Preparation And Investigations On The Biaxially Oriented Nylon 6-66 Nanocomposites For Packaging

The polyamides are some of the most important polymers in packaging field.In comparison with polyamide 6,the polyamide 6-66presents more excellent toughness,clarity,and lower melt point therefore low amount of the engergy comsuming.However,the strength and barrier properties of polyamide 6-66?PA6-66?need to be enhanced to broaden the application range and to substitute the high-barrier packaging materials.Most of the polyamide films used in the packaging fields have experienced the biaxial orientation process,which remarkably improved the mechanical and barrier properties.The microstructure transition of polyamide during biaxial orientation,such as the alignment of the crystallites,the variation of the crystal forms,would determine the macro properties like mechanical,barrier,optical properties,and shrinkage.Nevertheless,to the best of our knowledge,the literatures regarding the relationships between the microstructure transition and the ultimate properties of the PA6-66 films are rather scarce,which significantly restrain the application of PA6-66 films in packaging industry.In this work,the PA6-66 was used as polymer matrix and the montmorillonite?MMT?was introduced to prepare PA6-66/MMT nanocomposites and the mechanical strength of PA6-66 was improved.Furthermore,in order to overcome the deficiency of the toughness of the PA6-66/MMT,the nanosilca?SiO₂?was added and the toughness was eventually enhanced.Then the fabricated PA6-66 nanocomposites were formed into films,followed by biaxial stretching and the systematically investigations upon the effect of the biaxial stretching on the structure and the properties of the films.The primary conclusions are summarized as follows:1.The PA6-66/MMT nanocomposites were prepared via melt compounding to improve the properties of PA6-66.It was found that the MMT platelets were homogeneously dispersed in the polyamide matrices in an exfoliation pattern,and the MMT exhibited the heterogeneous nucleation effect to promote the crystallization process of PA6-66.It was indicated that as the inclusion of the MMT,the melt elasticity decreased,and the tensile strength of the PA6-66/MMT nanocomposites gradually increased,accompanied by the decreased elongation at break.Since the barrier properties were determined by the exfoliation of MMT platelets,and the melt-blended regime presented more pronounced strengthen effect,the meld-blending was used for further preparation of the PA6-66/MMT nanocomposites.2.The PA6-66/MMT/SiO₂ nanocomposites were prepared with the incorporation of SiO₂ into PA6-66/MMT via melt compounding to overcome the brittleness.The inclusion of SiO₂ improved the exfoliation and dispersion of MMT platelets.The two nanofillers exhibited synergistic effect on the crystallization behavior,the heat distortion temperature,nonlinear behaviors and mechanical properties.Moreover,the addition of SiO₂ enhanced the strength and the toughness simultaneously,with the later presented more appreciable enhancement.3.The effect of biaxial orientation on the structure and properties of the PA6-66 films were firstly investigated,aiming at evaluating the applicability of the PA6-66 and PA6-66 nanocomposites in packaging fields.The PA6-66 films were prepared via extrusion film casting,followed by the biaxial orientation with a laboratorial biaxial tester.It was found that the films mainly exhibited?-form crystals.The uniaxial stretching facilitated the b-axis orientated along MD and the c-axis along ND.In contrast,the orientation degree of b-axis decreased and the c-axis increased in the biaxial stretched films.It was revealed that as increasing of the stretch ratios,the crystallinity,long period of the lamella,barrier properties,tensile strength,thermal shrinkage were increased,the elongation at break was decreased,and the optical properties remained nearly unchanged.It was found that as increasing the stretch ratio,the uniaxially stretched films exhibited nearly unchanged shrinkage and mechanical properteis in the TD.The biaxially stretched films presented almost equal properties in the MD and the TD.These results indicated that the ultimate properties of the films are strongly dependent on the orientation of the crystals and the amorphous phase.4.Based on the investigations on the neat PA6-66 films,the structure and the properties dependent on the biaxial orientation were investigated.It was found that the primary crystal population and the orientation patterns were similar to those of PA6-66 films.The as-casted films presented an initial orientation of MMT platelets paralleled to the film surface,which was facilitated by stretching,and the biaxial stretching induced the highest degree of orientation.It is similar to the tendency of the PA6-66 films that as increasing the stretch ratios,the crystallinity,tensile strength,barrier properties,and thermal shrinkage were increased,and the elongation at break were decreased.Furthermore,the inclusion of MMT enhanced the tensile strength and barrier properties of films,and decreased the thermal shrinkage.These characteristics would give rise to PA6-66/MMT being a promising high-performance packaging material.5.Based on the PA6-66/MMT films,the structure and properties of the PA6-66/MMT/SiO₂ films under biaxial orientation were sequentially investigated.The insignificant effect of the SiO₂ addition on the primary crystal population and the orientation patterns was found.The stretching and the nanofillers facilitated the crystallization behavior of PA6-66 and enhanced the crystallinity of the films.The variation of the mechanical,barrier properties and thermal shrinkage of PA6-66/MMT/SiO₂ films induced by the stretching was equivalent to that of the PA6-66/MMT films.Moreover,the incorporation of SiO₂ increased the elongation at break without sacrificing the tensile strength.Meanwhile the barrier properties were improved and the thermal shrinkage was decreased.Therefore it is indicated that the biaxially oriented PA6-66/MMT/SiO₂films present excellent mechanical properties,barrier properties and dimensional stability,with favorable application prospect in packaging industry.