Álvaro Mendoza Ramírez

Investigación y comunicación

In the past the University was the centre of human progress, as it gathered together the researchers and the thinkers in concrete physical fields and because it facilitated the intercommunication between them and the harmonic progress of their sciences. This circumstance, which converted the universities in development centres, is being lost with a technical progress standing aside the university community, detached from the humanism, in the laboratories of the State and the enterprise, stimulated only by the political or economical success urge. Today the university has in front the challenge to recover a position of vanguard in the science as it has available intercommunicable research possibilities, which are supported in all the human knowledge, through technical means placed at their disposal. This investigation must necessarily be an interuniversity one and it is based in the communication between the researchers.

Preparation and Properties of Polyurethanes based on Castor Oil Chemically Modified with Yucca Starch Glycoside

We present novel polyurethanes from renewable materials of castor oil and starch. Castor oil is transesterified with pentaerythritol in order to obtain a wide range of polyols. Yucca starch is converted into glycoside through transglycosylation reactions with ethylene glycol and glycerol. The glycosides from starch are then chemically incorporated to the castor oil polyols by a second transesterification reaction to generate a sequence of polyol-glycosides with a high level of polyhydroxyl content. These products are characterized by the hydroxyl value, viscosity, and specific gravity as a function of the glycoside type content and the kind of castor oil polyol prepared. MALDI TOF mass spectroscopy is used to find the mass fraction of glycosides and polyol-glycosides. Polyurethanes are synthesized from the polyol-glycosides by reaction with isophorone diisocyanate, under different NCO/OH molar ratios. The polymer characterization is accomplished by Fourier transform infrared analysis, tensile stress—strain tests, Shore A hardness, thermogravimetric analysis, chemical resistance to solvents, scanning electron microscopy, and dynamic-mechanical thermal analysis.

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.

Determinación de la densidad de entrecruzamiento de poliuretanos obtenidos a partir de aceite de ricino modificado por transesterificación

Two series of polyols were obtained from castor oil modified by transesterification with various amounts of pentaerythritol and glycerol. The resultant polyol properties were characterized as a function of the hydroxyl functionality. Polyurethane elastomers (PU) were synthesized from the two series of polyols obtained. The crosslink density of those polyurethanes was determined by swelling tests data adjusted to the Flory-Rehners equation and according to the elasticity theory. The variation of the crosslink density of polyurethanes was studied by following the hydroxyl value of the modified polyol utilized in the synthesis and based on the average structure of each polyurethane repeating unit, as determined by the method of matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI TOF MS). The results show that the PU obtained through castor oil modified with pentaerythritol had a higher crosslink density than PU obtained from unmodified castor oil and from PU prepared by transesterification reaction of castor oil with glycerol. PU based on polyols with the higher hydroxyl functionality presented the higher crosslink density.

POLIURETANOS ELASTOMÉRICOS OBTENIDOS A PARTIR DE ACEITE DE RICINO Y ALMIDÓN DE YUCA ORIGINAL Y MODIFICADO CON ANHÍDRIDO PROPIÓNICO: SÍNTESIS, PROPIEDADES FISICOQUÍMICAS Y FISICOMECÁNICAS

Chemical modification of cassava starch was conducted through an acylation reaction by using pyridine and propionic anhydride to replace the functional groups of starch. Polyurethane elastomers were prepared using suspensions of the mixture obtained from castor oil and yucca starch that was modified by a propionic anhydride reaction. The suspensions were characterized by means of tests based on The Fourier Transform Infrared Spectroscopy and the Hydroxyl Index. The castor oil-AMP suspensions were used for the PU synthesis. The PUs were characterized by their physical-mechanical properties like tension- deformation and Shore A. hardness, thermal gravimetric analysis and swelling test. The density cross-linking of from swelling tests was determined by applying the Flory-Rehner equation.