Alexei Volkov
Plasticizers are small molecules with low molecular weight that are added to polymers to improve their flexibility and make them easier to shape and mold. They are commonly added to plastics such as PVC to facilitate the handling of raw materials during fabrication or to meet the demands of the end product's application. The addition of plasticizers affects the polymer structures by reducing the glass transition temperature and viscosity of the polymer, enhancing its flexibility and processability. Plasticizers work by embedding themselves between the chains of polymers, acting as a buffer and increasing the free volume. The selection of plasticizers depends on various factors such as solubility parameters, molecular weight, and chemical structure. The migration of plasticizers from the polymeric matrix over time can impact the physical and mechanical properties of the polymer.
Characteristics and Values of Adding Plasticizers to Polymer Structures
| Characteristics | Values |
|---|---|
| Plasticizers are added to polymers to | Facilitate the handling of raw materials during fabrication or to meet the demands of the end product's application |
| Plasticizers are | Small molecules with low molecular weight and low volatility |
| Plasticizers make polymers | More flexible, easier to shape and mold, and reduce friction on the surface |
| Plasticizers reduce | Glass transition temperature, viscosity, and modulus of a polymer |
| Plasticizers enhance | Flexibility, processability, and solubility |
| Plasticizer migration | May result in a substantial loss of plasticizer with resultant stiffening of the PVC |
| Plasticizers are compatible with | PVC, acrylates, and cellulose-type plastics |
| Plasticizers are selected based on | Low toxicity, compatibility with the host material, nonvolatility, and expense |
| Plasticizers are divided into four families | Phthalates, Dicarbonates, Phosphates, and Ortho-phthalates |
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What You'll Learn
- Plasticizers improve the flexibility of polymers
- Plasticizers lower the glass transition temperature of polymers
- Plasticizers migrate from the polymer matrix over time
- Plasticizers are added to raw polymers to make them easier to shape and mould
- Plasticizers are selected based on cost-performance evaluation
Plasticizers improve the flexibility of polymers
Plasticizers are small molecules with low molecular weight that are added to polymers to improve their flexibility and processability. They are commonly added to plastics such as PVC to make them softer, more flexible, and elastic. PVC, without plasticizers, is hard and brittle. However, with the addition of plasticizers, it becomes suitable for various applications, including vinyl siding, roofing, vinyl flooring, plumbing, and electric wire insulation.
The flexibility of polymers is enhanced by plasticizers through the reduction of the glass transition temperature (Tg). Tg is a critical property of polymers, indicating the temperature at which a polymer transitions from a hard, glassy state to a soft, rubbery state. Plasticizers lower Tg, resulting in a more flexible polymer. The amount of plasticizer added is directly proportional to the flexibility achieved; the more plasticizer added, the more flexible the polymer becomes.
Plasticizers work by embedding themselves between the chains of polymers, increasing the ""free volume" or spacing between the polymer chains. This disruption of polymer-polymer interactions leads to a decrease in viscosity and an increase in the plasticity of the material. The efficiency of plasticization is influenced by factors such as the molar mass, physical size, and solubility parameters of the plasticizer. Additionally, the chemical structure, molecular weight, and compatibility between the plasticizer and the polymer play a role in determining the effectiveness of plasticization.
The selection of plasticizers is based on specific criteria, including low toxicity, compatibility with the host material, non-volatility, and cost. Phthalate esters, for instance, are commonly used plasticizers in PVC due to their compatibility and ability to meet the desired performance characteristics. However, due to regulatory concerns, there has been a shift towards alternative plasticizers, especially in Europe.
While plasticizers improve flexibility, they can also present challenges. Over time, plasticizers may migrate from the polymer matrix, leading to changes in the physical and mechanical properties of the polymer. This migration can result in the stiffening of the polymer and the softening of other materials that come into prolonged contact with the plasticized polymer. To address this issue, strategies such as increasing the molecular weight of the plasticizer and adding nanoparticles of minerals have been explored.
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Plasticizers lower the glass transition temperature of polymers
Plasticizers are small molecules with low molecular weight that are added to polymers to promote their plasticity and flexibility. They are commonly added to polymers and plastics such as PVC to facilitate the handling of the raw material during fabrication or to meet the demands of the end product's application.
The glass transition temperature (Tg) is a critical property of polymers, measuring their chain mobility. It is the temperature at which a polymer transforms from a hard, glassy material to a soft, rubbery material. When a polymer is cooled below this temperature, it becomes hard and brittle, like glass. Plasticizers are used to lower the glass transition temperature of polymers, making them more pliable and easier to work with.
Plasticizers achieve this by embedding themselves between polymer chains, breaking down polymer-polymer interactions. This increases the free volume of the polymer material, allowing segmental diffusion to occur at a lower temperature. The polymer chain segments are relatively free to move and maintain their mobility at lower temperatures. This reduction in secondary interactions between polymer segments means that segmental mobility requires less energy, and the glass transition temperature decreases.
The effect of plasticizers on the glass transition temperature is influenced by factors such as temperature, plasticizer concentration, and chemical structure. At a certain concentration, known as the crossover concentration, a plasticizer can decrease the modulus of a material. Additionally, external plasticization reduces Tg more effectively than internal plasticization. The type of plasticizer used also plays a role, with plasticizers that have long chains being more effective than small molecules.
