Preparetion And Application Of Lignin Nanoparticles Based On Process Intensification Technologies

With the increasing scarcity of fossil energy,the problem of energy shortage has become more prominent.Lignin,as a green renewable resource,has attracted more and more attention.Lignin is difficult to be fully utilized because it has the characteristics of large molecular weight,complex structure composition,low content of active groups,and poor compatibility of blend copolymerization.Most of the lignin is directly emitted or burned as a by-product of the paper industry,and the utilization efficiency is low.How to improve the utilization efficiency of lignin has been the focus of many scholars' research.The nanocrystallization of lignin provides an important way to improve the utilization efficiency of lignin,but there are problems such as complex preparation process,inability to continuously produce,and easy agglomeration of nanoparticles.In this paper,two process intensification technologies(i.e.,"bottom-up" and "top-down")were proposed for the preparation of lignin nanoparticles,and the applications of lignin nanoparticles in anti-ultraviolet composite film and reduced graphene oxide are studied.The main contents and results of this thesis are as follows:1.Lignin nanopartciles were prepared by the microchannel reactor intensification technology(“bottom-top” method).Effects of solvent type,stabilizer ratio and flow rate ratio on the size of lignin nanoparticles were investigated.Suitable operating conditions were obtained,and lignin nanoparticles with average particle size of 13 nm were prepared.The continuous preparation of lignin nanoparticles was achieved by this method.The formation mechanism of lignin nanoparticles was explored.The stability study showed that the prepared lignin nanoparticles were placed at room temperature for 60 days,and their particle size and morphology of the prepared lignin nanoparticles were basically unchanged during a 60 days storage at room temperature.The antiultraviolet effect of polyethylene(PVA)composite film could be improved by lignin nanoparticles.With 0.5 wt.% of lignin nanoparitcles addition,the UV shielding effect of the composite film could reach 75% at 250 nm wavelength.2.Lignin nanopartciles were prepared by a novel gas-driven intensification technology(top-down).Thanks to the powerful shear force generated by high-speed gas,lignin nanoparticles with an average particle size of 230 nm were obtained without adding surfactant.The effects of cycle times,air flow rate,tube length,angle and circumference of outlet and initial lignin concentration on the particle size of lignin nanoparticles were investigated.The formation mechanism of lignin nanoparticles in gas-driven process was revealed.The lignin nanoparticles prepared by the gas-driven method contain rich-OH,C = C and other reducing functional groups,and can be used as a green reducing agent for the preparation of reduced graphene oxide.