Cynara Cardunculus seed oil: a promising source for the production of biodegradable Poly(lactic acid) plasticisers

Cardoon seed oil (Cynara Cardunculus) has been attracting an increasing interest in Italy for the bio-plastic industry. Cardoon is a wild robust perennial plant, native from the Mediterranean basin. Its production can reach 30–35 t/(ha year), and the dried flowers of this plant have been used since ancient times in southern Europe as vegetable rennet, to prepare high-quality traditional milk from goat and sheep. Cardoon seeds contain high oil content (25–33%), and their composition is based on mono-, di- and triglycerides [1]. The composition in fatty acids of the Cardoon oil (CO) is similar to that of the sunflower oil, around: 60.9% linoleic, 23.6% oleic, 12.1% palmitic and 3.4% stearic acid. Moreover, Cardoon does not compete for land as far as edible resources are concerned, and the related crop does not need high quality of arable land nor fertilisers/herbicide pre-treatment, differently from what happens for materials coming from sunflower or soybean [2]. CO represents an interesting potential non-food plant oil: it can be cultivated on the contaminated soils of the Campania region (Italy), i.e. the land known with the name “terra dei fuochi” (land of fires), because it very well adapts with the local climate conditions, and through a phytoremediation process it is possible to have available a suitable plant-oil otherwise not usable for the human food. The aim of this work is the preparation of biodegradable and non-toxic plasticisers by epoxidation reaction of CO and the study of their potential plasticising effect in environmentally friendly polymers like poly(lactic acid) (PLA). This aliphatic polyester, coming from plants fermented starch, is regarded as a promising alternative to some petro-based polymers due to its noteworthy mechanical properties such as tensile strength and Young’s modulus. As most of the polyesters, the main drawback of PLA that prevents some commercial applications, concerns its brittleness and lower impact resistance [3]. Over the past, the use of proper plasticisers has been shown as a valid solution to enhance its flexibility and toughness. The epoxidized soybean oil (ESO) is well recognised to be an efficient plasticiser for PVC and other plastics, in addition with the beneficial aspects derived by its biodegradable and non-toxic nature [4]. However, this edible plasticiser feedstock may raise serious issues concerning the competition with food supply and deforestation due to the massive propagation of edible plants. Therefore, the use of CO appears advantageous to prepare biodegradable plasticisers for PLA. For this purpose, in this work, after a preliminary characterization, CO has been successfully epoxidized by performic acid, in fed-batch modality. Then some blends of PLA_ECO, i.e. with different amounts of epoxidized Cardoon oil (ECO), have been prepared and characterised by thermal, mechanical and spectroscopic analysis. A final comparison with analogous blends of PLA_ESO has shown that ECO is an effective green plasticiser for PLA.