Volume 13 Issue 4

In Laos and neighboring countries, opportunities exist for the production of engineered wood products such as plywood and laminated veneer lumber to supply the rapid growth of construction, furnishing, and joinery activities. The objective of the present study was to assess the potential of peeling fast-growing high-yielding pulpwood from managed eucalypt stands in Laos for veneered products. Eucalyptus pellita, Eucalyptus camaldulensis, and eucalypt clone K7 (E. camaldulensis × E. deglupta) stands were characterized based on veneer quality and recovery. The influence of log position, log geometry, and other log traits during recovery were also investigated. The selected taxa achieved green veneer recoveries that ranged between 57% and 67%. End splitting and branch-related defects were the most important grade-limiting defects that restricted veneer sheet quality to a lower grade of most sheets. However, simple timely silvicultural decisions, such as pruning, could significantly help improve the quality of veneer obtained. The obtained results could be used in the formulation of recommendations to adopt better management practices in Laos to improve the value of plantation-grown wood.

Unfinished, polyvinyl chloride-faced (PVC-faced), and melamine-finished particleboards were examined to determine the effects of VOCs released from these particleboards on indoor air quality. A climate chamber and GC/MS was used to analyze the changes in the concentration of volatile organic compounds (VOCs) from these particleboards over a single cycle of 28 days. The main pollutants from the unfinished particleboard were esters, aromatic hydrocarbons, and aldehydes ketones; the pollutants released from the PVC-faced and melamine-finished particleboards were esters, and aldehydes and ketones. The VOCs from the PVC-faced particleboard had the lowest impact on indoor air quality. When the released VOCs from PVC-faced particleboard reached their stable floor-level values, the air quality was grade I, which is suitable for living. When unfinished and melamine-finished particleboards were used individually indoors, the air quality was grade IV and V. After the released VOCs reached their stable floor-level values, the indoor air quality was grade I or II, which met the standards for living conditions. Under the premise of ensuring that the indoor air was not polluted, the maximum loading rates of the unfinished, PVC-faced, and melamine-finished particleboards were 2.0 m²/m³, 3.8 m²/m³, and 3.8 m²/m³, respectively.

The characteristics of two novel types of technical lignin, namely Ecohelix (EH) and CleanFlow black lignin (CFBL), isolated from two different pulping process side streams, were analyzed. EH and CFBL were analyzed in terms of general composition, chemical functionalities, molar mass distribution, and thermal stability. For comparison, two relevant types of commercially available lignosulfonate and kraft lignin were used. The results showed that EH contains a large amount of sulfonated lignin, together with carbohydrates and ash. As such, it can be considered a lignin-carbohydrate hybrid molecule. CFBL was found to contain 91.5% Klason lignin and the lowest amount of carbohydrates (0.3%). EH showed the highest content of aliphatic OH groups (5.44 mmol/g) and CFBL a high content of phenols (4.73 mmol/g). EH had a molecular weight of 31.4 kDa and a sufficient thermal stability. CFBL had the lowest molecular weight (M_w = 2.0 kDa) and thermal stability of all kraft lignins analyzed in this study. These properties highlighted that EH is a suitable building block for material development and that CFBL is a promising material for the production of biofuel and biochemicals.

The compressive strength of irradiated hybrid composite materials was investigated via compression testing. The hybrid composites consisted of Kevlar fibre, oil palm empty fruit bunch (EFB) fibre, and epoxy. The hand lay-up method was used to fabricate the samples. The samples were then irradiated with different gamma radiation doses: 25 kGy, 50 kGy, and 150 kGy. Compression tests were performed in accordance with ASTM D695 (2015). Compressive strength in Group 1 increased to 30.4 MPa at 25 kGy. At 50 kGy, the compressive strength further increased to 39.6 MPa. Compressive strength for Group 2 also increased to 58.7 MPa when the radiation increased to 50 kGy. The compressive modulus showed the same trend in compressive strength for both Group 1 and Group 2. It was observed that the exposure of hybrid Kevlar/oil palm EFB/epoxy hybrid composites improved the compressive properties of the materials. Furthermore, a difference in the thickness and layering pattern also influenced the compressive strength with different doses. At 150 kGy, both layering patterns showed a degradation of compressive properties.

As an approach to decrease the fold cracking of coated paper, suspension-polymerized (SP) latexes were developed and tested as a surface sizing additive. Styrene, ethyl acrylate, butyl acrylate, acrylic acid, and itaconic acid were used as monomers for the SP latex, and oxidized starch and polyvinyl alcohol were used as stabilizers. The SP latexes were found to be more stable against the charge neutralization by salt solutions and flocculation by cationic polyacrylamide than conventional styrene-butadiene and styrene-acrylate latexes, and they were highly compatible with the conventional surface sizing solution. The effect of using SP latexes as a surface sizing additive on the mechanical properties of the paper was examined. The SP latexes had greater tensile strength and extensional properties than the emulsion-polymerized latexes, which suggested their potential applicability for reducing the fold cracking of coated paper. A mill trial was performed to test the use of SP latexes as a surface sizing additive, and the results showed that they had a positive effect in reducing the fold cracking of coated paper.

