Guozhang Ma

Preparation, properties and application of waterborne hydroxyl-functional polyurethane/acrylic emulsions in two-component coatings

A serious of waterborne hydroxyl-functional polyurethane/acrylic (PUA) emulsions for two-component coatings was prepared by copolymerizing different weight ratios of hydroxyethyl acrylate (HEA)/butyl acrylate (BA) with methyl methacrylate and acrylic-terminated polyurethane dispersion via an emulsion process. The results showed that increasing the weight ratio of HEA/BA led to a decrease in the average particle sizes and a narrowing in the particle size distribution, but an increase in the viscosity of their emulsions. Meanwhile, their films showed increased thermal resistance, adhesion on substrate, tensile strength, and hardness, but decreased water resistance and enhanced wettability. When the emulsions were applied in two-component coatings, their water resistance was greatly improved and the wettability was reduced; in addition, their glass transition temperature, thermal stability, adhesion on substrate, tensile strength, and hardness were further increased. It was suggested that hydroxyl groups of PUA can not only engage in the intramolecular and/or intermolecular hydrogen bonding, but also form covalently crosslinked networks with polyisocyanate in their films.

A comparative study of grafting steps on the preparation and properties of modified nanosilica for UV-curable coatings

Nanosilica was modified and functionalized with acrylsilane by the “grafting to” method via different grafting steps, i.e., prepared-grafting step and step-wise propagation. The prepared-grafting step was achieved by grafting the nanosilica surface with the prepared acrylsilane, which was obtained by thiol-ene click reaction between 3-mercaptopropyl trimethoxysilane (MPTMS) and trimethylolpropane triacrylate (TMPTA). The step-wise propagation was achieved by first grafting MPTMS onto the nanosilica surface and then using the mercapto groups as initiators to react with TMPTA. The acrylsilane was characterized by FTIR. The modified nanosilica was characterized by FTIR, TGA, and contact angle analysis. It was demonstrated that the thiol-ene click reaction can easily occur between MPTMS and TMPTA. The grafting ratio of modified nanosilica via prepared-grafting step was higher than that of step-wise propagation. The SEM images of fractured films containing modified nanosilica also indicated that the former is more effective than the latter in reducing the self-aggregation of nanosilica. The effects of modified nanosilica on the viscosity and hardness of UV-curable coatings were also investigated.

Progress in polydimethylsiloxane-modified waterborne polyurethanes

Preparing PDMS-modified WPU has attracted the attention of many researchers for two decades and this modification strategy has been proved to be an effective and feasible way to improve some key properties of WPU. In this review, both physical and chemical modification are introduced in depth. For chemical modification, the types of PDMS used, the copolymerization methods, the sub-classification of PDMS-modified WPU, and the synthesis processes are categorized and reviewed respectively; the effects of PDMS on colloidal, film-forming, surface, mechanical, and thermal properties as well as the effects of PDMS on microphase separation and hydrogen bonding behaviors of WPU are discussed in detail, with focus on the introduction to and understanding of the “structure–morphology–property” relationship of these hybrid materials. Besides, a current strategy to combine the PDMS modification technique with other modification methods to obtain novel WPU materials with superior properties is introduced. Finally, the challenges and future perspectives of this field are discussed.

Effects of glycidyl methacrylate content and addition sequence on the acrylic latexes with carboxyl groups

Acrylic latexes with epoxy and carboxyl groups have been synthesized via a two-stage emulsion polymerization process. Different contents of glycidyl methacrylate (GMA) were introduced by three addition modes to copolymerize with methyl methacrylate, butyl acrylate, acrylic acid (AA) in the presence of K2S2O8. To obtain stable latexes, NaHCO3 was employed as a buffer to compensate for the acidity from the thermal dissociation of K2S2O8, and triethylamine was used to neutralize the carboxyl acid from AA. The results showed that the stable latexes with core/shell structure were synthesized by this method, and higher GMA content or addition at earlier stage led to forming the latexes with higher content of coagulum and bigger sized particles. During the formation of films, the polymer epoxy groups underwent the crosslinking reaction with carboxyl acid. When the GMA content increased or GMA was introduced at a later stage, high crosslinking extent was formed in the films. As a result, the crosslinking provided the films with improved water resistance, chemical resistance, tensile strength, hardness, abrasion resistance, and thermal stability.