In the present work, a Si/Zr based sol–gel (SG) coating was deposited on 316L stainless steel plates, previously treated by passivation (SSO) or electropolishing (SSEP) producing two different surface states. The SG coatings were compared for SSO and SSEP substrates in terms of morphology, topography and tribocorrosion response. The coating topography revealed a smoother surface for the Si/Zr-SSEP system. The coating deposited on the smoothest surface (Si/Zr-SSEP) presented half of the thickness of the one deposited on the roughest surface (Si/Zr-SSO). Tribocorrosion behavior was studied under potentiostatic control at anodic potential with a continuous recording of current (I) during sliding (pin-on-disc and alumina ball counterbody). Both SG systems showed an increase of current upon 100 sliding contact cycles indicating corrosion activity. After tribocorrosion tests, both systems revealed scratches, typical of abrasion, and coating removal in the wear tracks; the alumina counterparts presented accumulation of wear particles adhered to their surfaces. In conclusion, the initial surface state of the substrate modified the coating thickness, topography but did not significantly alter the tribocorrosion response of the studied SG systems.

This investigation addresses the effect provided by industrial surface finishes on the tribocorrosion properties of 316L stainless steel exposed to NaCl solution. Three distinct surface treatments were evaluated: passivation (SSO), electropolishing-passivation (SSEP) and micro-undulation (SSM mechano-chemical + electropolishing + passivation). For the tribocorrosion tests, a potentiostatic approach was considered in order to highlight the alloy behavior under two opposite situations, where repassivation of the surface would be thermodynamically possible or not (anodic or cathodic polarization, respectively). The outcomes demonstrated that the surface treatments were either harmful (SSEP) or beneficial (SSM) in terms of resulting tribocorrosion resistance. The specific topography of the micro-undulated sample decreased the real contact area and improved the surface lubrication in aqueous medium. SSEP presented the highest chemical wear and several factors seemed to have contributed for it, including the chemical, mechanical and structural properties of the passive film. Regardless the surface treatment, the tribocorrosion response was modified by the applied potential and more severe damage was determined under anodic polarization. At this potential, calculations of the total surface degradation suggested that volume loss was mainly dominated by chemical wear.

The effect of three different cerium salts (Ce(NO3)3·6H2O, CeCl3·7H2O and Ce(OOCCH3)3·5H2O) on the ring-opening polymerization (ROP) of a model diamine-based benzoxazine (4EP-pPDA) was investigated. With the incorporation of the cerium salts, the curing temperature of 4EP-pPDA is reduced substantially, and the glass transition temperatures of the resulting networks are increased significantly. The three cerium salts exhibit different catalytic activities, which were analyzed by FT-IR, NMR, and energy-dispersive X-ray (EDX). Ce(NO3)3·6H2O was found to exhibit the best catalytic effect, which seems to be related to its better dispersibility within 4EP-pPDA benzoxazine precursors.

In this paper, a 4- ethylphenol- para- phenylenediamine ( 4EP- pPDA) benzoxazine has been applied and cured on previously anodized AA2024- T3 substrates. The porous surface oxide layers obtained from sulfo- tartaric anodizing appeared to be highly impregnated by the benzoxazine resin, sealing the anodic films. Through rheological, morphological and chemical characterization, the curing process has been identified to be the key step for the impregnation to occur, related to the low viscosity of the 4EP- pPDA benzoxazine attained during thermal curing. Moreover, the typical surface porosity of the anodic layer reappeared after curing, offering a good anchoring to possible top coats. Finally, high and enduring barrier properties of this hybrid organic- inorganic layer have been highlighted through Electrochemical Impedance Spectroscopy ( EIS) and correlated with recent results obtained by Molecular Dynamics Simulations ( MDS). These barrier properties appeared to be strongly influenced by the curing process parameters, as has been assessed using alternative curing cycles limiting their duration and lowering the curing temperature. Consequently, adapting the curing process enables the optimization of the barrier properties of the system while respecting the dependence of the mechanical properties of the AA2024T3 substrate on thermal treatment at high temperatures.

Phenol‐paraphenylenediamine (P‐pPDA) benzoxazines exhibit excellent barrier properties, adequate to protect aluminum alloys from corrosion, and constitute interesting candidates to replace chromate‐containing coatings in the aeronautical industry. For the successful application of P‐pPDA coatings, it is necessary to decrease the curing temperature to avoid the delamination of the coating while preserving the mechanical properties of the alloy, as well as the barrier properties of the coating. However, decreasing the curing temperature leads to less polymerized films, the extent of which requires a quantitative assessment.While the conversion rate of the polymerization reaction is commonly evaluated for bulk samples using differential scanning calorimetry (DSC), a tool for its evaluation in thin films is missing. Therefore, a new approach was developed for that matter using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The relation between the SIMS data integrated from inside thin films and the DSC results obtained on bulk samples with the same curing cycle allowed to calibrate the SIMS data. With this preliminary calibration of the technique, the polymerization of P‐pPDA coatings can be locally determined, at the surface and along the depth of the coating, using dual‐beam depth profiling with large argon cluster beam sputtering.

