Processing and properties of multifunctional bio-based poly(lactic acid) composites

Abstract

Following the eco-design concepts, this thesis investigated the manufacturing and properties of multifunctional bioplastic poly(lactic acid) (PLA) based composites. The main advantages of using bio-based polymer are to create performance products from sustainable resources, competing with fossil hydrocarbon sourced polymers, at the same time leaving open the possibility of composting as an alternative end-of-life option in addition to recycling.

In Part I, self-reinforced PLA (SR-PLA) composites were produced based on oriented PLA tapes and a thin layer of PLA matrix, which were combined using a film-stacking technique into a „brick-and-mortar‟ laminated structure. The optimization of the uniaxial drawing and structure of these tapes, together with a study of the interfacial, tensile, impact and thermal properties of the obtained SR-PLA composites were investigated. In order to be successful in more demanding engineering applications the important issue regarding biodegradation during the PLA-based product‟s lifetime needs to be addressed. Therefore, monitoring of degradation levels during usage is of a vital interest. This is the subject of study of the 2nd part of the thesis. In Part II the aim is to develop multifunctional engineering bioplastics with improved performances (mechanical and electrical) and added functionalities (sensing properties). An in-situ degradation monitoring system for biodegradable polymers was successfully developed through the incorporation of carbon nanotubes (CNTs) in PLA. Changes in electrical resistivity of the PLA/CNT nanocomposites were successfully correlated with degradation levels of this bioplastic. PLA/CNT nanocomposites demonstrated excellent degradation sensing abilities at CNT concentrations around the percolation threshold, In Part II the aim is to develop multifunctional engineering bioplastics with improved performances (mechanical and electrical) and added functionalities (sensing properties). An in-situ degradation monitoring system for biodegradable polymers was successfully developed through the incorporation of carbon nanotubes (CNTs) in PLA. Changes in electrical resistivity of the PLA/CNT nanocomposites were successfully correlated with degradation levels of this bioplastic. PLA/CNT nanocomposites demonstrated excellent degradation sensing abilities at CNT concentrations around the percolation threshold, with resistivity changes of about four orders of magnitude with biodegradation. The exceptional mechanical, electrical properties and 1D anisotropic geometry of CNTs also make them ideal reinforcing fillers for polymeric fibres. Therefore, the influence of CNT content and solid-state drawing on microstructure and the resulting mechanical and electrical properties of these nanocomposites were investigated.