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Application of Alkyl Glycoside APG in Dishwashing


1. How to remove the grease on the tableware

Dishwashing is the process of removing greasy dirt and other dirt from the surface of tableware. Dishwashing detergent is often used. Surfactant is a component of dishwashing detergent. Surfactant molecules usually contain a longer hydrophobic chain and a hydrophilic group. The hydrophobic chain is in an unstable state in water and has a tendency to migrate to the two-phase or multi-phase interface to minimize the contact area with water. As a result, the interfacial tension is reduced, thereby producing functions such as wetting and solubilization. When the surfactant concentration is large enough, the surfactant molecules aggregate in the water, the hydrophobic chains are close to each other to form micelles, and the hydrophilic groups form the micelle surface outward. The micelles can wrap oil stains, so that the solubility of oil in water is significantly increased (ie, solubilization). With mechanical action, the grease can be removed from the surface of the tableware.

There are many surfactants commonly used in dishwashing detergents, such as sodium dodecyl benzene sulfonate (LAS), fatty alcohol polyoxyethylene ether sulfate (AES), but they are in safety, skin impact, biodegradability, etc. All aspects are not ideal. Here is a green surfactant APG with ideal performance.

Second, what is APG

APG stands for Alkyl Polyglucoside, which is usually an alkyl glycoside compound of monosaccharides and oligosaccharides. The structure of the alkyl glucoside molecule is shown in Figure 2. The hydrophobic chain R in the molecule is generally a C8-C12 alkyl group, and the hydrophilic group is a monosaccharide or oligoglycoside (the degree of polymerization is generally 1 to 3, rarely exceeding 5). Since sugar molecules have multiple hydroxyl groups, for example, glucose has 5 hydroxyl groups, and sucrose and maltose have 8 hydroxyl groups, the structure of alkyl glycosides is complex and there are many isomers.

Three, the washing performance of APG

There is no strong ionizing group in the APG molecule. It belongs to non-ionic surfactants. Its surface activity is among the best. It is stronger than common non-ionic surfactants (such as fatty alcohol polyoxyethylene ether). (Such as sodium silicate, etc.) can still maintain high surface activity in the solution. The low concentration of surfactants forming micelles is called critical micelle concentration (cmc), which is an important parameter to measure the surface activity of surfactants. The smaller the cmc, the higher the surface activity. When the alkyl groups are the same, the cmc of the commonly used anionic sodium dodecylbenzene sulfonate and sodium dodecyl sulfate are 1.2×10-3mol/L and 9.3×10-3mol/L, respectively. Non-ionic lauryl alcohol Polyoxyethylene ether C12H25O(OC2H4)9H is 1.0×10-4mol/L, and various APGs can be as small as 8.0×10-5mol/L~2.2×10-4mol/L.

APG also has other advantages, including rich foam and similar foaming ability to anionic surfactants; synergistic effect when compounded with other surfactants, which can increase surface activity and reduce the amount of irritating surfactants; it feels mild and right Little skin irritation. Because it is non-toxic, easy to degrade, and is 100% produced from renewable natural raw materials, it has its advantages in energy consumption, physiology, and environmental compatibility, so it is known as a green surfactant. Its disadvantage is that it is greatly affected by water quality, as the water hardness increases, the decontamination ability decreases

Fourth, the synthesis of APG

APG is usually prepared by condensing natural starch and its hydrolysate with fatty alcohol. The hydrolysate of starch can be glucose or oligosaccharides such as disaccharides and trisaccharides. There are many synthetic methods, and chemical synthesis methods are currently mainly used.

Here are two mature industrial synthesis methods. One is often called a one-step method, which uses C8 to C16 fatty alcohols to directly react with starch hydrolysates to produce alkyl glycosides, usually requiring heating and catalysts. Commonly used catalysts are sulfuric acid and p-toluenesulfonic acid, and acids with emulsifying properties (such as dodecylbenzenesulfonic acid) are also used. These acids can make the raw materials form stable fine droplets and help the glycosylation reaction.

After the completion of the reaction, the fatty alcohol is removed, and then after neutralization and bleaching, the product APG is obtained. This method is relatively simple, but due to the poor solubility of higher alcohols and sugars, the reaction time is long, and the reaction conditions need to be carefully controlled, otherwise it is easy to form agglomerates. This method is mainly used abroad to synthesize alkyl glycosides.

Another synthesis method is often called the two-step method. Take the transacetalization method as an example. In the presence of acidic catalysts such as sulfuric acid and p-toluenesulfonic acid, low-carbon aliphatic alcohols (usually butanol) and starch (or their hydrolysates) are first generated into low-carbon alkane. Alkyl glycosides, and then replace the low-carbon chains in the glycosides with high-carbon fatty alcohols to prepare high-carbon chain alkyl glycosides. The reaction with glucose as raw material is:

At present, this method is mainly used in domestic production. The commonly used conditions are: after the first reaction for 2 hours, remove the n-butanol as soon as possible under vacuum at 100-120°C, and then proceed to the second reaction. After 40 minutes of reaction, neutralize with Na2CO3, remove dodecanol at 165°C and 0.27 kPa to obtain the product. The two-step method is characterized by short reaction time, simple operation, and a good solution to the problem of alcohol-sugar compatibility, but large-scale production requires additional separation procedures and equipment for lower alcohols, and the product purity is not as good as the one-step method. In addition to chemical methods, enzymatic methods can also be used to synthesize APG. This method has the advantages of good selectivity, mild conditions, simple process, and high product purity, but the conversion rate is low, the reaction speed is slow, and the establishment of a suitable enzyme system is complicated. Therefore, it is still in the laboratory research stage.

5. APG prepared dish detergent

Usually, dishwashing detergent formulations using APG also contain other surfactants, so the formulated detergent has rich foam, good hard water resistance, easy rinsing, and mild touch. It should be noted that there is no direct relationship between foam and detergent performance, but the gradual decrease of foam during the washing process can indicate that the effective components of the washing solution are reduced and the cleaning ability is reduced. Due to the relatively high price of APG, the amount of APG in general formulations is small (usually 1%-15%) to reduce costs. In order to further reduce costs and increase viscosity in commercial production, NaCl is often used as a thickener.

The following is a simple formula preparation experiment plan: Weigh APG (50%) 0.70 g, AES (70%) 1.20 g, add water to 10 g respectively, and slightly heat it in a water bath (or heating mantle) to dissolve it. Mix the two solutions, add 3.5 mL of saturated NaCl solution, and stir gently to obtain the product. This product has a strong decontamination ability, and the washing effect in hard water after it is diluted 5 times is still very good.

In the experiment, you need to pay attention to the following items: (1) AES is weakly acidic and has a certain irritation to the skin, so avoid direct contact with the skin. (2) When preparing detergent, APG and AES should be dissolved separately and then mixed, otherwise it will be difficult to dissolve. (3) APG is difficult to dissolve in water, but vigorous agitation will produce a lot of foam, and the solubilization effect is not obvious. Therefore, it is not advisable to stir vigorously when dissolving, it can be heated slightly to promote dissolution. (4) NaCl should be added as a saturated solution. Direct addition of solid will cause dissolution difficulties. The amount of NaCl should not be too large, otherwise the thickening effect will be lost and the detergent will become thinner. (5) The experimental supplies are mostly flammable organic substances, so there should be no open flame in the whole process.

In order to meet different needs, a moisturizer (usually a little glycerin) can be added to the detergent to avoid dry skin after washing, perfume (lemon flavor 0.02 g) can be added to improve the smell, and an appropriate amount of preservative (sodium dehydroacetate 0.01 g) can be added ) Extend product shelf life.

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