I think that everyone played with such toys in childhood. We call them "Baby Ocean". It was found that the small beads "grew" more than ten times and were soft and supple. when pinched, and it was not easy to crush them. However, such an unremarkable toy often appears in the news about children's accidents. Due to ingestion by children, it can cause airway obstruction or intestinal obstruction in children due to its expanding properties and has been included in the ranks of toys with a high safety hazard[ one]. . After checking the information, it turns out that "Baby Ocean" refers to super absorbent resins. Next, let's delve into the world of chemistry to see what super absorbent resins are.

Fig. 1. "Baby Ocean" before and after absorbing water (picture from the Internet)

Superabsorbent resin (SAP) is a water-swellable functional polymer that is insoluble in neither water nor organic solvents. The molecular chain contains hydroxyl (-OH) and carboxyl (-COOH) hydrophilic groups, such as amido (-CONH2 ), sulfonic acid (-SO3H) and loose network structure [2], have superabsorption capacity and can absorb water in hundreds and thousands times more than their own weight. When it absorbs water and swells after hardening with water, it will become a hydrogel, with the advantages of fast water absorption and good water holding capacity.

The reason why it performs such a powerful function is because the material has hydrophilic genes such as carboxyl groups and hydroxyl groups that interact with hydrogen bonds in water molecules, and its network structure of molecular chains can strongly swell to hold water molecules firmly. It is firmly bound in it, and the liquid is still not easy to squeeze out under conditions of heat and pressure. In addition, when the environment is relatively dry, the absorbed liquid may be slowly released. Due to the special and excellent characteristics of SAP, it is widely used in hygiene products, agriculture and other fields.

In recent years, SAP technology has developed rapidly and has abundant sources of raw materials. Depending on the raw material, it can be divided into three categories: synthetic polymers, biomass (based on starch, cellulose, etc.), and organic-inorganic composites [3]. Synthetic polymer water-absorbent resin is obtained by cross-linking small molecules through polymer parts. The raw materials mainly include polyvinyl alcohol (PVA), polyacrylate (PAA), polyacrylamide (PAM), etc. Among them, PAA raw materials are easy to obtain, have good heat resistance, good durability to most acids and alkalis, and is not easily spoiled after long-term storage. It is precisely because of its good characteristics that it has become the most studied and most widely used variety.

However, this kind of water-absorbent resin is difficult to biodegrade and easily pollutes the soil, so the search for degradable water-absorbent materials has become another hot topic for researchers. resins simply have such characteristics. Its raw materials include natural products such as starch, cellulose, protein, chitosan and citric acid. The raw materials of this type of water-absorbent resin are cheap and easy to obtain, and can be biodegradable, which greatly reduces environmental pollution. Therefore, in Russia there are great prospects in agricultural production. The organo-inorganic composite water absorbent resin is designed to overcome the shortcomings of conventional spas such as high water absorption, poor mechanical properties, poor salt resistance, and poor reswellability. BeforeAdd organic modification spa to improve the stability, mechanical properties, salt resistance and other comprehensive properties of water absorbent materials.

1. Application in cosmetics

Super absorbent resin materials can be used in cosmetics as additives, thickeners, hair dyes, etc. Adding this material to cosmetics has a certain moisturizing effect. For example, in order to achieve a cooling effect in some cosmetics, it adds Alcohol is added to cosmetics, and alcohol is volatile, adding a certain amount of super absorbent resin to it can prevent volatilization. Secondly, the resin, after absorbing water, becomes gel-like and has good viscosity, which allows it to be used as a thickener for cosmetics. In everyday life, people often dye their hair to look young and fashionable. more integrated and has a certain hair care effect, and the coloring effect shown as a result will also be improved.

The most widely used carrier material in cosmetics is superabsorbent resin. In addition to the above uses, people can add nutrients or drugs to SAP so that they can be made into food cosmetics and pharmaceutical cosmetics. Cosmetics have certain effects and better meet the needs of people's daily lives.

2. Application in agricultural production

SAP has excellent water absorption, water and fertilizer retention, so it has important applications in agricultural production. Under the conditions of drought and water shortage, it can be used as a water-retaining agent for tillage [4], so that the soil can maintain a high water content for a long time, the water utilization rate is greatly improved, and the greatest economic effect is achieved. When water is abundant , it can absorb a lot of water and release water slowly during drought, which can save accumulated rainwater very well, which not only reduces irrigation frequency, but also saves irrigation costs. The super absorbent resin can also improve the soil, which helps to form the structure of soil aggregates. These aggregates can stabilize the soil structure, improve soil permeability, greatly slow down evaporation from the soil surface, and the anti-erosion ability of the soil has also been greatly improved. Because SAP has the function of absorbing and storing water and fertilizer, people often use water-absorbent resin to wrap or compound fertilizer in it so that the fertilizer can be released slowly. Under the same water and fertilizer conditions, this method not only improves crop yield, but also improves the coefficient use of fertilizers.

3. Other Applications

In SAP daily care products, you canbe used in common hygiene products such as sanitary napkins, diapers, etc., which brings great convenience to people's lives. It can also be used in deodorant and perfume products. For example, when making solid flavors, you can mix the appropriate amounts of SAP and glycerin and add a certain amount of flavor after curing to get solid flavors with good performance. In addition, in the process of transporting fresh food, fresh food itself has a high water content, and it is easy to lose water after contact with dry air, and the longer fresh food is stored, the more likely it is to spoil. In order to improve the freshness retention period of fresh foods, a freshness agent containing SAP and propylene glycol with antibacterial effect can be used to keep foods fresh and extend the shelf life of foods.

Fig. 2. PVA Film (Image Source Network)

With the continuous development of science and technology, superabsorbent resins have become widely used in daily life, and then magical functional materials have their pros and cons. We must learn to use these materials dialectically. At the same time, it is also necessary to solve the problems found in a timely manner in order to better build our beautiful earthen house.