Improving bio-based content in PLA-based biodegradable thermoplastic polymer blends

The current global annual production of plastic materials is around 365 million tons. Their commercial success is related to a combination of different properties: strength, lightweight, flexibility and stability. However, there are many concerns related to the production and use of conventional plastic, originating from its excessive carbon footprint and its resistance to biodegradation. The increasing awareness about plastic pollution and its environmental impact are highlighting the need to develop sustainable materials to replace oil-based and non-biodegradable plastics. In this setting, biodegradable polyesters play a crucial role. Among all the biopolyesters, polylactid acid (PLA) has attracted attention as a biodegradable and bio-based material, reaching industrial-scale production. Some of its properties are very similar to conventional thermoplastic materials largely used in market products such as polystyrene and polyethyleneterphtalate. However, PLA has some drawbacks regarding the limited deformability and the brittleness, as well as the slow crystallization rate. These features limit its processability, and consequently its broad application on large scale, e.g. in blown-films for packaging application. To overcome PLA’s inherent drawbacks, the preparation of polymers blends is an attractive strategy. The goal of this thesis is to develop PLA blends with improved performance, maximizing their bio-based content. More specifically, the purpose is to obtain a polymer blend with a good processability suitable for film blowing, with the lowest content of non-biobased polymer, which is added as PLA plasticizer. PLA blends with other flexible biopolymers, such as Poly(butylene-adipate-terephthalate) (PBAT) and poly(ε-caprolactone) (PCL) have been studied. Additionally, the use of a high molecular weight polymers instead of conventional plasticizers can hinder the migration, reducing the materials aging. To face the chemical differences between these polymers, which lead to poor interface adhesion and phase separation, two compatibilizers have been employed. The performances of the blends were characterized using thermal, mechanical and morphological characterizations. As validation of the enhanced processability of the blend, film blow processing has been performed on the most suitable compositions.