Kraft lignin in phenol formaldehyde resin. Part 1. Partial replacement of phenol by kraft lignin in phenol formaldehyde adhesives for plywood

Ligneous resole adhesives for exterior-grade plywood

“…The cooking time required to reach the intended target viscosity of 150 mPa·s was confirmed to be significantly shorter for the LPF resins. This is well in line with previous observations (Danielson and Simonson 1998) and is attributed to the bigger size of the lignin molecules compared to phenol leading to a faster network (Ghorbani et al 2016). Both final pH (9.9-10.1) and solid content (45.1-47.3 wt%) of the resin did not vary significantly.…”

“…This is some improvement or extends previous studies which usually test 3-ply plywood (e.g. Danielson and Simonson 1998;Klasnja and Kopitovic 1992) combined with high hot pressing temperature resulting in correspondingly high and possibly not representative glue line temperature. Again adhesives using pre-methylolated lignin do not show any advantage over the in-situ modified kraft lignin.…”

“…At this strength level various adhesives already fail in fully cured state (e.g. Danielson and Simonson 1998). Passing this strength level, LPF adhesives slowdown drastically in bond strength development but have still the potential to double the measured tensile-shear strength measured in hot state (Fig.…”

“…Chen (1995) used up to 40% re-activated kraft lignin as phenol replacement and concluded their performance mainly from wood failure amount. Even higher levels were analysed by Klasnja and Kopitovic (1992) using hardwood kraft lignin and Danielson and Simonson (1998) using softwood kraft lignin, both produced plywood with satisfactory shear strength properties up to 50% phenol replacement. A recent study, aiming at analysing various filter systems used after the precipitation step, reported again the possibility of manufacturing plywood using 30% kraft lignin as phenol replacement without major change in shear strength properties (Kouisni et al 2011).…”

Toward Thermoplastic Lignin Polymers; Part II: Thermal & Polymer Characteristics of Kraft Lignin & Derivatives

“…Technical kraft lignins offer enhanced reactivity via their abundant phenolic OH groups with tangible possibilities for their utilization in adhesive and thermoset applications. For example, kraft lignin has been reported to replace up to 50% of the total amount of phenol required in phenol formaldehyde resins used in the production of plywood (Danielson and Simonson 1998). However, there are no reports of kraft lignin being used in single-component thermoplastics due to thermal stability considerations.…”