Developing High Performance Aramid Fibers Through Building Dopamine/graphene Oxide Double-layers With A Biomimetic And Green Method

Aramid fiber(KF),as a new type of high-tech synthetic fiber,has become an indispensable part of many cutting-edge areas.Its unique structure,which is composed of aromatic ring and amide bond,has a good comprehensive performance.Including light weight,high strength and modulus,good temperature resistance,super strong acid and alkali resistance,etc.Also,due to its regular internal structure,KF has poor surface activity and interfacial bonding with resins,so the resultant KF/resin composites don't have excellent comprehensive properties.In addition,amide bond in the molecular backbone of KF is easily broken under the ultraviolet(UV)light,this will greatly reduce the reliability of KFs during applications.Therefore,modification of KFs has been carried out for many years.Although the modification of KFs is endless,most of the modification methods need pretreat KFs at first,sacrificing its original structure and performances.This thesis will aims at prepareing the high performance KFs,without any pretreatment,through a novel chemical method which obviously improve the surface activity,UV resistance,tensile properties and flame retardancy,while maintaining excellent thermal stability.The main contents of this thesis include following aspects.First,using the super adhesion properties of dopamine(DA),which can form a polydopamine layer(PDA)on the surface of KFs,the modified KF(KF-PDA)was obtained.KF-PDA maintains the original internal structure and performance of KF.In addition,a large number of activated hydroxyl and amino groups on the surface of PDA can not only improve the surface activity of fiber,but also provide the second reaction platform,for reacting with graphene oxide(GO).GO nanosheets are evenly coated on the surface of KF to prepare the modified KF(KF-PDA-GO).At the same time,in order to investigate the effects of DA concentration,reaction temperature and GO concentration on the structure and properties of KF-PDA-GO,orthogonal test with three factors and three levels was designed.Results show that the reaction temperature is the decisive factor of surface activity and UV resistance.The surface activities and UV resistance of nine KF-PDA-GO fibers has been significantly improved,overcoming the two major problems of KFs;at the same time,KF-PDA-GO fibers show much better thermal stability and greater tensile properties than KFs.Among them,KF-PDA-GO3 was prepared under the optimal conditions has the highest level of tensile properties among modified fibers reported recently.Second,the surface modification of aramid fiber cloth(KFc)was carried out.Three kinds of modified KFc(KFc@PDA-GO1~KFc@PDA-GO3)with different GO contents were prepared.And their flame retardancies were studied emphatically.Although PDA and GO don't have good heat resistance,KFc@PDA-GO keep the excellent thermal stability of KFc.Inaddition,the coatings of PDA and GO made the flame retardancy of fibers further improved,and increased with the increase of GO concentration.Compared with KFc,KFc@PDA-GO3 has reduced heat release capacity by 41.6%,decreased char length by 60.3% after vertical combustion,and increased limiting oxygen index by 27.6%.These outstanding properties prove that this thesis has established a kind of meaningful modification method,which can endow KFc with good surface activity,UV resistance and flame retardancy.