Catégories
sustainable

Multifunctionality of structural nanohybrids: the crucial role of carbon nanotube covalent and non-covalent functionalization in enabling high thermal, mechanical and self-healing performance

Multifunctionality of structural nanohybrids: the crucial role of carbon nanotube covalent and non-covalent functionalization in enabling high thermal, mechanical and self-healing performance

Raimondo, M., Naddeo, C., Vertuccio, L., Bonnaud L., Dubois, Ph., Binder, W.H., Sorrentino, A., Guadagno, L.

Abstract : This study proposes new kinds of functionalization procedures able to preserve specific properties of carbon nanotubes (CNTs) and to improve compatibility with the epoxy matrix. Through a covalent approach, for the first time, CNTs are functionalized with the same hardener agent, 4,4′-diaminodiphenyl sulfone, employed to solidify the epoxy matrix and capable to fulfill mechanical requirements of industrial structural resins. The same CNTs are non-covalently modified through the polymer wrapping mechanism with benzoxazine (Bz) terminated polydimethylsiloxane (PDMS). The comparison between electrical and mechanical properties of the nanocomposites highlights the success of the non-covalent functionalization in determining an increase in the glass transition temperature (Tg) and in better preserving the unfunctionalized CNT electrical conductivity. Besides, tunneling atomic force microscopy (TUNA), powerful to catch ultra-low currents, has been used for revealing the morphology on nanoscale domains and detecting the conductivity on the same location of CNT/epoxy resins. No electrical contacts to the grounds have been used for the TUNA analysis; a procedure that does not alter the results on the interface domains which experience contact areas with strong differences in their properties. The effectiveness of performed CNT functionalizations as a route to impart self-healing efficiency to the resin formulations has also been proved.

Catégories
sustainable

Cerium Salts: An Efficient Curing Catalyst for Benzoxazine Based Coatings

Cerium Salts: An Efficient Curing Catalyst for Benzoxazine Based Coatings

Tao Zhang, Leila Bonnaud, Jean-Marie Racquez, Marc Poorteman, Marjorie Olivier and Philippe Dubois

Abstract :  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.

Catégories
sustainable

High‐Performance Bio‐Based Benzoxazines from Enzymatic Synthesis of Diphenols

High‐Performance Bio‐Based Benzoxazines from Enzymatic Synthesis of Diphenols

Leïla Bonnaud, Benjamin Chollet, Ludovic Dumas, Aurélien A. M. Peru, Amandine L. Flourat, Florent Allais, and Philippe Dubois

Abstract :  This paper reports the preparation, characterization, and performance of three low viscosity fully bio‐based benzoxazine resins synthesized from bio‐based furfurylamine, paraformaldehyde, and three new enzymatic originated diphenols obtained through a sustainable and highly selective lipase‐catalyzed enzymatic process from p‐coumaric acid, and three bio‐based diols (propanediol, butanediol, and isosorbide, respectively). The enzymatic method is used for the first time, to the authors’ knowledge, to design specific diphenolic structures dedicated to the preparation of benzoxazine thermosetting resins whose precursors exhibit easy handling within a wide processing window (from room temperature up to 200 °C). The resulting cross‐linked materials present high glass transition temperature (T > 200 °C) and inherent charring ability upon pyrolysis (≈50 wt% at 1000 °C). These results open a valuable and new pathway to develop enhanced benzoxazines and bring them new properties.

Catégories
sustainable

Enhancement of thermal conductivity in epoxy coatings through the combined addition of expanded graphite and boron nitride fillers

Enhancement of thermal conductivity in epoxy coatings through the combined addition of expanded graphite and boron nitride fillers

Isaac Isarn, Leïla Bonnaud, Lluís Massagués, Àngels Serra, Francesc Ferrando

Abstract :  Expanded graphite (EG) and boron nitride (BN) were used as fillers to impart thermal conductivity (TC) while maintaining electrical insulation of a homopolymerized cycloaliphatic epoxy matrix. Even though EG leads to a higher increase of TC than BN (550% of enhancement with only a 7.5 wt.% of EG), EG is also electroconductive and its ratio in the formulation must be lower than the percolation threshold. Formulations with proportions between 2.5–7.5 wt.% of EG as the filler and mixtures with EG and a 40 wt.% of BN were thermally polymerized and composites with 70 wt.% of BN and 2.5/5.0 wt.% of EG were also prepared under pressure and then cured in the oven. Over 2 W/m K was achieved (i.e. more than 1500% of enhancement in reference to the neat epoxy). The composites containing a 40 wt. % of BN and 2.5 wt % of EG or 70% wt. % of BN and 5 wt % of EG were found to keep the insulation character. Mechanical and thermal characteristics of the prepared materials were also evaluated.

Catégories
sustainable

Enhancement of thermal conductivity in epoxy coatings through the combined addition of expanded graphite and boron nitride fillers

Enhancement of thermal conductivity in epoxy coatings through the combined addition of expanded graphite and boron nitride fillers

Isaac Isarn, Leïla Bonnaud, Lluís Massagués, Àngels Serra, Francesc Ferrando

Abstract :  Expanded graphite (EG) and boron nitride (BN) were used as fillers to impart thermal conductivity (TC) while maintaining electrical insulation of a homopolymerized cycloaliphatic epoxy matrix. Even though EG leads to a higher increase of TC than BN (550% of enhancement with only a 7.5 wt.% of EG), EG is also electroconductive and its ratio in the formulation must be lower than the percolation threshold. Formulations with proportions between 2.5–7.5 wt.% of EG as the filler and mixtures with EG and a 40 wt.% of BN were thermally polymerized and composites with 70 wt.% of BN and 2.5/5.0 wt.% of EG were also prepared under pressure and then cured in the oven. Over 2 W/m K was achieved (i.e. more than 1500% of enhancement in reference to the neat epoxy). The composites containing a 40 wt. % of BN and 2.5 wt % of EG or 70% wt. % of BN and 5 wt % of EG were found to keep the insulation character. Mechanical and thermal characteristics of the prepared materials were also evaluated.

Catégories
sustainable

A benzoxazine/substituted borazine composite coating: A new resin for improving the corrosion resistance of the pristine benzoxazine coating applied on aluminum

A benzoxazine/substituted borazine composite coating: A new resin for improving the corrosion resistance of the pristine benzoxazine coating applied on aluminum

Alexis Renaud⁠, Leïla Bonnaud⁠, Ludovic Dumas⁠, Tao Zhang⁠, Yoann Paint⁠, Francesco Fasano⁠, Olesia Kulyk⁠, Eva Pospisilova⁠, Bernard Nysten⁠, Arnaud Delcort⁠e, Davide Bonifazi⁠, Philippe Dubois⁠, Marie-Georges Olivier⁠, Marc Poorteman

Abstract : 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.