Abstract
The waterborne coating uses water as its solvent, which will partially dissolve wood extractives when it is applied to wood surfaces. This influences both the coating curing process and the mechanical properties of the cured coating. To investigate these influences, the mechanical properties of waterborne polyacrylic coating on control and extractive-free wood surfaces were investigated by nanoindentation. Reductions to elastic modulus (Er) and hardness (H) of the coating layer was observed in the wood cell walls adjacent to or away from coating layers. Extraction treatment resulted in significant decrease of the Er and H of the coating layer on extractive-free wood surface comparing with control wood, but the values slightly increased for extractive-free wood cell walls compared to a control. Er and H of coating in wood cell lumen were higher than the average value of coating layer on wood surface in both the control and extractive-free wood. The Er of wood cell wall without coating filled in lumen was significantly higher than those of filling with coating. However, there was no distinct difference of H. The Er and H of CCML in extractive-free wood were 15% and 6% lower than those in control ones, respectively.
Highlights
Wood extractives are the un-bound organic molecules present in wood that dissolve and can be removed using fluxed solvents such as ethanol, benzene, ether, acetone, dichloromethane, or solutions containing set proportions of the aforementioned solvents
In analysis of the interactions between loblolly pine and an applied phenolic (“PF”) resin, Wang and Marcott [33,34] combined atomic force microscopy and infrared nanospectroscopy to elucidate the permeability of PF resin into wood cell wall forming an interpenetrating polymer network (IPN) structure
2, at at least least thirty validcell indents were performed on the(Berkovich coating layer (C1–C8), theAs control wood cell wall (W), thirty the wood lumen penetrated with tip type) was shown in
Summary
Wood extractives are the un-bound organic molecules present in wood that dissolve and can be removed using fluxed solvents such as ethanol, benzene, ether, acetone, dichloromethane, or solutions containing set proportions of the aforementioned solvents. The effect of extractives on the mechanical properties of an applied coating and how it interacts with wood cell walls was not established. In analysis of the interactions between loblolly pine and an applied phenolic (“PF”) resin, Wang and Marcott [33,34] combined atomic force microscopy and infrared nanospectroscopy to elucidate the permeability of PF resin into wood cell wall forming an interpenetrating polymer network (IPN) structure These techniques obtain mechanical information over a narrow region, this region does not necessarily reflect the mechanical properties of all surfaces. Further elucidation of the interface between waterborne coating and wood will be illustrative of the mechanisms that lead to macroscopic defects produced by extractives within coated wood products
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