Views: 4 Author: Site Editor Publish Time: 2024-05-28 Origin: Site
In order to improve the efficiency of washing, people try to make full use of various mechanical forces. Most of these washing processes are accompanied by intense agitation (such as with pressure spray, etc.), and the presence of a large number of bubbles not only affects the cleaning efficiency/fruit, but also makes the cleaning process impossible in many cases. One of the most common examples is that when you wash linen in a washing machine (especially a front-loading type), if it is filled with a lot of foam, the stain removal power will be significantly reduced. The reason is that the foam reduces the impact of the water flow on the fabric and the mechanical forces such as friction between the fibers. If it is in the industrial cleaning process, the existence of a large number of bubbles in addition to affecting the decontamination force, is bound to increase the number of water/rinsing, and may also cause unnecessary loss of working fluid (such as in the form of overflow), increasing costs. In the operation with pressure spray, the foam can also cause pump damage. It is not difficult to imagine that in such operations, people often take low or even no bubbles as a necessary condition for detergent.
What is a low-foam surfactant?
Defining a low-bubble surfactant is difficult. The main reason is that the formation and stability of bubbles are affected by many factors. These factors mainly have the following aspects: 1, the type of surfactant, 2, temperature, 3, water hardness, 4, the coexistence of components in the system - other surfactants, 5, acid and alkaline, etc. In other words, it is meaningless to discuss the foam behavior of surfactants in isolation from the actual conditions of use. Give an example. Fatty acid salts (the main active ingredient of soap) are multiple: in soft water, they belong to the high foam class; In hard water, it is often used as a defoamer. For the foam behavior of nonionic surfactants, the influence of temperature is even more important. Most widely used low-foam surfactants are included in this list. Their commonality is that when the temperature is below a certain range (generally below its turbidity point), there is a significant amount of foam, and the foam does not disappear quickly. However, when the temperature exceeds a certain value (generally above the cloud point), the number of bubbles is significantly reduced, and the stability has a "quality" change, and the newly generated foam is quickly generated at high temperature, and even bursts in an instant. Those situations where one side is produced and the other is burst instantly belong to the actual absence of bubbles. It is not difficult to see that the selection of low-foam surfactants needs to be combined with the actual conditions of use.
A few points to note
1, low-foam surfactants are not equivalent to non-foaming agents, they are controllable low-foam.
2, low-foam surfactant is not defoamer, can not be compared with defoamer;
3, low-foam surfactants have a variety of functions, such as decontamination, easy formulation and low controllable foam;
4, no low-foam surfactant can meet all application needs. The choice needs to be made according to the actual conditions and requirements of use.
Evaluation method of foam
Evaluation of foam behavior of surfactants mainly involves measurement of foam height. There are a variety of evaluation methods, Ross-Mile method, Blender (agitating) method, Graduated Cynlinder Shake method, Perforated Disk method, Dynamic method and Sparge (bubbling) method, and so on.
The most commonly used method in the industry is the Ross-Miles method. Considering that there are two main ways of mechanical force to cause foam in the actual application process, one is stirring, and the other is "impact" ---- such as with pressure spray. While Ross-Miles method is not suitable for describing foam behavior in continuous process, two corresponding evaluation methods are introduced here.
1. Dynamic foam cell: In principle, it is equivalent to the dynamic Ross-Miles method. The basic principle of this test method is that the speed and duration of air passing into the test liquid is controlled, and the amount of foam (height) generated is measured. by
In the treatment of irregular foam surface, multi-point height test is adopted, and then the corresponding mathematical model is used. Through computer processing, the error caused by human factors ---- is greatly reduced.
2, Beating method (beating method) (DIN 53902, Sheet 1)
In this method, the dishwasher is used as a test device, in which the rotating arm "whips up" foam as it rotates in the solution, and the higher the rotational speed, the greater the height of the foam. Under the specified temperature and other conditions, if a foam height is set, the height of the foam is limited by this, then the rotation speed of the rotating arm (RPM) and the foaming property of the surfactant can be associated. The higher the rotational speed that the rotating arm can achieve, the lower the foaming force of the corresponding surfactant, and vice versa. The experiment can also be used to evaluate the defoaming/defoaming performance of surfactants if proteins are added to the test solution while the rotating arm is rotating (simulating the situation of dirt during actual washing). That is, the higher the rotational speed that can be achieved by the rotating arm, the stronger the defoaming/defoaming ability of the corresponding surfactant, and vice versa.
Properties of low foam surfactants
Structural characteristics
Common low-foam surfactants are mainly non-ionic. Such as eO-po-EO or po-EO-PO block polyether, polyamine PO-EO block copolymer, fatty alcohol EO-PO block copolymer, fatty alcohol ether alkyl sealing products. It is not difficult to see that the common feature is that the so-called hydrophilic group part is mixed with oil-philic components, or the original water-philic group is directly blocked with oil-philic groups, such as fatty alcohol ether alkyl sealing products.
A small number of amphoteric surfactants are low-foam surfactants, such as Mackam JEM (caprylic imidazoline), Rewoteric AMV (caprylo ampho diacetate), octyl dimethyl hydroxy sulfobetaine) and Octyl dimethyl Hydroxy sulfobetaine. Although the foam of such substances is low, it does not have bubble inhibition. Obviously, in this class of low-bubble amphoteric surfactants, the lipophilic carbon chain is very short, not more than eight carbons.
Performance characteristics
1, acid/alkali resistance: under normal conditions can be considered to be acid/alkali resistance, especially alkyl terminated alcohol ethers can be stable for a long time under high temperature, high alkali/acid conditions (their own structure does not change).
2, freezing point: Because the hydrophilic end is closed by lipophilic (such as alkyl) or relatively lipophilic (propoxy) groups, the intermolecular force is weakened, resulting in a decrease in the freezing point of the product. This property provides convenience for the use of such products, especially in the low temperature season.
3, the trend of gel: The trend of this kind of product to form gel in water is greatly reduced, which is very beneficial to the preparation of the product.
4, conventional properties: here refers to the wetting, emulsification, dispersion, decontamination and other properties of surfactants. In general, the performance of low-foam surfactants in these aspects is generally poor. Due to the limitation of molecular structure, the polarity difference between the hydrophilic and the oil-philic groups in the amphiphilic structure of the surfactant is significantly reduced - usually the hydrophilicity of the hydrophilic group is reduced. This structural characteristic makes them difficult to balance properly between the "oil phase" and the "water phase" in many applications. For example, if an alkane substance such as kerosene is to be emulsified in water, a well-known example is the combination of a hydrophilic anionic active agent (which usually has a high HLB value) and an oil-philic non-ionic active agent (which generally has a significantly lower HLB value). By which water and kerosene are coupled respectively. When limited to the category of low-foam surfactants, there is basically no such choice. In other words, even ionic low-bubble surfactants, such as octylimidazoline, do not form an effective connection between oil and water because the lipophilic groups are too short. The effects on wetting and dispersion are similar.