Construction of amphiphilic comb-like waterborne polyurethane to balance emulsion stability and film hydrophobicity

For waterborne polyurethane (WPU), the emulsion stability and the water resistance of film is a pair of contradiction. Basing on this, a kind of amphiphilic comb-like waterborne polyurethane (SSPU) was synthesized by molecular structure design. Firstly, hydrophobic N, N-polydimethylsiloxane dihydroxyethyl aminopropionate (SDPSi) and hydrophilic N, N-methoxypolyethylene glycol dihydroxyethyl aminopropionate (SDPG) were synthesized, and then they were grafted on the matrix of polyurethane through chain extending. FTIR and 1H NMR proved that SDPG and SDPSi were successfully introduced into the matrix of polyurethane. AFM and SEM images showed that the phase separation degree of SSPU film increased. EDS showed that the enrichment content of Si element on the surface of SSPU film was 27 %, while the content in longitudinal section was 9 %. When the dosage of SDPG and SDPSi both were 10 wt%, the particle size of SSPU emulsion was reduced to 103.63 nm, while that of unmodified WPU emulsion was 123.85 nm. The comparison proved that the stability of SSPU emulsion was improved. Compared with unmodified WPU film, the water absorption rate of SSPU film decreased by 5.3 %, the water contact angle increased by 11.5°, and the elongation at break increased from 735 % to 861.0 %. These indicated that the water resistance of SSPU film was improved on the premise of ensuring the stability of the emulsion.