The Impact of Molecular Weight of Kraft-lignin on Adhesive Performance of Lignin Based phenol Formaldehyde Resins

摘要

Phenol Formaldehyde-resins (PF) relate to one major class of adhesives and have excellent properties such as high bonding strength or good resistance against moisture and temperature. However, resoles are generally synthesized using fossil components such as phenol and formaldehyde (1,2). Expected long term increase of oil prices, together with an increasing ecological awareness is a major drive to search for alternative resources to replace such fossil components (3). Beside this motivation an abundant availability of lignin puts research focus on the development of lignin based phenolic resins (LPF) for the wood panel industry. However, due to the lower reactivity of lignin to formaldehyde, a realizable breakthrough could not be achieved so far. Lignin is known for its' inherently heterogeneous structure, a wide molar mass distribution and partly less reactive aromatic sites (4). To overcome these challenges solvent fractionation was proposed as a potential methodology. A recently developed fractional precipitation procedure provides an easily controllable process to manipulate the yield and structural composition of produced lignin fractions without the use of harmful or hazardous solvents or expensive instrumentation (4,5).