Discussion on Rheology of Polymer Blends

Polymer blending system refers to mixing two or more polymers to form an apparently uniform mixing system. The processing rheological properties and morphology of polymer blend systems are extremely critical for the study of polymer materials. As the compatibility of various components in polymer blends has a direct impact on performance, processing, etc., research in this area has become increasingly urgent.

Very few polymers are compatible at the molecular level, and most polymers are partially compatible or incompatible, resulting in macroscopic separations that are not of value. Compatible polymer blends can form homogeneous systems with properties similar to homopolymers, such as having only one glass transition temperature. In order to meet the demand for the same properties of polymer materials, a large amount of work is focused on the research of polymer blends that have macroscopic uniform and microscopic phase separation with excellent properties and strong interfacial interaction between phases.

The main research objects of polymer rheology are polymer fluids and solids, which are: structural rheology, experimental rheology and processing rheology. Compared with smaller molecular fluids, polymer rheology has the following characteristics:

(1) Polymers have diversity

(2) Polymer morphology is temperature dependent

(3) Polymer morphology is time dependent

The rheological behavior of polymers occurs at a certain shear rate and shear stress. The entanglement between the polymer molecules is destroyed, the molecules are reoriented, the resistance is reduced, the fluid viscosity is reduced, and the rheological behavior varies with the polymer chain. Factors such as structure, degree of structuring between chains, relative molecular mass, and molecular mass distribution are related.

The polymer blending system group distribution ratio has a great influence on the flow properties of the blend. The effect of shear rate on non-Newtonian polymers is that viscosity decreases with increasing shear rate, but the degree of viscosity reduction varies with different blends. The apparent viscosity of flexible polymers decreases with increasing shear rate, while rigid polymers are relatively small.

The blending temperature has a significant effect on the rheological behavior of polymer blends. As the temperature increases, the free volume of the blend increases, and the resistance of the flow unit decreases accordingly. The energy of the flow unit increases, the degree of ordering decreases, the relaxation time decreases, the elastic effect increases, and the melt flows easily. Apparent viscosity decreases.