| Polypropylene(PP)foam material has excellent mechanical properties,good environmental adaptability and heat resistance,widely used in vehicles and aerospace and other fields.However,as a semi-crystalline polymer,the melt strength of PP is poor,which is not conducive to the formation of uniform fine cell structure,and its impact toughness is low,limiting the application of PP microcellular foam materials.In order to optimize the cell morphology and mechanical properties of PP microcellular foaming materials and expand its application,based on MuCell microcellular injection molding technology,the following researches were carried out:Firstly,the effects of melt temperature,injection speed,back pressure and supercritical fluid(SCF)on the foaming behavior(cell size and cell density)and mechanical properties(tensile,impact and flexural strength)of pure PP microcellular foaming materials were studied by single factor experiment.The results show that the apparent density were essentially unchanged,at the same position of the pure PP foam sample,with the weight reduction was 10%.And the proximal was maintained at about 0.775 g/cm3,while the filling distal was between 0.65 and 0.69 g/cm3.With the increase of the melt temperature,the cell size increased first and then decreased,and the cell density showed the opposite rule.The density of the filling distal was generally higher than that of the filling proximal end.With the increase of injection speed and back pressure,the cell size of the filling proximal and distal were decreased,and the number of cells increases.With the increase of SCF content,the cell size was obviously reduced.The cell density has an increasing trend.Under different conditions,the tensile strength of the unfoamed samples were about 30 MPa,with the foamed samples were between 16 and 19 MPa.Compared with the unfoamed samples,the tensile strength of the foamed samples were reduced by 36%-45%.The notched impact strength and flexural strength of the foamed specimens and the unfoamed samples were maintained about 3 KJ/m2 and 31-34.3 MPa,respectively,the impact strength and flexural strength of the foamed sample were generally larger than those unfoamed specimens.The effects of POE and talc on the foam behavior and mechanical properties of PP composite microcellular foaming materials were studied.After adding POE,the viscosity of PP/POE blends were increased,the melt flow rate decreased,with the melt strength of PP was improved,and then the foam behavior of PP were improved.With the increase of POE content,the average cell diameter of the foamed samples decreased first and then increased,and the cell density showed the opposite trend.When the POE content was 15%,the average cell diameter decreased to 73.8 μm,the cell density reached 13.1×105/cm3,which was 5-7 times of the cell density under other components,and the cell was evenly distributed without obvious merging and collapse.The tensile strength and flexural strength of the foamed and unfoamed samples showed a continuous downward trend.The impact strength of the foamed samples reached a maximum value of 18.24 MPa at the POE content was 25% and the impact strength of foamed samples with no POE was only 3.08 MPa.For PP/POE/talc blends,the addition of talc to the PP/POE blends has a limited effect on the foam behavior,but its overall foaming effect is still better than that of pure PP.When the talc content was 10%,The average cell diameter was 142.7 μm,the cell density was 1.33×105/cm3,the morphology of cells is superior to other components.Simultaneously,the tensile strength of the foamed samples reached to the maximum value of 17.5 MPa.With the increase of talc content,the flexural strength of the foamed and unfoamed samples increases greatly,reaching 33.57 MPa and 34.44 MPa,respectively.While the impact strength continued to decline,but still greater than the impact strength of pure PP foamed samples. |
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