New method for graphitizing polyurethane (PU) prepolymers over cellulose fiber surface and physical properties assessment on cementitious composites

Abstract

A new method to graft polyurethane groups on cellulose fiber surface in a propylene carbonate medium, followed by a washing step with methylene chloride is proposed. The synthesis process in propylene carbonate solvent medium is an effective and straightforward way to graft polyurethane prepolymers on cellulose fibers. Reaction was carried out in non-pressurized vessels and low temperature (60 °C). The cleaning step proposed with methylene chorine solvent was effective as no signal of isocyanate group (NCO) was found on Fourier-transform infrared spectroscopy performed on grafted fibers. X-ray photoelectron spectroscopy results from cellulose modified fibers show the presence of nitrogen and a corresponding increase in CC bonds on the cellulose surface, which suggests that polyurethane prepolymer was successfully grafted on fiber surfaces. Secondary ion mass spectrometry images collected from polyurethane grafted fibers indicate that the isocyanate is uniformly distributed on the cellulose modified with PAPI™ 27 Polymeric MDI. Application tests carried out on fiber cement composites showed promising results. PAPI™ 27 Polymeric MDI grafted on the cellulose fibers surface has reduced the water absorption on fiber cement composites by approximately 15 % (p < 0.05) compared to composites prepared with non-modified cellulose fibers. Nevertheless, further exploration on fiber cement composite application is required to understand the impact of the cellulose treatment on the mechanical properties, fiber preservation and overall durability aspects.