Lena Savoie
Glyptal polyesters, a type of thermoplastic polyester, were first produced in 1901 by heating glycerol, a traditional alcohol used in alkyd production, and phthalic anhydride. Alkyds are organic polyesters derived from a polybasic acid, such as phthalic acid, and a polyhydric alcohol. The esterification reaction between these two ingredients produces an ester molecule. Alkyd resins are made to low molecular weights, generally ranging from 2,000 to 10,000, and they contain unreacted hydroxyl and acid groups that can further react with other molecules or oxygen to form a solid binder.
| Characteristics | Values |
|---|---|
| Type of Alcohol | Glycerol, a polyhydric alcohol |
| Type of Anhydride | Phthalic Anhydride |
| Reaction | An esterification reaction between the two ingredients produces an ester molecule |
| Product | Glyptal Polyesters, a linear polyester |
| Other Ingredients | Drying Oil, Fatty Acid |
| Other Forms of Anhydride | Maleic Anhydride, Hexahydro-4-methylphthalic Anhydride (HHMPA) |
| Other Ingredients | Sunflower Acid Oil, Maleic Acid, Fumaric Acid |
| Use Cases | Alkyd resins, paints, surface coatings, wall panels, pipe applications, road and bridge overlays, adhesives, etc. |
| Properties | Brightness, colour consistency, thermal stability, acid resistance, salt resistance, water resistance, solvent resistance, etc. |
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What You'll Learn
- Glyptal polyesters were first produced in 1901 by heating glycerol and phthalic anhydride
- Alkyd resins are thermoplastic organic polyesters
- Phthalic anhydride is used to make Ortho resin
- Maleic anhydride is a commonly used raw material for unsaturated polyester resins
- Polyester resins are synthetic resins formed by the reaction of dibasic organic acids and polyhydric alcohols
Glyptal polyesters were first produced in 1901 by heating glycerol and phthalic anhydride
Glyptal polyesters, the first commercially available polyesters, were produced in 1901 by heating glycerol and phthalic anhydride. The product was used as sealing wax and was called Glyptal™. The secondary hydroxyl in glycerol is less active than the terminal, primary hydroxyl, so the initial product formed is a linear polyester. Further heating and reacting the third alcohol produces a cross-linked product.
In the 1920s, related compounds called alkyds were synthesized by Kienle from trifunctional alcohols and dicarboxylic acids. These reactions formed high molecular weight materials due to functionalities greater than 2, resulting in cross-linking. Around the same time, American chemist Wallace Carothers and his research group at DuPont began investigating the formation of polymers from the reaction of aliphatic diacids with diols, which have two alcohol groups. They aimed to create materials that would give them fibres. However, they initially only formed syrupy mixtures, and the polyesters they achieved had low melting points, rendering them useless as fibre materials.
Building on Carothers' work, British scientists Whinfield and Dickson patented polyethylene terephthalate (PET) in 1941. They overcame the shortcomings of Carothers' group by using aromatic acids, especially terephthalic acid. This classic reaction produces plastics and fibres sold under various trade names, such as Dacron, Fortrel, and Trevira.
Unsaturated oils, or alcohols and anhydrides containing double bonds, were also reacted with phthalic anhydride. This yielded polyesters with a double bond that could be further reacted to produce cross-linked products. The extent of cross-linking or "drying" depends on the amount of unsaturated oil present. Today, the term "alkyd" is often used to describe all polyesters produced from the reaction of a diacid or anhydride and a diol or triol.
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Alkyd resins are thermoplastic organic polyesters
Alkyds are a type of synthetic resin and are used in items such as paints. They are not the same as resins derived from natural sources such as plants. They are made to low molecular weights, generally between 2,000 and 10,000. However, they contain unreacted hydroxyl and acid groups that can react with other molecules or with oxygen to form a solid binder.
Alkyd resins are classified as drying (including semi-drying) and non-drying. The triglycerides in drying resins are derived from polyunsaturated fatty acids, which are often derived from plant and vegetable oils, such as linseed oil. These drying alkyds are cured by the oxygen in the air. The drying speed and the nature of the coatings depend on the amount and type of drying oil used. The more polyunsaturated oil, the faster the reaction in the air.
Alkyd resins are used in coatings and have properties such as brightness, colour consistency, and thermal stability. They are also used in casting for the creation of sand-based moulds.
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Phthalic anhydride is used to make Ortho resin
Phthalic anhydride is a toxic, white crystalline compound that is soluble in alcohol. It is an important industrial chemical, especially for the large-scale production of plasticizers for plastics. It is an intermediate in organic chemistry, in part because it is bifunctional and readily available. Phthalic anhydride is used in the manufacture of dyes, resins, plasticizers, and insecticides.
