Synthesis and characterisation of biobased polyamides and their cellulose nanocomposites

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.<br> <br>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. <br><br>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. <br><br>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.<br><i><br>Thesis embargoed until 31 December 2026</i>.