Facultad Regional San Francisco
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Item Mechanistic insight into hydroxy‑methylation of hardwood kraft lignin(2024-09-24) Peralta, Micaela; Pajer, Nicolò; Crestini, Claudia; Nicolau, Verónica V.In view of developing upcycling strategies for hardwood Kraft lignin, hydroxymethylation of Eucalyptus Kraft lignin under alkaline conditions (pH 9 and 11) at different temperatures (50 °C and 70 °C) was studied in the present effort with the double objective of optimizing the reaction conditions and understanding the functionalization mechanism of C5 in either terminal or internal guaiacyl units during hydroxy-methylation. Formaldehyde consumption was estimated via titration of the oximated free formaldehyde; the hydroxy-methylation degree under the reaction was estimated by calculating the ratio in Condensed hydroxyl/Guaiacyl (Condensed OH/G-OH) via a new difference UV-spectroscopy. The reliability of the difference UV-method results for the analyses of the hydroxy-methylated lignins was statistically analysed and compared with that of vacuum-dried and sonicated samples. Hydroxy-methylated samples were then fully characterised by NMR (31P and HSQC) and GPC. The reaction temperature of 50 °C, pH 11, and period time of one hour resulted as the optimal conditions for the hydroxy-methylation, preventing the side-reactions leading to the formation of dimethylene-glycol addition products.The 31P and 1H–13C HSQC NMR revealed the absence of undesirable formaldehyde Cannizzaro by-products and the lack of hydroxymethyl groups in the aliphatic side chain under the studied conditions. GPC analyses, comparing two methodologies, revealed increases in molar mass of the hydroxy-methylated samples upon the formaldehyde addition. The selective hydroxy-methylation at the C5 guaiacyl site demonstrates that Eucalyptus Kraft lignin is as a promising candidate for resolproductionItem Lignin-phenol-formaldehyde resol for high pressure decorative laminates evaluation of lignin levels on final properties(2023-06) Peralta, Micaela; Nicolau, Verónica V.High pressure decorative laminates (HPDL) are composite materials made of core layers of Kraft papers impregnated with a resol type phenol-formaldehyde resin (PF) and a surface décor paper saturated with melamine-formaldehyde resin (MF). The set of saturated papers is cured by compression moulding at high pressure and high temperature. In the aim of replacing non-renewable petroleum-based phenol (P), among biomass components, lignin (L) seems to be an attractive substitute owing to its structural similarity to PF resins. In this sense, hardwood Eucalyptus spp species are the main source of Kraft L in South America. However, the poor solubility and reactivity limit its exploitation in resol resins making necessary a previous chemical modification such as hydroxymethylation in alkaline conditions [1]. Free F increased with L levels in resols being less than 2% for P replacements up to 60 wt%. The resistance to immersion in boiling water test exhibited higher increase in weight and thickness with higher L levels. Delamination and blister defects were observed for HPDLs with 70 and 80 wt% P replacement. Weight increments for HPDL with 0% and 60% P substitution were 5.66 (±0.37)% and 7.60 (±0.56)% meanwhile thickness increments were 8.97 (±1.60)% and 10.22 (±0.45)%, respectively. Gaining on weight and thickness comply the Australian/New Zealand Standard AS/NZS 2924.1:1998 specifications, thus demonstrating hardwood L as a high potential substitute for P in HPDLs manufacturing.Item Determinación de grupos hidroxilo fenólicos reactivos en lignina Kraft de madera dura por titulación acuosa potenciométrica(AJEA- Actas de Jornadas y Eventos Académicos de UTN, 2023-12) Peralta, Micaela; Dobler, Santiago; Lesta, Mateo Ariel; Nicolau, Verónica V.Las ligninas Kraft son polímeros naturales polifenólicos de estructura compleja cuya baja reactividad puede sortearse mediante la activación por hidroximetilación con incorporación de grupos hidroximetilo reactivos necesarios en la fabricación de poliuretanos y adhesivos fenólicos. El trabajo experimental consistió en la optimización de una técnica potenciométrica para la determinación de grupos hidroxilo fenólicos y su monitoreo durante la funcionalización de una lignina de madera dura por hidroximetilación a temperaturas de 50 y 70 °C y pH 9 y 11. La optimización de la técnica potenciométrica permitió una reducción del 38 % en el tiempo de pretratamiento total de la muestra. La lignina hidroximetilada a pH 11 y 70 °C exhibió la mayor conversión (31 %) de