Plasticizers concentration effects

Historical Perspective General Theory of Plasticization Plasticizer Compatibility Compatibility Stability Fusion Properties of Plasticizers Plasticizer Concentration Effects Heat Stability Odor Development... 

Overall Assessment of Properties. Table 3 shows the effect for each criterion of increasing plasticizer concentration, increasing the size of the plasticizer molecule, increasing the linearity of the plasticizer molecule, and changing the acid constituent of the ester. An I indicates improved performance for a particular property, a P indicates poorer performance. I and P in parentheses indicate that any changes tend to be marginal. 

Fourth, molded-in metal should be avoided whenever alternate methods will accomplish the desired objective. If it is essential to incorporate such inserts, they should be shaped so that they will present no sharp inside comers to the plastic. The effect of the sharp edges of a metal insert would be the same as explained in the first point above, namely, brittleness and stress concentration can occur. The cross-section that surrounds a metal insert should be heavy enough that it will not crack upon cooling. A method of minimizing cracking around the insert is to heat the... 

Figure 8 Effect of plasticization or copolymerization on (A) the modulus-time and (B) modulus -temperature curves. The curves correspond to different plasticizer concentrations or to different copolymer compositions. Curve B is unplasticized homopolymer A is eithei a second homopolymer or plasticized B.

Ultrafiltration membranes are usually manufactured from tough plastic-based polymers, such as polyvinyl chloride or polycarbonate. A range of membranes are available which display different cut-off points (Figure 3.20). Membranes displaying cut-off points of 3, 10, 30, 50 and 100 kDa are most commonly used. Thus, if the protein of interest displays a molecular mass of 70kDa, it may be concentrated effectively by using an ultrafilter membrane displaying a molecular mass cut-off point of 50 kDa. Ultrafiltration is a popular method of concentration because ... 

Tarvainen et al. (2002) studied the film-forming ability of starch acetate (DS 2.8) and the effect of commotfly used plasticizers on the physical properties of starch acetate films. The properties were compared with ethylcellulose films. Mechanical studies, water vapor and drug permeability tests, and thermal analysis by differential scarming calorimetry (DSC) were used to characterize the film-forming ability of starch acetate and efficiency of tested plasticizers. Starch acetate films were foimd to be tougher and stronger than ethylcellulose films at the same plasticizer concentration. Also, in most cases, the water vapor permeability of starch acetate... 

The above experiment on the effect of plasticizer content was repeated at 35.5° instead of 23.5 °C. The accelerating effect of radiation on the creep rate of stressed samples again appears to disappear at about the same plasticizer content where the expansion of the unstressed samples disappears however, both vanish at a lower plasticizer concentration (approximately 20% ) at 35.5° than at 23.5°C. Hence, we can conclude that an increase in temperature also diminishes the acceleration of creep rate caused by the radiation. 

The analogy between the mechanical and the electrical damping measurements is also borne out by the effect of plasticizer concentration on the temperature of maximum damping as shown in Figure 14 (31, 32, 33). 

Effect of Plasticizer Concentration. It is generally agreed that AT-i.e., the lowering of T -for most systems is directly proportional to the plasticizer concentration in the polymeric material. While some investigators (37) have insisted on using molar concentrations, it was later shown that weight concentrations can be used for comparisons of plasticizer efficiency in most cases (34,17). 

At the crack tip, there is a stress concentration effect but, in LEFM, stress is limited to plastic zone. The dimensions of this plastic zone can be calculated using Irwin s theory and is ... 

Since they act as surfactants, copolymers are added in only small amounts, typically from a thousandth parts to a few hundredth parts. Theoretically, Leibler [30] showed that only 2% of a diblock copolymer may thermodynamically stabilize an 80%/20% incompatible blend with an optimum morphology (submicronic droplets). However, in practice kinetic control and micelle formation interfere in this best-case scenario. To a some extent, compatibilization increases with copolymer concentration [8,31,32], Beyond a critical concentration (critical micellar concentration cmc) little or no improvement is observed (moreover, for high amounts, the copolymer can act as a plasticizer). Copolymer molecular weight influence is similar to that of the concentration effect. For example, in a PS/PDMS system [8,31,32], when the copolymer molecular weight increases, domain size decreases to a certain extent. Hu et al. [31] correlated their experimental results with theoretical prediction of the Leibler s brush theory [30]. Leibler distinguishes two regimes to characterize the behaviour of the copolymer at the interface... 

The effects of plasticizers has also been studied by PAL [64, 65]. The addition of a plasticizer to polymers generally has the effect of lowering the Tg, however in some cases an anti-plasticization can occur. Borek et al [65] have shown that the fraction of free volume in PVC polymers could be fit with a fourth order polynomial as a function of plasticizer concentration. The decrease in th Tg with increasing amount of plasticizer is attributed to this increase in the free volume of the polymers. 

At the same stress amplitude, rubber modified polymers fail sooner in fatigue than do the unmodified polymers even though they have superior resistance to fatigue crack propagation. This is a result of much earlier initiation of crazing, localized plastic deformation, and subsequent crack development due to the stress concentrating effect of the dispersed second phase particles. 

Secondly, the above issues then need to be placed in a concentration-effect relationship. The main issue then is the determination of the appropriate dose metric. What is the amount (or concentration) of the chemical under study that is responsible for the effect In other words how do we determine the appropriate exposure at the site of toxic action related to the primary chemico-biological interaction that forms the basis of the compound s toxicity The commonly used practice is to relate the effects to the nominal concentration, i.e., the amount of compound added to the in vitro system divided by its volume. If data from this exposure-effect relationship are to be the basis of an estimation of risk for an organism, this approach may be a source of errors in those cases where the local exposure of the cells in vitro differs from the exposure of targets in the in vivo situation [9], These differences can result from differences in protein binding in plasma vs. culture medium or other processes that may influence the local exposure at the target, e.g., binding to culture plastic [10, 11], More appropriate dose metrics, depending on the in vitro system as well as on the chemical s mechanism of action, may be the freely available concentration, either as the peak concentration or as the area under the curve (AUC) for the free concentration, or the intracellular concentration [12]. 

The free-volume theory finds ready application in predicting the effect on Tg of diluents and molecular weight, among others. As an example, we shall derive an expression for the dependence of Tg on plasticizer concentration. The total fractional free volume of a polymer-diluent system may be written as... 

Measurement of low-temperature flexibility was significantly advanced by the method of Clash and Berg. This assessment of torsional modulus was adopted as an ASTM procedure (41). By its use, it can be shown that plasticizing with linear molecular structures enhances the low-temperature flex most efficiently (i.e., lower plasticizer concentration has a more pronounced effect) chain branching and ringed aromatic moieties show lower efficiency. Increasing any compatible plasticizer s concentration in the composition lowers the temperature at which brittleness develops. However, this formulation approach may sacrifice the optimum in other properties, such as tensile strength, modulus, or hand. 

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. 

The glass transition temperature of plasticized compositions is a function of the plasticizer fraction in the system. However, this effect occurs only when there is complete thermodynamic compatibility. In heterogeneous systems the plasticized composition shows two glass transition temperatures, Tg, an indication of the presence of two phases. The Tg of the polymer phase does not vary with change in plasticizer concentration. This effect has long been known for plastics and mbbers. 

At low concentrations of plasticizers other effects may occiu in systems containing glassy polymers. Although, Tg may be lowered by the addition of plasticizer, the modulus and tensile strength increase. This makes the polymer stiffer and more brittle. The effect is not related to compatibihty. ... 

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