Steam-exploded fibers of almond tree leaves as reinforcement of novel recycled polypropylene composites
Cinthya H. S. Souza Rosa, Michelle Gonçalves Mothé, Maria F. Vieira Marques, Cheila Gonçalves Mothé, Sérgio Neves Monteiro
Abstract
Fibers obtained from fallen leaves of the almond tree (Terminalia catappa L.) were incorporated into sustainable composites with recycled polypropylene (PPr) as a matrix. The fibers were used in two conditions: (i) as-collected from fallen leaves and (ii) after treatment by the steam explosion process. PPr composites with concentrations of 1, 5, 10, and 15 wt.% of raw or treated fibers. Thermogravimetric analysis showed that the addition of 1 wt.% of treated fibers of almond tree leaves increased the thermal stability of the PPr. Moreover, the composite residue at 700 °C decreased due to the lower content of lignin in the fiber. X-ray diffraction disclosed that the treated fiber had increased crystallinity, and the composites with 1 and 5 wt.% of theses fibers acted as β-nucleating agent, promoting its preferential growth on the (041) crystal face in α-PP. Tensile tests revealed that PPr composite with 1 wt.% of team-exploded, although less ductile, display superior tensile strength and elastic modulus, which characterizes a reinforcement effect. Scanning electron microscopy confirmed the less ductility of fibers treated composites. Moreover, voids in the fiber/matrix interface were attributed to fibers agglomeration for higher contents in the composite. It was concluded that the best obtained results for the reinforcement of 1 wt.% of fiber treated by steam explosion indicated a promising all recycled novel PPr composite.