Glass transition temperature blends

Figure 2. PBT/PET blends glass-transition temperatures, Tg vs. PET percent as determined by DSC.

PEC, in agreement with previous observations (19,20). and to the presence of crystalline i-PS. Amorphous, optically transparent, films could be prepared by heating the solution cast films for a few minutes at 270 °C, followed by rapid cooling to temperatures below the blend glass transition temperature, Tg, tj prevent crystallization of the i-PS. Once the phenylene ether crystals are melted out of the blend, crystallization of this material does not recur. The i-PS material will crystallize readily from the melt when the blend temperature is above Tg and below about 200 °C for several minutes. 

The determination of T of a blend is one of the calorimetric techniques used to elucidate the miscibility or partial miscibility in the amorphous phase of binary polymer blends. Glass transition temperature is the temperature at which the transition from the glassy to the rubbery state of the bulk material takes place. The establishment of miscibility using is based on the degree of dispersion of the second component in the amorphous region of the first component and that the size of the disperse phase domain is < 15 nm (Silvestre et al., 1996 Shultz and Young, 1980). It is noteworthy that blends which exhibit a are miscible whereas... 

However, these two effects are likely to be relatively small compared with the third effect, the variation of the segment fnction factor with composition. An appealing (but inadequate) Ansatz relates changes in the local friction factor with blend composition to changes in the blend glass transition temperature. If we use the Williams-Landel-Ferry form for the temperature dependence of the fnction factor... 

Growing numbers of commercial materials are blends of two or more polymers in which at least one of the components is a crystalline polymer. The crystallization in miscible blends is restricted to temperatures between the blend glass transition temperature and the equilibrium melting point, T ,e, i.e., to the crystallization temperature, Tc < Tm e- The difference, Dc = T ,e - Tc, depends on the cooling rate and the nucleation process. There are three mechanisms of the crystallization nucleation (Utracki 1989) ... 

What does it mean when blend glass transition temperature results are... 

What is the physical significance of the terms A, B, and C in the expression to predict the blend glass transition temperatures in Equation (6.15) ... 

An Example Calculation of Polymer Blend Glass Transition Temperatures... 

Small to moderate additions of LRs to UP resins may result in an increase, a decrease, or in no change of the cured UP resin s upper use temperature. From results reported in the hterature it is difficult to predict how a particular rubber addition will affect the blend glass transition temperature, Tg, which is an indicator of upper use temperature. Factors that may affect the Tg of the cured blend include resin chemistry, rubber chemistry, and the distribution of rubber between the phases. As the Tg of a typical LR modifier is in the subambient range an increase in the blend Tg is not expected. However, the liquid rubber molecules may act... 

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. 

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

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.

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