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This article presents the results of the synthesis and characterization of environmentally friendly polyurethanes based on renewable polyols, and specially highlights the use of Eucalyptus tar pitch, a byproduct of the charcoal making industry in Brazil, to obtain PUs. Eucalyptus tar pitch and castor oil PUs synthesized with MDI in THF, catalyzed by dibutyltin dilaurate, were prepared with NCO/OH equal to 1, and vacuum cured. The addition of Eucalyptus tar pitch to the formulation of PUs showed a tendency to increase the formation of rigid segments, and consequently, to modify thermal stability. SEM micrographs confirm this behavior, displaying different materials. Homogeneous polyurethane elastomers become rigid and acquire lamella structure with the addition of biopitch, as confirmed by tensile strength assays.

Polymeric materials are being developed with renewable resources to promote industrial progress with environmentally friendly technologies. For this reason, polyurethane samples were prepared with 4,4Ј-diphenylmethane diisocyanate (NCO/OH ϭ 1), eucalyptus tar pitch (biopitch), castor oil as a polyol, and dibutyltin dilaurate as a catalyst. These materials were reinforced with different contents of short sisal fibers (0, 2.5, 5.0, 7.5, and 10.0%) and were prepared by resin-transfer molding. The composites were characterized by IR absorption spectroscopy, thermal analysis (thermogravimetry and differential scanning calorimetry), impact resistance, scanning electron microscopy, and water absorption resistance. These materials showed hydrophobic characteristics, despite the addition of sisal fibers.

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New eco-composites were prepared from castor oil polyurethane reinforced with Luffa cylindrica fibres. These fibres were used without treatment as well as after mercerisation and mercerisation/benzylation surface treatments. TG curves of mercerised Luffa showed a small increase in thermal stability, associated with the removal of polyoses and soluble lignin. TG curves of benzylated fibres showed a decrease in thermal stability (Tonset and Tmax.) and an increase in residual carbon due to aromatic ring insertion. FTIR spectra and elemental analysis also confirmed benzylation, and X-ray diffractograms showed a decrease in cellulose crystallinity. The eco-composite (crude fibre) absorbed more water (14% after 4 – weeks' exposure) than the resin, because of the hydrophilic character of natural fibres, but mercerisation and benzylation reduced this value by about 50%. Tensile moduli of composites reinforced with untreated and mercerised fibres were comparable, but increased by 33% with the use of mercerised/benzylated Luffa cylindrica. SEMs of the fibres and fibres-matrix interfaces are presented.

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