Unsaturated Polyester Resins

Unsaturated Polyester Resins as an Industrial Raw Material Category

Polyester resins represent a class of thermosets produced by polycondensation of polyhydric alcohols (glycols) with dibasic acids or their anhydrides. The most common type is unsaturated polyester resins (UPR), which contain double bonds in the macromolecule that enable curing at room temperature without the release of by-products. Unlike epoxy resins, polyesters have lower viscosity, lower cost and faster curing, making them indispensable in the mass production of fiberglass, artificial stone and polymer concrete.

The specificity of the category is determined by the fact that the properties of the final product depend on the type of acid used (orthophthalic, isophthalic, terephthalic), the glycol and the monomer-solvent (usually styrene). Orthophthalic resins are standard and most economical, isophthalic resins have increased strength and chemical resistance, and terephthalic resins occupy an intermediate position. High flammability and toxicity of styrene require strict adherence to safety measures during processing.

Chemical Identification and Classification of Grades

Unsaturated polyester resins are identified by CAS number 26098-37-3 (orthophthalic polyester resin). In international trade, HS code 3907.91 is used for unsaturated polyesters in primary forms. Density of resins is 1.10 to 1.20 g/cm3, viscosity by VZ-246 ranges from 16 to 32 seconds depending on the grade.

In Russian practice, unsaturated polyester resins are regulated by GOST 27952-2017, which replaced GOST 27952-88. Depending on composition and properties, several groups are distinguished. General-purpose resins (orthophthalic) include grades PN-1, PN-2, PN-1UT (thixotropic). Increased heat resistance resins are represented by grades PN-3, PN-4, PNC. Reduced flammability resins include PN-1e, PN-6, PN-7. Water- and acid-resistant resins are represented by grades PN-10, PN-10/409, ZSP-6. Grade PN-609-21M is distinguished separately as a solution of polyethylene glycol maleinate phthalate in triethylene glycol dimethacrylate (TGM-3). The largest Russian producer is ZAO Electroizolit (Khotkovo), producing a wide range of grades including PN-1, PN-1UT, PN-609-21M, NPS-9101, NPS-9112, NPS-9502, EVS-9133.

Regulatory Framework and Quality Standards

Circulation of polyester resins and articles made from them in Russia and the EAEU is regulated by Customs Union technical regulations, in particular TR CU 005/2011 for packaging, TR CU 021/2011 for food contact, TR CU 004/2011 for electrical articles. For the resins themselves, GOST 27952-2017 applies, establishing technical requirements, acceptance rules and test methods. International standards used for identification and control include ISO 3001 for epoxy equivalent (for epoxy vinyl ester resins), ISO 1133 for melt flow rate, ISO 1183 for density, ISO 527 for tensile strength, ISO 178 for flexural modulus, ASTM D638 for mechanical properties.

Physico-Chemical Properties and Classification by Acid Type

Key physico-chemical parameters of polyester resins determine their behaviour during processing and operation. Density is 1.10 to 1.20 g/cm3. Viscosity by VZ-246 for PN-1 is 16 to 31 seconds, for PN-609-21M it is 20 to 32 seconds. Gel time at 25 degrees Celsius with a two-component system is 5 to 28 minutes for PN-1 and 100 to 200 minutes for PN-609-21M.

Mechanical properties of cured resins include flexural strength of 70 to 100 MPa, flexural modulus of 2200 to 2800 MPa, impact strength of 6 to 12 kJ/m2, Brinell hardness of 140 to 180 MN/m2, Vicat softening point of 85 to 120 degrees Celsius, dielectric constant at 10^6 Hz of 4.4 to 5.2. Chemical resistance depends on the acid type: orthophthalic resins have low chemical resistance, isophthalic resins have high resistance to hydrolysis and chemical media, terephthalic resins have intermediate resistance. All unsaturated polyesters are combustible and require flame retardants to improve fire resistance.

Mechanism of Action and Functional Role

In processing, polyester resins act as a reactive matrix that, when mixed with an initiator (usually methyl ethyl ketone peroxide) and an accelerator (usually cobalt naphthenate), cures at room temperature. The curing process is accompanied by an exothermic copolymerisation reaction of styrene with the double bonds of the polyester chain, leading to the formation of a three-dimensional crosslinked structure. This network formation provides the mechanical strength and chemical resistance of the final product. In compounds, polyester resins act as carriers for additives: fillers (chalk, talc, glass fibre, quartz sand) increase rigidity and reduce shrinkage, flame retardants impart fire resistance, pigments provide colour, thixotropic additives prevent resin drainage from vertical surfaces, UV stabilisers protect against yellowing.

Applications by Industry

Fiberglass remains the largest consumer of polyester resins. The material is used for boat hulls, automotive parts, construction panels, pipes, tanks and wind turbine components. High strength and low weight make fiberglass indispensable in transport and construction. Artificial stone (polymer concrete) is produced based on polyester resins with mineral fillers; the material is used for countertops, sinks, window sills and decorative elements. Construction uses polyester resins for self-levelling floors, waterproofing, repair of concrete structures and production of polymer concrete products. Electrical engineering uses resins for transformer casting, microchip encapsulation and insulator production. In shipbuilding, polyester resins are used for boat and yacht hulls. In medicine, they are used for dental filling materials and biocompatible coatings.

