Methods for evaluation of viscoelastic behavior of blends of amorphous polymers from those of component polymers were investigated by model experiments and the limitations of the methods were examined.
It is possible in principle to calculate the properties of polymer blends from those of component polymers for the system consisting of two separate phases. In order to establish the description method for this system, model specimens were prepared by bonding together the films of component polymers of known size, and dynamic modulus E' and loss modulus E" were measured at 138c/s over a temperature range from -170°C to 120°C. The film of polyvinyl chloride (PVC) and that of nitrile-butadiene rubber (NBR) were used as materials of the model specimens. The results of measurements were compared with the values calculated from dynamic properties of component polymers.
Close agreement was obtained between the observed values of E' and E" of various types of model specimens and the values calculated by the equation, in which the volume fraction and the construction form were taken into consideration.
As an example of the two phase system, Cycolac H of Marbon Chem. Co. was studied. Its temperature dispersion curve resembles closely to that of model specimen, which was constructed by putting the rubber phase (NBR) into the plastic phase (PVC). The location of the higher temperature dispersion of Cycolac H, 115°C, accorded with that of the dispersion of a styrene-acrylonitrile copolymer separately measured. The lower temperature dispersion at -185°C was found to correspond to that of polybutadiene. The dispersion curves of Cycolac H were successfully calculated by employing those of the component polymers based upon the two phase simple model.
As an example of molecularly mixed system, the measurements were performed on the specimens prepared from PVC and NBR of various compositions by the solvent casting method with tetrahydrofuran. Of all the compositions, only one main absorption was found at the temperature region between the absorptions of PVC and NBR. The shape of absorption becomes most broad at the intermediate compositions. This broadness is considered to be due to the microheterogeneity in segmental size, corresponding to the varieties of segmental environment. The general expression for this case was presented.
The shape of temperature dispersion curve for the partially miscible system showed an intermediate form between those of the typical two phase system and the molecularly mixed system. The behavior of blends of a styrene-acrylonitrile copolymer and NBR belongs to this type. Observed values for this system were compared with the values calculated on the basis of the typical two phase system of the same compositions. Definite deviations from calculated values were found, which were duly ascribed to the portion of molecularly mixed phase. Broadening of absorptions of both rubber and plastic phases could not be interpreted from the typical two phase model, but only from the consideration of the effect of molecularly mixing.
This circumstances were ascertained by the behavior of the model specimen specifically prepared for this purpose.