Processing and properties of a phenolic composite system

Phenolic resin systems generate water as a reaction by-product via condensation reactions during curing at elevated temperatures. In the fabrication of fiber-reinforced phenolic resin matrix composites, volatile management is crucial in producing void-free quality laminates. A commercial vacuum-bag moldable phenolic prepreg system is selected for this study. The traditional single-vacuum-bag (SVB) process is unable to manage the volatiles effectively, resulting in inferior voidy laminates. However, a double-vacuum-bag (DVB) process is shown to afford superior volatile management and consistently yield void-free quality parts. The DVB process cure cycle (temperature/pressure profiles) for the selected composite system is designed, with the vacuum pressure application point carefully selected, to avoid excessive resin squeeze-outs and achieve the net shape and target resin content in the final consolidated laminate parts. Laminate consolidation quality is characterized by optical photomicrography for the cross sections and measurements of mechanical properties. A 40% increase in short beam shear strength, 30% greater flexural strength, 10% higher tensile and 18% higher compression strengths are obtained in composite laminates fabricated by the DVB process.