The Effect Of The Structure And Properties Of Isotactic Polypropylene With Beta Nucleating Agent And The Injection Molding Process Conditions

Isotactic polypropylene (iPP), as one general thermoplastic, is of low tenacity,which can be widely used in such fields as car bumpers, tubular products after theincrease of tenacity and change of property.TMB-5, an effective β-nucleating agent,can induce the generation of β-crystal structure in iPP to improve the tenacity. Thisthesis, as a comprehensive study, with iPP as material, is conducted to investigate theimpacts of the β-nucleating agent, the melt temperature and the mold temperature onthe properties and crystal structure of TMB-5/iPP (including β-nucleating agents iPPinjection molded parts) by mechanical properties test, polarized light microscopy(PLM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction(WAXD). The main work is as follows:(1) The influence of β-nucleating agent contentβ-nucleating agent content has the greatest impact on mechanical properties ofTMB-5/iPP. The tensile strength of TMB-5/iPP is slightly decreased while its impactstrength is significantly improved; With the increase of β-nucleating agent content,the tensile strength and tensile modulus firstly decreases and then increased. But theimpact strength and the tensile breaking elongationis is the other way round.β-nucleating agent also have great impact on the crystal structure of iPP. It canbe observed from PLM that many crystals are attached to the surface of TMB-5, andbroaden the crystallization temperature of iPP melt and increase the nucleation rate.According to the study of DSC, the influence of β-nucleating agent content to XcDSC(general crystallinity characterized by DSC) of TMB-5/iPP is not obvious; while havegreat influence to φβDSC(β-crystal content characterized by DSC), φβDSCrose firstlywith the increase of β-nucleating agent content and then decreased slightly;αand βcrystals, on the thickness direction of TMB-5/iPP, are uneven distribution: the skinlayer have higherα-crystal content while the intermediate and core layer have higherβ-crystals levels, both skin layer and intermediate layer have two β-peaks. Accordingto the test of WAXD, β (301) peak changes significantly, in addition to the obvious β(300) peak.(2) The influence of melt temperatureMelt temperature have great impacts on mechanical properties both theTMB-5/iPP and the injection parts of pure iPP. The impact strength of pure iPPinjection molded parts decreases with the rise of melt temperature, contrary to TMB-5/iPP. The tensile strength and modulus of TMB-5/iPP and pure iPP injectionparts are substantially reduced with the increase of melt temperature, which iscontrary to the tensile breaking elongation.Melt temperature has certain impacts on the crystal morphology of TMB-5/iPPand pure iPP injection molded parts. It can be observed from PLM that the thicknessof injection molded parts of skin layer is substantially declined linearly with the riseof the melt temperature, the higher the melt temperature is, the thinner the cortex is.According to the research of DSC, melt temperature have not obvious influence onXcDSCof TMB-5/iPP and pure iPP injection molded parts, and have great influence onφβDSCof TMB-5/iPP, φβDSCincreases with the rise of melt temperature; XcDSCandφβDSC, on the thickness direction of TMB-5/iPP, are uneven distribution； the XcDSCand φβDSCof skin layer and intermediate layer are basically increases with the rise ofmelt temperature. XcDSCof core layer slightly decrease with the rise of melttemperature, which is contrary to φβDSC.(3) The influence of mold temperatureMold temperature have slightly influence on the mechanical properties of of pureiPP injection molded parts; the tensile strength substantially increases with the rise ofthe mold temperature, contrary to the impact strength and tensile breaking elongation.For the mechanical properties and crystal structure of TMB-5/iPP, the regularity of theimpact of mold temperature is not obvious.