Guy Raffin

Functionalized silica for heavy metal ions adsorption

Abstract Heavy metals adsorbents were prepared by co-condensation of tetraethoxysilane and functionalized trialkoxysilane RSi(OR′)3. Functionalized porous silicas with aminopropyl (H2N(CH2)3-), [amino-ethylamino]propyl- (H2N-(CH2)2-NH(CH2)3), (2-aminoethylamino)-ethylamino]propyl (H2N-(CH2)2-NH-(CH2)2-NH(CH2)3-), and mercaptopropyl (HS-(CH2)3-) groups were synthesized using dodecylamine as structure directing agent. These materials have been characterized by elemental analysis, powder X-ray diffraction, nitrogen gas sorption, Fourier transform infrared and Raman spectroscopies and thermogravimetric analysis. These organo-silicas were prepared for use in the removal of heavy metal ions from aqueous solutions. Samples synthesized with [amino-ethylamino]propyl- and (2-aminoethylamino)ethylamino]propyl- functions show a high loading capacity for Cu2+, Ni2+, Co2+ and the anion Cr(VI). The sample synthesized with a mercaptopropyl function has a high loading capacity for Cd2+.

Behaviour of nanoparticles during high temperature treatment (Incineration type)

The treatment of waste containing nanoparticles (NP) will become a matter of first importance being given the increasing production and use of engineered NP. At present no specific end of life treatment is planned for such waste and most of the time it follows the path of conventional waste in incineration plants. The study of the behavior of NP at high temperature may help to define dedicated procedures and eventually lead to new regulations. This work deals with the set up of an incineration mounting at a laboratory scale. This assembly tested on NP samples shows significant results and interesting trends.

Phenolic resins (III) - Solid state structures and thermal properties of cross-linked phenolic resins

Non-destructive, solid state physicochemical techniques were used to analyze the structure of phenolic resins prepared with precise syntheses and thermal parameters. The results obtained with solid state 13C NMR (CP/MAS) and FTIR were analyzed and related to the thermal characteristics of the networks (DSC and TGA/FTIR). The data were correlated with parameters and conditions of syntheses of resols and of the initial prepolymers.

Phenolic resins - Characterizations and kinetic studies of different resols prepared with different catalysts and formaldehyde/phenol ratios (I)

The physicochemical and kinetic properties of resols prepared with different catalysts (NaOH, LiOH and Ba(OH)2) and variable formaldehyde/phenol ratios (2.5 £ R £ 3.5) were followed to determine their effects on the mechanisms and reaction products at a fixed pH and temperature. Kinetic monitoring and quantification of residual monomers were carried out by liquid chromatography coupled with mass spectrometry (LC/UV/MS), by 13C nuclear magnetic resonance (NMR) and by chemical assay for formaldehyde. Oligomer formation (n ≥ 2) was determined by LC/UV/MS, size exclusion chromatography (SEC) and 13C NMR. It was found that minor compounds form during syntheses (phenol methanol hemiacetals, hemiacetals of phenol and of oligomers…) and that the ratio R affects primarily the kinetics of formation of monomers and oligomers, in contrast to the catalysts that modify reaction mechanisms. The understanding of the structure of the resols was an important step for the determination of the final properties of the material.

Synthesis, mechanisms and kinetics of formation of bi-component polyurethanes

In order to understand the single-step molten state reactivities of a diaromatic isocyanate (4,4’ dPDhenylmethane diisocyanate MDI), the mechanisms and reaction kinetics were modelled using a monofunctional aromatic isocyanate (para-tolyisocyanate p-TI) and hydroxytelechelic polyols (polyethylene glycol PEG) (polypropylene glycol PPG) with variable macromolecular chains and structure (from 200 to 2000 g.mol-1). The molar ratio of reactive functions NCO/OH was set at 1.1. We were able to characterise the bi-component polyurethanes synthesised and identify side products formed (urea, trimer, allophanate…). The results were obtained by the use of a panoply of classical analytical techniques (NMR, FTIR, HPLC/UV/MS, ESI/MS, DSC) or those more recent in the field of synthetic polymers (MALDI-TOF). This work shows the necessity of using several efficient and complementary techniques in order to understand the molten state reaction mechanisms and kinetics of these complex PU systems.

