Polylactic acid’s deforming characteristics challenge assumptions about brittleness as a property

Polylactic acid (PLA) is a sustainable, biodegradable plastic material made from renewable resources that has garnered attention for a wide range of uses, from tableware to medical devices. Relatively little is known, however, of how the material deforms and becomes damaged when it is scratched, which can hinder its performance.

Zhu et al. have provided in-depth characterization of how scratches affect different performance parameters of PLA. Integrating in-situ observation and polarized light imaging, the group investigated the material’s scratch behavior in increasing normal loads and found a ductile damage pattern — damage that degrades a material over an accumulation of microscopic defects.

The findings point to guidance for how to mitigate the damage mechanisms of PLA.

“This approach captures the full process from plastic deformation to ductile crack propagation and tearing,” said author Zhongmeng Zhu. “Crucially, it visually maps the subsurface plastic deformation layer and identifies significant scratch-induced temperature rise as the key factor triggering PLA’s ductile behavior. This provides a deeper physical understanding beyond traditional post-mortem morphology analysis.”

At low normal loads, brittle PLA exhibited plastic deformation beneath a scratch tip. At higher loads, this shifted to periodic 30-degree angled crack propagation linked to scratch-induced high temperature rise and lateral tearing with circumferential debris formation.

“Our work demonstrates that ‘brittleness’ is not an absolute property but is highly dependent on the stress state and loading conditions,” Zhu said. “This could influence the design and material selection for applications where surface wear and scratch resistance are critical, encouraging engineers to reconsider the damage tolerance of biodegradable materials.”

The group next looks to investigate surface texture effects on PLA and extend their in-situ methods.

Source: “Mechanism investigation of scratch-induced ductile damage in brittle polylactic acid revealed by in situ observation,” by Zhongmeng Zhu, Chutian Li, Jun Ma, Ziqi Wang, and Han Jiang, Nanotechnology and Precision Engineering (2026). The article can be accessed at https://doi.org/10.1063/5.0291021 .

This paper is part of the Recent Advances in Instrumented Scratching Collection, learn more here .