30 - Viscoelastic properties of biodegradable polyurethanes derived from coffee grounds

Abstract

Polyurethane (PU) films containing coffee grounds (CG) were prepared from coffee residue. CG mixed with either polyethyleneglycol (PEG having two functional groups, Mw=400) or polypropyleneglycol (PPG having three functional groups, Mw=400), was used as a polyol. PU films, prepared by reacting the mixture of CG polyol and catalyst of dibutyltin dilaurate with diphenylmethane diisocyanate (MDI), were obtained by solution casting. Thermal, mechanical and viscoelastic properties of PU films were measured. The glass transition temperature (Tg) and the tensile strength of PU films increased with increasing CG/polyol ratio. From viscoelastic measurements, a main dispersion peak (α) was clearly observed from 40 to 100 °C in the case of CG-PEG-MDI system and from 50 to 160 °C in the case of CG-PPG-MDI system. The two other small dispersion peaks were observed at about -80°C (β) and -130°C (γ) in the CG-PEG-MDI system and were observed at about -20 °C (β) and -100 °C (γ) in the CG-PPG-MDI system. The dynamic modulus (E') of the CG-PPG-MDI system was higher than that of the CG-PEG-MDI system since PPG, which is a polymer having three functional groups, forms high density crosslinks of PU networks to a greater degree than PEG. The tan δ peaks shifted to the higher temperature side with increasing CG content. From these results it was found that CG powder acted as a hard segment in PU and that viscoelastic properties of PU's were controlled by the amounts of CG and polyol.