Polyurethane reinforced with nano/micro sized cellulose fibers

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

Buenos Aires, Argentina

Conferencia; Internacional Conference on Science and Technology, COMAT 2005; 2005

This work makes use of shape memory polymers (SMPs), which in this case consist of segmented thermoplastic polyurethanes formed from soft amorphous segments and hard crystalline segments. The hard segments were generated using 1,4-butanediol (BD) and 4,4'-methylenebis (phenyl isocyanate) (MDI) and the soft segments were prepared from poly(oxytetramethylene glycol) (PTMG). The whole synthesis was carried out in two steps. Polymers with different ratios of hard segment content (HSC) to soft segment content (SSC) were synthesized. The reaction was checked by Fourier Transform infrared (FTIR) spectroscopy in order to determine the final conversion. and differential scanning calorimetry (DSC) was performed to determine the range of transition/melting temperatures. Native cellulose is an abundant and inexpensive macromolecular compound that reinforces most plant cell walls. The cellulose whiskers have polar groups that can interact with polar polyurethanes, leading to a composite material with good interfacial adhesion. This is essential to obtain a material with enhanced properties. Furthermore, the cellulose -OH groups can react with the PU, leading to strong interfacial adhesion, thereby improving the load transfer from the polymer matrix to the high modulus crystals. In this work, mostly defect-free cellulose crystals were produced from commercial microcrystalline cellulose by acid hydrolysis. The nano/micro crystals were characterized by AFM to determine defect content and morphology. The cellulose crystallinity was determined by x-ray diffraction. Composites from SMPU and cellulose were prepared in two different ways: in the first approach, the DMF cellulose suspension was mixed with the MDI/PTMG mixture in order to favor the reaction between filler and polymer. In the second approach, the SMP was fist synthesized, then dissolved in DMF and mixed with the cellulose suspension. Measurements of the dynamic mechanical response of the materials in a temperature scan were used to identify variations produced by the addition of the nano/micro filler in the transition/melting of soft and hard segments. The mechanical performance of SMPU and composites was studied by tensile and strain recovery tests.