Volume 14 Issue 2

This paper describes the high-value utilization of citrus peel waste, in which potassium carbonate (K2CO3) was used to assist the extraction of essential oils and served as the activating agent for the further preparation of activated carbons. A common alkali metal salt, K2CO3, was confirmed to be effective in promoting the extraction of essential oils from citrus peel. Compared to the 2.4 wt% extraction rate of essential oils obtained using regular steam distillation, a 6.2 wt% extraction rate was achieved when the citrus peel was pretreated with a K2CO3 solution. Meanwhile, its chemical composition remained stable, indicating that these additional essential oils can also be directly used in areas that have already been developed in the perfume industry. The solid residue collected after essential oil extraction was further used as the precursor for activated carbons. The specific surface area of activated carbons reached up to 1846 m2/g at a carbonization temperature of 800 ºC, and it exhibited a highly developed microporous structure.

Laminated surfaces of wooden composites are created from decorative papers and impregnation thermosetting resins, mainly melamine-formaldehyde (MF). This type of surface treatment is not always resistant to microorganisms, especially when polluted with organic substances. Bioactive additives are often needed to improve the microbial resistance. In this study, silver nanoparticles (Ag-NPs), in amounts of 0.15  10-3 wt.%, 0.5  10-3 wt.%, 1.5  10-3 wt.%, 5  10-3 wt.%, 15  10-3 wt.%, and 50  10-3 wt.% were added to MF resin. The presence of Ag-NPs in the laminated surfaces of the particleboards improved their anti-bacterial and anti-mold resistances. Growth of gram-positive bacterium Staphylococcus aureus on the sterilized surfaces decreased by approximately 53.7% at most, while the growth of gram-negative bacterium Escherichia coli decreased by up to 100%. The anti-mold resistance of the polluted laminated surfaces containing Ag-NPs increased against Penicillium brevicompactum by up to 62.5%, but there was almost no improvement against Aspergillus niger. The Ag-NPs did not affect the resistance of the laminated surfaces towards aggressive chemicals and only minimally towards dry heat at 180 °C. This inorganic biocide decreased the abrasion resistance of the laminated surfaces by up to 12.6%.

The anatomical, physical, and mechanical properties of 13 Malaysian bamboos and the trend of these properties along the bamboo culms’ height were examined. The results showed that these properties varied between the 13 species and they were also affected by the culm height. From the results obtained, the fibre morphology, as well as radial, longitudinal, and tangential shrinkage from green to oven-dry decreased from the basal to the top of the bamboo culm. In contrast, the opposite trend was observed for the density, modulus of rupture, modulus of elasticity, and percentage of the vascular bundle. The potential usage of 13 bamboo species is also considered.

Grape pomace (GP) generated from the winery industry is one of the abundant agro-waste in the Western Cape, South Africa and other regions globally. GP contains a significant quantity of holocelluloses that can be converted into fermentable total reducing sugars (TRS). This study reports on the recovery of TRS from GP treated Nepenthes mirabilis digestive fluids for mediated biovalorisation in comparison to a combination of conventional pretreatment methods (hot water pretreatment, dilute acid pretreatment, and cellulase pretreatment) in a single pot system. The recovery of TRS was facilitated while also reducing total residual phenolics (TRPCs) in the samples. Furthermore, powder X-ray diffraction (pXRD) was used to measure the crystallinity index and the functional groups of pre- and post-pre-treated GP were determined using Fourier-transform infrared spectroscopy (FTIR) to ascertain the efficiency of the pre-treatment methods, with quantification of lignin, holocellulose and ash being conducted. Overall, the TRS yield for N. mirabilis pre-treated agro-waste was 951±4.7 mg/L, with biomass having a lower CrI of 33%, and 62% residual lignin content. Furthermore, reduced TRPCs were observed in hydrolysate, suggesting limited inhibitory by-product formation during N. mirabilis pre-treatment.

The viscoelastic behavior of Sapindus mukorossi pericarp (the covering of the Indian soapberry fruit) was investigated. Samples were subjected to creep-recovery and oscillatory shear tests. The moisture content had a strong effect on the dynamic moduli, whereas the temperature had little effect. Both the storage and loss moduli had a weak dependency on the frequency. In general, the storage and loss moduli decreased and slowly converged with an increase in the moisture content. The storage and loss moduli decreased with an increasing temperature. The creep-recovery experiment and dynamic shear tests indicated that the pericarps with high moisture contents were more prone to permanent deformation. The dynamic shear tests further demonstrated that a low moisture content, temperature, and frequency resulted in the pericarps having a more solid behavior and undergoing elastic deformation. Images of the microstructure showed that cells in the raw pericarps were round, of similar size, and neatly arranged. In the treated pericarps, the cells gradually became smaller and finally disappeared. It was inferred that drying with hot air caused the loss of intracellular substances, which in turn strengthened the dynamic characteristics of the pericarps. The completely dried pericarps thus behaved as strong viscoelastic solid in contrast to the raw pericarps.

