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ORIGINAL PAPER

Development of Polypropylene Composites with Green Coffee Cake Fibers Subjected to Water Vapor Explosion Elisa Barbosa de Brito1 · Lucas Galhardo Pimenta Tienne1 · Suellem Barbosa Cordeiro1 · Maria de Fátima Vieira Marques1 Received: 18 July 2019 / Accepted: 30 December 2019 © Springer Nature B.V. 2020

Abstract  As a result of the demand to develop materials with improved properties having less impact to the environment, new techniques for obtaining cellulose have been developed. This material used as fillers in a polymer matrix reveals great potential to reinforce polymers and develop new composites. Besides, the utilization of lignocellulosic biomass from a huge amount of industrial waste associated with coffee production has been the object of this study. In the present work, the influence of the steam explosion treatment of fibers from green coffee cake (GCC) was evaluated in a system submitted to 2 bar, 180 ºC and 10 min explosion cycles. After this process, analysis of the materials collected from each explosion cycle revealed important aspects for the subsequent processing of the cellulose fibers with a commercial polypropylene. Composites were obtained by extrusion in the proportion of 2% and 5% m/m of fiber in the polymer matrix, comparing the screw speed of 60 rpm and 120 rpm. It was observed that the treated fiber by steam explosion caused an increase in the thermal stability of the composite material, shifting the degradation temperature to higher values, as in the case of sample containing 5% fiber and processed at 120 rpm, in which that temperature is 38 ºC higher than the reference polypropylene without fiber. The composite prepared using 2% m/m of filler processed at 60 rpm increased the storage modulus by more than 40%. Graphic Abstract

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Waste and Biomass Valorization

Keywords  Residues · Valorization · Coffee industry · Cellulose · Steam explosion · Polymer composites

Statement of Novelty The residues and by-products of the coffee industry are a source of severe contamination and represent serious environmental problems, especially in Brazil, the world’s largest producer and exporter. The valorization of coffee co-products converting the biomass in useful new materials that can add value to the coffee production chain needs more study. Thus, the present research brings as innovations in relation to the state of the art, the use of the green coffee cake, a solid residue obtained through the removal of the oil from the green grains by means of cold pressing, as a source of cellulose to reinforce a thermoplastic, which could be used as packaging for the coffee beans. In addition, the separation of the microfibrillated cellulose from this residue by the process of steam explosion in the absence of chemical substances allows a low energy expenditure, resulting in low environmental impact. The steam explosion process (water under pressure, followed by a sudden decompression) is a treatment