PU microcapsules

The microencapsulation method utilized is as follows. An oil phase containing a catalyst (1,4-diazobicyclo [2,2,2] octane), MCR, diol and crosslinker trimethylol-propane (TMP) is dispersed in paraffin oil containing a steric polymeric stabiHzer (poly(butadiene-b-ethylene oxide)) in a reaction kettle maintained at 35 °C. The emulsion is stirred at 1200 rpm and TDI is added dropwise to the reaction mixture. After stirring the system at a specific stirring rate and temperature, PU microcapsules are formed which are then isolated by filtering the mixture, washing with hexane, and drying under vacuum. 

Frere et al. have reported the synthesis and characterization of PU microcapsules containing water, by interfacial polycondensation using three different diols, viz. 1,5- pentane diol, poly(ethylene glycol)s (PEG 600, PEG 1500, PEG 4200), and two different isocyanates, viz. diphenyl methylene diisocyanate (MDl) and poly(hexa-methylene diisocyanate) [25]. The surfactant used is ABA block copolymer from... 

Ohtsubo et al. have described a method to identify those parameters which determine the physical strength of PU microcapsules containing liquid insecticide (viz., fenitrothion) [45]. These microcapsules have been found to be effective in con-troUing household pests such as cockroaches. As expected, the strength of the microcapsule depends mainly on the microcapsule mass mean diameter (D), the thickness of the membrane wall (T), and particle size distribution expressed as polydispersity (e.g., D /DJ. The coefficient of variation of the particle size distribution (CV) is first determined using any suitable instrument (particle size analyzer) and method. Wall thickness T is calculated from the following equation ... 

Pol5mrethane-phosphate combinations ate known to form flame retardant intumescent systems. However, the intumescent formulation caimot be permanent beeause of the water solubility of the phosphate. This problem could be solved by the teehnique of mieroeneapsulation. Microcapsules of diammoniiun hydrogen phosphate (DAHP) with a PU shell are synthesised. Cotton fabrics can be coated with PU formulations that enclose the microeapsules and show a signifieant FR effect. 

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