Chemical Name: Polyvinyl Alcohol
Synonym: PVA
CAS NO.: 9002-89-5
Molecular Formula: (C2H4O)n
Molecular Weight:44.05
Density:1.3
Melting Point:230-240℃
Flash Point: 79℃
Water Solubility:Soluble in hot water
Characteristic:
Polyvinyl Alcohol is a kind of non-ionic linear high polymer. It is non-toxic, non-smelly, and it looks white or light yellow, in theform of floccules, flakiness and solid powder. Its molecular formula is (C2 H4 O)n, of which "n" refers to the average degree of polymerization and the molecular weight is 44n. The molecular formula of PVA 17-88 is (C2 H4 O)n-(C2 H6O)m, of which "n + m" is the average degree of polymerization and the molecular weight is 44n+86m. The simulating specific gravity of flocculent PVA is (0.21-0.30)g/cm3, while that of flaky PVA is (0.47+-0.06)g/cm3.
Polyvinyl Alcohol has fairly good chemical stability, insulativity and film-forming properties. It has typical chemical properties of polyalcohol.
It can react with acid, ether and acetyl, and it can be esterified, etherified and actualized. In addition, it has unique characteristics of its own as follows:
Water Solubility:
Water solubility of PVA differs a little with different alcoholysises and viscosities. Based on the characteristics of our products, it's suitable to adopt the dissolving procedures as follow:
1. Add a moderate amount of clean water into the dissolving kettle on condition of room temperature.
2. Add calculated PVA into the dissolving Kettle little by little and fully stir it. The stirring speed should be controlled at about 100 revolutions per minute, and keep it soaked for 30-60 minutes after finishing stirring.
3. Heat with steam to a proper temperature step by step, and at the same time, keep stirring till PVA is completely dissolved. Heating can be done directly on an open fire without steam, but the density of the mixed liquor can never be higher the 10%. Remember constant stirring can prevent it from being burnt. The right temperature for PVA of thorough alcoholysis is between 95c and 98c, and no boiling has to be dome. Heating to 60c may do to PVA 17-88.
4. Methods to distinguish whether PVA is completely dissolved:
a. Base on the operating experiences.
b. Put some dissolved PVA liquor in a beaker, and observe it in a bright place, if it's clear and no transparent particles can be seen, then PVA in the kettle is completely dissolved.
c. Measure the viscosity. The viscosity of the liquid won't change under the same condition after about 30 minutes.
5. It is natural to blister when PVA is being dissolved. Heating and stirring at interval can be done if this phenomenon is serious, or lower down the dissolving temperature and stirring speed of revolutions to a proper degree. (If necessary, a moderate amount of deformers, such as caprylic alcohol and tributylphosphate can be added in.)
6. When the dissolution of flaky PVA is coming to the end, flow down from the kettle is to be employed, and the valve at the bottom must be opened and part of the bottoms have to be let out (This part can be put into the kettle again for dissolution). So that the valve at the bottom is unblocked.
Purpose & Application (for reference only)
3.1 Purposes
3.1.1 Papermaking & processing
In papermaking, water-soluble polymers are mainly applied to surface sizing agent, pigment binding agent, and paper addictive. In the past starch-based pigment was used as a surface sizing agent and casein as a binding agent. Today since the adhesion of PVA to fibers is stronger than casein, with better film-forming property and higher intensity of the film, the demand of PVA for paper processing is on the rise. Along with the large-equipment involving, high efficiency and high-grade papermaking and reasonable ways of packing, such demand will be even greater.
Main applications: (1) binding agent for paper; (2) re-moistening agent; (3) paper surface sizing; (4) paper pigment coating; (5) papermaking (paper internal sizing).
Applicable varieties: 24-99, 20-99, and 17-88 etc.
3.1.2 Plywood, artificial board and timber processing
PVA can be a de-characterizing agent of thermosetting resin mainly used as a binding agent such as carbamide, formaldehyde resin and melamine, for plywood, artificial board and timber processing.
