(465e) Encapsulated Nano- and Meso-Fiber Mesh Composites

Polymer-polymer composites comprised of vinyl ester or epoxy matrices and small diameter polypropylene fiber meshes were fabricated and tested in this work. The general goal was to develop toughened polymeric systems capable of absorbing and dissipating energy upon impact while maintaining structural attributes in advanced composite applications.

Commercial vinyl ester (VE) and epoxy resins were used and commercial small diameter (~1 µm) polypropylene (PP) fibers were selected as the modifying phases. Composites were prepared using the vacuum assisted resin transfer molding technique. The surface of the polypropylene fiber mats was treated in oxygen plasma and then grafted with polysiloxanes (such as using methyltrimethoxysilane (MTMS) and vinyltrimethoxysilane (VTMS)) in an effort to improve strength at the interface of PP fibers and resin matrices. The surface of the fibers was characterized using attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR) and environmental scanning electron microscopy (ESEM) to evaluate the extent of grafting, influence of plasma treatment and fiber surface morphology. Differential scanning calorimetry (DSC) was used to determine the melting temperatures of untreated and treated PP fibers. Characterization analysis of composites included determination of fracture toughness, flexural properties, thermomechanical behavior, and composite fracture surface morphology using Instron, dynamic mechanical analyzer (DMA) and ESEM.

Composites of 20% volume fraction PP fiber mats and VE/Epoxy matrices were successfully fabricated using VARTM. PP fibers showed good wetting characteristics in VE monomer, but void discontinuities were generated at the interface of VE and PP fibers during cure. PP fibers greatly enhanced fracture toughness but reduced strength of both VE and Epoxy matrices. Plasma surface modification under the investigated conditions appeared to damage fibers and did not diminish void formation at the interface. Polysiloxanes-grafting on the fiber surface after oxygen-plasma treatment solved the interfacial discontinuity problem at the cost of degradation of PP fibers. On the other hand, the unmodified PP and Epoxy matrices showed good interfacial continuity.