Abstract
To evaluate the effects of phenol formaldehyde (PF) resin modification on wood cell walls, Masson pine (Pinus massoniana Lamb.) wood was impregnated with PF resin at the concentrations of 15%, 20%, 25%, and 30%, respectively. The penetration degree of PF resin into wood tracheids was quantitatively determined using confocal laser scanning microscopy (CLSM). The micromechanical properties of the control and PF-modified wood cell walls were then analyzed by the method of quasi-static nanoindentation and dynamic modulus mapping techniques. Results indicated that PF resin with low molecular weight can penetrate deeply into the wood tissues and even into the cell walls. However, the penetration degree decreased accompanying with the increase of penetration depth in wood. Both the quasi-static and dynamic mechanics of wood cell walls increased significantly after modification by the PF resin at the concentration less than 20%. The cell-wall mechanics maintained stable and even decreased as the resin concentration was increased above 20%, resulting from the increasing bulking effects such as the decreased crystallinity degree of cellulose. Furthermore, the mechanics of cell walls in the inner layer was lower than that in the outer layer of PF-modified wood.
Highlights
Phenol formaldehyde (PF) is one of the most common resins used in the wood industry, such as in the manufacturing of oriented strandboard (OSB), plywood, and cross-laminated timber (CLT), due to the advantages of low initial viscosity, water repellency, and excellent temperature stability [1,2,3]
The nano-penetration of PF resin in wood cell walls has been intensively analyzed because it can provide the opportunity for cross-linking reactions between PF resins and the functional groups in wood polymers. Both the chemical and mechanical properties of wood cell walls penetrated by PF resin during the wood gluing were characterized by AFM-based infrared spectroscopy (AFM-IR), which further confirmed that the physical filling and the possible chemical reactions are increasingly considered as the major contributions to the improved wood properties such as bending strength and hardness [15,16]
The in situ quasi-static and dynamic mechanical properties of wood tracheid cell wall modified by phenol formaldehyde resin was investigated using nanoindentation and dynamic modulus mapping technique
Summary
Phenol formaldehyde (PF) is one of the most common resins used in the wood industry, such as in the manufacturing of oriented strandboard (OSB), plywood, and cross-laminated timber (CLT), due to the advantages of low initial viscosity, water repellency, and excellent temperature stability [1,2,3]. Both the chemical and mechanical properties of wood cell walls penetrated by PF resin during the wood gluing were characterized by AFM-based infrared spectroscopy (AFM-IR), which further confirmed that the physical filling and the possible chemical reactions are increasingly considered as the major contributions to the improved wood properties such as bending strength and hardness [15,16]. A modulus mapping was generated to provide dynamic mechanical properties, including the storage modulus (Er ) and loss modulus (Er”) This method has been successfully applied for analyzing the dynamic mechanical properties of wood cell walls. The in situ quasi-static and dynamic mechanical properties of wood tracheid cell wall modified by phenol formaldehyde resin was investigated using nanoindentation and dynamic modulus mapping technique. The local variation in micromechanics of PF-modified cell walls at different PF concentrations was analyzed to increase the understanding of wood chemical modification mechanism
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