Polyester core materials and structural sandwich composites thereof

Abstract

High-strength, chemically and thermally stable, closed-cell foams, useful as structural core materials in sandwich composites. The core materials of the invention display anisotropic properties. The core materials of the invention are amenable to vacuum-mediated resin bonding to composite skins to provide lightweight, high-strength structural sandwiches suitable for use in a variety of applications, such as marine applications, construction, aviation, rapid transit, and recreational vehicles.

What is claimed is:  
     
         1 . A method for making a composite comprising: 
 (a) extruding a foamable gel comprising a blowing agent and a foamable polyester through a multi-orifice die to give a plurality of strands;    (b) foaming the strands to form a multi-stranded foamed article;    (c) shaping the multi-stranded foamed article to give a core material; and    (d) bonding the core material to one or more structural skins.    
     
     
         2 . The method of  claim 1 , further comprising coalescing the strands after foaming the strands.  
     
     
         3 . The method of  claim 1 , wherein foaming the strands comprises expanding the blowing agent.  
     
     
         4 . The method of  claim 2 , wherein coalescing the strands produces inter-strand voids.  
     
     
         5 . The method of  claim 4 , wherein shaping the multi-stranded foamed article removes substantially all the inter-strand voids.  
     
     
         6 . The method of  claim 1 , wherein the core material is shaped to produce a plurality of discrete volumes, each discrete volume comprising an interior section and a corresponding jacket, wherein the average cell size in the interior section is larger than the average cell size in the jacket.  
     
     
         7 . The method of  claim 1 , wherein the core material is bonded between two structural skins.  
     
     
         8 . The method of  claim 1 , wherein the one or more structural skins comprises a thermoplastic polymer, a thermosetting polymer, wood, an inorganic material, or a metallic material.  
     
     
         9 . The method of  claim 8 , wherein the thermoplastic or thermosetting polymer comprises glass fibers, metallic fibers, inorganic fibers, or carbon fibers.  
     
     
         10 . The method of  claim 1 , wherein the one or more structural skins comprise a structural sandwich composite.  
     
     
         11 . The method of  claim 1 , wherein bonding the core material to the one or more structural skins comprises applying a resin to the core material or to the one or more structural skins.  
     
     
         12 . The method of  claim 1 , wherein bonding the core material to the one or more structural skins comprises applying heat.  
     
     
         13 . The method of  claim 1 , wherein bonding the core material to the one or more structural skins comprises vacuum bagging.  
     
     
         14 . The method of  claim 1 , wherein the foamable gel comprises a nucleating agent, a fire retardant, or a reinforcing agent.  
     
     
         15 . The method of  claim 1 , wherein the foamable polyester comprises foamable polyethylene terephthalate, foamable polybutylene terephthalate, foamable polyethylene naphthalate, a foamable copolymer of polyethylene terephthalate, a foamable copolymer of polybutylene terephthalate, a foamable copolymer of polyethylene naphthalate, or a mixture thereof.  
     
     
         16 . The method of  claim 1 , wherein the foamable polyester comprises foamable polyethylene terephthalate.