A cyclone gasifier is an effective technology for the gasification of low-density biomass containing a high ash content. The ash removal performance was improved in the gasifier due to being similar to a cyclone dust collector. The cyclone reactor is relatively simple, easy to use, and has low construction costs compared with a traditional fluidized bed gasifier. In this study, the air gasification characteristics of rice straw were investigated in a cyclone gasifier. The results showed that by increasing the equivalence ratio (ER), the gasifier temperature also increased. This, in turn, led to a higher gas quality (higher heating value (HHV) and lower tar content) and enhanced the gasification performance (gas yield, carbon conversion efficiency, cold gas efficiency, and hot gas efficiency). A high ER reduced the amount of the combustible gas component (CO and H₂) and caused the HHV of the producer gas to decrease. The optimum value range of ER was observed to be about 0.29 to 0.34. A smaller feedstock size was more favorable for higher producer gas quality and gasification performance. Biomass moisture content parameters played an important role in the cyclone gasification process. Higher moisture content decreased the gasifier temperature, leading to low gas quality (lower HHV and higher tar content), and resulted in lower gasification performance.

The tradition of using naturally occurring plant fibers is still alive in Africa. In the Uíge province of northern Angola, bast fibers from Triumfetta cordifolia serve as the basis for everyday objects, such as baskets, mats, fishing nets, and traditional clothing. The fibers exhibit a Young’s modulus of 53.4 GPa and average tensile strength of 916.3 MPa, which are comparable to those of commercial kenaf fibers. These values indicate a high potential for use as a reinforcement in biocomposites. Based on this promising mechanical and physical profile of individual fibers, different biocomposites were produced with polylactide (PLA) as a matrix. The obtained composites were analyzed mechanically, physically, and visually. Unidirectionally arranged PLA/33% T. cordifolia composites with continuous fibers showed the highest Young’s modulus (10.79 GPa ± 1.52 GPa) and tensile strength (79.37 MPa ± 14.01 MPa). These composites were comparable to those of PLA/30% hemp composites (10.9 GPa and 82.9 MPa, respectively) and therefore have economic potential.

Tannin and sucrose (TS) can be used in a biomaterial-based wood adhesive that requires a higher hot pressing temperature and longer time than traditional resins. To solve these problems, hydrochloric acid and citric acid were utilized as a catalyst during the curing process to decrease energy costs (forming TSH and TSC adhesives, respectively). Thermal analysis revealed that the addition of hydrochloric acid and citric acid resulted in decreases to the thermal thresholds associated with degradation and curing. The resultant insoluble matter ratio verified that the polymerization reaction happened at a lower temperature than the adhesive without acidic conditions. The FT-IR and solid state 13C NMR spectra showed that the addition of acid compounds acted catalytically and increased the generation of 5-HMF in uncured adhesives. The dimethylene-ether bridges and methylene bridge were formed during the heat treatment. The water resistance of the particleboards manufactured by TSC and TSH adhesives were notably enhanced when the hot-pressing temperature was 180 °C. However, an increased hot pressing temperature did not improve the mechanical properties of the particleboard bonded by TSH, which was due to cellulose and hemicellulose decomposition under strong acidity conditions.

Transgenic Populus trichocarpa wood was compared to the corresponding wild-type material. The static modulus of elasticity in three-point bending was measured and the chemical composition among the specimens were compared, including the glucose, xylose, and lignin contents as well as the S/G ratio. Changes in chemical composition, created by genetic manipulations of the lignin biosynthetic pathway, affect the mechanical properties of young small-diameter transgenic trees. There are indications that a decrease in lignin content causes severe reductions in mechanical properties. Changes in lignin structure, either from an increased S/G ratio or structural lignin modifications, also negatively influence the mechanical properties.

Epoxy-based nanocomposites were prepared by incorporating 0.3%, 0.5%, 0.7%, 1%, and 2% cellulose nanofibers (CNF) through a hand lay-up technique. The influence of the CNF as a reinforcement material on the morphology, and the physical, mechanical, and thermal properties of epoxy-based nanocomposites were investigated using scanning electron microscopy (SEM), density, void content, water absorption, tensile, flexural, impact strength, and thermogravimetric analyses. Compatibility between the nano-reinforcement and epoxy matrix was confirmed using SEM, which demonstrated that the CNF was homogeneously dispersed throughout the epoxy matrix. The mechanical properties were enhanced by increasing the CNF loading up to 1%. Moreover, the incorporation of CNF into the composites reduced the water uptake of the substrates in the water absorption test and resulted in a high thermal stability when exposed to a high temperature. Bamboo-CNF could be used as a potential reinforcement material to improve the properties of epoxy-based nanocomposites.