When mixed with melamine-formaldehyde resin, the PVA size paste helps increase the viscosity and shortens both curing and cooling time with stronger initial cohesion.
Commonly used varieties: 17-99, 20-99, and 24-99 etc.
3.1.3 Emulsifying and stabilizing agents
With its very low surface tension and its ability to disperse VAC in water into very fine granules, PVA is applied to produce PVAc emulsion. It is also a very good protective colloid that enables the polymerized, colloidal and granular PVAc to form a stable aqueous emulsion and keep it from coagulation or degradation. Selection from a variety of PVA products depends on their properties. As for latex with a strong cohesion at the beginning of production, the complete alcoholysis type PVA can be selected, such as those labeled 24-99, 18-99, 20-99 and 17-99; on the contrary, for production of latex with low viscosity despite high content of solid, a PVA with a low degree of polymerization may be mixed with a PVA with high alcoholysis, and 03-88 can be used together with 17-99.
3.1.4 Construction Industry
PVA is used as an addictive to cement and mortar for efficient increase of their cohesion and fluidity, and reduce the drying time for the concrete surface, thus increasing coating adaptability and preventing concrete cloth from chapping. Besides, due to its simple application method with desired effects, PVA is suitable for wall and ceiling decoration and tile facing.
PVA can be also used as an adhesive agent for profiles, e.g. prefabricated plasterboard and sound absorption board that are made of organic fibers (cane, residue and wood-shavings) or non-organic materials on which highly cohesive and waterproof PVA series can be applied to make profiles through compression and cohesion.
The PVA solution, a poly vinyl formal (PVFM) high molecular compound, finds its wide application in internal wall coating, plasterwork and joint sealing due to its favorable properties of weather resistance, waterproof, non-swell with water, non-embrittlement, non-poison, tastelessness, and inexpensive prices.
In the coating sector the traditional varieties can only be used in making profiles. PVA with a higher degree of polymerization, such as the models 20-99 and 24-99, are often selected as a substitute.
3.1.5 PVA Film
PVA film has many unique advantages unmatchable for general polypropylene and polyvinyl chloride (PVC) due to its properties of bearing static electricity, good optical transmission, good gloss, low oxygen permeability, and coriaceous coating.
In this sector traditional varieties are seldom used. Due to low viscosity of PVA 17-99 series, generally for membrane not easily soluble, PVA 20-99 and 24-99 may be used, whereas the PVA 17-95 and 17-88 may be often used for production of water-soluble membranes.
3.1.6 Printing
For the PVA film which contains dichromatidgelatin or cinnamon acid, after ultraviolet radiation, part of the PVA combines with dichromatidgelatin to produce insoluble complex salt, or with cinnamon acid to have a water-insoluble meshwork due to the bridging effect. After heat treatment for increase of physical strength, the meshwork can be used for screen printing.
3.1.7 Textile
Functional PVA is now the most efficient synthetic sizing agent for warp paste with the following advantages:
1. PVA membrane has a good sizing effect and can improve the weavability of high-density and high-grade textiles due to its excellent properties of obdurability, smoothness, wear resistance and adhesiveness on fibers.
2. PVA has a powerful cohesive force on fibers as well as good protective effects to reduce times of textile yarn breaking and improve weaving efficiency.
3. PVA size paste doest not get corrosive easily and degraded without any change in viscosity after long-time heating, which ensures stable sizing and minimizes hard size spots.
4. At textile factories the moisture of starch paste must be at 80-85%, while the moisture requirement for PVA size mixture is just 70-75%, which makes it possible to improve operating environment and production efficiency.
5. To minimize desizings in the process of sizing and weaving and keep the factory area clean, PVA series with medium degrees of polymerization and 90-97 (mol/mol)% alcoholysis, such as 20-95 and 17-95, are applicable.
