Interplay of polyurethane mechanical properties and practical adhesion of flexible multi-layer laminates

Abstract

ABSTRACT Polyurethane (PU) adhesives are widely applied on flexible multilayer laminates (FML) for food packaging. However, studies regarding the interplay of polyurethane mechanical properties and FML peeling resistance are still scarce in the literature. In this context, we investigated the mechanical properties of a commercial PU adhesive obtained under three different NCO:OH ratios (0.8, 1.0 and 1.2) and their connection to FML peeling resistance. First, the curing kinetic was characterized by temperature modulated optical refractometry (TMOR) and Fourier transform infrared spectroscopy (FTIR-ATR). Additionally, PU mechanical properties were measured by uniaxial tensile tests. Using TMOR and FTIR-ATR we identified effects of PU structural changes on curing kinetics, as a consequence of high NCO:OH ratio. Mechanical properties of PU adhesives were strongly affected by changes of NCO:OH ratio. A comparison between our current results with recently published works shed some light on the interplay between PU mechanical properties and FML peeling resistance. Results showed that higher PU mechanical properties provided higher peeling resistance for FML with pristine Al layers. In contrast, higher PU mechanical properties resulted in poor FML peeling resistance, for aged Al layers.