Isocyanate-functionalized castor oil as a novel bitumen modifier

Abstract

The use of biomaterials from renewable sources in the synthesis of polyurethanederived polymers is lately receiving great attention from social, environmental and economic standpoints. In this work, prepolymers having different -NCO/-OH ratio were synthesized, by reaction of 4,4´-diphenylmethane diisocyanate (MDI) with castor oil (CO), to be used as modifying agent of asphaltic bitumen. Reactions between MDI and CO, performed with -NCO/-OH molar ratios of 8:1 and 4:1, have led to suitable bitumen modifiers. Modification has been related to chemical reactions between -NCO groups, some bitumen compounds and air moisture (or added water), which gave rise to binders with enhanced resistance to permanent deformation. The results showed that a 2 wt.% of MDI-CO prepolymer leads to binders with higher viscosity than that corresponding to a 3 wt.% Styrene-Butadiene-Styrene (SBS) block copolymer, a polymer and concentration widely used in the paving industry. Furthermore, the resulting prepolymers are liquids that can be easily mixed with bitumen at 90 ºC, which significantly lowers the typical temperature used for commercial SBS-modified bitumen (about 180 ºC). This fact may represent energy savings, reduce bitumen oxidation and result in improvements of health and safety conditions during the product manufacture.However, if high processing temperatures are required, MDI-CO based modifiers have demonstrated much higher thermal stability than prepolymers derived from crude oil (e.g. based on polyethylene glycol). As a result, NCO-terminated prepolymers obtained from biomass-derived polyols (castor oil in this article) may become a promising alternative to the use of other petrochemicals in the paving industry.

Processing of bitumens modified by a bio-oil-derived polyurethane

“…In order to ensure an excess of non-reacted -NCO groups in the reaction product, an equivalent ratio -NCO/-OH of 8:1 was selected. This ratio was found optimal in a previous work [15]. The resulting reactive prepolymer (referred to as MDI-CO) has an average molecular weight of 2640 g/mol, and is expected to bring about "chemical" modification of bitumen, via -NCO groups.…”

“…Moreover, apart from the environmental benefits, the prepolymers thermal stability has been found to improve when castor oil, instead of a polyethylene glycol (PEG), is used [15]. Bitumen modification with this type of prepolymer is expected to take place by reaction of the free -NCO groups in the prepolymer and bitumen pendant groups which contain active atoms (-OH mainly, typically present in the asphaltenes) [16,17].…”

Influence of polymer melting point and Melt Flow Index on the performance of ethylene-vinyl-acetate modified bitumen for reduced-temperature application

“…Even though its content in the asphalt mixtures (composed of mineral aggregates and bitumen) never exceeds 5 wt.%, its contribution to the road performance is decisive [2]. In that sense, it is the only deformable component in the mixtures and actually constitutes their continuous matrix.…”

Rheology investigation of waste LDPE and crumb rubber modified bitumen

“…For reducing cost, some inexpensive polymeric materials, especially wastes and by-products e.g. waste rubber, waste plastics, could have potential applications with greater success in the future (Brovelia et al, 2015;Cuadri et al, 2013;Fuentes-Audén et al, 2008;Fang et al, 2012;González et al, 2016). 28 The various investigated polymers are plastomers (e.g.…”