The heating of cardboard was studied when it is in contact with ultrasonic sonotrodes, whose vibrations were orientated parallel and perpendicular to the material surface. The parameters that were varied included the contact pressure on the sonotrode, vibration amplitude, and moisture content of the material. It was shown that there was a major decrease in the contact pressure shortly after the beginning of the experiment when the gap between the sonotrode and anvil was kept constant and thus a decrease in the temperature gradient of the material occurred. With parallel vibration, the material heated up from the sonotrode side, whereas heating started from the center of the material in the case of vertical vibration. This suggested that in cases of vertical vibration, heat is mostly generated by internal dissipation, and in cases of parallel vibration, heat is generated by friction losses on the surface. Furthermore, the results revealed the influence of the parameters on the initial temperature gradient, the maximum temperature, and the moisture content of the material.

Functionalized layered double hydroxides (LDHs) based on a multi-modifier system composed of itaconic acid (ITA) and titanate coupling agent (NDZ-201) were designed and fabricated in this paper with the aim to develop high-performance fire retardant paper. The structure of LDHs were characterized using Fourier transform infrared spectroscopic analysis, X-ray diffraction analysis, thermogravimetric analysis (TGA), scanning electron microscopic analysis, cone calorimetry, and laser particle size analysis. The results showed that carbonate anions were partially replaced by ITA, whereas the titanate coupling agent was attached to the surfaces of the hydrotalcites. The limiting oxygen index (LOI), TGA curves, total heat release rate (THR), and heat release rate (HRR) indicated that as the addition of hydrotalcites increased, the modified LDHs’ LOI value and thermal stability noticeably increased compared to the unmodified hydrotalcites, and the HRR and THR of the material decreased. When the addition amount was 25%, the LOI of ITA-LDHs was 26.9%. However, the Mg-Al hydrotalcites adversely affected the strength index of flame-retardant paper; the modified hydrotalcites clearly reduced this effect, and the whiteness of paper increased and reached 83%.

The load-bearing capacity and bearing stiffness formula of pin connectors in the current standard Eurocode 5 does not consider the influence of the angle on the single shear connection, especially for inclined screws connecting laminated veneer lumber (LVL). Therefore, research was conducted into the influence of the angle and friction on the load-bearing capacity and bearing stiffness of self-tapping screws connecting LVL made from Douglas fir. This study analyzed the existing calculation model of bearing capacity and stiffness and then derived a model with friction. The results showed that the load-bearing capacity and bearing stiffness in the tensile-shear mode was better than in the compression-shear mode, and that it was better with a 45° to 60° self-tapping screw angle. The lateral support can remarkably improve the bearing capacity and bearing stiffness in the compression-shear mode. The theoretical calculation formula for self-tapping screws connecting solid wood can better reflect the bearing capacity of inclined screws connecting LVL in the tensile-shear stress mode after increasing the fitting coefficient to 1.25. The safety factor was approximately 0.97 to 1.19. The proposed models in this paper are suitable for situations with friction in the compression-shear mode.

The effects of microwave and steam mediated pretreatments were evaluated and compared relative to the hydrolysis of sweet sorghum bagasse (SSB) in the presence of sodium hydroxide. The results established the optimum parameters for energy consumption and sugar production after hydrolysis of the pretreated SSB. The energy balance was better in microwave treatment compared with the steam treatment. The results recommended pretreatment at 300 watts power setting in the microwave oven up to 10 min. At higher wattage setting and longer exposure time, increased sugar yields were obtained, although the efficiency of the process decreased when the energy balance was calculated. The energy balance was calculated as the proportion of energy consumed during the pretreatments to the energy that can be produced by fermenting released glucose to ethanol. In this study, the energy consumed during the different pretreatments varied from 1/33 to 1/200 of the energy obtainable by fermenting released glucose to ethanol. Overall, the pretreatment of SSB to produce fermentable sugars was effective, and the energy balance was positive both in microwave and steam pretreatments of alkaline suspension of SSB. In microwave treatment the energy applied can be more accurately dosed, and consequently the energy balance was improved compared to steam treatment.

Cross-laminated timber (CLT) is becoming increasingly adopted into wooden construction of South Korea. Due to the lack of standards and protocol for CLT, there are many problems in the production and utilization phases. This study focused on the deformation and defects of CLT due to humidity variations. In this study, small, cross-laminated specimens were manufactured using three layers of laminated larch planks that had various moisture contents. The dimensional changes of these specimens were measured in response to changing internal conditions including side adhesion or moisture content variation and external conditions such as humidity. Shrinkage in width and thickness was less than 1.0% when using dry planks as the cross-laminated specimen. However, high-moisture content (MC) planks were not suitable when used as the surface layer of the CLT, as the shrinkage in width and thickness were greater than 2.0%. When high-MC planks are used in the inner layer, their shrinkage must be less than 2% to prevent splitting caused by a MC difference between the surface and inner planks. For this purpose, laminates with a MC less than 15% should be used for CLT.