How to choose the best plasticizer for PVC and how does it work?
Selecting the optimal plasticizer for polyvinyl chloride (PVC) is a crucial consideration in various industries, ranging from construction to automotive manufacturing. The choice of plasticizer profoundly influences the flexibility, durability, and overall performance of PVC-based materials. There are some key factors to consider when choosing the best plasticizer for PVC that contribute to enhancing the material's properties. Understanding the role of plasticizers in PVC applications is essential for ensuring product quality and meeting specific performance requirements in diverse applications.
Flexible PVC, a widely used polymer to enhance the quality of our daily life
Many polymers can help produce plastic materials used in various industry segments where tailor-made formulations meet required specifications. Polyvinyl chloride (PVC) is the third largest consumed polymer and one of the most versatile polymers used in rigid, semi-rigid and flexible applications. Flexible PVC offers safety, softness and creativity. Compared to other polymers, PVC is:
- Durable
- Energy efficient, as it takes less energy to produce than many alternative plastic materials
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Cost effective
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Inherently fire retardant, due to chlorine content, offering fire safety
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Versatile, printable and paintable
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Adaptable, can be processed in multiple manufacturing operations
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Chemically resistant
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Recyclable and recycled
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Vinyl flooring
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PVC is a thermoplastic polymer that can be processed and reprocessed to be rigid or flexible, highly valued for its durability making it the material of choice for markets such as building and construction where long life-span of minimum 10 to 20 years and beyond are needed.
Many PVC products are required to be flexible to endure physical stress without breaking and to give specific attributes such as softness, flexibility and extensibility.
How plasticizers make PVC flexible?
Plasticizers are substances that are used in plastics or other materials to impart processability, flexibility, extensibility or other properties to the finished plastic material. Plasticizers make PVC highly flexible and impart the mechanical properties needed in each applications to make PVC soft and easy to shape. The process of plasticization is about developing strong attractive intermolecular forces between PVC and plasticizers (hydrogen bonding, Van Der Waals interaction, dispersion forces,…) brought in by polarity differences.
When the PVC resin is melted and fused, a network of strong physical bonds between individual PVC chains is created resulting in a stiff and rigid plastic material. The addition of plasticizers to PVC before fusion, increases the free volume between PVC chains and weakens the interactions between two adjacent PVC chains. This created free volume allows PVC chains to move past each other, increasing flexibility and extensibility.
Rigid versus Flexible PVC
Most workable plasticizers for PVC are esters for increased interaction with PVC chains. A phthalate is made by reacting an acid (phthalic acid) with two alcohols. The reaction is called esterification. When the acid used is ortho-phthalic acid, the plasticizer is called ortho-phthalate. When the acid used is tere-phthalic acid, the plasticizer is called tere-phthalate. They are isomers of each other: same chemical formula (same density, molecular weight) but different chemical structures. They are both phthalate plasticizers and calling tere-phthalates non-phthalates is not scientifically correct.
What are the key selection drivers for a plasticizer?
The bulk of useful plasticizers are phthalates, in particular ortho-phthalates. They can be divided into low and high molecular weight. Low molecular weight phthalates can be further divided into ortho and tere-phthalates. High molecular weight ortho-phthalates improve your processing and offer a high degree of permanency. There are no high molecular weight tere-phthalates, because they lack sufficient processability and compatibility with PVC. Actually DOTP is process able but not as compatible with PVC. Outside phthalates, several specialty plasticizers are offered to meet different needs, for example aliphthatics like adipates, sebacates, cyclohexanoates; trimelllitates; benzoates; phosphates; citrates; alkyl sulfonate and various specialty esters derived from vegetable oils with different degree of performance, permanence and compatibility but often quite costly.
Of course, not all plasticizer manufacturing processes are the same as some involve either more manufacturing steps or more complex manufacturing steps or different feedstock. As a result, not all plasticizers have the same chemical structure and performance.
Similar to your smartphone, the selection of the right plasticizer out of the large number of commercially available products requires meeting key attributes for a given application.
The first requirement for a plasticizer is to be compatible and permanent. In other words, stay in the finished article. Plasticizers need also to be thermally stable in order to sustain severe thermal processing and aging conditions.
Mixing plasticizers with PVC and processing the mixture need to be cost effective. Plasticizers are processing aids and influence converters processes like extrusion, calendaring, dipping, spread coating,…). Primary plasticizers like DINP, DIDP are versatile, suited to a wide range of applications and processes.
Since over 85 % of the PVC applications are durable (over 10 years lifespan), durability over harsh aging conditions is a key requirement. Therefore UV resistance, migration and extraction resistance of selected plasticizers are key requirements.
Plasticizers need to be safe for use but also safe in use: you have to consider wire insulation or sheathing becoming brittle due to migration or loss of plasticizers.
Finally sustainability gets more and more in the focus. Consumer products and also technical articles have to be sustainable. Life cycle analysis is a mean to evaluate the environmental impact of your products over their life span.