Publication: Effectiveness Evaluation of Molisch’s Test for the identification of Historical Cellulose Plastics
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2020
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Ludus
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Abstract
Como es bien conocido, la identificación de los plásticos es esencial para asegurar su correcta conservación. Este es el caso, concretamente, de los plásticos derivados de la celulosa (nitrato y acetato de celulosa), dado que ambos presentan graves problemáticas en el ámbito de la conservación-restauración. Además, ambos requieren unos parámetros medioambientales diferentes y específicos, por lo que la diferenciación entre ambos resulta fundamental para asegurar su futura conservación.
El denominado Molisch Test se ha venido empleado para detectar la presencia de celulosa en este tipo de plásticos. Aunque existen en la actualidad diversas técnicas analíticas que permiten identificar más certeramente dichos plásticos, éstas no son siempre accesibles para el conservador-restaurador. Por tanto, se trata de un test muy empleado en este ámbito, dado que es sencillo y de fácil realización; dependiendo del color de sus resultados, cada plástico podría ser diferenciado, dado que origina productos de reacción determinados. Sin embargo, los plásticos de moldeo históricos habitualmente presentan en su composición cargas añadidas para modificar sus propiedades (color, peso u opacidad, entre otros). Dentro de este grupo de cargas podemos encontrar el serrín o la pulpa de celulosa, que podrían dar originar equívocos en la interpretación del mismo.
Por tanto, esta investigación de centra en la evaluación de su efectividad, empleando para ello once casos de estudio de plásticos históricos celulósicos sometidos al test de Molisch y a espectroscopía ATR_FTIR. Las diferencias en la coloración de cada tipo de plástico se evalúan y comparan con las obtenidas en el caso de otros plásticos históricos con cargas celulósicas. Por último, se evalúan las posibles interferencias y positivos equívocos que pudieran producirse por determinados componentes de la mezcla polimérica.
As is well known, accurate identification of plastics is essential to ensure its future conservation. This is the case, especially, of the cellulose derivatives plastics (cellulose nitrate and acetate) given that both plastics have critical conservation. In addition, each of them requires specific and different environmental parameters, which also involves the differentiation between both, to ensure their permanence. A wipe method called Molisch's Test-usually used to detect cellulose can be used to identify modified cellulose plastics such as cellulose nitrate and acetate. Although currently there are many analytical techniques that allow us to identify this type of semi-synthetic plastics, they are not always accessible for the collectors and conservators. Therefore, this identification test is very used in this context, as it is very simple and reachable. According to it-and depending on its color results-each plastic can be differentiated since it produce singular reaction products. However, these molding plastics were often manufactured using fillers in order to modify the qualities of the polymer mixture (color, weight, opacity, among others). These fillers may also include cellulose compounds such as wood flour, paper, and cotton, which can also give equivocal positive results. This research focuses on the effectiveness evaluation of this test, using eleven case studies of identification of historical cellulose plastics using Molisch's test and ATR-FTIR spectroscopy. Thus, the differences in coloration obtained with each type of plastic are evaluated and compared with other results obtained with other historical plastics with cellulose fillers. Possible interferences and equivocal positives that may be produced by certain components of the polymer mixture are also evaluated.
As is well known, accurate identification of plastics is essential to ensure its future conservation. This is the case, especially, of the cellulose derivatives plastics (cellulose nitrate and acetate) given that both plastics have critical conservation. In addition, each of them requires specific and different environmental parameters, which also involves the differentiation between both, to ensure their permanence. A wipe method called Molisch's Test-usually used to detect cellulose can be used to identify modified cellulose plastics such as cellulose nitrate and acetate. Although currently there are many analytical techniques that allow us to identify this type of semi-synthetic plastics, they are not always accessible for the collectors and conservators. Therefore, this identification test is very used in this context, as it is very simple and reachable. According to it-and depending on its color results-each plastic can be differentiated since it produce singular reaction products. However, these molding plastics were often manufactured using fillers in order to modify the qualities of the polymer mixture (color, weight, opacity, among others). These fillers may also include cellulose compounds such as wood flour, paper, and cotton, which can also give equivocal positive results. This research focuses on the effectiveness evaluation of this test, using eleven case studies of identification of historical cellulose plastics using Molisch's test and ATR-FTIR spectroscopy. Thus, the differences in coloration obtained with each type of plastic are evaluated and compared with other results obtained with other historical plastics with cellulose fillers. Possible interferences and equivocal positives that may be produced by certain components of the polymer mixture are also evaluated.