Phenolic adhesives are widely used in the production of engineered wood products due to their exceptional moisture and thermal resistance, chemical stability, and bonding strength. The phenolic adhesive is currently produced through condensation polymerization of two fossil fuel-derived compounds: phenol and formaldehyde. However, due to fluctuations in the price of phenol and formaldehyde with the price of oil, environmental and health issues associated with using these compounds, there is a strong interest in finding alternative renewables feedstocks. Lignin is a natural polyphenolic compound with excellent potential to substitute phenol in phenolic adhesive formulations. Lignin is produced as byproducts during pulp and bioethanol processes. On the other hand, biobased aldehydes such as glyoxal have recently gained a lot of attention for replacing the toxic formaldehyde in production of environmentally friendly wood products. In this study, a wide range of lignin samples from different resources (hardwood, softwood, wheat straw, and corn stover), and isolated via various processes (kraft, organosolv, soda, sulfite, and enzymatic hydrolysis), were used to formulate 100% lignin-based phenolic adhesives. In a separate work, formaldehyderee phenolic adhesives were also developed using either glyoxal or gossypol (a dialdehyde from cotton seed) in combination with phenol. Chemical, physical, and thermal properties of lignin samples and developed phenolic resins and adhesive were measured using advanced analytical techniques and appropriate ASTM standard test methods. Based on two-way ANOVA analysis results of shear strength data, a biorefinery corn stover lignin that had the highest p-hydroxyphenyl and p-coumaric acid content was the most suitable lignin for replacing 100% of phenol in phenolic adhesive formulation. In addition, the developed lignin-based adhesive (formulated with biorefinery corn stover lignin) showed similar dry and wet adhesion strengths as that of commercially formulated phenol resorcinol formaldehyde (PRF) adhesive. On weight basis, the formaldehyde consumption in the developed lignin-based adhesive was 50% lower than the formaldehyde used in phenol formaldehyde (PF) resin. Moreover, two formaldehyderee formulated adhesives using glyoxal and gossypol (renewable feedstocks) had very similar physico-chemical properties to phenol formaldehyde adhesive.

Abstract The wood industries to this day use almost exclusively petroleum derived adhesives that are based mainly on the reaction of formaldehyde with urea, melamine or phenol. These adhesives have low cost and good adjustable properties which makes it hard for bio-based alternatives to compete. Phenol formaldehyde (PF), as an example of a synthetic adhesive, has been in use for over 100 years. In some parts of the world, legislation around formaldehyde is changing, and there is an increasingly voluntary awareness about the toxicity and unsustainability of formaldehyde. Industries realize that raw materials from oil is unstainable. The latter is currently a driving factor behind research on alternatives to amino based adhesives. Also, consumer interest in healthy and sustainable products, such as emitting less formaldehyde indoors, increases the need for bio based adhesives. Cellulose contained in plant cell walls is a renewable, abundant and nontoxic resource. During the last decades, many innovations have been achieved around cellulose and this trend does not seem to be slowing down. Cellulose shows excellent mechanical properties, high strength, high elastic modulus as well as having a low density. Research about cellulose reinforced adhesives has been increased the last years. This thesis studied the enhancement of phenol formaldehyde adhesive with Crystalline Nano Cellulose (CNC) at 5wt% and 10wt% loading levels for producing plywood boards. Indecisive results when using CNC higher than 3wt%, especially with PF resin, have been reported by other authors. In this thesis, European standards were applied. EN 314 was applied to test the panels shear strength. Three (3) treatment classes were selected, indoor room condition as well as pre-treatments 5.1.1 and 5.1.3. Other properties measured were modulus of elasticity, thickness swelling, formaldehyde emissions. Results showed a shear strength increase for all pre-treatment classes. 10wt% CNC mixture with phenol formaldehyde in water bath, pre-treatment (5.1.1) for 24h showed the highest increase in shear strength (+73,9%). The 10 wt% CNC mixture panels also showed the highest wood fibre failure of all panel types produced. A decrease in MOE has been observed with 10 wt% CNC compared to the 5 wt% CNC panels. Formaldehyde emissions tests were inconclusive, but since less PF was used, there was a general reduction in emissions. The 5 wt% CNC panels were superior in terms of modulus of elasticity and swelling and also showed improved shear strength.