Wood-polymer composite

Hardness is increased appreciably. Wood-polymer composites are currently used in certain sporting equipment, musical instmments, decorative objects, and high performance flooring. 

Fibres reacted with pre-heated MAPP always exhibited larger contact angles compared with fibres reacted with as-received MAPP. FTIR studies showed that there was a higher level of ester linkages when the fibres were reacted with the pre-heated MAPP. Wood polymer composites were made by shear mixing in a twin screw extmder, and the mechanical properties of these composites were found to be superior when pre-heated MAPP was used as the coupling agent. 

Furuno, T. and Goto, T. (1979). Structure of the interface between wood and synthetic polymer. Xll. Distribution of styrene polymer in the cell wall of wood-polymer composite (WPG) and dimensional stability. Mokuzai Gakkaishi, 25(7), 488 95. 

Rowell, R.M., Moisuk, R. and Meyer, J.A. (1982). Wood-polymer composites cell wall grafting with alkylene oxides and lumen treatments with methyl methacrylate. Wood Science, 15(2), 90-96. 

Schneider, M.H. (1995). New cell wall and cell lumen wood polymer composites. Wood Science and Technology, 29(4), 121-127. 

Schneider, M.H. and Witt, A.E. (2004). History of wood polymer composite commercialization. Forest Products Journal, 54(2), 19-24. 

Schneider, M.H., Brebner, K.I. and Hartley, I.D. (1991). Swelling of a ceU lumen filled and a cell-wall bulked wood polymer composite in water. Wood and Fiber Science, 23(2), 165-172. 

Simonsen, J. (1998). Lack of dimensional stability in cross-linked wood-polymer composites. Holzforschung, 52(1), 102-104. 

The book opens with a paper on the structure and composition of wood to define the material under discussion and then considers molds, permeability, wood preservation, thermal deterioration and fire retard-ance, dimensional stability, adhesion, reconstituted wood boards such as fiberboard and particleboard, plywood, laminated beams, wood finishes, wood-polymer composites, and wood softening and forming. A final paper treats the common theme of wastewater management. Only one of the papers presented at the meeting is not included in this volume, and its subject of conventional wood preservation methods is adequately treated in detail elsewhere (e.g., Nicholas, D. D., Ed Wood Deterioration and Its Prevention by Preservative Treatments, 2 vols., Syracuse University Press, 1973). 

Wood-Polymer Composites and Their Industrial Applications... 

Soluble dyes can be added to the monomer solution to color the final wood-polymer composite. Any color of the visible spectrum can be added, browns to simulate black walnut, red and blues for the bicentennial theme. The color emphasizes the grain structure of the particular species and combines with the polymer to add a three demensional depth not present in surface finished wood. A dense black wood-polymer is difficult to obtain because... 

Some research has been done on the addition of polar solvents to the nonpolar monomer in an attempt to swell the cell wall structure and anchor it in a swollen state (9). This can be done and the antishrink efficiency (ASE) does increase, but after the solvent evaporates, the wood is only partially loaded which in turn decreases the physical properties. Wood-polymer composites normally have about 10-15% ASE, which means that there is some penetration of the cell wall structure to reduce the swelling over that of untreated wood. 

Radiation Process. Commercial production of wood-polymer composites began in the mid 1960 s using the radiation process. 

Catalyst-heat Process. At the present time production using the catalyst-heat process for making wood-polymer composites is much smaller than the radiation process, but its use is much more widespread throughout the United States and the world. The simplicity of the catalyst-heat process and low initial cost to begin production is the key to the use by small companies who make high cost small volume items. 

Fifteen years ago, when wood-plastic composites were first introduced many people predicted that this process would solve the problem of wood dimensional stability and great claims were made for its future use. Now that the physical properties of wood-polymer composites are better understood, specific commercial products are being produced which take advantage of the desirable aesthetic appearance, the high compression strength, increased hardness and abrasion resistance and improved dimensional stability. Future use of wood-polymer composites will depend upon the imagination of the producer and the market place. 

Figure 2 Creep-recovery tests of chemically treated woods. U, untreated wood Fs, vapor phase formalization F, liquid phase formalization A, acetylation PO, etherification with propylene oxide MG, treatment with maleic acid and glycerol PFl, impregnation with low molecular weight phenol-formaldehyde resin PEG-ICP, impregnation with polyethylene glycol (PEG-IOOO) WPC, formation of a wood- polymer composite (PMMA) WIC, formation of a wood-inorganic material composite.

Figure 5 Effects of wood-polymer composite treatment on relationship between logarithm of E /y and logarithm of tan 5. (A, A) Experimental values of untreated and treated specimens. Dotted line represents experimental correlation line for untreated specimens. Various values of polymer rigidity ( p) and loss tangent (tan 8p) were simulated (curves a to 0-...

Treatment of solid wood over the years for increased utility included many chemical systems that affected the cell wall and filled the void spaces in the wood. Some of these treatments found commercial applications, while some remain laboratory curiosities. A brief description of the earlier treatments is given for heat-stabilized wood, phenol-formaldehyde-treated veneers, bulking of the cell wall with polyethylene glycol, ozone gas-phase treatment, ammonia liquid- and gas-phase treatment, and p- and y-radiation. Many of these treatments led to commercial products, such as Staybwood, Staypak, Im-preg, and Compreg. This chapter is concerned primarily with wood-polymer composites using vinyl monomers. Generally, wood-polymers imply bulk polymerization of a vinyl-type monomer in the void spaces of solid wood. 

Safety requirements must be satisfied before a cobalt-60 source can be installed and licensed. Radiation-trained personnel must be on the staffbefore a license can be issued. At least 500,000-1,000,000 Ci (curies) of cobalt-60 are required in a production source for making wood-polymers, and at 1.00 or more per curie, a considerable investment must be made before production can begin. Besides cost considerations, the cobalt-60 radiation process does have some distinct advantages in making wood-polymer composites. Because the monomer is not catalyzed it can be stored at ambient conditions as long as the proper amount of inhibitor is maintained. The rate of free radical generation is constant for a given amount of cobalt-60 and does not increase with temperature. 

When the heat of polymerization is released quickly in a wood-monomer composite the high temperature increases the vapor pressure of the moisture in the cell walls and distills the moisture out of the wood. The change in volume of the cell wall causes changes in dimensions which are manifested by shrinkage and distortion of the original wood shape. Wood-polymer composites cured by the catalyst-heat process must be machined to the final shape after treatment. Conversely, because the heat of polymerization by y-rays is released over a longer period of time, the temperature of the wood-polymer remains low and not as much cell w l moisture is driven off. Therefore, the amount of distortion and dimensional change is somewhat less (30, 31). 

Additives Effect on the Catalyzed Monomer Solution. Soluble dyes can be added to the catalyzed monomer solution to color the final wood-polymer composite. Any color of the visible spectrum can be added, browns to simulate black walnut, red and blues for national colors. The color emphasizes the grain structure of the particular species and combines with the polymer to add a three-dimensional depth not present in surface-finished wood. A dense black wood-polymer, so desirable for musical instruments, is difficult to obtain because of wood s light color and the tendency of the microstructure to chromatographically separate a dye of several components into its separate colors. Dyes have an inhibiting effect on the polymerization of wood-monomer composites, some more so than others. Additional catalyst can be added to overcome this inhibition, but in the radiation process of a given geometry additional time must be allowed for complete curing. 

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