Sintesis de poliuretanos a partir de polioles obtenidos a partir del aceite de higuerilla modificado por transesterificación con pentaeritritol

Abstract

Recebido em 24/4/08; aceito em 20/6/08; publicado na web em 10/11/08 POLYURETHANES SINTETIZED OF POLYOLS OBTAINED FROM CASTOR OIL MODIFIED BY TRANSESTERIFICATION WITH PENTAERYTHRITOL. Castor oil was reacted by transesterification with various percentages in mass of pentaerythritol to obtain different esters of pentaerythritol. Alternatively, glycerol was also used instead of pentaerythritol for the same reaction in order to establish comparative reference products. The products of the reactions were characterized by matrix-assisted laser desorption/ ionization time-of-flight mass spectroscopy in order to detect and quantify (in terms of the molecular mass and structural information) the components of the products obtained. Analysis for hydroxyl value, acid value, viscosity and specific gravity were used to complete the characterization of the polyols obtained and also of the original castor oil. The polymer characterization was accomplished by tensile stress-strain tests, Shore A hardness, thermogravimetric analysis and chemical resistance to solvents.Keywords: castor oil transesterification; MALDI TOF mass spectroscopy; polyurethanes. introducciónEl aceite de higuerilla se extrae de la semilla de la planta "Ricinus communis" y se caracteriza por ser uno de los pocos aceites vegetales cuya composición es casi la de un solo componente, puesto que el 90% corresponde al triglicérido del ácido ricinoléico. Desde el punto de vista de la innovación, la estructura química del aceite de higuerilla es de gran interés, porque permite un gran número de reacciones y productos derivados. 1El uso del aceite de higuerilla en la síntesis de elastómeros de poliuretano e IPNs ha sido reportado en numerosas investigaciones. 2-4Estos estudios muestran que se puede obtener un amplio rango de propiedades físicas y mecánicas dependiendo del contenido del poliol y el diisocianato. La composición y la relación NCO/OH de los segmentos del poliuretano afectan la estructura, organización y flexibilidad del polímero, y por consiguiente la morfología y las propiedades mecánicas. Sin embargo, los materiales obtenidos a partir del aceite de higuerilla presentan propiedades como bajo módulo de Young, baja resistencia al rasgado y también baja resistencia a tratamientos a alta temperatura. 5-7Una forma de modificar estas propiedades es la transesterificación del aceite con alcoholes polihidroxílicos para introducir grupos hidroxílicos reactivos. Al aumentar estos grupos se incrementa el grado de entrecruzamiento del poliuretano, por lo que las propiedades del poliuretano cambian. El término transesterificación se usa generalmente para describir una clase de reacciones orgánicas donde un éster es transformado en otro a través del intercambio del grupo alcoxi.8 En la transesterificación de aceites vegetales, un triglicérido reacciona con un alcohol, en presencia de un ácido o base fuerte, produciendo una mezcla de ésteres alquílicos de ácidos grasos y glicerol. El proceso total es una secuencia de 3 reacciones consecutivas irreversibles en la cual...

Polyurethanes from modified castor oil and chitosan

“…al. 29 through mass spectrometry, in which four main compounds were reported: ricinoleic monoglyceride, ricinoleic diglyceride, pentaerythritol monoricinoleate and pentaerythritol diricinoleate 30 . A scheme of the reaction and composition of product can be observed in Figure 2a.…”

“…al. 30 described the behaviour of PU from CO modified with PE and glycerol, and in both cases, mechanical properties of materials obtain a high level with the rise of modifier agent due to an increase in crosslinking. Therefore, in our case, an increase between intermolecular forces in PUs can be concluded.…”

Castor oil and commercial thermoplastic polyurethane membranes modified with polyaniline: a comparative study

“…Thus, the aim of this study was to synthesize the PAni, preparing the membrane and characterize and compare the membranes produced using doped PAni with the membranes produced using SPAN. Lastly, also was investigated the influence of the thermoplastic PU (TPU) and the results were compared with that PU produced with castor oil (CAPU) 22 .…”

Castor oil/trimethylol propane‐based polyurethane reactions: Modeling in a batch reactor

“…15 To offset these disadvantages, castor oil is transesterified or alcoholyzed with polyhydroxy alcohols, most commonly by glycerol, pentaerythritol and trimethylol propane. [16][17][18][19] Transesterification leads to increase in hydroxyl value of the system thereby rendering hardness to the product, while long chain fatty acids induce flexibility. Thus resulting polyurethane polymer is relatively tough.…”

“…PU obtained from castor oil have certain disadvantages, including: low hydroxyl number leading to low modulus materials; a slower rate of curing of secondary hydroxyl groups14 and structural irregularity due to steric hindrances offered by the long pendant fatty acid chains during polyurethane formation, resulting in low tear strength 15. To offset these disadvantages, castor oil is transesterified or alcoholyzed with polyhydroxy alcohols, most commonly by glycerol, pentaerythritol and trimethylol propane 16–19. Transesterification leads to increase in hydroxyl value of the system thereby rendering hardness to the product, while long chain fatty acids induce flexibility.…”