Lumen-filling modification

Outer = 0,5 mm thickness of exposed surface Inner = portion under exposed surface. 2/ Bonded = chemically bonded Filled = lumen-filled modification. 

Southern pine with a dual treatment of chemical modification with butylene oxide or butyl isocyanate followed by lumen-fill treatment with methyl methacrylate, or southern pine impregnated with methyl methacrylate and polymerized in situ, resulted in modified woods that were resistant to accelerated weathering and to ultraviolet light alone. Physical, chemical, and microscopic changes occurring as a result of ultraviolet light irradiation are described. 

Chemical modification will be defined for this chapter as any chemical reaction between some reactive part of a wood cell wall component and a simple single chemical reagent, with or without catalyst, that forms a covalent bond between the two components. This excludes in situ polymerizations of monomers in the lumen structure of the wood and those reactions that result in cell wall-penetrating polymer systems that do not result in any cell wall attachment. It is well known that lumen-filling polymer treatment results in large improvements in mechanical properties, but these are mainly a result of the properties of the new polymer introduced [ 1 ]. 

Figure 1 Model for the chemical treatment of wood. (A) Cellular level. (l)-(3) Untreated cell wall, (4)-(6) treated cell wall (1) untreated (4) no chemical deposits in lumen (2) and (5) deposits on cell wall surface (3) and (6) filling of lumen. (B) Modification of lignocellulosic material at molecular level, (o) Hydroxyl group available for hydrogen bonding ( ) substitution of hydroxyl group ( ) bulking agent.

We classify chemical modifications of wood with respect to their actions at both the cellular and molecular levels. Six types of modification of a single cell are represented in Fig. lA [1,2]. The cell wall remains untreated in A-1 to A-3 and the cell wall is modified in A-4 to A-6. A resin or any other product is deposited on the internal faces of the lumen in A-2 and A-5, whereas the lumen in A-3 and A-6 is filled partially or totally. 

Various theoretical cases of polymer properties were considered in Fig. 6. The values of Ep or Tp used in the simulation are not necessarily those of existing polymers. They were tried in order to illustrate the limits of properties modified by treatments involving no modifications of the cell walls. The case (f), for instance, equivalent to filling the lumens with pure cellulose, is the only one inducing an increase of E /y and a decrease of tan 8 at the same time. 

An endless variety of treatments have been contemplated by researchers. These involve filling accessible spaces (either the lumens or pores in the cell wall) with inert material, or some form of chemical modification of the wood tissue. 

Bednar and Fengel (11) deduced some modification of the cell wall constituents from the increased density in transmission electron microscopy (TEM) of secondary cell walls in this state. Especially in fiber cells, the swelling of the Sg layer can be so extensive that it bulges into the lumen and sometimes even fills it completely. This swelling starts from the lumen side of the Sg and stops at the Sg-Si boundary (Figure 3). 

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