The Influence Of Annealing On Aggregation Structure Of Isotactic Polypropylene Thin Films

The appearance and mechanical properties of the final productsare largelyinfluenced by the morphology and structure of polymer crystals. Generally, thepolymer crystalline structures can be significantly improved by two commonmethods. Firstly, crystallization behavior is linked tothe temperature and externalforce conditions during processing. Secondly, the properties and crystallinestructures of final products can also be controlled largely by annealingprocedure.The effects of annealing-based methods on regulating the aggregationstructure of polymer have been widely studied, however, most of resultsare carriedout at relatively low annealingtemperatures.In this thesis, the effects of annealing onthe aggregation structure of iPP thin filmsunder a wide range of temperatures havebeen investigated as well as the changes of the helical conformation during heatingand annealing processes. This work and relevant results are summarized as follows:1.iPP thin films, obtained from Haake Polylab System, were annealedatdifferentannealing temperatures for aconstant annealing time of40min, annealingtemperatures were set as80oC,100oC,140oC,155oC,160oC,165oC,170oCand180oC. Polarized Fourier Transform Infrared Spectroscopy (FTIR), DifferentialScanning Calorimetry (DSC)and Wide Angle X-ray Diffraction (WAXD) had beenused to study the effects of annealing on the crystal structuresof iPP thin films. Theresults indicated that, onlyα form crystal could be observed in the iPP thin films.Crystallinityand orientation degrees increased with increasing annealing temperaturefrom80oC to165oC but decreased when annealing temperature was up to170oCand180oC. When iPP thin films were annealed at140oC and170oC, it appeared doublepeaks in DSC melting curves corresponding to lamellarcrystals with differentthicknesses. The main interplanar crystal spacing nearly unchanged suggested thatthere was no significant altering of the unit cell.2. The in situ FTIR had been used to investigate the helical conformationbehavior of iPP thin films during heating and annealing processing. It was found thatall the conformational bands of iPP had a sudden reduction in intensity at about 170oC which was higher than the norminal melting point derived from DSC andrapidly reached a minimum level at around180oC. The ordering degree of helicalstructures near melting point melt was found higher than the equilibrium melt. Theinflection point temperaturehad no remarkable change with an increase of annealingtemperature from80oC to155oC,but changed significantly at high annealingtemperature region (160oC to170oC). When the annealing temperature was up to180oC, the inflection point temperaturewas found to be reduced rapidly. Comparedwith the DSC results, it was seggusted that the collapse of helical structure ensuedfrom the destruction of crystal lattice. During the annealing processing, all theconformational bands of iPP tended to be stable within less than9min.Theamorphous to crystal transformation in this study could be associated with suchresults:The intensity of amorphous phase conformational bands with no helicalsequences decreased with increasing intensity of long helices (crystal phaseconformational bands),and this process was accompanied byunchanged intensity ofamorphous phase conformational bands with some short helices.