Polyether 210, isophorone diisocyanate (IPDI) as the main raw material, dimethylolpropionic acid (DMPa) is a hydrophilic chain extender, amine silane coupling agent is a post-chain extender, according to different A series of silicone modified aqueous polyurethane dispersions were synthesized. The effects of the mass fraction of silane coupling agent on the stability of aqueous polyurethane emulsion, the particle size of the emulsion and the water absorption and heat resistance of the film were investigated. The results show that with the increase of the mass fraction of silane coupling agent, the particle size of the emulsion increases, the dispersion stability is good, the water resistance of the film is obviously improved; the heat resistance of the film is obviously improved, and the crosslinking reaction occurs; The urea bond formed in the aTR infrared display system increases as the mass fraction of the silane coupling agent increases.
Waterborne polyurethane (WPU) has been widely used in coatings, adhesives and inks, with water as a dispersion medium, non-combustible, non-toxic, environmental pollution, resource saving, and 4E principles in line with current economic development. [1] And gradually replace solvent-based polyurethanes. However, the polyurethane aqueous dispersion prepared by the internal emulsification method has a large water absorption rate and is not resistant to wet rubbing [2]. The test uses a carboxyl group as a hydrophilic group, and self-emulsifying to synthesize an aqueous polyurethane dispersion, using an amine silane coupling agent. The modification was carried out in order to improve the water resistance of the aqueous polyurethane, and the synthesis process and the influence on the properties of the final product were examined.
1 test part
1.1 Raw materials
Polyether 210, industrial products, Shanghai Gaoqiao Petrochemical No. 3 Plant, used after vacuum dehydration; isophorone diisocyanate (IPDI), industrial products, Rodia; dimethylolpropionic acid (DMPa), industrial products, Sweden Berstorp; Butylene glycol (BD), analytical grade, Shanghai reagent plant; ethylenediamine (Ea), acetone, triethylamine (TEa), analytical grade, Guangzhou reagent plant; silane coupling agent, industrial grade; deionized water.
1.2 Preparation of silicone modified waterborne polyurethane
In a three-necked flask equipped with a stirrer, a reflux condenser, and a thermometer, a metered IPDI and a dehydrated polyether 210 were added, and the temperature was gradually raised to 90 ° C for a certain period of time, and then DMPa and BD were sequentially added until the end of the reaction to obtain a polyurethane. Prepolymer, the reaction process is added with an appropriate amount of acetone to adjust the viscosity as needed. The prepolymer is cooled, neutralized, and water-dispersed at a high speed, and a silane coupling agent (or ethylenediamine and a silane coupling agent) is added, and acetone is extracted under reduced pressure to obtain a silicone-modified aqueous polyurethane dispersion.
1.3 Performance test
(1) Emulsion solid content: measured according to GB1725-79.
(2) Emulsion particle size: The sample was diluted to a certain concentration and measured at room temperature with a Malvern autosizer.
(3) Water resistance of the film: The fully dried film is cut into a square of 20 mm×20 mm, weighed to m0, and then taken out in water for 24 hours at room temperature, and then taken out, and the surface water or solvent is absorbed by a filter paper, and then weighed. Obtain m, calculate the water absorption rate according to the following formula:
Water absorption rate = (m-m0) / m0 × 100%
(4) Weight loss rate of the film: The film with the water absorption rate is measured and dried in an oven to obtain a constant weight m1, and the weight loss rate is calculated according to the following formula:
Weight loss rate = (m0-m1) / m0 × 100%
(5) Infrared spectrum of the film: Bruker Vector 33 was measured at room temperature using the aTR accessory.
(6) Polarizing microscope: ZEISSaxiolab Polarizing, Germany
Microscope, the program controls the temperature rise.
(7) Transmission electron microscopy: Dilute the microemulsion sample to a certain multiple, add a small amount of phosphotungstic acid solution for dyeing, and then dip it on the copper mesh. After 2 hours, observe the latex particles with JEM-100CXII transmission electron microscope.
2 Results and discussion
2.1 Effect of mass fraction of silane coupling agent on the properties of emulsion and film
The self-emulsifying PU introduces a hydrophilic group on the PU molecular chain (the COCO is a hydrophilic group in DMPa in this study), and the PU molecules are dispersed in water to form a stable dispersion by the hydrophilicity of the hydrophilic group. The polyamine group reacts with the residual isocyanate to expand the chain, and the siloxy group of the silane coupling agent undergoes hydrolysis and polycondensation to crosslink the system, and the internal crosslinking of the system is realized at the same time as the chain extension, and the prepolymerization is not affected. Dispersion of matter. Table 1 summarizes the basic properties of the synthesized silicone modified aqueous polyurethane emulsion. It can be seen from Table 1 that as the mass fraction of the silane coupling agent increases, the emulsion gradually changes from a nearly transparent liquid to white, and the average particle size of the emulsion gradually increases. At the same time, the emulsion maintained good dispersion stability except for the mass fraction of the silane coupling agent of 8.9%.
