The morphology of liquid crystalline polymers and their blends

• Main Author: Schaffer, Kevin Roman
• Language: ENG
• Published: ScholarWorks@UMass Amherst 1993
• Subjects: Plastics|Polymers
• Online Access: https://scholarworks.umass.edu/dissertations/AAI9329664

Nematic liquid crystals polymers (LCPs) encompass a large class of macromolecules exhibiting orientational order when in the melt or solution state. The intrinsic local orientation of these materials yields processing advantages due to lower viscosities than related isotropic (flexible coil) polymers of comparable molecular weight. Highly directional moduli and strengths in the solid state are further benefits of the ease of obtaining high orientations during processing in the melt or solution. Blending and composite fabrication with other materials are the practical methods that must be developed to use LCPs for structural applications. A nematic liquid crystal polymer such as poly(p-phenylene benzobisthiazole) (PBZT) is a rigid rod macromolecule with its length being essentially the mesogenic unit. Such rigid rod polymers are usually lyotropic liquid crystals and are infusible in the pure state so that any fabrication with other materials must be done in the solid or solution state. Thermotropic liquid crystalline polymers have molecular architecture usually consisting of shorter mesogenic units connected with flexible spacers that allow the mobility needed for the existence of flow at higher temperatures. The melt state allows the possibility of melt blending with other polymers using the liquid crystal as a processing aid or a reinforcement that forms in-situ. The purpose of this thesis is to characterize the morphology on various length scales of polymer composite materials obtained by these disparate methods of fabrication. The principle techniques utilized are optical, transmission electron, scanning electron microscopy, and X-ray diffraction. This work consists of an introductory and three subsequent chapters. Chapter 2 describes the morphology of composite films fabricated by attempting to infiltrate isotropic materials (glass or epoxy) into an existing nano-scale fibrillar network that naturally forms when PBZT is coagulated. The PBZT film that was formed by extrusion through a counter-rotating die. In Chapter 3, the morphology of fibers formed from spinning dopes composed of mechanically mixed PBZT and flexible polymer solutions is discussed. In Chapter 4 the morphology of a melt blended thermotropic liquid crystal polymer is compared with mechanical data.