Fully biodegradable modification of wood for improvement of dimensional stability and water absorption properties by poly(ε-caprolactone) grafting into the cell walls

Abstract

Materials derived from renewable resources are highly desirable in view of more sustainable manufacturing. Among the available natural materials, wood is one of the key candidates, because of its excellent mechanical properties. However, wood and wood-based materials in engineering applications suffer from various restraints, such as dimensional instability upon humidity changes. Several wood modification treatments increase water repellence, but the insertion of hydrophobic polymers can result in a composite material which cannot be considered as renewable anymore. In this study, we report on the grafting of the fully biodegradable poly(ε-caprolactone) (PCL) inside the wood cell walls by Sn(Oct) 2 catalysed ring-opening polymerization (ROP). The presence of polyester chains within the wood cell wall structure is monitored by confocal Raman imaging and spectroscopy as well as scanning electron microscopy. Physical tests reveal that the modified wood is more hydrophobic due to the bulking of the cell wall structure with the polyester chains, which results in a novel fully biodegradable wood material with improved dimensional stability.

Chemical modification of spruce wood with combination of mesyl chloride and poly(ε-caprolactone) for improvement of dimensional stability and water absorption properties

“…Mesyl chloride is generally used in organic chemistry as a leaving group on hydroxyl groups to be substituted later by nucleophilic chemicals (Netscher and Bohrer, 2002). However, a similar chemical reagent, tosyl chloride, has been used recently by Ermeydan et al (2012) to hydrophobize interior of wood cell walls by reaction and blocking of some hydroxyl groups on the wood polymers. In this manuscript, mesylation was carefully carried out to hydrophobize wood cell walls to be able to impregnate more hydrophobic ε-caprolactone monomer for further graft polymerization (Ermeydan et al, 2014b).…”

“…For example, reaction of reagents such as anhydrides, chlorides, cyanates by forming covalent bonds between hydroxyl groups of wood polymers is a well-studied approach (Rowell, 1984;Donath et al, 2004). Other approach for wood modification is in-situ grafting polymerization of monomers (Rowell, 2005;Hill, 2006;Nordstierna, 2008;Ermeydan et al, 2014). Wood cell wall modification has a lot of limits such as use of moderate reaction conditions to avoid cell wall deformation and harmful sideproducts.…”

“…Few of the studies reported successful modification with hydrophobic polymers in the cell walls, and few of them results an efficient and stable improvement of dimensional stability (Furuno and Goto 1979;Nakagami and Yokota, 1983;Ermeydan et al 2014aErmeydan et al , 2014bCabane et al, 2014, Keplinger et al 2015. Recently, Ermeydan et al reported a wood pretreatment method that enhances the introduction of hydrophobic molecules in the cell wall (Ermeydan et al, 2012;2014a). Hydrophobic flavonoid molecules were successfully inserted inside the pretreated cell walls.…”

“…In this study a different pre-treatment reagent, methane sulfonyl chloride (mesyl chloride) was used instead of tosyl chloride which was used in the previous studies (Ermeydan et al, 2012;2014a). Mesyl chloride is a reactive reagent that reacts with -OH groups.…”

“…Long-lasting wood material and less problematic recycling of wood are important arguments towards creating sustainable and environmental-safe wood products (Ermeydan et al 2014). …”