Resarch On Modification Of Polyamide 66 And PA 66copolymer Fibers By Nanomaterials

Polyamide 66,(nylon 66 or PA66),has excellent mechanical properties(high strength,good toughness,wear resistance,etc.).It was developed in 1937 by Dupont and used as fiber material.By 2016,the global output of PA66 has exceeded 2 million tons,which is widely used in related fields such as fiber and engineering plastics.It is an important fiber raw material that widely used in the fields of high-end clothing fabrics,tire cords,airbags,and parachutes.The research and development in the field of polyamide in China started late compared with foreign countries.At present,the tensile strength of high strength fiber of PA66 in China has a certain gap compared with foreign products.It is urgent to further improve the strength of PA66 fiber with the development of domestic economy.Nanomaterial modification of PA66 and its copolymer is generally carried out by means of melt blending,solution blending or in situ polymerization.But the melt blending method is suitable for additives with larger microscopic size.When the particle size of the additive is at the nanometer level,agglomeration will occur in matrix of the melt blending materials which will largely reduce the final performance of the composite.Moreover,it cannot meet the basic requirements of continuous and stability in the fiber preparation process,which brings many difficulties for the nanomaterial modification of polyamide 66 fiber.Solution blending needs to dissolve PA66 in an organic solvent,and then precipitate or evaporate the solvent to obtain a PA66 composite material.This method requires a large amount of organic solvents and is not easy to scale up.It is little significance to guide the preparation and production of nano-material modified PA66 fibers.Although researchers have used in-situ polymerization to prepare nanomaterial modified PA66,it is mainly aimed at the modification of PA66 plastic.At present,there are few reports on the preparation of nano-material modified PA66 fiber by melt spinning.Therefore,it is great significance to prepare spinning-grade nanomaterial modified PA66 by in-situ polymerization to meet the requirements of PA66 fiber forming process.This thesis mainly introduced graphene oxide(GO),nanoclay(Clay),carboxylated multiwalled carbon nanotubes(MWCNTs-COOH)and the third monomer caprolactam to modify PA66 by in-situ polymerization and copolymerization through batch polycondensation processand anyalyzed,the influence of nano-materials on the mechanical properties of PA66 and its copolymer fibers.The main contents of this thesis are as follows:(1)PA66/r GO(r GO: reduced graphene oxide)composites were in-situ polymerizized with ultrasonic assisted dispersion of GO with PA66 salt solution.GO powder can be effectively separated into mono-lamellar or less lamellar,and the thickness of the layer is about 1.5 nm.In the condensation polymerization process,GO was successfully thermally reduced to r GO,which improved the thermal stability of GO.The carboxyl group and other functional groups on GO reacted with the amine group in PA66 and grafted PA66 on its surface to form r GO-g-PA66.r GOg-PA66 can further improve the dispersion degree of r GO and interfacial interaction with PA66 matrix.The addition of r GO increased the tensile strength of PA66/r GO stretch spline.When the addition of r GO was 0.1 wt%,the tensile strength of PA66/r GO was increased by 17% compared with that of pure PA66.However,due to the large layer of GO,the pressure of spinning components rapidly rises beyond the limit of the instrument during the attempt of melt spinning,so that the spinning cannot be carried out continuously and stably.In the test of melt filter passability,PA66/r GO showed poor melt filter passability.(2)In order to solve the problem of blockage of spinneret due to the large lamellar size of nanomaterials,PA66 was modified by nano clay with smaller lamellar diameter.The organic modified Clay(Mclay)of CTAB was mixed with PA66 salt solution after ultrasonic treatment to form a uniformly dispersed PA66 salt mixture solution,and then the PA66/Mclay was prepared by in-situ intercalation polymerization.Compared with Clay,Mclay has larger layer spacing,which increases the possibility of intercalation polymerization of monomers or PA66 chains.After polymerization,the spacing of Mclay layers was further expanded and uniformly dispersed in the PA66 matrix.The introduction of Mclay hindered the perfect arrangement of PA66 crystal lamellae in ? phase,but the effect of heterogeneous nucleating agent increased the crystallization rate of PA66/ Mclay.PA66/ Mclay has low and stable melt shear viscosity and relatively excellent processability.The tensile strength of PA66/Mclay fiber was increased by 7.5% compared with that of pure PA66 fiber when 0.1 wt% of Mclay was added.(3)MWCNTs-COOH and Mclay were composited by wet ball-milling,and then introduced into PA66 by in-situ polymerization to prepare PA66/Mclay/MWCNTs and their fibers.Wet ballmilling treatment can prepare uniform and stable MWCNTs-COOH dispersion solution.During the polymerization process of treated carbon nanotubes(TMWCNTs),the carboxyl group of the TMWCNTs was aminated with the amine group of PA66,and PA66 was grafted on the surface of TMWCNTs(TMWCNTs-g-PA66),which effectively increased the dispersion of TMWCNTs in the matrix and the interfacial interaction force.The introduction of TMWCNTs reduced the crystallization rate of PA66/Mclay and the crystallinity of the undrafted fibers,thus improving the post-draft ratio,orientation and tensile strength of the fibers.Compared with pure PA66 fibers,the tensile strength of PA66/Mclay/TMWCNTs fibers was increased by 7% when the addition amount of Mclay and TMWCNTs was 0.1 wt% and 0.02 wt%.(4)PA66 was modified by caprolactam copolymerization to further reduce the crystallization rate of copolymer and improve the fiber draft ratio and strength.PA66-co-PA6 is a random copolymer with relatively low glass transition temperature,melting temperature,crystallization temperature and crystallization rate.Copolymerization of caprolactam changed the crystal form of PA66.With the increase of caprolactam content,the crystal form of PA66-co-PA6 gradually changed to ? crystal form.The properties of PA66-co-PA6 are changed due to the structural change,and the elongation at break of the tensile spline is obviously increased.On this basis,Mclay and TMWCNTs were introduced into PA66-co-PA6 by in-situ polymerization and copolymerization to prepare a series of PA66-co-PA6/Mclay/TMWCNTs composites and their fibers.Compared with pure PA66 fiber,the tensile strength of the modified fiber(20 wt% caprolactam,0.1 wt % Mclay,0.02 wt%TMWCNTs)was improved by 68%.