Analysis of the Degradation Behaviour of Polylactic Acid Packaging Films under Nigerian Tropical Climate Conditions

Polylactic acid is a commercially available biodegradable thermoplastic widely promoted as an environmentally sustainable alternative to petroleum-based packaging polymers. This study analyses the degradation behaviour of commercial polylactic acid packaging films subjected to simulated tropical climatic conditions representative of the South West Nigerian environment. Film specimens were exposed to controlled conditions of 30 degrees Celsius and 80 percent relative humidity simulating indoor storage, and outdoor weathering at 40 degrees Celsius with alternating UV irradiation cycles mimicking Lagos State seasonal conditions. Degradation was monitored over 180 days through measurements of tensile strength retention, molecular weight by gel permeation chromatography, water vapour permeability, and surface morphological changes by scanning electron microscopy. Results indicate that outdoor weathering conditions produced significantly accelerated degradation relative to controlled indoor storage, with tensile strength declining to 34 percent of initial values after 90 days of outdoor exposure. Molecular weight analysis confirmed hydrolytic chain scission, with weight-average molecular weight decreasing from 145,000 to 51,000 g/mol over 180 days under outdoor conditions. Water vapour permeability increased progressively with degradation, reflecting increasing film porosity. Surface cracking and embrittlement were observable by scanning electron microscopy from day 60 under outdoor conditions. The study concludes that polylactic acid packaging films degrade appreciably within commercially relevant timescales under Nigerian tropical conditions, supporting their suitability as short-shelf-life packaging for fresh food applications. Recommendations include optimising film thickness and UV stabiliser content for controlled shelf-life management. Keywords: polylactic acid, biodegradable packaging, tropical degradation, UV weathering, Lagos