Nanocomposites made from cellulose nanocrystals and tailored segmented polyurethane

M. L. AUAD; M. A. MOSIEWICKI; T. RICHARDSON; M. I. ARANGUEN; N. E. MARCOVICH

JOURNAL OF APPLIED POLYMER SCIENCE

Wiley

Lugar: New York; Año: 2010 vol. 115 p. 1215 - 1225

0021-8995

Linear segmented polyurethanes (SPUs) with potential shape memory effect were synthesized with 4,4-methylene-bis-phenyldiisocyanate (MDI) and poly(tetramethyleneglycol) (PTMG) with 1-4 butanediol (BD) as chain extender. These are two-phase materials containing soft and hard domains. The effect of the length of the polymer chains belonging to the soft domains was evaluated by preparing polyurethanes from PTMG with molecular weights of 650 and 2000 g/mol. Sets of polyurethanes (PU), with equal soft segment (SS) length (PTMG molecular weight 2000 g/mol), were prepared using a variable MDI/BD-based hard segment (HS) content ranging from 23 to 40 wt%. The effects of the hard segment content on the thermal and mechanical properties were investigated. In order to increase the stiffness of these polymers and still retain the shape memory behavior, the SPUs were reinforced with small amounts of nano size cellulose crystals. Thermo-mechanical and mechanical tests were performed on composite films prepared by casting. The results showed that the hard segments melting temperature was in the range of 172-186 °C and soft segment temperature in the range of 5-8 °C. As the HS content increases, the temperature and heat, involved in the high-temperature melting transition, increase. The polyurethane prepared with short soft segments (PTMG molecular weight 650 gr/mol) shows reduced crystallization. The tensile modulus and yield stress increase with higher amounts of HS while the deformation at break decreases. With increasing cellulose content, dynamic storage and tensile modulus as well as melting temperatures and melting heats of the soft domains increased. The incorporation of cellulose during or after the synthesis of the polyurethanes leads to important differences in the thermal and mechanical properties of the nanocomposite films. The shape memory behavior varies with the formulation, so that the fixity increases with the content of HS and also with the incorporation of cellulose.