Antiplasticization effect

In some polymers, addition of very small amounts of diluent seems to fill up the holes in the liquid structure and the dynamics actually slow down. This antiplasticizer effect has not yet been examined with PCS, but this technique should prove very useful. The whole area of the effect of dilution on the PCS of bulk polymers is very promising and virtually unexplored. 

Crosslink density directly affects E0 (through rubber elasticity), and has an indirect influence on E (through the antiplasticization effect). Cole-Cole plots open the way to analyzing the distribution of relaxation times (the exponents a and y or % or % are linked to the width of the distribution of relaxation times). According to the results of Table 11.3, these exponents seem to depend more on the molecular-scale structure (they vary almost... 

Sub-glass transitions are generally determined by the molecular (local) scale structure. Their location in the (t, T) space undergoes only a second-order influence of the macromolecular (network) structure through internal antiplasticization effects. By contrast, glass transition is directly under the influence of the network structure (Chapter 10), so that it appears interesting to study the influence of crosslinking on the parameters of the time-temperature relationship (WLF equation) ... 

In addition to lowering the water activity and forming sugar bridges between starch chains restricting flexibility, there is also an antiplasticizing effect of saccharide solutions relative to water.78... 

Some plasticizers used at low levels (up to 15 %) can increase brittleness, as a consequence of increased orientation of the plastic and formation of crystalline regions. This antiplasticizing effect may be overcome by increasing the amount of the plasticizer that dissolves the crystallites. 

Oxygen transport through membranes of iPP/HOCP blends was studied as a function of the weight fraction of the two components. The results showed that increasing HOCP content lowers oxygen permeability and difiusivity through the films. The HOCP has an antiplasticizing effect and produces a hmitation in penetrant mobfiity (11). 

Certain authors have shown that at low concentrations of non-volatile plasticizing agent, an antiplasticization effect can occur [LOU 97a]. Because of the strong interactions between the plasticizing agent and the starch, a network of... 

The concentration of plasticizer is important since too low a concentration results in rigid and brittle membranes. This is termed the antiplasticization effect, and the minimum plasticizer concentration required is dependent on the plasticizer type and the base polymer used. For example, for PVC PIMs, this concentration is around 20 wt%. If the plasticizer concentration is too high, then excess plasticizer can exude to the PIM surface and the thin film formed can inhibit transport across the membrane. Also, such PIMs are normally mechanically weak and difficult to use. 

FIGURE 13.1 Experimental T values resulting from the antiplasticization effect of PVP90 (o), PVP12 (o), or MD simulated values for PVP (>t) in amorphous mixtures with indomethacin. r predicted is based on the Gordon-Taylor equation with the value of K estimated using the Couchman and Karasz relationship. 

Miscibility is one of the key factors for the successful increase of tensile properties and decrease of Tg. Most literature studies used a maximum plasticizer concentration of 20 wt%, which allowed for the fabrication of a priori fully miscible blends. Correlation between yield stress and plasticizer concentration is a sign of miscible blends, as yield stress can serve as a measurement of macromolecular mobility. Miscibility limits in PLA observed by some authors were 5 wt% DOA measured by DSC, 10 wt% DINCH (by DSC and FESEM), 20 wt% for DBS (DSC) and CMS 15 wt% (DSC). Furthermore, below 10 wt% DOA, Muriaru et al. observed a decrease in the impact strength, explained by the antiplasticization effect. 

In addition, it is foimd that moisture increases the intensity of the relaxation and reduces its activation energy, as well as decreases the peak height of the Y relaxation with little change in activation energy. The decrease in y intensity has been referred to as an antiplasticization effect, since it is associated with an increase in modulus and decrease in impact strength. This is discussed further below in reference to impact behavior. The increase in intensity has been associated with the motion of water molecules H-bonded with carbonyl and amide groups about the H-bond axis (84,90). 

Similar observations are found in the case of PVC (Bohn 1963 Pezzin et al. 1967), where the addition of normal plasticizers actually results in antiplasticization until the level of 15-20% plasticizer is reached. At this point modulus and tensile strength begin to decrease because the Tg has been reduced to below room temperature. Pezzin et al. (1967) show that this antiplasticization effect is closely related to a reduction in the intensity of the p relaxation centered around -40 °C. The ability of polymers to be antiplasti-... 

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