Deepak Langhe

Coextrusion Processing of Multilayered Films

This chapter reviews the early coextrusion processing techniques with different types of manifolds in tubular and cast film production processes. The advances in the layer multiplication, feedblock technology, and related innovations are also reviewed. Many examples demonstrating the coextrusion process flexibility to create micro- or nanolayers are also demonstrated. Different factors affecting the layered structure and morphology are discussed in detail. The effect of viscoelastic properties of polymers on layer structure has also been summarized.

Optical Properties of Multilayered Films

Reducing multilayered film individual layer thickness below 1 μm, results in a polymer film that is capable of interacting and manipulating reflected or transmitted light. A review of submicron-induced optical effects in multilayered polymer films includes demonstrations of structural reflection in coextruded polymer Bragg crystals, composite nanolayered film systems with active optical dyes for nonlinear optical limiting or optical lasing, and refractive optical lenses, prisms, and beam shaping devices with a gradient refractive index based on nanolayered-enabled tailorable refractive index films. A historical review of commercial optical applications and nanolayered film manufacturer highlights increased multilayered film leveraging for technology-enabled modern consumer goods.

Dielectric and Electrical Properties of Multilayered Films

Multilayered films combining high dielectric constant and high breakdown strength polymers showed improved dielectric properties such as breakdown properties, hysteretic losses, ion migration, and effective dielectric constant of the layers. The dielectric breakdown mechanism revealed damage propagation along the interfaces and layer thickness-dependent microcavitations, crazing, and interfacial delamination were associated with the breakdown events. This chapter reviews various dielectric breakdown and different polarizations associated with the multilayered films. Discussion on multilayered films with different tie layer materials to investigate the effect of interface modification on dielectric properties, is also included in this chapter. An approach of biaxial stretching of PET-based multilayer film is also reviewed as a route to improve dielectric properties. Examples of metal-filled polymer composites as conducting structures are also reviewed to demonstrate increased resistivity anisotropy by increasing the particle orientation in the filled layers.

Novel Multilayered Structures and Applications

Many novel applications and recent innovations related to the coextruded multilayered films have been reviewed in this chapter. Multilayered films were used to create dispersion of layers as platelets to improve barrier and mechanical properties in molded products. Different types of layered film/foam structures have been also discussed in detail. Porous composites are also reviewed to demonstrate multilayered structures as gas separation membranes and modified atmosphere-packaging materials. Uses of multilayered films as corrugated porous structures, gradient structures, shape memory polymers, and fiber webs, have also been summarized in this chapter. These technologies demonstrate coextrusion process flexibility in a wide range of applications, in addition to packaging and optical applications.

Gas Transport, Mechanical, Interphase, and Interdiffusion Properties in Coextruded-Multilayered Films

In this chapter, the structure–property relationships in multilayered composites with micro- and nanoscale layer thicknesses are discussed. Recent advancements in confined crystallization of polymers in nanolayer films showed that the layer thickness played an important role in crystal orientation in confined layers. The lamellar orientation and the effect on the gas transport properties are discussed for various polymer systems. Various examples of layered composites showing improvements in the mechanical, adhesion, and failure properties of the composites due to improved interfacial interaction have also been reviewed. Because multilayer coextrusion process created a large number of interfaces, it was used to explore the interfacial properties such as interphase phenomena in immiscible polymers and interdiffusion in miscible polymers as discussed here.

7 – Future Trends

In this chapter, the future trends in coextruded multilayered film technology have been reviewed. This technology will continue to make an impact in packaging and optical applications. Many advantages of the micro- and nanolayered films will be incorporated in the next generation films, such as high-barrier nanolayers. Besides these applications, the emerging multilayered film applications such as dielectric materials, passive sensors, and porous structures have also been discussed. This chapter also comments on the recent advances in feedblock fabrication technology and its impact on the future of multilayered products.

Introduction to Multilayered Films

Coextrusion process was developed to combine two or more polymers to achieve synergistic effects in the composite products. This chapter introduces the summary of various coextrusion-processing techniques for manufacturing multilayered films, sheets, or annular profiles. Many early feedblock designs were focused on producing layered composites primarily for packaging applications. The tubular and cast film coextrusion techniques, feedblocks, and die designs are discussed briefly in this chapter. The coextrusion technology progress toward multilayered films with hundreds or thousands of layers is also reviewed. In addition, different property enhancements and novel applications are also summarized.