Abstract. Natural fibers are widely used as plastic composite material reinforcements. In this work, composites of postconsumer high-density polyethylene (HDPE) reinforced with sisal fibers were prepared. PE and sisal fibers were chemically modified to improve their compatibilities, try to increase the hydrophobic character of the sisal fiber and hydrophilic character HDPE. Sisal was mercerized with a NaOH solution and acetylated and the PE was oxidized with KMnO4 solution. The chemically modified fibers were characterized by Fourier Transformed Infrared Spectroscopy (FTIR) and 13 C Nuclear Magnetic Resonance Spectroscopy ( 13 C NMR). The composites were prepared by extrusion of modified and unmodified materials containing either 5 or 10 wt% fibers. The morphology of the obtained materials was evaluated by SEM. The fiber chemical modification improves it adhesion with matrix, but not benefit were obtained with HDPE oxidation. Flexural and impact tests demonstrated that the composites prepared with modified sisal fibers and unmodified PE present improved mechanical performance compared to pure PE.

Polyethylene terephthalate (PET) is a very stable polymer widely used in the modern world. Due to its stability, this polymer can remain in the environment for several years before its complete degradation. The glycolysis reaction of PET has emerged as a green approach to obtain the PET monomer, thus avoiding such environmental problems and adding value to this waste. In this work, PET waste was depolymerized by glycolysis using ultrasmall cobalt nanoparticles (1.5 wt %) as the catalyst for the production of bis-2-hydroxyethyl terephthalate (BHET). A capping agent (tannic acid, TA) and a borohydride reduction approach were used to obtain such ultrasmall cobalt nanoparticles (∼3 nm). A PET depolymerization yield of 96% was achieved within 3 h at 180 °C. The precipitation of 77% of pure BHET was achieved without the need for water. The remaining ethylene glycol solution containing the ultrasmall cobalt nanoparticle catalyst was reused five times for this glycolysis process, demonstrating the feasibility of solvent reuse without the need for any treatment. A reaction mechanism is proposed in order to explain the high BHET yield obtained by this ultrasmall cobalt nanoparticle catalyst stabilized with TA.

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