Description
Polyvinyl butyral (PVB) is a synthetic resin obtained by the condensation reaction
of PVA and butyraldehyde in the presence of acid catalyst. Since the acetalization
reaction cannot be carried out completely, the molecular chain of PVB contains three
functional groups, butyral, alcohol hydroxyl and acetate, the latter two of which come
from PVA. The chemical structure is:
The proportion of these three groups can be controlled by changing the reaction conditions, but they are randomly distributed in the long molecular chain. The proportion and distribution of the three are different, and the properties of PVB are also
different.
Chemical Properties
PVB resin is white or slightly yellow amorphous powder, with a particle size of
40–200 μm, fluidity and a density of 1.11 kg.m–1. It is a thermoplastic material, the
softening temperature is 60–65°C, the glass transition temperature is 70–78°C, the
molding temperature is 120–170°C, and the temperature adaptation range is 10–80°C.
PVB resin is insoluble in water, but soluble in a variety of organic solvents such as
alcohols, esters, benzene and ketones. It is miscible with various plasticizer including
phthalates, phosphates, and fatty acid ester. It has good compatibility with various
resins such as phenolic resin, urea–formaldehyde resin, melamine resin, epoxy resin,
nitrocellulose and natural resin. By mixing these resins in an appropriate ratio, the
physical and chemical properties are improved, and the cost is reduced.
PVB resin has certain chemical stability, but it can be decomposed in acidic or
alkaline (especially acidic) medium. It starts to decompose thermally after being
heated to 100°C, and will be almost completely decomposed at 200–240°C. Hydrolysis can occur in dilute acid, at this time intermolecular cross-linking can occur, a
small amount of double bonds is formed in the chain, and the acetate group will be
further hydrolyzed. Heated in concentrated acid to form a transparent solution, while
decomposing into aldehydes. Upon heating in dilute alkali solution with alkali concentration less than 1%, the free acid in PVB resin is neutralized and the thermal
stability of the resin is improved. However, when PVB resin is heated with 3% alkaline
solution to boiling, the acetate groups can be further hydrolyzed and saponified.
Uses
The main application of poly(vinyl butyral) is as interlayers in safety glass
laminates. In this application, a pure (colourless, light-stable) product with
high hydroxyl content (for good adhesion) is required. Such material is
preferably prepared from poly(vinyl alcohol) rather than directly from
poly(vinyl acetate). In a typical process, completely hydrolysed poly(vinyl
alcohol) is suspended in ethanol and then butyraldehyde and a small quantity of sulphuric acid (catalyst) are added. The mixture is heated at 800℃ for 6
hours. Water is then added to the product with rapid agitation and the
poly(vinyl butyral) is precipitated as granules, which are washed with alkali
and dried.
Poly(vinyl butyral) is generally softer than
poly(vinyl formal) with lower softening point, hardness and tensile strength.
In commercial polymers the hydroxyl content exerts a major influence on the
solubility characteristics. Most grades are soluble in alcohols, glycol ethers
and dioxan and as the hydroxyl content decreases the polymers become more
soluble in ketones and esters.
Poly(vinyl butyral) used in safety glass generally has 78-80% butyral
content, 18-19% hydroxyl content and less than 2% acetate content. For this
application the polymer is plasticized with an ester such as dibutyl sebacate
to the extent of about 30 parts of plasticizer per 100 parts of polymer; the
compound is then sheeted by calendering. To produce safety glass, the sheet is
placed between two pieces of glass and the laminate is then bonded under
heat and pressure.
Application
PVB is mainly used in safety glass interlayer materials.
It is also widely used in special coatings, adhesives, ceramic transfer paper, aluminum foil paper and others.
(1) Used as a safety glass interlayer: PVB resin has excellent optical clarity and weather resistance, and can maintain no
deformation in a wide range of temperatures. It also has rigidity combined with flexibility and excellent impact resistance. Moreover, it has excellent adhesion efficiency
with various glass surfaces. Therefore, the high molecular weight PVB resin is added
with 30–40% plasticizer and extruded into a film, which can be used as an interlayer material for safety glass. This is the main purpose of PVB.
(2) Application on ceramic transfer paper: PVB ceramic decal paper is made by pressing a layer of PVC film on wood paper, coating
with PVB film and printing patterns for ceramic printing. PVB decal is easy to use, involves
low cost and has a high color burn rate.
(3) Application in the coating industry: PVB is used in coatings for preparation of primers, baking paints, varnishes, etc. PVB is widely used in metal coatings. It is mixed with other components such as
phenolic, melamine, epoxy and isocyanate to improve the uniformity of the coating
film, increase the adhesive strength and elasticity and minimize the coating layer. PVB is used for
textile coating to improve the waterproofness, coloring and adhesion of fabrics.
(4) Application in the adhesive industry: PVB-containing adhesives are mainly high-performance structural adhesives, thermosetting and melt adhesives.
(5) Application on aluminum foil paper: With the rapid development of the national economy and export trade, the requirements for product packaging are getting higher and higher. In order to reduce costs,
vacuum aluminized paper with PVB coating has emerged and developed rapidly. At
present, this is the largest use of PVB resin in China, accounting for 44% of the total
PVB output.
(6) Other applications: PVB resin can also be applied to prepare special inks such as recording inks, letterpress printing and gravure printing inks. It can also be used to make waterproof
fibers, making the fabric antipollution without affecting the appearance, feel and
color of the fabric, which is suitable for treatment of almost all fabrics. Furthermore,
PVB can be used in dental restorations, wound dressing and wound sutures.
Synthesis
PVB is synthesized via the condensation reaction between polyvinyl alcohol and n-butanal catalyzed by protons, and can be produced using a reaction system containing a membrane dispersion microreactor and an aging vessel reactor or an improved batch reactor system with a microchannel mixer[1][2].
Toxics Screening Level
The screening level for Polyvinyl Butyral is set at the trace value of 0.1 μg/m3.
References
[1]
Lin, X., Wang, K., Zhou, B., Luo, G. (2020). A microreactor-based research for the kinetics of polyvinyl butyral (PVB) synthesis reaction. Chemical Engineering Journal, 383, 123181.
https://doi.org/10.1016/j.cej.2019.123181 [2]
Lin, X., Yan, S., Zhou, B., Wang, K., Zhang, J., Luo, G. (2017). Highly efficient synthesis of polyvinyl butyral (PVB) using a membrane dispersion microreactor system and recycling reaction technology. Green Chemistry, 19(9), 2155–2163.
https://doi.org/10.1039/c7gc00670e
