Polyurethane-urea-acrylic dispersion

Synthesis and Characterisation of Aqueous Hybrid Polyurethane-Urea-Acrylic/Styrene Polymer Dispersions... 

Hybrid polyurethane-urea-acrylic/styrene polymer dispersions were prepared according to methods la , lb , 2 and 3 described in Section 6.3.2. Dispersions designated as MDPUR-ASD were made by polymerisation of monomers in DPU according to the methods la, lb and 2 while dispersions designated as MDPUR were made by synthesis of DPUR in ASD according to method 3. In all syntheses the ratio of polyurethane-urea to acrylic/styrene polymer in the hybrid was 2 1. 

Figure 6.17 Particle size distribution for a typical polyurethane-urea-acrylic/styrene hybrid dispersion synthesised in this study (MDPUR-ASD 97 from Table 6.7 prepared according to method 2 using a water-soluble initiator).

Figure 6.23 Particles of hybrid polyurethane-urea-acrylic/styrene dispersion prepared according to method la using less hydrophobic monomer and water-soluble initiator (MDPUR-ASD 22). Photograph was taken using TEM.

Figure 6.31 Examples of different morphologies of particles of hybrid polyurethane-urea-acrylic/styrene dispersions synthesised in this study. Micrographs were taken...

Figure 6.32 Morphology of particles of hybrid polyurethane-urea-acrylic/styrene hybrid dispersion prepared according to method 2 (See Section 6.3.2) using water-soluble initiator (MDPUR-ASD 97). Micrograph was taken using TEM. Both single particle and coalesced particles are shown. Reproduced with permission from Professor A. E. Czalych, Institure of Chemical Physics of the Russian Academy of Sciences, Moscow.

Generally, based on the results shown above, it can be concluded that introducing double bonds into polyurethane-urea is undoubtedly one of the ways to obtain coatings of excellent properties based on hybrid polyurethane-urea-acrylic/styrene dispersions. 

In this study, aqueous hybrid polyurethane-urea-acrylic/styrene polymer dispersions were obtained using four different methods. The dispersions are stable and their viscosity, and pH as well as average particle size and particle size distribution are similar to those observed for DPUR. Most of the hybrid dispersions formed transparent films of good mechanical properties, water resistance and organic solvent resistance. 

The results of investigations of the effect of method of hybrid dispersion synthesis (la, lb, 2 or 3 - see Section 3.2) on the properties of dispersions as well as of films and coatings made from them are presented in Tables 6.9 to 6.11 (dispersions prepared using water-soluble initiator) and in Tables 6.12 to 6.14 (dispersions prepared using redox initiating system). In all dispersions the chemical structure of the polyurethane-urea and acrylic/styrene polymer component was the same (see relevant tables in Section 6.5.2). All the dispersions contained a similar low level (2-3.6%) of NMP. 

Properties of hybrid dispersions prepared according to the different methods (la, lb and 2 - see Section 6.3.2) and based on the same polyol (PTMG 2000), but differing in the presence or absence of double bonds in the polyurethane-urea part of the hybrid, as well as of films and coatings made of them, are presented in Tables 6.21 and 6.22. All dispersions have a similar low level (2.0-3.3%) of coalescent and have the same structure of the acrylic/styrene part of the hybrid. Redox initiator was used in the synthesis of dispersions according to the method 2, and in all other dispersions presented in these tables a water-soluble initiator was applied. 

The morphology of dispersion particles was investigated using the method described in Section 6.4.1. Examples of different morphologies of particles of hybrid dispersions synthesised in this study according to methods la, lb and 3 are presented in Figure 6.31 in comparison with particles of the starting dispersion of BA/MM/S copolymer. The contrast was selected so that in pictures d and c white colour represents the polyurethane-urea part of the hybrid and in picture b the same colour represents the acrylic/styrene part of the hybrid. 

The surface free energy of films made from hybrid dispersions was determined in order to look at the values of its non-polar and polar component which could provide some information on whether polyurethane-urea or acrylic/styrene polymer is on the film surface (see Table 6.30). 

Table 6X7 shows that the properties of hybrid dispersions prepared with additional crosslinking of acrylic/styrene polymer do not differ from the properties of dispersions of the same composition prepared without additional crosslinking. Also the properties of films made from both dispersions were very similar (see Table 6.28). However, lack of positive effects of additional crosslinking of the acrylic/styrene part of the hybrid may result from improper selection of starting materials for hybrid synthesis. Therefore, we intend to investigate this effect further in another study along with further studies on the effect of introducing double bonds to the polyurethane-urea part of the hybrid.

Here, the acrylic/styrene polymer constitutes an under-surface sphere embedded in a particle made of polyurethane-urea. This sphere is approximately 25-40 nm thick and is situated approximately 15-20 nm from the particle surface. After coalescence of the particles this specific structure is retained (see coalesced particles in Figure 6.32) so that the film made from a dispersion of this particular particle morphology should have the structure presented schematically in Figure 6.35. 

The morphology of dispersed particles revealed by TEM appeared to be very interesting. It was found that the method of hybrid synthesis had a substantial influence on the particle morphology and that usually core-shell or englued morphologies described earlier in the literature were observed. However, in one case the unusual embedded sphere morphology was seen. In these particles, the core made of polyurethane-urea is surrounded by a 25-40 nm thick sphere made of acrylic/styrene polymer and covered by a 15-20 nm thick outer layer of polyurethane-urea. The structure of film made from such dispersions is very interesting since it is a two-phase structure where nanospheres of acrylic/styrene polymer are suspended in a polyurethane-urea matrix. 

Water-based dispersions or emulsions such as polyvinyl acetate, acrylics, polyvinyl chloride and polyvinyl alcohol with plasticizers and tackifiers. In addition, this range can include urea formaldehyde and phenolic adhesives, resins, natural adhesives produced from starch, dextrin, casein, animal glues (see Polyvinyl alcohol in adhesives, Phenolic adhesives single-stage resoles. Phenolic adhesives two-stage novolacs. Animal glues and technical gelatins) and rubber latex (see Emulsion and dispersion adhesives). Solvent-free 100% solids such as polyurethane. Hot melt adhesives include Ethylene-vinyl acetate copolymers, polyolefins, polyamides, polyesters with tackifiers and waxes. More recent additions include cross-linkable systems. 

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