Adjuvants can increase the detergency effect of surfactants. Commonly used additives are phosphates, zeolites, silicates, carbonates, chelating agents, and oxygen-releasing compounds. Less used are borax, bentonite, colloidal silica and so on.
①Phosphate: The phosphates used in detergents include orthophosphates and polymeric phosphates, but the main ones are polymeric phosphates, especially tripolyphosphates. Other polymeric phosphates such as sodium pyrophosphate and sodium hexametaphosphate are easy to absorb moisture and should not be mixed into powder products, but only used in some special processes. These phosphates can chelate hard metal ions (mainly calcium and magnesium ions) in water, making them soluble compounds, thereby softening water. The chelating ability of calcium ions is the largest with hexametaphosphate, and the chelating ability of sodium tripolyphosphate to calcium and magnesium ions is between the two. Phosphate can also re-dissolve insoluble calcium and magnesium salts and insoluble calcium soaps, phosphates, etc. left in the previous washing process mixed with fibers, thereby increasing the detergency of the detergent. This mutual promotion effect of all polymeric phosphates, especially tripolyphosphates, on surfactants is called synergy. In addition, it can still make insolubles such as dust undergo deflocculation (ie peptization) to maintain a suspended state, and can emulsify oily substances.
②Zeolite: a new type of additive developed rapidly in the 1970s to reduce the environmental pollution caused by sodium tripolyphosphate. Also called molecular sieve. Its chemical name is sodium aluminosilicate. Zeolite has good ion exchange performance, especially A-type zeolite has high exchange capacity for calcium ions. The zeolite for detergent is 4A zeolite. Since zeolite is insoluble in water, in order to prevent it from remaining on the fabric, the particle diameter should be less than 10µm, of which more than 85% should be ≤4µm. Due to the poor ability of zeolite to complex magnesium ions, it cannot completely replace sodium tripolyphosphate for synthetic detergents. However, the content of magnesium ions in water in most areas is only 1/3 to 1/5 of the amount of calcium ions, so the potential for replacing the part of sodium tripolyphosphate complexed with calcium ions is still great. In addition, the combined use of zeolite and tripolyphosphate is better than the effect of using them individually. There are also mixed use of sodium tripolyphosphate, sodium nitrilotriacetate and zeolite.
③Sodium silicate: an important auxiliary agent. Commonly known as water glass. Its solution is called Paohua alkaloid. It has the functions of buffering, improving detergency, improving the fluidity of slurry and powder, protecting fabrics, resisting corrosion, softening water, etc.
④Carbonate: There are 4 kinds of carbonates commonly used in detergents, namely sodium carbonate (soda ash), sodium bicarbonate, sodium sesquicarbonate and modified alkali. Sodium carbonate can improve alkalinity, and can form calcium carbonate (magnesium) precipitation with calcium and magnesium ions in water, thereby softening water. There are two physical states, heavy and light, depending on the conditions of manufacture. In addition to being used as a cheap alkaline additive in powdered detergents, sodium carbonate is also used in dry products made by non-spray drying methods, especially light soda ash. It will adsorb a large amount of liquid materials on its surface, but It still maintains a dry feel and free-flowing properties. In this case, in addition to being used as an alkaline auxiliary, most of them are used as adsorbents and neutralizers. Sodium bicarbonate is added to the detergent to lower the pH value of the material. The performance of sodium sesquicarbonate (Na2CO3NaHCO3 2H2O) is between that of soda ash and sodium bicarbonate. Modified alkali is a mixture of soda ash and sodium bicarbonate, usually mixed in equimolar, without crystal water, so both sodium sesquicarbonate and modified alkali have the ability to soften water, moderate alkalinity, and neutralization. Since there is already crystal water in the sodium sesquicarbonate molecule, it can no longer absorb water or liquid, so if water absorption is required, a modified alkali is used.
⑤ Chelating agent: The main function is to prevent the deposition of calcium, magnesium ions and heavy metal ions in water. Usually divided into amino carboxylic acid, hydroxyamino carboxylic acid, hydroxy carboxylic acid 3 categories. The representative varieties of aminocarboxylic acids are ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethyltriaminepentaacetic acid (DTPA); hydroxyethylenediaminetetraacetic acid (HEDTA) and hydroxyethylenediaminetetraacetic acid (HEDTA) and Dihydroxyethylglycine (DEG); hydroxycarboxylic acids include grape acid, citric acid, tartaric acid, oxalic acid, etc. Other types of chelating agents are cyclic polycarboxylic acids, such as pyromellitic tetracarboxylic acid, benzopolycarboxylic acid, and tetrahydrofuran tetracarboxylic acid.
⑥Oxygen release compounds: mainly include sodium perborate and sodium percarbonate. In solution, sodium perborate releases nascent oxygen with bleaching effect at higher temperature, which is suitable for washing and bleaching of animal, plant fibers and synthetic fibers. Its action is not affected by pH. The bleaching temperature of sodium percarbonate is relatively low.
