INVESTIGADORES
MARCOVICH norma Esther
congresos y reuniones científicas
Título:
Thermomechanical behavior of nano-cellulose reinforced shape memory polyurethanes
Autor/es:
N. E. MARCOVICH; V. S. CONTOS; S. NUTT; M. L. AUAD; M. I. ARANGUREN
Lugar:
Buenos Aires, Argentina
Reunión:
Congreso; XXII Interamerican Congress of chemical Engineering - V Argentinian Congress of Chemical Engineering; 2006
Resumen:
Shape memory polymers (SMPs) possess the ability to store and recover large strains by the application of a prearranged thermomechanical cycle, thus, they are capable of fixing a transient shape and recovering to their original shape. On the other hand, A main drawback of SMPs is the relatively weak recovery force compared to shape memory allows, thus, in some applications, SMPs may not generate enough recovery force to be viable. The aim of this work is to enhance the performance of SMPs by reinforcing shape memory polyurethanes with nano-cellulose fibers. Incorporation of nano reinforcements into SMPs is expected to yield performance enhancements (such as elastic modulus) at small nanoparticle loadings (~1-5 wt%), producing stiffer yet deformable composites with deformation capacity comparable to that of unfilled polymers. A commercial, high performance polyester thermoplastic polyurethane (PU) was selected as the matrix. Nano cellulose crystals were produced from commercial microcrystalline cellulose by acid hydrolysis. The reinforcement was dispersed in dimethylformamide (DMF) by ultrasonication and subsequently incorporated in a DMF-PU solution. Films of reinforced PUs (about 0.5 mm in thickness), comtaining 0, 0.1, 0.5 and 1wt% fibers were obtained by casting the mixture on an open mold and drying it in a convection oven at 80 ºC for 24 hours. To characterize the resulting composites, thermal tensile cyclic tests and creep measurements were carried out. From the thermal cycling tests it was observed that the recovery ratio decreases as the number of cycles increases, while the fixity increases (or remain mostly unaffected) for both, composites and neat PU. The cellulose composites display essentially the same shape memory properties as those corresponding to the neat polyurethane, without important variations in the range of cellulose crystals content studied. Creep results showed that the deformation decreases as cellulose concentration increases, even with the small amount of fibers used in this work to prepare the composites. If filler wetting and dispersion are efficiently accomplished the expected effect of the cellulose addition is stiffening of the composite, since the reinforcement is more rigid than the polymeric matrix. For example, the deformation at 60 minutes decreases from 1.74% for the neat matrix to 1.19% for the sample with 0.5%wt. cellulose. Further cellulose addition causes only a marginal decrease (1.13% deformation for 1%wt cellulose).