Obtenção e caracterização de nanocompósitos de poliuretano termoplástico reforçado com nanocristais de celulose
Abstract
In this study the potential of cellulose nanocrystals (CNC) as a
reinforcement of a thermoplastic polyurethane partially obtained from renewable
sources (Bio-TPU) was investigated. The nanocomposites were obtained in the
melt state and from solution casting. The CNC were obtained from acid
hydrolysis of eucalyptus kraft pulp. They were freeze dried and used with and
without surface treatment. Two types of surface treatment were employed:
polymer grafting and oligomers grafting. Only the effectiveness of the second
treatment could be confirmed by FTIR. CNC’ structural and geometric
characteristics, crystallinity degree and thermal stability were determined by
infrared spectroscopy (FTIR), transmission electron microscopy (TEM), wide
angle X-ray diffraction (WAXD) and thermogravimetric analysis (TGA),
respectively. The concentrations of CNC were varied between 0.1 and 5.0 wt %.
The rheological properties of the nanocomposites were evaluated in the steady
state and oscillatory measurements in order to evaluate the level of dispersion
CNCs in TPU. The nanocomposites obtained by solution casting showed good
dispersion. In the melt state, only those obtained with treated CNC showed
good dispersion. The deformation and elastic recovery of the nanocomposites
tests in the melt state were evaluated through creep and constrained recoil
rheological essays. Their morphologies were studied by small angle X-ray
scattering (SAXS) and scanning electron microscopy (SEM). It was possible to
prove the inclusion of CNC in TPU did not change its conformation. The
nanocomposites were also characterized according to their: i) mechanical
properties, through tensile tests, ii) thermal properties, by using differential
scanning calorimetry (DSC) and TGA, iii) thermo-mechanical properties,
evaluated by dynamic mechanical thermal analysis (DMTA) and iv) optical
properties, through opacity the nanocomposites with 5.0 wt % of CNC shown
better performance and similar results were found from solution casting and
melt state processing techniques.