Volume 13 Issue 1

This research aimed to determine the isothermal drying kinetic parameters of grain sorghum using a thermogravimetric analyzer (TGA). The kernels were placed in the TGA under isothermal drying conditions, i.e., 40, 50, 60, 70, 80, 90, and 100 °C. Changes in the sample weight were determined from the TGA and the data were used to determine the moisture ratio and the derivative of the weight loss curves. The moisture ratio data obtained experimentally were fitted to four well-known models, namely Page, Newton, Logarithmic, and Henderson, to determine the best-fit model for the experimental data. The goodness of fit criteria was used to determine the best-fit model. An increased drying temperature from 40 °C to 100 °C accelerated the drying process and decreased the moisture ratio from 0.6091 to 0.2909, after 1 h. The Page model was the best fit for 71.4% of the drying curves, whereas the Logarithmic and Henderson models were the best fit for 28.6% of the studied cases. Increasing the drying temperature from 40 °C to 100 °C increased the effective moisture diffusivity from 0.96 × 10−8 m2/s to 1.73 × 10−8 m2/s. The drying activation energy value reached 9.4 kJ/mol under isothermal drying conditions.

An efficient method for the internal structural imaging of cultural wooden relics was explored through experimental techniques of three-dimensional (3-D) tomography and reconstruction. The techniques of filtering and segmentation were applied to the 3-D scanned data of wooden cultural relics.To obtain high resolution 3D data model, it was necessary to preprocess the raw data after CT scanning. Preprocessing included denoising, filtering, and segmentation. After completing these three steps, three-dimensional reconstruction experiments were carried out (including surface rendering and volume rendering). After the 3-D reconstruction, the wood internal properties were visually analyzed and used to create internal structural imaging of wooden artifacts. On the basis of volume rendering, wooden artifacts could be graphically divided at any angle and any position. The textures of local wooden relics were clearly revealed in the segmentation of the reconstruction pictures, and these were compared with the presented internal structural image testing of the wooden artifacts. This study showed that the proposed technology can successfully create internal structural images of wooden artifacts, as well as provide important data and models to support the renovation and recovery of the cultural wooden relics.

The effects of glycerol pretreatment and thermal modification on poplar wood was examined using thermogravimetric analysis (TGA). The total mass losses of thermally-treated samples before and after glycerol impregnation were studied. The thermal degradation process was divided into three stages based on natural breaks in the slope of the TGA curves. The set-on and set-off temperatures, mass loss, and activation energy (Ea) of each stage were compared. Pretreatment with 60% glycerol followed by thermal modification at 160 °C produced pronounced differences in the three decomposition stages. Fewer wood components were decomposed in the first stage in glycerol-pretreated wood, which suggested that the pretreatment had modified the wood components into more thermally stable substances. However, the mass losses were higher in the next stage, suggesting that the effect on thermal stability was limited. The Ea values of wood decomposition during the first stage were decreased, while those during the second and third stages were increased. These results illustrate the potential for using a glycerol pretreatment to alter the thermal stability of wood.

Densification parameters were investigated for the fast-growing pine and eucalyptus. Both woods showed optimal results in terms of apparent density and mechanical properties when milder treatments of 150 °C were applied. Pine showed mass loss and improved mechanical properties with a longer heating time of 60 min, while eucalypt performed better with shorter treatments of 30 min. Eucalypt has more highly acetylated hemicelluloses, mainly composed of xylose units, which degrade more quickly with consequent decrease in mass and mechanical properties. However, apparent densities close to 1.0 g·cm-3 were obtained, and greatly enhanced bending properties, hardness, and impact resistance were observed, especially when the optimal parameters were used. Treatments at 170 °C or greater, while resulting in well-densified specimens, yielded inferior mechanical properties. The densified woods also presented initial apparent contact angles greater than 85°, highlighting a considerable increase of hydrophobicity. The densification process therefore allows these less valuable timber species to be used in applications such as flooring and decking.

This article focuses on the evaluation of the process of planar milling of natural and thermally modified oak wood. The standard Thermowood process was used for the thermal modification. The quality of the machined surface was evaluated after planar milling. Various machining process parameters were set for individual samples. The effects of individual technical and technological factors on the quality of the newly created surface were subsequently evaluated. The mean arithmetic deviation of the waviness profile (Wa) was chosen as the evaluation parameter for milling. The effects of the following factors were monitored: cutting speed, feed rate, rake angle, and their mutual combinations. Natural and thermally modified oak wood were milled and subsequently evaluated. The quality of the machined surface was determined using a contact measuring device. Reducing the cutting speed increased the waviness, and decreasing the feed rate decreased the waviness. However, the cutting speed was not a statistically significant factor. The rake angle proved to be a factor that significantly affected the surface waviness. Thermal modification had a statistically significant effect on the surface waviness.

