Preparation And Properties Of Cellulose-organic（PLA） And Cellulose-inorganic（SiO₂） Composites

Cellulose,as a natural organic polymer with a wide range of sources in nature,has attracted the attention of many researchers due to its renewable,degradable and excellent mechanical properties.The compounding of cellulose with other organic or inorganic materials can give it more performance and application prospects.The combination of cellulose materials and organic polymer materials polylactic acid can be used for 3D printing,or the inorganic material silica can be used for antibiotic wastewater adsorption.It is of great significance to the high value and functional utilization of cellulose materials.In this study,cellulose materials were combined with organic polymer material polylactic acid（PLA）and inorganic material silica to prepare 3D printed composite filaments and composite hydrogel beads.The 3D printed composite filaments were characterized for performance.The printability of the filaments was also evaluated during 3D printing.The fine particles and total volatile organic compounds（TVOCs）volatilized during the 3D printing of lignocellulose/PLA composite filaments was tested.The structure of the prepared cellulose-SiO₂ composite hydrogel beads was characterized,and the adsorption performance of the composite hydrogel beads to amoxicillin was evaluated.This paper is composed of three parts as follows:（1）Raw wood flour（WF）,unbleached eucalyptus pulp（UBP）containing some lignin and bleached pulp（BP）were added to PLA matrix.Polyethylene glycol（PEG）was added as a plasticizer and lubricant.Three 3D printed composite filaments:PLA/PEG/WF,PLA/PEG/UBP and PLA/PEG/BP were prepared by melt blending with a single screw extruder.The prepared composite filaments were characterized in detail,and the 3D printing performance was tested.Using the above three composite filaments as raw materials,the tensile test specimen and grid structure were successfully printed by fused deposition modeling 3D printer,and the prepared composite filaments exhibited strong printability.Compared with pure polylactic acid filaments,the unbleached pulp powder in the three kinds of fillers showed the best compatibility with poly（lactic acid）filaments,but the mechanical properties of the three composite filaments have decreased to varying degrees.Thermogravimetric analysis results showed that the thermal stability of the three composite filaments has decreased,and PLA/PEG/WF had the highest thermal stability among the three composite filaments.The thermal degradation kinetics study of equal conversion rate showed that the addition of three fillers had different effects on the thermal decomposition mechanism of PLA.Differential scanning calorimetry analysis showed that the addition of three fillers improved the crystallization performance of PLA and promoted the crystallization efficiency of PLA.The results of isothermal melt crystallization studies showed that the addition of three fillers shortened the cold crystallization time of PLA.The three composite filaments reached the highest crystallization efficiency at 100℃,and the composite filaments with bleached pulp powder added at 100℃had the highest cold crystallization efficiency.（2）The 3D printer was transformed into a self-made chamber to detect the PM2.5 mass concentration（μg/m³）,total particle number concentration（particle size 0.2-10μm;particles/cm³）and total volatile organic compounds（TVOCs）concentration（ppm）volatilized by the lignocellulose/PLA 3D printing composite filaments in four different stages of the printing process（pre-printing stage,filaments feeding stage,printing stage,after printing stage）.The effects of air humidity,feed time,feed temperature and printing failure on pollutant release were studied.PM2.5 concentration and total particle number concentration of the lignocellulose/PLA composite filaments evaporating during the filament feeding stage increased rapidly,and a small amount of TVOCs were released during the printing stage.Air humidity had no obvious effect on the concentration of fine particles.However,as the air humidity increased,fine particle concentration declined to background concentration at a faster rate.The average concentration of TVOCs increased significantly with the increase of air humidity.Scanning electron microscopy characterization of the collected particles revealed that the particle size was larger under high humidity.With the increase of the temperature and the extension of the filament entry time,the concentration of particulate matter and TVOCs increased obviously.When using lignocellulose/PLA filament for 3D printing,we should be alert to the close exposure to air pollution caused by the printing process.（3）Cellulose-SiO₂ composite hydrogel beads with different silica contents were prepared by solution mixing/dropping beads method.The composite hydrogel beads were characterized and used to adsorb amoxicillin wastewater.The diameter of the prepared composite hydrogel beads was about 3.2±0.5μm.Scanning electron microscopy analysis showed that the silica particles were deposited in the cellulose network structure,which made the pore size of the network structure smaller.The results of energy spectrum and Fourier transform infrared spectroscopy confirmed the combination of cellulose and silica.The thermogravimetric results showed that the SiO₂ content of cellulose-SiO₂ composite hydrogel beads increased with the increase of the mass fraction of sodium silicate solution.X-ray diffraction characterization results showed that the silicon in the cellulose beads is amorphous.The adsorption capacity of cellulose-SiO₂ composite hydrogel beads for amoxicillin increased with the increase of silica contents.The adsorption process conformed to the Freundlich adsorption model and pseudo-second-order kinetic equation,which belonged to the chemical adsorption process of the multimolecular layer on the multiphase surface.Cellulose-SiO₂ composite hydrogel beads showed good recycling,and provided new ideas for the treatment of antibiotic wastewater.