Cresol formaldehyde polymer
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Product Description
Cresol formaldehyde polymer (CFP) is a high-performance phenolic thermoset prepared by acid- or base-catalysed condensation of cresol isomers (o-, m-, p- or their mixtures) with formaldehyde; the pendant –CH₃ group confers modestly higher hydrocarbon compatibility, lower water uptake and slightly greater flexibility than conventional phenol-formaldehyde resins. Depending on the F/C molar ratio and catalyst, either fusible novolacs (F/C < 1, acid-catalysed, cured later with hexa) or self-curing resoles (F/C > 1, base-catalysed, rich in reactive methylol groups) are obtained, both ultimately yielding densely cross-linked networks that display glass-transition temperatures up to ~200 °C, excellent resistance to acids, alkalis and solvents, high hardness and dielectric strength. Industrial grades are now optimised for <0.1 % free formaldehyde and <1 % free cresol, and are etherified with butanol or 2-ethylhexanol to give lower-viscosity, high-solids coatings or plasticised binders. Major applications include adhesive dips for polyester-cord/rubber bonding (replacing toxic RFL systems), heat- and chemical-resistant can and automotive coatings, grinding-wheel binders, moulding compounds, photoresists, ion-exchange/electrode nanomaterials, and bitumen modifiers that raise softening point and aggregate adhesion for longer-lasting asphalt.
Other Information
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Regulatory and Environmental Status: Even low-free-monomer grades of phenolic resins are often classified as harmful to aquatic life. The use of Tricresol Formalin in dentistry is controversial and declining in many regions due to safety concerns, with a search for safer alternatives like chlorhexidine and nanoformulations.
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Comparison to Phenol-Formaldehyde: CFP generally offers slightly better flexibility, lower water absorption, and improved hydrocarbon compatibility than phenol-formaldehyde resins (Bakelite) due to the presence of the methyl group, but it is typically more expensive.
Synthesis and Production
CFP is produced through a polycondensation reaction between cresol isomers (o-, m-, p-cresol) and formaldehyde. The process and catalyst determine the type of resin formed.
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Industrial Polymer Synthesis:
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Method: A step-growth polymerization via electrophilic aromatic substitution.
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Process: Cresol and formaldehyde are reacted under controlled temperature and pressure. The reaction can be acid-catalyzed to produce Novolac resins (thermoplastic, requiring a separate cross-linker like hexamine) or base-catalyzed to produce Resole resins (thermosetting, self-curing upon heat application).
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Optimization: Industrial processes focus on shortening reaction cycles and minimizing residual free formaldehyde and cresol monomers.
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Nanostructured Form (from File 2):
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Method: Nanoencapsulation via the nanoprecipitation method.
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Process: An organic phase containing Tricresol Formalin, a polymer (Poly-ε-caprolactone), a surfactant (Span 60), and an oil (Caprylic/Caproic triglyceride) in acetone is slowly added to an aqueous phase containing a stabilizer (Polysorbate 80). The suspension is stirred and concentrated.
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Purpose: This advanced production method is designed to encapsulate the active agents (formaldehyde and cresol) to control release and reduce cytotoxicity, creating a safer formulation for potential biomedical use.
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Uses and Applications
The applications of CFP are divided between its mature industrial uses and its specialized, albeit controversial, role in dentistry.
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Industrial Applications (Polymerized CFP):
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Coatings and Adhesives: Used for high-temperature, chemically resistant protective coatings and adhesives.
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Electrical Insulation: Serves as a key material for electrical components, laminates, and printed circuit board (PCB) substrates due to its excellent dielectric properties.
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Abrasive and Friction Materials: Primary binder for grinding wheels, brake pads, and clutch facings, leveraging its heat resistance and strength.
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Molding Compounds: Compounded with fillers to produce high-performance parts for automotive, electrical, and laboratory equipment.
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Foundry Resins: Used as binders for sand cores and molds in metal casting.
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Rubber Reinforcement: Cresol-formaldehyde latex (CFL) is used as an adhesive dip for bonding polyester fibers to rubber in tires and conveyor belts.
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Medical/Dental Application (Pre-polymer Form - Tricresol Formalin):
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Primary Use: As an intracanal dressing in endodontics (root canal treatment) for necrotic teeth with periapical lesions. It is used for its potent, long-distance disinfectant action via formaldehyde vaporization.
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Evidence of Efficacy: File 1 demonstrates that Tricresol Formalin, when placed at the canal entrance after initial disinfection with sodium hypochlorite, was completely effective at eliminating Enterococcus faecalis biofilm in an in vitro model.
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Emerging Application: File 2 explores the use of nanoencapsulated Tricresol Formalin to retain antimicrobial efficacy while significantly improving safety for direct contact with human cells.
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Chemical and Physical Properties
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Physical Properties:
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Polymer: High molecular weight, rigid, cross-linked solid. Can be formulated to have high stiffness, hardness, and dimensional stability.
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Tricresol Formalin: A liquid solution with a strong, characteristic odor. It is highly volatile.
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Nanocapsules (from File 2): Mean particle size of ~192 nm, low polydispersity index (PDI ~0.101), zeta potential of ~ -17.7 mV, and acidic pH (~5.48). The formulation reduces the characteristic odor.
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Functional Properties:
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Excellent Heat Resistance: Stable at continuous high temperatures (150-180°C).
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Outstanding Chemical Resistance: Highly resistant to acids, alkalis, solvents, and water.
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Superior Electrical Insulation: High dielectric strength and low electrical conductivity.
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Antimicrobial Activity: The free Tricresol Formalin solution and its nanoencapsulated form show potent antimicrobial efficacy against key pathogens like Enterococcus faecalis, Pseudomonas aeruginosa, and Escherichia coli (File 2).
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Safety and Handling
This is the most critical area of distinction between the polymer and its precursor.
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Cresol Formaldehyde Polymer (Cured):
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Considered to have low toxicity once fully polymerized, as the hazardous formaldehyde and cresol monomers are bound within the cross-linked network.
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Standard industrial handling of solid polymers and composites applies (e.g., dust control during machining).
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Tricresol Formalin (Free Form) - HIGH HAZARD:
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Cytotoxicity and Genotoxicity: File 2 provides conclusive evidence that free Tricresol Formalin is highly cytotoxic to human fibroblasts (HFF-1), with an IC₅₀ of 406.54 µg/mL. It also causes double-stranded DNA damage and induces inflammatory responses (nitric oxide production).
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Carcinogenicity: Formaldehyde, a primary component, is a recognized carcinogen.
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Handling: Requires extreme caution. File 2 specifies the use of an activated charcoal mask, protective goggles, and gloves during handling due to the volatility and toxicity of its components.
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Nanoencapsulated Tricresol Formalin (Safer Alternative):
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Reduced Toxicity: File 2 demonstrates that nanoencapsulation significantly improves safety. The IC₅₀ for the nanocapsules (NCTF) was 1029.03 µg/mL, over 2.5 times higher (less toxic) than the free form, while maintaining equivalent antimicrobial efficacy.
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Improved Safety Profile: The nanostructured form showed no double-stranded DNA damage in tests where the free form was positive, indicating a major reduction in genotoxic risk.
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Stability: The nanocapsule formulation is most stable when stored under refrigeration (4°C) for up to 90 days.
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