Surface free energy of polyurethane coatings with improved hydrophobicity

Piotr Król,Bożena Król

doi:10.1007/s00396-012-2598-x

Abstract

The polarity of polyurethane coats was studied on the basis of the goniometric method for determination of wetting angle values, on the basis of calculated surface free energy (SFE) values by the van Oss–Good and Owens–Wendt methods, and on the basis of polarity measurements with the use of the 1H NMR spectra. Test polyurethanes were synthesised in the reaction of methylene diphenyl 4,4′-diisocyanate (MDI) or 3-izocyanatomethyl –3,5,5- trimethylcyclohexyl isocyanate (IPDI) and polyoxyethylene glycols or polyesters poly(ε-caprolactone) diols and poly(ethyleneadipate) diol with different molecular weights, and some diols as chain extenders, in dioxane. The type of raw material was found to significantly affect the phase structure of the obtained polyurethane elastomers and to control physical interactions within those structures, thus influencing the SFE values. Fundamental reduction in the SFE value of a coating below 28 mJ/m2 was achieved by the use of 2,2,3,3-tetrafluoro-1,4-butanediol as the urethane prepolymer chain extender.

Highlights

The polarity of polyurethane coats was studied on the basis of the goniometric method for determination of wetting angle values, on the basis of calculated surface free energy (SFE) values by the van Oss–Good and Owens– Wendt methods, and on the basis of polarity measurements with the use of the 1H NMR spectra
We refer to our previous papers in which we presented the possibility of modifying the SFE values in polyurethane ionomer coats [13–15]
We were prompted to undertake that kind of research inter alia by the findings presented in our earlier report [16]: the investigation with the use of wide angle X-ray scattering (WAXS) and AFM methods demonstrated that polyurethane coatings performed like elastomers and they contained up to 30% of crystalline phases which formed clearly separated rigid domains against the background of the amorphous phase

Summary

Introduction

The polarity of polyurethane coats was studied on the basis of the goniometric method for determination of wetting angle values, on the basis of calculated surface free energy (SFE) values by the van Oss–Good and Owens– Wendt methods, and on the basis of polarity measurements with the use of the 1H NMR spectra. The chemical performance of polyurethanes was already demonstrated in earlier reports to be controlled by chain structures of polyurethanes, and in particular, by polar interactions and hydrogen bonds between their soft and hard segments [1, 2]. We were prompted to undertake that kind of research inter alia by the findings presented in our earlier report [16]: the investigation with the use of wide angle X-ray scattering (WAXS) and AFM methods demonstrated that polyurethane coatings performed like elastomers and they contained up to 30% of crystalline phases which formed clearly separated rigid domains against the background of the amorphous phase. In order to authenticate the calculations which involved numerous results collected (contact angle values) and to identify the physical interactions within the polyurethane chain structures, we calculated SFE data with the use of two complementary methods: by van Oss– Good and by Owens–Wendt

Objectives

Results

Conclusion