How is an elastic material synthesized? Summary of the process

Elastic materials are something that is present in our daily life. There is something for everyone, such as elastic bands to tie bags, rubber bracelets, balls, tires …

Then we will see how an elastic material is synthesized, Explain what are their components, the polymers, in addition to indicating their molecular properties and certain indices which are taken into account in the industry.

    What are Elastic Polymers?

    Elastic materials, called elastic polymers, are those that they can be deformed by the application of a force when it is applied. When the elastic object is no longer subjected to this force, it returns to its original shape. Otherwise, if the material is permanently deformed, we wouldn’t be talking about something elastic, but a plastic material.

    Elastic materials have been known to humans since time immemorial because they exist in nature. However, although polymers are naturally present in objects such as rubber, humans saw the need to create some synthetically, that is to say in the laboratory.

    Some examples of elastic materials, apart from the one already mentioned, we have elastic bands to close food bags, balloons, rubber bracelets, latex …

    What are polymers?

    Polymers are macromolecules formed by the union of covalent bonds of one or more of the single units, What would be the monomers. Usually, these macromolecules are organic, that is, they contain carbon atoms in their structure. These chains are generally long and are linked by Van der Waals forces, hydrogen bonds, and hydrophobic interactions.

    One way to classify polymers is based on their mechanical response to high temperatures. That is why there are two types of polymers.

    1. Thermoplastic polymers

    Thermoplastic polymers they soften when subjected to high temperatures, Even melt. When the temperature is low, they harden. These processes are completely reversible and can be repeated over and over again.

    However, if a very high temperature is reached, irreversible degradation can occur, as the molecular vibrations between the monomers of the substance are so violent that they can break their covalent bonds.

    These materials are typically made with the simultaneous application of high temperature and pressure. As the temperature increases, the resistance of the secondary bonds weakens, Facilitate the relative movement of the chains that make up the polymer.

    Most linear polymers and those with branched structures, with flexible chains, are thermoplastics, which are flexible and ductile.

    2. Thermostable polymers

    Thermostable polymers are those that remain hard regardless of the temperature applied to them.

    When they begin to be subjected to heat, covalent crosses occur between contiguous molecular chains. As a result, the movements between the monomers of the polymer are limited, preventing their vibration and their rotation. However, if the temperature is excessively high, the crosslinks break down and degradation of the polymer occurs.

    In general, thermoset polymers are harder than thermoplastics. Some examples of such polymers are epoxy, vulcanized rubber, and phenolic polyester resins.

    How are elastic materials synthesized?

    Elastic materials are made of elastomers, which are usually thermoplastic polymers, which gives them their main characteristics: elasticity and deformation easy but not permanent.

    There are many substances that can make a material elastic. Some of the polymers used to synthesize elastics are: polyol-polyester, polyisocyanate, copolymers of ethylene and propylene, polyisobutylene, polysulfides and polysiloxane, to name a few.

    When these substances are mixed, they react with each other through different polymerization mechanisms, Including condensation, addition or removal of free radicals.

    Molecular characteristics of elastomers

    In order for the combination of certain polymers to ultimately generate an elastomer or elastic material, the combination of these must create some kind of synergy, resulting in a sum slightly greater than the mere sum of the parts.

    The first requirement is that they have asymmetric structures and, therefore, that they be as different as possible. Their structures at the molecular level must be linear and flexible, allowing, as we have discussed with thermoplastic polymers, that the chains of molecules can vibrate without breaking the bonds.

    The second requirement is the that the polymer is not very polar, that is, it does not have too much charge of either sign, Since in this case the intermolecular interactions will be stronger and there will be greater rigidity due to attraction (as is the case with a positive magnet with a negative).

    The third requirement is that these polymers be flexible., Which admit some deformation when some kind of force is applied to them. In the event that these polymers meet these three requirements, then the ideal situation for the synthesis of an elastomer will be generated.

      Synthesis of elastomers

      The polymers that will give an elastomer must undergo a series of physical and chemical processes.

      1. Crosslinking

      In this process we get that the molecular chains are connected to each other by bridges, Which are capable of forming two or more strong covalent bonds.

      These molecular bridges allow the elastomer to roll on itself at rest or in static mode, while being subjected to a certain type of stretching, it could be in elastic mode thanks to the flexibility of these bonds.

      2. Vulcanization

      While this is a process that would be in intersections, it’s worth mentioning a more detailed explanation alongside.

      Vulcanization is one of the best known processes for obtaining elastomers. In this process, the polymer chains are interconnected by means of sulfur bridges (SSS …).

      3. After getting the elastomer

      Once the elastomers have been synthesized, the next steps are to subject them to different treatments to give them certain characteristics.

      Each material will be used for a different purpose, which is why it will also receive various treatments, Among which we can find heating, molding or other type of physical cures, that is to say to give them shape.

      It is at this stage of the process that the pigments are added to give color to the resulting elastic object, in addition to incorporating other chemicals that will ensure its elasticity. It is also at this stage that three fundamental aspects are evaluated to ensure that the elastic material is of quality: the Young’s modulus, the glass transition temperature (Tg) and the elastic limit.

      Young’s modulus is an index that indicates the behavior of an elastic material depending on the direction in which a force is applied.

      Tg is the temperature at which thermodynamic pseudotransformation occurs in glassy materials. The polymer decreases its density, rigidity and hardness at this temperature. This can be observed in amorphous glasses and inorganic materials.

      The elastic limit refers to the maximum tension that an elastic material can withstand without irreversibly deforming.

      After checking these indices and seeing that the elastomer is functional, it is then that it is generally called rubber of all types: silicone, nitrile, urethane, butadiene-styrene …

      Some elastic materials

      Below we will see some elastic materials and what they are made of.

      1. Polyester

      Polyester is a manufactured fiber and is composed of any polymer of synthetic long-chain origin. In this polymer about 85% of the compound is an ester of tereflalic acid.

      2. Nylon

      Nylon is an artificial polymer belonging to the group of polyamides. It is generated by the polycondensation of an acid such as a diamine. The best known is PA6.6.

      3. Lycra

      Lycra is a synthetic fiber known to be a very elastic and resilient substance. It is a urethane-urea copolymer, composed of approximately 95% segmented polyurethanes. In its elaboration, a wide variety of raw materials are mixed, such as prepolymers, which constitute the main structure of this fiber.

      Bibliographical references.

      • Odian G. (1986) Introduction to the synthesis of elastomers. A: Lal J., Mark JE (eds) Advances in Elastomers and Rubber Elasticity. Springer, Boston, MA

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