Kappagantula, Keerti S. [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000222105781)

DOE OSTI2025

Comparison of Mechanical Properties of Lignin/High-Density Polyethylene (HDPE) Composites and Wood/HDPE Composites

Lignin is a plant-derived, the second most abundant natural polymer, and a waste byproduct of the pulp industry. Incorporation of lignin into plastic composites using scalable approaches is commercially favored and low carbon-cost. Potential end applications for lignin plastic composites (LPCs) could be found in buildings and furniture where wood plastic composites (WPCs) are used in various components. This study compares the mechanical properties of LPCs and WPCs, aiming at the examination of the viability of the use of LPCs as alternative materials to WPCs in the building industry. Sodium ligninsulfonate (SLS)-based LPC blended with high-density polyethylene (HDPE) (45 wt.%) and maleic anhydride grafted polyethylene (MAPE) as a compatibilizer (5 wt.%) reached flexural strength (35.17 and 30.92 MPa respectively) and moduli (2.87 and 1.79 GPa respectively) comparable to benchmarking WPCs. Lignin dealkaline (LD)-based LPC exhibited higher ultimate strain but lower strength than SLS-based LPC, probably due to fragmentation during the post-sulfite treatment steps.

cellulose and other wood products↗

DOE OSTI2025

Meshfree simulation and prediction of recrystallized grain size in friction stir processed 316L stainless steel

Friction stir processing (FSP) is a promising solid-phase microstructural modification technique that can repair and enhance damaged stainless steel surfaces exposed to harsh environments. The quality of the repaired material is closely correlated to the recrystallized grain size in the stir zone (SZ), which is influenced by the thermomechanical conditions dictated by FSP process parameters. Thus, establishing a reliable relationship between these parameters and recrystallized grain size in the SZ is crucial for optimizing repair quality. However, existing experimental approaches often rely on indirect temperatures measured far from the SZ, along with rough strain rate estimations, which are imprecise and time-consuming. Meanwhile, existing mesh-based modeling methods usually face numerical challenges when dealing with the large material deformations inherent in FSP. Here, to address these issues, this study introduces a meshfree process model for FSP based on the smoothed particle hydrodynamics (SPH) method, aimed at predicting process conditions under different parameters. The model is validated using experimental data from 11 combinations of tool traverse and rotation speeds on 316 L stainless steel. Correlations between process parameters, material flow, temperature, strain, strain rate, and recrystallized grain size are revealed through SPH simulations and electron backscatter diffraction (EBSD) imaging. The results show that in situ SZ temperatures range from 1071 to 1322°C, which exceed the tool temperature by over 300°C. Furthermore, SZ temperature, strain rate, and grain size increase monotonically with higher tool temperature and faster traverse speed. A relationship is then established between the model-predicted Zener-Hollomon parameter and the recrystallized grain size based on EBSD data, expressed as ln(d) = -0.364 ln(Z) + 14.673. Finally, this relationship exhibits satisfactory accuracy with errors of less than 26.9% in predicting grain sizes at various SZ locations, which offers valuable insights for optimizing FSP repair processes for 316 L stainless steel.

316L stainless steel↗