Characterization of polyurethane/acrylic hybrids films by SAXS.

P.J. PERUZZO; O.R. PARDINI; J.I. AMALVY

Activity Report/Brazilian Syncrhrotron Light Laboratory

Lugar: Campinas; Año: 2006 vol. 2005 p. 1 - 2

1518-0204

Polyurethane-based coating systems have an established place in the coatings industry due to the high gloss and good weather stability. Developments in urethane chemistry and efforts to reduce emissions increased interest in the development of environmentally-friendly water-borne coatings. The incorporation of acrylic monomers lead to cost reduction and properties are affected depending on the amount and on the way of incorporation. Film-forming properties of physical blends are not satisfactory. The polymerization of acrylic monomers in the presence of preformed polyurethane chains with polymerizable terminal vinyl groups is a useful synthetic method to achieve better film-forming properties. Final products are known as polyurethane-acrylate or acrylic-polyurethane hybrids and should produce binders with better technological properties than physical mixtures. In this work the morphology of hybrids acrylic-polyurethane with different acrylic content on cured (60 ºC for 48 h) and non-cured films were studied using SAXS. The scattering intensity I(q) vs. q for pure PU, acrylic and hybrids films without termal curing show that a phase separation at 70 wt.% of acrylic content occurs. The SAXS spectra of cured and non-cured samples of pure PU show a broad maximum at ca. 0.1 ºA-1 due to the typically semi-crystalline nature of the PU polymers, indicating that the morphology does not change after curing. In the pure acrylics sample, however a di®erent behavior is observed after thermal treatment. Two peaks observed at 0.14 and 0.15 ºA-1 at room temperature are not observed alter curing at 60 ºC. The absence of peaks in the hybrids samples with acrylics ranking from 10 to 70 wt.% indicates a homogeneous morphology. The presence of acrylic component in°uence the crystallization process. Increasing acrylic content, látex particles of pure acrylic polymer are also formed during polymerization, which in turn segregates during film-formation. As expected, thermal curing facilitates the phase separation.