Rheological Properties of Waterborne Polyurethane Paints

The rheological properties of two specific waterborne polyurethane （PU） paints were studied by both macrorheological and microrheological methods. During the macrorheological measurement on a rotary rheometer, evaporation of solvent cannot be totally excluded, which has an influence on the reliability of rheological results. So, the linear oscillatory frequency sweep results （storage and loss modulus versus frequency） and steady shear results （viscosity versus shear rate） got from the rotary rheometer measurement are only used for qualitative analysis. As the evaporation of solvent can be neglected during microrheological measurements on a diffusing wave spectroscope （DWS）, the results of storage modulus （G3 and loss modulus （G＇~） versus frequency are more credible than the results obtained from the rotary rheometer measurement. Thus, the results of G＇ and G＂ versus frequency from DWS measurements are used for quantitative analysis in this work. The G＇ for both of the waterborne PU paints are larger than G＂ at low frequency and that is opposite at high frequency in the experimental angular frequency range. The values of modulus at same frequency and viscosity at low shear rate for the two PU paints have apparent difference, which determines the difference of their application.

4D printing of polyurethane paint-based composites

In recent studies,polyurethane has shown multiple properties that make it an excellent candidate material in 4D printing.In this study,we present a simple and inexpensive additive method to print waterborne polyurethane paint-based composites by adding carboxymethyl cellulose(CMC)and silicon oxide(SiO2)nanoparticles to the paint.The first function of CMC and SiO_(2) is to improve rheological properties of the polyurethane paint for making a printable precursor,which improves the printing resolution and enhances additive manufacturability.Second,the composite precursors improve the curing rate of the polyurethane paint without changing its inherited shape memory properties.Third,the printed composite parts shown enhanced mechanical strength compared with that of the parts printed with pure polyurethane.Finally,the 3D printedpolyurethane-CMCandSiO_(2) parts exhibit time-resolved shape transformation upon heat stimulation.To the best of our knowledge,this is the first study of using the polyurethane paint as the precursor for 4D printing,which would open new possibilities in future applications in biomedical engineering,soft robotics and so on.