyte complex, and the three-dimensional (3D) network structure was hardened by chemical crosslinking, resulting in suitable hydrogel properties. In the prepared CMC/PEI polyelectrolyte hydrogel, the surface charge was easily switched according to the pH change, and the resulting swelling and contraction was reversible. The pH sensitivity of the CMC/PEI hydrogel was effective in removing ionic dye contaminants, and as a result, it showed an excellent removal capacity of 319 mg/g for anionic acid orange (AO) and 129 mg/g for cationic methylene blue (MB). In addition, the CMC/PEI polyelectrolyte hydrogel maintained structural stability despite repeated changes in surface charge characteristics and shrinkage-swelling due to repeated pH conversion. As a result, in the reuse process through repeated adsorption and desorption, it showed an excellent reuse efficiency of more than 93% even after 10 reuse cycles.

The requirements for embossing of cardboard for print and packaging applications are constantly increasing. High degrees of forming, richness of detail, and high shape accuracy are desired. However, current embossing technology can only fulfill these requirements to a limited extent. A loss of detail and moderate degrees of forming are typical defects in the embossing process. In previous research work, a positive effect on the forming behavior of cardboard could be observed by the application of ultrasound. Therefore, the influence of ultrasound was also investigated for embossing. In order to quantify the effects of ultrasound, conventional and ultrasonic-assisted embossing results were compared. New approaches for analysis and evaluation of embossing results and new characteristic values for describing the forming were applied for the comparison. Two exemplary embossing geometries and a range of ultrasonic parameters were used to characterize the impact of ultrasound and showed positive effects to the forming results.

2,3-Butanediol (2,3-BDO) is an important industrial diol that could function in various fields. Currently, there are many substrates used for 2,3-BDO biosynthesis, but studies using green carbon sources such as corncob hydrolysate as a substrate are lacking. As a widely distributed waste lignocellulose-derived substrate, corncob hydrolysate is nutrient-rich and cost-effective. The present study evaluated 2,3-BDO production via an Enterobacter cholerae strain using corncob hydrolysate as carbon source. Chemical component analysis showed that concentrated corncob hydrolysate contained 233 g/L total sugar and showed no inhibitory effect, but it was beneficial for 2,3-BDO synthesis. Optimization experiments for fermentation resulted in a titer of 47.23 g/L 2,3-BDO with a yield of 0.30 g/g and a productivity rate of 0.66 g/L•h. This study is expected to provide insights for large-scale bioproduction of bulk chemicals utilizing corncob hydrolysates.

Given the well-known carcinogenicity of hardwood dust, occupational exposure to oak wood dust has been determined in a furniture factory on different wood processing machines during sanding, planing, and milling. Determination of the mass concentrations of respirable and inhalable oak wood dust from ambient air was performed using personal sampling pumps and two types of filter holders: the Higgins-Dewell respirable dust cyclone, manufactured by Casella (Bedford, UK), and the inhalable dust IOM sampler manufactured by SKC (Dorset, UK). Out of a total of 30 values of inhalable mass concentration, 7 (23%) exceeded the occupational exposure level (OEL). The highest exposure levels for inhalable and respirable wood dust from the belt sander were 1.569 to 3.710 mg/m3 and 0.243 to 1.342 mg/m3, respectively. Worker exposure may be below the level of increased risk of 2 mg/m3 if a machine such as a planer or router is connected to a suction system. The share of respirable particles in the inhalable fraction ranged between 12% and 31%, and for samples with an inhalable mass concentration exceeding 2 mg/m3, the share was lower than 16%, with a slightly decreasing tendency. Thus, the risk of lower respiratory tract diseases increases with higher exposure to inhalable particles, and the OEL is an indirect measure of protection against exposure to respirable particles.

