Surface modification of poly(p-phenylene terephthalamide) fibers with HDI assisted by supercritical carbon dioxide

2019

Polymers

High modulus aramid fiber, such as Kevlar 49, is conventionally prepared by the heat annealing of high strength aramid fiber under a suitable tension at high temperature, especially higher than 500 °C. This enables the mobility of a rigid molecule chain to be rearranged into a more perfect crystalline or orientation structure under tension. However, annealing decreases the tensile strength, since the thermal degradation of the molecular chain at high temperature cannot be avoided. Kevlar 49 fibers treated in supercritical carbon dioxide (scCO2) under tension could improve their mechanical properties at a low temperature. The effects of the tension on the mechanical properties and structure of the Kevlar 49 fibers were studied by mechanical testing, wide-angle and small-angle X-ray scattering (WAXS, SAXS), and scanning electron microscopy (SEM). The results show that the mechanical properties, crystallinity and orientation of the fiber can be improved when the tension is less than 0.6 cN/dtex, which may be due to the increasing of the mobility of a rigid segment with the help of the plasticization of scCO2 and re-arrangement of macromolecular chain into crystalline and orientation structure under tension. What’s more, the amorphous region also was enhanced by crosslinking reaction of toluene 2,4-diisocyanate (TDI) with the chain end groups of the macromolecules in the amorphous regions. However, a decrease of tenacity was found when the tension was higher than 0.6 cN/dtex, which is because the tension was so high that the microfibril was broken. The results indicated that treating the Kevlar 49 fiber in scCO2 under a suitable tension with TDI as a crosslink agent can simultaneously improve both the tenacity and modulus of the fiber.

Section: Methodsmentioning

confidence: 99%

Microstructural Changes of Aramid Fiber Due to Reaction with Toluene 2,4-diisocyanate under Tension in scCO2

2019

Polymers

“…Owing to their unique characteristics such as high strength, high modulus, low density and high resistance, aramid fibers has become one of the ideal reinforcements for various high-performance composites in the fields such as aerospace, sports, automobiles and aviation [1,2,3,4,5,6]. However, the application of AFs-reinforced composites has been largely limited due to poor adhesion to resin matrix.…”

Section: Introductionmentioning

confidence: 99%

Layer-by-Layer Self-Assembly Strategy for Surface Modification of Aramid Fibers to Enhance Interfacial Adhesion to Epoxy Resin

Liu

et al. 2018

Polymers

In this work, the layer-by-layer self-assembly technology was used to modify aramid fibers (AFs) to improve the interfacial adhesion to epoxy matrix. By virtue of the facile layer-by-layer self-assembly technique, poly(l-3,4-Dihydroxyphenylalanine) (l-PDOPA) was successfully coated on the surface of AFs, leading to the formation of AFs with controllable layers (nL-AF). Then, a hydroxyl functionalized silane coupling agent (KH550) was grafted on the surface of l-PDOPA coated AFs. The properties such as microstructure and surface morphology of AFs before and after modification were characterized by FTIR, XPS and FE-SEM. The results confirmed that l-PDOPA and KH550 were successfully introduced into the surface of AFs by electrostatic adsorption. The interfacial properties of AFs reinforced epoxy resin composites before and after coating were characterized by interfacial shear strength (IFSS), interlaminar shear strength (ILSS) and FE-SEM, and the results show that the interfacial adhesion properties of the modified fiber/epoxy resin composites were greatly improved.

“…[15] Supercritical carbon dioxide (scCO 2 ) is an environmental method because of its good penetrating and swelling effects, and it has been widely utilized in some applications. [16][17][18] Moreover, based on previous reports, scCO 2 is an effective way to uniformly transfer the precursor into a matrix. [19][20][21] Hutton et al impregnated the alkyl ketene dimers into filter paper substrates using scCO 2 , which demonstrated that the dispersion was greatly enhanced.…”

Section: Introductionmentioning

confidence: 99%

Effects of different supercritical temperatures on the modification of aramid pulp surface via coating silica to enhance the properties of EPDM composites

Ding

et al. 2020

Polymer Composites

Poor dispersion is a major disadvantage of aramid pulp (AP) reinforced composites. In this study, nano-silica (SiO 2), as the surface modifier and reinforcing agent, was synthesized on AP surfaces to improve the dispersed character in ethylene-propylene-diene elastomer (EPDM) using supercritical carbon dioxide (scCO 2). The influence of the temperature of scCO 2 on treated AP, configuration of the surface, and mechanical performance of AP/EPDM composites were studied. Based on the results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, SiO 2 was chemically grafted onto the AP surface. The SiO 2 nanoparticles were uniformly deposited on the AP surface, and the roughness of AP was increased based on the SEM results. The optimum temperature of the supercritical reaction was 100 C considering the results of all the tests. Under the optimum temperature and with 10 phr of AP, the mechanical properties, oil resistance, and dynamic mechanical properties of the SiO 2-AP/ EPDM composites were investigated. The tensile strength and tear strength of the SiO 2-AP/EPDM were improved by 121.1 and 134.9%, respectively, compared with that of the pure AP/EPDM composites. The fracture surface of the SiO 2-AP/EPDM composites showed that SiO 2-modified AP had a good dispersion in EPDM, and AP and EPDM had good interfacial bonding. Dynamic mechanical analysis results showed that the storage modulus of the composites was improved greatly compared with the pure AP/EPDM, and the loss factor also increased. The oil resistance of the composites was also improved.