Aging hydrolytic

Covers density, tensile voperties, tear, hardness, compression set, compression deflection, resilience, surface and core abrasion, heat aging, hydrolytic resistance, cut-growth resistance, impact strength, flexural modulus, ash, flexural recovery, and high-temperature sag. 

Foams prepared from phenol—formaldehyde and urea—formaldehyde resins are the only commercial foams that are significantly affected by water (22). Polyurethane foams exhibit a deterioration of properties when subjected to a combination of light, moisture, and heat aging polyester-based foam shows much less hydrolytic stabUity than polyether-based foam (50,199). 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

This is the last stage of the process. The neutralized mixture is heated to convert the y-sultones (3) into alkenesulfonates (6) and hydroxysulfonates (7). Here again it is advantageous to omit the aging stage as mixtures containing mainly (5) also contain the minimum amount of hydrolytically more persistent sultones. 

The hydrolysis reaction is very slow at ambient temperatures and is accelerated by boiling chromium salt solutions (5). The hydrolysis reaction is characterized by the transformation of the deep blue colored CrtHgOJg to green colored hydrolyzed olates. Another indication is tnatan aged or boiled Cr(III) salt solution has a higher neutralization equivalent than a fresh one due to the hydrolytically produced protons. One way to establish hydrolytic equilibria quickly is to add appropriate equivalents of bases such as NaOH to Cr(III) salt solutions. 

The decrease of peak numbers was observed, when the spectra of the same amounts of fresh (12 weeks old) and aged (9 months old) mortars were compared. This decrease might be caused by activity of ubiquitous microorganisms that live on the mortar surfaces in biofilms. Especially in mild climate conditions, algae and cyanobacteria [35] can appear here moulds (Aspergillus, Penicillium, Fusarium, Mucor) [36] and bacteria (Arthrobacter Bacillus, Micrococcus, Staphylococcus) [37,38] have been discovered as well. The microorganisms secrete various hydrolytic enzymes that can decompose the organic additives, namely proteins, and make their sample identification less sensitive... 

Fig. 1. The x-ray diffraction patterns of hydrolytic precipitation products of Al, showing how four different organic acids influence the transformation to more crystalline phases. The initial Al concentration was l.lxl 0 3M at an OH/A1 molar ratio of 3 and the solution was aged for 40 d at room temperature in the presence of 10 4M organic acid (Kwong and Huang 1979b).

The cascade of biochemical events described above enhances the cellular necrosis and tissue breakdown, leading to what meat scientists and food technologist call meat-tenderization. Since muscle is primarily protein in nature and since hydrolytic, and specifically proteolytic, activity increases during postmortem aging, muscle represents a remarkable pool of material for the production of flavor peptides and amino acids as well as other precursors for flavor development (2). 

Fe(OH)3 is somewhat arbitrary, since these materials become less soluble as they age, that is, become better crystallized as time passes here, mid-range values are chosen. Furthermore, the hydrolytic sequence given in Fig. 13.6 for iron(III) has been ignored. A small modification12 is needed to take this into account, but for simplicity we may represent the hydrolysis of Fe3+(aq) as leading directly to Fe(OH)3(s). Finally, certain of the boundary lines in Fig. 15.3 refer to a specific activity of aqueous iron ions. This is arbitrarily set at 10 3 mol L-1 (and, for convenience, activity is equated with concentration), but comparison with Fergusson14 for an iron ion activity of 10 5 shows that the qualitative features of the diagram are not very sensitive to this variable. 

We saw in Section 13.6 that hydrolysis and subsequent polymerization of aqueous metal cations can lead to the precipitation of gels. In the case of Fe(H20)63+ in mildly acidic solutions, the polymerization sequence of Eqs. 13.25 and 13.26 and Fig. 13.6 first reversibly forms cationic colloidal spherules, 2-4 nm in diameter, with the structure of 7-Fe0(0H) [double chains of Fe(0,0H)6 octahedra] on a timescale of about 100 s. These lose H+ and harden over several hours and then, over several days, form aged polymer rods, then rafts, and ultimately, after several months, needles of solid goethite [cc—FeO(OH)].1,2 Thus, aging is an important feature of hydrolytic polymerization. 

Although the general effect of the addition of bicarbonate was to increase the size of the colloidal species, Lindenbaum and Westfall obtained the opposite effect with citrate addition over the pH range 4-11, as measured by the percent of plutonium (IV) that was ultrafilterable (22). However, their plutonium concentrations were 2 X 10 5Af, and the solutions probably contained true colloids, rather than pseudocolloids, if one accepts Davydovs analysis. Lindenbaum and Westfall concluded that the mechanism of the citrate action was the complexation of plutonium, thereby preventing the formation of hydrolytic polymers. It should be noted, however, that even with a citrate-plutonium molar ratio of 1800 (3.4 X 10 4Af citrate), about 10% of the plutonium still could not pass through the ultrafilter for solutions aged up to four days (22). 

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