Composite Materials Based on Phenolic Resins Modified with Lignins: From the Laboratory to the Industry.

VERÓNICA NICOLAU; DIANA ALEJANDRA ESTENOZ; MARIA EUGENIA TAVERNA

Helzinki

Congreso; Congreso Iberoamericano de Celulosa y Papel; 2016

Congreso Iberoamericano de Celulosa y Papel

Phenol-formaldehyde resins (PF) are an important type of adhesives used in a wide range of industries such as construction, electronics, and aviation. Due to their binding properties, PF resins have been used mainly in the production of composites materials including decorative laminates. Decorative laminates are comprised of a paper-based decorative surface and a substrate impregnated with PF resins. In the last 20 years, there have been attempts to partially replace the harmful and unpleasant-smelling P by naturally derivatives such as lignin and tannin. Lignin is a low costing waste product in paper production, abundant and non-toxic, that exhibits a structure well suited for the replacement of P in PF resins. In this work, a study about the synthesis and characterization of PF resins modified with commercial lignins (sodium lignosulfonate and Kraft lignin) and their application for the production of decorative laminates is presented. The investigation deals with: i) the characterization of two industrial lignins from hardwood to determine: impurities (moisture and ash by gravimetric analysis, and sugars by HPLC), C, H, N and S content (by elemental analysis), functional groups (phenolic hydroxyls by UV-vis spectroscopy), distributions of molecular weights (by SEC), thermal properties (by TGA); ii) the reactivation of lignins by hydroxymethylation and the characterization of modified lignins by UV-vis spectroscopic and volumetric techniques; iii) the syntheses of traditional and modified resins (with replacement of 10, 20 and 30%w/w of phenol by lignins) and the characterization by rheological, gravimetric and volumetric techniques; iv) the study of curing using FTIR; v) the fabrication of laminates at laboratory and industrial scale by the paper impregnation with the resins (varying the number and the orientation of papers) and the curing at different pressures and temperatures. Viscoelastic properties of the final materials were determinate by DMA; and vi) the evaluation of mechanical properties of laminates including tensile, flexural, biaxial impact, and Mode-I interlaminar fracture tests.The obtained results showed that the hydroxymethylation degree is highly affected by the concentration of functional groups present in lignin structure. At the replacement levels studied, the modified resins exhibited similar properties (viscosity, density, solids and free F) to the traditional ones, similar curing mechanisms and similar thermal properties after curing.From the performed experimental study, the optimized conditions for the production of the decorative laminates with mechanical properties comparable to the traditional laminates resulted: temperature: 150ºC, pressure: 70kg/cm2, 10%w/w of P replacement and longitudinal orientation of papers.