Phenol formaldehyde resin

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Chemical compound

Phenol formaldehyde resins (PF) (phenolic resins or phenoplasts[1]) are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Used as the basis for Bakelite, PFs were the first commercial synthetic resins. They have been widely used for the production of molded products including billiard balls, laboratory countertops, and as coatings and adhesives. They were at one time the primary material used for the production of circuit boards but have been largely replaced with epoxy resins and fiberglass cloth, as with fire-resistant FR-4 circuit board materials.

There are two main production methods. One reacts phenol and formaldehyde directly to produce a thermosetting network polymer, while the other restricts the formaldehyde to produce a prepolymer known as novolac which can be moulded and then cured with the addition of more formaldehyde and heat.[2][3] There are many variations in both production and input materials that are used to produce a wide variety of resins for special purposes.

Formation and structure

Phenol-formaldehyde resins, as a group, are formed by a step-growth polymerization reaction that can be either acid- or base-catalysed. Since formaldehyde exists predominantly in solution as a dynamic equilibrium of methylene glycol oligomers, the concentration of the reactive form of formaldehyde depends on temperature and pH.

Phenol reacts with formaldehyde at the ortho and para sites (sites 2, 4 and 6) allowing up to 3 units of formaldehyde to attach to the ring. The initial reaction in all cases involves the formation of a hydroxymethyl phenol:

HOC6H5 + CH2O &#; HOC6H4CH2OH

The hydroxymethyl group is capable of reacting with either another free ortho or para site, or with another hydroxymethyl group. The first reaction gives a methylene bridge, and the second forms an ether bridge:

HOC6H4CH2OH + HOC6H5 &#; (HOC6H4)2CH2 + H2O

2 HOC6H4CH2OH &#; (HOC6H4CH2)2O + H2O

The diphenol (HOC6H4)2CH2 (sometimes called a "dimer") is called bisphenol F, which is an important monomer in the production of epoxy resins. Bisphenol-F can further link generating tri- and tetra-and higher phenol oligomers.

Novolaks

Novolaks (or novolacs) are phenol-formaldehyde resins with a formaldehyde to phenol molar ratio of less than one. In place of phenol itself, they are often produced from cresols (methylphenols). The polymerization is brought to completion using acid-catalysis such as sulfuric acid, oxalic acid, hydrochloric acid and rarely, sulfonic acids.[4] The phenolic units are mainly linked by methylene and/or ether groups. The molecular weights are in the low thousands, corresponding to about 10&#;20 phenol units. Obtained polymer is thermoplastic and require a curing agent or hardener to form a thermoset.

Hexamethylenetetramine is a hardener added to crosslink novolac. At a temperature greater than 90 °C, it forms methylene and dimethylene amino bridges. Resoles can also be used as a curing agent (hardener) for novolac resins. In either case, the curing agent is a source of formaldehyde which provides bridges between novolac chains, eventually completely crosslinking the system.[2]

Novolacs have multiple uses as tire tackifier, high temperature resin, binder for carbon bonded refractories, carbon brakes, photoresists and as a curing agent for epoxy resins.

Resoles

Base-catalysed phenol-formaldehyde resins are made with a formaldehyde to phenol ratio of greater than one (usually around 1.5). These resins are called resoles. Phenol, formaldehyde, water and catalyst are mixed in the desired amount, depending on the resin to be formed, and are then heated. The first part of the reaction, at around 70 °C, forms a thick reddish-brown tacky material, which is rich in hydroxymethyl and benzylic ether groups.

The rate of the base-catalysed reaction initially increases with pH, and reaches a maximum at about pH = 10. The reactive species is the phenoxide anion (C6H5O&#;) formed by deprotonation of phenol. The negative charge is delocalised over the aromatic ring, activating sites 2, 4 and 6, which then react with the formaldehyde.

Being thermosets, hydroxymethyl phenols will crosslink on heating to around 120 °C to form methylene and methyl ether bridges through the elimination of water molecules. At this point the resin is a 3-dimensional network, which is typical of polymerised phenolic resins. The high crosslinking gives this type of phenolic resin its hardness, good thermal stability, and chemical imperviousness. Resoles are referred to as "one step" resins as they cure without a cross linker unlike novolacs, a "two step" resin.

Resoles are major polymeric resin materials widely used for gluing and bonding building materials. Exterior plywood, oriented strand boards (OSB), engineered high-pressure laminate are typical applications.

Crosslinking and the formaldehyde/phenol ratio

When the molar ratio of formaldehyde:phenol reaches one, in theory every phenol is linked together via methylene bridges, generating one single molecule, and the system is entirely crosslinked. This is why novolacs (F:P <1) do not harden without the addition of a crosslinking agents, and why resoles with the formula F:P >1 will.

