Polymer-diluent mixtures temperature

Glassy polymer-diluent mixtures deformed in a temperature range close to are susceptible to exhibit a cavitational mode of plasticity at hi stresses and strains. Activation of this mechanism in mixtures of polycarbonate with esters of the phthalic acid results in extensive fibrillation and stress whitening of the material. There is strong evidence that the diluent plays an important role in enhancing chain slippage, which is required for the formation of craze fibrils. One of the most fundamental problems which is still unsolved is the elucidation of the molecular mechanism by which diluents become active. 

Empirically Tg of a polymer-diluent mixture could be expressed in terras of the glass transition temperature of the pure polymer 9V and that of the pure diluent Tgd by... 

A relation between Tg and composition of a polymer-diluent mixture can be derived [47] in a relatively straightforward manner from the free-volume concept by postulating that the free volumes of the polymer and diluent are additive in the mixture, and that the free volume fraction has a critical value fg, which is the same for the pure polymer, the diluent and their mixtures at their respective glass temperatures. The composition of polymer-diluent mixtures is conveniently expressed in terms of the volume fractions of polymer cj)p and diluent (f>d. 

One of the thermodynamic methods involves the adaptation of the classical freezing point-composition relation to the melting of polymer-diluent mixtures. The most common situation encountered when a low molecular weight diluent is admixed with a polymer, is that the crystalline phase remains pure. Under these conditions, for polymers of high molecular weight, the melting temperature of a polymer-diluent mixture, T, can be expressed as [7,21]... 

Here /ci and are the conventional entropy and enthalpy parameters and 9 is the Flory temperature for the polymer-diluent mixtures. We next examine Eq. (3.29) for physically meaningful solutions of T (E > 0), under the assumption that the quantities ir,6,a and b are independent of temperature. 

Gibbs and DiMarzio (1958) appear to have been the first to offer a molecular interpretation, via statistical mechanics, of the depression of glass transition temperature (Tg) of an amorphous polymer by the addition of low-molecular-weight soluble diluents, in terms of the size and stiffness of diluents and the diluent concentration. Subsequently, using both classical and statistical thermodynamics, Chow (1980) derived the following expression, which predicts the T depression of polymer/diluent mixtures ... 

The analysis of dependence of melting temperature on plasticizer content in the range in which PLA and acetyl tri-n-hutyl citrate (ATBC) are miscible gives indications of polymer-plasticizer interactions (Baiardo et al, 2003). The Flory (1953) equation fits well for miscible polymer-diluent mixtures ... 

DVB were valid in this system as well. These concern the dependence of surface area and pore volume on the amount of diluent and cross-linker. The surface area increases with the amount of EDMA and goes through a maximum with increasing amount of diluent. Using cyclohexanol-dodecanol as a solvent-non-solvent pair, the factors of importance for the structure and morphology of the polymers were studied by experimental design [34]. In these experiments the concentration of the diluent mixture was varied between 20 and 77% (volume/total volume), the concentration of EDMA between 25 and 100% (volume/monomer volume), the concentration of initiator (AIBN) between 0.2 and 4% (w/w), the concentration of non-solvent (dodecanol), between 0 and 15% (v/v) and the polymerisation temperature between 70° and 90°C. The surface area (determined by nitrogen sorption), pore volume (determined by mercury porosimetry) (see Section 2.11.6.) and the mechanical properties were chosen as responses. 

From these values, one may calculate and compare the effective glass transition temperature of the resin as a function of diluent concentration. Gordon et a1. have recently derived an expression relating the glass temperature of a polymer-plasticizer mixture to the glass temperatures of the components on the basis of the configurational entropy theory of glass formation (4). 

The influence of temperature on the porosity of a molded monolith prepared with a precipitating porogen is described by a simple rule the higher the temperature of polymerization, the smaller are the pores (Fig. 4.6) [383]. This tendency may be understood in terms of the classical mechanism of porosity formation via nucleation and subsequent aggregation of the primary nuclei. Phase separation occurs when the growing polymer becomes insoluble in the monomer—diluent mixture. 

The enthalpy change can be estimated by adding varying quantities of a diluent to the polymer, which serves to depress the observed melting temperature, and measuring for each polymer and diluent mixture. The results are then plotted according to the Flory equation ... 

Ho, K.-L.G. and Pometto, A.L. Ill (1999) Temperature effects on soil mineralization of polylactic acid plastic in laboratory respirometers. Journal of Environmental Polymer Degradation, 1, 101-108. Buchanan, C.M., Dorschel, D.D., Gardner, R.M. et al. (1995) Biodegradation of cellulose esters Composting of cellulose ester-diluent mixture. Journal of Macromolecular Science, Part A Pure and Applied Chemistry, A32,683-697. 

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