Performance by design: tuning hybrid parallel strand lumber properties through beech/poplar weight ratios

This study established the species weight ratio as a key design parameter for tuning the performance of hybrid parallel strand lumber (PSL). Moving beyond conventional waste valorization, a performance-by-design strategy was introduced using controlled beech/poplar compositions (100/0, 75/25, 50/50) engineered from approximately 1 mm industrial veneer waste. While increased poplar content led to reductions in bending strength (MOR: 98–78 N/mm²) and stiffness (MOE: 10,330–9,147 N/mm²), significant non-linear optimization points were identified. The 25% poplar hybrid (PSL-H25) exhibited superior impact resistance (0.536 kgf·m/cm²) and a distinct thickness swelling peak (33%). This anomaly is attributed to a higher compaction ratio of poplar within the beech matrix, triggering an intense ‘spring-back’ effect upon moisture exposure. Fracture analysis revealed that this optimal ratio enhances energy dissipation through tortuous crack paths and fiber bridging, effectively preventing brittle failure. The use of ultra-thin strands (approx. 1 mm) facilitated superior bond continuity, achieving performance competitive with commercial PSL. This work offers a robust framework for precision-tuned, sustainable, circular engineered wood products.