Preparation,Property And Mechanism Investigation On The Biaxially Stretched PA6/EVOH Film With High Barrier

With the improvement of living standards,people's demand for plastic packaging materials with high barrier and excellent comprehensive property has increased dramatically.Biaxially stretched polyamide 6(BOPA6)film is widely used in the packaging field,because of good barrier property,high strength,good impact resistance,excellent flexibility,non-toxic and harmless.However,the barrier property of conventional BOPA6 film still has a gap compared to high-barrier materials such as aluminum foil.Improving the barrier property of BOPA6 film can expand its application range,which has important practical significance.In this paper,the barrier property of BOPA6 film is improved by introducing ethylene-vinyl alcohol copolymer(EVOH)with high barrier property.The main research contents and innovations are as follows:Firstly,PA6/EVOH composite was prepared by mixing EVOH with PA6 matrix by melt blending method.Studies have shown that EVOH hinders the formation of?-type crystals of PA6 in the film,promotes the formation of?-type crystals,and improves the crystallization of PA6/EVOH composite.The relationship between the viscosity of the composite material and the shear rate can be fitted by a power-law model.The relationship between the viscosity and the temperature of the composite material can be described by the Arrhenius equation.The apparent viscosity(?_a)and complex viscosity of composites|?*|increase with the addition of EVOH,especially when the amount of EVOH is 15wt%,the viscosity is greatly improved.There is a good compatibility between PA6 and EVOH,and when the amount of EVOH added reaches15 wt%,a micro-phase separation structure forms inside the composite.When the content of EVOH reaches 35 wt%,the elongation at break and impact strength of the composite increase by 143%and 27.3%,respectively.Secondly,PA6/EVOH(15 wt%)film was extrusion casting onto a chill roll,and the casting film was uniaxially and biaxially stretched by a biaxial stretching experiment equipment.Studies have shown that uniaxial stretching causes the(020)crystal plane to be perpendicular to the MD(stretch direction).However,except the(020)crystal plane to be perpendicular to the MD,the biaxial stretching also causes the(002)crystal plane to be parallel to the MD-TD plane.Stretching promotes the crystallization of the PA6/EVOH film and its phase structure and crystal orientation.As the stretching ratio increases,the orientation of the crystal increases.Uniaxial stretching increases the tensile strength of MD and decreases the tensile strength of TD,while the mechanical properties of biaxially stretched film appear balanced in the MD and TD directions.Among them,a biaxially stretched film which have a stretching ratio of(3×3)has higher strength and good toughness.Both uniaxial and biaxial stretching can improve the barrier properties of PA6/EVOH films,and the barrier property is better after biaxial stretching.Finally,the biaxially stretched PA6/EVOH film with a stretch ratio of(3×3)was prepared by extrusion casting and biaxial stretching.The study found that PA6/EVOH composite is not degraded during processing.The barrier property of the biaxially stretched PA6/EVOH film increases significantly,and the film with an EVOH content of 35wt%increases by more than half.The strength,modulus and toughness of the biaxially stretched PA6/EVOH film has all been improved,with the maximum modulus reaching 2574 MPa,an increase of about 1.7times.It can be seen that the biaxially stretched PA6/EVOH film has excellent mechanical and barrier properties,and is expected to be used as a film with high barrier and excellent comprehensive properties in the packaging field.