How can textile manufacturers quickly and qualitatively identify commonly used sizing agents according to the existing test conditions, so as to grasp the performance and main structural characteristics of the sizing agent as a whole, and master the initiative of sizing formulation design and formulating sizing process parameters , Also easy to compare the application of different types of slurry. With the development of science and the advancement of textile production technology, various sizing materials at home and abroad are constantly emerging. A large part of the products are branded with various commercial names. Some companies have the basic composition or chemical composition of the sizing in the product description. Explain clearly, and some slurry production companies regard the basic ingredients of slurry products as technical and commercial secrets, and they are not obsessed with it. Most textile and printing and dyeing enterprises that are users of pulp lack scientific and advanced testing instruments and means, and there is no authoritative testing agency in the country to carry out quick and effective qualitative identification of pulp. This article discusses how to make a quick and easy qualitative identification of the size. The scope of the test is only starch, PVA, CMC, and polyacrylic acid sizes commonly used by cotton textile companies.
1. Iodine / potassium iodide method for preliminary identification of starch and PVA
Starch and PVA are the main sizing agents for textile warp yarns and are often used together in a sizing formulation.
The purpose of the iodine / potassium iodide identification test is to initially identify the presence of starch, PVA, or a mixture of the two in the slurry, and further related tests are required for the presence of other slurry.
A. Test instruments and reagents
Beaker (500 mL), glass rod.
Indicator A: 0.01 mol iodine solution, preparation method: Weigh 1.3 g of iodine, put it in a 50 mL beaker, add 2.5 g of potassium iodide and 25 mL of distilled water, and keep stirring to dissolve. Then add 0.2 mL of concentrated hydrochloric acid (volume mass 1.19g / cm3), dilute with water to 1 000 mL, store in an amber bottle, store in a low-temperature dark cabinet, and the validity period is 1 month.
B. Test principle
1. Starch reacts with iodine to form a blue color reaction
Whether it is a starch solution or a solid starch, a colored complex is formed when it interacts with iodine. This is due to the adsorption of iodine by starch molecules. The amylose molecule is in a spirally coiled state, and every 6 glucose can absorb one iodine molecule, so it has a strong ability to absorb iodine, forming a blue complex. Although the degree of polymerization of amylopectin is very large, the branching Many, each branch is only 20 to 40 glucose residues in length, can only form a few helixes, adsorb a very small amount of iodine, and produce a purple to red complex. Since the composition of starch is amylose (usually more than 73, depending on the type of starch, except for the ASP 100% amylopectin of Aveve in the Netherlands), the color appears blue or blue-black.
2. When PVA meets iodine, it will appear blue (complete alcoholysis) or red (partial alcoholysis) color reaction
PVA and iodine can form a complex and have a special colored reaction. The degree of color development has a certain relationship with the degree of alcoholysis. The fully alcoholylated PVA shows a blue color when it meets iodine, and the partially alcoholylated PVA shows a red or magenta color when it meets iodine. When mixed with starch, it will interfere with each other, so further testing is required to distinguish.
C. Test procedure
Use iodine solution A to drop 1 to 2 drops on the grey cloth. There may be 3 cases: dark blue indicates starch slurry or fully alcoholylated PVA (such as PVA? 1799); orange yellow (primary iodine liquid) indicates that It may be other slurries; it shows purple or brown red, indicating that there is a partially alcoholylated PVA.
2. Verification test of PVA
This test is based on the heating method test to further verify the PVA composition of the slurry. If the heating method has been identified as starch, this test is not necessary.
A. Verification method one-iodine / iodoboric acid method
1. Test equipment and reagents
Glass plates, pipettes, glass rods.
Indicator B: iodine, potassium iodide, boric acid solution, preparation method: 0.13 g iodine, 2.6 g potassium iodide, 40 g boric acid were added to water and diluted to 100 mL.
2. Test procedure
Drop the slurry pipette or glass rod onto the glass plate, use this indicator B to drop 1 to 2 drops on the slurry, and the purple color indicates PVA. This method is only used when no starch is known.
B. Verification method two-potassium dichromate method
1. Test equipment and reagents
Glass plates, pipettes, glass rods.
Indicator C, preparation method: 11.88 g potassium dichromate and 25 mL concentrated sulfuric acid are added to 50 mL water for dilution.
Indicator D, preparation method: 30 g of sodium hydroxide dissolved in 70 mL of water.
