Preparation And Properties Of Montmorillonite/Hyperbranched PA6 Nanocomposites For Packaging

Polyamide 6(PA6)films have becomed one of the important packaging materials due to the favorable transparency,high tensile strength and also have excellent resistance to cooking,organic solvents,puncture resistance and oxygen resistance.However,the structure of the traditional polyamide resin is linear,Although its mechanical properties are better,it also has some shortcomings such as high relative viscosity and poor melt fluidity.The polyamide-amine(PAMAM)is a dendritic polymer with a large number of active functional groups around the molecular chain.In recent years,dendritic branched macromolecules have exhibited a series of unique physical and chemical properties due to their highly branched structures,such as non-tangled molecular chains,low viscosity,high fluidity,good solubility and difficulty in crystallization,which are not available in linear polymers.Polyamide 6 with PAMAM(hyperbranched PA6)is a kind of polyamide resin with high melt flow rate,easy moulding,short processing time,low energy consumption and low cost,high strength and high toughness.A small amount of layered montmorillonite(MMT)nanomaterials are introduced into the polymer.MMT can exert the nano-effect of the nano-sheet layer,on the basis of ensuring the mechanical properties of composite materials,it can change the migration path of small molecular substances(water vapor,oxygen,etc.)and effectively improves the barrier properties of composite materials.In this study,PA6 is synergistically modified by PAMAM and MMT to prepare montmorillonite/hyperbranched PA6 nanocomposites by hydrolytic polymerization of polyamide 6 under high temperature and pressure.Thepreparedmontmorillonite/hyperbranchedPA6nanocomposites were characterized in a series of ways.The results show that compared with the other three types of montmorillonite,organic montmorillonite(DK5)is more feasible to combine with the matrix of hyperbranched PA6.Its tensile strength,elongation at break and notch impact strength increased from 52.67MPa,12.65%and 4.75kJ/m~2 of pure hyperbranched PA6 to 81.78MPa,26.31%and 6.98kJ/m~2,respectively.Based on the successful preparation of organic montmorillonite(DK5)/hyperbranched PA6 nanocomposites,and also focuses on the dispersion and grafting of organic montmorillonite(DK5)with different mass fractions in hyperbranched PA6 matrix,as well as the thermal,crystalline,rheological and mechanical properties of the nanocomposites,and the mass fraction of PAMAM is adjusted appropriately.Studies have shownthatthemechanicalpropertiesofmontmorillonite(DK5)/hyperbranched PA6 nanocomposites have been greatly improved on the basis of ensuring relatively low viscosity and easy molding of hyperbranched PA6.When the content of montmorillonite(DK5)is 3wt%,the tensile strength of the composite increases from 63.87 MPa of pure hyperbranched PA 6 to 86.57 MPa.Finnaly the biaxially stretched packaging films by using montmorillonite(DK5)/hyperbranched PA6 nanocomposite were prepared through the process of extrusion film casting and biaxial stretching and a series of macroscopic properties of biaxially stretched films were characterized.The characterization results show that on the basis of excellent macroscopic properties,the composite packaging films prepared with a content of 3wt%of montmorillonite and a tensile ratio of 3×3 have the best properties.The water vapor permeability and oxygen permeability are significantly reduced to 90.2gm·mil/m~2·day and26.2cc·mil/m~2·day,which are 3.4 times and 2.6 times higher than those of non-stretched films containing montmorillonite PA6,and about 4.4 times and 3.0 times higher than those of pure hyperbranched PA6 unstretched films.