Study On The Preparation And Properties Of Biaxially Oriented PET/PGA Functional Composite Film

Poly（ethylene terephthalate）（PET）is one of the five most versatile engineering plastics with excellent processing properties,mechanical properties and transparency,and is widely used in plastic sheets,bottles and chemical fibers.However,PET has poor oxygen barrier properties and antistatic properties that limit its development in high value-added fields.Traditional blending and compound modification have the advantages of simple operation,low cost and easy industrial production,but there are still problems such as limited improvement of barrier performance and decrease of mechanical properties.In view of this,this topic firstly introduces poly（glycolic acid）（PGA）into PET by melt blending and prepares biaxially oriented PET/PGA barrier film by combining with biaxial stretching process,and secondly further improves its barrier properties and antistatic properties by introducing graphene oxide（GO）and poly（ether-block-amide）（PEBA）components to prepare biaxially oriented PET/PGA functional composite film,which is expected to broaden the application of PET in food and electronic packaging.The main research contents and results of this thesis are as follows:Firstly,biaxially oriented PET/PGA films were prepared by melt blending and biaxial stretching process,and the effects of draw ratio on the microscopic morphology,crystalline properties,mechanical properties and barrier properties of biaxially oriented PET/PGA films were investigated,and the barrier mechanism was elucidated.The results show that the biaxial stretching transforms the dispersed PGA phase from a spherical structure to a two-dimensional lamellar structure and oriented parallel to the film surface.The length-to-thickness ratio of the dispersed PGA phase as a gas barrier unit was increased from 1 to 20,which effectively prolonged the permeation path of gases,thus significantly improved the barrier properties of the film.Meanwhile,the tensile strain significantly increased the crystallinity of the biaxially oriented PET/PGA film and reduced the dissolution and diffusion rate of the gas.As a result,the oxygen permeability（OP）of PET was decreased by 90%after incorporation of the PGA and biaxial stretching（λ=3×3）.In addition,the biaxially oriented crystals and ordered amorphous chain network induced by biaxial stretching increased the tensile strength and Young’s modulus of biaxially oriented PET/PGA films from 43 MPa and 1300 MPa to 118 MPa and 4000 MPa,respectively,and exhibited high ductility（elongation at break of 40%）and excellent overall performance.Secondly,graphene oxide（GO）was used as a filler to further improve the mechanical and barrier properties of the biaxially oriented PET/PGA films.Epoxidized GO（EGO）was obtained by surface grafting with silane coupling agent KH560,and the layer structure of EGO was introduced as a barrier filler into the PET/PGA blending system by multi-step melt blending,and biaxially oriented PET/PGA/EGO composite films were prepared by combining with the biaxial stretching process,and the effect of EGO on the barrier properties of biaxially oriented PET/PGA films was systematically investigated.The results indicate that EGO is uniformly dispersed in PET by surface grafting and multi-step melt blending,and orientated parallel to the film surface by biaxial stretching,which effectively increases the path of gas permeation.Meanwhile,EGO has the effect of promoting crystallization to the film,thus improving the barrier properties of the composite film.Therefore,the OP of the biaxially oriented PET/PGA/EGO composite film was significantly reduced to 3.5×10^-16 cm³·cm/（cm²·s·Pa）after the addition of 0.1 wt%EGO,which was 54%lower compared with the biaxially oriented PET/PGA film.In addition,EGO can be used as a reinforcing unit to increase the tensile strength of biaxially oriented PET/PGA/EGO films to 138 MPa.Finally,poly（ether-block-amide）（PEBA）was introduced into the PET/PGA blending system,and antistatic biaxially oriented PET/PGA/PEBA barrier films were prepared by melt blending combined with the biaxial stretching process,and the effects of PEBA on the microscopic morphology,antistatic properties and barrier properties of the films were systematically investigated,and the antistatic mechanism was discussed.The results show that the PEBA phase in biaxially oriented PET/PGA/PEBA films forms a continuum network due to the different viscosities and interfacial tensions by agglomeration on the surface,which constitutes a conductive pathway and gives the films the ability to conduct electrostatic charges with a transmissivity threshold between 5-8 wt%.At a PEBA content of 10 wt%,the surface resistivity of the biaxially oriented PET/PGA/PEBA film was 2.8×10⁹Ω,indicating that the film had antistatic properties.Meanwhile,the WVP and OP of the biaxially oriented PET/PGA/PEBA film were 1.04×10^-14 cm³·cm/（cm²·s·Pa）and 20.7×10^-16 cm³·cm/（cm²·s·Pa）,respectively,which were reduced by 54%and 82%compared with pure PET.