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Plasticizers migrate from the polymer matrix over time
Plasticizers are small molecules with low molecular weight. They are commonly added to polymers and plastics such as PVC to enhance their flexibility and processability. However, one of the main challenges with plasticizers is their tendency to migrate from the polymer matrix over time. This migration can occur through gas volatilization, liquid extraction, or solid migration.
Plasticizer migration can have several negative consequences. Firstly, it can lead to unwanted changes in the material's properties, such as reduced flexibility, toughness, and extensibility. This can limit the range of applications for the plasticized polymers, especially in areas where high material flexibility is required, such as films, cables, and tubing. Secondly, plasticizer migration can result in the contamination of the surrounding environment, including food, water, and air, which may pose risks to human health.
The migration of plasticizers is influenced by various factors, including the interaction between the polymer and the plasticizer. If the polymer and plasticizer do not mix well, migration is more likely to occur. Additionally, the mobility, ease of diffusion, efficiency of the plasticizer, and temperature play a role in determining the magnitude of migration.
To prevent plasticizer migration, manufacturers can use reactive plasticizers that chemically graft into the polymer matrix, making it difficult for the plasticizer to migrate out. Another method is to use specialist plasticizers with a high molecular weight or a high degree of branching, which hinders their movement within the polymer network. Coating the surface of the material can also prevent migration by creating a barrier that the plasticizer cannot pass through.
While plasticizer migration can be challenging to manage, it is important to note that ongoing research is focused on developing new methods to eliminate or hinder this process. By understanding the mechanisms and kinetics of plasticizer migration, scientists can work towards improving the performance and longevity of plasticized polymers.
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Plasticizers are added to raw polymers to make them easier to shape and mould
PVC, without plasticizers, is hard and brittle. However, with the addition of plasticizers, it becomes suitable for products such as vinyl siding, roofing, vinyl flooring, and electric wire insulation. Plasticizers are also added to concrete formulations to make them more fluid for pouring and workable, thus reducing the water content. Similarly, they are added to clays, stucco, solid rocket fuel, and other pastes before moulding and forming.
Plasticizers work by inserting themselves between the molecular chains of the polymer. This insertion reduces the intermolecular forces between the chains, allowing them to slide past each other more easily and reducing the material's overall viscosity. Plasticizers enhance the flexibility, softness, and flow characteristics of the polymer, making it easier to handle and shape.
The molecules of the plasticizer take control of the mobility of the polymer chain. If the plasticizer/water creates hydrogen bonds with hydrophilic parts of the polymer, the associated free volume can be decreased. The effect of plasticizers on elastic modulus depends on both temperature and plasticizer concentration. At a certain concentration, known as the crossover concentration, a plasticizer can decrease the modulus of a material.
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Plasticizers are selected based on cost-performance evaluation
Plasticizers are selected based on a cost-performance evaluation. Ester plasticizers are commonly chosen for their cost-effectiveness. The rubber compounder must evaluate ester plasticizers for compatibility, processibility, permanence, and other performance properties. The wide variety of ester chemistries in production include sebacates, adipates, terephthalates, dibenzoates, glutarates, phthalates, azelates, and other specialty blends. This broad product line provides an array of performance benefits required for various applications.
The selection of plasticizers is based on multiple criteria, including cost, compatibility with the host material, non-volatility, and low toxicity. Phthalate esters of straight-chain and branched-chain alkyl alcohols are commonly chosen as they meet these specifications. Ortho-phthalate esters were once the most dominant plasticizers, but due to regulatory concerns, there has been a shift towards non-classified substances, including high-molecular-weight ortho-phthalates and other alternatives, particularly in Europe.
The cost-performance evaluation considers the effectiveness of plasticizers in modifying the thermal and mechanical properties of polymers. Plasticizers are low-molecular-weight substances added to polymers to enhance their plasticity and flexibility. They improve the processability of polymers, making them more suitable for applications such as film coating. The molecules of the plasticizer embed themselves between the polymer chains, disrupting the polymer-polymer interactions and increasing the free volume.
The choice of plasticizer also depends on the specific application and the desired properties. For example, in wire and cable applications, plasticizers with high temperature performance are preferred, such as ditridecyl phthalate (DTDP), which is the highest molecular weight phthalate plasticizer. In contrast, for automotive interiors, trimellitates are used for their resistance to high temperatures. Energetic plasticizers, which increase the specific energy yield of the material, are often selected for rocket propellants, but non-energetic plasticizers may be used due to safety or cost considerations.
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Frequently asked questions
Plasticizers are small molecules with low molecular weight that are added to polymers and plastics to improve their flexibility, make them easier to shape and mold, and reduce friction on their surface.
Plasticizers work themselves into the polymer chains, acting like a buffer between the segments of molecules. They enhance the polymer's flexibility and processability. Plasticizers also reduce the glass transition temperature of the polymer, which is the temperature at which a polymer transforms from a hard, glassy material to a soft, rubbery material.
Examples of plasticizers include polyethylene glycol 6, triethyl citrate, propylene glycol, and glycerin.
