Research Articles

An increased demand for sustainable materials has led to intensive research in the field of three-dimensional paperboard forming. To date, this work has focused on forming processes with shape-giving tools. However, individual shapes are often required, especially for large-format products. Incremental forming can be used in metal processing for small batches. In this article, the technology of incremental forming is transferred to paperboard. The results showed that elevated moisture content and a superimposed counter pressure significantly increased the forming limits. In addition, the use of polymer layers increased the shape accuracy. An extended understanding of the underlying mechanisms was achieved by analyzing the forming behavior. In uniaxial and biaxial characterization tests the influence of the moisture content on the forming behavior was investigated with conditions relevant for incremental forming. It was found that the bulge test is suitable to determine the most suitable moisture content regarding the forming limits and the spring back behavior in incremental forming. In addition, it was observed that the bearable elongations during the incremental forming of paperboard are significantly higher than in the established characterization tests. The reason for this is a compression of the fiber network during forming.

Natural rubber latex foam (NRLF) based on kenaf core and bast were prepared by using the Dunlop method. Mechanical properties, foam density, compression, hardness, thermal aging, and microstructural characteristics of kenaf-filled NRLF with different loadings of kenaf core and bast were analysed. The tensile strength, elongation at break, and compressive strength of kenaf bast filled NRLF samples decreased as the content of kenaf was increased. However, the modulus at 100%, hardness, and density of NRLF increased with increasing kenaf contents. The addition of kenaf core into NRLF increased the swelling percentage and aging of the foam compared to the bast. Scanning electron microscopy (SEM) results indicated that the fibrous kenaf bast had a stronger adhesion compared to the particulate kenaf core, resulting in higher tensile strength, elongation at break, and compression strength.

Indoor air quality is crucial to human health because poor air quality can easily lead to disease. To improve indoor air quality, it is essential to increase the concentration of negative oxygen ions in the air. Consequently, it is necessary to design a material that can generate negative oxygen ions indoors. In this study, a wood-based functional material was developed by anchoring TiO2/graphene oxide (GO) and silica nanoparticles (SiO2) onto wood. The results showed that the TiO2/GO- and SiO2-treated wood greatly enhanced the mechanical properties of the wood and increased the negative oxygen ion production to 1580 ions/cm3 after 60 min of ultraviolet irradiation, which met the standard for fresh air. These treated wood materials could fulfill the pursuit by an individual for a healthy and environmentally friendly life, and represents a highly promising material in the application of indoor decoration materials.

The objective of this study was to characterize the wood anatomical structure of a rubber tree clone, under the influence of two different canopy grafts. The following rubber trees were selected in the system of a double-grafted PB 311 + FX 2784 and PB 311 + MDF 180. For each tree, discs of wood were cut from the affected branch immediately below the insertion of clone at right angles to the axis, from which the regions corresponding to tension, in opposite and normal wood, were identified. The anatomical analyses were conducted in accordance with the standards established by the International Association of Wood Anatomy Committee. The Kruskal-Wallis nonparametric test was applied for multiple comparisons among the types of woods and radial positions studied, at 5% of significance. Still, multivariate associations were assessed among the anatomical characteristics of both double-grafted rubber trees, by means of a two-step cluster analysis. Quantitative morphological differences were observed in the wood cells of the double-grafted studied clones. The ray height and the vessels diameter were the most important morphologic characteristics for the distinction. The canopy clone exhibited the ability to modulate the quantitative anatomical characters of the panel clone, depending on the plant’s needs.

Oil palm fresh fruit bunch (OPFFB) is the main export product of the oil palm industry. A good oil palm is between 17 to 18 weeks of age with full fruitless maturity. An automated detection system should be implemented to determine the OPFFB’s maturity and expedite the harvesting process. Various automated detection methods have been proposed for conventional method replacement. In a preliminary study, a new oil palm fruit sensor was proposed for detecting the maturity of OPFFB, and a microstrip ring resonator was designed for determining the moisture content in oil palm fruit. The coaxial feeder of the microstrip ring was a Sub-Miniature A (SMA) stub contact panel with outer and inner conductors of 4.1 mm and 1.3 mm, respectively. The measurement system consisted of a sensor and a PC controlled network analyzer. This system was tested successfully on seeds and fruits of oil palm with various degrees of maturity. The microstrip ring resonator operated between 2.2 and 3 GHz and required low frequency that enabled the electromagnetic field in the first half of the ring resonator to be transferred to the second half and subsequently cause the collinearity of the maximum field points in the feed lines and resonator.

