[en] The current work is focused on a practical case and two studies with a bibliographic approach about the lignin, a polymeric compound of natural origin. In the practical case, the molecular masses of several samples of lignocellulosic materials are compared to try to determine experimentally the effect caused by the method of obtaining on their analysis by gel permeation chromatography (GPC) and their molecular mass. To accomplish the aforementioned analysis, we study three types of lignins of different origin (alkaline lignin, organosolv and an industrial effluent from defibering wood by steam explosion) that are analyzed with the same chromatographic method. Two pretreatments were applied to the samples prior to their analysis: direct dissolution in tetrahydrofuran (THF) and/or derivatization prior to their dissolution in THF. It is only possible to solubilize the sample without derivatization in the case of organosolv lignin. The data provided by the GPC analysis vary quite depending on the method of obtaining the sample, so that the lignin from the industrial effluent has the lowest molecular mass values. The first bibliographical study reviews the methodology used to determine the molecular mass of lignins by means of GPC. The influence of the method of obtaining and pretreatment of the sample on the analytical conditions and on the molecular mass of the sample are evaluated. Finally, another bibliographical study of the use of lignins in composite polymeric materials endowed with electrical conductivity is carried out and a comparison of the electrical properties underlying the obtaining of the different composites is made.

[gl] No presente traballo realízanse un caso práctico e dous estudos bibliográficos arredor do composto polimérico de orixe natural que é a lignina. No caso práctico, compáranse as masas moleculares de varias mostras de materiais lignocelulósicos para tratar de determinar experimentalmente o efecto xerado pola forma en que se obteñen na análise de cromatografía de permeación en xel (GPC) e a súa masa molecular. Para iso estúdanse tres tipos de ligninas de distinta orixe (alcalina, organosolv e un efluente industrial procedente do desfibrado de madeira por explosión de vapor) que se analizan co mesmo método cromatográfico. Sométense a dous pretratamentos previos á análise: disolución directa en tetrahidrofurano (THF) e/ou derivatización previa á disolución en THF. Só é posible solubilizar a mostra sen derivatización no caso da lignina organosolv. Segundo o seu método de obtención, os datos proporcionados pola análise GPC varían bastante de xeito que a lignina procedente do efluente industrial ten os valores de masa molecular máis baixos. O primeiro estudo bibliográfico consiste en revisar a metodoloxía empregada para determinar a masa molecular das ligninas mediante GPC. Avalíase a influencia do método de obtención e do pretratamento da mostra nas condicións de análise e na masa molecular da mostra. Por último, realízase un novo estudo bibliográfico do uso das ligninas en materiais poliméricos compostos dotados de condutividade eléctrica e realízase unha comparación das propiedades eléctricas subxacentes á obtención dos distintos compostos.