Transcrystallization Mechanisms in Polymer Composites

Transcrystallization refers to the formation of a highly oriented crystalline layer at the interface between a reinforcing fibre and a semi-crystalline polymer matrix. Unlike equiaxed spherulites that grow in the bulk, transcrystalline layers develop perpendicular to the fibre surface and comprise lamellae whose chain axes align with the fibre axis. This interfacial morphology arises through heterogeneous nucleation and can profoundly influence composite stiffness, strength, toughness and thermal stability. Key drivers of transcrystallization include the chemistry and topography of the fibre surface, the degree of epitaxial matching between fibre and polymer crystal lattice, local shear stresses generated during processing and the presence of nucleating additives. The resulting interphase can enhance stress transfer, mitigate crack initiation and tailor macroscopic properties in applications ranging from automotive and aerospace components to bioresorbable medical devices. Recent advances in three-dimensional imaging, synchrotron scattering and spectroscopic mapping have elucidated the interplay of nucleation kinetics, chain orientation and flow in establishing multi-phase interfacial architectures. Understanding and controlling transcrystallization are thus central to designing next-generation polymer composites with optimised performance and sustainability.

Research from Nature Portfolio

Recent studies have demonstrated that macroscopic carbon-nanotube (CNT) fibres can induce rapid formation of a distinct transcrystalline layer in a variety of semi-crystalline polymers, including polypropylene, poly(vinylidene fluoride) and polylactic acid. Investigations combining differential scanning calorimetry, polarized optical microscopy and X-ray scattering reveal that wetting of the CNT surface by the polymer melt promotes chain adsorption and the formation of a transient, mesomorphic precursor layer. This layer facilitates accelerated heterogeneous nucleation and oriented lamellar growth without strict lattice matching, suggesting that polymer chain orientation at the fibre interface is the dominant factor. The resulting interphase exhibits uniform lamella orientation parallel to the CNT axis and markedly enhanced nucleation rates, offering a general strategy for engineering transcrystallinity on a wide range of nano- and micro-fibre reinforcements.

Transcrystallization Mechanisms in Polymer Composites publication trend

The graph below shows the total number of articles in transcrystallization mechanisms in polymer composites across all publications each year (not limited to Nature Index journals).

Technical terms

Transcrystalline layer (TCL): A shell of highly aligned lamellar crystals that nucleate at and grow perpendicular to a fibre surface within a polymer composite.

Heterogeneous nucleation: The initiation of crystal growth at interfaces or impurities that lower the energy barrier compared with homogeneous nucleation in the bulk.

Epitaxy: Alignment of a polymer crystal’s lattice to that of a substrate, facilitating low-energy nucleation when lattice parameters are compatible.

Spherulite: A roughly spherical aggregate of radially emanating lamellae commonly formed during the crystallization of semi-crystalline polymers.

Shish–kebab morphology: A composite crystalline structure in which extended-chain “shish” fibrils align with the fibre axis and are periodically decorated by folded-chain “kebab” lamellae.

References

1. Macroscopic CNT fibres inducing non-epitaxial nucleation and orientation of semicrystalline polymers. Scientific Reports (2015).
2. Synergy of Fiber Surface Chemistry and Flow: Multi-Phase Transcrystallization in Fiber-Reinforced Thermoplastics. Polymers (2022).
3. Enhancing Sustainability and Antifungal Properties of Biodegradable Composites: Caffeine-Treated Wood as a Filler for Polylactide. Materials (2024).
4. Origin of Transcrystallinity and Nucleation Kinetics in Polybutene-1/Fiber Composites. Macromolecules (2020).