Glass transition temperature blend systems

Fig. 2. Glass-transition temperature, T, for two commercially available, miscible blend systems (a) poly(phenylene oxide) (PPO) and polystyrene (PS) (42) ...

Differential scanning calorimetry (DSC) is fast, sensitive, simple, and only needs a small amount of a sample, therefore it is widely used to analyze the system. For example, a polyester-based TPU, 892024TPU, made in our lab, was blended with a commercial PVC resin in different ratios. The glass transition temperature (Tg) values of these systems were determined by DSC and the results are shown in Table 1. 

Small amounts (usually <10%) of plasticizer could be used in the blending system to improve the processing properties of the material by lowering the melting and glass-transition temperatures. The addition of liquid plasticizer also makes the material soft but at the same time, the strength and toughness of the material decreases. 

The all-important difference between the friction properties of elastomers and hard solids is its strong dependence on temperature and speed, demonstrating that these materials are not only elastic, but also have a strong viscous component. Both these aspects are important to achieve a high friction capability. The most obvious effect is that temperature and speed are related through the so-called WLF transformation. For simple systems with a well-defined glass transition temperature the transform is obeyed very accurately. Even for complex polymer blends the transform dominates the behavior deviations are quite small. 

In general, the miscibility between two polymers can be predicted by thermal characterization of the blends [36], One of the most simple and effective ways to predict miscibility between two polymers is to consider the behavior of the glass transition temperature in the blend systems, which is known as the Tg method. In miscible blend systems, only a single 7 g intermediate between two components appears in the amorphous state. Therefore, we studied the change of... 

Phase separation through NG mechanism cannot be observed for polymer-polymer blend systems that show interfacial tension lying in the range 0.5-11 mN/m. In addition, they predicted that a secondary phase separation could take place inside dispersed rubber particles in the case when the average composition of dispersed domains lies in the unstable region at the end of the phase separation [2], They were not able to observe a phase separation inside dispersed domains with TEM micrographs however, they concluded that there are two phases inside the dispersed domains by the fact that the glass transition temperature of the rubber-... 

Recently, alternative theoretical expressions have been developed by using classical thermodynamic treatments to describe the compositional dependence of the glass transition temperature in miscible blends and further extended also to the epoxywater systems 2S,27). The studies carried out on DGEBA epoxy resins of relatively low glass transition have shown that the plasticization induced by water sorption can be described by theoretical predictions given by ... 

The homopolymers poly(methyl methacrylate) and poly-(ethyl methacrylate) are compatible with poly(vinylidene fluoride) when blended in the melt. True molecular com-patibility is indicated by their transparency and a single, intermediate glass transition temperature for the blends. The Tg results indicate plasticization of the glassy methacrylate polymers by amorphous poly(vinylidene fluoride). The Tg of PVdF is consistent with the variation of Tg with composition in both the PMMA-PVdF and PEMA-PVdF blends when Tg is plotted vs. volume fraction of each component. PEMA/PVdF blends are stable, amorphous systems up to at least 1 PVdF/I PEMA on a weight basis. PMMA/ blends are subject to crystallization of the PVdF component with more than 0.5 PVdF/1 PMMA by weight. This is an unexpected result. 

Mixtures of poly(vinylidene fluoride) with poly (methyl methacrylate) and with poly (ethyl methacrylate) form compatible blends. As evidence of compatibility, single glass transition temperatures are observed for the mixtures, and transparency is observed over a broad range of composition. These criteria, in combination, are acceptable evidence for true molecular intermixing (1, 19). These systems are particularly interesting in view of Bohns (1) review, in which he concludes that a compatible mixture of one crystalline polymer with any other polymer is unlikely except in the remotely possible case of mixed crystal formation. In the present case, the crystalline PVdF is effectively dissolved into the amorphous methacrylate polymer melt, and the dissolved, now amorphous, PVdF behaves as a plasticizer for the glassy methacrylate polymers. 

The foam processing window of the blend systems is also controlled by the glass transition temperature of the blend phases. With regard to the neat blend system, the addition of PS continuously lowers the glass transition temperature of the PPE/PS phase, as predicted by the Couchman equation [77] (Fig. 25). For the carbon dioxide-laden case, the plastifying effect needs to be taken into account, which lowers the glass transition temperature of both PPE/PS and SAN. 

Between 160 and 180°C slightly above the glass transition temperature of the PPE/PS phase, a similar expansion for all blend systems can be observed. 

For further understanding the influence of the viscosity ratio on the foaming behavior, an additional blend system with a PPE/PS ratio of 25/75 and a SAN content of 40 w% was investigated. Due to the high PS content, the PPE/PS matrix phase shows a lower viscosity and a similar glass transition temperature when compared to the dispersed SAN phase. As can be seen in Fig. 29a, the decrease in viscosity of the PPE/PS clearly promotes the formation of elevated SAN phase in comparison to the previously shown blends. 

Table 6 Glass transition temperature of (PPE/PS)/SAN blend systems compatibilized by SBM in absence and in presence of carbon dioxide...

The excellent foamability of the quaternary blend also relates to the microstructure. All selected quaternary blend systems revealed a PPE/PS matrix phase able to stabilize the formed cells, as a result of the higher glass transition temperature and viscosity compared to the dispersed SAN. 

The phase behavior of polymer blends comprising amorphous polymers is experimentally well accessible in a window which is bounded at high temperatures by the thermal decomposition temperature of the polymer components and at low temperatures by the glass transition temperature of the system (cf. Fig. 1). Below the glass transition temperature the phase behavior can be estimated only tentatively. 

Several hybrid epoxy emulsions have been commercially prepared. An epoxy emulsion blended with waterborne aliphatic urethanes exhibited peel strength on aluminum of 10 lb/in—1.5 times greater than with the polyurethane itself. The optimum concentration of urethane in the final emulsion was about 50 percent by weight.13 Epoxy-phenolic dispersions have also been developed to provide waterborne adhesive systems with high glass transition temperature and chemical resistance. 

It can be expected, then, that one of the major problems in adhesives technology is the development of adhesives that must withstand both elevated temperatures as well as periodic excursions to low temperatures. Several solutions have been developed. Certain adhesive systems, notably blends of epoxy resin with more elastic resins, have been formulated with a very broad glass transition temperature range or with multiple glass transitions at both high and low temperatures. These have found some success in the applications discussed in this chapter. 

The PS-2100/PMMA thermal data of Figure 3 also show two glass-transition temperatures for the 25% blend, indicating incompatibility. The dynamic mechanical results for blends of PS-600 in PMMA are consistent with the thermal and optical results, as Figure 4 shows. The PMMA secondary loss shoulder is diminished somewhat as the concentration of PS-600 is increased, in a manner similar to that observed in other polymer-diluent systems in which the diluent is monomeric (15) until phase separation occurs. Thereafter, the phase-separated PS-600 shows up as a characteristically narrow peak at about — 10°C. 

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