Preparation And Properties Of Degradable Benzoxazine And Its Carbon Fiber Composite

Benzoxazine resin is widely used in the fields of electronics,aerospace,and mechanical manufacturing due to its flexible molecular design,nearly zero curing shrinkage,no small molecule release during curing and excellent thermal stability of the cured materials.However,due to its three-dimensional network structure with permanent crosslinking after curing,benzoxazine resin and its composite materials cannot be recycled after reaching their service life.The traditional methods(mechanical crushing,oxidative pyrolysis,etc.)used to treat benzoxazine resin and its composite waste are costly and difficult to obtain carbon fiber with high reuse value.By introducing dynamic covalent bonds into polymer crosslinking networks through molecular design,it is difficult to obtain biodegradable benzoxazine resins with good thermal and mechanical properties,which further limits its application.Therefore,for benzoxazine resin and its carbon fiber composites,how to balance the relationship between the biodegradable and recyclable properties,thermal and mechanical properties while studying the recyclable properties of resin biodegradable fibers is a problem worthy of deep thinking by researchers.The research idea of this paper is to copolymerize benzoxazine monomer with cyclic olefin monomer containing cracking bond through ring-opening translocative polymerization(ROMP),prepare an olefin copolymer with side chain of benzoxazine group and main chain containing cracking bond,and study the properties of the copolymer.The main work includes two parts:(1)A new benzoxazine(PH-5N2m)containing norbornene was successfully synthesized from 5-norbornene-2-methylamine,phenol and polyformaldehyde.Poly(PH-5N2m)side and copolymers of PH-5N2 m with 2,3-dihydrofuran(DHF)were prepared by ROMP reaction.The structural of PH-5N2 m,poly(PH-5N2m)side and copolymers were investigated by 1H NMR and FT-IR spectroscopy.By differential scanning calorimeter(DSC)test showed that the introduction of norbornene structure did not affect the ring-opening polymerization of benzoxazine,and the addition of DHF could reduce the peak curing temperature(Tpeak)of benzoxazine.When the mass fraction of DHF was 50 wt%,the Tpeak of system reduced from251 oC to 242 oC.By thermogravimetric analysis(TGA),the order of 10% weight loss of copolymer system was poly(PH-5N2m/DHF-30)(366.3 oC)> poly(PH-5N2m/DHF-15)(365oC)> poly(PH-5N2m/DHF-50)(344.3 oC)> poly(PH-5N2m)(270 oC).The mechanical properties of the copolymer system were studied by the impact testing machine and scanning electron microscope(SEM).When the mass fraction of DHF was 30 wt%,the impact properties of the copolymer system were increased from 0.97 k J/m2 to 4.56 k J/m2.In addition,the solvent resistance and degradability of the copolymer system were tested.The results showed that the copolymer system has excellent solvent resistance and the copolymer with mass fraction of 50wt% can be completely degraded in 12 h at room temperature.The carbon fiber reinforced resin matrix composites were prepared and the carbon fiber(CF)was recycled.It was found that the surface morphology of the recycled carbon fiber was not damaged and the mechanical properties of the recycled carbon fiber were comparable to those of the original fiber.(2)A new benzoxazine(o HPNI-a)containing norbornolic anhydride was synthesized from o HPNI,aniline and paraformaldehyde.The copolymer of o HPNI-a and α-al was prepared by ROMP reaction.Their chemical structures were characterized by 1H NMR and FT-IR spectra.The curing behavior of copolymer system was studied by DSC and FT-IR tests.The results showed that the introduction of α-al could significantly reduce the curing temperature of benzoxazine,because α-al,as a weak acid,could catalyze the ring-opening of benzoxazine.The thermal stability of copolymer system was analyzed by TGA,and it was found that the addition of α-al did not affect the thermal stability of pure benzoxazine resin.The hydrophobic properties of pure resin and copolymer systems have been studied.It is found that the copolymer system increases in hydrophobicity due to the increased content of hydrogen bonds of type-OH???N in the system.The degradation of copolymer system was tested but the degradation effect was not satisfactory.The electrochemical test results show that the copolymer coating has better anticorrosion performance than the pure benzoxazine coating.