CMC in Glaze Slurry

The core of glazed tiles is glaze, which is a layer of skin on the tiles, which has the effect of turning stones into gold, giving ceramic craftsmen the possibility to make vivid patterns on the surface. In the production of glazed tiles, stable glaze slurry process performance must be pursued, so as to achieve high yield and quality. The main indicators of its process performance include viscosity, fluidity, dispersion, suspension, body-glaze bonding and smoothness. In actual production, we meet our production requirements by adjusting the formula of ceramic raw materials and adding chemical auxiliary agents, the most important of which are: CMC carboxymethyl cellulose and clay to adjust viscosity, water collection speed and fluidity, among which CMC also has a decondensing effect. Sodium tripolyphosphate and liquid degumming agent PC67 have the functions of dispersing and decondensing, and the preservative is to kill bacteria and microorganisms to protect methyl cellulose. During the long-term storage of the glaze slurry, the ions in the glaze slurry and water or methyl form insoluble substances and thixotropy, and the methyl group in the glaze slurry fails and the flow rate decreases. This article mainly discusses how to prolong the methyl The effective time to stabilize the performance of the glaze slurry process is mainly affected by methyl CMC, the amount of water entering the ball, the amount of washed kaolin in the formula, the processing process, and staleness.

1. Effect of methyl group (CMC) on the properties of glaze slurry

Carboxymethyl cellulose CMC is a polyanionic compound with good water solubility obtained after chemical modification of natural fibers (alkali cellulose and etherification agent chloroacetic acid), and it is also an organic polymer. Mainly use its properties of bonding, water retention, suspension dispersion, and decondensation to make the glaze surface smooth and dense. There are different requirements for the viscosity of CMC, and it is divided into high, medium, low, and ultra-low viscosities. High and low-viscosity methyl groups are mainly achieved by regulating the degradation of cellulose—that is, the breaking of cellulose molecular chains. The most important effect is caused by the oxygen in the air. The important reaction conditions for preparing high-viscosity CMC are oxygen barrier, nitrogen flushing, cooling and freezing, adding cross-linking agent and dispersant. According to the observation of Scheme 1, Scheme 2, and Scheme 3, it can be found that although the viscosity of the low-viscosity methyl group is lower than that of the high-viscosity methyl group, the performance stability of the glaze slurry is better than that of the high-viscosity methyl group. In terms of state, the low-viscosity methyl group is more oxidized than the high-viscosity methyl group and has a shorter molecular chain. According to the concept of entropy increase, it is a more stable state than the high-viscosity methyl group. Therefore, in order to pursue the stability of the formula, you can try to Increase the amount of low-viscosity methyl groups, and then use two CMCs to stabilize the flow rate, avoiding large fluctuations in production due to instability of a single CMC.

2. The effect of the amount of water entering the ball on the performance of the glaze slurry

Water in the glaze formula is different due to the different processes. According to the range of 38-45 grams of water added to 100 grams of dry material, the water can lubricate the slurry particles and help the grinding, and can also reduce the thixotropy of the glaze slurry. After observing Scheme 3 and Scheme 9, we can find that although the speed of methyl group failure will not be affected by the amount of water, the one with less water is easier to preserve and less prone to precipitation during use and storage. Therefore, in our actual production, the flow rate can be controlled by reducing the amount of water entering the ball. For the glaze spraying process, high specific gravity and high flow rate production can be adopted, but when facing spray glaze, we need to increase the amount of methyl and water appropriately. The viscosity of the glaze is used to ensure that the glaze surface is smooth without powder after spraying the glaze.

3. Effect of Kaolin Content on Glaze Slurry Properties

Kaolin is a common mineral. Its main components are kaolinite minerals and a small amount of montmorillonite, mica, chlorite, feldspar, etc. It is generally used as an inorganic suspending agent and the introduction of alumina in glazes. Depending on the glazing process, it fluctuates between 7-15%. By comparing scheme 3 with scheme 4, we can find that with the increase of kaolin content, the flow rate of glaze slurry increases and it is not easy to settle. This is because the viscosity is related to the mineral composition, particle size and cation type in the mud. Generally speaking, the more montmorillonite content, the finer the particles, the higher the viscosity, and it will not fail due to bacterial erosion, so it is not easy to change over time. Therefore, for glazes that need to be stored for a long time, we should increase the content of kaolin.

