Waste Rapeseed Oil Used as a Binder for Masonry Units: NMR Spectroscopic Analysis

The chemistry of unsaturated oils used as binders for masonry units is under investigation, as it is likely to be relevant to their long term properties and may be used to improve the manufacturing requirements. The mixing process is followed by heat curing for 24 h, during which time the unit gains strength. The chemistry of this process has been assumed to be a complex series of oxidative and thermal reactions due to the double bonds present in the triacylglycerol (TAG) hydrocarbon chains, producing a heterogeneous, cross-linked solid matrix which encapsulates solid aggregates. A number of model samples and binder obtained from cured blocks were analysed via several NMR techniques. The reactions are characterised by consumption of polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA) and formation of oxygenated compounds, chain-shortened TAG, free fatty acids (FFA), di- and monoacylglycerols (DAG and MAG) and cross-linked material. The analysis facilitates identification of specific products and mechanisms of formation as the curing progresses, and evidence for instability of particular species in the matrix from samples retrieved after 6 months of storage.