Morphological and Mechanical Characterization of Pinus radiata  Wood Treated with Two Organic Phase Change Materials via Vacuum Impregnation

The present study examines the mechanical and morphological properties of Pinus radiata wood impregnated with two different organic phase change materials (PCM). Specifically, paraffin-type aliphatic PCM and fatty acid PCM were used to impregnate the samples in the tangential flow direction. The first aim is to analyze the effect of impregnation with a fatty acid on the morphological properties of wood, such as cell wall thickness, lumen diameter, tracheid diameter, and open ray pit diameter. Moreover, the research emphasizes wood's transport properties, such as longitudinal permeability—measuring fluid flow along the wood's longitudinal axis—and tangential permeability, which quantifies fluid flow perpendicular to the growth rings. These properties are correlated with the impregnation ratio using Pearson's correlation. Additionally, the study focuses on how impregnation with an aliphatic and fatty acid PCMs affects the mechanical properties of wood, specifically the variation in the longitudinal Young's modulus. The Young’s modulus was measured using the impulse excitation technique, following ASTM E1876. Experiments were conducted at three manometric pressures (55, 70, and 85 kPa) at two constant temperatures (30 \((^{\circ})\)C and 70 \((^{\circ})\)C). PCM incorporation ranged from 18 Wt.% to 80 Wt.% depending on pressure and time. The longitudinal Young’s modulus increased by up to 29.99%. Microscopic analysis showed a homogeneous distribution of PCM within the cellular microstructure. These findings suggest that O-PCM impregnation alters the mechanical properties of Pinus radiata wood by increasing stiffness and promoting uniform PCM distribution, supporting its potential application in passive thermal conditioning systems.