Biodegradable PLA/Bio-PE Thin-Film Encapsulation of Bio-PCMsfor Geotechnical Freeze–Thaw Applications

This study introduces biodegradable thin-film encapsulation of bio-based phase change materials (Bio-PCMs) using PLA and Bio-PE polymers as a novel materials-engineering solution for geotechnical freeze–thaw applications. Expansive subgrade soils in cold climates suffer severe deterioration due to freeze–thaw cycling, leading to premature pavement distress. By embedding PLA/Bio-PE encapsulated Bio-PCMs (coconut oil, soy wax, lauric acid) into black cotton soil, the approach combines thermal buffering with environmental sustainability. This study evaluates the feasibility of using biodegradable thin-film encapsulated phase change material (Bio-PCM) capsules to enhance thermal stability and mechanical durability of black cotton soil subgrades. Bio-PCMs (coconut oil, soy wax, lauric acid) were encapsulated in PLA/Bio-PE films using a heat-seal process and incorporated into soil at dosages of 0–6% (by dry weight). Laboratory tests included compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), and freeze–thaw durability over 20 cycles, complemented by thermal profiling. Results showed that PCM-treated soils reduced freeze–thaw temperature amplitude by ≈4.5 °C, delaying freezing onset and mitigating frost penetration. The 4% PCM dosage achieved the best balance of properties: after freeze–thaw cycling, the UCS was 230 kPa compared to 145 kPa for the control, representing 74.2% retention of its own initial strength versus only 58.0% for the control. Similarly, the post-cycle CBR was 5.1% for PCM-4 compared to 3.0% for the control, corresponding to 78.5% retention of its initial value versus 57.7% in the untreated soil. While 6% PCM produced a slightly higher CBR (5.2%), it also lowered maximum dry density, indicating diminishing compaction efficiency. These findings demonstrate that biodegradable thin-film PCM capsules can significantly improve freeze–thaw resilience in expansive soils while offering an environmentally sustainable alternative to conventional stabilizers.