The Study On Preparation And Properties Of Polypropylene Modified By Polyesters

The applications of polypropylene (PP) is restricted in many aspects because of its insufficient strength and toughness. Recently, the modification of PP by engineering plastics has become a hot spot in polymer materials. In this thesis, firstly putting polyethylene terephthalate (PET) and poly (butylene terephthalate) (PBT) as modifiers, the effects of PP/polyesters blending process and conditions on the performances of polypropylene were studied. Besides, the effects of maleic anhydride grafted polypropylene (PP-g-MAH) and glycidyl methacrylate grafted EPDM (EPDM-g-GMA) on the structure and properties of the blends were also investigated. The results showed that, with the amount of PET increased, the tensile strength and bending strength of PP/PET firstly increase and then decrease. When the content of PET was 2%, the tensile strength of PP/PET blend reached 34 MPa, and the notched impact strength was about 38 KJ/m2. EPDM-g-GMA and PP-g-MAH could improve the compatibility of PP/PET blends, and the compatibility of PP/PP-g-MAH/PET blend was better than that of PP/EPDM-g-GMA/PET. The notched impact toughness of PP/PP-g-MAH/PET blends was about twice as high as that of polypropylene. When the content of PBT was 2%, the mechanical properties of PP/PBT was better than that of PP/PET under the same conditions. The addition of PP-g-MAH or EPDM-g-GMA was able to improve the interface compatibility of PP/PBT. The tensile strength of PP/PP-g-MAH/PBT could reach 44 MPa. The notched impact toughness of PP/PP-g-MAH/PBT was better than that of PP/PP-g-MAH/PET blend. Moreover, the thermal resistance and heat shrinkage rate of PP/PP-g-MAH/PBT blend were better than those of PP/PP-g-MAH/PET blend when they were under the same conditions. Scanning electron microscopy (SEM) analysis of the blends microstructure showed that PP-g-MAH could allow PP/polyester to obtain ideal compatibility, and the toughness of the blend was improved. Therefore, PP-g-MAH could improve the compatibility of the blends effectively.Polycarbonate (PC) which is polar material has rigid molecular chains and high strength. PBT has similar polarity with PC and excellent toughness. In this paper, PC and PBT were used together to modify PP. The process conditions of PP/PP-g-MAH/PC/PBT blend and the effects of different structures on properties of the blend were researched in detail. The results showed that, with the total content of polyesters (PC/PBT) increased, the strength and toughness of the blends increased at first and then decreased. When the ratio of PC/PBT was 2:1 and the content of polyesters was 7.5%, the tensile strength of PP/PP-g-MAH/PC/PBT blend was about 24 MPa. The notched impact toughness reached 28 KJ/m2, and the impact strength of the blend was seven times higher than that of PP. When the content of PC and PBT were 10% and 5%, the mechanical properties of the blend firstly increase and then decrease with the amount of PP-g-MAH increased. When the amount of PP-g-MAH was 2-5%, the blends had better mechanical properties. The notched impact toughness of the blend reached 13 KJ/m2, as the content of PP-g-MAH was 5%. In short, when the amount of PC/PBT were 10% and 5% and PP-g-MAH was in an amount of 5%, the PP/PP-g-MAH/PC/PBT blend with excellent overall performances could be obtained.