Abstract
The activities of this paper were focused on an in-situ fabrication process for producing two self-healing systems containing dicyclopentadiene and 5-ethylidene-2-norbornene monomers encapsulated in a urea-formaldehyde shell and integration methods applied in the epoxy matrix to analyse and compare the influences of their integration into the neat epoxy matrix. The self-healing systems were first synthesized according to a literature review, and subsequently, an optimization process was conducted for the fabrication process. Neat epoxy specimens were fabricated as reference specimens and subjected to flexural tests. Several integration methods for incorporating the self-healing systems into the epoxy resin were investigated. The optimal method presenting the best dispersion of the healing system was achieved by reducing the viscosity of the epoxy matrix with 10 vol % acetone solution, the addition of a microcapsule in the matrix, and homogenization at 60 °C at 100 rpm. Thermal analysis was performed in order to observe the mass loss obtained with an increasing temperature and phase changes for both poly-urea-formaldehyde (PUF)-dicyclopentadiene (DCPD) and melamine-urea-formaldehyde (MUF)-5-ethylidene-2-norbornene (ENB) systems. The thermogravimetric analysis performed for the PUF-DCPD system indicates a total loss of mass in the range of 30–500 °C of 72.604% and for the MUF-ENB system, indicates a total mass loss in the range of 30–500 °C of 74.093%. Three-point bending tests showed higher mechanical properties for PUF-DCPD (80%) than MUF-ENB (40%) compared to the neat epoxy systems. Numerical simulations were performed to obtain a better understanding of the microcapsule behavior when embedded in an epoxy matrix.
Highlights
As thermoset polymers possess good physical and mechanical properties, are easy to process, and have a low cost of production, they are extensively used in the manufacturing process of fiber reinforced polymer (FRP) composite structures.Polymers 2020, 12, 1052; doi:10.3390/polym12051052 www.mdpi.com/journal/polymersDuring their service life, these polymer composite materials are exposed to several mechanical loads that cause distinctive failure mechanisms with respect to their morphology, when compared to metals.As crack formation appears as a result of mechanical loads, the necessity of repairing these materials became an important aspect in the development of such materials
The thermogravimetric analysis performed for the PUF-DCPD system indicates a total loss of mass in the range of 30–500 °C of 72.604%
Because the the stirring themain main factor of microcapsule formation, therate stirring rate was to 500 rpm to overcome the traces of non-encapsulated DCPD, halving the unreacted monomer
Summary
As thermoset polymers possess good physical and mechanical properties (good wettability, corrosion resistance, and high strength), are easy to process, and have a low cost of production, they are extensively used in the manufacturing process of fiber reinforced polymer (FRP) composite structures.Polymers 2020, 12, 1052; doi:10.3390/polym12051052 www.mdpi.com/journal/polymersDuring their service life, these polymer composite materials are exposed to several mechanical loads that cause distinctive failure mechanisms with respect to their morphology, when compared to metals.As crack formation appears as a result of mechanical loads, the necessity of repairing these materials became an important aspect in the development of such materials. During their service life, these polymer composite materials are exposed to several mechanical loads that cause distinctive failure mechanisms with respect to their morphology, when compared to metals. As crack formation appears as a result of mechanical loads, the necessity of repairing these materials became an important aspect in the development of such materials. Several self-healing techniques have emerged and been investigated in order to overcome this limitation [1,2]. Self-healing techniques are rapidly growing, comprising a wide range of self-healing polymer systems. Drawing inspiration from natural healing systems, researchers have designed and developed materials that can cure themselves after a damage event, extending their lifetime
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