Despite major efforts in recent years, lignin as an abundant biopolymer is still underutilized in material applications. The production of lignin nanoparticles with improved properties through a high specific surface area enables easier applicability and higher value applications. Current precipitation processes often show poor yields, as a portion of the lignin stays in solution. In the present work, lignin was extracted from wheat straw, spruce, and beech using ethanol organosolv pretreatment at temperatures from 160–220 °C. The resulting extracts were standardized to the lowest lignin content and precipitated by solvent-shifting to produce lignin micro- and nanoparticles with mean hydrodynamic diameters from 67.8 to 1156.4 nm. Extracts, particles and supernatant were analyzed on molecular weight, revealing that large lignin molecules are precipitated while small lignin molecules stay in solution. The particles were purified by dialysis and characterized on their color and antioxidant activity, reaching ASC equivalents between 19.1 and 50.4 mg/mg. This work gives detailed insight into the precipitation process with respect to different raw materials and pretreatment severities, enabling better understanding and optimization of lignin nanoparticle precipitation.
Abstract. Polyether ether ketone (PEEK) is a high performance thermoplastic due to the high thermal and mechanical properties. To improve more toughness and flexibility of the PEEK, thermoplastic vulcanized (TPV) was applied and mixed with PEEK matrix. The multi-walled carbon nanotubes (MWCNTs) were also used to prepare nanocomposites and they were mixed through melt blending. Mechanical test results showed that the flexibility improved by addition of TPV up to 10 w% and also CNTs nanoparticles increased tensile strength of the nanocomposites. FTIR spectroscopy confirmed the compatibility between the components. Thermogravimetric analysis (TGA) indicated an improvement in the thermal stability of the PEEK matrix by applying CNTs nanoparticles. Scanning electron microscopy observations demonstrated that the CNTs nanoparticles have been uniformly distributed into the PEEK matrix. Optimal thermal and mechanical properties was found for the nanocomposite contained 10 w% of TPV and 0.5 w% of CNTs and a super tough nanocomposite could be successfully prepared.
The dynamic of Unmanned Aerial Vehicle (UAV) is nonlinear, strongly coupled, multi-input multi-output (MIMO), and subject to uncertainties and external disturbances. In this paper, an adaptive sliding mode controller (ASMC) is integrated to design the attitude control system for an inner loop fixed wing UAV. In the proposed scheme, sliding mode control law parameters due to uncertainty are assumed to be unknown and are estimated via adaptation laws. The synthesis of the adaptation laws is based on the positivity and Lyapunov design principle. Navigation outer loop parameters are regulated via PID controllers. Simulation results indicate that the proposed controller design can stabilize the nonlinear system, and it is robust to parametric model uncertainties and external disturbance.
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