Variation of MUF and PMUF resins mass fractions during preparation

The variation of molecular mass distribution with the progress of the reaction was studied for the following: (i) sequential‐type melamine–urea–formaldehyde (MUF) resin formulations in which the sequence of addition of chemicals follows well‐defined species reactivity principles; (ii) a nonsequential MUF formulation in which simultaneous melamine and urea competition for formaldehyde yields a MF resin cocondensed with small amounts of urea. This resin became soaked with reacted and unreacted monomeric urea species. (iii) A PMUF resin, namely a MUF resin with a small proportion of phenol (7.8% by weight on melamine and urea) cocondensed with the main MUF fraction. All the formulations used were industrial resins formulations in current use. Development and variation of molecular mass fractions, from which performance and other useful resin parameters depend, have been found to depend on the type of resin formulation used for these type of aminoplastic resins. The two very different MUF resin formulations yielded different variations in molecular mass fractions during the progress of the reaction and during the so‐called ambient temperature “maturing” of the resin. The PMUF resin also showed both similar and different fractions present during manufacturing and during short term ageing at ambient temperature. While similarities in recurrent fractions and in trends are common to all the three different formulations, differences between them are also clearly observed. A major proportion of the reaction of some of the aminoplastic resins examined also occurs on ageing (i.e.“maturing” of the resin at ambient temperature), this appearing to be an essential phase of the resin preparation process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4842–4855, 2006     

Ester acceleration mechanisms in phenol–formaldehyde resin adhesives

An analysis of phenol–formaldehyde (PF) resins obtained by the addition of 0.5–5% glycerol triacetate (triacetin) as an accelerator during resin preparation showed the presence of intermediates involved in the acceleration mechanism. ¹³C-NMR spectroscopy, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy (MS), and gel permeation chromatography allowed us to identify some of the intermediates left over in the PF resin itself. The permanence in the resin of these labile intermediates, not easily observed otherwise, appeared to be due to the reaching of the diffusion-controlled phase of the reaction. The mechanism involved appeared considerably more complex and different from any of the mechanisms presented previously. As a consequence of the evident complexity of the mechanism, it was not really possible to advance a complete mechanism of the reaction nor determine the real cause of the increase in the strength of the final network. The mechanism involved the phenate ion of the resin to apparently give a carbonyl or carboxyl group attached to the aromatic ring. Either directly or by subsequent rapid rearrangement after the initial attack, these CO groups were found on sites different from the ortho position. The appearance gathered from NMR shift calculation indicated preferential positioning or repositioning to the para site and, surprisingly, to the meta sites of the phenolic ring. The shifts of these CO groups correspond to those of an anhydride and to no other intermediate structures previously thought of. Anhydride-like bridges were clearly shown by MALDI-TOF MS to contribute to oligomer structures in which linkages between phenol rings were mixed methylene bridges and anhydride bridges. These structures appeared to be temporary, possibly due to the instability of the anhydride bridges; hence, they were in small proportions at any given moment of the reaction. MALDI-TOF analysis clearly indicated that these structures were at some moment an integral part of the structure of the liquid resin and that they existed parallel to the methylene bridges pertaining to a normal PF resin structure. Previous spectra showed that similar but not identical intermediates were present also in organic and inorganic catalyzed PF resins. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:3075–3093, 2006     

Plant Chemical Defense Induced by a Seed-Eating Pollinator Mutualist

Plant-seed parasite pollination mutualisms involve a specific pollinator whose larvae develop by consuming a fraction of the host plant seeds. These mutualisms are stable only if the plant can control seed destruction by the larvae. Here, we studied the chemical response of the European globeflower Trollius europaeus to infestation by an increasing number of Chiastocheta fly larvae. We used liquid chromatographic analysis to compare the content of phenolic compounds in unparasitized and parasitized fruits collected in two natural populations of the French Alps, and mass spectrometry and nuclear magnetic resonance to elucidate the structure of adonivernith, a C-glycosyl-flavone. This compound is present in many of the organs of T. europaeus, but not found in other Trollius species. Furthermore, it is overproduced in the carpel walls of parasitized fruits, and this induced response to infestation by fly larvae is density-dependent (increases with larval number), and site-dependent (more pronounced in the high-altitude site). Mechanical damage did not induce adonivernith production. This tissue-specific and density-dependent response of T. europaeus to infestation by Chiastocheta larvae might be an efficient regulation mechanism of seed-predator mutualist population growth if it decreases survival or growth of the larvae.     

