The past several decades have seen considerable advancement in engineering materials through the development of improved composite materials. Composites allow designers to combine advantageous features of multiple component materials to arrive at a material that typically has one or more different properties than the component materials individually.
One area that has seen particularly rapid advancement is the area of reinforced plastics. For example, it is popular to improve properties of a plastic by incorporating an inorganic reinforcement phase, such as the employment of a fiber that is made of glass, carbon, metal or another inorganic material. In a number of instances, a form is provided that incorporates the inorganic reinforcement material, and is impregnated or otherwise intermixed with a thermoplastic or thermoset plastic matrix. One particular example that has seen increased popularity in recent years is a Glass Mat Thermoplastic (GMT) composite, which ordinarily employs a glass mat reinforcement phase that is impregnated with a thermoplastic such as polypropylene.
One approach to the preparation of a polymeric reinforcement phase for use in a composite is to employ co-extruded multi-layer tapes, having fewer than four layers.
Microlayer structures that employ four or more layers have been disclosed in the art for various purposes, such as in U.S. Pat. Nos. 5,126,880 and 6,837,698, and Dooley, “Viscoelastic Flow Effects in Multilayer Polymer Co-extrusion”, Technische Universiteit Eindhoven (2002) (ISBN 90-386-2983-4), incorporated by reference all incorporated by reference. It would be attractive to employ microlayer structures in plastic composites. It would also be attractive to have improved microlayer structures, regardless of their intended application.