Study on the factors affecting the thickening effect of polyurethane-to-thickener (2)

effect of
2 end hydrophobic group
The total hydrophobicity of the end group of thickener not only controls the fluidity of its aqueous solution, but also has a great effect on its thickening efficiency. The polymer end group determines the relaxation time of the physical connection network rather than the physical network structure. Relatively long end hydrophobic chain is the key to HEUR to produce thickening effect, only when the hydrophobic end base has sufficient hydrophobic action, heUR polymer end can be connected with each other and hydrophobic connection, forming a hydrophobic network structure. Usually the chain length of the end hydrophobic chain of HEUR needs to reach C12, because the chain segment is not long enough, which is not conducive to the generation of HEUR hydrophobic interaction. The increase of the length of the hydrophobic chain is conducive to the formation of the bonding network and the increase of the viscosity of the solution.
, such as PEG and IPDI as raw materials, hexaol as a sealing agent, prepared a two-parent polyurethane thickener. It is found that when the concentration of thickener solution is the same, increasing the hydrophobic chain segment of the thickener molecular chain can increase the zero shear viscosity and reduce the shear rate when shearing becomes thinner. Kim and others prepared HEUR thickeners with the length of the end chain length of the hydrophobic group C8, C12 and C18, respectively, and examined the effect of the tail chain length of the hydrophobic group on the thickening effect. The results show that the polyurethane-combined thickener at the end of the short-chain hydrophobic chain can not form a glue cluster in the aqueous solution, and its thickening effect can be ignored. Only when the heUR hydrophobic base group tail chain length reaches C12 and C18, the system can form enough glue beam aggregation and perfect network structure to thicken the effect is obvious, the end hydrophobic long chain is conducive to HEUR in relatively low concentration to form a complete glue beam and perfect instantaneous network. Secondly, the structure and size of the end hydrophobic group are another important factor affecting the effect of HEUR thickening.
Xu and so on introduced C6F13 and C8F17 as end hydrophobic groups into THEUR molecules. Because fluorodeane hydrophobics are very hydrophobic, so in the water solution is also very strong connectivity. Compared to the two, because the C8F17 is longer in length and withdraws from the beam at a slower rate, it is more cooperative and more viscous.
Barmar and others used HEUR thickeners at the ends of cyclohetol, C12 and C16, respectively, to study the effect of the size and size of hydrophobic end base on thickening performance. Heur at the end of cyclohexol is not thickened due to the small size of the end hydrophobic group and its low adhesive beam aggregation capacity. In addition, studies such as Lundberg have shown that the size of the end hydrophobic group affects the increase in the viscosity of the solution system, and that the hydrophobic co-use of HEUR increases with the increase in the size of the hydrophobic end group.3 Effects of hydrophobic group structure
Traditional polyurethane thickeners are wire-type structures that contain hydrophobic groups at both ends of the molecular chain and thicken by two-point connectivity in the water phase or emulsion system. With the increasingly high requirements of the thickening efficiency of polyurethane-combined thickeners, traditional two-point combined polyurethane thickeners can no longer meet the requirements of the application, so people expect thickeners with more obvious thickening effects and excellent properties of polyurethane thickeners. In order to improve the thickening effect of polyurethane-combined thickeners, the hydrophobic side-based content of thickeners can be increased by introducing hydrophobic side-based methods on the hydrophobic main chain, thus improving the thickening effect.
Huang Yanling and other use of butyl shrinkage glyceline ether with twelveamines, sixteenamines, eighteen amines reaction synthesis contains different lengths of hydrophobic alkyl binary alcohol, in the chain segment of polyurethane prepolymers to introduce those binary alcohols, to obtain a series of chain segments containing multiple hanging groups of combed polyurethane-combined thickeners. The effect of the size of the hydrophobic base hanging in the middle on its thickening effect was studied. The results showed that the binary alcohol obtained from 18amines was introduced into the polyurethane system, and its thickening effect was the best. The more carbon atoms in the alkyl chain segment suspended in the middle, the stronger the hydrophobic joint, resulting in better thickening performance. It is the introduction of multiple suspended hydrophobic groups between each thickener molecule. This combed polyurethane thickener converts the original two-point bonding into a multi-point bonding. Multi-point comb polyurethane thickeners and latex particles form a more complex three-dimensional mesh structure, so that the viscosity of latex paint greatly increased, thickening effect is good.
researchers also increased the consistency effect by preparing polyurethane thickeners for branched structures. Such as Peter T. Elliott, the wire-type hydrophobic base group and the branched hydrophobic group are coupled into the POE chain to produce a HEUR containing different shape end hydrophobic groups. It was found that when hydrophobic groups were introduced into the POE chain, due to the spatial bit resistance effect of the POE chain, the hydrophobic groups could not be fully combined like surfactants, and in the comparison of equivalent hydrocarbons, the line hydrophobic groups were better than the thickening effect of the branched hydrophobic groups.
Tielemans Michel and other studies have found that polyurethane-connected thickeners with branch-chain structures can achieve denser physical network structures in thickener solutions and have better thickening effects than straight-chain thickeners. When thickeners are added to the solution, the external morphology and surface area of thickener particles will have some effect on the formation of network structure, and the volatility of particle size distribution will also affect the thickening effect of thickeners.4 molecular weight and molecular weight distribution
Glass team systematically studied the effect of HEUR molecular weight and molecular weight distribution on thickening efficiency. When the molecular weight of HEUR reaches greater than 23,000, its thickening effect is most obvious.
