In Situ Ftir Study On Crystallization Process Of IPP

Crystallization of polymer is a fundamental issue which is not only veryimportant but also really controversial in the polymer science. Generally,crystallization of polymer can be investigated by several common methods such asDSC, XRD, PLM which can only detect the morphology and structure of polymerafter crystallization processing on the minimum measure of unit cell. In this paper, thechangs of chain conformations of isotactic polypropylene (iPP) during isothermalcrystallization under different temperature is studied with in situ Fourier transforminfrared spectroscopy (FTIR) technology, three aspects of work are listed as below:1. In-situ FTIR observation of the conformational change of during isothermalcrystallization process: in the first stage, short helices existed in the melt, the meltremained relatively stable, as time grows, As soon as the helices length exceeds acritical value (12monomer units), the long helix conformations extends quickly,thenshort helices and long helices increased together, the crystallization occurs. Before thestart of crystallization process, it has a process of transformation from short helices tolong helices, namely conformational ordering before crystallization. Our experimentalresults confirm the viewpoints of Strobl crystallization theory.2. Compared the changes of conformations of iPP during isothermalcrystallization process at different temperatures. is shows that, below the meltingpoint(Tm) of iPP, with the increase of temperature, the long helices in iPP melt occurmore slowly and crystallization process longer.We also find that, above the nominal melting point of iPP(Tm), at170°C, shorthelical segments in the melt can still exist.3. compared with the ordered melt (melt temperature between nominal meltingpoint(Tm) and equilibrium point(Tm0)) and blank melt (melt temperature above theequilibrium melting point(Tm0))of iPP at the same temperature.The results show thatbelow the melting point(Tm) of iPP, ordered melt start crystallization earlier and havea faster crystallization rate than the blank melt at the same temperature duringisothermal crystallization process, and as temperature increased, the phenomenon of ordered melt crystallization faster is more obvious. It shows that some helixconformation in the ordered melt, which can accelerate the primary nucleation rateduring isothermal crystallization process, and the conformational order of polymercan speed up the crystallization rate.