Study On The Preparation And Properties Of High Density Polyethylene/Nylon Laminar Barrier Materials

In this paper, high density polyethylene (HDPE)/modified polyamide(MPA) laminar materials have been prepared by laminar-blend blow-molding process to improve permeation resistance of HDPE. The relationship between the barrier properties, processing technology and morphology were studied. The research was focused on solvent resistant property of HDPE)/ MPA6 blends, HDPE/MPA54 and HDPE/MPA54/MMT series.First of all two types of compatibilizer precursors (CPs), Zinc-neutralized ethylene/acrylic copolymer (CPa) and non-neutralized ethylene/acrylic copolymer (CPb), were selected to modify polyamide 6 (PA6). The compatibility effect of CPs were studied by dynamic mechanical thermal analysis (DMTA) and atomic force microscope (AFM). The results show that CPa has stronger compatibility effect than CPb in HDPE/PA blend.Compatibilizer modified polyamid(MPA) were prepared in twin screw extruder and the reacting extrution processing were studied in detail. The barrier property of MPAa series are better than MPAbs. As the content of CPa was 15phr and the rotation speed was 300rpm, the melting index of MPAa was lowest, and the barrier property was best. Under these conditions the ethanol permeation resistance of MPAa were 4.5 times better than pure PA.Bottles of HDPE/MPA were produced by a laminar-blend blow-molding process. The effects of preparation temperature, screw speed, and compositions were investigated systematically, and optimal preparation parameters were obtained. The results showed that the HDPE/MPA blends exhibit significantly better barrier properties than those blow-molded from pure HDPE. The barrier resistance of HDPE / MPAa blends are improved gradually with increasing CP content in MPAa and the lowest toluene permeability is obtained. The barrier improvement of the best sample is 308 times better than pure HDPE. The barrier properties of HDPE/MPAa bottles are better than that of HDPE/MPAb. The further investigation on the morphology showedthat MPAa exhibits strong interfacial adhesion with a HDPE matrix and forms a multi-lamina morphology, but MPAb only formed the "broken" and "discontinuous" orientation structure.In order to further improve the barrier property of PA, Nylon6/clay nanocomposite was prepared by mixing organically montmorillonite(MMT) with nylon6 in HAAKE mixer, and solvent permeation resistance of nanocomposite is measured. The nanocomposite shows the resistance against solvent permeation superior to that of pure nylon6.The maximum improvement in barrier properties of nylon6/clay composite was found when the content of clay was about 0.1%. Using proper composites and under suitable processing conditions, the permeation rate of toluene and ethanol in nylon6/clay nanocomposite is about 3 and 4 times slower than that in purenylon6at 50"C.Our studies indicated that the crystalline property of nylon6 has a strong impact on the sorption and diffusion of small molecules in the polymer. The improvement in solvent barrier properties of nylon6/clay nanocomposite is attributed to incorporation of an impermeable phase such as layered silicate, improvement in crystallinity and the decrease of crystalline dimention, which are evidenced by XRD, AFM, DSC and polarized optical micrographs (POM). In PA6/ MMT nanocomposites, the addition of MMT favors the formation of the y crystalline phase was investigated by XRD. The result showed that d-spacing of y crystalline phase is smaller than that of a crystalline phase, and the crystallinity is higher in nanocomposites as compared with neat PA6. POM analyses show that spherulites of nylon6 are fairly big and perfectly grown with the maltese cross, but nylon6/ MMT nanocomposite has fine and uniform spherulite. This result implies that MMT reduces the size of nylon6 crystallites.Non-isothermal crystallization experiments involving differential scanning calorimetry (DSC) were conducted to understand the nucleat effect of MMT, The result shows that the addition of MMT increased the rate of crystallization and decreased the time of crystallization. The nucleating activity of MMT() is about 0.56.The transparency of nanocomposite was investigated by ultraviolet-visiblespectrometer. Although the degree of crystallinity of the nanocomposite is higher than that of the pure nylon6, interestingly the nanocomposite prepared under suitable cooling conditions shows better transparence than pure PA6. This can be attributed to the smaller sizes of spherulites in nanocomposites. In addition, the rheological properties of nanocomposite were studied. It shows that the addition of MMT increased the melt viscosity at lower shear rate but decreased the melt viscosity at higher shear rate.Finally, the bottles of HDPE/MPA54 and HDPE/MPA54/MMT were prepared by laminar-blend blow-molding process, and their barrier property and morphology were studied, the investigations indicate that the best processing temperature of HDPE/MPA54 and HDPE/MPA54/MMT are about 40°C lower than HDPE/MPA6 blend. Clearly defined laminas were observed on the fracture surfaces of the PE/MPA54 bottles. The toluene permeation resistance of HDPE/MPA54 were improved more than 80 times compared with pure HDPE.