Forced assembly polymer coextrusion utilizes layer multiplication to produce films with tens or thousands of micrometer to nanometer thick layers. The development of novel uneven split layer multiplying dies has produced gradient multilayer films with at least a 10 times difference between the thickest and thinnest layers. Coextrusion through a series of equal and uneven split multiplier dies allows for flexibility in the unique design of layer thickness distributions by: (1) altering the multiplier offset and (2) changing the sequence of a series of uneven split multiplying dies with different splitting ratios. This new technology has created highly reflective, multilayered photonic films with gradient layer thickness distributions exhibiting, as examples, a 600 nm wide reflection band and dual optical reflection bands within a single film. Also, gradient multilayers exhibit unique mechanical behavior. A layer thickness dependent craze to shear banding deformation mechanism was observed. In addition, gradient controlled buckling was observed across a single film due to foaming-induced layer delamination.

The sustainability of current and future plastic materials is a major focus of basic research, industry, government, and society at large. There is a general recognition of the positive impacts of plastics, especially packaging; however, the negative consequences around end-of-life outcomes and overall materials circularity are issues that must be addressed. In this perspective, we highlight some of the challenges associated with the many uses of plastic components and the diversity of materials needed to satisfy consumer demand, with several examples focused on plastics packaging. We also discuss the opportunities provided by conventional and advanced recycling/upgrading routes to petrochemical and bio-based materials and feedstocks, along with overviews of chemistry-related (experimental, computational, data science, and materials traceability) approaches to the valorization of polymers toward a closed-loop environment.

Forced assembly processing provides a unique opportunity to examine the effects of confinement on block copolymers (BCPs) via conventional melt processing techniques. The microlayering process was utilized to produce novel materials with enhanced mechanical properties through selective manipulation of layer thickness. Multilayer films consisting of an elastomeric, symmetric block copolymer confined between rigid polystyrene (PS) layers were produced with layer thicknesses ranging from 100 to 600 nm. Deformation studies of the confined BCP showed an increase in ductility as the layer thickness decreased to 190 nm due to a shift in the mode of deformation from crazing to shear yielding. Postextrusion annealing was performed on the multilayer films to investigate the impact of a highly ordered morphology on the mechanical properties. The annealed multilayer films exhibited increased toughness with decreasing layer thickness and resulted in homogeneous deformation compared to the as-extruded films. Multilayer coextrusion proved to be an advantageous method for producing continuous films with tunable mechanical response.

Multilayer coextrusion offers a diverse platform to examine layer dependent confinement effects on self-assembling nanomaterials via conventional extrusion technology. A triblock copolymer (BCP) with a cylindrical microstructure was processed via "forced assembly" to elucidate the effect of microdomain orientation on the mechanical behavior of multilayer films. The mechanical response was investigated in both the extrusion (ED) and transverse directions (TD) of the multilayer systems, revealing an influence of both cylinder-orientation and the interface on the mechanical response with decreasing layer thickness. The stress-strain curves for samples with the stress field along the cylinder axis revealed a sharp yielding phenomenon, while curves for specimens with the stress field applied perpendicular to the axis exhibited weak yielding behavior. The extensibility of the multilayer films stressed in the ED increases with decreasing layer thickness, but remains constant when deformed along the TD. Coextrusion technology allows for tunable mechanical toughness in industrial grade polymers via a continuous process. By altering the layer thickness of the two polymeric materials, we can tune the mechanics from strong, brittle behavior to a tough, ductile response by manipulation of the hierarchical structure. The enabling technology provides a unique platform to couple the inherent mechanical response of dissimilar polymers and allows for the design of composite materials with tailored mechanics.