Study On Synergistic Modification Of Polylactic Acid By Nanoscale Cellulose Whiskers/Inorganic Materials

Polylactic acid(PLA)can be an ideal substitute for petroleum-based polymers due to its renewability,biodegradability,biocompatibility and good thermomechanical properties.However,its inherent brittleness greatly limits its wide application.Therefore,increasing attention has been paid to toughening PLA.At present,a variety of materials have been blended with PLA for toughening.In this paper,carboxylated nanocellulose whiskers(C-CNC)were introduced into the polylactic acid matrix by using cellulose,which is abundant in nature,in order to achieve the toughening effect.First,by analyzing the effect of the content of carboxylated nanocellulose whiskers on the properties of toughened polylactic acid materials,the optimal addition amount was found;then,the carboxylated nanocellulose under the action of different types and amounts of silane-based coupling agents was investigated The difference between the properties of whiskers/PLA composites,to find out the type and amount of silane-based coupling agent that can promote the effective dispersion of carboxylated nanocellulose whiskers in the PLA matrix;finally,introduce inorganic nanoparticles(Graphene oxide GO or montmorillonite MMT),respectively prepared C-CNC/GO/PLA and C-CNC/MMT/PLA series composite materials under the action of coupling agent,and passed the universal tensile testing machine,infrared spectroscopy(FTIR),Scanning electron microscopy(SEM),X-ray diffraction(XRD),thermal analyzer(TG/DTG)and other techniques were used to characterize the properties of polylactic acid-based composites,and the carboxylated nanocellulose with the best synergistic toughening effect under this system was found.Whisker/inorganic material/polylactic acid combination.(1)Nanocellulose whiskers were prepared by sulfuric acid hydrolysis.Due to the existence of hydroxyl groups on the surface of nanocellulose,it is easy to form hydrogen bonds,so that nanocellulose is prone to self-agglomeration phenomenon,so nanocellulose was modified by carboxylation.A series of characterization tests have proved that the carboxylation modification is more conducive to the role of nanocellulose whiskers in the polylactic acid matrix,and the carboxylation modified nanocellulose whiskers have higher carbon content.(2)Polylactic acid composites with different amounts of carboxylated nanocellulose whiskers were prepared by solution casting,and the effects of different amounts of carboxylated nanocellulose whiskers on the composites were explored.Through mechanical properties,thermal properties,Microscopic fracture cross-section,infrared spectrum analysis,X-ray diffraction and other tests are analyzed.The results show that when the addition amount of C-CNC is 2 wt%,the elongation at break of the composite material is increased from 97.9%to 139.2%,which is 41.3%higher than that of pure PLA,and the fracture energy of the composite material is increased from the original 755.0 k J/m~3increased to 982.8 k J/m~3,an increase of 227.8 k J/m~3 compared with pure PLA.Carboxylated nanocellulose whiskers have a certain toughening effect on polylactic acid,but the dispersibility of carboxylated nanocellulose whiskers in polylactic acid matrix is poor,which limits the further improvement of the performance of composite materials.(3)Vinyl triethoxysilane(A-151),3-Aminopropyl triethoxysilane(KH-550),KH-570,KH-590four coupling agents,and the effects of their different concentrations in the range of 1-11wt%on the dispersion of C-CNC in PLA matrix were investigated.The results show that the effect of KH550 and KH590 is not obvious,but A151 and KH570 have a certain toughening effect:when A151 is added at a concentration of 7 wt%,the elongation at break of C-CNC/PLA composites is increased from that of pure PLA.97.9%of KH570 increased to 155.4%,and the breaking energy increased from 755.0 k J/m~3 of pure PLA to 1317.1k J/m~3;when the concentration of KH570 was 5 wt%,the elongation at break of the composite increased from 97.9%of pure PLA to 212.7%,the fracture energy increased from 755.0 k J/m~3 of pure PLA to 1697.9 k J/m~3.Comprehensive analysis shows that when KH570 is selected and the addition concentration is 5 wt%,the performance of polylactic acid material is improved the best.(4)KH570 coupling agent was used to promote dispersion,and graphene oxide,carboxylated nanofiber whiskers,and polylactic acid were blended by solution casting method to prepare C-CNC/GO/PLA ternary composites.Effects of ternary composites on properties.The results show that when the amount of GO added is 0.2 wt%,the toughness of the composite material reaches the maximum value.At this time,the elongation at break of the composite material is 238.2%,which is 140.3%higher than that of the pure PLA material,and the breaking energy is 1741.4 k J/m~3,an increase of 986.4 k J/m~3 compared to pure PLA(5)C-CNC/MMT/PLA ternary composites were prepared by physical blending of montmorillonite with polylactic acid and carboxylated nanocellulose whiskers under the action of KH570.The results show that when the amount of MMT added is 0.2 wt%,the elongation at break of the ternary composite reaches a maximum of 246.1%,which is 148.2%higher than that of pure PLA;the breaking energy is 1759.3 k J/m~3,which is 1004.3k J/m~3 higher than that of pure PLA.