Synthesis of melamine-formaldehyde microcapsules containing oil-based fragrances via intermediate polyacrylate bridging layers

A general and versatile strategy to prepare melamine-formaldehyde (MF) microcapsules encapsulating oil-based fragrances by combining solvent evaporation and in situ polymerization was proposed in this work. The oil-based fragrance was pre-encapsulated by an inner polyacrylate membrane via solvent evaporation, followed by in situ polymerization of MF precondensates as an outer shell. The polyacrylate membrane is used as an intermediate bridging layer to stabilize the oil-based fragrance, and to provide driving forces for in situ polymerization of MF precondensates through electrostatic attractions between carboxyl groups and ammonium ions. It was demonstrated that MF microcapsules containing clove oil were prepared successfully. The amount and the composition of the intermediate polyacrylate bridging layer were critical. Smooth and sphere-shaped MF-clove oil microcapsules were prepared when the weight ratio of polyacrylate to clove oil was over 60 wt% and the concentration of acrylic acid (AA) increased to 10 wt% in polyacrylate. In addition, MF microcapsules containing sunflower oil and hexyl salicylate were prepared by using this method. The work suggests that this new approach can be potentially used to encapsulate various core materials, tuning the shell properties of microcapsules such as thickness, mechanical strength and release properties.