Glass transition temperature of Blend

With Nishi and Wang results as reference points, the glass transition temperatures of blends shown in Figure 7.1 can be reorganized by the shifting factor AFg, which is defined by... 

Table 6. Glass-transition temperatures of blends of PCL with PVC data taken from [96]...

Develop mathematical framework to predict two-glass transition temperatures Explore physical signihcance of entropic difference model Apply the quadratic expression for Tg to different systems Derive expression for change in change in entropy of mixing Cubic equation for prediction of glass transition temperature of blend Effect of chain sequence distribution of copolymer Entropy of copolymerization Dyads and triads... 

Figure 10.2 Crystallization temperature ranges for crystalline/amorphous miscible polymer blends (A amorphous polymer, B crystalline polymer) as a function of volmne fraction of the crystalline component. Tg, glass transition temperature of blend TgA < (sohd Une), (dashed line). T, ...

Stronger in the blend than in the pure components, q is positive and the resultant Tg will be higher than predicted for an ideal blend. This is shown in Figure 5.3a, where the glass transition temperatures of blends of two substituted poly(vinyl cinnamate) polymers with OCH3 and Cl groups in the para position ofthe phenyl ring are plotted... 

More recently, test products were created of a blend of PMMA with a phenyl-substituted methacrylate these products have a glass-transition temperature of around 125°C, a significantly reduced water absorption compared to pure PMMA of about 0.32%, but also a higher birefringence (a stress-optic coefficient of 5.2 X 10 , compared with 0.3 X 10 for PMMA and 6.8 x 10 for BPA-PC). 

Polycarbonate—polyester blends were introduced in 1980, and have steadily increased sales to a volume of about 70,000 t. This blend, which is used on exterior parts for the automotive industry, accounting for 85% of the volume, combines the toughness and impact strength of polycarbonate with the crystallinity and inherent solvent resistance of PBT, PET, and other polyesters. Although not quite miscible, polycarbonate and PBT form a fine-grained blend, which upon analysis shows the glass-transition temperature of the polycarbonate and the melting point of the polyester. 

Alloys exhibit physical properties, the values of which are typically the weighted average of those of its constituents. In particular, the blend exhibits a single glass-transition temperature, often closely obeying semitheoretically derived equations. Blends of two compatibiLized immiscible polymers exhibit physical properties which depend on the physical arrangement of the constituents and thus maybe much closer to those of one of the parent resins. They will also typically exhibit the two glass-transition temperatures of their constituent resins. 

Before providing such an explanation it should first be noted that progressive addition of a plasticiser causes a reduction in the glass transition temperature of the polymer-plasticiser blend which eventually will be rubbery at room temperature. This suggests that plasticiser molecules insert themselves between polymer molecules, reducing but not eliminating polymer-polymer contacts and generating additional free volume. With traditional hydrocarbon softeners as used in diene rubbers this is probably almost all that happens. However, in the... 

Tackifying resins enhance the adhesion of non-polar elastomers by improving wettability, increasing polarity and altering the viscoelastic properties. Dahlquist [31 ] established the first evidence of the modification of the viscoelastic properties of an elastomer by adding resins, and demonstrated that the performance of pressure-sensitive adhesives was related to the creep compliance. Later, Aubrey and Sherriff [32] demonstrated that a relationship between peel strength and viscoelasticity in natural rubber-low molecular resins blends existed. Class and Chu [33] used the dynamic mechanical measurements to demonstrate that compatible resins with an elastomer produced a decrease in the elastic modulus at room temperature and an increase in the tan <5 peak (which indicated the glass transition temperature of the resin-elastomer blend). Resins which are incompatible with an elastomer caused an increase in the elastic modulus at room temperature and showed two distinct maxima in the tan <5 curve. 

Fig. 23. Evolution of the glass transition temperature of polychloroprene-aromatic hydrocarbon resin blends as a function of the resin content. values were obtained from DSC experiments.

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-... 

Table 9 Glass transition temperature of EPDM/CR rubber blends...

Figure 7.1. Glass transition temperature of PVDF/PMMA blends after high-speed quenching as a...

Figure 7.2. Glass transition temperatures of quenched PVDF/PMMA blends after adjustment with a shifting factor (+) Martinez-Salazar et al. (A) Nishi and Wang (o) Noland et (+) Morales et al. (A) Roerdink and Challa. ...

Mijovic et al. analyzed the annealed blends from melts using dynamic mechanical thermal analysis and achieved similar results after an adjustment for shifting factors, AT s, as shown in Figure 7.3. The results were extended to include blends having a PVDF concentration greater than 80 wt %. It can be observed that the glass transition temperatures of the annealed blends reduce rapidly when the PVDF concentrations are above 80 wt %. 

Figure 7.3. Glass transition temperatures of annealed and cast PVDF/PMMA blends (+) Mijovic et aiy (o) Nishi and Wang (A.) Paul and Altamirano (-) calculated results for quenched blends.

Figure 7.4 shows the glass transition temperatures of PVDF/PMMA blends as a function of PVDF content after a melt process. The results " show agreement with Gordon-Taylor relation up to about 40 wt %, which is much higher than the 20wt % obtained from the annealed blends. This is certainly a result of the increased content of amorphous PVDF matrix in melt-processed blends compared with annealed blends. 

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