| By reason of the rising demand for environmentally friendly materials on a global scale, biodegradable co-polyester has been greatly promote in commercial application as the most widely used biodegradable material. From the perspective of rheology, this issue studies the capillary rheological and dynamic rheological behavior of PBAT, PBSA,discussed the rheological properties of biodegradable co-polyesters and the influence of shear,molecular weight, moisture, temperature on rheological property;then prepared PBAT/PBSA/TPS composite film by blown film proecss, and studied the effect of different type materials,proportion,extrusion and blowing process conditions on the flim property,then ultimately determined the optimum composite material formula and blown film process conditions of PBAT/PBSA/TPS composites.Firstly, rheological properties of aromatic-aliphatic co-polyester PBAT and aliphatic co-polyester PBSA were studied by capillary rheometer,and were compared with that of blown film grade LDPE.We found that the three kinds of materials are all pseudoplastic fluid,and the viscosity-shear dependency of PBAT and PBAT decreased significantly under 210℃,while compared with the n value of LDPE. On the other hand,the viscosity-temperature dependency of PBAT and PBAT are stronger than that of LDPE.Under different moisture content, PBAT and PBSA were significantly decreased with the rise of moisture content.When the moisture content is less than 500 PPM,the decline degree of shear viscosity lead to less,and this conclusion can be used as the basis for drying degree of PBAT and PBSA. By use of Cox- merz rules and rotary rheometer, the determination of fitting the PBAT and PBSA zero shear viscosity was developed.The results showed that the zero shear viscosity of PBAT and PBSA are all related to weight-average molecular weigh.The higher the weight-average molecular weight, the zero shear viscosity of the materials was higher.This method can be used to choose the maxis resin according to weight-average molecular weigh,for the demand of melt strength.Secondly, with TPS as modifier, biodegradable co-polyester composite was blended and compounded.It was studied that particle size and the proportion of glycerin have influence on the capillary rheological property of TPS.In consideration of viscosity,it is more appropriate to choose corn starch with particle size d50 4.95μm and 30% ratio of glycerin in preparation of TPS material.The rheological curve of different proportions between PBAT and PBSA showed that these two materials have good blending compatibility.And after adding TPS,the result showed that 20% of TPS content is most suitable in PBAT/PBSA/TPS composites.Finally, results of bubble spiral instability DHI values,which is detected by online blown film process, show that the bubble stability of PBAT and PBSA blown film related to the value of molecular weight,with better film stability at higher molecular weight.And the minor difference of the film bubble stability is perhaps,with the PBAT/PBSA/TPS composite of 20% ~ 40% content of TPS in it. If BUR 4.0 and DDR 33 were adopted, the tear strength and tensile strength, elongation at break of PBAT/PBSA/TPS composite film samples will reach maximum.The PBAT/PBSA/TPS composite blown film were prepared by using the test results of material formula and the extrusion blown film process in this issue : TPS was prepared by using 30% proportion of glycerine at first,and then compound PBAT/PBSA/TPS in 40:40:20 proportion.PBAT/PBSA/TPS composites were blown film in the condition including 170℃ temperature,400~600rpm motor speed,BUR 4.0 and DDR 33.Compared with that of LDPE blown film,the mechanical property of PBAT/PBSA/TPS composite blown film was nearly the same.The composites film can be used in as a replacement in the field of LDPE flexible packaging materials, and can realize the biodegradability to fulfill the requirements of environmental protection and energy saving. |
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