Al Mezrakchi, Ruaa Yaseen Hammoudi (2019-03). Manufacturing Processing and Properties Manipulations of Thick Advanced Performance PEEK Polymer and Composites for Biomedical and Extremely Harsh Environments. Doctoral Dissertation.
Thesis
This study's aim is to investigate manipulating the compression molding manufacturing process to influence morphology and mechanical properties of thick wall and tall advanced performance thermoplastic polymers, as well as to highlight the mechanisms that cause property deterioration in those products. Two advanced performance polymer systems, neat poly(etheretherketone) (PEEK) and its composite (CF/PEEK), were considered as model systems to fundamentally understand structure-property relationships in thick wall advanced polymeric materials. An instrumented compression molding setting with thermal control and 3D embedded thermocouples is designed and fabricated to produce thick polymer parts and investigate how altering processing procedures influences properties. A novel hybrid sealing method is invented to enhance compression molding quality and avoid leaking issues associated with this process. The temperature distribution profiles throughout the compression molding and the bushing are collected during heating and cooling processes. The resultant temperature profiles are analyzed to further understand the compression molding process behavior, and thus adjust the processing procedure to enhance products morphology and properties. Crystal structure formation is controlled via templating material manufacturing cooling process. The influence of holding temperature at the crystallization temperature while increasing the hold time is examined by characterizing samples throughout bushings processed using various strategies. Manipulating the cooling is expected to guide the polymer amorphous arrangement toward a uniform crystal structure and grow this structure equivalently throughout the thick cross-section and the extended length of the final product. Remarkable crystallinity improvement with adequate consistency was achieved throughout thick wall and tall compression molded PEEK bushing that improved the compression molding product properties. Carbon fiber reinforcement's influence on crystal morphology and mechanical properties of thick products is addressed in this dissertation. Different techniques and tests are used to investigate the bushings produced using different processing strategies such as dynamic scanning calorimetry (DSC), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), wide angle x-ray scattering (WAXS), polarized optical microscopy (POM), compression test, and 3-point bending test. Those techniques assisted in establishing correlation between the morphology modification and the material properties response. Predictive numerical models are developed to simulate the compression molding heating process. Experimental validations provide beneficial tools to predict the heating time required for various thick compression molded materials. The predictive models established in this study can substitute building an expensive thermal control system and performing compression molding with embedded thermocouples to estimate material processing time. These models can provide a great assist for industrial applications. This study highlights an intelligible processing procedure for developing thick compression molding bushing with consistent crystallinity and enhanced mechanical properties. The processing protocol introduced in this study acquired based on analyzing compression molding temperature profiles and studying the possibility of using different methods to control the process during the cooling stage to produce neat and composite polymers with better properties. The produced products can be used for many applications such as aerospace, biomedical, automotive, food processing, oil and gas industry, etc.