Non-toxic, zero emission tannin-glyoxal adhesives for wood panels

In this study different tannin-glyoxal glue mixes for particleboard were studied. Gel times at 100 °C of 45% water solutions of commercial pine tannin extract (Pinus radiata ex Diteco Ltda, Chile) with respectively 8% paraformaldehyde and 9% glyoxal were done at different pHs. Duplicate one layer laboratory particleboards were prepared by adding 12% total resin solids of adhesives composed of commercial pine tannin extract (Pinus radiata ex Diteco Ltda, Chile) with paraformaldehyde, or glyoxal or polymeric 4,4’ diphenylmethanne diisocianate (pMDI), respectively. It was found that tannin-glyoxal panels which do not contain formaldehyde and with an emission equal to that of unbounded wood can be obtained by the use of glyoxal as hardener.     

Comparative 13C‐NMR and matrix‐assisted laser desorption/ionization time‐of‐flight analyses of species variation and structure maintenance during melamine–urea–formaldehyde resin preparation

The preparation of an industrially used sequential formulation of a melamine–urea–formaldehyde resin was followed by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry and ¹³C‐NMR analysis. The analysis allowed us to identify and follow the appearance, increase, decrease, and disappearance of a multitude of chemical species during the preparation of both the initial urea–formaldehyde (UF) phase of the reaction and the subsequent reaction of melamine with the UF resin that formed. The analysis indicated that (1) the increase and decrease in the species that formed proceeded through a cycle of the formation and degradation of species occurring continuously through what appeared to be a series of complex equilibria, (2) even at the end of the reaction a predominant proportion of methylene ether bridges was still present, (3) some small proportion of methylene bridges already had formed in the UF reaction phase of the resin even under rather alkaline conditions, and (4) the addition of melamine to the UF prepolymer induced some noticeable rearrangement of methylene ether bridges to methylene bridges. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Wood preservation by a mixed anhydride treatment: A 13C‐NMR investigation of simple models of polymeric wood constituents

The treatment of wood by a mixed aceto/oleic (or other fatty acid residue) anhydride promoted as a safe and environmentally friendly wood preservation system was examined quantitatively by liquid‐phase ¹³C‐NMR and solid‐phase magic angle spinning–DEC (proton decoupling) ¹³C‐NMR through of all its different stages to determine which reactions occurred with simple model compounds of the polymeric constituents of wood. The preparation of the mixed aceto/oleic anhydride under different conditions was also undertaken. The anhydride formed, but its percentage yield was only 30%. The mix composed of unreacted acetic anhydride, the mixed aceto/oleic anhydride, and a large proportion of free acetic and oleic acid, which are used for wood preservation, yielded the acetylation of the lignin model compound (1) by the reaction of the acetic anhydride with it and (2) by the reaction of the acetic part of the mixed anhydride. In this reaction, all of the mixed anhydride was consumed. The oleic part of the mixed anhydride was unable to form esters with either lignin or wood holocellulose as it was far less reactive than the acetic part. Some acetylation of holocellulose occurred, and some traces of its oleic acid ester also occurred under some conditions. This system of treatment through a mixed anhydride appeared to consist of just an acetylation with acetic anhydride mixed with some oleic acid as a water repellent, both of which are already known processes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Colourless formaldehyde-free urea resin adhesives for wood panels