Fig. 1 is a TEM photograph of the morphology of latex particles of a modified aqueous polyurethane emulsion synthesized under different silane coupling agent mass fractions, each having a magnification of 100,000 times. The latex particles in all the emulsions have an irregular shape. Without the addition of a silane coupling agent, the particle size of the latex particles is small (the particle size measurement result is 47 nm), and the agglomeration is obvious; the mass fraction of the silane coupling agent is 1.9. The case of % is similar. The particle size of the latex particles is not large (57 nm), and there is also agglomeration. When the mass fraction of the silane coupling agent is 7.6%, the substantially spherical latex particles increase and the particle size also increases significantly.
This is because the active hydrogen of the amine group in the silane coupling agent can react with the residual -NCO group, and the hydrolyzable group on the coupling agent hydrolyzes and undergoes a dehydration condensation reaction, resulting in formation of a certain internal crosslinking in the system. This cross-linking may occur between different latex particles, so the particle size of the emulsion becomes larger as the degree of crosslinking increases. The water resistance of the film is an important quality index in many applications. From Table 1, the water absorption rate of the film after 24 hours of film formation decreases substantially with the increase of the mass fraction of the silane coupling agent, and the values ​​are small (<10). %) Soaking in water for 72h will not turn white. On the one hand, certain internal cross-linking can reduce the water absorption of the film; on the other hand, due to the hydrophobicity of silicon itself, the water resistance of the synthesized product is improved.
All the film immersed in water for 24h, there is a certain weight loss. Although the weight loss rate is not very large, it also indicates that the film has a small amount of dissolved matter in water, which may be the result of unreacted complete BD dissolution.
2.2 Heat resistance of the film
The surface morphology of the film with different silane coupling agent mass fractions was observed by polarized light microscopy during temperature programming, as shown in Fig. 2. The film with a silane coupling agent mass fraction of 1.9% (Fig. 2a) began to deform at 210 °C, and began to flow at 225 °C, while the film with a silane coupling agent mass fraction of 7.6% (Fig. 2b) remained at 250 °C. No deformation occurred, indicating that the mass fraction of the silane coupling agent was 7.6%, and the system had basically formed a crosslinked network structure, neither dissolved nor melted. Although it did not deform at 250 ° C, the film had some yellowing at 220 ° C, so the maximum use temperature of this material does not exceed 200 ° C. When the mass fraction of the silane coupling agent is 1.9%, although the material exhibits thermoplasticity, the temperature at which it is thermally deformed is increased by about 30 ° C than the polyurethane material without the coupling agent at all.
2.3 aTR infrared spectrum of film
Figure 3 shows the aTR infrared spectrum of the polyurethane film obtained without the silane coupling agent and the silane coupling agent mass fraction of 1.9% and 7.6%, respectively. It can be seen that the infrared difference of the three is not large, and there are no characteristic peaks at 2270 cm-1, indicating that -NCO has all reacted; 3327 cm-1 is the N-H stretching vibration peak, and 3400 cm-1 has no obvious absorption. The peak indicates that N-H on the urethane group is almost completely hydrogenated, the hydrogen bonding is beneficial to the microphase separation of the soft and hard segments of the PU; the 2970-2870 cm-1 is the characteristic absorption peak of the methyl and methylene groups in the polyether. 1703cm-1 is the stretching vibration peak of CO in the urethane group; the strong absorption peak at 1099cm-1 is the characteristic absorption of C-O-C in the polyether. The main difference between the three samples is the absorption of carbonyl groups in the urea group at 1655 cm-1. In the absence of a silane coupling agent, the amine chain extender is used, the urea group has a high mass fraction, and the absorption peak is obvious. The silane coupling agent is added. After that, the absorption peak of 1655 cm-1 becomes inconspicuous, but in the case of an increase in the mass fraction of silicone, the intensity of the absorption peak is still increased, because the increase in the mass fraction of the silane coupling agent actually increases the mass fraction of the active amine. The reaction forms more urea bonds. The increase of urea bonds leads to the strengthening of intermolecular hydrogen bonding. The mass fraction of hard segments in the molecule increases, and the inter-chain entanglement increases, thus forming larger particles, which in turn affects the appearance of the emulsion. Stability, consistent with the results in Table 1. However, the rate of reaction of the reactive amine with the isocyanate group in the silane coupling agent is still slower than that of ethylenediamine.
3 Conclusion
(1) With the increase of the mass fraction of silane coupling agent, the particle size of the emulsion increases, but the water resistance is obviously improved, and the obtained film is immersed in water for 72 hours without whitish. (2) The TEM results of the emulsion showed that the obtained latex particles were irregular in shape, and the particle size increased as the mass fraction of the silane coupling agent increased. (3) Observing the surface morphology of the film with the change of temperature with polarized light microscope, it was found that the temperature resistance of the film was obviously improved after the addition of the silane coupling agent, and the crosslinking reaction occurred. The infrared spectrum showed the urea formed in the system. The bond increases as the mass fraction of the silane coupling agent increases, but the rate of reaction of the reactive amine with the isocyanate group in the silane coupling agent is slow.
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