(618v) POSS-Sorbitol Interactions and Their Effects On the Reinforcement of Polypropylene Spun Fiber

Templated, self assembly of molecules polyhedral oligomeric silsesquioxane (POSS) was used to obtain polypropylene (PP) nanocomposite fibers. A nucleating agent 1,3:2,4-dibenzylidenesorbitol (DBS) compatible with phenyl silanol-POSS promoted dispersion of POSS molecules and provided templates for self-assembly into cylindrical nanoparticles having close to 100 nm in diameter and 200 nm in length in the spun fibers. It was found that at the optimum combination of phenyl-POSS and DBS, PP can be spun into fibers with close to 40% reduction in diameters compared to unfilled PP and 60% improvement in tensile strength and modulus, and 100% improvement in yield stress. Optimum formulation was established with 1% of DBS and 5% of tri-silanol phenyl-POSS (Tri-POSS), and 1% of DBS and 2% of tetra-silanol phenyl-POSS (Tetra-POSS). Rheological studies revealed phenyl silanol-POSS prevented fibrillation of DBS. The interactions between silanol POSS and DBS was investigated using DSC, FT-IR, XRD, NMR and mass spectrometry. The mixtures of tri-POSS and tetra-POSS with DBS when heated at the processing temperature of 200°C, formed a transparent liquid whereas tri-silanol cyclopentyl POSS (cyclo-POSS) failed to do so. The transparent liquid was amorphous as confirmed by XRD with a glass transition temperature above the room temperature as identified by DSC. The amorphous material was believed to be consisted of supramolecular complexes which failed to form crystalline structures. The cylindrical shaped nanoparticles as found in spun fibers were believed to have resulted from the stretching of this liquid complex. The compounds formed between cyclo-POSS and DBS were crystalline in nature as confirmed from XRD. No chemical reaction occurred between DBS and POSS as identified from the solid state ²⁹Si and ¹³C NMR and complexes of different molecular ratios were identified from mass spectrometry (Electrospray Ionization) study. Only complexes with 1:1 molecular ratio were identified between cyclo-POSS and DBS, whereas higher molecular ratio complexes were observed for tri-POSS and tetra-POSS with DBS. From the above observations it can be concluded that although hydrogen bonding interactions was the prime force for the complex formations, intermolecular π- π stacking between the phenyl rings play a major role towards the formation of supramolecular complexes.