Hygroscopicity anti-swell efficiency and dimensional stability of castor oil – treated Caribbean pine (Pinus caribaea morelet) wood

Abstract

Wood is hygroscopic, rendering it to become dimensionally unstable when exposed to moisture fluctuations during service, none more so in Pinus caribaea wood. Preventing such occurrences in the wood is therefore crucial to its sustainable utilization. This can be achieved by treating the wood with hydrophobic substances such as castor seed oil (CSO). Five (5) trees of 31-year-old P. caribaea wood were harvested at Shasha Forest Reserve, Southwest Nigeria. Bolts of 50 cm long were obtained from each felled tree at the top (90%), middle (50%) and base (10%) of their merchantable lengths. The samples were oven-dried and treated with four formulated oil concentrations prepared from mechanically extracted CSO - 0%, 10%, 20% and 30% using the soaking method. The treated and control samples were evaluated for their water absorption, dimensional swelling (WA) and anti-swell efficiency (ASE). Data analysis was performed using ANOVA. The results show that sampling height had no significant influence (P>0.05) on the evaluated parameters while CSO concentration significantly influenced both the water absorption and tangential swelling (P<0.05) of the wood samples. All the oil treatments significantly reduced the water absorption in the wood (P<0.05). ASE value was highest for the wood treated with the 30% CSO. Overall, the 30% CSO concentration performed best for most of the properties evaluated. However, the little effectiveness of the CSO in improving the wood's dimensional stability may be associated with its method of application. Further study on the thermal treatment of the wood with CSO is therefore suggested.