Adhesives for Achieving Durable Bonds with Acetylated Wood
Abstract
:1. Introduction
2. Materials and Methods
2.1. Bond Strength Study
2.1.1. Experimental Design
2.1.2. Acetylation
2.1.3. Bonding
2.1.4. Adhesive Testing
- Submerged specimens in tap water at room temperature in a pressure vessel.
- Maintained a vacuum of 635 ± 85 kPa for 30 min.
- Maintained a pressure of 448 ± 35 kPa for 30 min.
- Remained submerged in water until tested.
2.1.5. Shear Data Analysis
2.2. Analysis of Hydroxyl Groups on Wood Surface
2.2.1. Treatment with Trifluoroacetic Anhydride
2.2.2. X-ray Photoelectron Analysis
2.2.3. Curve Fitting
3. Results
3.1. Surface Treatment and Analysis
3.2. Bonding Studies
4. Discussion
- As the degree of acetylation increases, the wood absorbs less water.
- ○
- This slows the setting of the waterborne adhesives, leading to overpenetration or disruption of polymer formation of those that cure by condensation (water formation).
- ○
- This also slows the setting of adhesives that need water for curing, such as isocyanates, which is normally provided by adsorbed water for unmodified wood for curing.
- Acetylation bulks up the wood, allowing for less water absorption to occur upon soaking.
- ○
- This reduces the swelling and shrinking of wood as the humidity changes, putting less internal force on the bondline.
- ○
- Upon water soaking, the acetylated wood is not plasticized like the unmodified wood; thus, for wet tests, more of the applied load is transferred to the bondline.
- ○
- This reduces the free volume for the adhesive to enter into the cell wall.
- ○
- This may allow different adhesive components to infiltrate the cell wall compared to the unmodified wood.
- Not all acetylated wood surfaces are the same.
- ○
- Method of acetylation may influence the distribution of acetyl groups, and post-treatment steps, such as washing to remove unreacted acetic anhydride and acetic acid, may extract some wood components.
- ○
- As shown in this study, planing of the surface alters the surface by increasing the surface hydroxyl content.
5. Conclusions
Supplementary Materials
Acknowledgments
Author Contributions
Conflicts of Interest
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Specimen | [CF3]/[ΣCarbon] | Free OH Relative to Control |
---|---|---|
Yellow-poplar | 0.13 | 1.00 |
Acetylated poplar | 0.011 | 0.09 |
Acetylated poplar with planing | 0.054 | 0.42 |
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Frihart, C.R.; Brandon, R.; Beecher, J.F.; Ibach, R.E. Adhesives for Achieving Durable Bonds with Acetylated Wood. Polymers 2017, 9, 731. https://doi.org/10.3390/polym9120731
Frihart CR, Brandon R, Beecher JF, Ibach RE. Adhesives for Achieving Durable Bonds with Acetylated Wood. Polymers. 2017; 9(12):731. https://doi.org/10.3390/polym9120731
Chicago/Turabian StyleFrihart, Charles R., Rishawn Brandon, James F. Beecher, and Rebecca E. Ibach. 2017. "Adhesives for Achieving Durable Bonds with Acetylated Wood" Polymers 9, no. 12: 731. https://doi.org/10.3390/polym9120731