Catastrophic fire incidents due to high flammability of polymers necessitate developing fire-proof polymer composites. Halogen-free flame retardants (FR) are being incorporated in polymers at high contents, which adversely affects other polymer properties. This includes:​ i) decreased foaming ability of the matrix, and ii) deteriorated mechanical properties. Accordingly, the main objectives of this work are enhancing foaming ability of highly-filled FR polymers, improving the efficiency of conventional FRs to reduce the FR content, and addressing the deteriorated mechanical properties.

Nano-fibrillation technology was used as an effective approach to address these challenges. The fabrication of foams with high cell density and small cell size, and excellent fire retarding properties and stiffness were achieved by including in situ nanofibrils in highly-reinforced composites. Polytetrafluoroethylene (PTFE) nanofibrils were employed to improve foaming behavior of highly-filled FR polystyrene (PS) to achieve fine microcellular structures. Also, inclusion of PTFE nanofibrils enhanced FR efficiency in both solid and foam composites by generating a dense char layer to achieve V0 rating in vertical burning test.

We also demonstrated that including heat-resistant nanofibers is an effective approach to increase the efficacy of the current halogen-free FRs. Formation of heat-resistant nanofibers creates a continuous nanoscale network-structured layer/shield to preserve the matrix against burning and suppresses dripping during combustion. Heat-resistant nanofibers also lead to promoting a graphitized carbonaceous layer to thoroughly protect the polymer against fire and meet V0 rating.

Lastly, nanofibrillar elastomers effectively improves the toughness of the composites with minimum drop in the stiffness. Elastomeric nanofibrils slows down and limits the propagation of nano-micro cracks which enhances the matrix capability to dissipate the stresses and improves the toughness of the matrix from 2 MPa to 8.8 MPa. Soft nanofibers also compensate detrimental effect of hexagonal boron nitride (hBN) as the FR additive on toughness of the PS. Interestingly, FR efficiency of hBN was boosted by presence of nanofibers due to enhanced exfoliation of hBN sheets.

Thus, the thesis reports a solid approach to improve FR properties of polymers. The careful engineering of nano-fibrillated polymer composites was shown to improve FR properties, mechanical properties, and foaming ability for various applications.