Cost-effective processing of immiscible polymer blends into value-added fiber-based products
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The current practice for recycling of mixed plastics relies on complex and time-consuming procedures for materials separation or the use of expensive compatibilizers for improving mechanical properties. A simple method for direct reuse of waste plastics without the pre-separation procedure or the compatibilizer will be beneficial for efficient and cost-effective recycling. This emerging need provides a motivation to study how to process immiscible polymer blends into value-added fiber-based products without using compatibilizers, which, on the other hand, are also helpful for the development of new polymer blend products. In this thesis study, we adopt a “nearly co-continuous structure” and employ such a morphology for materials processing and products realization when immiscible polymer blends are encountered. This nearly co-continuous structure is considered significant from both engineering and economics perspectives. The thesis starts with constitutive modeling of the dynamics of complex interfaces, leading to equations for the Cauchy stress tensor and the evolution of interfacial orientation in both affine deformation and situations where relaxing effects need to be considered. With the help of constitutive modeling and characterization, a methodology has been designed for producing valuable fiber-based products from immiscible polymer blends. Two case studies are used to demonstrate the methodology. Fiber prepared from the PP/PS blend shows improved mechanical properties compared with the fiber obtained via traditional melt spinning. In addition to improved mechanical properties, efforts have also been made to process polymer blend products with novel properties. Particularly, PCL/OBC blend is used as a model system to produce reusable supercontraction fiber which possesses a supercontraction ability upon heating. The overall methodology developed in this thesis work is formulated on the basis of the interfacial dynamics during blends processing where a compatibilizer is absent. Therefore, it may provide a potential route for direct recycling of waste plastics without the use of compatibilizers.