| A water-borne polyurethane (WPU) is defined as a binary colloidal system in which PU particles are dispersed in a continuous aqueous medium. In contrast to the solvent-borne polyurethane, the water-borne polyurethane have advantages of being free from toxicity and pollution etc., which thus was steadily expanded its application in textile coatings, sizing and adhesives for numbers of polymeric materials, leather surface etc..In this paper, the stable aqueous polyurethane was prepared based on anionic self-emulsified process, incorporated dimethylol propionic acid (DMPA) into the prepolymer backbone. The structure-property relations of WPU were further discussed and blocking modification was primarily researched. The results showed that firstly, the different structures of polyesterols resulted in different properties of PU, such as particle size, viscosity of emulsions, tensile strength of films. Secondly, the study on the dynamic mechanics properties of unblocked systems showed that the glass transition temperature (Tg) of the soft-segments rose and the phrase compatibility of soft- and hard-segments was improved when the contents of hard-segments increased by elevating the ratio of -NCO/-OH and the dosages of DMPA and extender. Thirdly, the influences of the structure, dosage and mix of chain extenders on the properties of emulsions & films were studied. The results indicated that the emulsion extended with ethylene diamine (EDA) had better properties than that of the emulsion extended with diols. Moreover, the counter-ion worked strong effects on the physical properties of PU.In addition, it was found from the investigation of the blocked system that the storage stability of blocked PU emulsions was improved, different blocking agents resulted in different deblocking temperatures (the deblocking temperatures were determined by Differential Scanning Calorimeter, DSC) and the post-curing films were better than uncured films in both aspects of hardness & water-resistance. |
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