Environmentally friendly poly(butylenesuccinate-co-butyleneazelate) (P(BS-co-BAz)s) aliphatic copolyesters with composition-dependent thermomechanical properties were synthesized from succinic acid (SuA), 1,4-butanediol (BDO), and dimethylazelate (DMAz) through a two-step polycondensation reaction. The molar SuA/AzA ratio was varied from 4:1 to 1:4, and the chemical structure and molecular characteristics of resulting (co)polyesters were characterized by NMR and SEC, whereas thermal properties and crystallinity were studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analyses (DMTA), and X-ray diffraction (XRD). A good agreement between theoretical and experimental SuA/AzA molar ratios in the copolyesters was achieved, together with the recovery of semicrystalline random copolymers of uniform composition along the chains. NMR, DSC, DMTA, and XRD results show that depending on their composition the P(BS-co-BAz) copolyesters might find applications from elastomers to high-impact thermoplastics.
Aluminum alloys are widely used in aircraft applications, especially series 2xxx (Cu) and 7xxx (Ti). Those alloys offer improved mechanical properties compared to pure aluminum, but are strongly sensitive to corrosion. Chromic anodizing combined with chromate containing epoxy primer was used as an efficient system to prevent corrosion. Nevertheless, due to health and environmental issues, this treatment is going to be forbidden. Alternative solutions have to be developed to reach aircraft standards considering health and environmental concerns. This work aims at proposing an alternative protective system, consisting in an oxide layer obtained from sulfotartaric anodizing (TSA) and coated with benzoxazine organic layers. Benzoxazine resins offer high chemical resistance and low shrinkage and so are very good candidates for coating applications. Investigated layers have been prepared on both bare and clad Al-2024 T3 substrates. The morphology and the thickness of coating systems were determined using Field Emission Gun Scanning Electron Microscopy (FEG-SEM). Electrochemical Impedance Spectroscopy (EIS) was used to characterize the electrochemical behaviour of obtained systems and separated layers in order to emphasize synergetic effects. The AC/DC/AC electrochemical tests were carried out to evaluate the cathodic disbonding sensitivity of these new coating systems. The results were fitted by Equivalent electrical circuits to model the electrochemical properties of different layers and the evolution of their properties over immersion time in an aggressive saline solution and during AC/DC/AC cycles. The results confirmed the strong potential of such systems for future corrosion protection applications.
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