Poly(L-lactic acid) (PLLA) is the most widely used biobased, biodegradable/compostable and biocompatible synthetic polymer, increasingly adopted as a sustainable alternative to conventional petrochemical plastics [1,2]. PLLA applications span from food packaging and agriculture to high-value biomedical devices [3].

Despite its many advantages, PLLA exhibits intrinsically slow crystallization kinetics, which represent a technological limit. Under typical industrial processing conditions, which require fast cooling, the slow crystallization prevents the development of adequate crystallinity fractions. As a result, PLLA molded products often display limited mechanical properties and poor thermal resistance [3]. Enhancement of PLLA crystallization kinetics is essential to overcome these drawbacks, unfortunately the huge research efforts devoted to date have allowed only partial improvement, not sufficient to guarantee adequate crystallinity upon industrial processing. Sizable improvement of PLLA crystallization rate is the main goal of the BORN Project (GA 101223095), funded by European Union under EIC- Pathfinder program [4]. This will be achieved via development of a crystal nucleating agent with sizably enhanced efficiency compared to the current formulations, able to allow PLLA crystallization upon industrial processing. Compared to the otherwise amorphous polymer, semicrystalline PLLA exhibits significantly improved thermal resistance, References up to 100 °C, broadening the range of possible applications. In food packaging, this may translate into compostable microwaveable containers for ready-to-eat meals, or cost-effective cups for hot beverages, contributing to the transition toward high-performance, sustainable plastic alternatives.

Moreover, proper manipulation of PLLA crystallization behavior can be transformed from a constraint into a powerful engineering tool, unlocking new processing technologies. This is exampled by fabrication of multilayered monomaterial foams, attained via tailored crystal formation in only a part of the material before foaming. A layered crystalline structure was developed in an initially amorphous PLLA disk, by precisely regulating the process parameters that control mass diffusion of the foaming agent. This allowed to fill the polymer with a gradient of foaming agent, able to induce crystal formation in a part of the sample that became not foamable, and bubble formation in the parts exposed to lower amounts of foaming agent. PLLA foams with multilayered structured morphology, made of alternating layers of either crystalline or amorphous materials, and of either foamed or unfoamed parts, were produced with a single polymer, which made them easily recyclable [5]. This surpasses the up-to-date state of art of multilayered foams, which are currently made with alternating layers of different materials, hardly and costly to recycle.

References

1-M.L. Di Lorenzo, R Androsch, Eds. Synthesis, Structure and Properties of Poly (lactic acid), Adv. Polym Sci. 279 (2018). Cham, Switzerland: Springer International Publishing.

2-M.L. Di Lorenzo, R Androsch, Eds. Thermal properties of bio-based polymers., Adv. Polym Sci., 283 (2019). Cham, Switzerland: Springer International Publishing (2019).

3- M.L. Di Lorenzo, R Androsch, Eds. Industrial Applications of Poly (lactic acid), Adv. Polym. Sci. 282. Cham, Switzerland: Springer International Publishing (2018)

4- A. Longo, E. Di Lorenzo, L. Miele, A. Bernardi, E Di Maio, M.L. Di Lorenzo, J. Polym. Env. (2026), under review.

Acknowledgments

Financial support was received from European Union, BORN Project, GA 101223095, financed by European Innovation Council (EIC) and SMEs Executive Agency (EISMEA), HORIZON-EIC-2024-PATHFINDERCHALLENGES-01.