Plasticizers for Adhesives and Sealants

Plasticizers for Adhesives and Sealants In this issue, we examined the topic of plasticizers. As is known, plasticizers are one of the commonly used additives in adhesive and sealant formulations. They enhance the performance of adhesives by creating the much-needed flexibility, optimizing viscosity, toughness, setting time functionality, impact resistance and even adhesion. A plasticizer is an additive used to increase the flexibility or processability of a polymer system. Plasticizers typically affect viscosity, lower the glass transition temperature and reduce the elastic modulus of a product. Phthalates and terephthalates are examples of effective plasticizing chemicals used in sealants and putties. This group includes plasticizers such as Butyl Benzyl Phthalate (BBP), DIHP, Diisononyl Phthalate (DINP), Dioktyl Terephthalate (DOTP) and DBT. Dibenzoate plasticizers such as Dipropylene Glycol Dibenzoate are also commonly used. Plasticizers are typically selected based on polymer compatibility and the desired properties of the final product. By selecting a plasticizer compatible with the polymer, migration of the plasticizer out of the product is prevented, thus avoiding loss of plasticizing benefits. Plasticizer permanence or resistance to migration from adhesive or putty plays a role in the longevity of a product. Permanence can be affected by exposure to weather conditions such as sunlight and extreme temperatures or extraction with substances such as soapy water. Loss of plasticizer causes hardening, shrinkage or brittleness of the sealant or putty. Putties made from acrylics, polyvinyl acetate (PVA) and polyvinyl chloride (PVC) generally work well with phthalates, terephthalates, benzoates and epoxidized oils such as Epoxidized Soya Oil (ESO). Polyamides and polysulfides may yield good results with a phosphate ester such as Tributyl Phosphate (TBP) or Trioctyl Phosphate (TOF), while polyurethanes and epoxies may perform better with the use of polymeric polyesters. The amount of plasticizer required varies depending on the formulation, but can range from 5-50 per cent by weight of the product. However, due to increasing complexity in adhesive and sealant formulations each year, you need to select a specific plasticizer to modify the characteristics of your formulations in a particular direction to meet requirements. By understanding the fundamentals of plasticizers used in adhesives and sealants, how to achieve the desired flexibility should be well learned.

Plasticizer Requirements

Plasticizers are used in all types of adhesive and sealant formulations. They are primarily used for the final bond and to provide improved low-temperature properties. However, plasticizers can also provide additional benefits that are important to both the formulator and the end user. Many different resins and plasticizers are used with adhesives and putties. There are many general chemical plasticizer families and multiple types. This makes the process of selecting a plasticizer for a specific adhesive or sealant formulation a very difficult task.

Plasticizers should be considered with regard to:

• Compatibility with the base polymer in the formulation, • The final properties the formulator is trying to achieve, • The type of processing the adhesive will be exposed to during assembly and application.

Use of Plasticizers in Adhesives and Sealants

Similar to diluents, plasticizers are non-volatile solvents for the base resin and, when added to the formulation, separate polymer chains and allow them to deform more easily. In this way, plasticizers can improve both the processing properties and also the final properties of the adhesive. Plasticizers can also be one of the cheapest additives used in adhesives and putties and can be used in relatively large concentrations depending on the application and formulation. For these reasons, they are sometimes used as extenders with the aim of reducing costs. Plasticizers generally affect the viscoelastic properties of the base resin; whereas diluents simply reduce the viscosity of the system. While diluents ultimately result in brittle, rigid adhesive systems, plasticizers result in increased flexibility and lower modulus. Plasticizers have been used to give polymers a permanent adhesive character (pressure sensitivity) or to regulate the adhesion-cohesion balance to provide removability. For example, plasticizers can be incorporated into removable pressure-sensitive adhesives to soften the adhesive and thus improve peel and clean removal. In adhesives and sealants, plasticizers also have numerous secondary functions driven by both; these are expectations regarding improvements in the polymer's original physical properties, expectations for improvements in the processing properties of the formulation. For example, plasticizers can be used to provide softness and flexibility, but they can also be used to increase melt processability, compounding efficiency or reduce drying time in water-based systems. In some cases, they also perform additional functions such as flame retardancy. Plasticizers are important for adapting the application and property requirements of these products. As Boyss Petrokimya, we are pleased to celebrate our 5th anniversary. We have managed to place ourselves among the leading companies in the sector with the products and services we provide to our customers and stakeholders. We hope to achieve new successes in the years to come. Sertaç Güler Technical Sales Manager Boyss Petrokimya