Comparison of organic acid-based organosolv lignins extracted from the residues of five annual crops

Organosolv lignins were extracted from corn stover, wheat, rice straw, reed straw, and sugarcane bagasse using a mixture of acetic and formic acids, at relatively low temperature and atmospheric pressure. Lignin content, residual carbohydrates, ash levels, proteins, and molecular weights were determined in each extracted lignin. The lignin content of all samples was relatively high, confirming the performance of the pretreatment process. The low molecular weights were in a narrow range, in accordance with the organosolv lignin molar masses. However, some differences between studied lignins were highlighted, in particular in rice straw lignin, which contained the highest silica, calcium, and nitrogen contents. Nuclear magnetic resonance spectroscopies (31P and semi-quantitative Heteronuclear Single Quantum Correlation) underlined the structural similarities and differences between these organosolv lignins. Corn stover and sugarcane bagasse lignins were rich in non-methoxylated (H-Unit) or mono-methoxylated (G-Unit) phenolic units, making them the best promising candidates for production of phenolic resins. Wheat straw lignin was richer in aliphatic OH than in phenolic OH. This is an advantage for use as polyol substitute in polyurethane synthesis. Reed straw lignin was less specific, with a balanced content of OH groups. However, it contained a high concentration of β-O-4 linkages, which is favorable for depolymerization.

Preparation of Reed Straw-Based Panels Bonded by Soy-Based Adhesives: Optimization via Response Surface Methodology

The optimization of manufacturing conditions for reed straw-based particleboard by soy-based adhesive was performed through response surface methodology. The interactions of various conditions, including adhesive amount, hot-pressing temperature, and hot-pressing time on wet internal bonding strength were investigated. A 3-level-3-factor Box–Behnken design was used to test the optimal preparation conditions of reed straw particleboard. The polynomial regression model for manufacturing conditions had a very significant level ( p < 0.01 ). In addition, the determination coefficient (R2) and the adjust determination coefficient ( R 2 ) of this model were found to be 0.969 and 0.9292, respectively. The conditions optimized by the model were 25% of adhesive amount, 138°C of hot-pressing temperature, and 27 min of hot-pressing time. Under the optimal conditions, validation tests were performed, and the average value of parallel experiments was 0.17 ± 0.02 MPa. Moreover, the thickness swelling of water absorption after soaking and mechanical properties (MOE and MOR) of samples prepared under optimized conditions were further measured, which all met the requirement of Type P6 particleboard. It could provide an efficient method for massive production of reed straw particleboard.