Ef fec t of Maleic Anhydride Content on the Polymerization of Fur fur yl Alcohol in Wood Veneer

N. Herold, T. Dietrich, W. J. Grigsby, R . A . Franich, A . Winkler, B. Buchelt , A . Pfriem

Eberswalde University for Sustainable DevelopmentUniversity of Applied Sciences Faculty of Wood Science and TechnologyFriedrich-Ebert-Str. 2816225 Eberswalde - Germanyalexander.pfriem@hnee.denadine.herold@hnee.de

The furfurylation of wood is a long-known process for wood preserva-tion and modification and is based on the wood impregnation with furfuryl alcohol and an initiator followed by curing at elevated temperatures. A few years ago, Schneider (2002) and Wes-tin (2004) implemented cyclic carbox-ylic anhydrides, mainly maleic anhy-dride, as initiator, but little is reported on its role in the reaction.

In the current study, DSC measure-ments have been utilised to deter-mine the impact of different concen-trations of maleic anhydride on the furfuryl alcohol polymerization. DSC results have been correlated to weight up-takes of furfurylated veneer sam-ples in relation to maleic anhydride concentrations used.

All analyses were conducted on ve-neer samples from maple (Acer spec.). Samples were impregnated with the solutions prepared as shown in Scheme 1.

After impregnation, samples were left in aluminium foil to soak for 24 h. Residual ethanol was removed under low pressure.

A high amount of maleic anhydride (10 wt.%) leads to one intense exo-thermic peak at 122 °C (Figure 1). A reduced maleic anhydride content (5 wt.%) retards the curing reactions and requires higher temperatures dis-

played in two exothermic peaks at 124 and 147 °C.

The DSC thermogram of wood ve-neer treated with furfuryl alcohol alone is characterized by an endo-thermic peak at 154 °C consistent with furfuryl alcohol evaporation.

Similar effects are observed for samples treated with ethanol diluted solutions (Figure 2). Thermograms of those samples treated with 10 wt% maleic anhydride exhibit a formation of two exothermic peaks with a shift of the second exothermic to higher temperatures with increasing ethanol content.

These results are consistent with the masses of polymer inside the wood ve-neer cured at 140 °C showing a linear relation to the maleic anhydride con-tent used. Ethanol dilution as well as low maleic anhydride contents lead to a reduced mass of polymer (Figure 3).

Acknowledgments:

The authors are grateful for the financial support of

the German Research Foundation (DFG, PF 686/4-1),

AiF (16735 BR), and COST (STSM-RA - New Zealand-

06283).

We also greatly appreciate the supply of the furfuryl

alcohol by International Furan Chemicals B.V.

References:

Schneider, M.H. (2002). Furan Polymer Impregnat-

ed Wood, Method for Preparing the Polymer and Uses

Thereof. Patent. WO/2002/030638.

Westin, M. (2004). Furan Polymer Impregnated Wood.

Patent. WO/2004/011216.

Scheme 1.Composition of solutions for sample impregnation

Figure 1. DSC thermogram. Samples being impregnated with undiluted furfuryl alcohol and different amounts of maleic anhydride (0, 5, and 10 wt%)

Figure 2.DSC thermogram. Samples being impregnated with the same ratio of maleic anhydride (10 wt%) and different dilutions (100, 75, and 50 vol% furfuryl alcohol)

Figure 3.The impact of the furfuryl alcohol/ethanol ratio and different amounts of maleic anhydride (0, 5, and 10 wt%) on the yield of cured polymer