Performance of laminated bamboo lumber and bamboo strand lumber coated with solvent and water-based polyurethane against accelerated UV and natural weathering

The performance of two bamboo composites namely laminated bamboo lumber (LBL) and bamboo stand lumber (BSL) coated with solvent-and water-based polyurethane (PUS and PUW) surface protectants against accelerated UV and natural weathering was evaluated and compared. Thin strips and crushed strands of B. bambos were processed using phenol formaldehyde (PF) adhesive in a hydraulic hot press to prepare the LBL and BSL respectively. The uncoated LBL and BSL exhibited severe darkening of the surfaces on exposure to both weathering regimes. All the polyurethane (PU) coated LBL and BSL showed tendency to undergo photo-yellowing after UV exposure. The roughness, wettability and reduction in glossiness of the coated samples was observed to be increased with increasing exposure period however, the rate of changes in these parameters were lower compared to their uncoated counterparts. The FT-IR spectroscopy results revealed that the lignin present in uncoated LBL and BSL deteriorated rapidly on exposure to UV and natural weathering conditions. It was concluded that the both PUS and PUW coatings on the bamboo composites provided substantial resistance against UV irradiation. The PUS coated LBL exhibited better performance by showing lower colour changes and surface cracking compared to coated BSL on exposure to natural weathering. Overall the performance of PUS coated specimens against natural weathering condition was found to be strongly influenced by the surface properties of the bamboo composites.

Automated summary

The performance of two bamboo composites, laminated bamboo lumber (LBL) and bamboo stand lumber (BSL), coated with polyurethane surface protectants (PUS and PUW) against UV and natural weathering was evaluated. The presence of the protective coatings on the bamboo composites provided resistance against UV irradiation. However, the coated surfaces still showed tendencies of photo-yellowing after UV exposure. The performance of the PUS-coated specimens against natural weathering was better than the coated BSL, with lower color changes and surface cracking.