Research Articles

The objective of this work was to evaluate the physical characteristics of the thermophilic granular aerobic sludge used in the treatment of bleached kraft pulp mill effluents. Four sequential batch reactors (SBRs) were operated with cycles of 12 hours. Reactor (R1-FSR) with flocculent sludge was used as control. The other three reactors (R2-GSR, R3-GSR+100, and R4-GSR+200) were operated with granular aerobic sludge. Concentrations 100 and 200 mg. L-1 of calcium were applied in the R3-GSR+100 and R4-GSR+200, respectively. The pH was maintained in the neutral range in all reactors. The experimental plan was carried out for 490-day period, in 5 phases at different temperatures of 35 °C to 55 ºC. All SBRs showed COD removal efficiency above 60% in all temperature ranges. The granule average diameter in the R2-GSR, R3-GSR+100, and R4-GSR+200 ranged from 5 to 8 mm. The reactor R3-GS+100 showed better stability due to the addition of 100 mg. L-1 of calcium. The granular sludge sedimentation velocity was 40 m.h-¹, which was eight times higher than the flocculent sludge. Thermophilic treatment (55 °C) using aerobic granular sludge proved to be a promising way for treating bleached kraft pulp mill effluent without a prior cooling process.

Fiber processing is an important factor that affects the physical and mechanical properties of long kenaf fiber. The physical-mechanical properties, such as color, tensile strength, and moisture regain (MR), are the main characteristics that influence the processing and performance on the final products from kenaf fiber. The objective of this research was to evaluate the physical and mechanical properties of kenaf fiber at the week of planting, with different processing methods that were planted in a selected location in Malaysia. Kenaf fiber was separated by the water retting method, where the combination of water retting and mechanical retting was based on the available facilities and proficiency at the sites. The tensile strength and chemical composition of kenaf fiber showed large variability for every location collected and for each processing technique used. Visual observations and color testing indicated that kenaf fiber with extended water immersion exhibited higher lightness and smoother fiber. A slight reduction in moisture regains was observed with increased crystallinity index. The differences among properties of the kenaf fiber that were influenced by harvesting week and processing methods could give some references and overview for the planters, suppliers, industries, and researchers to identify the suitable fiber quality for their targeted final products.

The present work presented an approximate solution for a compact test (CT) specimen that was employed as a standard test provided by ASTM E399-19 (2019). The variational method was employed to obtain the solution. The method used a two-step strategy to approximate the displacement response of the CT specimen. The first step was to obtain the general form of displacement solution, and then, the Rayleigh-Ritz approach was employed to modify the solution of the first step. A compliance equation of the CT specimen was obtained, and furthermore, the formula to calculate the stress intensity factor was obtained. The solution was validated by finite element (FE) model and the formula specified in ASTM E399-19 (2019). It was concluded that the calculation results of the proposed solution agreed well with the results of the FE model prediction for the ratio of initial crack length-to-ligament length, which was in the range of 0.25 to 0.35. Furthermore, compared to the results predicted by using the formula addressed in ASTM E399-19 (2019), the method proposed in the present study can achieve closer results than that of the FE model.

Mathematical modelling is a powerful tool in science. Causal mathematical models based on a clear picture of how key variables interact enable a deeper understanding of a given situation and provide reliable predictions. This is a classic approach in science. Unfortunately, this approach is declining in pulp and paper-related research in favour of simply reporting experimental data. The lack of a framework provided by a model diminishes the value of much experimental work. Therefore, the increased use of mathematical models is encouraged, and this approach is illustrated via several practical examples from our work.

The radial variation was examined for tracheid lengths of Norway spruce (Picea abies (L.) Karst.), European larch (Larix decidua Mill.), and Scots pine (Pinus sylvestris L.) wood from dominant trees coming from an even-aged stand, and growing under identical forest site and climatic conditions. The measurements were completed on macerated material. The variation of tracheid lengths in annual rings from the core to the bark was used for determination of the border between the juvenile and mature wood in the trunk cross-section. The boundary age between the juvenile and mature wood zones established for the examined species was comparable, as it was 25 annual rings for Scots pine and 29 for European larch and for Norway spruce. In the juvenile zone, the tracheid lengths increased 2.2-fold in Norway spruce wood, while in Scots pine and European larch wood it was approximately 1.7-fold. By contrast, in the mature wood zone the tracheid lengths was stabilized at a certain level, showing slight fluctuations. The differences in the tracheids length of early and late wood in the examined annual rings were also determined, and it was established that for the majority of annual rings they are statistically significant (p<0.05).

