Polyester resins: production and handling

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

In recent years, polyester resins have become very popular. First of all, they are in demand as leading components during the production of fiberglass, strong and lightweight structural materials.

Resin making: first step

How does the production of polyester resins begin? This process begins with the distillation of oil - during this, various substances are released: benzene, ethylene and propylene. They are necessary for the production of antihydrides, polybasic acids, glycols. After cooking together, all these components create the so-called base resin, which at a certain stage must be diluted with styrene. The last substance, for example, can be 50% of the finished product. As part of this stage, the sale of ready-made resin is also allowed, but the production stage is not yet completed: one should not forget about saturation with various additives. It is thanks to these components that the finished resin acquires its unique properties.

The composition of the mixture can be changed by the manufacturer - a lot depends on where exactly the polyester resin will be used. Experts select the most optimal combinations, the result of thiswork will be substances with completely different properties.

Resin production: second stage

It is important that the finished mixture is solid - usually they wait until the polymerization process reaches the end. If it is interrupted, and the material is on sale, it is only partially polymerized. If nothing is done with it, the polymerization will continue, the substance will definitely harden. For these reasons, the shelf life of the resin is very limited: the older the material, the worse its final properties. Polymerization can also be slowed down - refrigerators are used for this, hardening does not occur there.

In order for the production stage to be completed and the finished product to be obtained, two important substances must also be added to the resin: a catalyst and an activator. Each of them performs its function: heat generation begins in the mixture, which contributes to the polymerization process. That is, a heat source from the outside is not required - everything happens without it.

The course of the polymerization process is regulated - the proportions of the components are controlled. Since an explosive mixture can result from contact between the catalyst and the activator, it is customary to introduce the latter into the resin exclusively as part of production, the catalyst is added before use, it is usually supplied separately. Only when the polymerization process is completely completed, the substance hardens, it can be concluded that the production of polyester resins is completed.

Original resins

What is thismaterial in its original state? It is a honey-like, viscous liquid that can range in color from dark brown to light yellow. When a certain amount of hardeners is introduced, the polyester resin first thickens slightly, then acquires a gelatinous state. A little later, the consistency resembles rubber, then the substance hardens (becomes infusible, insoluble).

This process is called curing, as it takes several hours at normal temperature. When the resin is solid, it resembles a tough, durable material that can be easily dyed in a variety of colors. As a rule, it is used in combination with glass fabrics (polyester fiberglass), it performs the function of a structural element for the manufacture of various products - such is polyester resin. Instructions when working with such mixtures are very important. It is necessary to comply with each of its points.

Key features

Polyester resins in the cured state are excellent structural materials. They are characterized by hardness, high strength, excellent dielectric properties, wear resistance, and chemical resistance. Do not forget that in the process of operation products made of polyester resin are safe from an environmental point of view. Certain mechanical properties of the mixtures that are used in conjunction with glass fabrics, in terms of their performance, resemble the parameters of structural steel (in some cases even exceed them). The manufacturing technology is cheap, simple, safe, since the substance is cured at normal room temperature.temperature, even the application of pressure is not required. There is no emission of volatile or other by-products, only slight shrinkage is observed. Thus, in order to manufacture a product, expensive bulky installations are not needed, and there is no need for thermal energy, thanks to which enterprises quickly master both large-capacity and small-capacity production. Do not forget about the low cost of polyester resins - this figure is two times lower than that of epoxy counterparts.

Production growth

It is impossible to ignore the fact that at the moment the production of unsaturated polyester resin is gaining momentum every year - this applies not only to our country, but also to general foreign trends. According to experts, this situation will certainly continue in the foreseeable future.

Disadvantages of resins

Of course, polyester resins also have some disadvantages, like any other materials. For example, styrene is used as a solvent during production. It is flammable and highly toxic. At the moment, such brands have already been created that do not have styrene in their composition. Another obvious drawback: flammability. Unmodified, unsaturated polyester resins burn just like hardwoods. This problem is solved: powder fillers are introduced into the composition of the substance (low molecular weight organic compounds containing fluorine and chlorine, antimony trioxide), sometimes chemical modification is used - tetrachlorophthalic,chlorendic acid, some multimers: vinyl chloroacetate, chlorostyrene, other compounds that contain chlorine.

