學 生：符昌中 指導老師：王振乾 老師

1. 學生：符昌中 指導老師：王振乾 老師

2. Introduction • Waterborne polyurethanes (WPUs) have excellent mechanical properties and are environment-friendly. • WPU resins have poor resistance against water and chemicals compared with the crosslinked two-pack solvent-based urethanes. • A separate polymer could be incorporated to polyurethane to form a multiphase structure in the dispersions through various techniques such as blending, seeded emulsion polymerization.

3. Introduction • Using epoxy resin to modify WPU can combine the advantages of both of these materials and results in improved film performance. • Epoxy resin and a blocked NCO prepolymer were mixed to avoid the high viscosity of precrosslinked poly-urethane and the difficulty of emulsification. • In this work, we explored a novel postcrosslinking method to form crosslinked polyurethane–epoxy hybrid emulsion.

4. Materials • 2,4-Toluene diisocyanate (TDI, 80/20) • Polyether diol (PED) with a molecular weight of 1000 Da(N210) • Dimethylol propionic acid (DMPA) • Epikote 1001 (hereinaftercalled type 1 epoxy)

5. Materials • 1,4-Butanediol • Diethylene triamine • Acetone • 1-methyl-2-pyrrolidone(NMP) • Isopropanol • Triethylamine (TEA)

6. Unmodified polyurethane dispersion Blocking agent Isopropanol 70 ℃ 3 h TDI, PED, 1,4-butanediol,and DMPA/NMP 40 ℃ Triethylamine Neutralizing Ethylene diamine Chain extension The unmodified aqueous polyurethane dispersion was thus obtained.

7. Epoxy resin-modified polyurethane dispersion Precrossinking Type 1 epoxy /NMP 60-70 ℃ 2-3 h TDI, PED,1,4-butanediol, and DMPA /NMP 70 ℃ 3 h Isopropanol Triethylamine Neutralizing Blocking agent Primary diamines Chain extension An aqueous dispersion of polyurethane ionomer was thus obtained.

8. Epoxy resin-modified polyurethane dispersion Postcrossinking Isopropanol Blocking agent TDI, PED,1,4-butanediol, and DMPA /NMP 70 ℃ 3 h 30 ℃ Type 1 epoxy /NMP Triethylamine Neutralizing 80 ℃ 2 h Diethylene triamine Chain extension The crosslinked polyurethane–epoxy hybrid emulsion was thus obtained.

9. Results and discussion Fig. 2: IR spectra of emulsion before chain extension by amine N–H stretching of polyurethane was shifted to 3294 cm-1. The band at 1745 cm-1 was C=O stretching of the urethane group. The band at 1223–1267 cm-1 corresponded to the stretching vibrations of C=O combined with NH. The bands at 1533–1539 cm-1 correspond to carbamate. The absorption peaks of epoxy group and free isocyanate group at 917 and 2277 cm-1vanished after chain extension in, which indicated that a chain extender reaction occured between the isocyanate group, epoxide groups, and amine chain extender. Fig. 3: IR spectra of emulsion after chain extension by amine

10. Results and discussion Fig. 4,5: DSC thermogram of PUPE1,2(before chain-extension) There were two endothermic peaks at about 100 and 150 ℃, which represented the epoxide group curing and the deblocking of isocyanate, respectively.

11. Results and discussion Fig. 6: DSC thermogram of PUPE3(after chain extension) Fig. 8: DSC thermogram of PUPE4 cured at 180℃ for 2 h Fig. 7: DSC thermogram of PUPE4(after chain extension)

12. Results and discussion Fig. 9: TEM images of (a) polyurethane emulsion, (b)emulsion prepared with precrosslinking, and (c) emulsion prepared with postcrosslinking

13. Results and discussion Since the crosslinking density of the films increased with an increase in epoxy content, the ratio of the rigid segment in resin was enhanced.

14. Results and discussion

15. Conclusions • The postcrosslinking method could improve the film performance and the emulsion stability, and did not result in increased viscosity of the prepolymer before phase inversion because the epoxy resin did not react with prepolymer. • The type of amine chain extender significantly affected the stability of emulsion. • The molar ratio of NH/NCO at 1:1 showed the best film performance, and the optimal reaction temperature of amine extending chain was around 80℃.