2. Test procedure
Drop the slurry pipette or glass rod onto the glass plate, drop 1 to 2 drops on the slurry with the indicator C, immediately add indicator D for about 3 to 4 drops to neutralize, and rub the two with the glass rod after 5 s. The brown spots on this solution proved to be PVA.
Third, the heating method further distinguishes starch and PVA
The test undertakes the iodine-potassium iodide method test, the purpose is to further distinguish starch and PVA on the premise that starch or PVA is known to exist in the slurry.
A. Test principle
When the starch slurry is heated above 70 ° C, the thermal motion of the macromolecular chain of starch is intensified, the macromolecular chain is straightened, and the complex formed by starch glucose residues and iodine is disintegrated. The blue color disappears and cools down again, and the blue complex is re-formed. PVA and iodine form a colored complex, which will not disintegrate when heated, and the color will not change.
B. Test equipment
Beaker (500 mL), glass rod, electric stove (1 000 W), alcohol thermometer.
C. Test procedure
Heat the slurry on an electric furnace to above 70 ℃. If the blue color disappears, the blue color will appear again after cooling, indicating the presence of starch. This is due to the straightening of the molecular chain of starch and the disintegration of the formed complex. Otherwise, the solution contains PVA.
In order to further eliminate the interference of the color development of starch and iodine, the sample can be heated and boiled with hydrochloric acid or sulfuric acid for a period of time to hydrolyze the starch into oligosaccharides, and then tested with iodine solution A. PVA; if it no longer develops color, it turns out to be starch, because oligosaccharides and monosaccharides do not develop color when they encounter iodine.
4. Qualitative judgment of PVA alcoholysis degree
To undertake the last test, this test is used on the premise that the slurry is known to have PVA, and the iodine and boric acid mixed solution method or iodine liquid is used to legally verify the alcoholysis degree of PVA, that is, partial alcoholysis PVA and complete alcoholysis PVA There is a big difference in the nature of the PVA. Partially alcoholylated PVA, such as PVA1788, PVA0588, has more acetate groups on the molecular chain. According to the similar compatibility principle, it has strong adhesion to polyester fiber (polyester) and is suitable for Sizing on the warp yarns of hydrophobic fibers, but its abrasion resistance and strength of the sizing film are not as good as the fully alcoholylated PVA, so part of alcohol is generally used in the formulation of warp yarns of hydrophobic fibers or blended warp yarns with a higher proportion of hydrophobic fibers. The solution PVA or the two PVA are shared to achieve the effect of complementing the shortcomings (of course also mixed with other slurries to play their respective advantages). For the sizing of hydrophilic fibers such as cotton, hemp, viscose, etc., generally fully alcoholylated PVA is commonly used, so it is necessary to qualitatively identify the alcoholysis degree of the PVA of the slurry.
A. Test method one-iodoboric acid method
PVA with different degrees of alcoholysis and iodoboric acid have different color reaction to qualitatively identify PVA with complete alcoholysis and partial alcoholysis.
1. Test equipment and reagents
Glass plates, glass rods, filter paper, glass straws. Preparation of indicator E, iodoboric acid solution: dissolve 3 g of crystalline boric acid (H3BO3) in 100 mL of 0.01 mol / L iodine solution and stir it
2. Test procedure
Use the mixed solution of iodine and boric acid to determine whether it is a complete alcoholysis grade PVA or a partial alcoholysis grade PVA. Liquid and air-dried in the air, forming stains.
Add 1 drop of water in the middle of the stain, and after 10 s, the red halo of wine appears around the stain, which indicates that it is a partial alcoholysis grade PVA, while the complete alcoholysis grade PVA does not appear halo.
B. Test method two-iodine solution method
The properties of iodine solution and PVA with different degrees of alcoholysis to form different colored complexes were used to qualitatively identify PVA with complete alcoholysis and partial alcoholysis.
1. Test equipment and reagents
Beakers, glass rods, filter paper, straws, etc.
Indicator A
2. Test procedure
Make the slurry into a slurry of about 1%, drop 1 drop on the filter paper, and after drying, take the iodine droplets on it. The complete alcoholysis of PVA showed blue spots, and the partial alcoholysis of PVA showed red spots; further observation showed that the degree of alcoholysis = 94-95mol% of PVA was the transition point from blue to red. When the PVA alcoholysis degree is less than 80 mol%, there is no color reaction with iodine. The alcoholysis degree of sizing used in general is 88% -99.6% (spinning grade PVA).
