Ageing dried

Hydrolysis and Polycondensation. As shown in Figure 1, at gel time (step C), events related to the growth of polymeric chains and interaction between coUoids slow down considerably and the stmcture of the material is frozen. Post-gelation treatments, ie, steps D—G (aging, drying, stabilization, and densification), alter the stmcture of the original gel but the resultant stmctures aU depend on the initial stmcture. Relative rates, of hydrolysis, (eq. 2), and condensation, (eq. 3), determine the stmcture of the gel. Many factors influence the kinetics of hydrolysis and... 

High amounts of a,co-dicarboxylic acids (mainly suberic, azelaic and sebacic) in a paint sample are indicative of the presence of an aged drying oil. This is because dicarboxylic acids, of which azelaic is the most abundant, are produced during the auto-oxidation of the polyunsaturated acylic chain present in drying oils. 

The chromatogram in Figure 7.6 shows a typical profile of an aged drying oil. It was obtained in the analysis of a reference layer of linseed oil on glass pertaining to the reference paint material collection of Opificio delle Pietre Dure (Florence, Italy), artificially aged by irradiation with a mercury lamp at 365 nm for 21 days, at a temperature of 20 °C and 80% relative humidity [9]. 

The sol is made of a stable suspended solution of metal salts or solvated metal precursors containing solid particles of nanometer diameter. Polycondensation or polyesterification results in the appearance of particles in a new phase called the gel . Aging, drying and dehydration are steps required to achieve solid-form ultra-fine particles. Coarsening and phase transformation occur simultaneously with aging. Gel drying is associated with the... 

Following are the tests described in this Spec wet tensile strength, adhesion at low temp, moisture-vapor transmission rate, water-penetration rate corrosion, accelerated aging, dry tensile strength and tearing resistance... 

TABLE 1. EAP TYPING OF AGED-DRIED BLOODSTAINS STORED AT 25 C... 

Light and Electron Microscopy Studies in Aged Dry Skin. 119... 

LIGHT AND ELECTRON MICROSCOPY STUDIES IN AGED DRY SKIN... 

Glycerol is effective in enhancing hydration of the stratum corneum in dry skin.29 Recently it has been shown that the epidermal water/glycerol transporter aquaporin-3 in deficient mice leads to severely impaired stratum corneum hydration.9 In these mice, stratum corneum glycerol content was reduced threefold. And it was shown that glycerol replacement corrects the defects in these mice.30 However, it has not yet been published whether changes in the aquaporin-3 transporter occur in human dry skin or in aged dry skin. 

Jin, K., Higaki, Y., Takagi, Y., Higuchi, K., Yada, Y., Kawashima, M., and Imokawa, G., Analysis of beta-glucocerebrosidase and ceramidase activities in atopic and aged dry skin, Acta Derm. Venereol., 74, 337-340, 1994. 

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