S. Alamercery

Assessment of the biochemical composition of oilseed rape (Brassica napus L.) 13C-labelled residues by global methods, FTIR and 13C NMR CP/MAS

The biochemical composition of stems, pod walls and roots of oilseed rape (Brassica napus L.) plants, grown in a growth chamber with two levels of N fertiliser, was assessed by two global methods, i.e., serial extraction with the Van Soests technique and temperature-programmed pyroanalysis (TP-Py). Statistical analysis of the effect of various parameters on the proportion of soluble components, hemicellulose, cellulose and lignin-like components in oilseed rape organs showed that the composition of plant materials depended on the N nutrition conditions during plant growth. Contents of soluble and hemicellulose fractions were affected by the technique used. Elsewhere, both global techniques resulted in similar proportions of skeletal cellulose (respectively 41 and 36% in low and high N stems, 37 and 30% in low and high N pod walls, 32 and 29% in low and high N roots) and of lignin-like components which ranged from about 7% in high N stems and pod walls to 16% in low N roots. Spectroscopy by FTIR showed a significant band at 1650 cm−1 (amide I in proteins) in the root material (organ with the lowest C/N ratio) and the absence of lignin-specific bands. Carbon distribution by 13C NMR CP/MAS of labelled plants indicated that 60–64% was (cellulose + hemicellulose)-C, close to the values obtained by global methods. The proportion of aromatic-C (110–160 ppm) and phenolic ether was higher in roots than in stems and pod walls. Organs from oilseed rape plants with higher N contents exhibited a larger proportion of C in the 171 ppm chemical shift attributed to the peptide bond. The concomitance of a high level of aromatic and proteinaceous components in roots would reveal the presence of tannin–protein complexes in addition with true lignin.

Chemical Composition of Algerian Cypress Essential Oil

ABSTRACT A combination of GC, GC/MS and GC/FTIR was used to characterize the chemical composition of Cypress essential oil (Cupressus sempervirens L.) from Algeria. Seventy compounds were identified or tentatively identified in the oil. The main compounds were found to be α-pinene (47.00–52.76%), δ-3-carene (19.35–21.13%), α-terpinyl acetate (4.10–6.47%), cedrol (2.03–3.92%), myrcene (3.11–3.48%) and limonene (2.28–3.31%).

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.

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.

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.

Commercial Dental Composite: Determination of Reaction Advancement and Study of the Migration of Organic Compounds

This work on organic dental composites was undertaken to determine the role of residual reactive methacrylate functions at the end of the photopolymerization cycle, and to investigate the fate of the residual monomers and oligomers in organic (ethanol) and aqueous (water and artificial saliva) media. The results show that all the methacrylate monomers present in dentine migrate into ethanol (about 1% (w/w)). In aqueous media on the other hand, only the most hydrophilic monomer (UDMA) migrates (0.05% (w/w)) into water and 0.03% into artificial saliva (pH = 9). This desorption in the three media is accompanied by the hydrolysis of monomers, leading to the formation of monohydrolyzed urethane dimethacrylate (UDMA) and bis-phenyl glycidyl dimethacrylate (BISGMA); UDMA and BISGMA are completely hydrolyzed in artificial saliva. The alkalinity of the milieu apparently favours the hydrolysis of methacrylate functions.

Thermal stability and degradation of thermally stable prepolymers under controlled atmosphere. IV-Thermal stability and degradation of cross-linked systems prepared from cyanate monomers

We report the results of a study on the thermal degradation of cyanate prepolymers and corresponding materials prepared in the molten state by the homopolymerization of monomers in a controlled atmosphere (nitrogen) and in the temperature range of 100 to 500°C. We propose degradation mechanisms for these materials based on the analysis of physicochemical data obtained by the differential scanning calorimetry, thermogravimetric analysis, gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy of volatile organic compounds and residues after the thermal cycle. These mechanisms depend on the structure of the carbon skeleton.