Nano Cellulose Fibers as Reinforcement for Shape Memory Polyurethanes

N. E. MARCOVICH; V. S. CONTOS; S. NUTT; M. I. ARANGUREN; M. L. AUAD

Ischia, italia

Congreso; III International Conference on Times of Polymers (TOP) and Composites; 2006

The objective of this work is to study the effects of hard-segment content, soft-segment molecular weight and cellulose nanofibers concentration on the thermal and mechanical properties of shape memory polymers (SMP). The SMP selected for this work was a thermoplastic polyurethane (TPU) prepared from 4,4-diphenylmethane diisocyante (MDI), 1,4-butanediol (BD) and poly(ethylene glycol) (PEG). Three sets of TPUs were synthesized containing a constant soft-segment molecular weight of 2000 and a variable MDI/BD-based hard-segment content ranging 23-45 wt%. Another TPU, based in a soft-segment molecular weight of 650, with a hard-segment content of 48% was also synthesized. X-ray measurements revealed that the crystallinity of the TPU decreases as the hard segment content increases however it increases as the soft-segment molecular weight decreases. Thermal cyclic tensile tests indicated that the shape fixity capacity increases and the shape recovery ability decreases with hard segment concentration, but the opposite trend was found as the soft-segment molecular weight decreases. Reinforced polyurethanes were obtaining by adding very low amounts of cellulose nanofibers during the first step of the polymer synthesis, thus TPUs reinforced with 0.1wt%, 0.5wt% and 1wt% of cellulose were obtained. DSC and DMA measurements show that hard-segment crystalline melting temperature was in the range of 175-200 ºC and soft-segment melting temperature was in the range of 10-25 ºC and both increased with increasing cellulose content. Moreover, tensile and dynamic storage modulus increased with cellulose concentration. Although the tensile ultimate deformation decreases as fiber concentration increases, the shape memory behavior is still observed in the composites.