Blending polymers for packaging applications

Blending of polymers is becoming increasingly important in packaging applications to enhance properties, improve processing or reduce cost. Tailoring surface properties, such as coefficient of friction (COF), adding color, promoting adhesion, increasing output, improving stability, and obtaining easy-opening features, are just a few of the attributes that can be achieved by blending. The simplest blends can be made by mixing ingredients in the extruder that is used to convert the resin into a film or coating. For more complex blends, specialized screw designs or customized compounding equipment may be required to achieve the desired properties. These machines incorporate various mixing modes, such as flow rearrangement (distributive mixing) or high stress levels to break up particles (dispersive mixing). Complex shear and elongational flow fields may also be used to obtain optimum mixing. The final blend properties will depend not only on the flow and stress history, which is process dependent, but also on the thermodynamics and the polymers’ thermal and rheological properties. Most polymer blends are immiscible the minor component forms a separate dispersed phase or domain within the major component, and the major component forms a continuous phase or matrix. The phase size and shape is known as the blend morphology. Blend morphology has a profound effect on final properties and is the subject of much study. Morphology is influenced by: 

• interfacial tension (thermodynamics), 

• dispersed to continuous phase viscosity ratio, 

• elasticity of each phase, 

• minor component concentration, 

• mixing and melting order, 

• and much more.

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