Preparation And Performance Of Poly(Latic Acid) Fiber Reinforced And Toughened By Carbon Nanotubes

Polylactic acid(PLA)fibers,owing to its advantages such as plant-based sources,excellent biocompatibility and biodegradability,lightweight,quick-drying,antimicrobial properties,mild acid and mildew resistance,are widely used in medical and health,textile and garment,agriculture and forestry,construction and many other fields.However,PLA fiber also has some defects,such as low strength and poor toughness,which severely limit its application and development.So it is necessary to improve the strength and toughness of PLA fiber to expend its application range and its economic value.Considering the tiny diameter of single PLA fiber,it is much more strict in shape,size and dispersion of reinforcing and toughening material.Carbon nanotubes(CNTs)with one dimensional nanoscale,having ultra high strength and toughness,good thermal stability and special electrical performance,is often used to improve the mechanical and thermal properties of polymers.Thus,CNTs is one of the best materials for reinforcing and toughening PLA fiber.When doped with CNTs,CNTs/PLA composite fibers are faced with two key problems:one is the dispersion of CNTs,the other is its compatibility with PLA matrix.In order to solve the problems mentioned above,a core-shell structure of PLA-coupling agent-CNTs has been designed,in which the core was carbon nanotubes,the link-layer was coupling agents,and the cover-layer was PLA,toimprove the dispersion of CNTs and its poor compatibility with PLA matrix.Firstly,the pristine CNTs was modified by silane coupling agent KH570,and then PLA enclosure was formed on surface of CNTs modified by KH570 through ring-opening polymerization of Lactide(LA),and using the method of in-situ polymerization,the CNTs with core-shell structure(CNTs-KH570-LA)was prepared.In this experiment,the optimum parameters of modification by coupling agent and in-situ polymerization of lactide were optimized,the morphology,structure and properties of CNTs before and after the modification and coating were analyzed and compared.Secondly,pure PLA chips and CNTs treated with different modification methods were melted and blended into CNTs/PLA composite masterbatch.And the properties of different PLA composite masterbatch were contrasted to verify whether the CNTs-KH570-LA core-shell structure has a better dispersibility and compatibility or not.Finally,PLA composite fibers doped with different content of CNTs-KH570-LA were prepared by melt spinning method,and the influence of different additive amount of CNTs-KH570-LA on PLA fibers was studied to analyze the best dosage of CNTs-KH570-LA.The conclusions can be reached through experimental analysis:(1)The optimum parameters of KH570 modification are as follows: dosage of coupling agent was 3%,reaction time was 5 h,and reaction temperature was60?.The dispersion of CNTs was significantly enhanced by coupling agent modification.The optimum parameters of lactide ring-opening polymerization are as follows: reaction temperature was 140?,reaction time was 18 h,the molar ratio of CNTs to lactide was 1:20,and the molar ratio of catalyst to lactide was 1:500.The CNTs were coated with PLA enclosure via ring-opening polymerization of lactide,and it turns out that the core-shell structure of CNTs was successfully prepared.(2)The core-shell structure of CNTs-KH570-LA in the PLA matrix has excellent dispersibility and good interfacial compatibility,and core-shell structure can obviously improve the strength and toughness of PLA matrix.Compared with pure PLA,the tensile strength of CNTs-KH570-LA/PLA composites was increased by 39.97%,and the impact strength of that was increased by 51.61%.Carbon nanotubes played an important role of heterogeneous nucleating agent in PLA matrix,which can refine the grain size,speed up the crystallization rate of PLA,improve the crystallization properties of PLA,and enhance the thermal stability of PLA.(3)A reinforced and toughed CNTs-KH570-LA/PLA composite fiber was successfully prepared and the optimum dosage of CNTs-KH570-LA was 0.5%.The strength and toughness of PLA fiber was significantly improved by adding CNTs-KH570-LA.Compared with the pure PLA fiber,breaking strength was increased by 30.62%,and the elongation at break was increased by 32.2%.In addition,CNTs-KH570-LA improve the thermal stability and conductive properties of PLA fiber considerably.