4. Effect of milling time

The crushing process of ball mill will cause mechanical damage, heating, hydrolysis and other damage to CMC. Through the comparison of scheme 3, scheme 5 and scheme 7, we can get that although the initial viscosity of scheme 5 is low due to the serious damage to the methyl group due to the long ball milling time, the fineness is reduced because of materials such as kaolin and talc (the finer the fineness, the Strong ionic force, higher viscosity) is easier to store for a long time and not easy to precipitate. Although the additive is added at the last time in plan 7, although the viscosity rises larger, the failure is also faster. This is because the longer the molecular chain, the easier it is to obtain the methyl group Oxygen loses its performance. In addition, because the ball milling efficiency is low because it is not added before the trimerization, the fineness of the slurry is high and the force between the kaolin particles is weak, so the glaze slurry settles faster.

5. Effect of preservatives

By comparing Experiment 3 with Experiment 6, the glaze slurry added with preservatives can maintain the viscosity without decreasing for a long time. This is because the main raw material of CMC is refined cotton, which is an organic polymer compound, and its glycosidic bond structure is relatively strong under the action of biological enzymes Easy to hydrolyze, the macromolecular chain of CMC will be irreversibly broken to form glucose molecules one by one. Provides an energy source for microorganisms and allows bacteria to reproduce faster. CMC can be used as a suspension stabilizer based on its large molecular weight, so after it is biodegraded, its original physical thickening effect also disappears. The mechanism of action of preservatives to control the survival of microorganisms is mainly manifested in the aspect of inactivation. Firstly, it interferes with the enzymes of microorganisms, destroys their normal metabolism, and inhibits the activity of enzymes; secondly, it coagulates and denatures microbial proteins, interfering with their survival and reproduction; thirdly, the permeability of the plasma membrane inhibits the elimination and metabolism of enzymes in the body substances, resulting in inactivation and alteration. In the process of using preservatives, we will find that the effect will weaken over time. In addition to the influence of product quality, we also need to consider the reason why bacteria have developed resistance to long-term added preservatives through breeding and screening. , so in the actual production process we should replace different types of preservatives for a period of time.

6. The influence of the sealed preservation of the glaze slurry

There are two main sources of CMC failure. One is oxidation caused by contact with air, and the other is bacterial erosion caused by exposure. The fluidity and suspension of milk and beverages that we can see in our lives are also stabilized by trimerization and CMC. They often have a shelf life of about 1 year, and the worst is 3-6 months. The main reason is the use of inactivation Sterilization and sealed storage technology, it is envisaged that the glaze should be sealed and preserved. Through the comparison of Scheme 8 and Scheme 9, we can find that the glaze preserved in airtight storage can maintain stable performance for a longer period of time without precipitation. Although the measurement results in exposure to the air, it does not meet expectations, but it still has a relatively long storage time. This is because through The glaze preserved in the sealed bag isolates the erosion of air and bacteria and prolongs the shelf life of the methyl.

7. The impact of staleness on CMC

Staleness is an important process in glaze production. Its main function is to make its composition more uniform, remove excess gas and decompose some organic matter, so that the glaze surface is smoother during use without pinholes, concave glaze and other defects. The CMC polymer fibers destroyed during the ball milling process are reconnected and the flow rate is increased. Therefore, it is necessary to stale for a certain period of time, but long-term staleness will lead to microbial reproduction and CMC failure, resulting in a decrease in flow rate and an increase in gas, so we need to find a balance in terms of time, generally 48-72 hours, etc. It is better to use glaze slurry . In the actual production of a certain factory, because the use of glaze is less, the stirring blade is controlled by a computer, and the preservation of the glaze is extended for 30 minutes. The main principle is to weaken the hydrolysis caused by CMC stirring and heating and the temperature rise Microorganisms multiply, thereby prolonging the availability of methyl groups.