AbstractThe development of biobased polyamides has attracted growing interests in recent years due to the availability of more biobased monomers, namely dicarboxylic acids, and diamines. This doctoral thesis is focused on the preparation of wholly biobased polyamides and their nanocomposites and the investigation of various factors that influence the properties.
A novel wholly biobased, self-healing, polyamide-based thermoplastic elastomer (PA36,36) was synthesised using a fatty dimer acid and a fatty dimer amine, both containing multiple alkyl chains, through a simple one-pot condensation polymerisation under different polymerisation times. The resulting elastomer shows high toughness, superior stretchability and remarkable shape recovery after being stretched to 200% and 500% strains. This elastomer also displays high autonomous self-healing efficiency after damage and zero water uptake during water submersion. The highly entangled main chain, the multiple dangling chains, the abundant reversible physical bonds, the inter-molecular diffusion and the low ratio of amide to methylene group within the elastomer are proposed to be responsible for these extraordinary properties. The polymerisation time affect the properties of the elastomer. The use of the optimal PA36,36 in anti-corrosion coating, piezoresistive sensing and highly stretchable fibres is also demonstrated.
The monomer chain length and the ratio of amide linkages to the methylene, among others, contribute to the properties of polyamides. A series of fatty based polyamides including PA36,4, PA4,36, PA36,9 and PA9,36 were synthesised by melt polycondensation and the effects of monomer chain length on the properties were studied. Apart from PA36,4, the other three polyamides exhibited melting temperatures of 83.6 oC – 94.7 oC, glass transition temperatures of ~ 17 oC, high stretchability (up to 1450%) while maintaining high strength (up to 24 MPa), excellent impact, flexural, and tear behaviour, as well as superhydrophobicity. The length of monomer chain in the repeating unit influences the ratio of rigid amide linkage and thus the properties of the resulting polyamide.
Cellulose nanocrystal (CNC) is considered an excellent candidate to reinforce biobased polyamides while maintaining the materials’ sustainability. CNC was isolated from microcrystalline cellulose by sulphuric acid hydrolysis. CNC was added to PA36,36, PA36,9 and PA4,36 through solution casting and the effects of the filler on the properties of the polyamides were studied. The integration of CNC to PA36,36 increases the tensile strength and Young’s modulus by up to 900%. However, the presence of the CNC in the nanocomposites decreased the thermal stability of the nanocomposites due to its lower thermal degradation temperature compared to that of the polymer matrices.
These biobased polyamides and polyamide/CNC nanocomposites are promising candidates to substitute some petroleum-based thermoplastic elastomers in applications such as anti-corrosion coating, piezoresistive sensors, elastane microfibres, soft robotics, and other engineering applications including automotives, construction and adhesives.
Thesis embargoed until 31 December 2026.
|Date of Award||Dec 2021|
|Sponsors||Indonesia Endowment Fund for Education (Lembaga Pengelola Dana Pendidikan/LPDP) Scholarship|
|Supervisor||Biqiong Chen (Supervisor) & Brian Falzon (Supervisor)|