How to distinguish the true and false SAP water retention agent?
How to distinguish the true and false SAP water retention agent?
Although the water retention agent is a high-tech product, but it is not as some people imagine, that after the application of water retention agent "need not be watered from now on", the water retention agent when "all kinds of gold"!
Water retaining agent is not a water making agent, its itself can not make water, to the plant is an indirect regulation, only in a certain precipitation, irrigation and other conditions, water retaining agent can play its bibulous, water and fertilizer.
The water retaining agent must be permeated when applied for the first time. In the areas with little rain in the north, water should be supplied regularly. In the areas without water for dry crops, water should be applied before the rainy season. At the same time, although the water retaining agent has a certain effect on soil evaporation, but the effect of deep layer application is not obvious, so it is necessary to take cover measures to prevent soil moisture evaporation after application. In general, it is advisable to apply the water retaining agent into the topsoil at a depth of 5cm-20cm after fully mixing with the soil. Applying too deep will not have the corresponding effect, nor can it be applied on the soil surface, because the product will be exposed to light for a long time and accelerate the decomposition, shortening the service life.
The application effect of water retaining agent is also affected by the characteristics of water retaining agent, climatic conditions, soil texture, soil moisture conditions, soil salt and ion types, irrigation water quality and amount of irrigation, etc. Keep water agent also is not bibulous rate is jumped over taller had better, its comprehensive performance and quality index are decided by many sided factor place.
Mechanism of action of water retaining agent
Water retaining agent is different from general resin and is not in the form of monomer. It does not burn, explode, is non-toxic, non-corrosive and insoluble in water. It absorbs natural water through the network structure of hydrophilic groups, expands into hydrogel after absorbing water, and slowly releases water due to the evapotranspiration of soil water caused by environmental drought and the root pumping force of plants, so as to keep the surrounding soil moist for the absorption and utilization of plant roots.
Water retaining agent not only has the function of absorbing water, but also can absorb water-soluble fertilizer (such as nitrogen, phosphorus, potassium fertilizer) in the soil for plant application. Effectively reduce fertilizer and pesticide leakage, reduce environmental pollution. Because water retaining agent absorbs a lot of water, reduce the change of soil temperature, has a certain soil heat preservation effect, namely heat insulation in summer, heat preservation in winter, avoid the soil temperature difference caused by climate change affect the normal growth of plants. At the same time its repeated contraction and expansion to the soil to build lots of pore, improve soil permeability, improve the rhizosphere environment, but also enhance the rhizosphere microbial activity, accelerate the decomposition of organic minerals around rhizosphere, root absorption, promote root and plant growth and development, improve soil environment, prevent soil harden.
Classification of water retaining agents
First, from the structure of the points
From the structure of the polymer water-retaining agent is divided into two types:
A method of grafting polymerization in which a hydrophilic polymer is joined in a hydrophilic polymer chain;
The other is to convert synthetic water-soluble polymers into products that are insoluble but can swell in water.
Although they are insoluble in water, insoluble in organic solvents, can absorb hundreds to thousands of times their own weight in water. Starch and cellulose products cost low, but easy to corrupt failure. Synthetic polymers are a larger category. Due to their different raw materials and crosslinking ways, their hydrophilic, crosslinking and hydrophilic groups are different, and the products made of hydroscopicity, water retention, water release, weather resistance, stability (light, heat, freeze, microorganism), adaptability of biological tissues are quite different.
Two, because of the different raw materials and divided into three categories: starch, cellulose, polymer
1. The main component of starch graft is starch/polyacrylate graft polymer. Using crop starch synthesis, stability and salt resistance is poor, water absorption rate and rate is large, the cost is relatively low, the disadvantage is short service life, degradation fast, the service life can only maintain 3 to 12 months or so.
2. The main component of cellulose is carboxymethyl cellulose crosslinked. Synthesized from humus, valid for 3 ~ 8 months.
3. Polymer is the main component of acrylic acid, acrylamide through polymerization. Good stability and salt resistance, long service life, the service life in soil can be as long as 3 ~ 5 years. Water absorption capacity for its weight 150 ~ 400 times, pH value 6 ~ 8 range, for white powder or granular, namely the general agricultural and forestry water retention agent.
Three, from the appearance of points
From the appearance of water retention agent, can be divided into particle type, powder type and flake type, particle and flake type permeability is better, longer life than powder.
Absorbent principle of water retaining agent
Water retention agent water absorption principle is the polymer electrolyte molecular chain in water amide group and carboxyl group of the same sex repulsion of molecular chain expansion tension and due to the cross-linking point limit molecular chain expansion tension and interaction. A large number of amide and carboxyl hydrophilic groups, the use of its internal ions and groups and the concentration of the difference between the components of the osmotic pressure and the affinity of polymer electrolyte and water, a large number of water absorption until the concentration difference disappeared. And the control of water retention agent to achieve a satisfactory degree of water absorption is rubber elasticity. The higher the crosslinking degree of molecular structure, the stronger the rubber elasticity, and the balance point between rubber elasticity and water absorption is its apparent water absorption capacity.
