Viscosity aging data

Analysis of the viscosity aging data, Table III, reveals one significant trend. In general, as dryer temperatures are increased, plastisol viscosity aging decreases, Figure IX. The... 

Fig. 3.15. Aging effects in polymer solutions. Quotient of the time dependent viscosity of a polymer solution, and the viscosity of a freshly prepared solution, tiq, as a function of the time f. The viscosity can Increase with time as shown for poly(vinyl alcohol) (PVA), or decrease as shown for poly(acrylamide) (PAAm) in aqueous solution. Changing the solvent to dimethylsulfoxide (DMSO) or ethylene glycol (EG) can prevent the aging. Data from [30]...

In the following sections, synthesis of the anionic polymers, copolymer molecular weight, limiting viscosity number, electrolyte effects, solution shear thinning, screen factor, polymer radius of gyration, and solution aging will be discussed and data on the copolymers presented. 

Table IV gives the Attrition Indexes for the commercial and experimental samples. These values are reported for microspheres that were spray dried before the viscosity of the slurry exceeded 100 cP. The data show, again, that sol age and particle size of the CP alumina affect attrition. Sol age also seems to reduce the influence of the CP-2 as a binder. The Reference (4) has an AI of about 3 which is comparable to the index for CP-2(4). The important point here is that the alumina particles can be incorporated into a standard FCC formula to change catalytic activity without a detrimental effect on attrition resistance.

Data on Uvimer 740 Is presented in Table VII, while Uvimers 765 and 775 are compared in Table VIII, Uvlmer 740 is somewhat stiffer and harder than either 765 or 775, primarily due to the difference in the structures of oligomers D and E. It should also be noted that Uvimers 765 and 775 have better color and do not exhibit yellowing on aging. Since the latter two resins employ the same basic oligomer, it is evident that on the basis of viscosity reduction 2-ethoxyethyl acrylate is a more effective diluent than the 2-ethylhexyl acrylate/hydroxyethyl acrylate combination. Thus, it is possible in Uvimer 775, to employ a lower level of reactive diluent and thereby obtain a harder, stiffer, faster-curing formulation. 

Ryles (1988) observed that the HPAM solution viscosity remained stable at >100% retention until the polyacrylamide was hydrolyzed to about 60 mol%, when the concentration was below 200 ppm. Between 60 and 80 mol%, polymer solutions lost almost one half of their original viscosity. Thus, when hydrolysis is limited to less than about 60 mol%, excellent long-term stability can be achieved. This observation is supported by data from Han et al. (2006a). Increasing the concentration to 500 ppm had a more pronounced effect on viscosity retention, even though the polyacrylamide remained soluble. Mg " had similar but less effect than Ca +. At 50°C, the rate of hydrolysis was so slow that viscosity was retained essentially intact after 21 months of aging. Note that the tests were under anaerobic condition. 

A follow-up study of 343 Finnish viscose rayon workers was performed to examine the incidence of cardiovascular mortality from 1967 to 1982 (Nurminen and Hemberg 1985). Exposure to carbon disulfide varied greatly (approximately 22 ppm to <10 ppm), with a decrease in exposures after 1972. Within the first 5 years of follow-up (1967-1972), there was a 4.7-fold increase in ischemic and heart disease mortality compared with a cohort of paper mill workers. In the period of 1972-1974, the relative risk ratio was 3. 2. After all workers with high coronary risk factors were removed from exposure (19% of the cohort was exposed in 1977 compared to 53% in 1972), the risk of cardiovascular death was reduced to a ratio of 1.0 in the years 1974-1982. This study indicates that the cardiotoxic effects of carbon disulfide may be reversible with removal of individuals from the toxic environment. Caution must be used in interpreting these data because of the increase in the incidence of cardiovascular events in the aging cohort population and the possibility that carbon disulfide accelerates death in high-risk individuals. 

Interestingly, the viscosity of polysoap solutions is frequently subject to important ageing effects [75,99,130,163,284] and temperature effects [75,130], dropping asymptotically towards its final value. The decrease can amount to 90% of the initial value and can endure for up to one month [99, 163]. These effects are not well understood but are putatively attributed to conformational changes. The phenomenon has to be kept in mind when evaluating viscosity data, and should always be verified - or excluded - in viscosity studies of polysoaps. 

Stability testing was conducted at 50°C for 10 and 30 days. The pH of the latexes was adjusted to 7.0 using triethylamine, then, the pH and viscosity measured after oven aging. The data is listed in Table VI. The pH data indicates no difference among the samples (Figure 6). There are some differences in the change of viscosity (Figure 7), however, these results do not indicate a problem of latex stability as a result of VEC incorporation. 

Solutions of starch-acrylamide, graft copolymers, were prepared by J. J. Meister and the solution viscosity was researched with the goal to prepare highly viscous solutions He was able to prove, that graft copolymers also age. However, the data have another feature not found in the viscosities of the PAAm-solutions. That is, that graft-copolymer solution viscosity increases between 24 and 48 hours. After this a typical viscosity decrease can be observed as was mentioned earlier. 

Blood and lymphatic vessels are soft tissues with densities which exhibit nonlinear stress-strain relationships [1]. The walls of blood and lymphatic vessels show not only elastic [2, 3] or pseudoelastic [4] behavior, but also possess distinctive inelastic character [5, 6] as well, including viscosity, creep, stress relaxation and pressure-diameter hysteresis. The mechanical properties of these vessels depend largely on the constituents of their walls, especially the collagen, elastin, and vascular smooth muscle content. In general, the walls of blood and lymphatic vessels are anisotropic. Moreover, their properties are affected by age and disease state. This section presents the data concerning the characteristic dimensions of arterial tree and venous system the constituents and mechanical properties of the vessel walls. Water permeability or hydraulic conductivity of blood vessel walls have been also included, because this transport property of blood vessel wall is believed to be important both in nourishing the vessel walls and in affecting development of atherosclerosis [7-9]. 

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