Thermal Analysis Kinetics Of Lignin-containing Lignocellulosic Nanomaterials

In the past few decades,with rapid economy development,increased energy demand,and ensued environmental pollution,utilization of biomass resources has attracted a great attention from all countries in the world.The biomass materials are generally low cost,renewable,biodegradable,abundant,light,and environmentallyfriendly.In recent years,studies on the thermal degradation characteristics of biomass have gradually emerged,but studies on the characteristics of woody nanomaterials such as bark and tobacco stem waste?such as thermal decomposition?have been very limited,and domestic research in this area is much rarer.In China,a large amount of bark residues and tobacco stem wastes are discarded or directly burned by forest products processing plants and cigarette factories each year.This not only causes great waste of energy,but also seriously pollutes the environment.Therefore,the study of the thermal analysis kinetics of biomass has important implications for the use of biomass in China.Thermal Analysis Kinetics is a method of using thermal analysis techniques to study the physical properties of materials and the rate and mechanism of chemical reactions.Today,thermal analysis kinetics has a history of about 70 years.It has evolved from an initial homogeneous system to a heterogeneous system.Especially in recent years,it has made great progress in the research of solid-phase systems.This dissertation studies three kinds of solid-phase systems including pine bark,tobacco stem?control?,and steam exploded tobacco stem.This paper adopts the multiple scanning rate method,"free-model" iso-conversional methods?including the Friedman method and Kissinger method in differentiation method,Coats-Redfern method and Flynn-Wall-Ozawa method in integration method?and model fitting method to investigate the thermal analysis kinetics of lignocellulosic nanomaterials.In this dissertation,super-fine grinding and homogenization treatments were carried out to produce lignocellulosic nanomaterials?LCNMs?from biomass of pine bark and tobacco stem.The three solid-phase systems of pine bark lignocellulosic nanomaterials?BLCNMs?,tobacco stem?control?lignocellulosic nanomaterials?T₁LCNMs?,and steam exploded tobacco stem lignocellulosic nanomaterials?T₂LCNMs?were studied.In this thesis,Transmission Electron Microscopy?TEM?,Field Scanning Electron Microscopy?FE-SEM?,Fourier Transform Infrared Spectroscopy?FTIR?and X-ray Diffraction?XRD?were used to study the morphology and chemical structure of the three samples.Studies have shown that BLCNMs, T₁LCNMs,and T₂LCNMs all exhibit a mixed state of nanofibers and free lignin nanoparticles.The diameters of nanofibers and free lignin nanoparticles were calculated to be 12±6 nm and 13±4 nm for BLCNMs,4±1 nm and 8±4 nm for T₁LCNMs,and 5±1 nm and 21±8 nm for T₂LCNMs,respectively.During the thermogravimetric analysis?TGA?study of the thermal decomposition behavior of samples,it was found that the decomposition process of BLCNMs is two stages,but the decomposition processes of T₁LCNMs and T₂LCNMs are three stages.The entire reaction process is a superposition of the thermal decomposition processes of cellulose,hemicellulose and lignin.T₁LCNMs had a relatively lower onset degradation temperature,higher thermal degradation degree,lower temperature interval and lower residue weight percentage compared with those of BLCNM.However,the thermal decomposition degree and decomposition temperature interval of T₂LCNMs are higher than those of T₁LCNMs,but the residue weight percentage of T₁LCNMs is larger than that of T₂LCNMs.The paper also studied the effect of different heating rates on the thermal decomposition process of three LCNMs.The activation energy ranges of the three LCNMs were calculated by the Friedman method,Coats-Redfern method and Flynn-Wall-Ozawa method,respectively: BLCNMs were 229.3-239.0 kJ/mol;T₁LCNMs were 229.2-233.0 kJ/mol;the T₂LCNMs were 297.3-317.4 kJ/mol.The results showed that BLCNMs and T₁LCNMs have similar activation energies,while T₂LCNMs have higher activation energies than the other two.The activation energy of the three samples obtained by the Kissinger method was lower than those obtained by the Friedman method,the Coats-Redfern method and the Flynn-Wall-Ozawa method.