Synthesis and characterisation of thermally expandable microcapsules by suspension polymerisation

Purpose - The purpose of this paper is to synthesise and characterise novel thermally expandable microcapsules having poly (acrylonitrile (AN)-methyl methacrylate (MMA)-butyl acrylate (BA)) copolymer shells and p-toluenesulphonylhydrazide (TSH) cores. Design/methodology/approach - The novel thermally expandable microcapsules are synthesised by suspension polymerisation. The effects of various parameters including monomers and surfactant compositions on thermal expandability and stability, and particle size and size distributions of the microcapsules obtained are studied. Fourier transform infrared (FTIR) and scanning electronic microscopy (SEM) analyses are employed to characterise the chemical structure and morphology of the microcapsules obtained. Findings - Suspension polymerisation with the monomers composition of 70 per cent AN/20 per cent MMA/10 per cent BA can yield microcapsules having a good expansion property and heat stability at 150 degrees C. The paper also finds that when the amount of the incorporated PA reaches 20 percent, the shells of microcapsules obtained will adhere together and some shells rupture resulting in the collapse of many of the expanded microcapsules. During the course of polymerisation, high-molecular surfactant styrene - maleic acid copolymer sodium salt can help to achieve microcapsules with more uniform size distribution. FTIR and SEM characterisation show that the chemical structure of microcapsules contain core material and copolymeric shell and the morphology of microcapsules is very well defined, core-shell type, respectively. Research limitations/implications - The shell copolymer in the present context is synthesised from acrylonitrile-methyl methacrylate- and butyl acrylate. Besides, it can be synthesised from other monomers also. In addition, the expansion efficiency of microcapsules can be studied. Practical implications - The learning gained through this paper can be applied to the synthesis and application of other microcapsule or even nano-capsule systems. Originality/value - The method for preparation of TSH microcapsules by suspension polymerisation is novel and the microcapsules could find applications in water-based intumescent and flame retardant wood coatings.