Swelling cell wall

Saka and Yakake (1993) chemically modified wood samples with 3-isocyanatopropyl-triethoxysilane (IPTES) (Figure 7.9c). Wood was impregnated with acetone solutions of IPTES of different concentrations. Where the wood had been pre-swollen by treating with pyridine vaponr, a maximnm WPG of 27 % was obtained, whereas without pre-swelling of the cell wall a WPG of only 7 % was obtained. Pyridine also serves as a catalyst for the reaction of isocyanate with wood. SEM-EDXA showed the presence of silicon in the cell walls of the treated wood. Becanse of the lower WPG obtained without cell wall swelling, ASEs of the order of 20 % were obtained, compared to about 60 % when swelling of the cell wall was used prior to reaction. 

The plant cell wall is a composite of cellulose (the main fibre) plus shorter lengths (hemicellulose) that help bind the fibre, plus pectin (the main matrix adhesive) and some proteins. There are fruits that have a soft melting texture when ripe (e.g., avocado and blackberry) in which the cell wall swells noticeably. This swelling is related to the degree of solubilisation of the pectin (Redgwell et al. 1997) which can be removed in vitro using enzymes or other chemicals. 

Maximum Shrinking and Swelling of the Cell Wall. When dry wood is immersed in water the cell wall swells in proportion to the volume of water adsorbed. If it is assumed that the sorbed water has the same density as free liquid water, the percent swelling Su of the cell wall can be approximated by Equation 5. 

Pectin concentration can be estimated from the in vitro experiments on cell wall swelling (qv). For the determination of ion and organic add content, two complementary approaches may be used. Apoplastic sap may be expressed after application of pressure and its ion and solute content determined.14 This will... 

Many monomers have been studied, including acrylonitrile, acrylates, methacrylates, styrene, and t-butylstyrene (ii). Most of the research done with these monomers has shown that the formed polymer is in the lumen rather than in the cell wall. Swelling, cell-wall-penetrating solvents can be used to achieve cell wall penetration, so that the polymers that form are in both the cell wall and the lumen. 

Many classes of adhesives are used in wood bonding because of different production and end-use conditions. Most adhesives can give acceptable wood bonds if the use conditions are not too strenuous or at high moisture levels. The interaction of a hot-melt adhesive with wood should be quite different from that of a water-borne adhesive, not only because of viscosity differences but also because of the lack of cell wall swelling by hot-melt adhesive. In addition, some adhesives penetrate and change the mechanical properties of cell walls [10,18], but it not known if all adhesives that penetrate cell walls change their mechanical properties. 

Y. Li, X. Dong, Y. Liu, J. Li, and F. Wang, Improvement of decay resistance of wood via combination treatment on wood cell wall Swell-bonding with maleic anhydride and graft copolymerization with glycidyl methacrylate and methyl methacrylate. Int. Biodeter. Biodegrad. 65 (7), 1087-1094(2011). 

Cell wall Peptidoglycan a rigid framework of polysaccharide cross-linked by short peptide chains. Some bacteria possess a lipopolysaccharide- and protein-rich outer membrane. Mechanical support, shape, and protection against swelling in hypotonic media. The cell wall is a porous nonselective barrier that allows most small molecules to pass. 

The penicillins have the same type of action against bacteria. Fbnicillins prevent bacteria from using a substance that is necessary for the maintenance of the bacteria s outer cell wall. Unable to use this substance for cell wall maintenance, the bacteria swell, rupture, assume unusual shapes, and finally die (Pig. 7-1). 

Pectins is a general term for a group of natural polymers based on polymerized galacturonic acid partly esterified with methanol. In addition these polymers must be considered as copolymers due to existence of neutral sugar branched zones. [1]. Some uronic acid units may also be esterified on 0-2 or 0-3 position with acetic acid. The pectins occur in the cell wall of higher plants and control at least partly the mechanical properties, the ion exchange properties and the swelling of the cell walls. 

Wood modification can improve the dimensional stabilization of wood by two mechanisms. Where the cell wall is filled in some way by the reagent (whether covalently bound or not), the cell wall is swollen. When the dimensional stability of the modified wood is subsequently determined, the wood can then only swell by an additional amount, which is dependent upon the bulking of the cell wall due to the volume occupied by the modifying agent. This is illustrated in Figures 2.8 and 2.9b. 

Figure 2.11 The change in volumetric swelling behaviour due to (a) loss of cell wall material but not cell wall bulking agent, and (b) loss of cell wall cross-linking agent.

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