Study On The Surface Modification Of Polyester Fiber And Its Composites Performance

As an important branch of composites,fiber-reinforced composite material has achieved rapid development with its excellent properties and has been used more and more widely in all fields of our society.Among the reinforcing fibers,polyester fibers are widely used due to their lower density than glass fibers and lower processing costs than carbon fibers and aramid fibers.Polyester fiber has the advantages of high strength,high modulus,low elongation,good impact resistance,good fatigue resistance,and good chemical stability,etc.Therefore,it is widely used in the fields of construction,automobile engineering and so on.However,polyester fiber as a reinforcement in possession of a series of excellent performance,there are also some unavoidable problems.Polyester fibers are not easy to infiltrate the resin,and the resin adhesion is very poor that limits its application in the field of composite materials because of the linear symmetry molecular structure,the lack of polar groups,large intermolecular force,high crystallinity,smooth and dense surface morphology and strong chemical inertness.As the largest synthetic fiber in the world,polyester fiber has great potential in the field of composites.However,the application of polyester fibers has been limited in composite materials,due the poor interfacial adhesion between polyester fiber and resin matrix.Therefore,it is of certain value to study the surface modification of polyester fibers and the properties of the composites.In this paper,polyester fiber was treated with alkali treatment,plasma treatment and silane coupling agent treatment.The composite was prepared by the vacuum infusion molding process,with untreated and treated polyester fiber as reinforcement,vinyl resin as the matrix.The surface properties of the fibers were characterized by Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM)and surface contact angle.The properties of the fibers were characterized by XRD,fiber weight change rate and monofilament strength.The effects of different surface modification treatments on the the properties of composites were characterized by the interlaminar shear properties,tensile properties,impact properties and water absorption of polyester fiber reinforced composites.The main conclusions are as follows:(1)The surface properties of the untreated and treated polyester fibers were characterized,and the functional groups on the surface of the fibers were analyzed.It was found that the alkali treatment did not change the functional groups on the surface of the polyester fibers.Plasma treatment increased the surface active groups and the hydrophilicity of the fibers;Different pretreatment silane coupling agent treatment effect is different,after plasma treatment,the fiber can be better with the silane coupling agent graft polymerization.The changes of fiber surface morphology were analyzed.It was found that the surface of the fiber treated by alkali appeared different degree and randomly distributed dimples and grooves due to the hydrolysis.After plasma treatment,the fiber surface appeared convex sediment and etching trench;After silane coupling agent treatment,the fiber surface coated with a layer of a certain thickness,rugged silane coupling agent.The change of contact angle of the surface of polyester fabric was measured to characterize the change of fiber wettability before and after the modification.It was found that the contact angle of the surface continued to decrease after alkali treatment at different time.The contact angle decreased to83.71°at the time of 2.5h.The fractional alkali treatment also decreased the contact angle of the fiber surface continuously.When the mass fraction of the solution was25%,the contact angle of the surface was the smallest,which was 99.43°.After different temperature treatment,the contact angle of the surface decreased with the increase of temperature.When the treatment time is 85°C,the minimum is 58.03°.After plasma and silane coupling agent treatment,the contact angles of the surfaces all decreased to some extent,and the wettability was improved.(2)The properties of polyester fiber before and after modification were characterized,and the changes of the crystal structure of the fiber were analyzed.It was found that the crystal structure of the fiber did not change after the surface modification treatment,indicating that the fiber structure was not damaged and the modification occurs only on the fiber surface.The fiber weight change rate was tested,and the influence of different surface modification treatments on the fiber was analyzed.It was found that the fiber weight decreased with different treatment time,mass fraction and treatment temperature.The fiber weight decreased after plasma treatment by 1.04%.After treated with silane coupling agent,the fiber quality all increased to a certain extent.Among them,the sample treated with plasma-treated silane coupling agent increased most significantly,the mass increased by 1.05%.The strength of monofilament of polyester fiber was tested.The influence of different surface treatment methods on the strength of fiber was analyzed.It was found that the strength of monofilament fiber increased to 0.7257GPa at 1.5h after alkali treatment at different treatment time.The filament strength rose to a maximum of 0.7357GPa at15%.The strength of monofilament decreased after alkali treatment at different treatment temperatures,and reached the maximum of 0.7012Gpa at the treatment temperature of 40°C.After plasma treatment,the fiber monofilament strength increased by 6.58%to 0.7604Gpa;after silane coupling agent treatment,the fiber monofilament strength decreased.(3)The properties of polyester fiber reinforced composites before and after surface modification were characterized.The shear properties of the interlaminar layers showed that the interlaminar shear strength of the composites was higher than the untreated samples after alkali treatment at different time.When the treatment time is 2h,the maximum reaches 19.7447MPa.The shear strength of the composite first increases after alkali treatment with different mass fraction,and at the mass fraction of 10%it reached the maximum of 22.9779MPa,then the interlaminar shear strength began to decrease,and reached the lowest level at 20%mass fraction,lower than the untreated sample and then began to increase at 25%.After alkali treatment at different temperatures,the composite interlaminar shear strength was higher than that of the untreated sample,showing the trend of increasing at first,then decreasing,and then increasing.When the treatment temperature was 40?,the maximum rose to35.3549Mpa.After plasma treatment,the interlaminar shear strength of the composites increased by 23.93%.After the silane coupling agent treatment,the interlaminar shear strength of the composites increased.Tensile properties of the composites show that the tensile strength of the composites first increases and then decreases after alkali treatment at different time,and reaches 137.8852MPa at the time of 1.5h;with different mass fraction of alkali treatment,The tensile strength of the composites increased first and reached 155.4566MPa at the mass fraction of 25%.The tensile strength of the composites first increased after the alkali treatment at different temperatures,and then rose sharply to 129.6664Mpa at the treatment temperature of 55?.After plasma treatment,the tensile strength of the composites increased by 2.06%.After the silane coupling agent treatment,the tensile strength of the composites decreased.The impact properties of the composites show that the impact toughness of the composites increases with the untreated samples.After alkali treatment at different time,the impact toughness of the composite first increases and then decreases,reaching the highest 1.9704KJ/m~2 at 1h treatment time;the impact toughness of the composite first increases and then decreases after treatment with different mass fraction,When the mass fraction is 10%,the maximum value is 2.0296KJ/m~2.After alkali treatment at different temperatures,the content of the composite increases first,then decreases and then increases.The impact toughness of composite increases to 2.6222 KJ/m~2 at the treatment temperature of 40?.After plasma treatment,the impact toughness of the composites increased by 162.71%.After the silane coupling agent treatment,the impact toughness of the composites increased.The results of water absorption of the composite showed that the water absorption of the composite first increased and then decreased after alkali treatment at different times,and rose to the highest at the treatment time of 1.5h with an increase rate of21.00%.After alkali treatment with different mass fractions,the water absorption firstly increased and then decreased,and increased by 23.64%when the mass fraction was 20%.After alkali treatment,the water absorption of the composite decreased first,then increased and then decreased,the highest was at the treatment temperature of25?.After plasma treatment,the water absorption of the composite increased by25.50%,the corresponding silane coupling agent sample also increased the water absorption by 1.67%.After the silane coupling agent treatment,the water absorption of the composite decreased.