Properties and paper sizing application of waterborne polyurethanemicroemulsions: Effects of extender, cross-linker, and polyol

ABSTRACT A series of waterborne polyurethane (WPU) microemulsions were synthesized through self‐emulsification methodology, using toluene‐2,6‐diisocyanate, polytetramethylene glycol (PTMG), poly‐caprolactonediol (PCL), and dimethylol propionic acid (DMPA) as monomers; isophorone diamine (IPDA) as chain extender; and aziridine as cross‐linking agent. The resultant WPU microemulsions were utilized as surface‐sizing agents for cellulose fiber paper. The influences of IPDA content, PTMG/PCL molar ratio, and aziridine content on the physicochemical properties of the resultant emulsions and sized paper have been investigated in detail. The WPU microemulsion displayed better surface sizing properties when it was prepared under the following conditions: the IPDA content of 2.96%, PTMG/PCL molar ratio of 0:4, and aziridine content of 2.0 wt %. The relationships between the WPU structure and properties of WPU films and sized paper were clearly illustrated. The mechanical properties and water resistance of sized paper were not only depended on the interactions, chain entanglements, and cross‐linking density among the WPU chains, but also relied on the interactions among polymers and fibers, as well as the polarity and stiffness of surface sizing agent. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43211.