Generally speaking, the lower the crosslinking degree of the same polymer, the higher the relative water absorption, the lower its water retention, stability and gel strength, and vice versa. Therefore, the international water retention agent with a long service cycle naturally needs a higher cross-linking degree, and does not pursue high water absorption rate and speed. Due to the long production cycle, forestry requires high water retention agent, stability and gel strength. Because the water retaining agent is generally mixed into the underground 5 ~ 20cm, 80% ~ 95% of the water absorbed can be used by plants.
International for the use of water retention agent more emphasis on pressure under water absorption. The apparent water absorption rate of water retaining agent is obviously different from that under pressure, and the water absorption rate decreases with the increase of ion concentration in water. The water absorption rate under pressure is the main index of water retaining agent. Most of what is absorbed can then be used by the soil and roots. The water retaining agent absorbs water by balancing water potential and releasing it by pumping plant roots.
The results showed that the water absorption capacity of water retaining agent was as high as 13 ~ 14kg/cm2, and the water absorption capacity of tree roots was 17 ~ 18kg/cm2, so there was no water backflow of plant roots, but tree roots could directly absorb water and nutrients stored in water retaining agent.
The difference of water retaining agent
The main raw materials of water retaining agent are polyacrylic acid salt and polyacrylamide. There are sodium salt and potassium salt in the raw materials. Sodium salt is harmful to soil environment and plants. There are many kinds of crosslinking agents, such as the crosslinking agent of multi-reaction functional group, polyvalent metal ion, polyvalent acid and polymer compound, etc. The price of crosslinking agent is relatively expensive, and the synthesis effect is quite different. The price of water-retaining agent with less cross-linking agent is lower, the water absorption ratio is high, but the water release is poor, and the gel strength is low. The price of raw materials in the market is different. In order to reduce costs, the proportion of polyacrylic acid salt and polyacrylamide can be adjusted at will, which will affect the quality of products.
In terms of synthetic raw materials, acrylic acid is a very active polymerization monomer, carboxyl group, was ionic, its polymerization crosslinking water absorption capacity and rate is strong, salt resistance and poor stability, short life. If the salt is all sodium, it will be bad for the plants and the soil. Starch is a natural polymer, cheap but easy to degrade, its water absorption capacity is worse than acrylic salt. Acrylamide is a polar and relatively inert monomer, and its polymer has poor water absorption than polyacrylate, but good stability and salt resistance, and better gel strength.
Water retaining agent contains a large number of hydrophilic groups, using osmotic pressure and group affinity can absorb 100 times its own weight of water, due to molecular mechanism crosslinking, molecular network absorbed water can not be extruded by general physical methods. Therefore, the more dense the molecular network, the slower the water absorption rate, the higher the gel strength, the longer the stability and service life.
At present, the international mainstream product polyacrylamide type water retaining agent is the result of the optimization combination of the characteristics of the above components. Its gel strength is high, the service life can be up to 3 ~ 5 years. Because potassium is much more expensive than sodium, acrylic acid may be potassium type, may be sodium type, potassium salt type water retention agent used in agriculture and forestry, sodium can be used under a certain content. If the sodium content is too high, it will bring harm to plants, soil and the environment, and is not conducive to the long-term exposure of human body. Sodium water-retaining agents are mostly used in industry.
Molecular structure of acrylamide - potassium acrylate crosslinked copolymer water retaining agent
Some users often enter error when product of choose and buy, think price is low, bibulous multiple is tall just good, exceed commonly 500 times bibulous material cannot be used at agriculture forestry production. International more attention is paid to water retention agent mixed into the topsoil 5cm below the soil in the water absorption rate, the international commonly used polyacrylamide water retention agent pressure under the general water absorption 200 ~ 400 times. If a company introduces its product with pressure water absorption more than 500 times, you need to do a water absorption experiment to observe whether the decomposition speed is too fast, whether it can be repeated water absorption, gel strength after water absorption, whether there are pores (if not, the root system can not penetrate water absorption, water utilization rate is too low), etc. Through short-term indoor repeated bibulous water observation, can judge its quality actor or actress.
In the purchase of water retention agent should be considered in the following aspects:
1. Agriculture and forestry water retaining agent is related to the safety of plants and ecological environment. Whether imported or domestic products, they must be registered and recognized by the relevant departments of agriculture and forestry. If you buy from the agent distributor, please check the agent distribution authorization certificate, the "fertilizer Registration certificate" issued by the Ministry of Agriculture and the test report of the product.
