Characterization of the Mechanical Properties of Urea-Formaldehyde Microcapsules

The mechanical properties of urea?formaldehyde (U?F) microcapsules were determined using a micromanipulation technique and a theoretical model. Loading?unloading, compressing and holding, and compressing to bursting tests at different speeds between two parallel plates for single microcapsules were carried out. It was found that the U?F microcapsules were visco-elastic (mainly elastic) at small compressive deformation, and plastic under large deformation. The transition point from elastic to plastic occurred at about (14±0.2)% compressive deformation. All the microcapsules would disrupt when compressed to about (17±0.2)% deformation, and the burst force increased linearly with their diameter. Compressing speed had no remarkable effect on both burst force and burst deformation. Liquid filled non-permeable and linear elastic spherical membrane model was used to simulate the uniaxial compression of single microcapsule, and its membrane modulus Eh was determined by fitting model prediction to experimental data. The average value of Eh was estimated to be (478±8) N/m.