Comparison with Alternative Materials

Compared to epoxy resins, polyester resins have lower viscosity, lower cost and faster curing but are inferior in adhesion, mechanical strength and chemical resistance. Epoxies are preferred for critical adhesives and coatings, polyesters for mass fiberglass and artificial stone. Compared to vinyl ester resins, polyester resins are cheaper but inferior in chemical resistance and water resistance. Vinyl esters are used for corrosion-resistant structures, polyesters for standard articles. Compared to phenolic resins, polyester resins have better processability and lower toxicity but are inferior in fire resistance and heat resistance.

Common Processing Challenges

The most frequent problems in polyester resin processing are:

• Inaccurate ratio of resin, initiator and accelerator. Deviation from the formulation leads to incomplete curing or excessively fast gelation. Precise dosing control is necessary.
• Insufficient mixing. Uneven distribution of components leads to local areas of uncured material and defects.
• Incorrect temperature regime. Low temperature slows curing, high temperature causes exothermic overheating, cracking and darkening.
• Moisture and contamination. Moisture and oils on the filler or substrate surface reduce adhesion. The surface must be cleaned and degreased.
• Insufficient holding time. Full curing requires the time specified by the manufacturer. Accelerating the process can lead to internal stresses.

Quality Control and Laboratory Methods

Quality control of polyester resins includes incoming analysis, document verification and laboratory testing. Key parameters: viscosity by VZ-246 (GOST 8420), density (ISO 1183), styrene mass fraction (GOST 13549), gel time (GOST 22181), non-volatile content, acidity, colour. For cured samples, flexural strength (ISO 178), elastic modulus, impact strength, Vicat softening point (ISO 306) and dielectric properties are controlled. For food contact and medical devices, sanitary-chemical and toxicological tests are carried out.

Storage and Transportation Conditions

Polyester resins are stored in sealed steel or plastic containers at temperatures from 5 to 25 degrees Celsius. Resins are sensitive to heat and light, so they should be protected from direct sunlight. Shelf life is usually 3 months for PN-1 and PN-609-21M. After the shelf life expires, changes in viscosity and gel time are possible. Transportation is carried out in steel drums, aluminium drums, rail tank cars and road tankers. Polyester resins are classified as dangerous goods (class 3, flammable liquids) and require special marking.

Analogue Selection and Interchangeability

Polyester resin analogue selection is one of the key services of the portal. We help replace imported grades with comparable alternatives based on viscosity, gel time, acid type and curing properties. The algorithm includes analysis of the current grade and its technological parameters, determination of permissible deviations in key parameters, selection of options from available sources (Russia, China, Turkey, other regions), verification of certificates and laboratory data, and organisation of trial batches for testing on the customer equipment. When selecting an analogue, not only viscosity and gel time but also the resin type (orthophthalic, isophthalic, terephthalic), presence of thixotropic additives and flame retardants, and compatibility with specific initiators and fillers are considered.

Supply Scheme: Worldwide

The portal organises polyester resin supplies worldwide. In Russia, key producers are ZAO Electroizolit (Khotkovo), Dugalak and Yaroslavl Polyesters. However, a significant part of demand is covered by imports. China and Turkey are the main suppliers: in 2025, imports of unsaturated resins from these countries dominated the Russian market. The largest global producers are AOC, Polynt, Scott Bader, Tianhe Resin, Eternal Materials and DIC Corporation. Each supply is treated as a separate project with an individual scheme covering grade selection, quality verification, logistics and customs clearance.

Logistics and Customs Clearance

Polyester resin logistics includes sea, rail and road routes. For large batches of liquid resins, tank containers and tankers are optimal; for smaller batches, drums and IBC containers. Customs clearance is supported by the portal broker: document preparation, HS code 3907.91 classification, certification and interaction with control authorities. The logistics scheme is built for the specific route and customer requirements.

FAQ

How does PN-1 differ from PN-609-21M?

PN-1 is an orthophthalic general-purpose resin based on styrene, used for fiberglass and composites. PN-609-21M is a resin based on oligoester acrylate in triethylene glycol dimethacrylate, used for premixes and composite materials with special requirements.

Which resin is suitable for artificial stone?

For artificial stone, orthophthalic general-purpose resins (e.g., PN-1) or special grades such as NPS-9101 are typically used, with mineral fillers and thixotropic additives.

Can polyester resin be used for food products?

Yes, provided the grade is approved for food contact and has the appropriate sanitary documents. Special polyester compositions are used for food equipment coatings.

Why does polyester resin require a precise ratio with the initiator?

Deviation from the formulation leads to incomplete curing or excessively fast gelation. Precise dosing ensures full crosslinking and maximum properties.

What documents accompany a supply?

Material safety data sheet (MSDS), quality certificates, declarations of conformity with TR CU, origin documents. For export batches, documents confirming compliance with the importing country requirements.

Are small batches available for testing?

Yes, trial batches from 25 kg are available for most grades. Terms are agreed individually.

Conclusion

Polyester resins remain key thermosets for fiberglass and artificial stone due to their unique combination of processability, curing speed and cost. A processor success depends on the correct choice of grade considering acid type, viscosity and gel time, confirmed quality and stable supply. The portal helps select analogues, organise logistics and customs clearance, ensuring supply chain transparency worldwide.

Contact Us

If you are looking for polyester resins or need advice on grade selection, analogue search and worldwide supply organisation, please contact our team at info@apptrade.ru. We will help you find the right product, verify documentation and organise supply.