2. Do not unilaterally pursue the high water absorption ratio and rate, ignore its stability, water retention effectiveness and gel strength (life); The nutrient requirement of plant root growth and the effect of water retaining agent on soil permeability should be considered. It is better to protect water agent with amine, potassium polymer commonly, in order to prevent long-term and large amount of application of soil damage.
3. According to their own use to choose their own use of products, according to the different types of soil application of water retention agent, sand is suitable for the use of smaller particles of water retention agent, clay and loam suitable for the use of larger particles of water retention agent. Granular products have good ventilation, long life and are suitable for soil mixing. Powdery water retention agent mix soil when used, if mixed with soil is not even, after absorbing water, easy to cause soil local water content is too much, affect soil permeability, even cause seedling root rot, it is generally not used for mixing soil, and suitable for seed coating or dip in the root.
4. Do not use sodium ion products that are harmful to plants and soil and can be easily decomposed for agricultural and forestry planting, because sodium salts in its components will increase the PH value of the soil and lead to soil salinization, causing structural damage to the soil and great harm to the natural environment.
5. Different types of water retaining agents have different application scopes and application methods, so they should be used in accordance with the requirements of the specifications to achieve good results. At present, the application methods of water retaining agent include soil mixing, fertilizer mixing, seed mixing, coating, dipping root and spraying.
6. Super absorbent resin for sanitary use is prohibited. Health water absorption resin is made of polyacrylic acid sodium salt self-crosslinking reaction, water absorption multiple can reach thousands of times, easy to degrade, especially poor water release, and can not be repeated application, water absorption multiple is too large will suck plant water, counterproductive.
7. Understand the manufacturer's production process and technical conditions, raw material purity and product water content. The reaction container is not clean or the synthesis reaction is not complete, the product will leave extremely harmful substances to human body and ecological environment.
How to preserve water retention agent
1. Water retaining agent should be stored away from light. Long time to see the light, will obviously shorten the service life.
2. Indoor should be kept ventilated and dry, pay attention to moisture. Water retention agent can absorb water vapor in the air, the bacteria in the air will also reproduce in the moisture absorption water retention agent, making the water retention agent mildew deterioration. Water retaining agent is sealed by bag. When applying water retaining agent, try to open one bag of water retaining agent at a time and use it up at a time. If it is not used up and needs to be saved, be sure to seal the opening of the bag to pay attention to moisture-proof deterioration.
In recent years, more and more people notice the broad market prospect of super absorbent polymers, individual manufacturer and individuals in the interests of the driven, mass production and selling fake and shoddy, forestry and water retention agent, individual manufacturer and lack of the core of the production technology and equipment, simple production technology, what is more, in order to reduce the production cost for profiteering that cut corners, a large number of adding fillers, The composition of the product itself, there are serious defects of water retention agent products not only in line with international environmental standards, there is also a short service life, easy cause the issue such as difference of compaction, the effect of salinity, drought, shoddy, the sham as the genuine, health, industrial absorbent resin products such as dumping to the market, forestry man deceive the masses of users, endangering the survival of our environment.
The identification and evaluation of water retaining agent should be comprehensively considered from its water absorption capacity, water retention capacity, water release capacity, water absorption speed, stability, service life, gel strength, salt resistance, functionality and safety. Should see bibulous rate and speed not only, more important is to see its chemical composition, effect and safety. Water absorption rate, speed and gel strength contradict each other. The gels do not stick to each other, the life of water retention agent and improve soil permeability ability is good. The higher the water absorption rate and the faster the speed, the worse the gel strength of water retaining agent, the shorter the life, and vice versa. Do not look at the price alone, according to their needs and use of comprehensive consideration of its cost-effective. Cannot light graph is cheap and buy inferior product, after affecting use effect, increase project cost instead, gain outweighs loss. At present, the market supply of multi-functional composite long-term water retention agent, such as polyacrylamide type water retention agent period of validity is generally 3 ~ 5 years, the price is 3 ~ 50 thousand yuan/ton, suitable for agriculture, forestry, water conservancy, highway, railway, mine, garden engineering construction and other fields.
Generally speaking, water absorption capacity between 200 ~ 400 times, 15 minutes to absorb enough water is more ideal. Excellent water retaining agent in water absorption saturated crystal transparent granular, still granular in the soil, indicating that its gel strength is good, can increase the soil permeability, conducive to the improvement of soil structure, conducive to plant growth; On the contrary, inferior products will be sticky after water together into a paste, in the light of the color blackened dark, the surface can absorb water but virtually no repeated water absorption and release of water, in the soil moisture easy to corrosion of plant roots, in drought conditions will cause soil hardening.