It is a completely atactic, highly branched, noncrystalline thermoplastic, prepared by conventional free-radical polymerization. In the PVAC coatings, decrease of adhesion to the substrate during thermal aging is observed.PVAC coatings show a decrease in adhesion strength to the substrate during thermal aging. It is defined as follows. For PVAC coatings, if thermal aging follows moistening, then it causes a smaller change in the adhesion strength as compared to the sum of the individual impacts.
It is made from vinyl acetate, and has the chemical formula of (C 4 H 6 O 2) n. Polyvinyl acetate is used to make latex paints.
It dissolves in cold water at a slow rate, but the dissolution is fast at higher temperatures, especially around 90°C. History at your fingertips PVOH is produced by hydrolysis of PVA and the strong hydrogen bonding imparted by the –OH groups means that pure PVOH is water soluble. This translates to an average molecular weight of between 850 and 40,000. After 600 hours of humidification a decrease in the mass of the coatings is observed, At the first moment of humidification of coatings a sharp increase in internal stresses is characteristic, then a slow relaxation followed by stabilization (For PVAC coatings a temporary factor is also characteristic; an increase in internal stresses (in the first 4–5 days of moistening) is observed, followed by slow relaxation and after 26 days of moistening their stabilization at the level of 0.08 MPa is seen.Humidification causes a sharp change in the modulus of elasticity of coatings.
In this case, the rigidity of the films increases, and an increase in the modulus of elasticity is observed.
Samples of the polymer-lime, PVAC coatings and coatings from a dry finishing mixture after 3 days of moistening were dried for 2 weeks at an air temperature of 18°C–20°C and a relative humidity of 60%–70%, after which they were tested for tension.
It was found that the effective activation energy for destruction after 1200 hours of moistening the PVAC coating is The experimental and calculated data allow us to understand in more detail the mechanism of aging of coatings and to establish the factors that regulate the rate of structure-forming and destructive processes, which will improve the life of coatings.This research shows the complexity of the mechanism of aging of coatings of cement concretes. The influence of the climatic factors on the change in the properties of the coatings manifests in different ways. Amorphous density at 25 o C: 1.19 g/cm 3.. Molecular weight of repeat unit: 86.09 g/mol. In most cases symptoms will go away once exposure stops, but a lot depends on individual tolerance and the duration of the exposure in the first place. Spontaneous leveling of the surface microrelief also occurs. The number of units so combined is typically between 100 and 5,000. Glass transition temperature: 30 o C. . This indicates that the process of changing hardness is a reflection of the course of several parallel processes.
In the case of polyvinyl acetate, each repeating unit contains an acetate group. The most important member is polyvinyl acetate (PVAC). The research results and calculations are given in Analysis of experimental data shows that the influence of the hereditary factor on the change of the durability of the adhesion of coverings is ambiguous. Because of magnesium's sensitivity to moisture and the galvanic couple, water-based adhesives would be expected to cause problems.
These data show that at the first moment of moistening in the silicone-organic coating of KO-168 swelling processes prevail. This increase in surface area is associated with the resulting macro- and microcracks.Moisturizing is one of the aging factors. We denote by However, the results of the studies show that the constant of change in hardness is not a constant.
Polyvinyl acetate water-based emulsions are applied as a liquid, then hardens to a solid when the water evaporates or or is absorbed into a substrate.
Preparation can be carried out by dissolving polyvinyl acetate in methanol or ethanol with alkaline or acid or acid catalyst and heating to precipitate the polyvinyl alcohol from the solution. Properties. The polyvinyl ester family has the general formula -[RCOOCHCH2]-.
Hydrolysis accelerates with increasing air humidity and temperature In the process of moistening at the initial stage swelling is observed in coatings.
But after 50 hours of testing, destruction processes prevail. It is a nonstructural adhesive with low price, convenient usage and wide application range.