Plasticizers are an important component of many adhesives and sealants. A plasticizer is an additive used to increase flexibility or workability of a polymer system. Plasticizers typically affect the viscosity, lower the glass transition temperature (Tg), and lower the elastic modulus of a product. By making the adhesive/sealant more elastic, it helps to prevent cracking or delamination under stress or temperature changes. In cold environments, rigid adhesives may fail. Plasticizers maintain flexibility at low temperatures, preventing brittle failure.
Phthalates and terephthalates are an example of effective plasticizer chemistries used in caulks and sealants. This group includes plasticizers such as Dibutyl Phthalate (DBP), DIHP, Diisononyl Phthalate (DINP), Dioctyl Terephthalate (DOTP), and DPT. Dibenzoate plasticizers such as Dipropylene Gycol Dibenzoate are also commonly used. Plasticizers are typically chosen based on polymer compatibility and the desired properties of the end product. By choosing a plasticizer that is compatible with the polymer, it protects the plasticizer for leaching out of the product and thus losing the benefits of plasticization. Plasticizer permanence, or resistance to migration out of the adhesive or sealant, plays a role in the longevity of a product. Permanence can be affected by weathering such exposure to sunlight and extreme temperatures, or extraction by substances such as soapy water. Loss of plasticizer results in stiffening, shrinkage or the caulk or sealant becoming brittle.
Generally speaking, sealants composed of acrylics, polyvinyl acetate (PVA), and polyvinyl chloride (PVC) would do will with phthalates, terephthalates, benzoates, and epoxidized oils such as Epoxidized Soybean Oil (ESO). Polyamides and polysulfides may do well with a phosphate ester such as Tributyl Phosphate (TBP) or Trioctyl Phosphate (TOF), whereas, Polyurethanes and epoxies might be better off with use of polymeric polyesters. The amount of plasticizer needed varies by formulation, but can be anywhere between 5 – 50% of the product by weight.
Common Applications:
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Construction sealants (e.g., expansion joints)
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Pressure-sensitive adhesives (e.g., tapes and labels)
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Automotive adhesives (e.g., weatherstrip bonding)
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Flexible packaging laminates
Common Plasticizers in Adhesives and Sealants
| Plasticizer Type | Chemical Family | Key Properties | Advantages | Limitations | Typical Applications |
|---|---|---|---|---|---|
| Dioctyl Phthalate (DOP) | Phthalate | Medium viscosity, good compatibility | Cost-effective, widely available | Regulatory restrictions (toxicological concerns) | PVC-based sealants, construction adhesives |
| Diisononyl Phthalate (DINP) | Phthalate | High molecular weight, low volatility | Good permanence and flexibility | Restricted in some regions | Automotive sealants, flexible adhesives |
| Di(2-ethylhexyl) Adipate (DOA) | Adipate | Low Tg, low viscosity | Excellent low-temp performance | Lower plasticizing efficiency than phthalates | Flexible packaging adhesives, cold-temp sealants |
| Acetyl Tributyl Citrate (ATBC) | Citrate (bio-based) | Biodegradable, low toxicity | FDA-approved, phthalate-free | Higher cost, lower permanence | Medical adhesives, food contact sealants |
| Epoxidized Soybean Oil (ESBO) | Bio-based (epoxidized oil) | High molecular weight, non-toxic | Renewable, good heat stability | Compatibility issues with some polymers | Green sealants, eco-friendly adhesive formulations |
| Sebacates (e.g., DOS, DBS, DMS) | Sebacate | Excellent cold flex, low volatility | High performance in cold climates | Higher cost, limited availability | Aerospace sealants, cold storage adhesives |
| Paraffinic Mineral Oil | Petroleum-derived (aliphatic) | Low polarity, light color | Good UV resistance, stable, low odor | Limited compatibility with polar resins | PSAs (especially SIS-based), hygiene tapes |
| Aromatic Mineral Oil | Petroleum-derived (aromatic) | High solvency, polar | High tack, excellent compatibility with rubber | Color instability, VOC concerns | PSAs using butyl/SBS rubber, industrial tapes |
| Naphthenic Mineral Oil | Petroleum-derived (cyclic) | Intermediate polarity, balanced solvency | Good low-temp flexibility, processability | Moderate UV stability, may yellow over time | PSAs, automotive tapes, rubber-based sealants |
| Castor Oil | Bio-based (hydroxylated triglyceride) | Reactive, hydroxyl functional | Renewable, chemically bonds to PU, flexible, hydrolysis resistant | Slower cure rate, higher viscosity | Polyurethane adhesives & sealants, moisture-cured systems |