Waterproofing of bottle gourd (Lagenaria siceraria) with castor oil polyurethane resin

Castor oil is widely used in chemical industry as raw material for paints, coatings, lubricants and a wide variety of other products. It is an important alternative to petrochemical feedstocks for the synthesis of polyurethanes (PU), besides being cost competitive and environmentally friendly alternative. It is used as a substitute for formaldehyde adhesives to produce composites and particleboards. Higher percentages of the resin tend to cause low water absorption and dimensional changes in the panels, so it has potential to use as waterproofing of natural materials. Bottle gourd is a fruit, used worldwide by different peoples as a raw material for the production of artifacts since many thousands of years. After the drying period, the inner part of the shell acquires characteristics similar to wood and the outer shell becomes impermeable. The objective of the work is increasing the durability and extend the useful life of the bottle gourd for use in the product design by waterproofing the material with polyurethane resin derived from castor oil. Untreated samples were compared with one and two layer resin samples. For the water absorption test, reference was made to standard NBR 15316: Medium density fiberboard. The analysis of the results was made through Scanning Electron Microscopy (SEM), water absorption test and contact angle. As a result, the application of the PU resin of castor oil reduced the water absorption indexes, and the samples with two layers of resin obtained the best results.