May and so on through different HEUR polymerization methods, prepared two types of HEUR thickeners with the same molecular weight and hydrophobic end base, but different molecular weight distribution, by examining its thickening effect proved that the molecular weight distribution of HEUR will form an imperfect network structure, low molecular weight part of HEUR too much formation of molecular intrusion, so that thickening efficiency is reduced.
Kaczmarski and others also studied the effect of wide molecular weight HEUR on its thickening performance, and found that HEUR with wide molecular weight distribution contained unresponsive polyethylene alcohol inlays.
by adding chain expander can also change the molecular weight of HEUR system, and then affect its thickening effect, such as Cai Jinyong and other studies on the effect of different chain expanders on polyurethane thickener thickening performance. When the thickener is synthesized, the pre-polymer is synthesized with PEG and hemethyl isocyanate, and 4 different chain-spreading agents are added, and then the end is sealed with heterool as an end agent, and the resulting product is then tested for thickening effect. The results show that the addition of the chain-expanding agent can extend the molecular chain of the thickener, the relative molecular mass will increase, and the thickening effect of the thickener synthesized with 1,4-butyl glycol as the chain-expanding agent is best.
can be concluded from the above: in a certain range, relative to the molecular mass of large, narrow molecular weight distribution of polyurethane-combined thickener thickener effect will be relatively obvious. And related studies have found that at low molecular regions (Mw 10 000), viscosity increases with molecular weight and reaches maximum values in polymer regions. However, in order to avoid undesirable phase separation (bridge flocculation), the molecular weight of heUR thickeners must be controlled to a certain extent. The influence of molecular weight and molecular weight distribution on the effect of thickener is manifested by the change of hydrophobic chain segment and hydrophobic group.effects of
5 surfactants
Polyurethane-linked thickeners have similar molecular structures to surfactants, both containing hydrophobic and hydrophobic groups. Therefore, when the system contains ingredients with surfactant properties, to a certain extent, it will have an effect on the thickening effect of polyurethane-to-thickeners. Surfactants can be divided into cation surfactants, anion surfactants and non-ion surfactants.
D. J. Lundberg and others began to study the effects of surfactants on the thickening effect of the compound thickener as early as 1990. They added the anionic surfactant sodium tyranyl sulfate (SDS) to the HEUR solution and found that even at lower concentrations, because of the addition of SDS, the viscosity of the HEUR solution increased, and it was clearly observed that there was no SDS under the low shear rate viscosity, the solution basically did not have shear thickening. At critical concentrations, such as Philip Kaczmarski, the anionic surfactant SDS and non-ion surfactants, acylphenol compounds containing 10 ethylene oxide units (C8H17C6H4O (EO)10H) were added to THESE, HMHEC and HEUR aqueous solutions, respectively. When SDS is added to THESE and HMHEC aqueous solutions, the viscosity increases, but with the addition of C8H17C6H4O (EO) 10H, the viscosity is only a small increase. When these two surfactants are added to the gradually polymerized HEUR, the reaction is very different from that of CASE and HMHEC, and the addition of C8H17C6H4O (EO) 10H is greater than that of SDS. This is because the PEO main chain of HEUR thickeners makes the SDS beam smaller through ion-even interaction. Non-ion surfactants form a larger beam than the SDS beam can accommodate more HYDRO hydrophobic groups, so the formation of a better network, so thickening effect is better.
Do-Hoon Kim and others added the non-ion surfactant polyvinyl oxide hard ester ether (C18(EO)20) to the HEUR aqueous solution system, indicating that C18 (EO)20 plays an important role in inducing hydrophobic connectivity with HEUR polymers, and has flexible control over the viscosity of the solution.
kewei Zhang and others studied the interaction between the cation surfactants Twelfthanetromethyl Bromide (DTAB) and SDS and HEUR.
it was found that the addition of surfactants dominated the mixing beam formed by hydrophobic groups and surfactants in the system, and that the polymer's bonding would be completely interrupted with the increase in the concentration of surfactants. And the bond force between SDS and HEUR is bigger than that of DTAB.
If there are fewer surfactants, it will help the formation of the glue beam in the system, so that the hydrophobic connectivity points of polyurethane-combined thickeners increase, which is conducive to the improvement of the three-dimensional mesh structure, increase the efficiency of thickening, thickening effect is good. When there are too many surfactants in the system, the hydrophobic group on the surfactant will be associated with polyurethane thickener on the hydrophobic group to grab the joint position on the surface of the emulsion particles, so that the thickener's chances of contracting are reduced, resulting in the system thickening effect is not good or the viscosity is reduced. Therefore, it should be noted that for the joint thickener, the coating has been made if you want to replace the desiccant, film-aid, dispersant type, need to re-determine the viscosity of the coating, in order to ensure that does not affect the performance of the coating. 6 Conclusion
Traditional thickeners, such as alkali-soluble and cellulose thickeners, are used in water-based latex paint with low mobility, poor leveling, heavy brush marks and easy splashing when rolling. The polyurethane-combined thickener can effectively improve the defects in the above applications. Because it takes a certain amount of time for the conceding thickener to re-form, the recovery of viscosity is not as fast as cellulose, thus allowing a certain flow time to facilitate the leveling (playing the role of leveling agent), which is conducive to improving the film plumpness, improve the film feel, do not cause the phenomenon of de-lighting. At the same time, polyurethane-type thickener also has a good gloss, cover, water resistance, wash resistance, splash resistance, scratch resistance, and its relative molecular quality is low, low viscosity, with thickening capacity Strong, thickening efficiency, low dosage, good effect, strong stability, anti-microorganisms and non-mouldy and other satisfactory results, the most important advantage is that the combined thickener can provide less elasticity than conventional line-type polymers, which is very important for the coating industry. .