Physicochemical characterisation of polyester and nylon synthetic fibres as potential plant growth substrates for green roof systems: a preliminary study

Abstract

Green roofs are recognised as effective urban sustainability infrastructure, yet the conventional use of soil-based growing media poses challenges, including high dead loads, progressive structural decomposition, and costly long-term maintenance. This study presents a preliminary physicochemical characterisation of shredded Polyester and Nylon textile waste fabrics as novel, lightweight, synthetic growing substrates for green roof systems, evaluating their suitability against established benchmarks. No plant growth trials were conducted; the scope is limited to laboratory characterisation of key physicochemical properties. Growing medium containers filled with shredded polyester and Nylon fabrics were characterized for bulk density, particle density, total porosity, Water Holding Capacity (WHC), Water Retention Capacity (WRC), pH, and Electrical Conductivity (EC). Mean bulk densities of 0.22 ± 0.015 gcm-³ (Nylon) and 0.145 ± 0.019 gcm-³ (Polyester) represent reductions of 63-89% relative to conventional green roof soils. Total porosity exceeded 74% for nylon and 84% for polyester, exceeding the FLL minimum of 35%. WHC ranged from 63-66% (Nylon) and 72-78% (Polyester), satisfying the FLL requirement of ≥35% by volume. The water retention curves demonstrated that polyester maintained consistently higher water retention throughout the drying period, retaining approximately 17% of absorbed water, indicating polyester’s superior capillary water-holding capacity driven by its fibrous matrix structure. Both substrates exhibited pH values within the optimal horticultural range and EC values indicating minimal salinity stress risk. These preliminary results suggest that recycled synthetic textile waste fibers warrant further investigation as lightweight, chemically inert, and structurally stable growing media for green roof systems, pending validation through plant growth trials.