Phenolic resins (IV). Thermal degradation of crosslinked resins in controlled atmospheres

The study involved the thermal degradation of phenolic resins in controlled atmospheres (inert and oxidizing). Its aim was to characterize volatile organic compounds (VOC) and inorganic compounds released during heat treatment. The methods used were thermogravimetry coupled with thermodesorption/gas chromatography/mass spectrometry (TG/TCT/GC/MS) and thermogravimetric analysis coupled with infrared (TGA/IR). At the end of the heat cycle, residues were characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (solid state 13C NMR (CP/MAS)). The data show that the synthesis conditions of the crosslinked resins, the controlled environment and the temperature of the degradation heat cycle, all affect the composition of volatile compounds and residues at the end of the cycle. The data have enabled us to propose decomposition reaction mechanisms for these resins in oxidizing and inert environments.

Heat stability and degradation of thermally stable prepolymers in a controlled atmosphere. III. Thermal homopolymerization cycle of dicyanate monomers and physicochemical characterization of the crosslinked system

Monitoring the homopolymerization of cyanate monomers during heat treatment shows that triazine rings formed during the 180°C step. Oligomers were composed of 1 to 15 triazine rings. Analysis of compounds formed before the gel point revealed the presence of side products containing terminal phenolic functions: the phenol-cyanate (M0-OH) and oligomers with one or two hydroxyl functions (M1,2,…-OH). Kinetic and mechanistic monitoring during treatment at 210°C in the solid state allowed the determination of the structure of the final system and the detection and quantification of unreacted cyanate functions. Kinetic and thermal studies in the temperature range of 100 to 220°C showed that the homopolymerization of hexafluorobisphenol A dicyanate starts at a lower temperature and is slower than that of bisphenol A dicyanate. Thermogravimetric data showed that residual monomers volatilized between 150 and 300°C, while the degradation of crosslinked products occurred between 400 and 600°C and involved two distinct steps.

Thermal degradation of polyurethane bicomponent systems in controlled atmospheres

Although the thermal degradation of polyurethanes has been extensively studied in the past, the use of a panoply of recent analytical techniques has provided more detailed data and enabled us to confirm prior findings on the thermal degradation of bicomponent polyurethanes. The thermal behaviour of bicomponent polyurethanes in conditions of controlled atmosphere and temperature was characterized by determining their heat stability by on-line TGA/FT-IR coupling and off-line TGA/TCT/GC/MS coupling in order to identify the volatile compounds released. Degradation residues were analyzed by FT-IR and MALDI-TOF (matrix assisted laser desorption/ionization coupled with time-of-flight) mass spectrometry. A major drawback of these thermoplastic elastomers is that one of the components, isocyanate, is toxic. Based on the data obtained with model urethane compounds (p-TI-based) and bicomponent polyurethane polymer (MDI- and PEG-based), we show that the thermal degradations are different. The widespread application of these materials exposes them to extreme working conditions, which is why we propose reaction mechanisms for their degradation.

Phenolic resins. (II): Influence of the chemical structure of high molecular weight molecules on the mechanisms of cross-linking and on the final structure of the resins

The physicochemical characterization of the structures of the oligomers (n < 4) in resols has been carried out by fragmenting monomers in LC/UV/MS and LC/UV/MS/MS. Fragmentation mechanisms are related to the numbers and positions of substituents on the aromatic ring and to the types of oligomer junctions. It was more difficult to determine the structures of phenol hemiacetals and dimer hemiacetals because of the large number of position isomers. The resols were prepared with differing molar ratios R = Formaldehyde/Phenol and catalysts. They were cross-linked using two industrially recommended heat cycles. The progression of resin cross-linking was determined by solid state 13C NMR (CP/MAS). The residual percentage of monomers and oligomers at n < 4 was determined in leachates (water and methanol) and characterized by LC/UV/MS. The results for cross-linking advancement were correlated with the various synthesis parameters (ratio R, type of catalyst and heat cycle).

Heat stability and degradation of thermostable prepolymers in a controlled atmosphere. I : The heat cycle of propargylic monomer homopolymerization, and characterization of adducts

The liquid study of propargylic monomers during heat treatment has shown the formation of secondary phenolic products in the reaction mixture. They are in the form of propargyl-phenol and chromene-phenol and could be the weak links in the thermal properties of the final polymer. Moreover, we note some differences between the reactivities of the two monomers, probably related to the nature of the central pivot of the skeleton. Solid state analyses by FTIR and solid state crossed polarization magic angle spinning 13C NMR have confirmed the structure of the final polymer, and the reaction paths proposed and have enabled the heat cycle used to be validated. Thermal analyses have shown that the fluorine pivot confers the best thermal properties on the crosslinked material and influences the reactivity and degradation mechanisms of the compounds. In addition, the degradation of the crosslinked compounds occurred as a single step for the dipropargyl ether of bisphenol A and as two steps for the dipropargyl ether of hexafluorobisphenol A.