Investigation Of POE, POP And LLDPE Improving Low-temperature Toughness Of Transparent Polypropylene

The application of transparent polypropylene (PP) for medical use is restricted because of brittle fracture. In this dissertation, the suit toughening agent was used in toughening transparent PP through Twin-Screw Extruder.Firstly, polyolefin elastomer (POE), polyolefin plastomer(POP) and Linear Low Density Polyethylene(LLDPE) are used in toughness of transparent PP. The effect on mechanical properties was investigated by impact test and tensile test, the impact fracture surface microstructure, phase structure, crystal structure,and compatibility were studied by scanning electron miscroscope (SEM), differential scanning calorimeter(DSC), wide-angle X-ray diffraction (WXRD). The effect of the microstructure on the transparency of the blends was analysed. The result shows that with increasing the toughening agent content, the room-temperature, 0℃and -35℃impact strength of the blends improved. Toughened PP by POE exhibited better room-temperature and low-temperature tougheness compared to POP and LLDPE. The room-temperature and -35℃impact strength for the PP/POE blends which contain 25% POE were reach to 42 KJ/M2 and 6.32 KJ/M2, improved 6 times and 5 time of that of pure PP, respectively. Impact fracture surface revealed POE / PP binary system is a micro-particle distribution by the POE in the PP matrix, with the increase of POE content , micro-particle size increased. The impact fracture damage mechanism translated from craze– hole theory to shear yield. DSC results show that with increasing the POE content, the crystallinity of PP phase in POE / PP binary blends decreased. And a new phase formed between POE and PP melting peak, WXRD analysis that it is a new PE crystalline form, and it proved that PP and POE has better compatibility. The results of transparency test shows that POE greater damaged on transparency of the composites, the transparency reduced to 44% when POE content was 15%. The toughening effect of POP on PP is less than POE, DSC results showed that the crystallinity of PP phase decreased when the POP added, PP and POP have some compatibility. LLDPE almost has no low-temperatures toughening effect on the transparent PP, DSC results show that the PP / LLDPE is the thermodynamic incompatibility system, but LLDPE made less raising in impact strength, but also the least reduing in tensile strength and transparency.In order to maintain transparency while toughening, LLDPE was added in the PP/POE blend as synergistic toughening agent. In PP/POE/LLDPE blends, kept the mass ratio of PP/POE was 90/10, the effect of LLDPE conten on the performance was investigated. The result shows that with increasing the LLDPE content, the room-temperature and low- temperature impact strength and the transparency first increased and then decreased. PP / POE / LLDPE blends which mass ratiois 90/10/5 has the best overall performance, its room- temperature impact strength of 10.25 KJ/M2 is 2 times of pure PP; the impact strength under -35℃is 4.25 KJ/M2, is 3.5 times of pure PP. The transparency is 54% and tensile strength is 28.42MPa.