During the last decades, the increasing ecology in the reduction of environmental impact caused by traditional plastics is contributing to the growth of more sustainable plastics with the aim to reduce the consumption of non-renewable resources for their production

Green composites, with more than 78 wt.% of products obtained from linen linum usitatissimum, were developed in this research work. Epoxidized linseed oil (ELO) was used as bio-based resin, a mix of nadic methyl anhydride (MNA) and maleinized linseed oil (MLO) were used as cross-linkers and finally, flax fabrics were used to obtain composite laminates by resin transfer molding (RTM). The flax fibers were modified using amino-silane, glycidyl-silane and maleic anhydride treatment in order to increase the compatibility between lignocellulosic fibers and the polymeric matrix. Mechanical and thermal properties were studied by flexural, tensile and impact test, as well as dynamic mechanical analyses (DMA) to study the viscoelastic behavior. Contrary to what could be expected, when fibers are previously treated in presence of MLO, a reduction of anchorage points is obtained causing a substantial increase in the ductile properties compared with composites without previous fiber treatment or without MLO.

Hydroxyapatite (HA) and Halloysite nanotubes (HNTs) percentages have been optimized in Polycaprolactone (PCL) polymeric matrices to improve mechanical, thermal and biological properties of the composites, thus, to be applied in bone tissue engineering or as fixation plates. Addition of HA guarantees a proper compatibility with human bone due to its osteoconductive and osteoinductive properties, facilitating bone regeneration in tissue engineering applications. Addition of HNTs ensures the presence of tubular structures for subsequent drug loading in their lumen, of molecules such as curcumin, acting as controlled drug delivery systems. The addition of 20% of HA and different amounts of HNTs leads to a substantial improvement in mechanical properties with values of flexural strength up to 40% over raw PCL, with an increase in degradation temperature. DMA analyses showed stability in mechanical and thermal properties, having as a result a potential composite to be used as tissue engineering scaffold or resorbable fixation plate.

This work investigates the feasibility of using coffee silverskin (CSS) as a reinforcing agent in biobased polyethylene (BioPE) composites, by adding it in bulk and thin film samples. The effect of two different treatments, alkali bleaching (CSS_A) and esterification with palmitoyl chloride (CSS_P), on mechanical, thermal, morphological and water absorption behavior of produced materials at different CSS loading (10, 20 and 30 wt %) was investigated. A reactive graft copolymerization of BioPE with maleic anhydride was considered in the case of alkali treated CSS. It was found that, when introduced in bulk samples, improvement in the elastic modulus and a reduction in strain at maximum stress were observed with the increase in CSS fraction for the untreated and treated CSS composites, while the low aspect ratio of the CSS particles and their poor adhesion with the polymeric matrix were responsible for reduced ductility in films, decreasing crystallinity values and reduction of elastic moduli. When CSS_A and CSS_P are introduced in the matrix, a substantial reduction in the water uptake is also obtained in films, mainly due to presence of maleated PE, that builds up some interactions to eliminate the amounts of OH groups and hydrophobized CSS, due to the weakened absorption capacity of the functionalized CSS.

In this study, hemp seed oil was reacted with maleic anhydride in an ene reaction to obtain maleinized hemp seed oil (MHO). The use of MHO as a plasticizer and compatibilizer has been studied for polylactic acid (PLA) and thermoplastic starch (TPS) blends (80/20, respectively). By mechanical, thermal and morphological characterizations, the addition of MHO provides a dual effect, acting as plasticizer and compatibilizer between these two partially miscible biopolymers. The addition of MHO up to 7.5 phr (parts by weight of MHO per hundred parts of PLA and TPS) revealed a noticeable increase in the ductile properties, reaching an elongation at break 155% higher than the PLA/TPS blend. Furthermore, contrary to what has been observed with maleinized oils such as linseed oil, the thermal properties do not decrease significantly as a result of the plasticizing effect, due to the compatibilizing behavior of the MHO and the natural antioxidants present in the oil. Finally, a disintegration test was carried out in aerobic conditions at 58 °C, for 24 days, to demonstrate that the incorporation of the MHO, although causing a slight delay, does not impair the biodegradability of the blend, obtaining total degradation in 24 days.