Development of tough, transparent materials from poly(lactic acid)

Polylactic acid (PLA) is a bio-based polymer which is on economic point of view a promising alternative for petroleum-based plastics such as polypropylene and polystyrene. However, at this time, the properties of PLA limits a variety of applications. One of the main shortcomings is the high brittleness at room temperature, which is partially coupled with the high glass transition temperature (Tg) of PLA (± 60 ° C). This brittleness can be translated into a small impact strength, small elongation at break, lack of flexibility and conformability. Also, properties such as abrasion resistance, tear strength, progress in mechanical properties are sometimes linked to the high Tg and low crystallinity. The objectives of this project are (1) the delivery and (2) understanding of recipes (product composition and -process conditions) to fabricate tough and transparent polylactic acid products with good barrier properties for (mainly) applications within the packaging industry. The formulations include the blending of PLA with combinations of plasticizers and crystallization-promoting gelators via extrusion and product formation via (mainly) injection molding.

In order to achieve the objectives, gelators which act as nucleating agent for the crystallization of PLA and suitable plasticizers will be identified, selected and optionally synthesized. The causal relationship on the one hand between the type and the concentration of the gelator and plasticizer and the other hand, the material properties during processing (viscosity, crystallization kinetics) and use in the solid state (mechanical, optical and barrier properties, migration of additives) are dominated by the intrinsic properties of the components (viscosity, glass transition temperature) and the way in which these are spatially ordered (phase morphology, crystallinity, location of plasticizer, size of crystal aggregates, polymorphism, distribution of nucleating agent, orientation of the nucleating agent and the PLA-crystals as a result of flow, ...). For a good understanding, in addition to the measurement of the relevant properties also a profound morphological characterization will be carried out. Because the  structure or morphology is dependent on the processing conditions, the impact of varying the processing conditions (cooling rate, on / off-presence of flow) within the relevant limits will also be studied. The conceptualization will be supported by model calculations that also have a predictive power in the selection of new and better nucleating gelators and plasticizers.