Abstract
The adoption of bio-based polyesters like poly(L-lactide) (PLLA) and polyhydroxyalkanoates (PHAs) is hindered by low crystallization rates, causing thermal instability and brittleness. Hydrogen-bonding oxalamide-based compounds (OXAs) have been synthesized as nucleating agents to enhance crystallization in these polymers. OXAs dissolve into the polymer matrix, self-assembling during cooling to provide surfaces for heterogeneous nucleation. The nucleation mechanisms were investigated under quiescent and flow conditions using thermal, morphological, rheological, and conformational techniques, enabling the construction of phase diagrams for two OXAs. Flash Differential Scanning Calorimetry (FSC) and small-angle X-ray scattering (SAXS) under shear conditions were pivotal in interpreting nucleation behaviors. OXAs’ nucleating ability depends on parameters like concentration, undercooling, interface, and molecular weight, suggesting surface-driven and stretch-induced rather than epitaxial nucleation. In PLA stereocrystals, epitaxial growth was observed, with mechanisms studied using wide-angle X-ray scattering (WAXS), Transmission Electron Microscopy, and Nano XRD at the European Synchrotron Radiation Facility (ESRF). Additionally, the thermostability of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has been studied and improved to mitigate degradation from biosynthesis residuals and expand their processing windows. Finally, a polyolefin system is studied with the ultimate nucleating agent (KB25) as a proof of concept, demonstrating that growth in one dimension is the most efficient.
Impact on science and/or technology
The developed analytical methods using fast chip calorimetry and nanometer spatial resolution X-Ray imaging provide decisive insight in the mechanisms of nucleation. The gained structural – and in relation chemical insights direct our pathway in designing the ultimate nucleating agent for biobased polyesters. The next mechanism is no longer entropy based and so limited to a very narrow functional window, but epitaxy controlled.
Impact on innovation (companies)
Based on the generated expertise in analytical tools, the fundamental understanding and new direction in research, the company that excels in the development and commercialization of nucleating agents contacted us to explore joint research and technology transfer. Based on epitaxy controlled nucleating agents that fosters the concept in chemical compatibilization of OXA, a generic and broadly applicable platform of nucleating agents will be developed.
Impact on society
With the development of OXA and new nucleating agents, the applicability and commercial use of biobased polyesters will be promoted with respect to the current status as disclosed in Figure 11.
Figure 11: Climate change (kg CO2 eq./kg), cradle to gate (in red) – exemplary LCA parameter
Visual Summary – Poster
