Polyester resins: production and handling

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

Production of resins: first stage

How does the production of polyester resins start? This process begins with the distillation of oil - during this period, various substances are released: benzene, ethylene and propylene. They are necessary for the production of anti-hydrides, polybasic acids, glycols. After the joint cooking, all these components create a so-called base resin, which at a certain stage needs to be diluted with styrene. The last substance, for example, can be 50% of the finished product. Within the framework of this stage it is also possible to sell the already prepared resin, but the production stage is not yet over: do not forget about the saturation with various additives. It is thanks to such constituents that the finished resin acquires its unique properties.

The composition of the mixture can vary by the manufacturer - there is a lot that depends on where the polyester resin will be used. Experts select the most optimal combination, the result of this work will be substances with completely different properties.

Production of resins: second stage

It is important that the finished mixture is solid - usually waiting for the polymerization process to come to an end. If it was interrupted, and the material was on sale, it was only partially polymerized. If nothing is done with it, the polymerization will continue, the substance will necessarily 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 - for this use of refrigerators, there is no hardening.

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

The course of the polymerization process is controlled - the proportions of the components are controlled. Since a potentially explosive mixture can result from contact between the catalyst and the activator, the latter is usually introduced into the resin solely within the production, a catalyst is added before use, it is usually supplied separately. Only when the polymerization process is completely finished, the substance will harden, we can conclude that the production of polyester resins is over.

Starting resins

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

This process is called curing, since it occurs in a few hours at ordinary temperature. When the resin is in a solid state, it resembles a tough, durable material that is easy to paint in a variety of colors. As a rule, it is used in combination with fiberglass (polyester fiberglass), it serves as a structural element for the manufacture of various products - such is a polyester resin. The instruction when working with such mixtures is very important. It is necessary to comply with each of its points.

Main advantages

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

Production growth

One can not ignore the fact that at present the production of unsaturated polyester resin is gaining momentum every year - this applies not only to our country, but also to general foreign trends. If you believe the opinion of experts, this situation is sure to remain in the foreseeable future.

Disadvantages of resins

Of course, polyester resins also have some drawbacks, like any other materials. For example, during production, styrene is used as a solvent. It is flammable, very 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: powdered fillers (low-molecular organic compounds containing fluorine and chlorine, antimony trioxide) are sometimes introduced into the composition of the substance, sometimes chemical modification is used-tetrachlorophthalic, chloroendic acids are introduced, some multimers: vinylchloroacetate, chlorostyrene, and other compounds that contain chlorine.

Composition of resins

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

If we talk about polyhydric alcohols, then there is demand for diethylene glycol, ethylene glycol, glycerin, propylene glycol, dipropylene glycol. As anhydrides, adipic, fumaric acids, phthalic and maleic anhydrides are used. The casting of polyester resin would hardly have been possible had the polyester been in a state of readiness for processing with a low molecular weight (about 2000). During the molding process, it is converted into a polymer having a three-dimensional network structure, a high molecular weight (after the curing initiators are introduced). It is this structure that provides chemical resistance, high strength of the material.

Solvent-monomer

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

On the other hand, the monomer takes an active part in the copolymerization with polyester, thereby ensuring an optimum polymerization rate and a high curing depth of the material (if polyesters are considered separately, their curing takes place rather slowly). Hydroperoxide is the same component that is required to convert to a solid state from a liquid - only so that all its qualities are acquired by polyester resin. The use of the catalyst is also mandatory when working with polyester unsaturated resins.

Accelerator

This ingredient can be incorporated into the polyesters both at the time of manufacture and when processing takes place (before the initiator is introduced). To cure polymers, the most optimal accelerators are cobalt salts (cobalt octoate, naphthenate). Polymerization should not only be accelerated, but also activated, although in some cases it is slowed down. The secret is that if you do not use accelerators and initiators, free radicals will be formed in the finished substance , due to which the polymerization will occur prematurely - directly during storage. To prevent this phenomenon, you can not do without a retarder (inhibitor) curing.

The principle of the inhibitor

The mechanism of action of this component is this: it interacts with free radicals, which periodically arise, as a result, the formation of low-active radicals or compounds that do not have a radical nature. The function of inhibitors is usually performed by such substances: quinones, tricresol, phenon, some of the organic acids. In the composition of polyesters, inhibitors are introduced in small quantities during manufacture.

Other additives

The components described above are basic, 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 molding products a large number of additives are introduced into polyesters, which in turn carry a variety of functions, modify the properties of the starting material. Among these components can be noted powder fillers - they are introduced specifically to reduce shrinkage, reduce the cost of material, increase fire resistance. It should also be noted fiberglass (reinforcing fillers), the use of which is due to increased mechanical properties. There are other additives: stabilizers, plasticizers, dyes and so on.

Glass mats

As for the thickness, so the structure of glass fibers can be different. Glass fibers - fiberglass, which are chopped in small pieces, their length varies within the range of 12-50 mm. The elements are glued together with another temporary binder, which is usually a powder or an emulsion. Epoxy polyester resin is used for the manufacture of glass mats, which consist of fibers, located randomly, fiberglass with its appearance resembles ordinary fabric. To achieve the maximum possible hardening, you should use different grades of fiberglass.

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

Where to use glass mats

Mat finds its application in the sphere of contact molding, so that it is possible to produce goods of complex shapes. Products made from such material are used in a variety of areas:

• In the shipbuilding industry (construction of canoes, boats, yachts, fish cutters, various internal structures, etc.);
• Glass mat and polyester resin are used in automotive production (various parts of machines, cylinders, vans, diffusers, cisterns, information panels, cases, etc.);
• In the construction industry (certain elements of wooden products, the construction of bus stops, dividing partitions, etc.).

Glass mills have different density, as well as thickness. Separate the material by the weight of one square meter, which is measured in grams. There is a fairly thin material, almost airy (glasswool), there is also a thick, almost like a blanket (used to ensure that the product has the required thickness, has the required strength).