Preparation And Properties Of Polyoxamides And Their Carbon Fiber Reinforced Composites

Chapter 1 presents the review of carbon fiber reinforced thermoplastics(CFRTP)and polyoxamides.Nowadays,CFRTP are intensively investigated for automotive applications as the processing cycle is much shorter than that of conventional carbon fiber reinforced thermosets(CFRT).However,the development of CFRTP is greatly hindered by the difficulty of impregnating the fiber bundles with thermoplastics because of the high viscosity of molten resin.Polyoxamides are thermoplastics with low water absorption,high melting temperatures,high modulus,high chemical resistance and high UV light stability,which make them attractive for matrix of CFRTP.Although several techniques for their preparation have been studied,their commercialization however not been realized as the explored synthesis approaches have a wide range of limitations.Being a class of polyamides,the outstanding properties of polyoxamides have not yet been explored,especially in applications as matrix for carbon fiber(CF)composites where the general polyamide PA6 are faced with numerous challenges such as high-water absorption,which limits their application.However,just like their counterparts,polyoxamides occur in solid form making them difficult to impregnate carbon fibers for fabrication of their carbon fiber composites.In this study,a novel,simple,solvent free method is developed to quickly synthesize and in-situ impregnate polyoxamides into carbon fibers for preparation of composites.In Chapters 2 and 3,a novel solvent-free process of spray polycondensation is firstly explored to synthesize polyoxamides.In this process,the diamine and dibutyl oxalate monomers are separately injected through a nozzle,atomized simultaneously under nitrogen flow,mixed and polymerized at room temperature within a short period of time to give the prepolymer and then the prepolymer is subjected to solid state polycondensation(SSP)or melt polycondensation to increase the molecular weight.Employing this process,a series of novel polyoxamides such as poly(pentamethylene oxamide)(PA52),poly(2-methyl-1,5-pentamethylene oxamide)(PM52),poly(1,3-bis(aminomethyl)cyclohexamethylene oxamide)(PBAC2),poly(1,3-bis(aminomethyl)cyclohexamethylene oxamide-co-2-methyl-1,5-pentamethylene oxamide)(PBAC2-co-PM52)and poly(m-xylylene oxamide-co-2-methyl-1,5-pentamethylene oxamide)(PMXD2-co-PM52)with high molecular weight are prepared and their structures and properties are systemically investigated with FTIR,~1H-NMR,GPC,DSC,DMA and so on.The results reveal that these polyoxamides generally possess high heat resistance,excellent crystallizability,high storage modulus,low saturated water absorption and good thermal stability,which suggest that these polyoxamides are a promising matrix for CF composites.After careful consideration of the thermal properties and the SSP rate,PA52 and PBAC2-co-PM52(70/30)are selected as the matrix resins for the fabrication of CF composites in this study.In Chapter 4,the spray polycondensation is employed to provide a novel in-situ impregnation process,where the CF fabrics are placed under the nozzle and the monomers are sprayed,mixed and in-situ polymerized in the CF fabrics to give prepolymer and prepregs.The prepregs are then subjected to SSP and vacuum compression molding to prepare the polyoxamide/CF composites.Using this method,PA52/CF and PBAC2-co-PM52/CF composites are prepared and the effects of processing parameters on the mechanical properties of composites were studied in details.PA52/CF composite prepared at molding temperature of 325oC,pressure of3.0 MPa and time of 10mins exhibits good tensile strength at break,flexural strength and ILSS of 435 MPa,364 MPa and 51 MPa,respectively.SEM results suggest good adhesion between the PA52 and CFs.PBAC2-co-PM52/CF composite prepared via the same route possess tensile strength at break of 553 MPa,flexural strength of 448MPa and ILSS of 67 MPa,which are better than those of PA52/CF composites due to better interface between PBAC2-co-PM52 and CF as demonstrated by the SEM micrographs.Chapter 5 tries to prepare PA52/CF composites via in-situ spray impregnation and direct vacuum compression molding without SSP.Direct vacuum compression molding of the prepreg at 325oC and 3.0 MPa for 25 minutes results in PA52/CF composites with tensile strength at break of 398 MPa,flexural strength of 270 MPa and ILSS of 50 MPa,which are all lower than those of PA52/CF composites prepared with SSP in Chapter 4.The reasons are analyzed and suggestions are put forward to improve this method.Chapter 6 summarizes this thesis and lists the recommendations for future research.