Preparation And Properties Of Waterborne Polyurethane With Low Water Absorption Ratio

As an environmentally friendly finishing material, waterborne polyurethane (WPU) have increasingly won people’s favor, while its poor water resistance made it difficult to satisfy the requirements in some operation environment. In order to expand its scope of applications, researches of improving its water resistance had paid more attention gradually.In the first section of this thesisa series of stable SiPU emulsions with polydimethylsiloxane (PDMS) side chains would were made using the twice-self-emulsifying method and by the reaction between amino groups in aminoethylaminopropyl polydimethylsiloxane (AEAPS) and-NCO in PU prepolymer. The effect of AEAPS content in SiPU on properties of the emulsion and the film were investigated. DSC analysis results showed that the introduction of AEAPS made the WPU form the cross-linked structure, nevertheless the micro-phase structure of WPU was damaged. With an increase of AEAPS content, the tensile strength firstly increased and then decreased, while the elongation at break changed more complicated; the water absorption ratio first decreased and then increased. When AEAPS content reached to8wt%, the water absorption ratio reached4.2%of the minimum value.Acrylic-modified WPU is another important WPU modification technology. In the second section of this thesis, a series acrylic-polyurethane (PUA) composite emulsion were obtained by radical polymerization between acrylic monomer and PU prepolymer on which partly introduced double bonds. By observing the deposit generated in the process of polymerization and investigating the water absorption ratio and tensile properties of PUA films, we found that when PU/PA(wt)=50:50, NCO/OH=1.7, DMPA (wt)=6%, HEMA (wt)=6%, MMA/BA(wt)=60:40, and initiator dosage was up to1%of the total mass of acrylic monomer, the PUA emulsion has better stability and the films has lower water absorption ratio than the unmodified WPU.PUA emulsion has good film-forming properties, but its water resistance remains to be further improved. In the third section of this thesis, PUA was modified with AEAPS to form SiPUA emulsion. Fixed other chemical components, effect of AEAPS content on SiPUA performance was studied. The results showed that with the AEAPS content increasing, the water contact angle increased, while the tensile strength and water absorption decreased. When AEAPS content in SiPUA reached to6wt%, SiPUA emulsion has good stability and water absorption of film down to3.8%. At the same time, SiPUA film has the best thermal stability compared with PU, SiPU and PUA.