Preparation Of Poly(Lactic Acid)/Cellulose Nanocrystal Composite And Study On Its Meltblown Nonwoven Materials Properties

Meltblown nonwowen materials are widely used in wipes,medical sanitary materials,filter materials,battery separators,disposable materials and so on.In the new period when the “plastic restriction order” is issued and implemented,poly(lactic acid)(PLA)is of great significance as a completely biodegradable material to replace petroleum-based meltblown materials such as polypropylene.Although PLA has complete biodegradability to achieve zero environmental pollution,the shortcomings of itself such as brittleness,insufficient flexibility and poor heat resistance greatly limit the application of PLA.Similar to PLA,cellulose nanocrystal(CNC)is a recyclable and naturally degradable and environmental green material.It has excellent mechanical properties,high mechanical strength,high crystallinity,good heat resistance,high transparency,light weight,low density and other characteristics.After the two are blended,CNC can improve the shortcomings of PLA and achieve a better comprehensive performance while maintaining complete degradation.However,CNC is hydrophilic,while PLA is hydrophobic.After the two are blended,CNC is prone to agglomeration in the PLA matrix.Therefore,the CNC needs to be hydrophobically modified firstly,and then melt blending with PLA and melt blown.The CNC prepared by sulfuric acid hydrolysis or hydrochloric acid hydrolysis is needleshaped or rod-shaped nanoscale cellulose with a length of about 200?300 nm and a diameter of10?20 nm.CNC prepared by the sulfuric acid hydrolysis begins thermal degradation at 243°C,and CNC prepared by hydrochloric acid hydrolysis begins thermal degradation at 361.8°C.CNC prepared by hydrochloric acid has a better thermal stability so it is more suitable for meltblown nonwoven processing.Stearic acid was used to esterify the hydroxyl groups on the CNC surface for hydrophobic modification to improve its compatibility with the PLA matrix.The analysis shows that the dispersion of the modified CNC is better than that of the unmodified CNC,showing single shape.Due to the presence of ester groups,the thermal stability of modified CNC is lower than that of unmodified CNC.The thermal degradation temperature is reduced from 361.8°C to321.8°C,but it is still higher than the temperature of meltblending and meltblown processing.Modified CNC can be applied to subsequent processing.CNC/PLA blending masterbatches with different mass ratios were prepared by meltblending.Compared with the unmodified CNC,the modified CNC can be uniformly dispersed into the PLA matrix,and its compatibility with PLA gets improved.After stretching to fracture,the fracture surface of PLA is rough and shows ductile breaking.The toughness of PLA gets improved by modified CNC.However,when the addition of CNC reaches 2 wt.%,the agglomeration phenomenon is obvious,and the compatibility gets worse.The addition of modified CNC promotes the crystallization of the matrix,and improves the crystallinity of PLA from 35.24% to 37.81%,and increases the thermal degradation temperature,which effectively enhances the thermal stability of PLA.The tensile testing shows that the modified CNC has a significant strengthening and toughening effect on PLA,comparing with the unmodified CNC.When 1 wt.% modified CNC is added,the tensile strength is increased from 20.33 MPa to 40.67 MPa,and the elongation at break is increased from 5.17% to 10%,when the mechanical properties are the best.Therefore,the modified CNC with an addition of 1 wt.% was used to prepare CNC/PLA meltblown materials.For modified CNC/PLA meltblown nonwoven materials with CNC addition of 1 wt.%,the addition of CNC can reduce the composite viscosity of PLA.Compared with the pure PLA meltblown nonwoven materials,the fibers diameter and the average pores diameter of CNC/PLA meltblown nonwoven materials both get thinner or smaller.With the increase of machining temperature,the filtration efficiency of CNC/PLA meltblown nonwoven materials gradually increases,and the air permeability gradually decreases.The crystallinity and heat resistance increase firstly and then decrease.After 240°C,the crystallinity and heat resistance decrease due to thermal degradation.The crystallinity and heat resistance of pure PLA begin to decrease at220°C and are lower than those of CNC/PLA at 240°C.The tensile testing shows that with the increase of machining temperature,the longitudinal tensile strength and elongation at break of CNC/PLA meltblown nonwoven materials increase firstly and then decrease and reach the maximum at 4.17 N/5cm and 43.33% at 230°C.The best longitudinal tensile strength of pure PLA meltblown nonwoven materials is 4 N/5cm at 210°C,and the elongation at break is 34%.The mechanical property decreases obviously when the temperature is higher than 210°C.