Plasticizer sorption

Such a marked variation of dielectric properties does not occur in sorbed (or desorbed) samples of monolithic phenol oligomers. Therefore, for monolithic plastics, sorption of air moisture is a secondary phenomenon, in relation to dielectric properties, whilst for plastic foams it is a primary one. 

Plasticizer testing is frequently done with polyviitylchloride, PVC, compositions. In such cases reference standard polymer is specified in Table 4 of standard. The standard also contains requirements for plasticizer sorption for various PVC grades. The method of determination of plasticizer sorption included in this standard is discussed under a separate heading in this chapter. 

ASTM D3367-98 Standard Test Method for Plasticizer Sorption of Poly(Vinyl Chloride) Resins Under... 

DIN 54802-1, Publication date 1997-09, Testing of plastics - Determination of plasticizer sorption and rate of plasticizer sorption in the heat of vinyl chloride (VC) polymers - Part 1 Planetary mixer method... 

D 3354 BLOCKING LOAD OF PLASTIC FILM D 3367 PLASTICIZER SORPTION OF PVC... 

Figure 3.221. Influence of vibratory milling time (in dry medium) on some characteristics of PVC-S. 1) M 2) specific surface (AS, %) 3) plasticizer sorption (W, %).

D3367 Plasticizer Sorption of Poly (Vinyl Chloride) Resins... 

PVC resins for general use—Determination of hot plasticizer absorption D 3367-75 (1989) Test method for plasticizer sorption of poly (vinyl chloride) resins under applied centrifugal force... 

The Q value in the majority of solvents is below 50% (Table 6.5.3). The maximal sorption was obtained for segmented polyurethane with lower physical network density. Preliminary strain leads to increase in plasticizer sorption. 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

Fig. 3. Effects of composition on physical properties. A, acetyl B, butyryl C, cellulose. 1, increased tensile strength, stiffness 2, decreased moisture sorption 3, increased melting point 4, increased plasticizer compatibiUty 5, increased solubiUties in polar solvents 6, increased solubiUties in nonpolar...

Plasticization and Other Time Effects Most data from the literature, including those presented above are taken from experiments where one gas at a time is tested, with Ot calculated as a ratio of the two permeabihties. If either gas permeates because of a high-sorption coefficient rather than a high diffusivity, there may be an increase in the permeabihty of all gases in contact with the membrane. Thus, the Ot actually found in a real separation may be much lower than that calculated by the simple ratio of permeabilities. The data in the hterature do not rehably include the plasticization effect. If present, it results in the sometimes slow relaxation of polymer structure giving a rise in permeabihty and a dramatic dechne in selectivity. 

Selective sorption by the filler sorption of one of the matrix components (residual monomer, low molecular homologs, various impurities) may lead to plasticization of the boundary layers and appearance of soft interphases [115,116]. 

Water molecules combine the tendency to cluster, craze and plasticize the epoxy matrices with the characteristic of easily diffusion in the polymer1 10). The morphology of the thermoset may be adversaly influenced by the presence of the sorbed moisture. The diffusion of the water in glassy polymers able to link the penetrant molecules is, therefore, characterized by various mechanisms of sorption which may be isolated giving useful information on the polymer fine structure. 

As a consequence, the overall penetrant uptake cannot be used to get direct informations on the degree of plasticization, due to the multiplicity of the polymer-diluent interactions. The same amount of sorbed water may differently depress the glass transition temperature of systems having different thermal expansion coefficients, hydrogen bond capacity or characterized by a nodular structure that can be easily crazed in presence of sorbed water. The sorption modes, the models used to describe them and the mechanisms of plasticization are presented in the following discussion. 

Sorption is defined as the bonding of a solute to a plastic. It is a physicochemical phenomenon related to the properties of the plastic and the chemical structure of the drug or other soluble components of the preparation. Interactions of this type can be determined by measuring the loss of the solute to the plastic at equilibrium under constant temperature conditions [11]. 

The difference between this technique and GC or HPLC is that the separation process occurs on a flat essentially two-dimensional surface. The separated components are not usually eluted from the surface but are examined in situ. Alternatively, they can be removed mechanically for further analysis. In thin-layer chromatography (TLC), the stationary phase is usually a polar solid such as silica gel or alumina which is coated onto a sheet of glass, plastic, or aluminium. Although some moisture is retained by the stationary phase, the separation process is predominantly one of surface adsorption. Thin layers are sometimes made from ion-exchange or gelpermeation materials. In these cases the sorption process would be ion-exchange or exclusion. 

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