Behavior of sulfur-polymer matrix composites with different fillers under acid and salt influence

Abstract

Based on the nature of the matrix material, modern composites can be generally classified into three categories: polymer matrix composites, metal matrix composites, and ceramic matrix composites. Polymer matrix composites are not as strong or heat-resistant as metal matrix and ceramic matrix composites and therefore are restricted to secondary structures in which operating temperatures are lower than 300° C while for higher temperatures, metal matrix and ceramic matrix composites are required. Polymeric materials based on inorganic components can play an important role in various technological processes but their production on an industrial scale is still problematic. However, inorganic polymers, in combination with other materials can generate composite materials of very high quality and possibilities of applications. Among plenty of inorganic materials that can generate polymer chains, special attention should be paid to sulfur. One of the most popular applications of waste sulfur from the oil refining process is to produce a modified sulfur binder, which is predominantly implemented in different compositions of sulfur- polymer matrix composite materials used for diverse applications. Using sulfur as a binder is based on its physical and chemical characteristics: chemical passivity, excellent resistance to aggressive agents (mainly acids and salt solutions, but not bases) and hydrophobic properties. Sulfur implementation for composites production has started with using unmodified sulfur as a binder. However, despite excellent mechanical properties after preparation, samples exhibited low stability, so spalling and failure occurred after a short period. The development of modified sulfur binder contributed to better endurance of sulfur- polymer matrix composites, which focused its application for roads construction and repairing and as a building material. Sulfur itself tends to polymerize to a large extent while chemical modification increases this tendency or prolongs the time required for the polymerization. Except the prevention of sulfur transformation from monoclinic to orthorhombic form, the degree of sulfur polymerization is increased and long chains are created due to modification. Sulfur- polymer matrix composites are thermoplastic materials made of mineral aggregate and filler, with sulfur as a binder (instead of cement and water) at temperature above the hardening point of sulfur (120 ºC). The proportion of aggregate, filler and binder for the preparation of sulfur- polymer matrix composite mixture may vary depending on the application. The choice of filler is important because it forms with sulfur paste that coats and binds the aggregate particles. In this chapter, various fillers were used for the production of sulfur- polymer matrix composite samples: talc, alumina, microsilica and fly ash. Durability of the obtained sulfur- polymer matrix composite samples was investigated under influence of acids (hydrochloric and sulfuric acids) and salt (sodium chloride) by monitoring their physico-mechanical characteristics. It was concluded that the used filler had influence on the behavior of the sulfur- polymer composite samples in the investigated environments.