Research On Preparation,Structure And Properties Of Carbon Nanotubes Nanocapsule/Poly (Lactic Acid) Composite Fiber

With the more and more seriously environment pollution and shortage of nature resources,the environmental friendly materials,whose raw materials were reproducible and products could degrade,were paid more and more attention in recent years.The Poly(lactic acid)(PLA)fiber,also called ―Corn fiber‖,was one of such materials which derived from grain(such as corn)or straw.And PLA fiber not only could degrade thoroughly,also had many merits,such as high crystallization,excellent mechanical and physical properties,fine air permeability,also eminent hand feeling,draping or uvioresistant.Therefore,it was widely used in industrial textiles of different areas and deemed to be one promising new type fiber in future.However,some inherent defects of PLA,as poor impact strength,bad toughness,or inferior thermal stability,had severely impeded its application extension,especially for the fields where the toughness was major factor.So this research used the one-dimensional nanometer fiber materials with super high strength and toughness,carbon nanotubes(CNTs),to ameliorate the strength and toughness of PLA.Due to super high surface energy,these CNTs easily agglomerated in matrix,which prevented their role from playing,so the dispersibility and compatibility of CNTs became the key points to reinforce and tough the PLA fiber.This paper developed nanocapsule modification mode on CNTs and consutructed multilayered interfaces to solve the dispersibility and compatibility of CNTs with PLA matrix.And then,the subsequent PLA blend yarns made by reinforced and toughened PLA complex fibers were designed and their degradation behaviours were also analyzed.The main contents of this research were as the following five parts:(Ⅰ)The modification on CNTsTo weaken the high surface energy and improve the dispersibility of CNTs,three methods were adopted to modify the CNTs,namely coupling agent(KH570)modification,lactide(LA)modification and nanocapsule modification.According to some text indexes,for instance sedimentation time and velocity,the number of surface hydroxyls,etc.,the optimal techniques were obtained.And as for KH570-CNTs,the optimal techniques were as following: the amount of KH570 was 3%,reaction time was 6 h,reaction temperature was 70℃.For LA-CNTs,the optimal techniques were as following: the content of catalyst was 0.5%,the mass ratio of CNTs to LA was 5%,reaction time was 12 h,reaction temperature was 130℃.And the optimal techniques of CNTs-KH570-LA nanocapsules were as following: the mass tatio of catalyst to LA was 1:500,the mass ratio of CNTs to LA was 1:20,reaction time was 18 h,and reaction temperature was 140℃.The characterization on the CNTs modified before and after through SEM,FT-IR,TEM,etc.showed that the dispersibility of these mofied CNTs had been improved obviously,moreover,these CNTs reacted with the modifier and the two combined together firmly.The linkage between CNTs and modifier reduced the high surface engery of CNTs,thus the dispersibility of CNTs had been greatly improved.(Ⅱ)Preparation and properties of CNTs/PLA composite master batchesCNTs modified by different techniques and PLA slices were melt blended into different types of PLA master batches(KH570-CNTs/PLA,CNTs-LA/PLA,CNTs-KH570-LA/PLA).In this part the effect of different modification techniques on PLA master batches and the dispersibility and compatibility of different contents of carbon nanotubes capsules in PLA matrix were investigated.SEM images of different PLA master batches showed that these modified CNTs disperse in PLA matrix homogeneously and combined with matrix into a complete whole.The CNTs and PLA matrix had superior compatibility and their interfaces combined firmly.XRD,POM showed that the addition of CNTs refined the PLA crystal grain and made them arrange regularly and closely,thus the crystalline degree of PLA had been improved.And certainly,the mechanical and thermal properties were enhanced obviously,then the PLA master batches were reinforced and toughened.Compared the three modification techniques,the strengh and toughness of PLA master batch reinforced by carbon nanotubes capsule were highest,so the CNTs-KH570-LA modification effect was the best.The nanocapsule modification mode,whose core