Wettability of Cellular Polyurethane CRISTINA M. GOMES, M. HELENA ADA ˜ O, BENILDE J. V. SARAMAGO, and ANABELA C. FERNANDES* Centro de Quı B mica Estrutural, Complexo I, IST, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal SYNOPSIS Cellular polymers constitute an important field of investigation due to their unique properties as shock absorbers and thermal or acoustic insulators. The knowledge of the wetting properties of these materials is important in applications where adhesion or weathering behavior are an issue. In this study, cellular polyurethane polymers were used to investigate the effect of the cellular structure on the wetting properties. The polymeric substrates were analyzed by scanning electron microscopy and the wet- ting properties were studied by goniometry. The contact angles of water and diiodo- methane were measured as a function of time and the surface tension of the expanded polymers was evaluated by the geometric and harmonic mean methods. It was found that the wettability and the surface energy of the cellular polymers increase as the density decreases.  1997 John Wiley & Sons, Inc. Keywords: wettability j cellular polymers j surface tension INTRODUCTION take into account, namely in the adhesion to other materials and in their weathering behavior. The objectives of this study are threefold. Cellular materials, like wood or cork, have been Firstly, to study of the influence of the cellular used for centuries by man. Recently many syn- structure on the wettability of expanded poly- thetic cellular materials have been developed. mers, using polymers of different densities. Sec- Among these are the polymeric foams used in ev- ondly, to study the kinetics of the wetting process. erything from disposable coffee cups to the crash And, finally, to estimate the surface energy of padding of an aircraft cockpit. Their uses as shock polymers that were subjected to different degrees absorbers or thermal insulators exploit the unique of expansion. combination of properties which derive from their cellular structure. 1 The wettability of polymers is a broad subject EXPERIMENTAL which produced an enormous number of scientific papers in the last years. 2–4 However, among the Materials existing studies, and to our knowledge, the re- The cellular polymers used as substrates were ported results on the wettability of cellular mate- three-dimensional foams with closed cells consti- rials refer solely to natural cellular materials 5 tuted by polyurethanes having polyether and po- and we could not find any study relative to the lyesther chains, and were kindly supplied by CPB wettability of synthetic cellular polymers. The na- Sistemas de Poliuretanos, Ltd. ture of the surface of cellular polymers and partic- The cellular structure was obtained by blowing ularly their wettability are important factors to a gas into the reaction mixture during polymer- ization. The foaming agent used was a freon, trichloromonofluoromethane ( CFC11 ) . Using dif- ferent gas pressures it was possible to obtain poly- * To whom correspondence should be addressed. mers with different degrees of expansion and con- Journal of Polymer Science: Part B: Polymer Physics, Vol. 35, 407 – 414 (1997)  1997 John Wiley & Sons, Inc. CCC 0887-6266/97/030407-08 sequently with different densities. The densities 407 9508015 / 8Q20$$0008 07-29-97 18:04:08 polpa W: Poly Physics