| Dynamic Melt Control has tremendous potential in altering the properties of an injection molded polymer part. By controlling temporal rheology of the polymer melt, an enhancement in a directionally dependent molecular orientation can be obtained. Furthermore, molded parts can be molded with specific levels of molecular orientation, allowing for the potential to manufacture parts with a range of different properties. Specifically, vibration assisted injection molding (VAIM), a novel processing procedure, induces oscillatory flow of a molten polymer during the injection and packing phase of the injection molding cycle. VAIM has proven successful in molding polymer parts with increased mechanical properties.;In applying the VAIM technology to the field of medical implants, the goal was to analyze the effect of molecular orientation on biodegradation. It was revealed through different analyses that biodegradation was occurring in different ways. FTIR and mass measurements were used as measurements of biodegradation, in which mass was found to remain constant throughout the study due to the overall resistance to degradation common to hydrophobic PLA. FTIR analysis revealed changes in molecular bonding structure. However, firm conclusions could not be reached by FTIR results alone.;Enhanced orientation was found to lead to increased mechanical strength in both grades of PLA used, and the importance of a constant orientation region was noted. The effects of VAIM processing on polymer properties (in addition to molecular orientation) was determined, in which VAIM appears to cause increased degradation and increased crystallinity compared to conventional molding. Due to mechanical testing results, it appears that the excess degradation caused by VAIM is insignificant compared to the strength of the increased molecular orientation. Further analysis is necessary to understand the properties of the initially processed part and the molecular evolution which occurs during biodegradation. Dynamic melt control offers promise as a potent injection molding technique for tailoring the properties of biodegradable polymer medical implants, and its effect on biodegradation warrants further investigation. |