Resin Composition

If we consider the composition of unsaturated polyester resins, here we can note a multicomponent mixture of chemical elements of different nature - each of them performs certain tasks. The main components are polyester resins, they perform different functions. For example, polyester is the main component. It is a product of the polycondensation reaction of polyols that react with anhydrides or polybasic acids.

If we talk about polyhydric alcohols, then diethylene glycol, ethylene glycol, glycerin, propylene glycol, dipropylene glycol are in demand here. As anhydrides, adipic, fumaric acids, phthalic and maleic anhydrides are used. Casting of polyester resin would hardly be possible if polyester had a low molecular weight (about 2000) when ready for processing. In the process of molding products, it turns into a polymer with a three-dimensional network structure, high molecular weight (after curing initiators are introduced). It is this structure that provides chemical resistance, high strength of the material.

Solvent-monomer

Another obligatory component is the solvent monomer. In this case, the solvent performs a dual function. In the first case, it is required in order to reduce the viscosity of the resin to a level that is required for processing (since the polyester itselftoo thick).

On the other hand, the monomer takes an active part in the process of copolymerization with polyester, due to which an optimal polymerization speed and a high depth of material cure are ensured (if polyesters are considered separately, their curing is rather slow). Hydroperoxide is the very component that is required to solidify from a liquid state - this is the only way polyester resin acquires all its qualities. The use of a catalyst is also mandatory when working with unsaturated polyester resins.

Accelerator

This ingredient can be added to polyesters both during manufacture and when processing takes place (before the addition of the initiator). Cob alt s alts (cob alt octoate, naphthenate) can be called the most optimal accelerators for polymer curing. Polymerization must not only be accelerated, but also activated, although in some cases it is slowed down. The secret is that if accelerators and initiators are not used, free radicals will independently form in the finished substance, due to which polymerization will occur prematurely - right during storage. To prevent this phenomenon, a curing retarder (inhibitor) is indispensable.

Inhibitor principle

The mechanism of action of this component is as follows: it interacts with free radicals that periodically arise, resulting in the formation of low-active radicals or compounds that do not have a radical nature at all. The function of inhibitors is usually performed by suchsubstances: quinones, tricresol, phenone, some of the organic acids. Polyesters are formulated with small amounts of inhibitors during manufacture.

Other supplements

The components described above are the main ones, it is thanks to them that it is possible to work with polyester resin as a binder. However, as practice shows, in the process of forming products, a sufficiently large amount of additives is introduced into polyesters, which, in turn, carry out a variety of functions and modify the properties of the original substance. Among these components, powder fillers can be noted - they are introduced specifically to reduce shrinkage, reduce the cost of the material, and increase fire resistance. It should also be noted glass fabrics (reinforcing fillers), the use of which is due to an increase in mechanical properties. There are other additives: stabilizers, plasticizers, dyes, etc.

Glass mats

Both in thickness and in structure, fiberglass can be different. Glass mats are fiberglass that are chopped into small pieces, their length varies between 12-50 mm. The elements are glued together using another temporary binder, which is usually a powder or emulsion. Epoxy polyester resin is used for the manufacture of glass mats, which consist of fibers arranged randomly, while fiberglass in its appearance resembles an ordinary fabric. To achieve the highest possible strength, different grades of fiberglass should be used.

In general, glass mats have lessstrength, but they are much easier to process. When compared with fiberglass, this material better repeats the shape of the matrix. Since the fibers are quite short, have a chaotic orientation, the mat can hardly boast of great strength. However, it can be very easily impregnated with resin, since it is soft, while being loose and thick, somewhat reminiscent of a sponge. The material is really soft and moldable. Laminate, for example, which is made from such mats, has excellent mechanical properties, has a high resistance against atmospheric conditions (even within a long period).

Where glass mats are used

Mat is used in the field of contact molding to be able to produce goods with complex shapes. Products made from this material are used in a variety of areas:

• in the shipbuilding industry (building canoes, boats, yachts, fish cutters, various internal structures, etc.);
• Glass mat and polyester resin are used in the automotive industry (various machine parts, cylinders, vans, diffusers, tanks, information panels, housings, etc.);
• in the construction industry (certain wood products, building bus shelters, partition walls, etc.).

Glass mats have different density, as well as thickness. The material is divided by the weight of one square meter, which is measured in grams. There is a fairly thin material, almostairy (glass veil), there is also a thick one, almost like a blanket (used to ensure that the product acquires the desired thickness, obtains the required strength).