Abstract:

Objective The conventional matting resin is prepared by adding matting agent, however, this method has some shortcomings, such as easy sedimentation and insufficient stability when added in high dosoges, which is not conducive to storage and use. This research aims to prepare self-matting waterborne polyurethane without adding extra matting agent.

Method A series of internal crosslinking self-matting waterborne polyurethane emulsions and films were prepared from isophorone diisocyanate (IPDI) and polypropylene glycol (PPG) as monomers, 1,4-butane-diol (BDO) and 2,2-dimethylolbutyric acid (DMBA) as chain extenders, dipentaerythritol (DPE) as crosslinking agent, and hydrazine hydrate as post chain extender. The chemical structure of the film was characterized by Fourier transform infrared spectrometer. The surface morphology of the films was observed by scanning electron microscope. The thermodynamic properties of the films were tested. The Influences of DPE and hydrazine hydrate on the surface glossiness of the films were investigated. The influences of DPE dosage on the particle size, storage stability, mechanical properties, water resistance and thermal stability of the film were studied.

Results The glossiness of the films decreased with the increase of DPE dosage, indicating that the self-matting property of waterborne polyurethane could be improved by internal crosslinking modification. When the mass fraction of DPE was 1.75%, the glossiness of the film surface reached 4, which was consistent with the self-matting mechanism. In addition, the self-matting property of waterborne polyurethane resin was also affected by post chain extension. With the increase of the mole fraction of hydrazine hydrate, the 60° glossiness of the films surface decreased gradually, and when the mole fraction of hydrazine hydrate reaches 40%, the 60° glossiness of the film reached the minimum, indicating that the glossiness was also affected by the degree of post chain extension. The average particle size of the emulsion reached 1 192 nm, indicating that crosslinking modification can effectively increase the average particle size of the emulsion. The water absorption of the films was decreased from 65.2% to 7.1%, suggesting that the water resistance of the films was significantly improved. With the increase of DPE mass fraction, the break strength of the films was gradually increased while the elongation at break gradually was decreased, when the DPE mass fraction was set to 1.75%, the tensile strength reached 20.24 MPa, and the elongation at break was decreased to 420%. Compared with the pure waterborne polyurethane film, the break strength was increased by 122.2% while the elongation at break was decreased by 39.9%, indicating that the physical properties of the films were improved. The temperatures of 10% and 50% thermal weight loss were increased by 6.5 ℃ and 8.0 ℃, respectively, indicating that the same percentage of weight loss of the films require a higher temperature, and the thermal stability of the films was enhanced.

Conclusion The self-matting property of waterborne polyurethane resin can be effectively improved by internal crosslinking modification and post chain extension. In addition, the mechanical properties and water resistance of resin were significantly enhanced by crosslinking modification, but excessive crosslinking agent is not conducive to the stability of the emulsion. Finally, the decomposition temperature corresponding to the same percentage of weight loss of the films was increased, indicating the thermal stability of the films was improved.

Key words: internal crosslinking, waterborne polyurethane, self-matting, dipentaerythritol, post chain extension, hydrazine hydrate, finishing agent