Lumen-filling Treatments

The types of chemical treatments involved in the conservation of archaeological wood are (i) lumen-filling treatments that fill the spaces within the wood with an inert chemical to provide structural support and prevent collapse, (ii) bulking treatments that enter the cell walls and reduce cell wall shrinkage, and (iii) surface coatings that cover the surface of a dry object. 

Lumen-filling chemicals used by conservators include high molecular weight, solvent-based polymers such as styrene, methyl methacrylate and butyl methacrylate. These are usually polymerised by heat or gamma irradiation. The problem with these chemicals is that they produce a composite object in which a significant part is the polymer. This often results in a considerable increase in object density. 

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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 ]. 

There are two types of pressure treatment, the full-cell and the empty-cell. The full-cell process seeks to fill the cell lumens of the wood with the preservative liquid, giving retention of a maximum quantity of preservative. The empty-cell process seeks deep penetration with a relatively low net retention of preservative by forcing out the bulk liquid in the wood cells, leaving the internal capillary structure coated with preservative. 

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.

For simplicity, we assume that no filling of the cell wall is provoked by the treatments, so that Vp = 0, as well as no change of lumen sizes and specific gravities or Young s moduli of microfibrils. Only the matrix volume, specific gravity, and mechanical properties are modified by the treatment. 

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. 

WPC), WPG 138%, indicates that a small amount of this polymer may enter the cell wall, but in general this treatment only fills the lumen space. The increase in specific gravity decreases E /y. Water can still enter the cell wall and act as a plasticizer, so that tan 8 increases as the RH increases. 

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. 

Fig. 5.12a, b. A 71-year-old male patient with bronchogenic carcinoma invading the mediastinum and brain metastasis. Superior vena cava obstruction syndrome was treated by placement of a Wallstent endoprosthesis in the superior vena cava. At 3 weeks after endoluminal treatment, obstruction symptoms recurred, a Phlebography obtained by a femoral approach and catheterization of the stent lumen showed stent obstruction, and extensive filling of mediastinal veins, b After balloon dilatation at the junction of the stent with the internal jugular vein, a residual stenosis (arrow), due to insufficient stent covering of mediastinal tumor extent was evident... 

Fluid-filled glass micropipettes are inherently more noisy than their metal counterparts. In addition to feTRA/ noise associated with the metal-electrolyte connector in the stem, we must deal with ionic flow. Ion flow occurs between the electrolyte in the lumen and the external electrolyte of the medium in which the electrode is placed. Ion movement depends upon tip size, ion concentrations in the two electrolytes, current in the electrode, pressure differentials, and other factors. It is a complex problem and not amenable to easy theoretical treatment. In general, the smaller the tip diameter, the lower the noise figure for glass electrodes. Little ionic flow occurs in pipettes with tips < 1 /x diameter. 

Metcalfe et al. (2003) tested cold hibernated elastic memory (CHEM) polyurethane for the treatment of lateral wall aneurysms on the carotid arteries of dogs. The SMP polyurethane was made in open cellular (foamy) structures with the glass transition temperature of 60 C. After 3 weeks, in vivo experiments showed that the CHEM foam led to improved aneurysm embolization, and a thick neoin-tima formation by favoring the ingrowth of cells. However, residual necks and recurrences were observed in some cases due to the incomplete filling of the vascular lumen. 

Antibiotic-lock therapy (ALT) is used in addition to systemic treatment for CVC-related infections. After filling both catheter lumens with a mix of antibiotic and anticoagulant at the end of dialysis (catheter locking), antibiotic concentrations inside the catheter reach very high levels, much higher than the con-... 

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