In the last few years there has been an increased demand to change the natural color of valuable hardwoods without chemicals for use mainly in indoor parquet floors. In this study, wood samples from oak (Quercus petraea L.), one of the most used species for parquet, were heat treated (ThermoWood method) at 190 °C for 2 h and at 212 °C for 1 and 2 h. Untreated and heat treated wood surfaces were coated following two different applications: type 1, with a single layer of sealer (50 g/m2) and type 2 with two layers (35 g/m2) using a nanolacke varnishing system. The objective of this study was to investigate surface properties including adhesion, glossiness, pendulum hardness, and color (L*, a*, b*, ΔE*, ΔL*, Δa*, and Δb*). With heat treatment the lightness decreases, and its decrease is higher for higher temperatures and treatment times. Type 2 coated wood presented a slightly lower lightness decrease. The experiment showed a slight increase followed by a decrease in redness (lower a*) and a clear decrease in the yellow tone (b*). The total color variation increased with the intensity of the treatment, while the glossiness decreased (more for Type 1 coated wood). The adhesion strength and surface hardness decreased with the heat treatment in both the Type 1 and Type 2 coated wood samples. The decrease in adhesion was higher for Type 2, reaching 67%, while the decrease in surface hardness reached about 18%.

The aim of this work was to investigate the influence of nanocellulose on the storage stability and rheological properties of urea formaldehyde (UF)-based adhesive compositions for wood-based panels. Three types of UF resins characterized by different F/U molar ratios were used for this research. Resin modifications with nanocrystalline cellulose and a nanofibrillated cellulose content of 1.0% to 5.0% by dry weight of resin were prepared. The flow curve characteristics and storage stability were studied. The viscosity values mainly depended upon the type of nanocellulose used, as well as its loading in the composition. The UF resins modified with nanocrystalline cellulose kept their rheological behavior and proper viscosity after 4 weeks in storage, which lowered the percentage of viscosity retention by approximately 1.5 times compared with that of industrial resins. Nanocrystalline cellulose might be used as a stabilizer in resin compositions during long-term storage, while nanofibrillated cellulose might act as a thickening agent through the limited extent of loading in a composition.

Mechanical, thermal, and water barrier properties of poly(lactic acid) (PLA) film reinforced with cellulose nanofibrils (CNF) and bacterial nanocellulose (BNC) were studied and compared. The in-situ formation of sodium carbonate (Na2CO3) on the BNC surface may aid in reducing the interchain hydrogen bonding and agglomeration of BNC fibers. At optimum loading, both CNF/PLA and BNC/PLA nanocomposite films exhibited higher tensile strength and Young’s modulus than the neat PLA without sacrificing its toughness. The BNC/PLA nanocomposite films displayed lower water vapor transmission rate (WVTR) as compared to neat PLA and CNF/PLA films at 0.5 and 1.0 wt%. BNC was found to induce imperfect crystal structures and exhibited higher overall crystallinity than neat PLA and CNF/PLA composites at 0.5 wt%. The BNC/PLA showed higher mechanical properties than CNF/PLA nanocomposites. Nanocellulose derived from plants and bacteria could provide promising solutions to develop high performance biobased-nanocomposites film for packaging application.

Various natural products are potentially suitable for wood protection, particularly against fungi attack. Caffeine is a well-known compound of natural origin, commercially and economically available, which could facilitate its future use for wood protection. This work investigated the antifungal resistance of the sapwood of Scots pine (Pinus sylvestris L.) treated with a water solution of caffeine and then thermally modified. The samples after impregnation were thermally modified at different temperatures selected on the basis of thermogravimetric analysis (TGA) of caffeine. The paper presents preliminary results of resistance of treated pinewood towards Aspergillus niger van Tieghem (ATCC 6275). The treated samples were subjected to both a leaching procedure and to the artificial aging procedure imitating natural weather conditions. Thermal modification of wood treated with caffeine improved the fungistatic properties of samples after artificial aging. It occurred through partial elimination of caffeine leaching from the wood structure.

Peanut shells were liquefied in phenol using sulfuric acid as the catalyst. The effects of the liquefaction conditions, such as the phenol/peanut shells ratio, catalyst loading, reaction temperature, and time, on the residue ratio, percent combined phenol, and formaldehyde reactivity of the liquefied products were investigated. The results showed that increasing the phenol/peanut shells ratio decreased the residue ratio and increased the combined phenol and formaldehyde reactivity. Increasing the catalyst loading decreased the residue ratio and increased the combined phenol, but a higher catalyst loading caused the formaldehyde reactivity to decrease. A higher reaction temperature and prolonged reaction time did not lead to a further decrease in the residue ratio and it further increased the combined phenol and formaldehyde reactivity. Fourier transform infrared spectroscopy and gas chromatography-mass spectroscopy showed that the liquefied products contained a large amount of polyphenol compounds and a small quantity of furan compounds and furfural. The SEM images showed small particles were the main portion of the liquefaction products and cellulose fibers could still be clearly seen.