was CNTs,medium layer was coupling agent and the shell was wrapped by PLA polymerized from LA,effectively ameliorate the CNTs agglomeration in matrix.Moreover,CNTs and PLA shell were connected by coupling agent(KH570)via coupling theory tightly,thus stable multi-interfaces were developed and the interface bonding was strong.Besides,the PLA shell was the same as PLA fiber matrix,which could greatly improve the compatibility of CNTs with PLA.Through research on micro-morphology,mechanical and thernal properties of PLA master batches with diferent contents of CNTs nanocapsules,it showed that at 5wt% load the CNTs-KH570-LA disperse the most homogeneously,and the mechanical properties of PLA master batches was the best.(Ⅲ)Properties investigation on CNTs nanocapsules/PLA complex fiberFurther,through melt spinning method,the master batches and PLA slices were blended and spun into complex fiber with different contents of carbon nanotube capsules.Section and longitude SEM images of complex fibers showed that the CNTs nanocapsules dispersed in PLA fiber matrix homogeneously,and had superior compatibility with fiber matrix.Moreover,the enhanced degree of orientation represented that these complex fibers had higher strength and toughness to suffer external damage.And degree of orientation of complex fiber at 1wt% content of CNTs nanocapsules was the highest.The test results of POM and XRD,etc.,indicated that CNTs played as nucleating agent and accelerated the crystallinity behavior,and even optimized the size and arrangement of PLA crystal grain,so the PLA complex fiber was reinforced and toughened.And further,summarized with mechanical test results,it can be deduced that the comprehensive properties of PLA complex fiber with 0.5-1wt% CNTs nanocapsules was the best,which implied that the reinforcement and toughening effect of CNTs nanocapsules on PLA complex fiber was the best.Besides,the reinforcement and toughness mechanism of multi-interfaces was also discussed.(Ⅳ)The design and preparation of PLA blend yarnThe reinforced and toughened PLA complex fibers blend with other yarn were spun into different types of PLA complex yarn to further expand the PLA application fields.Firstly,the CNTs nanocapsules/PLA complex fibers were spun into pure PLA complex yarn through twisting,heat setting and some other processes.The spinning technique parameters,including twisting,heating temperature and time,were analyzed to discuss their effect on mechanical properties of PLA yarn and obtained the optimal techniques: the twist was 350T/m,heat setting temperature was 75℃,and the heat setting time was 1.5 h.And further,the PLA/cotton blended yarn was also prepared,in which the blend ratio,the space of filament-strand and twist were discussed to disclose their effect on mechanical properties of blend yarn.And the optimal techniques were as following: the blend ratio was above of 40/60,space of filament-strand was less of 10 mm,and the twist was no more than 800T/m.Moreover,PLA/flax-viscose blended yarn was spun and analyzed the effect of technique parameters(twist factor,bead ring and tension)on mechniacl performance of yarn.The optimal techniques were: twist factor was 250,15 size of bead ring should be adopted,and the number of tension pieces was 4.(Ⅴ)The degradation of PLA complex yarnThe major advantage of PLA products was the degradation,so in this part PLA complex yarn with different loads of CNTs nanocapsules were put in various degradation conditions(human body simulation fluid,distilled water,ultraviolet radiation,vacuum,and air condition)to investigate their mechanics,thermotics and some other properties change,and then explored the influences of CNTs nanocapsules loads on PLA complex yarns in diverse degradation conditions,the relationship of toughening and reinforcing with degradation,and the degradation behavior difference of PLA complex yarn in different degradation enviroments.The results showed that CNTs nanacapsules/PLA complex yarn degraded more easily in alkaline conditions;the degradation was more influenced by temperature and humidity,and at high temperature the complex yarn degraded more quickly;the relationship of degradation with toughness and reinforcement was inverse correlation,and PLA complex yarn with high strength and toughness at 1wt% CNTs nanocapsules content was difficult to degrade.