Plasticization by water

It is speculated that the water does not diffuse as easily into the polycarbonate as into the PTMEG urethane, making the polycarbonate more resistant to plasticization by water and subsequent hydrolysis. The tensile properties of the PTMEG polyurethane eventually returned to nearly the original tensile properties, if the material was allowed to dry at room temperature for 2 weeks. This observation lends credence to the idea that the PTMEG urethane was plasticized by water. 

Dannenberg s experiments were carried out in a dry environment, and he found results that satisfied Equation (1). These stresses were only slightly relaxed when the sample was placed in a wet environment, showing small plasticization by water, and also this effect was shown to be reversible. Therefore, Dannenberg s satisfaction of Equation (1) was for low plasticization by moisture, putting doubt on Croll s explanation for moisture as the reason for variation between thick and thin coatings. 

Many of these polymers are "plasticized" by water, due to the strong influence of water on the molecular interaction. The polymers can therefore be called "hydroplastics" in contradistinction to thermoplastics. Moisture may cause a tremendous depression of the glass transition temperature. 

Maltodextrins of varying molecular weights are plasticized by water and decrease the glass transition temperature. Maltodextrins retard the crystallization of amorphous sucrose and at high concentrations totally inhibit sucrose crystallization (Roos and Karel 1991c). 

As acid paper ages, the amorphous regions of the cellulose fiber that are plasticized by water and/or humectant tend to disappear. The sorbi-tol/Kymene treatment becomes ineffective with degraded paper. This suggests that somewhat the same effect would be observed between new and degraded papers when humidified. Adrian Sclawy of the Library of Congress Preservation Research and Testing Office, carried out the experiments on humidification which are reported in Chapter 16 of this volume. 

In summary, it has been observed that the hydrogen bonding interaction of water with amorphous polymers depends both on the chemistry of the polymer and to a lesser extent, on the changes in structural relaxation accompanying plasticization by water. In addition, the plasticizing effect of moisture produces other subtle effects on the polymer spectrum. 

The results of DSC analyses of freeze-dried plum (skin and pulp at the natural proportion) presented different behaviors for each domain. At Uy, 0.75, two glass transitions (Tg) were visible (Figure 58.1a) as a deviation in base line and shifted toward lower temperatures with increasing moisture content and caused by the plasticizing effect of water (Slade and Levine, 1991). The first one, clearly visible at lower temperatures, was attributed to the glass transition of a matrix formed by sugars and water. The second one, less visible and less plasticized by water, was probably caused by macromolecules of the fruit pulp. Two Tg are normally visible in systems formed by blends of polymers (Verghoogt et al., 1994) and in edible films (Sobral et al., 2002) caused by phase separation between polymers and between proteins and plasticizers, respectively. However, Sobral et al. (2001) and Telis and Sobral (2002) also observed two Tg for persimmon and tomato, respectively, at low domain. 

To illustrate the ability of TSC to discriminate between different physical structures, the example of the two preceding hemihydrate batches has been chosen (28). As shown in Figure 11.8 and Figure 11.9, each batch presents a single intrinsic relaxation process by TSC, plasticized by water with a maximum temperature characteristic of the batch. As dehydration has the same consequence for the two hemihydrate batches, in terms of translation direction and magnitude, these modes might have the same origin. 

This discussion deals with the poly and meta acids and their derivatives made by heating appropriate combinations of reactants to form a melt or a labile solid composition from which the desired product crystallizes. Such labile solid compositions often include an amorphous phase, plasticized by water, in which ring-ring and ring-chain interconversions take place. ... 

The moisture content of both the wood and the adhesive affect the fracture behavior of adhesive bonded joints. Wood joints are especially sensitive to moisture effects as a result of the porosity and permeability of wood, which allows ready access by water to both the interior of the wood member and the adhesive layer. Irle and Bolton [57] showed that the superior durability of wood-based panels bonded with an alkaline PF adhesive compared to panels bonded with a UF adhesive was due to the ability of the phenolic adhesive to absorb and be plasticized by water. In the plasticized state, the phenolic adhesive is able to reduce stress concentrations that otherwise fracture the wood or the adhesive in urea-bonded panels. 

The low hot-wet strength of acrylics can be attributed to the maimer in which water plasticizes the unique laterally bonded acrylic fiber structure. The water lowers the Tg to approximately 70°C, but this is not sufficient to account for the extremely low modulus near the boil, since other fibers including nylon are also highly plasticized by water. However, these fibers contain a well-defined, stable, three-dimensional crystalline phase that is thought not to be penetrated by the water. Therefore, they can act to reinforce the fiber and limit the drop in modulus at temperatures above the Tg, where the amorphous phase has become rubbery. The crystalline phase in the acrylic fiber is highly imperfect (as was discussed in Section 12.4) and can probably be easily penetrated and plasticized by the water. 

WG cast films appeared red coloured, translucent, flexible, with small amounts of insoluble residues dispersed in the gelatin matrix. WG values of mechanical properties corresponded to WG plasticized by water and glycerol present in the scraps. WG cast films presented 116% Elongation at Break (El), 11 MPa for Ultimate Tensile Strength (UTS) and 78 MPa for Young s Modtilus (YM) as reported in Table 4. 

Wood is a naturally occurring composite material consisting of lignin, cellulose, hemicelluloses (= pentoses), and water a composite consisting of oriented cellulose fibers in a continuous matrix of cross-linked lignin plasticized by water. Freshly felled (green) wood contains about 40%-60% water and air-dried wood contains about 10%-20%. The composition of wood varies according to type of tree (Table 24-14). 

Stabilized acrylic fibers are extremely hygroscopic [196], gaining about 8% in moisture and elongating about 15% and can be considered as plasticized material. PAN is strongly plasticized by water. 

An adhesive is a linear or branched amorphous polymer above its Tg. It must be able to flow on a molecular scale to grip surfaces. (This definition is not to be confused with polymerizable adhesive materials, present in monomeric form. These are tacky or sticky only in the partly polymerized state. Frequently they are cross-linked thermoset, finally. Contact with the surface to be adhered must be made before gelation, in order to work.) An example is the postage stamp adhesive, composed of linear poly(vinyl alcohol), which is plasticized by water (or saliva) from below its Tg to above its Tg. On migration of the water away from the adhesive surface, it sticks. ... 

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