Processability-polymer Blends

In manufacturing and processing polymer blends, it is thus important that the viscosity ratio be within the optimal range in the actual processing conditions. Not only the polymers to be blended but also the temperature and processing conditions (shear, elongation) should be carefully selected. Other factors, such as interfacial tension [46,47] and elasticity of the blended polymers, may also influence the blend morphology. 

M Eglin, A Montali, ARA Palmans, T Tervoort, P Smith, and C Weder, Ultra-high performance photoluminescent polarizers based on melt-processed polymer blends, J. Mater. Chem., 9 2221-2226, 1999. 

Melt-processable polymer blend or copolymer in which a continuous elastomeric phase domain is reinforced by dispersed hard (glassy or crystalline) phase domains that act as junction points over a limited range of temperature, or... 

It is usually difficult to isolate and characterize a copolymer from a melt-processed polymer blend. Model studies of copolymer formation between immiscible polymers have been performed either in solution (where there is unlimited interfacial volume for reaction) or using hot-pressed films of the polymers (where the interfacial volume for reaction is strictly controlled at a fixed phase interface). Model smdies using low molecular weight analogs of the reactive polymers are useful but their applicability to high molecular weight reacting systems is limited. 

Owing to the absence of electronic effects in most polymers, heat conduction occurs as a result of lattice vibrations, similar to dielectrics. It is known that the thermal conductivity of an amorphous polymer increases to T with increasing temperature while it decreases above T [Godovsky, 1992]. Thermal conductivity is a fundamental and important factor in processing polymer blends [Agari, 1992]. 

T. Taka, P. Passiniemi, J.-E. Osterholm, Y. Cao, et al. Counter-Ion Induced Processibility of Polyaniline Conducting Melt Processible Polymer Blends. Synth. Met. 1995, 69,97-100. 

In processing polymer blends, equipment selection, conditions, and formulation are highly important to control the final morphology. In this chapter, a review of the fundamentals in mixing (laminar, chaotic, dispersive, and distributive) is given before presenting the main limitations/problems related to interfacial properties, coalescence, and measure of mixing quality. Then, different methods and equipments are presented for lab-scale and industrial applications. A special focus is made on reactive system and phase compatibilization to improve the properties of the final blends. Also, nonmechanical techniques (solutions) are presented. 

During transportation of polymer solutions in production units and processing polymer blends the system is subjected to considerable shear rates. It is therefore very important to know the effect the shearing forces have on the phase behavior of a (co-)polymer system. Over the years there have been many discussions about the possible influence of flow/shear on the demixing behaviour of polymer blends. Very recently the importance of shear was clearly demonstrated by several groups, e.g. by Aelmans et al. [10]. 

The most appropriate mixing tool and the most widespread in processing polymer blends is the twin-screw extruder. Corotating and counterrotating twin-screw extruders... 

The evaluation of interfacial behavior of die in situ formed copolymer allows to indicate whether or not the copolymer stays at the interface as a frmction of time under quiescent or dynamic conditions. It is important to emphasize that the location of the copolymer at the interface is one of the important requirements for the interfacial adhesion between the blend phases. The in situ formed copolymer should not leave the interface upon further melt-processing. Polymer blends are very often subjected to different melt-processing operations for the fabrication of end-use products. 

Li G, Sarazin P, Favis BD. 2008. The Relationship between Starch Gelatinization and Morphology Control in Melt-Processed Polymer Blends with Thermoplastic Stoch. Macromol Chem Physic 209(10) 991-1002. Lichtenthaler FW. 2006. Biorefineries - Industrial Processes rmd Products. Status Quo rmd Future Directions. 

Figure 1. Phase morphology development in melt processing polymer blends.

---