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Physical properties are one of the drawbacks of oil palm wood (OPW) and they need to be improved via an appropriate method. The response surface methodology (RSM) based on central composite design (CCD) was used to evaluate and optimize the parameters of a hydrothermal treatment and to create an empirical model of the mass loss (ML, %), equilibrium moisture content (EMC, %), and anti-swelling efficiency (ASE24h, %) responses. This study focused on the effect of hydrothermal treatment (HTT) in buffer solutions to control the destructive effects of released acids caused by the degradation of hemicellulose acetyl groups. A CCD, as the most common RSM design, was applied with three treatment factors including the buffer solutions (acidic, neutral, and alkaline with pH of 5 to 8), temperature (80 to 140 °C), time (40 to 120 min), and a total of 20 experiments. The results showed that the effect of the treatment temperature was more notable than time. The medium acidity (pH) variations in HTT can lead to the removal of extractives and starch, hemicelluloses hydrolysis, the destruction of the parenchymal cells wall, and weight loss. Based on the variance analysis, the quadratic and linear models proved to be highly significant with minimal probability values (< 0.0001). The optimum conditions predicted for the HTT were a pH of 7.3, a temperature of 112.7 °C, and a time of 109.6 min. [ABSTRACT FROM AUTHOR]

The present research aims to shed light on the effect of activated sludge (from a paper mill) and nanochitosan on the physical and strength properties of recycled pulp. Firstly, activated sludge was treated with 3% acetic acid for 30 min and then placed in a beaker for 90 min at 100 °C. Then, the ingredients were mixed and refined with recycled newsprint pulp in different proportions (0, 5, 10, and 15%). Finally, 2% nanochitosan was optionally added. Test specimens were prepared according to TAPPI standards with a basis weight of 120 g/m2, and their physical (water absorption) and strength (tear strength, tensile strength, burst strength, and ring crush test) properties were measured and compared. The results showed that with the increase of untreated activated sludge in recycled paper pulp, the indicators of tear resistance, ring crush test, and burst strength decreased and water absorption increased. Strength properties increased and water adsorption decreased when adding activated sludge treated with 3% acetic acid. Through the addition of nanochitosan to activated sludge treated with acetic acid, a significant increase in strength properties and a decrease in water absorption were observed. [ABSTRACT FROM AUTHOR]