The Ethylene-Propylene-Diene Monomer (EPDM) is a material used for the housing of the high voltage composite insulators. The stress conditions related to that outdoor exposure causes alteration of the material's properties. Several characterization techniques were used in this study for the evaluation of the thermal aging of the EPDM. The FTIR technique was used to evaluate the molecular behaviors of the material. The Carbonyl Index measurement was used to assess the oxidation rate of the material along the aging by means of FTIR spectroscopy. The crosslink density was measured using the solvent swell method. For the macroscopic characterization, the surface roughness of the aged samples was measured. This study showed that both crosslinking and oxidation were observed within the studied samples with a linear variation along the aging time. The correlation between the molecular and morphological properties was investigated. This study showed that for each structural scale a phenomenon of degradation is observed during the aging. The erosion of the material observed by the use of the surface roughness measurement has an impact on the oxidation of the material which was monitored by the use of the FTIR spectroscopy. Both of these measured parameters increase along the aging time. This increase is more important when the aging temperature became higher.

In this paper, laboratory synthesized Phenol-paraPhenyleneDiAmine (P-pPDA) benzoxazine containing different amounts of B-trimesityl-N-triphenylborazine was applied by spin coating on aluminum and thermally cured. The addition of the borazine derivative (borazine 1) does not appear to modify the curing characteristics of the P-pPDA matrix itself as shown by FTIR, DSC and DEA analyses; however, some interactions - chemical and/or physical (co-crystallization) - between P-pPDA and borazine 1 cannot be excluded. The microstructure of the composites is characterized by a two phase system consisting of a dispersion of nanosized (10-20 nm) clusters for the lowest borazine 1 concentration (0.5 wt%), evolving towards bigger (100-200 nm), agglomerated clusters for higher borazine 1 concentrations (3 wt%) and finally, continuous, dendritic structures within the P-pPDA matrix for the highest borazine 1 concentration (10 wt%). The benzoxazine composite coating containing 0.5 wt % trimesitylborazine derivative showed a largely increased and durable ability to protect the aluminum substrate. It is shown that a highly capacitive behavior and durable barrier properties can be obtained for P-pPDA coatings containing such a low amount of borazine derivative homogeneously dispersed in the benzoxazine matrix. For concentrations of 3 wt%, as agglomeration took place and dendrites appeared for the highest concentration of borazine derivative (10 wt%), the corrosion resistance decreased with time.

A convenient and efficient approach is presented in this study for developing advanced thermosetting composite laminates reinforced or not with 0.5 wt% of pristine CNTs. A highly aromatic benzoxazine monomer was selected as the matrix for the preparation of carbon fiber composites due to its strong intrinsic affinities with CNTs. Fine CNT dispersion was achieved within the whole composite after fabric impregnation leading to a considerable increase of the glass transition temperature of about 50 degrees C. The resulting multiscale composite exibits an improved thermomechanical stability, up to 300 degrees C and its room temperature flexural strength is enhanced from 520 to 700 MPa. Moreover, the confinement of neat CNTs within the whole composite is also found to have a beneficial effect on the fire properties and the water sensitivity of the composite. These promising results highlight that when neat CNTs are able to develop strong interactions with the aromatic resin, the resulting system can provide a new and efficient way to design and improve the properties of composite laminates. (C) 2016 Elsevier Ltd. All rights reserved.

In this paper, the feasibility to apply a laboratory synthesized Phenol-paraPhenyleneDiAmine (P-pPDA) benzoxazine by spin coating on anodized aluminum substrates followed by thermal curing, has been investigated. Prior to coating, sulfo-tartaric anodizing has been carried out aiming at growing porous oxide layers either on 1050 or 2024-T3 aluminum substrates. Optimization of the performance of the benzoxazine coatings to protect the aluminum substrates was achieved by working out conditions preventing delamination of the coatings as observed for non anodized coated substrates and reducing its curing temperature to a level compatible with the requirements of the aerospace industry. Compared to bare substrates coated with P-pPDA, it is shown that highly capacitive and durable barrier properties can be obtained for the same kind of coatings when applied on the anodized substrates. Moreover, in order to respect the thermal sensitivity of aeronautical aluminum substrates, such as 2024-T3, the curing temperature can be limited to 140 degrees C only if the substrates are previously anodized in a sulfo-tartaric acid bath.

A novel biobased benzoxazine monomer containing additional allyl functionality was synthesized using a solventless approach from the reaction of a natural occuring phenol: chavicol, para-phenylene diamine and formaldehyde. The chemical structure of this functionalized benzoxazine monomer was confirmed by H-1 NMR and FTIR. Its polymerization was investigated and monitored by DSC showing two well defined exotherms allowing the selective ring-opening polymerization of benzoxazine functions and the preservation of the allyl functionality. The network crosslink density could be further increased via the controlled polymerization of allyl functionalities with a post-cure in order to adjust the thermo-mechanical properties. When both networks were polymerized, the thermoset presented an excellent thermo-mechanical stability with a T alpha higher than 350 degrees C as measured by DMTA. This exceptional behavior for a potentially biobased benzoxazine resin will allow the preparation of sustainable high performance biocomposite materials. (C) 2016 Elsevier Ltd. All rights reserved.

This work presents a scalable and solventless synthesis of two fully bio-based bis-benzoxazine resins derived from resorcinol, hydroquinone and furfurylamine. The structures of the two synthesized precursors have been studied by H-1 NMR and FTIR spectroscopies and SEC. The polymerization and degradation of the precursors have been investigated and monitored by DSC and TGA. The properties of the resulting polybenzoxazine networks were found to be dependent on the precursor molecular structure. In both cases, an excellent thermomechanical behavior associated with high charring ability were obtained which highlights the great potential of these fully bio-based resins as new matrices for the preparation of structural composites following a sustainable approach. (C) 2016 Elsevier Ltd. All rights reserved.