Impregnated Paper-Based Decorative Laminates Prepared from Lignin-Substituted Phenolic Resins

Abstract

High Pressure Laminates (HPL) panels consist of stacks of self-gluing paper sheets soaked with phenol-formaldehyde (PF) resins. An important requirement for such PFs is that they must rapidly penetrate and saturate the paper pores. Partially substituting phenol with bio-based phenolic chemicals like lignin changes the physico-chemical properties of the resin and affects its ability to penetrate the paper. In this study, PF formulations containing different proportions of lignosulfonate and kraft lignin were used to prepare paper-based laminates. The penetration of a Kraft paper sheet was characterized by a recently introduced, new device measuring the conductivity between both sides of the paper sheet after a drop of resin was placed on the surface and allowed to penetrate the sheet. The main target value measured was the time required for a specific resin to completely penetrate the defined paper sample ("penetration time"). This penetration time generally depends on the molecular weight distribution, the flow behavior and the polarity of the resin which in turn are dependent on the manufacturing conditions of the resin. In the present study, the influences of the three process factors: (1) type of lignin material used for substitution, (2) lignin modification by phenolation and (3) degree of phenol substitution on the penetration times of various lignin-phenolic hybrid impregnation resins were studied using a complete twolevel three-factorial experimental design. Thin laminates made with the resins diluted in methanol were mechanically tested in terms of tensile and flexural strains, and their cross-sections were studied by light microscopy.

Paper-Based Laminates Impregnated with a Hybrid Lignin-Phenol-Formaldehyde Resin

“…In contrast, with the other variants, sample breakage was observed in one or more layers of paper; this fracture penetrated a considerable length of the laminate sample. A similar fracture of L-LPF-1 samples was achieved by Thébault et al [ 16 ]; in this case it was, however, an undesirable phenomenon compared to the mere bending of the samples without major damage. In the work of Thébault et al [ 16 ], laminates in which phenol was replaced in the resin with different contents of lignin did not achieve comparable flexural strength to the reference sample.…”

“…The dry matter of such resin was 49.2%, and the density 1.06 g/mL [ 26 ]. The influence of resin interaction on the resulting mechanical properties of high-pressure laminates is confirmed by Thébault et al [ 16 ], where they state that resins with a tendency to deposit residues on the surface of the laminate (i.e., liquids with a long penetration time) subsequently resulted in an inhomogeneous distribution of the resin in HPL, thereby reducing the mechanical properties. The lowest tensile strength of 63.2 MPa was achieved by laminate produced with a LPF resin where 50% of phenol was substituted with lignin, whereas the highest tensile strength of 133 MPa was reached using laminate made from pure PF resin.…”

“…The utilisation of lignin-phenol-formaldehyde (LPF) resins in the production of plywood, particleboard, or fibreboard has already been investigated. The possibility of using lignin in the production of high-pressure laminates has previously been investigated [ 2 , 13 , 14 , 15 , 16 ]. In the above-mentioned cases, a proprietary lignin-phenol-formaldehyde resin was always synthesised, where a certain proportion of phenol was replaced with unmodified or modified lignin.…”

Advances in the Structural Composition of Biomass: Fundamental and Bioenergy Applications

“…This technique involves steps like a steam explosion, oxidation, ozonolysis, alkalis, and implementation of acids and ionic liquid during the pretreatment. These steps increase the efficiency of the pretreatment processes but its harmful impact on the environment reduces its practical demand [86]. Similarly, in the biological technique of pretreatment, the major role is played by different fungi such as white rot or brown rot which breaks the structure of lignin.…”

Preparation of lignin-based vinylogous urethane vitrimer materials and their potential use as on-demand removable adhesives

“…Therefore, the recycling of thermosets has been a major challenge in the polymer field. With the emergence of partial lignin substitution methods, 9,13,14 it was possible to reduce the dependence of thermosets on petrochemical materials and add a green concept to traditional thermosets. Nevertheless, the fundamental problem of the difficulty of disposal and recycling of thermosets has not been completely solved from the perspective of material recycling.…”