Phthalic anhydride is the anhydride of phthalic acid and can be prepared from it. It is also obtained by catalytic oxidation of ortho-xylene or naphthalene. Phthalic anhydride can be used to produce ortho-phthalic anhydride-type resin, which is a general-purpose unsaturated polyester and one of the most commonly used thermosetting resins. It is a condensation polymer made from maleic anhydride, phthalic anhydride, and propylene glycol, to which a certain amount of styrene monomer is added as a thinner/curing agent.
The use of phthalic anhydride to produce ortho-phthalic anhydride-type resin is an example of the synthesis of unsaturated polyesters. These are generally copolymers prepared by polymerizing one or more diols with dicarboxylic acids or their anhydrides. The double bond of unsaturated polyesters reacts with a vinyl monomer, typically styrene, resulting in a 3D cross-linked structure. This structure acts as a thermoset.
The curing rate of ortho-phthalic anhydride-type resin depends on the reactivity ratios between the polyester and the monomer. The addition of the monomer to the polyester is proportional to the concentration of unsaturated acids in the polyester. The presence of additives such as metal soap and redox catalyzers does not significantly impact the curing rate.
The ageing mechanism of ortho-phthalic anhydride-type resin has been studied, and it has been found that in the early stages of the ageing period, the polyester undergoes post-cure and physical ageing. After a longer ageing period, it undergoes degradation due to the combined effects of UV, high temperature, and oxygen. The main factor leading to the failure of the polyester is UV irradiation.
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Maleic anhydride is a commonly used raw material for unsaturated polyester resins
Polyester is a synthetic polymer that can be a thermoplastic or thermoset, depending on its chemical structure. Thermoplastic polyesters can change shape after the application of heat. Polyester fibres have high tenacity and E-modulus, low water absorption, and minimal shrinkage compared to other industrial fibres.
Polyester resins are synthetic resins formed by the reaction of dibasic organic acids and polyhydric alcohols. Maleic anhydride is a commonly used raw material with diacid functionality in unsaturated polyester resins. Unsaturated polyesters are condensation polymers formed by the reaction of polyols (polyhydric alcohols) with unsaturated dibasic acids. The double bond of unsaturated polyesters reacts with a vinyl monomer, typically styrene, resulting in a 3D cross-linked structure. This cross-linking is initiated through a catalyst, usually an organic peroxide.
Maleic anhydride is a versatile compound in the production of unsaturated polyester resins. It can be used as a raw material or as an adduct with other compounds such as rosin or maleopimaric acid. The use of maleic anhydride in unsaturated polyester resins imparts several desirable properties. For example, maleic anhydride and styrene form alternating copolymers, contributing to the challenge of displacing styrene as the industry-standard reactive diluent.
Additionally, maleic anhydride plays a crucial role in the production of Tere resins, a subset of Terephthalic acid-based UPR resins. The addition of maleic anhydride to the production process results in a more cost-effective end product without sacrificing strength. This is achieved by using cheap scrap PET as a source of terephthalic acid.
In conclusion, maleic anhydride is a commonly used raw material for unsaturated polyester resins. Its versatility in resin production, ability to form copolymers with styrene, and cost-saving properties in Tere resins contribute to its importance in the field of polyester synthesis.
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Polyester resins are synthetic resins formed by the reaction of dibasic organic acids and polyhydric alcohols
The reaction between dibasic organic acids and polyhydric alcohols produces an ester and water. This reaction, along with the addition of saturated dibasic acids and cross-linkable monomers, forms the basis for manufacturing polyester. There are numerous polyesters made from different acids, glycols, and monomers, each with distinct properties.
Polyester resins can be further classified into two standard types in the composite industry: Orthophthalic (Ortho) and Isophthalic (Iso) polyester resins. Ortho resins primarily contain phthalic anhydride, while Iso resins are composed of isophthalic acid. Ortho resins are suitable for various applications and offer a cost-effective option, whereas Iso resins are sought after when high modulus and strength are required.
The versatility of polyester resins extends to their ability to be cured using an appropriate hardener through a catalyst, accelerating the decomposition process. Hexahydro-4-methylphthalic anhydride (HHMPA) is commonly employed as a hardener for thermosetting epoxy materials with ester linkages. The choice of hardener and catalyst can be tailored to the specific type of material being cured.
The production of polyester resins has been a subject of exploration since the early 20th century, with Glyptal polyesters being produced as early as 1901 by heating glycerol and phthalic anhydride. The development of polyester resins has led to their widespread use in various applications, including wall panels, pipe applications, and road and bridge overlays.
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Frequently asked questions
Polyesters are a category of polymers in which ester functionality repeats within the main chain.
Polyols are molecules containing hydroxyl groups. Examples include polyvinyl alcohol and cellulose.
Phthalic anhydride is a typical dibasic acid. It is a commonly used raw material with diacid functionality in unsaturated polyester resins.
Glycerol, a traditional alcohol used in alkyd production, produces a thermoplastic polyester with phthalic anhydride.
Thermoplastic polyesters are used in sheet moulding compounds, bulk moulding compounds, and the toner of laser printers. They are also used in wall panels, pipes, and road and bridge overlays.