Wood flour, PLA, and other additives were mixed evenly in a high speed mixing machine. The granules were prepared by melt blending and extrusion granulating with a twin-screw extruder, and test specimens were molded by a plate curing machine. By changing the heating temperature, the molding pressure, the holding pressure time, and azodicarbonamide (AC foaming agent) contents, the influences of four factors on the apparent density, the mechanical properties, and the morphology of the biodegradable foamed WPCs were investigated. The best processing parameters and the optimum AC foaming agent content were obtained. When heating temperature was 178 °C, heating time was 10 min, holding pressure time was 25 s, and molding pressure was 7 MPa, the test specimen was lighter in color, with a smooth surface and dense, uniform cross section. The mechanical properties (flexural strength and impact strength) of the foamed WPCs were relatively good. When adding 1% AC foaming agent, the foamed WPCs showed uniformly distributed microcellular structure, and the average pore diameter was about 67 µm. The density was reduced by 18.6%, and the flexural strength and impact strength were increased by 128.6% and 40%, respectively, compared with non-foamed WPCs.

Chemical modifications have been widely adopted for improving the dispersibility of cellulose nanocrystals (CNCs) in nonpolar matrixes. Nonetheless, an engineering design for improving the CNC structure is still challenging due to the differences in the dispersion level of CNCs depending on the modification strategies in a desired matrix. The current study was conducted to find an appropriate functionalization technique for CNCs and an effective manufacturing process for CNC-polypropylene (PP) nanocomposites. The surface structures of CNCs were successfully changed using toluene diisocyanate (TDI) and maleic anhydride grafted PP (MAPP). The tensile properties and thermal stability of the nanocomposites with MAPP grafted CNCs were higher than those of pristine and TDI grafted CNC systems. A melt-extrusion process with pre-dispersion processing exhibited more positive effects on the properties of the nanocomposites in comparison to the systems without pre-dispersion. Scanning and transmission electron microscopes also provided clear evidence of the dispersion levels of unmodified and modified CNCs in the PP matrix.

The growing consumption of tender coconut water in Brazil has resulted in a generation of green husk, which in turn has led to pollution, as it takes eight to ten years to degrade. With the objective of finding applications for these fibers, the characterization of their chemical composition, tensile properties, and structural properties is presented in this paper. The density of the green fibers was 1200 kg/m3, and the diameter ranged between 272 μm and 513 μm. The length of the ultimate fibers was 940 μm, while the cell wall thickness and size of lumen were approximately 3.6 μm and 11.8 μm, respectively. The crystallinity index, ultimate tensile strength, Young’s modulus, and elongation of the lignocellulosic fiber were 48%, 114 MPa to 159 MPa, 1.20 GPa to 1.96 GPa, and 41% to 44%, respectively. These results were compared with previously published results of both green and brown coir fibers with the purpose of exploring the addition of value to this abundant agro-industrial residue.

The physical-mechanical properties of bamboo-polyethylene composites (BPCs) change depending on the environmental temperature and exposure to moisture during outdoor use. In this study, the water absorption, density, mechanical properties, and wear rate of the composites were tested after immersion in water, and four water temperatures were examined. Bamboo charcoal (BC) was used to improve the properties of the BPCs after hydrothermal aging. The composites were improved because of the strong interfacial interactions between the BC and polymers. The experimental results showed that the water diffusion rate accelerated as the water temperature increased. The BC reduced the water absorption at all of the water temperatures and the diffusion coefficient at temperatures above 39 °C. The wear rate of the composites first increased, and then decreased as the water temperature increased. The density and flexural properties decreased with an increased hydrothermal aging temperature. Overall, hydrothermal aging decreased the water resistance and mechanical properties. Additionally, these effects were enhanced as the water temperature increased, but were countered by the incorporation of the BC.

The toughening of wood-plastic composites (WPC) based on silane/ peroxide macro crosslink poly(propylene) (PP) systems was studied. A 23 experimental design was adopted to initially optimize three parameters: silane, wood flour, and talc contents of the WPC formulation. The WPCs were manufactured on a co-rotation twin screw extruder. Test specimens were prepared via injection molding. The WPC compounding formula with 8 phr of silane, 35 phr of wood flour, and 20 phr of talc was used to study the effect of ultra-high molecular weight polyethylene (UHMWPE) as a toughener. The impact strength was improved up to a 10-phr UHMWPE loading. The flexural properties and heat distortion temperature (HDT) slightly decreased. When exceeding 10 phr of UHMWPE, the unmelted UHMWPE agglomerated and the mechanical properties were inferior. The fiber/matrix interfacial adhesion was enhanced by the sauna treatment. A marginal increase in the fracture toughness was observed. The impact strengths increased with the addition of ethylene propylene diene terpolymer (EPDM) as a rubber toughener. However, high EPDM contents caused a decrease in the HDT. The sauna incubation of the EPDM-toughened WPC enhanced the impact strengths. The EPDM effectiveness was determined by the better PP matrix toughness and UHMWPE/PP interfacial adhesion.