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and crystallization behavior were essentially unaf ected. h e authors considered these
i ndings as a potential method of increasing the strength and the elongation at break of
typically brittle and weak lipid-based TPUs without altering the other physico-chemi-
cal properties of the polymer.
3.4.2
Biobased Composites Obtained by Using Water as a Solvent
Waterborne polyurethanes based on CO and PEG are considered as novel, potential
biomedical materials for implants and tissue engineering [2, 67-69]. Gao
et al.
[10]
obtained biobased composites using castor oil, containing about 90% ricinoleic acid,
as a tri-hydroxyl functioned monomer [70] and PEG, usually known for its good bio-
compatibility [71], as a low molecular weight diol for the PU synthesis. h e waterborne
PUs were reinforced with cellulose nanocrystals, obtained by sulfuric hydrolysis of
Eucalyptus globulus (ECN). h e crystals had a 'rod-like' shape with average lengths and
diameters of 518.0 ± 183.4 nm and 21.7 ± 13.0 nm, respectively. h e addition of low-
level loadings of cellulose crystals to the thermoplastic PU signii cantly enhanced the
tensile response of the samples: the tensile strength increased from 5.43 to 12.22 MPa
for 1 wt% cellulose while the Young's modulus reached the maximum of 4.83 MPa at a
loading of 4 wt% (neat PU modulus = 1.16 MPa). h e dispersion of cellulose crystals
within the nanocomposite was analyzed by SEM. Figure 3.11 shows the SEM images
of the frozen-fractured surfaces of the nanocomposite i lms (0, 1, 3 and 5 wt% of ECN,
Figure 3.11
SEM images of the ECNs/WPU nanocomposite i lms with dif erent ECNs content: (a) 0 wt%,
(b) 1 wt%, (c) 3 wt%, and (d) 5 wt% (scale bar: 20 μm). Reproduced with permission from [12] .
