The room temperature morphology of quench-cooled isotactic polypropylene (iPP) films and its development were investigated by scanning transmittance electron microscopy (STEM) and differential scanning calorimetry (DSC). STEM dark field images revealed that within an amorphous matrix there exist microcrystalline regions, 160 A in size on the average, having the $ alpha$-monoclinic crystal form. Regions of lower crystalline order were also observed which have an $ alpha$-monoclinic crystal form that has a substantially longer b crystallographic axis. DSC studies indicate that during quench-cooling to the glassy state iPP samples attain a low degree of crystalline order to an extent that depends on sample mass. Upon heating from the glassy state, an exothermic transition is observed following the glass transition temperature which corresponds to the formation of the room temperature morphology. / Cross polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy was used to monitor morphological changes in the purely crystalline phase of quench-cooled iPP films and spunbonded fabrics during annealing. The spectra were obtained using a pulse sequence that incorporates a delay period with a reduced spin locking field prior to cross polarization. Morphological changes occurring within the purely crystalline phase of iPP were related to observations made by DSC. Upon annealing, the CP/MAS NMR spectrum of the purely crystalline phase of both iPP samples changed by a redistribution in the intensity of the various peaks within a given carbon resonance. This redistribution of intensity was found to reflect the conversion from the $ alpha sb1$ to the $ alpha sb2$ monoclinic crystal forms. It is shown that the double melting endotherm observed by DSC for the spunbonded fabrics is due to the exothermicity which is associated with this conversion. It is concentrated in the temperature region between 156 and 163$ sp circ$C. / The tensile properties of the spunbonded iPP fabrics and fibers were enhanced by the dispersion of a silica/silicone additive and by changing the resin characteristics. This additive acts as a nucleating agent for iPP under isothermal crystallization conditions. This nucleating ability manifests itself in smaller crystal sizes and higher nucleation densities in the iPP fibers and bond points. The improved tensile properties are attributed to the smaller crystal sizes which form a more homogeneously dispersed crystalline phase in the amorphous phase as well as to increase the number of load-bearing tie molecules.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.40026 |
| Date | January 1995 |
| Creators | Caldas, Victor. |
| Contributors | Brown, G. R. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001536507, proquestno: NN19696, Theses scanned by UMI/ProQuest. |
Page generated in 0.0071 seconds