Biological durability of natural fibre reinforced composites: Fid-Bau Portal

Biological durability of natural fibre reinforced composites

Defoirdt, Nele / Windt, Imke De / Bulcke, Jan Van den / Acker, Joris van

Composite materials reinforced with wood or non-wood natural fibres have the potential to be a lighter and lower-cost alternative construction material. Until better availability and properties and a lower cost price of degradable polymers makes their use more prevalent, the application of natural fibre reinforcements in synthetic polymers is an intermediate step towards products that are completely degradable or compostable after their service life. The inherent degradability of natural fibres makes the circumstances of their composite applications, more specifically the moisture conditions, very important regarding potential development of fungal communities and the related damage. For wood and wood-based panels different Use Classes (UC) are defined and for every UC laboratory and field test methods were developed that each determine the (maximum) potential damage caused by the fungi that act in that specific UC. These tests can be used for natural fibre reinforced composites (NFCs) if the specific slower moisture ab- and desorption are taken into account. However the question arises whether the most appropriate way to assess the material resistance is yet developed. Surface stain or mould fungi develop on NFCs when used in high relative humidity conditions (e.g. UC 2). In UC 3 Basidiomycetes can degrade natural fibres as well as derived composites if the natural fibres reach the critical moisture content. In addition to laboratory tests, a 5 year field test showed that fungal growth is not problematic when moisture traps are not present. Finally a graveyard test (UC 4) only revealed superficial softening after 5 years exposure, confirming the good durability of NFCs. Fungal growth thus seems to be mainly an aesthetical problem. Moisture uptake, more than fungal decay, also results in a decrease in mechanical properties, which seems, up to now, relatively unimportant regarding the actual use of such composites. However, if used in structural applications once a better fibre/matrix adhesion leads to enhanced mechanical properties, the damage by moisture and fungi could become critical.