Preparation And Functionalization Of Toughened Biaxially Oriented Polyamide 6 Film

Biaxially oriented polyamide 6 film（BOPA）is one of the key components of packaging material for soft-packaged lithium-ion battery,which is widely used in new energy vehicle power battery,and the battery for portable electronic products such as mobile phone,notebook computer,and other application.Currently,the packaging material for the soft-packaged lithium-ion battery is aluminum-polymer laminated film,usually consisting of biaxially oriented polyamide 6 film（BOPA）/aluminum foil（Al）/cast polypropylene film（CPP）.In order to protect the aluminum foil layer against external force damage during the cold stamping of the aluminum-polymer laminated film,the BOPA film is required to have outstanding toughness to support it.Although the BOPA film used for the soft-packaged lithium-ion battery already has been realized the manufacture domestically,there is still a certain gap between the BOPA film with excellent toughness and ductility and the congeneric products abroad,which still cannot meet the requirements of some special fields.In addition,the BOPA film still has some areas such as poor matting property and no high gas barrier property to be improved,which limits its application in the packaging field to some extent.In this paper,aiming at the problem of insufficient toughness of BOPA film,poly（ether-b-amide）thermoplastic elastomer（PEBA）and bio-based polyamide 1010（PA1010）were applied to toughen BOPA film based on the simultaneous biaxial stretching process.Effects of the contents of toughening agent on the microstructures and macro-properties of the BOPA film were investigated,in order to explore the toughening mechanism of the BOPA film toughened by toughening agent.Meanwhile,the effect of stretching process on the structure and property of toughening modification of polyamide 6 films was also discussed.Furthermore,on the basis of the toughening modification,the high barrier modification and matting modification of the biaxially oriented PA6/PA1010 film were also performed respectively in this paper.The aromatic polyamide（poly（m-xylylene adipamide）（MXD6）and amorphous polyamide（PA6I-6T））and silica（Si O₂）were employed as modifiers to prepare BOPA films with high barrier property and excellent matting effect,respectively,so as to improve the above-mentioned problems of the BOPA film.The main contents and results of this work are summarized as follows:（1）In order to solve the problem of insufficient toughness of the BOPA film,poly（ether-b-amide）thermoplastic elastomer（PEBA）was incorporated into the BOPA film as toughening phase,and the biaxially oriented polyamide 6 film with high toughness was prepared by extrusion casting method and simultaneous biaxial stretching process.Results show that the addition of PEBA increases the melt viscosity and elastic properties of the PA6/PEBA blends,and the toughness of BOPA film can be effectively enhanced by appropriate amount of PEBA incorporation.The improvement in toughness of the BOPA film is attributed to the shear yielding of the PA6 matrix and wire drawing phenomenon caused by the addition of PEBA.In addition,the biaxially oriented PA6/PEBA film predominantly containsα-crystal form.On the other hand,the biaxial stretching induces theβ→αphase transformation of the PA6/PEBA film.With the increase of stretching ratios,the crystallinity,barrier performance and tensile strength of the biaxially oriented PA6/PEBA film are gradually increased,and the toughness still maintains at a relatively high level.The enhancement of the barrier performance is closely related to the stretch-induced crystallization and both the decrease of the number of free volume holes and the decrease of the free volume content in the stretched film.（2）In addition to using thermoplastic elastomer toughening,high-toughness PA1010 was also selected to toughen BOPA film.PA6/PA1010 cast film was prepared by extrusion casting method,and the biaxially oriented PA6/PA1010 film with high toughness was produced by simultaneous biaxial stretching process.Meanwhile,the effect of stretching process on the structures and the properties of the stretch-oriented PA6/PA1010 film was also investigated.The study found that the addition of PA1010 can effectively improve the toughness of biaxially oriented PA6/PA1010 film,which is closely related to the shear yielding of the PA6 matrix and wire drawing phenomenon caused by the addition of PA1010.It is revealed that the biaxially oriented PA6/PA1010film predominantly containsα-crystal form.In addition,uniaxial stretching of the PA6/PA1010 film induces theβ?α+?phase transformation and causes a preferential orientation along the the drawing direction,while the biaxial stretching at various stretching ratios and stretching temperatures induces theβ→αphase transformation,showing no preferred orientation.Both the increase of stretching ratios and stretching temperatures can increase the crystallinity,long period and lamellae thickness,and the oxygen barrier performance of the stretch-oriented PA6/PA1010 film.At the same time,the increase of stretching ratios and stretching temperatures is benefited for the reinforcement of the stretch-oriented PA6/PA1010 film by increasing the tensile strength,and the toughness still maintains at a relatively high level.（3）In order to solve the problem of insufficient barrier property of the BOPA film,biaxially oriented PA6/PA1010/aromatic polyamide（MXD6 and PA6I/6T）films with high barrier property were prepared by the incorporation of MXD6 and PA6I-6T into the PA6/PA1010 blend based on the simultaneous biaxial stretching process.It is found that both the addition of MXD6 and PA6I/6T have no influence on the crystalline form,orientation,the nucleation mechanism and geometry of crystal growth of the film,but increase the activation energy for the non-isothermal crystallization process and decrease the crystallization rate and crystallinity.Compared with the biaxially oriented PA6/PA1010film,the oxygen permeability of the biaxially oriented PA6/PA1010 films containing 30 wt%MXD6 and 30 wt%PA6I/6T shows 50.42%and47.09%decrements,respectively.The result indicates that both the addition of MXD6 and PA6I/6T can significantly improve the oxygen barrier property of the biaxially oriented PA6/PA1010 film.（4）In order to make up the shortcoming of poor matting property of the BOPA film,biaxially oriented PA6/PA1010/Si O₂film with excellent matting property was prepared by the incorporation of silica（Si O₂）into the PA6/PA1010 blend based on the simultaneous biaxial stretching process.Results show that the addition of Si O₂particles can play heterogeneous nucleation effect,which promotes the crystallization of the biaxially oriented PA6/PA1010/Si O₂film,and decreases the half-time of crystallization and the crystallization activation energy of the film,accompanied by the increase of crystallization rate and crystallinity.At the same time,the addition of Si O₂particles has no influence on the crystalline form,the nucleation mechanism and geometry of crystal growth of the film.In addition,both the increase of Si O₂contents and the increase of biaxial stretching ratios can improve the matting property of the biaxially oriented PA6/PA1010/Si O₂film.The improvement of the matting property is attributed to the increase of film surface roughness.