Introducing catalytically induced polyolefin polymerization methods into the field of wood science may open up a vast number of novel wood modification possibilities, i.e. tuning the hydrophobic properties and with that creating the option of new functionalization to enhance the property profile further. The scope of our ongoing research is focused on polymerizing ethylene within the wood structure by in situ polymerization techniques. This is achieved by a highly specialized catalytic system, consisting of a metallocene catalyst and an aluminum alkyl co-catalyst. This system exhibits promising features in the fields of polyolefin nanocomposite production, and it has attracted interest in the macromolecular science community as well as in the industry. The approach followed in this study comprises three steps. In the first step, small solid wood samples of pine sapwood are pre-treated with the co-catalyst trimethyl aluminum (TMA), which is adsorbed by the wood surface and adsorbed within the pores. In the second step the metallocene catalyst is introduced, which is binding to the immobilized co-catalyst. Hence, catalytically active sites are foremost formed on the wood surface and within the pores. In the third step, ethylene is introduced under low pressure. Upon initiation of the ethylene polymerization, polyethylene (PE) is formed on the wood surface and inner pores. Field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX) were utilized to analyze cross sections of the treated wood samples. The FESEM images did show filled, partially filled as well as empty cell lumen. The EDX analysis of the same cross sections displayed high shares of oxygen distributed along the cell walls, whereas negligible shares were distributed in the empty and filled cell lumen. The aluminum distribution, which is attributed to the co-catalyst, cumulates within the voids. This finding makes us assume that the cell lumen contain or even are filled with PE.
Keywords: wood modification, metallocene catalyst, trimethyl aluminum co-catalyst, polyethylene, in situ polymerisation
Authors
Gurr, J.
Research Associate, Centre of Wood Science and Technology, Universität Hamburg, Hamburg
Luinstra, G. A.
Professor, Institute of Technical and Macromolecular Chemistry, Universität Hamburg, Hamburg
Krause, A.
Professor, Centre of Wood Science and Technology, Universität Hamburg, Hamburg
Login to download the PDF