Sythesis And Properties Of Polymerthane Dispersions By Pellet Process

Polyurethane dispersion in which water was dispersion medium was binary mediumsyetem, and it has caused public attention because of its non-toxic and lower VOC. Thestructure of polyurethane resin molecules was the embedded structure which was made ofhard segment and soft segment. We could get different performance polyurethanes throughchanging the hard segment and soft segment and their composition proportion, making beenwidely used in the adhesive, coating and printing industries. There are many the synthesismethods for synthesizing the polyurethane dispersions, such as acetone method, prepolymeremulsification method, malt dispersion method and cetimine-cetazine method. The acetonemethod and prepolymer emulsification method were most widely used processes. When usingacetone method for synthesizing polyurethane dispersion, a lot of solvent had been used and itrequired highly purity solvent of ammonia ester level. When the prepolymer emulsificationmethod had been used for synthesizing polyurethane dispersion, the reaction betweenIsocyanate and the water made not easy to control its reproducibility. This method was onlysuitable for aliphatic isocyanate.In this paper, the stably polyurethane ionomeric polymer pellets were synthesized bythe pellet process with polytetramethylene glycol (PTMG) as soft segment，isophoronediisocyanate (IPDI) and1,4-butanediol (BDO) as hard segments, and dimethylolpropionicacid (DMPA) as hydrophilic monomer. After the polyurethane ionomeric polymer had beenpelleted, dissolved in acetone, emulsificated and removed acetone, the polyurethanedispersion(PUDs) with solid content about40%were obtained. This process had been calledpellets process. By contrast with acetone method and prepolymer method, pellets method costlow energy consumption, through bulk polymerization; this method required lower purityacetone, which could be recycled directly. Both aromatic isocyanate and aliphatic isocyanantecould be used. The product packing and transportation cost lower, reducing the dispersionstorage period and increasing the dispersion stability. If the double screw extrusion methodhad used for preparing polyurethane ion-exchange polymer, the pellets process would becomethe continuous product peocess.In this paper, through laser light scattering particle size analyzer and TransmissionElectron Microscope (TEM), the effect of different parameters on dispersions’ viscosity,particle size, particle size distribution and particle morphology were investigated. The resultshowed that the particle size decreased, the viscosity increased and the particles sizedistribution narrowed with the increasing of polyurethane ion polymer molecular and hydrophilic group content (HGC), but the particle size increased, the viscosity decreased andthe particles size distribution broaded with the decreasing hard segment content. Soft segmenttypes had great effect on emulsion properties of PUDs. TEM showed that PUD particles wereinerratic sphericity and with the increase of polymer ion polymer molecular and hydrophilicgroup content, the particles became smaller and the anomaly particles decreased. PUD Filmswere tested by mechanical properties, Dynamic mechanical thermal analysis (DMA) andthermogravimetry analysis (TG). The results of tensile tests showed that the max ultimateelongation of PUDs cast film decreases and tensile strength increases with the increase ofhard segment content. The DMA dynamic mechanical analysis shows that PUD films havetwo glass transition temperatures of soft segment glass transition temperature and hardsegment glass transition temperature. As the hard segment content is increased, the degree ofphase separation is increased, the soft segment glass transition temperature is lowered, and thehard segment glass transition temperature is elevated. Thermogravimetric analysis indicatedthat the degradation of PUD cast films started at about280℃and completely degradation atabout450℃that showed excellent thermal stability.