This study presented a comprehensive techno-economic analysis (TEA) and life cycle assessment (LCA) of autothermal

co-gasification of wood chips and waste-HDPE for sustainable hydrogen production. Unlike previous studies that primarily

examined syngas composition at the gasifier outlet, this work evaluated the entire hydrogen production process, from

gasification through syngas upgrading to purification, and illustrated that maximizing hydrogen content in the raw syngas

would not necessarily maximize the overall hydrogen yield after downstream processing, underscoring the importance

of a system-level assessment. Parametric studies on equivalence ratio (ER) and feed plastic content (FPC) revealed that

while the maximum hydrogen content in the raw syngas was obtained at ER~0.4, the maximum hydrogen yield along

with upgrading was achieved at lower ER~0.16, driven by higher methane availability for reforming. The levelized cost of

hydrogen (LCoH) with 20% FPC under the optimal condition (i.e., ER~0.16) achieved 45% reduction compared to cases

with high ER values. Sensitivity analysis on waste plastic price identified a threshold value of $0.88/kg, below which cogasification

becomes more economically attractive than biomass-only gasification. Life Cycle Assessment (LCA) results

showed carbon intensities (i.e., CO2 emissions per kg of H2) ranging from 3.8 to 11.1 kg-CO2/kg-H2 depending on FPC,

increasing with higher plastic content in the feed. As hydrogen yield increased with higher FPC, these results highlighted

the key trade-offs between hydrogen yield and carbon intensity, providing useful insights for process design and feedstock

strategy under emerging carbon accounting frameworks, including the U.S. Inflation Reduction Act (IRA).