Enhanced peel resistance of fiber reinforced phenolic foams

Abstract Short-fiber reinforced phenolic foams were synthesized and characterized by climbing drum peel tests and tensile tests. Significant improvements in mechanical properties were realized, including a multiple-fold increase in peel strength. Because peel strength is closely linked to the fracture toughness of foams, particular attention was focused on the mechanism responsible for the enhanced peel resistance. Scanning electron microscope observations revealed that phenolic foams reinforced with aramid fibers exhibited a unique ‘micro-peel’ process. This process was caused by a moderately weak interface between the flexible aramid fibers and the surrounding phenolic matrix, resulting in higher toughness relative to similar foams reinforced with stiffer glass fibers. In addition, a design-of-experiments analysis supported the expectation that fiber loading and length were primary factors contributing to the improved peel strength.