Micro-/nano-fibrillated composites (M/NFC) are a new generation of composites containing well-dispersed, high aspect ratio polymeric fibrils. The novel composites have shown great promise as next-generation materials for construction, gas barrier packaging, and foaming applications. However, it is still not fully understood how the fibrils’ development during processing and their final morphology are impacted by the manufacturing and material parameters. Moreover, the applications of M/NFC have been limited, mainly focused on taking advantage of the mechanical properties. Therefore, this dissertation aims to show the fundamental mechanisms of the fibrils’ formation, and the practical applications of M/NFCs in thermal insulation and antistatic fields.

The first part of the thesis includes in-depth analysis of some crucial parameters and their influence on the evolution of the fibrils’ morphology. Experimental results indicate that tuning the reinforcement to matrix viscosity ratio significantly impacts the fibrils’ morphology. By choosing a low viscosity ratio system, the fibrils’ diameters are refined, and continuity is enhanced, resulting in composites with improved mechanical properties. Moreover, a new method of applying coupling agent is proposed to further enhance the dispersion of the fibrils and improve the interfacial adhesion between the matrix and fibrils. The results indicate that the new method can improve the interface without damaging the fibrils’ morphology. The second part of the thesis focuses on the development of new applications of M/NFC. With the formation of the physical network of the dispersed fibrils in the polymer matrix, the viscoelastic properties and crystallization kinetics are enhanced, making the M/NFCs a great candidate for foaming. Low-density, closed cell foams are successfully manufactured from M/NFC showing ultra-low thermal conductivity (~32 mW∙m⁻¹∙K⁻¹). Furthermore, we demonstrated a new approach to generate electrically percolated core-sheath fibrils with low reinforcement concentrations in a polymer matrix. We first designed a completely wetted morphology where the reinforcement phase was coated with conductive layers within the polypropylene matrix. The subsequent melt spinning process transformed the dispersed, completely wet droplets into high aspect ratio core-sheath fibrils, which percolated into conductive network structures. Since the content of the matrix can be maintained at a very high level (> 90%), the resultant materials, even without compatibilization, have both good electric conductivity and excellent mechanical properties.

This dissertation developed fundamental understanding and in-depth analysis of structure-property relationships and propose new manufacturing approaches of micro/nano-fibrillate composites for various applications.