Estudio de la degradación térmica del POLI(cloruro de Vinilo) modificado mediante reacciones de hidrogenación y cloración

Study of Thermal Degradation of POLY ( Vynyl Chloride) modified by mean hydrogenation and chlorination reactions

  • Jesús Miguel Contreras Ramírez Universidad de Los Andes - Venezuela
  • Gerardo Martínez Albillos Instituto de Ciencis y Tecnología de Polímeros - España
  • José Luis Millán Rodríguez Instituto de Ciencis y Tecnología de Polímeros - España

Resumen

 
En este trabajo se estudió la degradación térmica del poli(cloruro de vinilo) (PVC) después de ser sometido a: i) hidrogenación parcial usando como agentes reductores el tetrahidruro de litio y aluminio (HLi), el Hidruro de trietil-boro y litio (SH) y el hidruro de tri-n-butil estaño (HSn) y ii) reacción de cloración. Las muestras fueron degradadas a 180 °C en estado sólido hasta un 0,3% y la velocidad de la degradación fue obtenida mediante el método conductimétrico; mientras que la distribución de polienos fue investigada por espectroscopia ultravioleta/visible (UV/VIS). En el caso de las muestras de PVC hidrogenadas, los datos cinéticos indicaron que se produjo una fuerte estabilización del polímero de partida como consecuencia de la hidrogenación, obteniéndose el máximo grado de estabilización a conversiones en torno al 9 %. La correlación entre la tacticidad-conversión-velocidad de degradación térmica demostró el carácter lábil de las estructuras mmr terminales de secuencias isotácticas que desaparecieron de la cadena como consecuencia de la hidrogenación. Por otra parte en el caso de las muestras cloradas, los resultados obtenidos evidenciaron que la estabilización del polímero aumenta como consecuencia de la formación de estructuras 1,2-dicloradas. Mientras que, la aparición de estructuras 1,1,2-tricloradas (-CHCl-CCl2-) representan la presencia de estructuras lábiles nuevas.
 
Palabras clave: Cloración; degradación térmica; hidrogenación; poli (cloruro de vinilo) (PVC); tacticidad.
 
Abstract:
 
In this work, the thermal degradation of polyvinyl chloride (PVC) was studied after being subjected to: i) partial hydrogenation, using lithium aluminum hydride (HLi), lithium triethylborohydride (SH) and tri-n-butyltin hydride (HSn), as reducing agents; and ii) chlorination reaction. The samples were degraded at 180 °C in the solid state up to 0.3% and the degradation rate was obtained by the conductimetric method; while the distribution of polyenes was investigated by ultraviolet/visible spectroscopy (UV/VIS). In the case of the hydrogenated PVC samples, the kinetic data indicated that there occurred a strong stabilization of the starting polymer as a consequence of the hydrogenation, obtaining the maximum degree of stabilization at conversions of around 9%. The correlation between the tacticity-conversion-degradation rate demonstrated the labile character of the mmr structures terminal of isotactic sequences that disappeared from the chain as a consequence of hydrogenation. On the other hand, in the case of the chlorinated samples, the results obtained showed that the stabilization of the polymer increases while the formation of 1,2-dichlorinated structures predominated. On the contrary, the appearance of 1,1,2-trichlorinated structures (-CHCl-CCl2-) represented the presence of new labile structures.
 
Keywords: Chlorination; hydrogenation; poly (vinyl chloride) (PVC); tacticity; thermal degradation.

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Publicado
2019-01-31
Sección
Ciencias Químicas