grupos hidroxilo fenólicos.Item Synthesis and mechanical characterization of high pressure laminates modified with Kraft lignin(255th ACS National Meeting Exposition New Orleans, 2018-04) Estenoz, Diana; Taverna, María E.; Nicolau, Verónica V.Phenol-formaldehyde resins (PF) are thermosetting polymers used as adhesives for plywoods and other structural wood products including high pressure laminates (HPLs). HPLs are composite materials comprised of a paper-based decorative surface and a substrate impregnated with PF resin. PF adhesives are synthesized using two reagents made from petrochemicals: phenol and formaldehyde. The substitution of such substances by natural products including lignin, tannin, and furfural among others has been increased in the last 20 years due to environmental and economic benefits [1]. Lignin is an inexpensive, abundant and non-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 with 10, 20 and 30 wt% of Kraft lignin from hardwood were studied. The Kraft lignin was activated by hydroxymethylation in all cases. The resols characterization involved industrial measurements of free formaldehyde, viscosity, total solids and density. The resins were used for the industrial impregnation of Kraft-type paper and the production of laboratory laminates. The mechanical and thermal properties of the laminates were measured. Mechanical measurements included tensile, flexural, impact and interlaminar tests. Thermogravimetric and dynamic mechanical analysis were used 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 found with replacement up to 20 wt% of phenol. Modified laminates exhibited better water resistance due to the lignin hydrophobicity. For practical applications, this study suggests that resols modified with 20 wt% of Kraft lignin could be used 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.Item Technical lignins modified by hydroxymethylation for the production of decorative laminates: Synthesis, characterization and mathematical modelling(2017-03) Nicolau, Verónica V.; Taverna, María E.; Estenoz, DianaTechnical lignins are natural and renewable poly-phenolic polymers obtained mainly as a subproduct from the pulp industry. It presents a complex structure that depends on the wood type and the pulping process adopted to separate cellulose. Nowadays, lignins are used as a partial replacement of phenol (P) -non renewable resource, expensive and toxic- in the formulation of phenolic resins (PF). However, lignins must be chemically-modified in order to increase their reactivity toward formaldehyde (F). In the literature there is a lot of information about the use of PF resins modified with lignins (LPF) as adhesives for the production of particleboard. However, the use of LPF resols for paper impregnation to obtained laminates has been scarcely studied. A decorative laminate comprises a decorative surface and a substrate of papers. In this work, technical lignins (sodium lignosulfonate and kraft lignin) were activated by hidroxymethylation and used to replace P in PF resins. The resins obtained were employed to produce decorative laminates. The work involved: i) the modification of sodium lignosulfonate and kraft lignin from hardwood, by hydroxymethylation at different temperatures (40, 50 and 70 ºC) and pH (9 y12); ii) the characterization of the hydroxymethylation by spectroscopic and volumetric analysis; iii) the development of a mathematical modeling of hydroxymetilation of sodium lgnosulfonate and the estimation of kinetic constants of reactions; iv) the synthesis of industrial traditional and modified PF resins by replacement of 10, 20 and 30%w/w of P, v) the production of laminates and their characterization including dynamic mechanical analysis used to compare conditions of curing and the determination of tensile modulus, bending strenght, biaxial flexural impact strenght and Mode- I Interlaminar Fracture Toughness in both processing directions to evaluate the mechanical performance. In this work, the optimal conditions of hydroxymethylation were 50 ºC and pH<10. Simulated results from mathematical model were in accordance with experimental measurements. All resins (traditional and modified) had similar properties. The best conditions of curing used to obtained laminates were 70 kg/cm2 and 150ºC. The higher content of lignins in the PF resins decreased the crosslinking of laminates obtained. Finally, modified laminates exhibited mechanical properties comparable with those of traditional laminates, indicating a negligible depreciation of them. Industrial tests were carried out at Centro S.A, San Francisco, Córdoba.