Welding temperature is an important factor of rotary welding and affects the strength of the joint or the embedded force. This research focused on the parameters that affect the welding temperature and the effect of welding temperature on the embedded force of the dowel. Welding temperature was measured using measuring probes that were moved away from the dowel being welded. The results indicate that the speed of the dowel feed (duration of the welding process) influenced the welding temperature; the embedded force was then determined. With increased rotation frequency with the same duration of the welding process, there was a slight increase in the welding temperature. The influence of the rotational frequency on the extraction force was not unambiguously determined, because the rotational frequency is related to the duration of the welding process. As the welding temperature increased, the embedded force decreased. To avoid difficulties in contact measurement of welding temperature, it is necessary to develop a mathematical model of heat transfer to more accurately determine the welding temperature.

Ionic liquids (ILs) have been widely used for lignocellulose fractionation and lignin isolation. However, the effect of IL treatment on lignin structure has been less explored. This study aimed to explore the chemical structure of lignin isolated by widely used imidazolium based ILs and compare it with the well-known milled wood lignin structure (MWL). Four types of ILs were used, and the effects of the treatment conditions on the isolated lignin (ILL) characteristics were evaluated. As the treatment temperature was increased from 60 to 140 °C, the ILL yield increased, whereas the molecular weight and hydroxyl group content decreased. Among the ILs, [EMIM]Ac produced the highest lignin yield (5.28%), and the ILL obtained had the lowest hydroxyl content (1.27 mM/g) and a molecular weight (Mw) of 29,500 g/mol. Esterification of the ILL isolated with [EMIM]Ac was performed using three fatty acid chlorides, octanoyl chloride (C8), lauroyl chloride (C12), and palmitoyl chloride (C16), to extend its applicability. The effects of esterification on the characteristics of ILL were evaluated, and successful esterification was confirmed using Fourier transform infrared and nuclear magnetic resonance spectroscopies.

The physical properties of wood, particularly the dimensional stability, are affected by the water content. Most wood properties can be detected by near infrared spectroscopy (NIRS), which is used as a nondestructive testing method. At different wavelengths, different absorption peaks are presented with the moisture absorbed by wood. According to this feature, the absorption peaks can be collected, and the data can be processed by partial least squares method combined with NIRS. In this study, softwood oak and hardwood ash tree specimens were studied. In the infrared spectrum range, the wood moisture absorption curve was noticeable and the curve trend was similar, although the tree species were different. After centralization, standardization, and derivative processing of the spectral data, the correlation coefficients of oak and ash tree validations were high, reaching 0.9021 and 0.9661, respectively. The wood moisture content was predicted using NIRS and an algorithm. The experiments showed that this method is feasible.

The extraction of essential oil from pine needles was optimized by response surface methodology, and the following optimal conditions were obtained: a fresh pine needle of 100 g, an extraction time of 2 h, a water dosage of 850 mL, and a NaCl concentration of 2.50%. The extraction yield of essential oil was 0.611% under optimal conditions, which was extremely close to the predicted value. The extraction yields of essential oil from needles of 12 common pines in Guangxi were compared. The contents of essential oil in needles of Pinus massoniana, Pinus crassicorticea, and Pinus taeda were relatively higher than other pines. A total of 44 chemical components were identified by GC-MS, including 12 monoterpenes, 14 sesquiterpenes, and 12 alcohols. The chemical components of essential oil from different pines have their own features, and it is speculated that they have good and diversified application potential in the fields of medicine, food, spices, and so on. The chemical compositions of essential oil with high extraction yield have similar characteristics. This phenomenon can be used as the basis and means for the selection of pines with high content of essential oil in needles.

This study examined the effects of lignin used in EPDM elastomer composites in place of carbon black. For that purpose, lignin was added in amounts of 3.5, 7, and 10.5 phr to investigate the chemical, thermal, rheological, mechanical, and morphological properties of the EPDM elastomers. At the end of the study, tear strength and elongation were enhanced, whereas thermal stability was lowered due to the lignin. The lignin facilitated the vulcanization process and improved the torque values. In the morphology, the lignin was dispersed homogeneously in the matrix, and no voids or cracks were observed except with 10.5 phr. In conclusion, when incorporated at a specified ratio, lignin is economical and provides ecological benefits. Its use as a natural filler can be recommended to automotive industries to provide enhanced properties and ecological properties as a substitute for carbon black.