Protection of wood in ancient timber construction by surface painting of waterborne siloxane-modified polyurethane against water destroy

To protect the ancient wood against water destroy, the waterborne polyurethane was modified siloxane and then painted on the wood surface. The coated surface was characterized and the surface physical and mechanical properties were tested. The results showed that the siloxane can be grafted onto the polyurethane by reacting between Si-OH groups and the end N=C=O groups. Thus, after coating on the wood surface, a network structure was formed for improvements. The polyurethane can form a layer of film on the wood surface while the siloxane can help to make a smooth coating film owing to the improved interfacial adhesion. With the increase of siloxane content, the surface became better with improved water contact angle, swelling dimensional stability, and hardness. At 3 wt% siloxane, the surface properties of the wood showed high water repellency and acceptable mechanical properties, which can be used for ancient timber protection.