High‐performance fiber‐reinforced composites with a polydopamine/epoxy silane hydrolysis‐condensate bilayer on surface of ultra‐high molecular weight polyethylene fiber

Abstract

A bilayer structure with polydopamine (PDA) transition layer and 3-glycidyl ether oxy-propyl trimethoxy silane (GOPTS) hydrolysiscondensate strengthened layer on the surface of ultra-high molecular weight polyethylene (UHMWPE) fiber is prepared to improve the damage resistance of composites and more efficient stress transmission in composites. PDA is covered on the surface of UHMWPE fiber and then GOPTS is hydrolyzed and condensed to form inorganic -O-Si-O-with epoxy groups on the PDA layer. In addition, the surface activated nano-SiO 2 is dispersed in the epoxy resin to increase the strength of the matrix resin. The results show that the interfacial shear strength (IFSS), the impact strength, the flexural strength and flexural modulus of UHMWPE-PDA-GOPTS/EP-SiO 2 increase by 99.1%, 54.1%, 76.8%, and 36.6% respectively compared with unmodified UHMWPE/EP. The chemical compositions of the treated fiber surface are characterized by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (ATR-FTIR). With the help of the scanning electron microscopy, the interface failure and reinforcement mechanism of the composites are further explored due to UHMWPE fiber shear yield deformation, UHMWPE fiber fracture, matrix resin cracking and the relative sliding friction between the fiber and matrix.

Surface modification of UHMWPE fibers with chlorination and polydopamine for enhancing the mechanical properties of composites

“…The amino groups of the PDA layer could react with the epoxy groups of epoxy resin to form chemical bonds, thereby improving the interfacial bonding between fibers and resin. More epoxy block residues adhered on the surface of the UHMWPE fibers with chlorinated and following PDA deposition were found in Figure 9d, which indicated that the efficient dispersion of the stress in composites causes matrix resin to break into the small blocks attributing to the strong interfacial adhesion, and the fiber necking deformation was not widely observed because the stress transfer was interrupted between the short UHMWPE fibers with 5–8 mm in our composites, which was different form the stress transfer of fiber felts composites as the reported literature 28 …”

“…It showed that four characteristic peaks of 2917, 2848, 1472, and 717 cm −1 were attributed to methylene asymmetric stretching vibration, methylene symmetric stretching vibration, methylene asymmetric vibration and methylene in‐plane swing of UHMWPE, respectively 35 . For UHMWPE‐PDA fibers and UHMWPE‐Cl‐PDA fibers, the broad reflection bands around 3200–3600 cm −1 exhibited relatively stronger intensities compared with UHMWPE fibers and UHMWPE‐Cl fibers due to the asymmetric tensile vibration of OH and NH 28 from PDA deposited on the surface of UHMWPE fibers. While 1604 cm −1 was attributed to the CC stretching vibration of indole, suggesting that PDA had been successfully wrapped on the surface of the fibers.…”

“…The stress‐displacement curves were obtained by recording the procedure of the single‐fiber pull‐out test as shown in Figure 7c. And the integral area of the stress‐displacement curve, which represented the absorbed energy when the material yielded, implied that UH‐Cl‐PDA had the strongest impact performance 28 …”

“…The test was carried out using a universal testing machine with a tensile speed of 2 mm/min, and the end of a bundle of fibers with a depth of 1.5 mm was pull‐out from resin matrix. Ten tests per sample were run to obtain the average value of maximum pull‐out force ( F max ) 28 . The IFSS ( τ ) was calculated from the following equation 34…”

“…Recently, a biomimetic surface modification method with dopamine (DA) had attracted much attention because it could attach to most materials in mild conditions, 25,26 that was formation of polydopamine (PDA) through the oxidative self‐polymerization of dopamine. Hu et al and Zhang et al 27,28 explored the use of DA to improve interfacial adhesion between the fibers and resins, which certainly increased the impact strength of UHMWPE fibers/resin matrix composites while maintaining the inherent properties of the fibers. Especially, it is very impressive that the flexural modulus and flexural strength of composites were enhanced to 17.1% and 29.2% because the formation of rigid PDA coating increased the stiffness of UHMWPE fibers, which, to a certain extent, can overcome the defect of low modulus of UHMWPE fibers.…”