Studies On Preparation And Properties Of Polyester Adhesive Based On Gallic Acid

Adhesives are widely used in industrial production and daily life.Commercially available adhesives only adhere firmly to substrate surfaces in a dry environment.However,in a humid environment,the adhesion strength significantly decreases because the hydration layer in the interface prevents the adhesive from infiltrating the substrate surface and reduces effective bonding areas.Mussels can firmly adhere to various substrate surfaces in turbulent seawater.Many studies have shown that the excellent underwater adhesion properties of mussels are attributed to the synergistic effect of polyphenols and aliphatic hydrophobic segments.Inspired by the underwater adhesion of mussels,in this thesis,gallic acid(GA)was used as the functional adhesion monomer,which copolymerized with different aliphatic monomers to prepare polyester adhesives with well underwater adhesion properties by adjusting the structure of other monomers.The main works of this paper are shown as follows:(1)Polyester adhesive P(GA-co-LA)was prepared by copolymerizing natural polyphenol GA with bio-based monomer lactic acid(LA).By changing the ratio of the two monomers,a series of P(GA-co-LA)polyesters with different functional group contents were obtained.The hydrophobic LA segments driven out the interface hydration layer and increased the infiltration area of GA on the substrate surface,leading to forming strong interface interactions.The results of fourier transform infrared spectroscopy(FT-IR)and proton nuclear magnetic resonance spectroscopy(~1H NMR)demonstrated successful synthesis of P(GA-co-LA).The presence of the pyrogallol groups at the end of polymer chains was confirmed by ultravioletvisible spectr-ophotometer(UV-Vis)and arnows’colorimetric assay.The glass transition temperature of P(GA-co-LA)was higher than 25℃,resulting in high cohesion at room temperature.After hot-pressing under temperature at 60℃ and preload of 70 kPa,the wet adhesion strengths of P(GA-co-LA)on glass,iron,aluminum and polyethylene terephthalate(PET)were up to 3.20 MPa,2.35 MPa,2.37 MPa and 0.81 MPa,respectively,which were superior to commercially available underwater adhesives.P(GA-co-LA)exhibited low cytotoxicity and a bond strength of 28 kPa with pigskin,which demonstrated good biocompatibility and tissue adhesion.(2)The long hydrophobic aliphatic chain is beneficial to improve the long-term underwater stability of the adhesive.Underwater adhesives P(GA-co-CL)with different functional group contents were prepared by copolymerizing polycaprolactone(PCL)with GA monomer.The structures of the copolymers were confirmed by FT-IR,~1H NMR,UV-Vis and arnows’colorimetric assay.The melting temperature of P(GA-co-CL)was low,and hot melt bonding could occur at 60℃.The wet adhesion strengths on glass,aluminum,iron and PET were up to2.48 MPa,1.28 MPa,1.48 MPa,and 0.60 MPa,represently.Since the CL segment improved the hydrophobicity of the polymer,the wet adhesion strengths of glass-bonded samples did not significantly decrease after being immersed in water for 4 weeks.Meanwhile,adhesives could also achieve strong bonding of substrates in acidic and salt solutions,exhibiting good long-term stability,salt and acid resistance under water.P(GA-co-CL)exhibited low cytotoxicity with a bond strength of 25 kPa on pig skin,which was superior to the commercially available fibrin glue.(3)On-demand debonding of adhesive enables recycling of bonded substrates,which is meaningful in practical applications.A photo-controlled reversible underwater adhesive azo-P(GA-co-CL)was prepared by grafting photoresponsive azobenzene groups to P(GA-co-CL).The results of FT-IR,UV-Vis and X-ray photoelectron spectroscopy(XPS)confirmed azobenzenes were successfully grafted to P(GA-co-CL).Arnows’colorimetric assay proved the existence of polyphenol groups in polymer.The wet adhesion strengths of azo-P(GA-co-CL)on glass,quartz,PET and polymethyl methacrylate(PMMA)were up to 2.03 MPa,1.53 MPa,0.82 MPa and 0.60 MPa,represently.After UV light irradiation,the azo-P(GA-co-CL)realized solid-liquid transition due to the cis-trans isomerization and photothermal effect of the azobenzene groups,which sharply decreased the cohesion of the polymer,thus achieving on demand debonding.Then,the adhesive could be re-adhered to the substrate surface under visible light irradiation.The adhesion strength of azo-P(GA-co-CL)still reached 1.68 MPa after four cycles of bonding-debonding,exhibiting well cyclic bonding properties.