Synthesis and mechanical characterization of high pressure laminates modified with Kraft lignin

D. ESTENOZ; M. E. TAVERNA; V, NICOLAU

New Orleans

Encuentro; 255th ACS National Meeting & Exposition; 2018

Phenol-formaldehyde resins (PF) are thermosetting polymers used as adhesives for plywoods and otherstructural wood products including high pressure laminates (HPLs). HPLs are composite materials comprised of apaper-based decorative surface and a substrate impregnated with PF resin.PF adhesives are synthesized using two reagents made from petrochemicals: phenol and formaldehyde. Thesubstitution of such substances by natural products including lignin, tannin, and furfural among others has beenincreased in the last 20 years due to environmental and economic benefits [1]. Lignin is an inexpensive, abundant andnon-toxic by-product from pulp production, used as replacement of P, due to its similar structure to PF resins.In this work, the industrial synthesis and characterization of three resol-type phenol-formaldehyde resins modified with10, 20 and 30 wt% of Kraft lignin from hardwood were studied. The Kraft lignin was activated by hydroxymethylation inall cases. The resols characterization involved industrial measurements of free formaldehyde, viscosity, total solidsand density. The resins were used for the industrial impregnation of Kraft-type paper and the production of laboratorylaminates. The mechanical and thermal properties of the laminates were measured. Mechanical measurementsincluded tensile, flexural, impact and interlaminar tests. Thermogravimetric and dynamic mechanical analysis wereused for the thermal characterization. In addition, the aging of materials in water was studied.No significant differences in mechanical and thermal properties between traditional and modified materials were foundwith replacement up to 20 wt% of phenol. Modified laminates exhibited better water resistance due to the ligninhydrophobicity. For practical applications, this study suggests that resols modified with 20 wt% of Kraft lignin could beused for the production of HPLs, while resols modified with 30 wt% of lignin for postformable laminates.Industrial tests were carried out at Centro S.A, San Francisco, Córdoba.