The Relationship Between Structure And Properties In Polypropylene,Polybutene-1and Its Blends:an In Situ FTIR Imaging Study

The relationship between structure and properties of polymer materials is an important issue in polymer physics research. Unique long chain of crystalline polymer structure laid an important position in condensed matter, and makes it becoming the largest category of polymer application. Polymer with multiscale and multiphase characteristics has become complex and interesting study of the relationship between microstructure and properties mechanical properties. In this paper, we combined in situ sample devices and Fourier Transform Infrared Sepectroscopic imaging (FTIRI) to study the spatial evolution of structure in crystalline polymer materials of polypropylene (iPP) and Polybutene (PB) during the deformation process. Meanwhile, we foucs on the correlation between structure evolution and mechanical behavior. On the basis of the structure and properties of a single polymer system, we turn to study the unique crystal morphologies in iPP/PB blends. We have a better understanding on the phase transformation coupled with the competition for the physical mechanism of crystal morphology regulation.Crystal-crystal transition of Polybutene-1(PB-1) from forms Ⅱ to Ⅰ inside and outside a large hedrite or spherulite during deformation is investigated with in situ FTIRI technique and miniature tensile tester. Three stages have been observed for both of samples. In the first stage, form Ⅰ crystal formed slowly under the effect of deformation. When entering the second stage Ⅱ, the crystal-crystal transition was accelerated significantly. In the third stage, form Ⅱ translates into form Ⅰ almost completely. It was also found that the transition rate inside large hedrite and spherulite is slightly faster than the surrounding initially, especially for the hedrite. However, the difference inside and outside becomes negligible when ε>0.8. We proposed that the difference in crystal-crystal transformation between spherulite and hedrite is attributed to the different alignment of lamellar stacks in two samples. The results demonstrate the effect of different morphologies on the crystal-crystal transition during deformation.In this study, microstructural change of isotactic Polypropylene (iPP) inside and outside a large spherulite during tensile deformation is monitored with in situ Fourier Transform Infrared Sepectroscopic Imaging (FTIRI) with polarized radiation technique. Two different mechanical processes are identified when stretching at room temperature. Polymer chains are first oriented accompanying with fibril formation outside the spherulite, whereas spherulite remains unchanged basically in necking propagation region. When entering the strain hardening region, spherulite starts to deform under external stress until destruction, resulting in the significant decrease of crystallinity. The polymer chains inside the spherulite are also oriented along the tensile direction. Furthermore, the evolution processes of crystalline and amorphous fractions are also monitored with their characteristic bands at998and973cm-1. respectively. Analysis demonstrates the positive correlation between the orientation evolutions in crystalline and amorphous phases. During the plastic deformation, crystalline orientation is higher than amorphous orientation outside the spherulite, while that is opposite inside the spherulite. When necking appears, the higher degree of crystalline orientation comparing with amorphous is attributed to the fast relaxation of amorphous phase than crystalline phase. The difference in the orientation direction of crystalline and amorphous phases was ascribed to the crosshatched structure of α crystal.The study of crystal morphologies in iPP/PB blends shows that the influence of thermal history on the crystal morphologies is attributed to the regulation of the concentration distribution. At the same crystallization temperature, the growth rate of iPP spherulite is decreasing with the number of heating treatments, in which the phase behavior presents the irreversibility. Through the characteristic infrared peaks of each composite, we determine the PB concentration at the growth front of iPP spherulite. Meanwhile, the relative intensities of1219and998cm-1were calibrated the concentration distribution of PB and iPP during crystallization. The experimental results show that the phase morphologies were inhomogeneous after different thermal history. Starting from high melting temperature, PB-rich phase remains relatively concentrated, and bifurcation was found in the corresponding region. However, the growth rate in all directions almost keeps constant, and the corresponding concentration of PB at the growth front of iPP presents large fluctuation. As the increasing of the number of heating treatment, the dendrite appears at the growth front of the spherulite. There is no change with the spherulite growing until reach to100μm, accompanying with the growth rate was deviated from the linear growth behavior. The concentration fluctuation of PB at growth front was decreasing, which promote the compatible between the two components.