Glass point

Determination of the glass-transition temperature, T, for HDPE is not straightforward due to its high crystallinity (16—18). The glass point is usually associated with one of the relaxation processes in HDPE, the y-relaxation, which occurs at a temperature between —100 and —140° C. The brittle point of HDPE is also close to its y-transition. 

Functional groups Glassing point temperature (Tg) K Thermo- mechanic analysis (TMK), K... 

Note that nearly all of the characteristic "glass points" can be determined, i.e.-... 

Note that the linear coefficient of expansion, at is obtedned finm the slope of the straight fine. The glass softening point is also easily observed as is the glass transitional temperature (which is the point where the amorphous assy phase begins its transition to a crystalline phase. These glass-points can also be used to cross-check values obtained by the DTA method. 

Chompff AJ (1971) Glass points of polymer networks. In Chompff AJ, Newman S (eds) Polymer networks. Plenum Press, New York, p 145... 

TMA expansion study of an epoxy printed circuit board showing the determination of the glass point (71). 

Figure 10. Forming of a glass structure in a composed glass. The curve c-f-i shows the correlation between glass temperature and the plasticizer concentration. According to the sequence history (see text) the structure of the glass with the composition x and the temperature T is described by the coordinates of the glass point /, (x = x T0>) or the glass point f, (x = x", T ) respectively x = 1 corresponds to the pure polymer.

At conversion levels near the glass point of the monomer/ polymer solution, the free volume is low enough that the propagation reaction becomes diffusion controlled. In a development analogous to that for kt> the k behavior is written as... 

For diffusion in amorphous polymers at temperatures above their glass point, Tg, one can assume a behavior with some analogy to a liquid. On the other hand the Stokes-Einstein Eq. (6-4) for liquids was derived under the assumption that the diffusing particle is much larger in size than the matrix particles. If we let the matrix be a... 

Polymer foams are made by first mixing (molten) polymer and compressed gas at high pressures, where the gas dissolves in the polymer. The mixture is then pressed through a die, after which it has ambient pressure and cools rapidly. The solubility of the gas in the polymer drops sharply, causing the gas to desorb and to form cavities. As temperature drops below the glass point of the polymer (which is a function of pressure and thus, gas content), the bubbles are "frozen" into the polymer, thereby creating the foam. Specifications commonly require foams to contain many small bubbles. At the same time, the polymer should retain a smooth surface and its intended shape. 

Gas uptake initially is low. At a pressure of 25 bar, however, the temperature of 40°C at which the experiments were performed corresponds to the glass point of the polymer, which at ambient pressure is at 100°C. The polymer macromolecules possess the ability to move more freely against each other hence, solubility rises sharply at 25 bar. 

Three small glass points are drawn out near the shoulder and uniformly spaced round the circumference. The length of these projections is adjusted so that the float will just enter the jacket with only two projections touching the inside wall. 

Calculated from the solid. The heat capacity function of the solid was assumed to approximate those of the liquid up to the estimated glass point of 2150 K. Above the glass point the heat capacity was estimated. 

Pull off the tip with the pliers and crush and pick out the bits of baked tar. Then pull out the filaments and what you can grasp of the glass pointing up. Now, use any screwdriver, file or whatever, to give a sharp tap to the rest of the glass holding the filaments. Rotate the tool around the inside of the bulb until no more glass juts out. 

Transmission Electron Microscopy 1 glass point temperature 2.2.1 pre-wetting critical point 3.1 reference temperature 2.2.3,3.1.2.3,3.1.2.5 wetting temperature 3.1 ... 

Figure 2. Thus, the heat capacity results for collagen, elastin, and methyl cellulose confirm the dielectric results that a glass point of absorbed water occurs near 150°K.

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