Blends of high-density polyethylene and polypropylene are foamed by means of extrusion using azodicarbonamide as a chemical blowing agent to study the effect of blending on the morphological and mechanical properties. At 0.5 wt% of blowing agent, optimum foam density is found to be around 417 kg/m3 for each blend composition, but the average cell size ranges between 130 and 301 mm depending on the blend composition. It is believed that the dispersed polymer phase acts as nucleating sites producing foams with smaller cell sizes. Owing to the incompatibility between both the polymers, the best tensile and impact properties are obtained for neat polymers. Simple semi-empirical models are proposed to predict the tensile and impact properties of the foams.
RESUMENLas mezclas semicalientes permiten una reducción de la temperatura de fabricación respecto a las mezclas tradicionales, mediante la modificación del proceso de producción en planta o el empleo de aditivos. En esta investigación se analiza el empleo de zeolita natural procedente de Cuba como aditivo para la fabricación de mezclas semicalientes, en comparación con el empleo de zeolitas artificiales. Para ello, a través de pruebas de estabilidad Marshall, sensibilidad al agua y módulos de rigidez se realiza un estudio comparativo. El resultado obtenido mostró un comportamiento similar entre las mezclas con zeolita natural y la sintética, resultando en ambos casos ligeramente inferior al obtenido por la mezcla patrón. Además, se evaluó la influencia de la adición de zeolita natural a la mezcla en diferentes porcentajes, como filler o como arena, obteniendo mejores resultados con la incorporación en la fracción filler.Palabras clave: mezclas asfálticas semicalientes; zeolitas; impacto ambiental; reducción de emisiones. ABSTRACTZeolite can be used as an ingredient in warm bituminous mixes to reduce manufacturing temperatures. The zeolite for this purpose is usually synthetic, but natural zeolite can also be used. The research presented in this paper analyzed the use of natural zeolite from Cuba in the form of sand and filler as an additive in warm asphalt mixes and compared it to asphalt mixes with synthetic zeolite. The mixes were given the Marshall tests, and their moisture sensitivity and stiffness modulus values were also obtained. The results showed that both types of mix had a similar performance, which was only slightly lower than that of the reference mix. The use of different dosages of natural zeolite in the mixes gave the best results when the zeolite was incorporated as filler. This study demonstrated that the use of natural zeolite is an effective way of reducing the temperature of bituminous mixes.
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