Elaboración de madera sintética a partir de lignina extraída de carbón de bajo rango, modificada por radiación UV y por acción de enzimas lignolíticas.
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The purpose of this research was to determine the optimal conditions for lignin depolymerization by UV action and study the viability of a new method of depolymerization by the action of lignolytic enzymes. Both methods aim to increase the reactivity of lignin to elaborate a product with good mechanical properties. To do this, this research project was divided into three stages. The first one involved the extraction and characterization of lignin. First, 3 coal samples of the municipality of Paipa, Boyaca were collected and characterized by proximate analysis, ultimate analysis and its calorific value. All this was done in order to select the sample that was classified as low-rank coal. Subsequently, from the selected sample, lignin extraction was performed by the method Sosa using 15% NaOH, and from the lignocellulosic material obtained, lignin was precipitated by acid hydrolysis using H2SO4 (98%). The purified lignin was characterized with a standard Kraft lignin by IR spectroscopy, UV, elemental analysis and solubility. The second stage was to structurally modify the lignin to increase its reactivity. For this, two modifications were made separately. In the first one, lignin was depolymerized by UV irradiation at 10, 12, 14, 16 and 18h of exposure, and subsequently hydroxymethylated with formaldehyde by the method of el Mansouri [1], a process which incorporates hydroxymethyl groups to lignin structure. The increased reactivity of lignin was determined by the increasing of OH groups, a process which was verified by elemental analysis and IR spectroscopy. Regarding the second type of modification, the possibility of depolymerizing lignin was studied by the action of lignolytic enzymes extracted from Pleurotus ostreatus. To this end, syringaldazine and Guiaicol methods were standardized to measure the activity of laccases and peroxidases, respectively, from standard solutions of these enzymes. Subsequently, the enzyme extract obtained was measured laccase and peroxidase activity by the methods mentioned above from the third day for a week. Then a pre-purification of enzymes with ammonium sulfate and ultrafiltration was performed. Finally, seven trials for depolymerization varying the concentration of enzyme extract and using sinapic acid as mediator were performed. Each sample obtained was hydroxymethylated with formaldehyde and was characterized by elemental analysis. The third stage was the development of wood products. It was made a preliminary test with the modified lignin at 12h by UV radiation and reacted with melamine and rice hulls (using formaldehyde as polymerizing agent) by two different conditions: first, the reaction was carried out at 80 ° C for 24h; while the second was performed by autoclaving at 15 psi and 121 ° C for 3.5h. Based on this, the other wood products were prepared using the following types of lignin: unmodified extracted lignin, standard Kraft lignin, hydroxymethylated lignin (without depolymerizing) and 6 products obtained from the enzymatic modification of lignin. Finally, each of these samples was characterized by its roughness using the technique of atomic force microscopy (AFM) and were compared with a sample of natural wood. The sample 3 was the one that had the characteristics of low rank coal. Percentage of humic acids was 14.26%. The percentage of lignin extraction was 28.02%. The extracted lignin presented very similar characteristics to the standard Kraft lignin except because the latter was slightly more polar. As regard of structural modification, for UV radiation depolymerization it was found that the optimal exposure time was 12h, where an increase of 32.1% oxygen and increased band OH groups was achieved in the spectrum IR confirming the addition of hydroxymethyl groups. For enzymatic modification, was determined that the lignolytic enzymatic extract showed Lacase activity itself, and this was higher on day six (1.76 U / mL); on the contrary no peroxidase activity was found. After pre-purification and ultrafiltration, the enzyme extract showed a total activity of 38.66 U Lacasa, and the purification percentage was 0.71%. C% for the samples obtained at the elemental analysis indicated that the coupling of oxygen was lower than the UV method depolymerization therefore were less reactive samples. For enzymatic depolymerization, the best results were obtained using 8.40 U of Lacase activity per 500mg lignin (Sample 4). As for the production of wood products, the preliminary test showed that the polymerization reaction was optimized in terms of the autoclave. The product with better organoleptic and structural properties roughness was synthesized with depolymerized lignin by UV radiation for 12h and hydroxymethylated; being its value very close to that of natural wood roughness. It was also found that the hydroxymethylation without depolymerizing lignin, generates a significant increase in its reactivity; Similarly, it was discovered that the sinapic acid could react with lignin further increasing its reactivity, without the use of enzymes as the M6 generated the second best product in terms of roughness. Finally, it was shown that enzymatic depolymerization is not a viable option for the development of wood products as depolymerization with UV light generated products of better quality, less time and less investment.