Asphalt binders modified by SBS and SBS/nanoclays: effect on rheological properties

J. Braz. Chem. Soc., Vol. 23, No. 4, 639-647, 2012. Printed in Brazil - ©2012 Sociedade Brasileira de Química 0103 - 5053 $6.00+0.00 Article Asphalt Binders Modified by SBS and SBS/Nanoclays: Effect on Rheological Properties Thaís F. Pamplona,a Bruno de C. Amoni,b Ana Ellen V. de Alencar,a Ana Paula D. Lima,b Nágila M. P. S. Ricardo,b Jorge B. Soaresa and Sandra de A. Soares*,b a Departamento de Engenharia de Transportes and bDepartamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, Campus do Pici, CP 12200, 60455-760 Fortaleza-CE, Brazil Neste trabalho, investigou-se o efeito da vermiculita e montmorilonita organicamente modificadas (OVMT e OMMT, respectivamente) em ligante asfáltico (AB) modificado por SBS (butadieno-estireno-butadieno). As propriedades físicas e reológicas foram avaliadas para AB, 4,0% SBS MB e nanocompósitos AB modificados por 2,5% SBS com 2,5% de organoargilas. Os ligantes modificados (MB) resultaram no aumento do módulo complexo (G*) e na redução do ângulo de fase (δ), o que significa maior resistência destes à deformação permanente. A viscosidade, penetração e suscetibilidade térmica foram adequadas. Nos diagramas black, observou-se que o efeito da presença das nanoargilas OVMT e OMMT foi semelhante ao efeito da Cloisite®. As propriedades reológicas dos nanocompósitos foram comparáveis às do 4,0% SBS MB, identificando uma redução de custos, dado o potencial de substituição de polímero pela argila. A presença da OVMT melhorou a estabilidade à estocagem do SBS MB, um resultado importante, visto que a separação de fases é um dos maiores obstáculos ao uso do SBS na pavimentação. In this work, it was investigated the effect of organically modified vermiculite and montmorillonite (OVMT and OMMT, respectively) in asphalt binders (AB) modified by SBS (styrene-butadiene-styrene). The physical and rheological properties were performed for AB, 4.0% SBS MB and nanocomposite AB modified by 2.5% SBS with 2.5% of organoclays. The modified binders (MB) result in the enhancement of complex modulus (G*) and reduction of phase angle (δ), which means greater resistance to permanent deformation. The viscosity, penetration and thermal susceptibility were appropriate. The black diagrams show that the effect of nanoclays OVMT and OMMT was similar to the effect of Cloisite®. The rheological properties of the nanocomposite were comparable to the 4.0% SBS MB, identifying a cost reduction due to the potential of replacing polymer with clay. The presence of OVMT improved the storage stability of SBS MB, an important result, as the phase separation is a major obstacle to the use of SBS in paving. Keywords: asphalt binder, SBS, montmorillonite, vermiculite, rheology Introduction Petroleum asphalt has been widely used as binder in road pavements to provide adhesive and protective coating to aggregates. The rheological behavior of a binder is complex, varying from viscous to elastic depending on loading rate and temperature. It has to be fluid enough at high temperature when pumped and mixed with aggregates and has to be stiff enough at service temperature so that, it can resist rutting. In addition, it can not be too stiff in order to avoid thermal cracking. Thus, rheological properties of asphalt binders are of major concern since they are directly related to the field performance. *e-mail: For many years, conventional pure asphalt performed satisfactorily. Due to the increase of traffic loads and also to environmental factors, pure asphalt does not always perform as it is expected. Polymer modified asphalts were developed to overcome distress problems.1-3 The use of polymers as additives has shown to greatly improve the performance of conventional asphalt binders,4 i.e., greater resistance to rutting and fatigue as well as decrease of the thermal susceptibility. In addition, it promotes increased resistance to cracking at low temperature.5 The most important and restrictive requirement is the compatibility between the polymer and the asphalt, which needs be guaranteed to minimize the risk of phase separation for storage stability. Styrene-butadiene-styrene (SBS) copolymers have proven to improve the bitumen properties.6,7 The A 640 Asphalt Binders Modified by SBS and SBS/Nanoclays: Effect on Rheological Properties thermoplastic nature of SBS has the ability to combine elastic, strength and adhesion properties that help to increase pavement durability. The rigid domains (polystyrene blocks) interconnected through the flexible chains (butadiene blocks) form a physical elastomeric network. Unfortunately, SBS tends to separate from the asphalt when stored at high temperatures. The polymeric phase segregates in the storage tank and pumping is no longer possible to move the material.8,9 This is a major obstacle to the application of SBS in the paving industry. In spite of the small proportions of the polymer added to the binder, its high cost also somewhat restricts its broad use in road construction. Nanoscale mineral clays have been used for polymer modification, either as an agent to improve the physical and mechanical properties of the polymer or as a filler to reduce the amount of polymer used.10 Thermal stability, high gas barrier and flame retardation properties were also observed.11-15 Clays, which are cheap and abundant in nature, mostly consist of aluminosilicates. They also includes montmorillonite (MMT), vermiculite (VMT), rectorite (REC) and kaolinite clays (KC). The separation of the clay layers results in a nanoclay with a very special active specific surface area (700-800 m2 g-1).11 In the clay mineral, the silicate layers are joined through weak dipolar forces, and the cations (for example, Na+, Mg2+ and Al3+) are located in the interlayer. An important and necessary prerequisite for better interaction of the clay with the thermoplastic matrix is the modification of the clay polarity. This occurs through an ion exchange reaction by exchanging cations (present on the surface and in the basal spacing of the clay) with charged organic molecules, such as alkylammonium salts, resulting in a larger intercalary spacing.16-18 This increased spacing between the layers allows the intercalation of polymers or other materials, which results in nanocomposites.10,19,20 The effect of the clay as a third component in polymer modified asphalt has been investigated. This is achieved by adding the clay either separately or premixed with the polymer.21,22 In both cases, the results were intercalated nanocomposites. A physical mix of the asphalt binder and nanoclay leads to changes in rheological properties due to intercalation of the asphalt molecules in the nanoclay layers. From the rheological point of view, the premixed blend (SBS/clay as a nanocomposite) is not equivalent to the physical blend (adding polymer and clay separately to the asphalt). In all cases,23 the term triple nanocomposite is used to characterize a blend of asphalt/polymer/ nanocl (...truncated)