Amino resin precursors prepared by the addition of a new, colourless, non-volatile and non-toxic aldehyde, dimethoxyethanal (DME), to urea gave resins for boards that while able to harden were underperforming due to the lower reactivity of DME in relation to formaldehyde. Urea reacts with one and even two molecules of DME to form UDME and U(DME)₂ (called DU) but the subsequent cross-linking reaction to form bridges between two ureas, although existing as observed by CP MAS ¹³C NMR, was too slow at temperatures lower than 140 °C to be of significance for wood panel adhesives. However, addition of 20% isocyanate (pMDI) contributed to cross-linking of DU by its reaction with pMDI to also form urethane bridges, their existence being confirmed by CP-MAS ¹³C NMR. The adhesive resins so formed had excellent performance, were colourless, and produced boards that satisfied well the requirements of the relevant norms for interior panels (EN 120 and EN 312). The results were good enough to decrease the proportion of pMDI to 14% at pressing times starting to be of significance for industrial panel products. Formaldehyde emission, by perforator method was down exclusively to the formaldehyde produced by heating the wood chips. The panel emission was sufficiently low to even satisfy the relevant F^**** JIS A 5908 Japanese standard (JIS A 5908, 1994 ). These adhesives are colourless, as UF resins.     

Storage of NO2 on BaO/TiO2 and the influence of NO

The influence of NO on the adsorption and desorption of NO₂ on BaO/TiO₂ has been studied under lean conditions. The adsorption of NO₂ involves the disproportionation of NO₂ into an adsorbed nitrate species and NO released to the gas phase with a 3:1 ratio,

BaO+3NO₂→NO+Ba(NO₃)₂.

Three different nitrate species form on the catalyst: surface nitrates on the TiO₂ support, surface nitrates on BaO, and bulk barium nitrate. The stability of the three species in different gas feeds was investigated by temperature-programmed desorption (TPD).

The reverse reaction of the NO₂ disproportionation has also been observed. If NO is added to the feed, nitrates previously formed on the sorbent will decompose into NO₂. Therefore, the above chemical equation should be considered as an equilibrium reaction. Applying this finding to the NO_x storage and reduction catalyst means that NO probably reacts with the previously formed nitrates yielding NO₂ as an intermediate product. This NO₂ is subsequently reduced by the reducing agents (hydrocarbons and CO) present during the regeneration period.     

13C NMR investigation of the reaction in water of UF resins with blocked emulsifiable isocyanates

A solid state ¹³C NMR study of hardened networks obtained by the reaction of blocked and nonblocked isocyanates (pMDI) with urea‐formaldehyde (UF) resins in water showed different results according to the temperature of the reaction. At high temperature, in water, both a nonblocked or an emulsifiable, blocked isocyanate, appear to crosslink with UF resins through the formation both of traditional methylene bridges connecting urea to urea and of urethane bridges. The latter have been confirmed by ¹³C NMR to form in water by reaction of the isocyanate ? N?C?O group with the hydroxymethyl groups of the UF resin. At ambient temperature, UF/pMDI resins where the pMDI is a emulsifiable blocked isocyanate, do not appear to form urethanes to any great extent but rather to crosslink through the usual UF resin urea to urea methylene bridges. Even in this case, when urethane bridges appear to be absent, evidence of crosslinking in water through reaction of the isocyanate with the ? NH₂ and ? NH? amide of the UF resin has not been observed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 589–596, 2006     

In vitro and in vivo studies of creatine monohydrate supplementation to Duroc and Landrace pigs

Duroc and Landrace pigs as well as primary myotubes from these breeds were used to investigate mechanisms behind differences in their response to creatine monohydrate (CMH). Pigs were supplemented with 0, 12.5, 25 or 50g CMH/d for 5 days (n=10 per treatment and breed). Plasma levels of creatine increased dose-dependently in both breeds, while muscle-creatine phosphate content increased only in the Duroc pigs. (1)H NMR metabolic profiling showed a tendency towards clustering according to CMH supplementation only among Duroc pigs, revealing a stronger response compared to Landrace pigs. The abundance of insulin-like growth factor I and myostatin mRNA was decreased by CMH supplementation while that of type 1 IGF-receptor and creatine transporter was unaffected. Protein synthesis, increased in the myotubes from both breeds, indicating protein accretion, but no effect was observed on the mRNA abundance of IGF-I, type 1 IGF-receptor, myostatin or the creatine transporter in myotubes.