Synthesis of composite foam from thermoplastic microspheres and 3D long fibers

A method is described for preparing composite foam using expandable PAN-based microspheres reinforced with continuous fibers. Composite foams were produced by mixing expanded and non-expanded microspheres in select proportions, packing the dry microspheres into a fibrous preform in a closed mold, and heating the assembly to expand and weld the microspheres and fibers together. The composite foams exhibited mechanical performance and formability that surpassed the unreinforced foams. The tensile modulus and strength were increased by 750 and 400% respectively, and showed enhanced resistance to crack propagation compared with unreinforced foam samples. The improvement in compression properties was modest by comparison (< 10%). Fiber performs were comprised of 3D, stochastically arranged long fibers, and typical fiber loadings were similar to 8 wt%. Long fibers were deeply anchored in the foam and bridged crack wakes, resisting crack growth and delaying catastrophic failure of the foams during tensile tests. (C) 2003 Elsevier Ltd. All rights reserved.