Study On Transparent Polypropylene Processed By α And β Nucleated-iPP Blending And Its Properties And Structure

Recently, the special transparent polypropylene is used widely but it can not be directly used for preparing medical equipment because its poor notched impact strength. In this dissertation it was studied that a transparent polypropylene for medical application was preperaed by using an ordinary iPP as a raw material with addingαnucleating agent andβnucleating agent or POE in order to modify its transparent and toughened properties to meet a suitable performance requirement. The best formula and process conditions can be found by explorating process and characterizating the performances.A set of transparent polypropylene material were produced by melt-blending polypropylene with different contents of ZC-2 typeαnucleating agent using the twin-screw extruder. The effect of different contents ofαnucleating agent on the light transmittance rate, tensile strength and breaking strength of the transparent polypropylene was studied. PLM observation and DSC analysis showed that theαnucleating agent can accelerate the crystallization of iPP. The increase of the content ofαnucleating agent from 0.1% to 0.4% leads to a decrease of the spherulite size of polypropylene and an increase in crystallinity obviously. Therefore,αnucleating agent can effectively improve the light transmittance rate, stiffness and tensile strength of polypropylene. However, the increase in crystallinity for PP significantly becomes a main reason why the impact strength of PP decreases obviously, especially when the content ofαnucleating agent of 0.4%, its impact strength decreases to approximately 45.3% of pure polypropylene.It was studied that the light transmittance rate, tensile strength and impact toughness of the transparent polypropylene prepared by melt-blending of polypropylene with 0.4%αnucleating agent in the twin-screw extruder with different blending temperature of 190℃, 210℃and 230℃. The results showed that the best light transmittance rate of specimens achieved with the blending temperature of 230℃. This is owing to that at a high temperature, the solubility ofαnucleating agent and the nucleation density become larger and the crystal size become smaller. Although the tensile strength of the specimen was increased, the static and dynamic fracture toughness decreases, respectively. Therefore, in this dessitation it was investigated whether specimen PA4 can be toughened withβnucleating agents and POE, respectively.It was investigated that the effect ofβnucleating agent on the toughening of PP blends extruded. The impact strength of specimen PB1 at the both room and low temperature can achieve the best with theβnucleating agent content of 0.1%. The impact strength of specimens began to decrease when the content ofβnucleating agent is higher than 0.1%. PLM and WAXD analysis showed that there are someβcrystal andαcrystal in modified polypropylene, so the specimens were toughened. Also the increase ofβnucleating agent leads to an increase in total crystallization andβcrystallization as well as a decrease in the size ofβcrystal, which could be the reson why the impact strength and the break elongation ratio decreased significantly.After adding 0.4%αnucleating agent and 0.1%βnucleating agent in polypropylene, then melt-blending prepared the sample PAB1 by one-step and PAB2 by two-step. PLM, WAXD and DSC analysis showed that both of PAB1 and PAB2 containαcrystal andβcrystal, there were both have moreαcrystal thanβcrystal. The two samples both have good light transmittance rate asαcrystal existence and at the same time the appearance ofβcrystal make the samples both have a good impact toughness, so theαandβnucleating agent have a synergistic effect on modifieding polypropylene. PLM, WAXD and DSC microcosmic analysis also showed that the spherulite size of PAB1 was lager than that of PAB2, and theβcrystal content of PAB1 was higher than that of PAB2, so the sample PAB1 has good toughness. However, the spherulite size of PAB2 was smaller than that of PAB1 and theαcrystal content of PAB2 was higher than that of PAB1 also, so the sample PAB2 has good transmittance. So it is indicating that one-step method to prepare specimens is more conducive toβcrystallization, while two-step method is more conducive toαcrystallization.When using POE to modify the polypropylene sample PA4 which contain 0.4%αnucleating agent, the results showed that the light transmittance rate of specimens decreased as the content of POE increased and lower than that of PAB1 and PAB2; but the low-temperature impact strength and room-temperature impact strength both increased significant, the impact strength of the specimens achieved 3.32KJ/m~2 is 3.3 times as PA4 when the POE content of 20%.