Poly(3-hydroxybutyrate) (PHB) based on nanocomposites containing different amounts of a commercial organically modified clay (viscogel B7) were prepared employing solution intercalation method. Three solvents, such as: CHCl3, dimethylchloride (DMC) and tetrahydrofuran (THF) were used. The relationship among the processing conditions; molecular structure and intermolecular interaction, between both nanocomposite components, were investigated using a nuclear magnetic resonance (NMR), as a part of characterization methodology, which has been used by Tavares et al. It involves the hydrogen spin-lattice relaxation time, T1H, by solid state nuclear magnetic resonance, employing low field NMR. X ray diffraction was also employed because it is a conventional technique, generally used to obtain the first information on nanocomposite formation. Changes in PHB crystallinity were observed after the organophilic nanoclay had been incorporated in the polymer matrix. These changes, in the microstructure, were detected by the variation of hydrogen nuclear relaxation time values and by X ray, which showed an increase in the clay interlamelar space due to the intercalation of the polymer in the clay between lamellae. It was also observed, for both techniques, that the solvents affect directly the organization of the crystalline region, promoting a better intercalation, considering that they behave like a plasticizer.

The qualitative characterization of two commercial ethyneamines epoxide hardeners marketed by ACROS (U.S.A.) was carried out by using carbon-13 nuclear magnetic resonance spectroscopy. The products were triethylenetetramine (TETA) and tetraethylenepentamine (TEPA). TETA had four components, the most importante one being triethylenetetramine, an ethyleneamine of lineal structure, in a concentration of 60 mol%. Another component had ramified structure, while the other two exhibited recurrent structures of the piperazina type. TEPA had five components with similar structures. The major component was tetraethylenepentamine in an approximate concentration of 55 mol%. These results agree with the composition of similar products marketed by Dow Chemical Company, namely DEH 24 and DEH 26, respectively.

La caracterización cualitativa de dos agentes de curado comerciales de resinas epoxídicas del tipo etilenaminas comercializados por la ACROS (U.S.A.) fue realizada usando la espectroscopia de resonancia magnética nuclear de carbono-13. Los productos comerciales corresponden a la trietilentetramina (TETA) y a la tetraetilenpentamina (TEPA). El producto TETA presentó cuatro compuestos diferentes. El compuesto mayoritario correspondió a la trietilentetramina en una concentración de 60% molar que corresponde a una etilenamina de estructura linear. Los otros tres compuestos, uno de ellos mostró estructura ramificada, y los otros dos compuestos presentaron estructuras cíclicas del tipo piperazina. El producto TEPA mostró cinco compuestos con estructuras semejantes a las encontradas en el producto TETA. El compuesto mayoritario correspondió a la tetraetilenpentamina en una concentración aproximada de 55% molar. Los resultados encontrados en este trabajo están de acuerdo con la composición cualitativa de los productos semejantes comercializados por la Compañía Química Dow, productos DEH 24 y DEH 26, respectivamente.

El trabajo revisa un conjunto representativo, aunque no exhaustivo, de interpretaciones sobre el pobre desempeño de la economía argentina entre la Gran Guerra y la crisis de 1989. Analiza la bibliografía agrupándola según dos aproximaciones distintas; quienes asumen que dicha performance estuvo condicionada por factores estructurales, y quienes la atribuyen a decisiones de política económica y circunstancias coyunturales. Entre los primeros, destaca la importancia que se ha dado a los legados coloniales, el peso de las instituciones, la asimetría en las relaciones internacionales, problemas en la formación de capital y la inadecuación del empresariado que dirigió el proceso de industrialización. Entre las segundas, quienes señalan la falta de (o tardía) intervención estatal, los que por el contrario atribuyen a esta intervención la distorsión de los parámetros económicos que facilitan el crecimiento y desarrollo, quienes señalan problemas en la institucionalidad político-social, o atribuyen la performance simplemente a la resultante de una serie de procesos circunstanciales. En la parte final del artículo se apunta a subrayar el papel que la distancia entre el grado de crecimiento del producto en el momento inicial (favorecido por la dotación de recursos naturales) y el nivel de desarrollo general de la sociedad, fundamentalmente en cuanto a su capital humano y calidad institucional, pueden haber tenido en este proceso.

This study reviews a representative though not an exhaustive set of representative explanations of the poor performance achieved by Argentina’s economy between the Great War and the 1989 crisis. It analyzes the literature by dividing it in accordance with two different approaches: one that assumed that economic performance was conditioned by structural factors, and another that attributes it to decisions on economic policies and conjunctural circumstances. Regarding the firts approach, it highlights the importance of colonial legacies, the asymmetry of international relations, problems related to the formation of capital, and the flaws of the entrepreneurial class that led the industrialization process. Among the second approach, emphasis is laid on those who point to the lack of State intervention or the State’s belated decision to intervene, those who hold the opposite view by stating that it was precisely because of State intervention that the economic parameters favorable to growth and development became distorted, those who point to problems about political and social institutions, and those who attribute poor performance to a series of citcumstancial processes. The last part of the study intends to underscore the role played in this process by the distance separating initial levels of development (aided by natural resources) and the levels of societal general development, chiefly in relation to the available human capital and to the quality of the institutions involved.

O sistema epoxídico constituído pelo éter diglicidílico do bisfenol A (DGEBA), produto DER 331 com endurecedor 24 comercializados pela Dow Química do Brasil foi caracterizado por métodos espectroscópicos, calorimétricos e de determinação de grupos funcionais. O endurecedor 24 é constituído por trietilenotetramina (60 % molar) e uma mistura de etilenoaminas polifuncionais com estruturas lineares, ramificadas e cíclicas. O equivalente epoxídico da resina resultou de 187 g eq-1. A funcionalidade média, o equivalente de amina, e a concentração do endurecedor que satisfaz a estequiometria, corresponde a 5,54, 27,5 g eq-1, e 14,7 phr, respectivamente. O sistema epoxídico manifestou uma entalpia de reação de 486 J g-1 (106,6 kJ eq-1), e uma temperatura de transição vítrea (Tg<FONT FACE=Symbol>¥</FONT>) de 124 ºC. O trabalho apresenta ainda um programa de cura em duas etapas onde se alcança a conversão máxima, e se apresenta o diagrama de transformações conversão vs temperatura (CTT).

Diglycidyl ether of the bisphenol A (DGEBA), product DER 331 and hardener 24 system marketed by Chemical Dow of Brazil were characterized by spectroscopic, calorimetric and determination of functional groups methods. The hardener 24 is constituted by triethylenetetramine (60 % molar) and a mixture of ethylene polyfunctional amines with linear, ramified and cyclic structures. The epoxy equivalent of the resin corresponds to 187 g eq-1. The functionality average, equivalent amine, and the concentration of the hardener that satisfy the stoichiometry corresponds to 5.54, 27.5 g eq-1, and 14.7 phr, respectively. The epoxy system displayed an enthalpy of reaction of 486 J g-1 (106.6 kJ eq-1), and a glass transition temperature (Tg¥) of 124 ºC. Also presented in this work is a cure program in two stages where the maximum conversion was reached.