Rubbery-Modified CFRPs with Improved Mode I Fracture Toughness: Effect of Nanofibrous Mat Grammage and Positioning on Tanδ Behaviour

Abstract

Carbon Fiber Reinforced Polymers (CFRPs) are widely used where high mechanical performance and lightweight are required. However, they suffer from delamination and low damping, severely affecting laminate reliability during the service life of components. CFRP laminates modified by rubbery nanofibers interleaving is a recently introduced way to increase material damping and to improve delamination resistance. In this work, nitrile butadiene rubber/poly(ε-caprolactone) (NBR/PCL) blend rubbery nanofibrous mats with 60 wt% NBR were produced in three different mat grammages (5, 10 and 20 g/m2) via single-needle electrospinning and integrated into epoxy CFRP laminates. The investigation demonstrated that both mat grammage and positioning affect CFRP tanδ behaviour, evaluated by dynamic mechanical analysis (DMA) tests, as well as the number of nano-modified interleaves. Double cantilever beam (DCB) tests were carried out to assess the mat grammage effect on the interlaminar fracture toughness. Results show an outstanding improvement of GI,R for all the tested reinforced laminates regardless of the mat grammage (from +140% to +238%), while the effect on GI,C is more dependent on it (up to +140%). The obtained results disclose the great capability of NBR/PCL rubbery nanofibrous mats at improving CFRP damping and interlaminar fracture toughness. Moreover, CFRP damping can be tailored by choosing the number and positioning of the nano-modified interleaves, besides choosing the mat grammage.

Self-Assembled NBR/Nomex Nanofibers as Lightweight Rubbery Nonwovens for Hindering Delamination in Epoxy CFRPs

“…The obtained structure, that is, nitrile butadiene rubber (NBR) blended with poly­(ε-caprolactone) (PCL), behaves similar to a thermoplastic elastomer (TPE). The interleaving of such nonwovens in epoxy CFRP laminates provides an extraordinary enhancement of the interlaminar fracture toughness in Mode I ( G I up to +480%) and a slight improvement in Mode II, besides a better damping behavior. − However, the resulting laminates suffer from some important T g lowering, strongly depending on the nanomodification extent and the nanofiber rubber amount. Such results suggest the need for a compromise between improved interlaminar fracture toughness, damping, and overall mechanical properties.…”

New Application Field of Polyethylene Oxide: PEO Nanofibers as Epoxy Toughener for Effective CFRP Delamination Resistance Improvement

“…A wide range of thermoplastic polymers have been tested as nonwoven interleaves for increasing interlaminar fracture toughness. Most of them are polyamides (mainly Nylon 6 and Nylon 66) and the polyester poly­(ε-caprolactone) (PCL). ,,− Specialty polymers, such as polyvinylidene fluoride (PVDF), and aromatic ones, such as polysulfone (PSU) and polyetherimide (PEI), have also been explored. ,, Recently, new elastomeric nanofibers based on nitrile butadiene rubber (NBR) were developed , and used for increasing the interlaminar fracture toughness of epoxy-based carbon FRP (CFRP) laminates ,, as well as for enhancing their damping. , These nanofibers enhance the energy release rate ( G ) up to +480%, an enhancement higher than the one usually achieved by interleaving conventional thermoplastic membranes, whose improvement is no more than 150% in general. ,,− …”

“…In the first case, the three-dimensional nanofibrous structure, still present upon composite curing, helps keep adjacent laminates together, hampering the delamination (e.g., Nylons, PVDF, PSU, and PEI). By contrast, in matrix toughening, the polymer melts or “fluidizes” and mixes with the resin before its gel-point: the latter thus becomes less fragile due to plasticization phenomena (e.g., PCL and uncrosslinked NBR , ). In both cases, the energy required for the crack propagation increases, making the delamination more difficult to occur.…”

“…Researchers have made a great effort to enhance the toughening effect of well-established polymeric nanofibers by adding nano-reinforcements, such as carbon nanotubes, ,, or by combining different polymers, for example, producing core–shell nanofibers, , polymer-impregnated nanofibers, , and blended ones, such as the above-mentioned rubbery nanofibers. ,, However, searching for new uses of “basic” and well-established materials is equally important for reducing costs and complexity of manufacturing advanced materials such as nanofibers with integrated high-performance nano-reinforcements or core–shell ones.…”

“…3,36,37 Recently, new elasto- meric nanofibers based on nitrile butadiene rubber (NBR) were developed 25,38 and used for increasing the interlaminar fracture toughness of epoxy-based carbon FRP (CFRP) laminates 25,39,40 as well as for enhancing their damping. 40,41 These nanofibers enhance the energy release rate (G) up to +480%, 39 an enhancement higher than the one usually achieved by interleaving conventional thermoplastic membranes, whose improvement is no more than 150% in general. 3,4,27−35 The nanofibers can act against delamination either by the socalled "bridging" mechanism or by matrix toughening 34 depending on the nanofiber polymer thermal properties.…”