Soumen Jana

Chemorheology of reactive graphitic nanofiber-reinforced epoxy as a composite matrix

Based on the development of a series of nanofiber/epoxy matrices with reactive graphitic nanofibers (r-GNFs) in our previous work, the flow behavior and cure process of the nanofiber/epoxy materials with 0.1, 0.3 and 1.3 wt% of r-GNFs were investigated by rheological method and differential scanning caloremetry (DSC) tests. Non-isothermal and isothermal viscosity curves (at 110, 115 and 120°C, respectively) were obtained. The gel time was obtained from the isothermal tests for the neat epoxy resin and the nanofiber/epoxy systems. Nanofiber/epoxy matrix has longer gel time. Arrhenius activation energies obtained from both DSC and rheological tests showed close values for the nanofiber/epoxy matrices with different contents of r-GNFs. These results on the flow and curing characteristics of the nanofiber/epoxy matrices indicated that the nanofiber/epoxy matrices have good processability for manufacturing fiber composites and are expected to improve the properties of the fiber composites. Both isothermal and non-isothermal viscosity models were applied to describe the rheological behaviors of the nanofiber/epoxy matrices. On the one hand, a four-parameter isothermal model was found to be valid in simulating the isothermal process; on the other hand, a five-parameter non-isothermal model was constructed and found suitable for describing the non-isothermal behavior of the nanofiber/epoxy matrices. The theoretical results from the chemorheological models were found to be in good agreement with the experimental data.

Evaluation of Adhesion Property of UHMWPE Fibers/Nano-epoxy by a Pullout Test

Ultrahigh-molecular-weight polyethylene (UHMWPE) fibers have poor wetting and adhesion properties to polymer resins because of the inert surface of the fibers. In our previous study, a reactive nano-epoxy matrix, developed by making a modification on the matrix with reactive graphitic nanofibers (r-GNFs), showed improved wettability to UHMWPE fibers. In this work, fiber bundle pullout tests were conducted to evaluate the adhesion property between the UHMWPE fibers and the nano-epoxy matrices. Analysis of load–displacement curves from pullout tests shows that debonding initiation load and ultimate debonding load increased considerably, because of effective improvement of adhesion between the UHMWPE fibers and nano-epoxy matrix. Stress-controlled and energy-controlled models of interfacial debonding were applied for theoretical analyses. Results from ultimate IFSS, frictional shear stress, and critical energy-release rate are in good agreement with experimental results. Nano-epoxy matrix with 0.3 wt% r-GNFs shows effective improvement in terms of adhesion property between UHMWPE fiber and epoxy.

Preliminary study on solid-state foaming of PMMA/CNT nanocomposites

Polymer nanocomposites with carbon nano tubes (CNTs) added in the polymer matrices have been shown to have improved material properties comparing to their neat forms. Foaming of polymer nanocomposites is even more interesting because these foams promise higher strength-to-weigh ratio and multifunctionality. However, many foaming results on polymer nanocomposites are inconclusive, for example, the effect of nano-additives on the bubble nucleation. In this study, solid-state foaming of pure PMMA and PMMA/CNT composite were performed. CNTs were dispersed in PMMA solution with ultrasonication. Microcellular foams were achieved in both cases. The resulted relative density and microstructures were investigated. It was found that nano carbon tubes aggregated on the cell walls of the microcellular foams. In terms of the cell size and relative density, there is no significant difference between pure PMMA and PMMA/CNT foams. Better dispersion of CNTs is needed in order to further study the CNT effect on the solid-state foaming process.Copyright