RESUMENSe presenta una revisión sobre el efecto del sistema de vulcanización en la estructura formada durante la reacción de vulcanización, en la cinética de la reacción y en las propiedades de formulaciones que emplean caucho natural. Se encontró que aún existen aspectos por investigar dada la variedad de acelerantes, proporciones acelerante/azufre, tipos de caucho natural y formulaciones que emplean caucho natural. La mayor parte de la literatura evalúa la reacción de vulcanización mediante reometría de vulcanización y calorimetría diferencial de barrido (DSC), pero estas técnicas no permiten identificar el tipo de enlaces sulfídicos formados ni la densidad de enlaces entrecruzados. La temática es de gran interés científico e industrial pues el caucho natural es el caucho más comercializado a nivel mundial, y su vulcanización se realiza en la gran mayoría de las formulaciones empleando azufre como agente entrecruzante. PALABRAS CLAVES:Caucho natural, sistema de vulcanización, reacción de vulcanización, red entrecruzada, agente vulcanizante, acelerantes Revista EIA, ISSN 1794-1237 / Año XIV / Volumen 14 / Edición N.28 / Julio-Diciembre 2017 / pp. 99-115 Publicación semestral de carácter técnico-científico / Universidad EIA, Envigado (Colombia)

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In this article, the effect of leather residues from chrome tanning on the vulcanization kinetics and rheometric properties of a natural rubber composite was evaluated using three kinetic models proposed in the literature. Leather wastes were classified according to their size as fine (smaller than 0.6 mm) or coarse (between 0.84 and 2 mm). Subsequently, they were chemically treated with a sodium bicarbonate solution to neutralize their acidic nature derived from the tanning processes. The composites studied in this paper were obtained using a torque rheometer. Fine and coarse leather wastes were added to a natural rubber matrix in proportions of 20, 40, 60, 80, and 100 phr. The rheometric properties of all the composites were monitored during the curing process using a moving die rheometer. The addition of leather wastes increased the vulcanization time and stiffness of the composites; however, materials with fine leather wastes achieved lower vulcanization times than materials with coarse residues. The curves obtained during vulcanization rheometry were fitted to the three kinetic models, which made it possible to determine the kinetic parameters k and n. The fits for the three models were satisfactory based on the R-squared results. The values and trends of the kinetic parameters of each model were analyzed and related to the vulcanization phenomenon of each composite.

In this work, the impact of good manufacturing practices (GMP) on the specific energy consumption (SEC) of plastic injection molding process, in 9 representative companies in Colombia, was studied. The GMP applied to the injection molding process and the degree to which they are adopted by the companies were defined. Afterwards, the SEC of 17 representative injection molding processes in those companies were evaluated. Finally, the impact of applying the GMP and their effect on SEC were studied. The degree of application of GMP on the analyzed companies ranges from 35 to 72%. A single SEC value could not be established for all the injection systems, because it depends on the injected weight and the productivity of each mold-machine-material combination. Nevertheless, a characteristic curve was defined for different systems. A relationship between the application of GMP and SEC was found. It was observed that all GMP contributed to improve the SEC, with different significance, ranging the relevance from 6 to 14%. Finally, it was concluded, taking in consideration a representative company, that “Plasticizing” and “Drive Units” were the most relevant categories to impact the SEC.