Polyformaldehyde (commonly called PFA) is a solid polymer of formaldehyde, formed by polymerizing formaldehyde gas. Its chemical formula is HO(CH₂O)ₙH, where n typically ranges from 8 to 100 repeating units. At room temperature, it appears as a white crystalline powder, particles, flakes, or pearl-like solid, with a pungent odor unique to formaldehyde because it slowly decomposes and releases formaldehyde vapor. Its CAS number is 30525-89-4, and it is widely used as a convenient solid source of formaldehyde for industrial and laboratory applications.
Unlike gaseous formaldehyde or liquid formalin (an aqueous formaldehyde solution), polyformaldehyde is a concentrated, low-moisture solid. It has no true melting point. Instead, when heated between 120 °C and 180 °C, it decomposes (depolymerizes) back into formaldehyde monomer gas. This reversible depolymerization is its most important chemical property: users can release formaldehyde as needed by heating or mixing it in water under alkaline conditions.
| Property | Specification / Value |
|---|---|
| IUPAC Name | Polyoxymethylene / Polyformaldehyde |
| Common Synonyms | PFA, Polymerized formaldehyde, Paraform |
| CAS Registry Number | 30525-89-4 |
| Chemical Formula | HO(CH2O)nH (n=8–100) |
| Formaldehyde Content | 90.0% – 97.0% (commercial grade) |
| Appearance | White crystalline powder, granules, or flakes |
| Odor | Characteristic pungent, irritating aldehyde odor |
| Melting Point | 120 °C to 170 °C (decomposes with gas evolution) |
| Flash Point | Approx. 70 °C (158 °F) (closed cup) |
| Auto-ignition Temperature | Approx. 300 °C (572 °F) |
| Bulk Density | 0.50−0.80 g/cm3 |
| Solubility | Insoluble in cold water, soluble in hot water with depolymerization |
A common point of confusion is that polyformaldehyde is different from formalin. Formaldehyde is an aqueous solution containing 37-40% formaldehyde (by weight) and a stabilizer. Polyformaldehyde is a dry solid with much lower moisture content, making it ideal for reactions where excess water can disrupt resin curing or chemical synthesis.
Because of its high formaldehyde content per unit mass and ease of handling, polyformaldehyde is widely used in life science research and commercial manufacturing.
In molecular biology, histology, and pathology, tissue preservation is crucial. Fixation preserves cell morphology, prevents autolysis, and stabilizes macromolecular structures.
Crosslinking mechanism: When recombined into a 4% formaldehyde aqueous solution, the aldehyde group mainly reacts with the uncharged primary amino group of lysine residues in the protein, forming a covalent methylene bridge
Advantages of methanol-free imaging: Unlike commercial formalin, fresh PFA solution contains no methanol. As a coagulation fixative, methanol can cause membrane permeation, lipid extraction, and artificial epitope masking. Therefore, PFA fixation is crucial for confocal laser scanning microscopy, super-resolution microscopy (STED, PALM/STORM), and flow cytometry.
In industrial chemistry, polyformaldehyde is an important source of formaldehyde in anhydrous organic reactions and low-water systems.
Thermosetting resin: It is a key reactant in producing phenolic resin, urea-formaldehyde resin, and melamine-formaldehyde resin for plywood adhesives, laminates, and particleboard.
Specialty Chemicals: PFA is used to synthesize agricultural chemicals (such as glyphosate herbicides), pharmaceuticals, dye intermediates, and polyacetal plastics (polyoxymethylene engineering thermoplastics).
Due to its broad-spectrum antibacterial, bactericidal, and antifungal properties, polyformaldehyde is applied for biosafety and decontamination:
Gas fumigation: Heating and drying polyformaldehyde in a sealed enclosure releases formaldehyde gas, commonly used to purify biosafety cabinets (BSCs), animal husbandry facilities, and poultry hatcheries.
Agricultural preservation: It acts as a preservative and fungicide in specialized agricultural storage systems.
Paraformaldehyde is classified as a hazardous chemical and a potent occupational health risk. It poses acute toxicological hazards upon inhalation, ingestion, or skin contact, and releases formaldehyde vapors, which are classified as a known human carcinogen.
Inhalation Risks: Inhaling PFA dust or formaldehyde vapors causes severe upper respiratory irritation, coughing, bronchospasms, and chemical pneumonitis. Chronic exposure is linked to nasopharyngeal cancer and leukemia.
Skin and Eye Contact: Direct contact causes acute skin irritation, chemical burns, and allergic contact dermatitis (skin sensitization). Eye exposure can cause severe corneal damage or irreversible blindness.
Carcinogenicity & Mutagenicity: Both the International Agency for Research on Cancer (IARC, Group 1) and the US National Toxicology Program (NTP) classify formaldehyde as a confirmed human carcinogen.
To minimize exposure risks when working with paraformaldehyde, laboratories and industrial plants must implement strict engineering controls and personal protective equipment (PPE):
Engineering Controls: Always weigh, dissolve, and handle PFA solid and liquid formulations inside a certified chemical fume hood. Never handle open containers on an open bench.
Personal Protective Equipment (PPE):
Gloves: Nitrile gloves provide basic splash protection (double-gloving recommended). For prolonged exposure, use butyl rubber or neoprene gloves.
Eye & Face Protection: Chemical splash goggles or a full-face safety shield.
Body Protection: Buttoned laboratory coat with long sleeves and closed-toe chemical-resistant footwear.
Respiratory Protection: If working outside a fume hood during maintenance or large-scale spill response, use a NIOSH-approved half-mask or full-face respirator fitted with organic vapor/formaldehyde cartridges.
Storage Requirements: Keep containers tightly closed in a cool, dry, well-ventilated area away from direct sunlight, ignition sources, heat, and incompatible materials (such as strong oxidizing agents, strong acids, and bases).
Hazardous Waste Disposal: Collect all liquid PFA waste and contaminated solid materials (pipette tips, tubes, gloves) in designated, labeled hazardous chemical waste containers. Follow local regulatory and environmental safety guidelines for neutralization protocols (e.g., treating with glycine, ammonium carbonate, or specialized aldehyde neutralizers).
Q1: Is polyformaldehyde the same as formaldehyde?
A1: No. Polyoxymethylene is a polymer composed of many connected formaldehyde units. It becomes an active formaldehyde monomer only after depolymerization.
Q2: Can polyformaldehyde dissolve directly in cold water?
A2: No, polyformaldehyde is almost insoluble in cold water. To dissolve and depolymerize it into an aqueous formaldehyde solution, the water must be heated to about 55-60 ℃, catalyzed by trace amounts of alkaline compounds such as sodium hydroxide.
Q3: What are the advantages of polyformaldehyde over formalin?
A3: Formaldehyde has a high concentration and is almost anhydrous. It avoids excessive water that can damage resin polymerization and reduces transportation weight and cost.
Q4: Is polyformaldehyde used in food?
A4: No. Industrial polyformaldehyde is not food-grade and must not contact food or drinking water.
Polyformaldehyde is a practical solid formaldehyde polymer widely used in resin manufacturing, chemical synthesis, and biological fixation. Its key advantage is controllable depolymerization: it remains stable during storage and releases formaldehyde only when needed. If you are purchasing raw materials for amino resin, adhesive, or fine chemical production, polyformaldehyde is usually a better choice than liquid formalin when low moisture content is required. If you need it, please get in touch with us!