3.1.8 Vinylon
Though its clothing property may be far less popular than other synthetic fibers, Vinylon is still known for its properties of moisture absorption and wear resistance and can substitute some cotton-made bedding, knitwear, decorative cloth, canvas, uniform, work clothes, fishing net and curtain. Other properties of vinylon meet industrial requirements, such as high strength, low elongation, high modulus, acid/alkali/weather resistance, good adhesiveness to rubbers. So high-strength and high-membrane vinylon can be used as an alternative to asbestos.
Specification:
Grades |
Viscosity |
Hydrolysis |
Volatile |
Ash |
PH |
PVA1799 |
26.0-35.0 |
98.0-100.0 |
5.0 |
0.7 |
5-7 |
PVA1788 |
20.0-26.0 |
86.0-90.0 |
5.0 |
0.7 |
5-7 |
PVA2099 |
43.0-56.0 |
98.0-100.0 |
5.0 |
0.7 |
5-7 |
PVA2088 |
28.0-35.0 |
86.0-90.0 |
5.0 |
0.7 |
5-7 |
PVA2499 |
68.0-78.0 |
99.0-100.0 |
7.0 |
0.7 |
5-7 |
PVA2488 |
44.0-56.0 |
86.0-90.0 |
5.0 |
0.7 |
5-7 |
PVA0599 |
4.5-7.0 |
98.0-99.8 |
5.0 |
0.7 |
5-7 |
PVA0588 |
4.5-6.5 |
86.0-90.0 |
5.0 |
0.7 |
5-7 |
PVA2699 |
80.0-98.0 |
98.0-100.0 |
7.0 |
0.7 |
5-7 |
PVA2688 |
60.0-68.0 |
86.0-90.0 |
5.0 |
0.7 |
5-7 |
User Instruction
Solubility:
PVA is water soluble with transparent solution. Most PVA series are used while dissolved in water. Its solubility depends mainly on degrees of polymerization and alcoholysis. At the same temperature, the solubility increases along with reduction of the degree of alcoholysis, and decreases with increase of the viscosity; for the PVA series with the same degree of polymerization, if their degrees of alcoholysis are low, their temperatures get low upon completion of dissolution, and vice versa; for the PVA of the same alcoholysis, if the degrees of polymerization are high, their temperatures get high upon completion of dissolution, and vice versa. The PVA at the degrees of alcoholysis above 99 (mol/mol)% depends greatly on temperature changes, that is, dissolution or partial swelling may not take place at a particular temperature.
Ways of dissolution:
In order to prevent the size paste from contamination in the process of dissolution, stainless steel dissolving vessels are usually used; jacketing or water bathing can be the heat source, and heating can be achieved from direct steam, but heating from direct fire may lead to paste burning at the bottom of the kettle and should be avoided where possible.
At the ambient temperature, add a certain amount of cold water into dissolving vessels. If steam is blown directly into the vessel to heat the water, 10-15% of water can be saved due to production of condensate. To avoid lumping, direct use of hot water for dissolving should be avoided where possible.
Add PVA slowly while stirring for sufficient decentralization and swelling before heated. 10- to 30-minute stirring to swell PVA at the ambient temperature can efficiently shorten the dissolving duration.
When heated to temperatures above 90-95℃, the complete alcoholysis type PVA can be fully dissolved within 30-60 minutes approximately; for the medium alcoholysis type PVA, when heated up to above 80-90℃, within 30-60 minutes approximately; the partial alcoholysis type, up to 60℃ and then below 30℃, for about one hour to clear solution. In order to have a better effect of use, the completely dissolved PVA should be screened with a mesh of 100-120 μm.
When dissolved, the PVA of medium and partial alcoholysis types blisters easily. Stirring during dissolution at the speed of 60-90 rotations per minute ensures that the temperature will not increase too fast, otherwise foam and spillage may easily arise. If there are too much foam during dissolution, the steam can be closed, and the stirring be either slowed down or stopped. Gradual increase of the temperature and stirring up may be followed after the foam gradually disappears. Generally, after two or three times of repetition of such procedures, the quantity of foam can be dramatically decreased and the certain dosage of all foam-removing additives is just 0.008-0.04% by proportion to the consumption of PVA. The commonly used foam-removing agents include tributyl phosphate.
