Modification of polyamide flock fibers and their use in composites

Date

2024-9-06

Author

San, Murat

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Electrostatic flocking is a scalable and cost-effective method which enables the placement polymeric fibers vertically on an adhesive coated surface. This feature makes electrostatic flocking a promising method to overcome delamination which is considered as a critical failure mode of laminated composites. In this study, polyamide 6,6 (PA6,6) flock fibers were used to toughen laminated composites by electrostatic flocking method. Contrary to previous studies utilizing electrostatic flocking in interleaving, here surface modifications of PA6,6 flock fibers were performed to induce effective toughening mechanisms such as bridging and straining. To induce mechanical interlocking by increasing surface area of flock fibers, surface roughening was studied by surface swelling based non-solvent induced phase separation method. Effect of swelling solution concentration and type of non-solvent on morphology was studied. Sufficient swelling to induce phase separation was obtained with 70wt% formic acid and when butanol was used as non- solvent rough morphology formed consists of interconnected crystalline particles. To generate active bonding sites for further modifications and epoxy matrix, silane functionalization was performed. Then, to ensure movement along electric field and enhance interfacial interaction with epoxy, flock fibers were further modified by coating with graphene oxide (GO). This approach possessed novelty in that GO could be utilized in aligned scaffolds prepared using electrostatic flocking. Oxygen containing functional groups of GO were intended to provide sufficient charging within electric field, and surface functionalities which can form strong hydrogen bonds with epoxy. Surface modified flock fibers were placed vertically on composite prepregs by using electrostatic flocking method. Then composites were fabricated by prepreg hand lay-up. Both glass fiber/epoxy (GFRP) and carbon fiber/epoxy (CFRP) composites prepared by flock fiber interleaving and mode I fracture toughness was measured by double cantilever beam (DCB) testing. Fracture surfaces of un-flocked and flocked composites were characterized by SEM to understand toughening mechanisms activated by flock fibers. It was found that flocked GFRPs resulted in decreased fracture toughness compared to un-flocked GFRP. On the contrary, surface modified PA6,6 fibers flocked CFRP showed 83.1% improvement in initiation toughness and 65.1 % improvement in propagation toughness compared to un-flocked CFRP. Surface modifications enhanced the interaction between flock and epoxy. Hence, the main toughening mechanism activated by flock fibers at the interlayer changed compared to un-modified flock fibers.

Subject Keywords

Electrostatic Flocking, Glass fiber/epoxy, Carbon fiber/epoxy, Delamination, Surface modification

URI

https://hdl.handle.net/11511/111447

Collections

Graduate School of Natural and Applied Sciences, Thesis