Modulation of interchain hydrogen bonding and its impact on the mechanical and crystalline properties of polyamide fibers

Hydrogen bonding is crucial to the processing and properties of polymer materials, and copolymerization provides effective regulation of interchain hydrogen bonding in macromolecules. However, the relationship between intrachain hydrogen bonding, the parity and length of the monomer carbon chains, and the mechanical properties of copolyamides remain insufficiently explored. Polyamide fiber membranes with excellent mechanical properties were prepared by finely tuning the chain length and parity number of the monomers achieved, by using electrospinning processing of polyamide 6, polyamide 12, polyamide 11, copolyamide 6/66 (CoPA 6/66), copolyamide 6/11 (CoPA 6/11), and copolyamide 6/12 (CoPA 6/12). In particular, CoPA 6/11 has a longer carbon chain and an odd-numbered structure, which results in a lower enthalpy of hydrogen bond breaking (enthalpy of fracture, 41.65 kJ/mol) compared with CoPA 6/66 (86.46 kJ/mol) and CoPA 6/12 (66.26 kJ/mol). This makes CoPA 6/11 more susceptible than other materials to interchain hydrogen bond rearrangements during high-speed rotation in the collector in electrospinning processing. Differential scanning calorimetry also corroborated that CoPA 6/11 molecular chains are more prone to shifting from the γ-crystal to the α-crystal form in response to external forces. As a result, CoPA 6/11 showed the greatest increase in tensile strength (51%, 8.47–17.4 MPa) after high-speed rotation. This study presents an easy method for producing high-strength fibers by controlling the rotation speed to modulate hydrogen bonding between polyamide chains. The approach provides a promising pathway for manufacturing high-strength polyamide fibers for applications in the textile industry, the automotive industry, and other fields.