Storage after dissolution may result in formation of a layer of membrane on the surface of the paste and affect inconvenience in use. To avoid this, first use 2/3 cold water to dissolve PVA, then after dissolution, add the rest 1/3 cold water, and stir solution up until it cools down.
Compared with other water soluble macromolecule substances (CMC), the PVA solution is a low viscosity polymer very stable at the ambient temperature. It does not denature during storage. With its alcoholysis equal or greater than 99 (mol/mol)%, it can turn into gel at a low temperature, and easily turn into solution once it is heated.
Marking and Packing:
Packing: PVA is packed in laminated plastic woven bags each containing 12.5kg of floccule products and 20Kg of flake products (net weight), with manufacture dates, work shifts, batch numbers and anti-falsification labels sewn on the bags.
Storage Method:
PVA can be storaged for a long period without denaturalization unless it contacts water directly. During the storage, volatilization matter may slightly cause both moisture and weight loss but that will not affect the quality of PVA. Then, when the volatilization matter gets low, PVA absorbs easily moisture and adds weight to it.
If it is not contaminated, PVA solution does not rot or deteriorate easily which makes it easier for storage than any other macromolecular solution.
PVA 24-99, 18-99, 17-99 13-99 series are high viscosity and complete alcoholysis types. If they are made into a paste with a concentration higher than 8%, they can be stored at the ambient temperature lower than 20℃ with increased viscosity, forming gel due to molecule crystallization without any change in nature. Their fluidity can be restored to the original after heated and stirred. To avoid such happenings, in winter the frost resistance type PVA can be selected, or similar products with alcoholysis degrees of 88-97（mol/mol）%, which perform slightly poor in PVA water resistance, or by combination of complete and partial alcoholysis types for freeze resistance.
For the PVA with a degree of alcoholysis smaller than 99 (mol/mol)%, its viscosity is consistent with few possibilities to gel at low temperatures.
Stainless steel tanks are suitable for storage of PVA paste. If only iron or carbon steel containers are available, 0.05% sodium nitrate or sodium benzoate can be added into the PVA paste to avoid rusting.
Given a long period of storage, the untreated PVA solution in water mildew and rot easily, when some 0.01%-0.05% antiseptic can be added, e.g. salicylic acid.
Attentions on Safety, Storage and Transport, and Emergency Measures:
Briefing on Toxicity
Toxicity: the hamster LD50 of this product is greater than 2000 mg/kg, which shows the product is a nontoxic.
Harm to health: contact of PVA containing steam may cause slight irritation to the eyes, nose and throat.
Skin contact: constant skin contact may cause irritation.
Eye contact: this may cause clouded vision and irritation to the eyes.
Attentions on Transport
Gently load and unload; keep from being hooked or bumped during handling; avoid damages to packing.
Packing should be made completely ready upon start of shipping, and loading be safe. Mixed loading and shipping with strong oxidizer and food-grade chemical products are strictly prohibited.
Exposure to the blazing sun or heavy rain should be prevented during transport.
Attentions on Storage
Based on batch number, grade and specification, each finished product should be stored in a shady, cool, dry and ventilative warehouse.
Keep it far from any fire and heat source, use explosion proof type ventilating system and equipment, and avoid production of dust. .
Pile products on the level of the warehouse, respect the “five distances” requirements – from lamp, wall, ceiling, stack and pillar, to ensure stable and firm for each pile.
Equip the warehouse with a variety of fire-fighting apparatus and materials, adequate in quantity.
Prevent from direct sunshine and store away from oxidants.
Emergency Measure:
The fire extinguishing agents for the product can be spray water, foam, dry powder or carbon dioxide. When putting out fire, the fire fighter should stand windward to operate fire extinguisher downwards.
