*2.1. Materials*

The piassava fibers used in this work were obtained as an industrial waste from a broom factory in the city of Campos dos Goytacazes, Brazil. After they were received, the fibers were washed in running water to eliminate any contaminant and put to dry in a stove for 24 h at 60 ◦C. For use as reinforcement material in HPCFs the piassava fibers were processed in a knife mill until the ground powder material passed through a 16-mesh sieve in accordance with the NBR 14050 standard [10]. Prior to the ground processing, however, a group of fibers was separated and went through preliminary characterization.

The polymeric matrix used in this study was the castor oil-based polyurethane (COPU) produced and commercially supplied by Imperveg, Brazil (Commercial tag AGT 1315). The COPU consisted of a bi-component. Both components—"A" (polyol) derived from castor oil and "B" (isocyanate)—were obtained as liquid. When the initiator (B) was added in A with 55% mass fraction, the polymerization process occurred and the resin hardened.
