The study demonstrated that a combination of 2D and 3D nanodiffraction imaging can resolve hierarchical crystalline architectures, providing insight into how processing conditions affect nanoscale structure.
Peering into the Nanoscale Crystal Architecture of a Common Bioplastic
A study published in Communications Materials has used advanced electron nanodiffraction and microscopy to investigate the nanoscale crystalline architecture of poly(L-lactic acid) (PLLA), a semicrystalline thermoplastic. The research, led by Sedova A. and Houben L., examined how different thermal processing methods affect the polymer's lamellar crystal organization.
Methodology
Researchers employed 4D scanning transmission electron microscopy (4D-STEM) with nanobeam electron diffraction, parallax-filtered integrated differential phase contrast (ΔiDPC) imaging, and nanobeam tomography to resolve crystalline features at the nanoscale. Complementary data were obtained using atomic force microscopy (AFM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC).
Key Findings on Crystalline Architecture
- Polymer-Chain Orientation: Two-dimensional diffraction maps revealed uniform polymer-chain tilts of 11–17° within individual lamellae. This consistency was also observed across multi-lamellar bundles, indicating coherent crystallographic registry, with bundles behaving as quasi-single crystals.
- Lamellar Structure: Three-dimensional nanobeam tomography showed lamellar bundles extending hundreds of nanometers to micron scales, with a preference for vertical stacking. Interlamellar spacing was measured at approximately 3.1 nanometers.
- Structural Effects: Non-annealed samples displayed lamellar twisting, which was attributed to mechanical stresses.
Effects of Thermal Processing
The study linked thermal processing conditions to changes in crystalline morphology. Extrusion and injection molding, followed by thermal annealing at 90°C and 160°C, led to alterations in crystalline domain sizes and packing order. Specifically:
- Injection molding produced a more homogeneous lamellar distribution compared to extrusion alone.
- Thermal annealing promoted the interconnection of lamellar stacks into extended networks, supporting a model of templated crystallization.
Background
The degree of crystallinity in semicrystalline thermoplastics like PLLA influences their mechanical and physical properties. Traditional optical microscopy lacks the resolution necessary to analyze these nanoscale crystalline features. The study demonstrated that a combination of 2D and 3D nanodiffraction imaging can resolve hierarchical crystalline architectures, providing insight into how processing conditions affect nanoscale structure.
Journal Reference
Sedova A., Houben L., et al. (2026). Evolution of multi-lamellar crystals in thermoplastic revealed by 2D and 3D nanodiffraction imaging. Communications Materials. DOI: 10.1038/s43246-026-01176-z.
Note: This article reports on an unedited version of the paper accepted for publication. The study should not be regarded as conclusive.