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Viscosity is one of the key factors which influence the application of polyacrylamide (PAM) in enhanced oil recovery (EOR). In this study, we have demonstrated the viscosity reduction of PAM solution by using carbon quantum dots (CQDs) through rheological, spectroscopic and thermal analyses. The stability of PAM, CQDs, and PAM/CQDs composites, and the chemical interactions between PAM and CQDs were investigated. The addition of CQDs into PAM solution decreased its viscosity, demonstrating a phenomenon which contradicts the expression normally derived from the Einstein–Batchelor law for the viscosity of particle suspensions. Consequently, the elastic properties of PAM/CQDs composites were lower than those of the pure PAM solutions. Moreover, the presence of CQDs in the PAM increased its flow activation energy and decreased its yield point, leading to an increased sensitivity to both temperature and shear rate. The mechanism behind the reduced viscosity behaviour of PAM/CQDs composites appears to be the formation of free radicals and the elimination of ammonia molecules, leading to the deterioration of the polymer backbone.

In this study, the suitability of four chemically different melamino cross-linkers for use in formulating epoxy coatings was investigated on the basis of the composition and of the tendency of cured coatings to hydrolyse to melamine and to formaldehyde when they were retorted in aqueous food simulants. The four cross-linkers were characterised for their composition identity, flow behaviour, thermal stability and for the presence of residual species. The different cross-linkers were used individually to cross-link selected epoxy coatings. The effects of the cross-linker chemistry, the curing conditions and the kinetics of the hydrolysis and subsequent migration processes, leading to melamine and formaldehyde were investigated following thermal treatments that were designed to represent the conditions of food sterilisation. The results show that each cross-linker type is different in its rheological characteristics, its solids content, its thermal behaviour and its physical properties. The chemistry of each cross-linker plays a major role in the manner in which the epoxy coatings undergo hydrolysis to release melamine and formaldehyde. The greatest migration of melamine (from an unpigmented epoxy anhydride coating, cured with the hexamethoxymethyl melamine cross-linker) into the 10% (v/v) aqueous ethanol food stimulant, after retorting at 131 °C, for 1 h was 525 μg/6 dm 2 . The greatest migration of formaldehyde into the simulant was also from this coating at 11 μg/6 dm 2 , when retorted at 131 °C for 1 h. The curing conditions affected the extent of the cross-linker hydrolysis. The influence of varying the curing time and the curing temperature was used to control the hydrolysis of the cross-linked, epoxy-based coatings. A decrease in the extent of cross-linker hydrolysis by 50–80% was achieved in all cases as the temperature of the curing was increased, in stages, from 160 °C to 200 °C.

Pigmented (TiO2), amino resin crosslinked coatings, designed for applications in can coatings’ internal lacquers, were formulated, characterized, applied, and cured. Three grades of a pigmentary form of TiO2 were characterized in terms of their particle size, their particle morphology, their zeta potential, and their moisture retention behavior. Epoxy coatings that were crosslinked using one of several, different amino crosslinkers were prepared. The effect of the presence of the TiO2 pigments on the hydrolysis of the cured coatings was monitored via the controlled retorting of the coatings. The different grades of TiO2 pigment were selected, to establish whether or not they could be used interchangeably with respect to hydrolysis and to melamine release. Also, the effects of the aging of the fluid coatings on the amount of melamine released from the coatings (after curing and retorting) were monitored. Storage under laboratory conditions for 2, 20, and 40 weeks was used for this purpose. The TiO2 pigment contributed significantly to the hydrolysis behavior of the epoxy coatings in that their presence substantially reduced the amount of melamine released and the extent of crosslinker hydrolysis. Typical results show that excluding the TiO2 pigment particles from the formulation results in there being 50% more hydrolysis of the crosslinker to melamine. With respect to the melamine release and crosslinker hydrolysis, the different grades of the pigment gave similar results.