Abstract
In the present research, the effect of Zn2Al layered double hydroxides (LDH) and nickel (II)-EDTA complex intercalated LDH (LDH-[Ni(EDTA)]-2) on the cure kinetics of glass fiber/epoxy prepreg (GEP) was explored using nonisothermal differential scanning calorimetry (DSC). The results showed that LDH caused a shift in the cure temperature toward lower temperatures while accelerating the curing of epoxy prepregs. The use of LDH-[Ni(EDTA)]-2 more profoundly influenced the acceleration of the curing process. The curing kinetics of prepregs was assessed through the differential isoconversional Friedman (FR) technique and the integration method of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS). A decrease was detected in the E α value of glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELP) and glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELNiP) prepregs at small cure degrees relative to GEP, suggesting the catalytic effect of LDH or LDH-[Ni(EDTA)]-2 on the initial epoxy/amine reaction. Furthermore, LDH-[Ni(EDTA)]-2 performed better due to the catalyst role of nickel (II). Moreover, the activation energy exhibited lower reliance on the degree of conversion in the cases of GELP and GELNiP rather than pure epoxy prepregs. An autocatalytic model was used to evaluate the curing behavior of the system. Based on the results, the curing reaction of the epoxy prepreg can be described by the autocatalytic Šesták-Berggren model even after the incorporation of LDH or LDH-[Ni(EDTA)]-2. The kinetic parameters of the autocatalytic model (such as E α , A , m , n ) and the equations explaining the curing behavior of prepregs were introduced as well whose predictions were in line with the experimental findings.
Highlights
Glass fiber/epoxy prepregs have been extensively utilized in the structures of automobiles as well as aerospace and space industries owing to their excellent strength-to-weight ratios and proper thermal and electrical features [1,2,3]
The Eα of glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELP) and glass fiber/LDH-[Ni(EDTA)]-2/epoxy (GELNiP) was less than glass fiber/epoxy prepreg (GEP) which might be assigned to the improved reactivity of the system upon layered double hydroxides (LDH) and LDH-[Ni (EDTA)]-2 incorporation
The FR-obtained average activation energies (61.24, 48.8, and 35.8 kJ.mol−1 for GEP, GELP, and GELNiP, respectively) were more than those determined by the KAS (56.9, 40.5, and 27.3 kJ mol−1 for GEP, GELP, and GELNiP, respectively), both approaches predicted the same trend of the apparent activation energy
Summary
Glass fiber/epoxy prepregs have been extensively utilized in the structures of automobiles as well as aerospace and space industries owing to their excellent strength-to-weight ratios and proper thermal and electrical features [1,2,3]. The ongoing works in the field of composites show that further modification of the systems with nanomaterials could improve their other characteristics such as the interlaminar strength of laminated composites through prepregs. These structures can be fabricated by two general methods; incorporation of nanofillers in the epoxy resin and using the resultant modified epoxy resin to prepare the composite laminate or the introduction of nanofillers on the reinforcing fabric and/or into the interlaminar zone prior to preparing the composite laminate [10, 11]. The layered double hydroxides (LDHs) belong to a class of nanofillers in which positively charged metal hydroxide layers are rested on the brucite structures with intercalated hydrated anions. LDHs are regarded as hydrotalcite-like compounds or anionic clays with the general formula which MII and MofIII[MreIfIe1-rxMtoIIIdxiv(aOleHn)t2]an(Ad nt-rxi/nv.amleHnt2Om),etianl
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