<p>Most microplastics (MPs) are generated as a result of photodegradation during the life of plastic products and after the end-of-life as mismanaged waste. At present, it is impossible to avoid plastic-based materials altogether because of their unique properties, versatility, and price. An option is to set limits on how much MPs these materials can release over their lifetime, which would not only reduce MPs pollution, but also improve product quality. However, there is a lack of reliable methodologies for assessing the generation of MPs from these products during use or when they are left as unmanaged waste. The objective of this study was to develop a novel method to assess (collect and quantify) MPs formation from plastic-based materials during weathering. The developed process design is based on a well-established accelerated weathering tester that has been modified by incorporation of a sieve system and water recirculation. The case study is carried out on a recycled polypropylene (rPP) and wood plastic composite (WPC) made from wood particles and the same rPP. Despite the lower plastic content, WPC released significantly more MPs (up to 9.4&#xa0;g/m²) than the rPP (up to 0.3&#xa0;g/m²) in the same weathering conditions and duration. Examination of the degraded surfaces revealed that the wood particles facilitated the release of MPs most likely due to moisture fluctuations causing wood swelling induced internal stresses. The collected MPs were mainly below 500&#xa0;μm and their properties were different comparing to MPs made by cryogenic milling. PY-GC-MS did not detect MPs smaller than 20&#xa0;μm that could pass through the smallest sieve and end up in the effluent. The reproducibility of the measured MPs release using the process design was very good during the tested weathering period, with variations of less than 7%.</p>