polymers Article Contribution to a Circular Economy Model: From Lignocellulosic Wastes from the Extraction of Vegetable Oils to the Development of a New Composite Ivan Dominguez-Candela 1 , Daniel Garcia-Garcia 2 , Aina Perez-Nakai 2 , Alejandro Lerma-Canto 2 , Jaime Lora 1 and Vicent Fombuena 2, *   Citation: Dominguez-Candela, I.; Garcia-Garcia, D.; Perez-Nakai, A.; Lerma-Canto, A.; Lora, J.; Fombuena, V. Contribution to a Circular Economy Model: From Lignocellulosic Wastes from the Extraction of Vegetable Oils to the Development of a New Composite. Polymers 2021, 13, 2269. https:// doi.org/10.3390/polym13142269 Academic Editor: Le Quan Ngoc Tran Received: 4 June 2021 Accepted: 6 July 2021 Published: 10 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Instituto de Seguridad Industrial, Radiofísica y Medioambiental (ISIRYM), Universitat Politècnica de València (UPV), Plaza Ferrándiz y Carbonell 1, 03801 Alcoy, Spain; ivdocan@doctor.upv.es (I.D.-C.); jlora@iqn.upv.es (J.L.) 2 Technological Institute of Materials (ITM), Universitat Politècnica de València (UPV), Plaza Ferrándiz y Carbonell 1, 03801 Alcoy, Spain; dagarga4@epsa.upv.es (D.G.-G.); aipena@epsa.upv.es (A.P.-N.); allercan@epsa.upv.es (A.L.-C.) * Correspondence: vifombor@upv.es Abstract: The present works focuses on the development of a novel fully bio-based composite using a bio-based high-density polyethylene (Bio-HDPE) obtained from sugar cane as matrix and a by-product of extraction of chia seed oil (CO) as filler, with the objective of achieving a circular economy model. The research aims to revalorize an ever-increasing waste stream produced by the growing interest in vegetable oils. From the technical point of view, the chia seed flour (CSF) was chemically modified using a silane treatment. This treatment provides a better interfacial adhesion as was evidenced by the mechanical and thermal properties as well as field emission scanning electron microscopy (FESEM). The effect of silane treatment on water uptake and disintegration rate was also studied. On the other hand, in a second stage, an optimization of the percentage of treated CSF used as filler was carried out by a complete series of mechanical, thermal, morphological, colour, water absorption and disintegration tests with the aim to evaluate the new composite developed using chia by-products. It is noteworthy as the disintegration rate increased with the addition of CSF filler, which leads to obtain a partially biodegradable wood plastic composite (WPC) and therefore, becoming more environmentally friendly. Keywords: chia seed flour; wood plastic composite; silane treatment; bio-polyethylene; circular economy 1. Introduction A global polymer production of 368 million tons was recorded in 2019. In Europe 58 million tons were produced and almost 25% of plastic post-consumer wastes is directly deposited in landfills [1]. The majority of conventional polymers are manufactured from fossil resources and are non-biodegradable. The most used polymers are polypropylene (PP), high- and low-density polyethylene (HDPE and LDPE) and polyvinylchloride (PVC), which represent some 60% of the plastics used [1,2]. Due to the mismanagement of these plastic products, most of which are single-use products, they can end up in landfills, oceans or other terrestrial ecosystems where they can affect wildlife and probably human health [3]. The use of biopolymers could be an excellent proposal for the plastics industry in order to overcome these drawbacks. In recent years, biopolymers are gaining importance as a sustainable alternative to conventional polymers. They provide a 65% energy savings as well as between 30% and 80% less greenhouses gases emissions during their production compared to conventional polymers [4]. A biopolymer material is defined as a polymer that either is biodegrad- able, bio-based or has both properties [5]. This definition provides for three different Polymers 2021, 13, 2269. https://doi.org/10.3390/polym13142269 https://www.mdpi.com/journal/polymers