Synthesis And Study Of Thermally Expanded Microspheres With Excellent Foaming Performance

Thermally expandable microspheres (TEMS) are core/shell structures comprised of thermoplastic polymer shells and encapsulated inert hydrocarbon cores. The expanded TEMS have advantage in light weight and uniform expansion. Therefore TEMS have special features in heat insulation, sound insulation, shock absorption and weight loss, and have been widely used in industry.In this paper TEMS were synthesized via suspension polymerization using magnesium hydroxide as main dispersant agent. And an optical microscope with hot stage, a light scattering apparatus, an infrared spectroscopy (FT-IR), a differential scanning calorimeter (DSC), thermomechanical analysis (TMA), a scanning electron microscope (SEM) and a thermogravimetric analysis apparatus (TGA) were used to analyze properties of TEMS. Monomers of acrylonitrile (AN), methyl methacrylate (MMA), ethyl methacrylate (EMA), methyl acrylate (MA), butyl acrylate (BA), vinyl acetate (VAc), N,N-dimethyl acrylamide (DMAA), methacrylic acid (MAA), glycidyl methacrylate (GMA), styrene (St) were used to synthesize TEMS and some conclusions were achieved as followed:TEMS comprised of AN/MA, AN/BA, AN/EMA and AN/GMA had bad foaming effect; TEMS comprised of ternary system including AN/MMA/VAc and AN/EMA/MAA showed a fast thermal response property; monomers of AN, MA and VAc were used to synthesize low-temperature foaming TEMS with good expansion characteristics under aTmaxospheric pressure; porous microspheres were prepared by the same way using AN, MMA and St as monomers.MAA was chosen as the third monomer of AN/EMA system to synthesize TEMS with fast thermal response property, after being compared with MA, BA, DMAA and GMA. The results showed TEMS possessed high Dmax when initiator dosage was 2.5 wt%, the amount of crosslinking agent was 0.44wt%. The morphologies of the TEMS were influenced by the amount and boiling point of propellants. And the TEMS tended to be shriveled when more amounts of isooctane or n-hexane were encapsulated. AN/EMA/MAA TEMS possessed the highest Dmax when the mass fraction of the encapsulated blowing agents was about 18.5% and the TEMS were spheres with some dents. TEMS showed no expansion when the encapsualton efficiency of the propellant was low.TEMS with excellent low-temperature foaming property were prepared by combining AN/MA/VAc as monomers. The results showed that the increasing proportion of AN had good effect on improving Dmax of TEMS, but excessive AN had opposite effect due to bigger diameter and formation of two-phase polymers. TEMS showed bad expanding characteristics when the addition amount of MA was low because of the formation of two-phase polymers. The foaming Dmax of TEMS was significantly improved when VAc was used. Scanning electron micrograph (SEM) showed that the TEMS containing 0.46 wt% crosslinking agent kept shriveled morphology when the amount of n-hexane increased, but turned from irregular concave shape to sphere following the content increase of n-hexane when the amount of crosslinking agent reduced to 0.26% or 0 the morphologies. Spherical TEMS were confirmed faster foaming speed and higher foaming Dmax.