The polyvinyl alcohol is a polymer of vinyl alcohol of molecular formula (CtwoH3OR) n, where R represents H or COCH3. Due to an instability of vinyl alcohol, it is synthesized using vinyl acetate as monomer, which polymerizes to form polyvinyl acetate..
Subsequently, there is a hydrolysis of the polyvinyl acetate esters, in the presence of sodium hydroxide, the acetate being replaced by the oxyhydryl group (OH), thus forming the polyvinyl alcohol. This is mainly composed of 1-3 diol [-CHtwo-CH (OH) -CHtwo-CH (OH) -].
This alcohol can form films with emulsifying and adhesive capacity, which can withstand strong stresses. In addition to being a flexible material, polyvinyl alcohol is hygroscopic and very soluble in water, its properties being affected by the degree of hydration.
Initially, it was prepared by Hermann and Haehnel in 1924, hydrolyzing polyvinyl acetate with potassium hydroxide in the presence of ethanol..
Polyvinyl alcohol can be used in the manufacture of sheets or films that are oxygen and aroma barriers. This has allowed it to be used in food packaging, this being its main use, since more than 30% of its production is used for this purpose..
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The top image illustrates a small segment of a polyvinyl alcohol polymer chain. The atoms enclosed within the parentheses are repeated n times until reaching the methyl ends, CH3. Thus, its structure consists of a series of repetitions of the -CH groupstwo-CH (OH)-.
Note that all bonds are simple and, therefore, carbons and oxygen have sp hybridization3. What does it mean? That the chains of polyvinyl alcohol are not straight, but zigzagged and with the H atoms alternating on their sides. The same goes for hydroxyl groups OH.
That is, the OH may be facing one side of the chain or the other, so the polar character of the structure is uniformly conserved throughout it..
Furthermore, the order of appearance of the OHs can be alternated. For example, the -CH linkstwo-CH (OH) -CHtwo in the image are not the only repeating pattern: so are CHtwo-CH (OH) -CH (OH). In the second pattern there is an increase in polar character, due to the fact that two OH groups are found on adjacent carbons..
Polyvinyl alcohol can have a simple, but dynamic and polar polymeric structure, which has a special affinity for water molecules and other solvents with which it can interact through hydrogen bonds: CH (O-H) - OHtwo.
Odorless white cream, granules or powder.
Toilet.
644º F at 760 mmHg (approximately).
442º F (experiences decomposition).
175º F (79º C) open cup.
It is soluble, increasing the solubility by decreasing the molecular weight of the polymer.
It is soluble in ethanol, but insoluble in other organic solvents. It is insoluble in solvents from petroleum. Practically insoluble in vegetable and animal oils, aromatic hydrocarbons, esters, ethers and acetone.
1.19 - 1.31 g / cm3.
Almost inexistent.
Stable under recommended storage conditions.
When heated above 200ºC it decomposes, emitting acrid and irritating smoke.
Between 4.8 and 5.8 mPa (4% solution at 20 ° C corresponding to an average molecular weight of 26,000 to 30,000 g / mol).
Polyvinyl alcohol has different grades based on its viscosity: super high (molecular weight 250,000 -300,000 g / mol), high viscosity (molecular weight 170,000 - 220,000 g / mol, medium viscosity (molecular weight 120,000 - 150,000 g / mol) and viscosity low (molecular weight 25,000 - 35,000 g / mol).
There is a direct proportional relationship between the viscosity of polyvinyl alcohol and its molecular weight.
5.0 to 6.5 (4% solution).
-It is material for the synthesis of other polymers such as polyvinyl nitrate, an ester of nitric acid and polyvinyl alcohol. Polyvinyl Nitrate is used in some castable propellants and explosives.
-Polyvinyl alcohol fibers have a water absorption capacity 30% higher than other fibers. This allows it to replace cotton in those uses where the fiber is in contact with the body. The tactile sensation of the fabric made from polyvinyl alcohol can vary from that experienced before wool to that similar to linen..
-Polyvinyl alcohol sheets are used in food packaging, because it has the ability to serve as a barrier to oxygen and aromas. This prevents food from oxidation and loss of flavor. In addition, it prevents outside odors from interfering with the original taste of food.
-It is used to thicken and modify polyvinyl acetate glue. It is used in sachets made with polyvinyl alcohol sheets in laundries to measure the release of detergents..
-The pads for feminine hygiene, as well as for urinary incontinence, are packaged in bags made with a film of biodegradable polyvinyl alcohol. It is used as a fixative for the collection of biological samples, especially those of feces.
-Used in eye drops, such as artificial tears, to treat dry eyes and as a lubricant for contact lens wear.
-A polyvinyl alcohol film or sheet is used in the water transfer process in printing. In addition, its fibers are used to reinforce concrete. Gloves for working with strong acids have a polyvinyl alcohol coating.
-They are used in the manufacture of capsules that can be used in the supply of medicines. Low molecular weight polyvinyl alcohol is used as a component of contraceptive products designed for intravaginal administration..
When polyvinyl alcohol is heated above 200ºC, it releases an irritating smoke to the eyes, nose and throat. Eye symptoms include watery, itchy, and red eyes. Meanwhile, in the nose and throat there is a burning pain.
It is not expected to be harmful.
It is not expected to be harmful.
Mechanical irritation only.
There are no human data. Some potentially harmful health effects were found in animal studies. A drop in the concentration of hemoglobin and in the number of erythrocytes and a possible complete inhibition of coagulation was observed. There is the possibility of carcinogenesis as seen in animal studies.
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