Preparation And Foaming Properties Of Low Temperature Thermal Expandable Microcapsules

The low temperature thermal expandable microcapules with thermoplastic polymers as shell and low boiling point hydrocabon as foaming agent core were prepared by suspension polymerization. Some influences on particle size distribution and foaming properties of thermal expandable microcapules were investigated, then screened suitable complex system recipe of disperse phase, technological conditions and oil phase components; And explored preparation of thermal expandable microspheres with polyurethane/acrylate shell materials, besides effects on properties.Influences of NaCl contents, the type and dosage of inorganic powder dispersants and organic polymer dispersants, emulsifying rate, emulsifying time, stirring speed and the mass ratio of water and oil were discussed on particle size distribution. Thermal expandable microcapsules of uniform particles and relatively narrow distribution mainly concentrating in the 10-30μm can be obtained when 60g NaCl, added 4g nano-Mg(OH)2, 1g PVP-K30 which constituted complex dispersants were dissolved in 200g water, determining emulsifying rate for 6000rpm, emulsifying time for 10 min, stirring speed for 400rpm, and choosing the mass ratio of water and oil for 40:9.Influences of different monomers composition were investigated on expantion performance. The low temperature thermal expandable microcapsules with starting foaming at 105-110℃, foaming for 3-4 times, keeping their expantion for 25-30℃ and foaming ratio for 85-90% when determining mass ratio of capsule and core for 2:1, choosing AIBN whose dosage is 0.89% of oil phase as initiator by comparing AIBN and BPO, dropping 0.14g HDDMA as crosslinking agent in 30g monomers, determining mass ratio of MM A and AN for 3:5, VAc contents for 10% of all monomers, adding 10% BA.Polyurethane/acrylate copolymer shell materials can improve foaming times and expantion persistance of thermal expandable microcapsules. Influences of dual isocyanate structures, dihydric alcohol structures and contents of polyurethane were investigated on the expansion performance of thermal expandable microspheres. Linear polyurethane oligomer with double terminal bonds was obtained with dual isocyanate of n(TDI)/n(HDI)=5/5 as hard segment, polytetrahydrofuran glycol PTMG-300 as soft segment and hydroxyethyl acrylate as capping agent. After adding blowing agent n-isooctane and initiator AIBN to the mixure of 9.1wt% polyurethane and acrylate monomers, thermal expandable microcapsules whose yield of about 73% with starting foaming at 100-105℃, keeping expansion for 40℃ and foaming times 5 were obtained by free radical polymerization.