## 1 Introduction
In fact, the next generation of packaging materials should fulfil the requirements to support the transition to a circular economy, which comprise a ban on single-use traditional plastics by the end of 2020 [20,21]. Moreover, from an environmental point of view, TPS is not only bio-based but it is also biodegradable, allowing the loop of circular economy to be closed. However, TPS industrial application is limited by its fragility, low water resistance, and the re-crystallization and retrogradation that its structure is subject to, which leads to undesirable changes in the thermomechanical properties of the material [5,17]. In this context, several strategies have been focused on improving biopolymer performance for extending its industrial applications in the packaging field, such as blending, copolymerization and/or the addition of either micro- or nano-fillers for the development of composites and nanocomposites [2,22]. Among all strategies, physical blending seems to be one of the most convenient routes to create new bio-based polymeric formulations, with the required combination of properties, by simply mixing two or more bio-based polymeric matrices in the melt state with no chemical reactions taking place [8,23]. Thus, melt-blending strategies have many advantages since they offer the opportunity to improve the final performance of biopolymers through relatively simple and readily available processing methods that are cost-effective for the industrial sector with respect to the development of new starting monomers and/or polymerization techniques [8,23]. Therefore, to improve TPS performance and extend its industrial applications, the blending approach has been widely studied. In fact, TPS have been blended with either fossil-based polymers (i.e., polypropylene (PP) [24], polystyrene (PS) [25], polyethylene (PE) [26] and ethylene-vinyl acetate (EVA) [27]) as well as with other biopolymers (i.e., PLA [28], and polyhydroxybutyrate (PHB) [29]) to improve its performance and increase its range of applications. Gum rosin (GR) is a natural alternative to fossil-based polymers obtained from heating and evaporation of pine resin [30, 31, 32]. It possesses many advantages for the plastic industry since it is abundant in the nature, has a relatively low cost, and is easily converted into high performance macromolecular materials [30; 33]. Untreated rosin is rigid and brittle and has a thermoplastic behaviour. It is insoluble in water and soluble in acids and most organic solvents (i.e., glacial acetic acid, chloroform, ether and alcohol) [30]. GR is composed of 10-20% of neutral compounds and 80-90% of resin acids [32]. Resin acids structure is composed by a tricyclic skeleton with two double bonds and a carboxylic functional group. This structure provides GR the possibility to be chemically modified in order to obtain a wide range of derivatives, including polymerizable structures for both linear and crosslinked materials [10]. Chemical derivatives of GR can be obtained from oxidation, hydrogenation, dehydrogenation, isomerization, Diels-Alder couplings, esterification, saponification reactions with formaldehyde and phenol [30; 32; 34; 35; 36]. These GR derivatives can be used for the synthesis of homopolymers and copolymers with traditional monomers in order to modulate the properties of the resulting material [35]. In our previous studies, GR and two GR esters derivatives have been used as additives in a Mater-Bi(r) type biopolymer, a commercial blend based on TPS developed by Novamont. It has been determined that neat GR provided a plasticising, compatibilising and solubilising effect in the polymeric matrix which facilitates the processability of the material by decreasing the processing temperature. Meanwhile, the GR esters used in previous works improve the miscibility of the TPS-based matrix components and improve its mechanical performance [5; 37]. The present work aims to study the effect of GR and some GR derivatives on the TPS matrix obtained from native corn starch.