Preparation Of Cellulose Nanofiber/Polylactic Acid Composite And Its Application On 3D Printing

Cellulose is a renewable natural polymer with excellent biocompatibility and biodegradability.Its refined product,nanocellulose,has some more excellent physicochemical properties in addition to the above characteristics.The polylactide polymer,which is also derived from biomass,is high in strength,biodegradable,and has the advantage that traditional petroleum-based plastics cannot match,especially in the field of 3D printing.In order to improve some existing defects of polylactic acid for 3D printing,it is of great practical significance to prepare 3D printing materials with better performance by adding nanocellulose into the polylactic acid matrix through different processes.In this study,microcrystalline cellulose and polylactic acid particles were used as raw materials to prepare cellulose nanofibers by enzymatic hydrolysis and high pressure homogenization.A cellulose nanofiber/polylactic acid composite film and a cellulose nanofiber/polylactic acid 3D printed composite filaments were prepared by a solution blending method combined with a hot press molding process and a melt blending extrusion process.The characterization and test results show that cellulose nanofibers with uniform size can be prepared by enzymolysis and high pressure homogenization.Both the solution blending method and the melt blending method can successfully disperse the cellulose nanofibers in the polylactic acid matrix.Fibers play a role in improving and enhancing the partial properties of composites.The prepared 3D printed composite filaments prints well.This paper is mainly divided into the following three parts:(1)Microcrystalline cellulose is pretreated by enzymatic hydrolysis,followed by high pressure homogenization and controlled homogenization times in order to reduce energy consumption.The results showed that cellulose nanofibers with uniform size can be obtained through 10 times of homogenization process.The diameter of cellulose nanofibers is less than 50 nm and the length is several hundred nanometers.It has good dispersion properties.Fourier infrared spectroscopy analysis,X-ray diffraction analysis showed that it has a typical cellulose chemical structure,buta slight decrease in crystallinity,thermal weight loss analysis showed that the thermal stability of cellulose nanofibers decreased.The enzymatic hydrolysis combined with the homogenization method can rapidly and efficiently prepare cellulose nanofibers.(2)The cellulose nanofiber/polylactic acid composite sheet was prepared by combining the polylactic acid solution with the cellulose nanofiber solution and combining the hot-press molding process.Scanning electron microscopy showed that the cellulose nanofibers were uniformly dispersed in the polylactic acid matrix.The composite material has a significant barrier effect on ultraviolet light,and the tensile strength first increases and then decreases with the cellulose nanofiber content.When the cellulose nanofiber mass fraction is 2.5%,the tensile strength is increased by 8.5%;Scanning calorimetry analysis showed that the cellulose nanofibers acted as nucleating agents in the composites,improving the cold crystallization efficiency of the composites.Thermogravimetric analysis showed that the thermal stability of the composites decreased first and then increased with the cellulose nanofiber content.The composite sheets prepared by solution blending and hot pressing process have broad prospects in the fields of clothing sun protection and packaging.(3)The cellulose nanofibers,polylactic acid,and polyethylene glycol are extruded "one-step" by a single-screw extruder and can be used for the filaments of a fused deposition type 3D printer.The mechanical properties test showed that when the mass fraction of cellulose nanofibers was 2.5%,the tensile strength and elongation at break of the composite filamentss increased by 33.8% and 19.5%,respectively.Differential scanning calorimetry and crystallization kinetic analysis showed that nanofibers and PEG can significantly increase the crystallization rate of composite filamentss.The thermal stability of the composite filaments decreases first and then increases with the increase of the mass fraction of cellulose nanofibers.The process can effectively add cellulose nanofibers to the polylactic acid matrix,providing a new way for the high value of cellulose.