Investigations on ageing of wood-plastic composites for outdoor applications: A meta-analysis using empiric data derived from diverse weathering trials

•MOR and MOE are appropriate indicators to quantify a WPC’s ageing.•Accelerated weathering using xenon-arc light most degrades a WPC’s strength.•A PE-based matrix has a favourable effect on a WPC’s durability.•Strength losses are transferable to a WPC cladding design value. The successful development of durable wood-plastic composite (WPC) cladding is a challenge for the industry. Due to the organic fibres in the compound it is though doubtable if WPC performs satisfyingly in a façade application which is expected to last 50years. This paper provides insights from a study to find out how ageing of WPC cladding can be assessed by relevant norms and which material components best support durability aspects. Based on these, a meta-analysis using 44 empirically generated data from 12 papers in the field of accelerated weathering, thermohygric conditioning and fungal decay of WPCs was conducted. It was found that high values of modulus of rupture (MOR) and Young’s modulus (MOE) are considered key to an engineering design of WPC façades. Both parameters are appropriate indicators to describe the ageing of WPC cladding. Weathering of WPC decreases MOE more than MOR. Exposure to UV-radiation is more harmful than frost-thaw cycling. In order to minimize a loss in value in MOR and MOE, the use pf polyethylene in extruded panels with large-sized hardwood fibres under low content is recommended. Hence, these basic findings add higher value to a product development.