MALDI-ToF investigation of furanic polymer foams before and after carbonization: Aromatic rearrangement and surviving furanic structures

doi:10.1016/j.eurpolymj.2008.06.029

European Polymer Journal

Volume 44, Issue 9, September 2008, Pages 2938-2943

https://doi.org/10.1016/j.eurpolymj.2008.06.029 Get rights and content

Abstract

A MALDI-ToF investigation of furanic foams before and after carbonization at 900 °C has been carried out. Comparison between MALDI-ToF spectra, before and after carbonization, shows how original building blocks of the network are modified, rearranged or survived during the process. Even if most of the constituents are transformed to more stable aromatic structures, some of the starting compounds resist intact the process of carbonization. The results appeared to indicate that some furanic oligomers are particularly stable and unaffected by carbonisation. The hypothesis that these may be cyclic furanic oligomers has been checked by molecular mechanics calculation of their relative energies.

Introduction

Furfurylic alcohol, obtained by catalytic reduction of furfural, has to be considered a completely natural product derived by plant hulls, sugar cane bagasse and corn cobs. It is used principally to produce furans and furanic resin, but also as solvent.

Furanic foams are prepared by polycondensation of furfuryl alcohol under acid conditions [1], [2], [3]. Furanic foams are commonly used in foundries, because of their high resistance to heat and their relatively low price, to bind the sand of moulds or cores for casting engine heads or other kind of steel tools [4], [5].

Interesting products can also be obtained by carbonizing (900 °C) of furanic foams under nitrogen flow [6]. As carbonization yields in this case a more rigid and resistant product, it is of interest to analyze what occurs at molecular level during carbonization.

Matrix-Assisted Laser Desorption/Ionization Time of Flight (MALDI-ToF) mass spectrometry could be used to characterize the rearrangements occurring in this kind of products.

MALDI-ToF mass spectrometry has increased the use of mass spectrometry for large molecules analysis and has revealed itself to be a powerful method for the characterization of both natural and synthetic polymers [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. Fragmentation of analyte molecules upon laser irradiation can be substantially reduced by embedding them in a light absorbing matrix. As a result intact analyte molecules are desorbed and ionized along with the matrix and can be analyzed in a mass spectrometer. This soft ionization technique is mostly combined with time-of-flight (ToF) mass analyzers. This is so as ToF -MS present the advantage of being capable to provide a complete mass spectrum per event, for its virtually unlimited mass range, for the small amount of analyte necessary and the relatively low cost of the equipment.

Section snippets

Samples

Furanic foams are obtained by mixing 20.0 g of furfuryl alcohol with 3.0 g of 65% p-toluene-sulphonic acid (p-TSA). Exothermic condensation happen after 5–7 min in a few seconds. The foam obtained has been broken into tiny bits between 0.5 and 10 mm diameter by pestel and mortar. Foam (0.5 g) has been finely pulverized and collected for MALDI- ToF analysis of non-carbonized foam. The same foam (1.5 g) has been carbonized.

Carbonization of the foam was carried out inside a quartz boat, itself installed

Results and discussion

The interpretation of the MALDI-ToF spectrum non-carbonized furanic foam (Fig. 1, Table 1) shows several peaks of interest to understand the phenomenon of carbonization. The information of most interest in this spectrum is the sequence of compounds obtained by the subsequent addition of a 80 Da repeating unit. This series of compounds is explained as follows: The most evident series (228.6 – 307.8 – 387.9 – 468.0 – 546.1 – 628.2 – 708.3 – 788.4 Da) is explainable by adding furan units

to the

Conclusions

MALDI-ToF spectra of furanic foams shows that the signals before and after carbonization are different. The non-carbonized furanic foam spectrum shows clearly that the variety of structures observed derive from the polymer network and that the furfuryl group is the main repeating unit. The carbonized furanic foam spectrum shows that many polynuclear aromatic hydrocarbons are present. The average molecular weight of the fragments increases during carbonization because of the rearrangement of

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