Polyethyleneimine (PEI) modified corncob-derived carbon material (CCM) was prepared by the simple wet-impregnation technique. Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FT-IR), and nitrogen isothermal adsorption/desorption measurements were used to compare the structural differences between the CCM and the PEI-modified CCM (PEI-CCM). In the single-pollutant removal experiment, the PEI-CCM showed high adsorption capacities for methyl orange (MO) and Cr(VI). However, the CCM only showed high adsorption capacity for MO. Moreover, the PEI-CCM exhibited high removal efficiencies in the simultaneous removal of MO and Cr(VI), with final removal efficiencies of 100% and 95%, respectively. The reusability experiment of PEI-CCM indicated that, after four recycles, PEI-CCM maintained high performance with the removal efficiency of MO and Cr(VI) decreased less than 3% and 16%, respectively. The prepared PEI-CCM could be a high-performance adsorbent for the simultaneous removal of MO and Cr(VI) from water containing multiple pollutants.

Cellulose nanofibers (NFC) have attracted special attention in the field of extrusion-based three-dimensional (3D) bioprinting due to their good biocompatibility, excellent mechanical properties, and outstanding shear-thinning property. In this study, by mixing cellulose nanofibers suspension with sodium alginate (SA) and gelatin (GEL) solution, five groups of composite bio-inks with different NFC concentrations were prepared. The effects of NFC on the performance of the SA/GEL matrix hydrogels were analyzed by morphological observation, rheological property testing, mechanical property testing, swelling property testing, and printability analysis. The rheological results showed that the addition of NFC noticeably increased the viscosity of biological inks with low shear rates; therefore, the printed scaffolds maintained their structure better during the 3D printing process. After crosslinking with calcium chloride (CaCl2), the fidelity of the NFC/SA/GEL composite hydrogel structure was better than that of the SA/GEL hydrogel. Moreover, the structural properties were strengthened, and the mechanical stabilities of the composite hydrogels improved when NFC was added. Therefore, this study provided an easy way to improve the printability of extrusion-based 3D printing and the potential use of nanocellulose.

It is desirable to develop biodegradable ultraviolet (UV)-shielding materials from renewable resources, as the demand for sustainability is ever increasing. In this work, a novel lignin-TiO2 UV-shielding composite was synthesized successfully via a hydrothermal method induced by nanofibrillated cellulose (NFC). Comprehensive characterization showed that the lignin-TiO2@NFC composite induced by NFC had good nanoparticle size, shape, and thermal stability. The sunscreen performance of lignin-TiO2@NFC was investigated via mixture with unmodified hand cream. The UV-visible (vis) transmission spectra results revealed that the unmodified cream with 10 wt% lignin-TiO2@NFC absorbed approximately 90% of UV light in the full UV band (200 nm to 400 nm), which indicated that lignin-TiO2@NFC had a good UV-shielding ability.

The production of low-density binderless bark particleboards (LDBBP) from gelam wood bark (GWB) using a hot pressing method at low temperature (128 °C) and pressure (30 kg × cm-2) was explored by examining their physical properties according to SNI 03-2105-2006 (2006). They were also examined via scanning electron microscope (SEM)-energy dispersive X-ray (EDX) observation. The LDBBPs were manufactured using two types of GWB particles: (1) bark waste that was peeled off of small-diameter trees < 10 cm (A) and, (2) bark that was directly peeled off from a standing tree with an average diameter of 10 cm to 15 cm (B). Results showed that the average values of the physical properties of LDBBP(A) and LDBBP(B) met the SNI 03-2105-2006 (2006) requirements in terms of density, moisture content, and thickness swelling after being immersed for 24 h for particleboard type 24-10 and type 17.5-10.5 with maximum thickness swelling requirement 20%. However, they failed to meet the maximum thickness swelling criterion of 12% for other particleboard types. Subsequent internal morphology observation using SEM indicated the presence of cracks on LDBBP (A), so only LDBBP (B) could be manufactured without delamination. Gelam bark could potentially be used to produce non-adhesive particleboards.

A phantom material was prepared with different percentages of soy-lignin bonded with Rhizophora spp. particleboard and different coating materials, including epoxy resin, gloss wood finish, and a mixture of epoxy resin and gloss wood finish. A set of samples without coating was prepared for comparison. Each sample was bonded with 6% or 12% soy-lignin adhesives. The aim was to investigate the suitability of different coating materials at low energy range. The water absorption, thickness swelling, surface roughness, and mass attenuation coefficients of the samples with various coating materials were examined. Water absorption and thickness swelling of the samples coated with different coating materials followed a similar trend, but only one sample (coated with gloss wood finish) was within the recommended value of 12% according to JIS A 5908 (2003). Surface roughness testing revealed that the sample coated with gloss finish was smoother than other coated and non-coated samples. The mass attenuation coefficient of the sample coated with gloss finish was similar to that of water, indicating its suitability as a coating material for the Rhizophora spp. particleboard in medical physics applications.