Cresyl Diphenyl Phosphate (CDP)

Cresyl Diphenyl Phosphate (CDP)

1. Chemical Identification and Properties

Chemical Name: Cresyl Diphenyl Phosphate

Common Abbreviation: CDP

CAS Number: 26444-49-5

Molecular Formula: C₁₉H₁₇O₄P

Appearance and Characteristics: CDP is typically a clear, viscous, colorless to pale yellow liquid. It may have a mild, characteristic aromatic odor. It is an organophosphorus compound belonging to the aryl phosphate esters family.

2. Primary Functions and Applications

CDP is predominantly used as a flame retardant and plasticizer in various polymer systems. Its key applications include:

Vinyl Polymers: It is extensively used as a primary or secondary plasticizer in Polyvinyl Chloride (PVC) formulations. CDP imparts flexibility and, crucially, flame retardancy to soft PVC products like wire and cable insulation, roofing membranes, and flooring.

Engineering Plastics: It is an important additive in engineering thermoplastics and their blends, such as modified Polyphenylene Oxide (PPO), polycarbonate alloys, and polyamides (nylons). In these applications, it provides effective flame resistance while maintaining good mechanical properties.

Rubber Industry: CDP is used as a flame-retardant plasticizer in various synthetic and natural rubber compounds.

Specialty Fluids: In some cases, it is also employed as an additive in hydraulic fluids, lubricants, and other functional fluids.

3. Mechanism of Action

The effectiveness of CDP stems from its dual functionality:

Flame Retardancy: CDP acts mainly in the gas phase. When exposed to fire, it thermally decomposes to generate phosphorus-containing radical species. These radicals efficiently scavenge the high-energy hydrogen (H·) and hydroxyl (OH·) radicals that propagate the combustion chain reaction in the flame, thereby quenching the fire.

Plasticization: As a plasticizer, CDP works by interposing itself between the polymer chains. This reduces the polymer-polymer chain interactions, increasing the free volume and thus making the material more flexible, extensible, and easier to process.

4. Health, Safety, and Environmental Considerations

As with many organophosphate esters, there are important health and environmental considerations associated with CDP.

Toxicology: While generally considered to have low to moderate acute toxicity compared to some halogenated flame retardants, CDP can pose health risks upon exposure. Toxicological studies have indicated potential for neurotoxicity, developmental toxicity, and endocrine-disrupting effects. Appropriate handling procedures and personal protective equipment (PPE) are essential to minimize inhalation, ingestion, and dermal contact.

Environmental Impact: CDP is considered a substance of concern due to its potential for persistence and bioaccumulation. It can leach out from products during their use and disposal, and it has been detected in various environmental matrices, including indoor dust, water, and sediments.

Regulatory Status: The use of CDP is subject to chemical regulations in many regions, such as the European Union's REACH regulation. Its application in electronic and electrical equipment must also comply with directives like the EU RoHS (Restriction of Hazardous Substances).

In summary, Cresyl Diphenyl Phosphate is a commercially significant flame-retardant plasticizer valued for its performance in polymers like PVC and engineering plastics. However, its potential health and environmental impacts necessitate careful handling, responsible use, and adherence to all relevant regulatory guidelines.