Applications

Phenolic resins are found in myriad industrial products. Phenolic laminates are made by impregnating one or more layers of a base material such as paper, fiberglass, or cotton with phenolic resin and laminating the resin-saturated base material under heat and pressure. The resin fully polymerizes (cures) during this process forming the thermoset polymer matrix. The base material choice depends on the intended application of the finished product. Paper phenolics are used in manufacturing electrical components such as punch-through boards, in household laminates, and in paper composite panels. Glass phenolics are particularly well suited for use in the high speed bearing market. Phenolic micro-balloons are used for density control. The binding agent in normal (organic) brake pads, brake shoes, and clutch discs are phenolic resin. Synthetic resin bonded paper, made from phenolic resin and paper, is used to make countertops. Another use of phenolic resins is the making of duroplast, famously used in Trabant automobiles.

Phenolic resins are also used for making exterior plywood commonly known as weather and boil proof (WBP) plywood because phenolic resins have no melting point but only a decomposing point in the temperature zone of 220 °C (428 °F) and above.

Phenolic resin is used as a binder in loudspeaker driver suspension components which are made of cloth.

Higher end billiard balls are made from phenolic resins, as opposed to the polyesters used in less expensive sets.

Sometimes people select fibre reinforced phenolic resin parts because their coefficient of thermal expansion closely matches that of the aluminium used for other parts of a system, as in early computer systems[5] and Duramold.

The Dutch painting forger Han van Meegeren mixed phenol formaldehyde with his oil paints before baking the finished canvas, in order to fake the drying out of the paint over the centuries.[citation needed]

Atmospheric re-entry spacecraft use phenol formaldehyde resin as a key component in ablative heat shields (e.g. AVCOAT on the Apollo modules). As the heat shield skin temperature can reach - °C, the resin pyrolizes due to aerodynamic heating. This reaction absorbs significant thermal energy, insulating the deeper layers of the heat shield. The outgassing of pyrolisis reaction products and the removal of charred material by friction (ablation) also contribute to vehicle insulation, by mechanically carrying away the heat absorbed in those materials.

Trade names

• Bakelite was originally made from phenolic resin and wood flour.
• Ebonol is a paper-filled phenolic resin designed as a replacement for ebony wood in stringed and woodwind instruments.
• Novotext is cotton fibre-reinforced phenolic, using randomly oriented fibres.
• Oasis Floral Foam is "an open-celled phenolic foam that readily absorbs water and is used as a base for flower arrangements."

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• Paxolin is a resin bonded paper product long used as a base material for printed circuit boards, although it is being replaced by fiberglass composites in many applications.
• Tufnol is a laminated plastic available as sheet and rods, which is made from layers of paper or cloth which have been soaked with phenolic resin and pressed under heat. Its high resistance to oils and solvents have made it suitable for many engineering applications.

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• Richlite is a paper-filled phenolic resin with many uses, from tabletops and cutting-boards to guitar fingerboards.

Biodegradation

Phenol-formaldehyde is degraded by the white rot fungus Phanerochaete chrysosporium.[8]

See also

References

Phenolic paper laminated sheets are revolutionizing the engineering world. These sheets utilize layers of paper and phenolic resin and boast advantages that suit a wide range of industrial applications. Capital Resin Corporation understands these applications and is here to explain all about the benefits of phenolic paper laminated sheets and their uses in various industries.

What Are Phenolic Paper Laminated Sheets?

Phenolic paper laminated sheets are composite materials fabricated by layering sheets of paper impregnated with phenolic resin and then chemically bonding them through heat and pressure. This process results in a high-density, durable product that exhibits excellent mechanical strength and resistance to heat, moisture, and chemicals.

Phenolic paper laminated sheets are commonly available in various thicknesses, and industries can utilize them in a wide range of practical applications. Some of the more common examples are insulation, structural components, and even decorative surfaces. Because of their versatility and robustness, phenolic paper laminated sheets are incredibly valuable in industries such as aerospace, automotive, and construction, where reliability and performance are critical.

Durability and Strength

One of the primary benefits of phenolic paper laminated sheets is their exceptional durability and strength. These sheets can withstand significant mechanical stress without deforming or breaking. This makes them ideal for use in environments where high strength is essential, such as in electrical insulation and mechanical components.

Products made with this substance are more robust and last longer than those made with traditional materials that may wear out or corrode over time. Phenolic paper laminated sheets do a much better job maintaining their integrity, which provides reliable performance over extended periods.

Electrical Insulation Properties

Phenolic paper laminated sheets have an industry reputation for their excellent electrical insulation properties. This is particularly important in industries where electrical safety and performance are vital, and where employee safety is at a greater risk. These sheets can effectively prevent electrical currents from passing through, reducing the likelihood of short circuits and electrical fires.

Furthermore, their insulating properties contribute to the efficiency and safety of electrical systems. By using these sheets, engineers can design electrical components and systems that operate more reliably and safely, enhancing overall performance.

Temperature Resistance

In addition to their electrical insulation capabilities, one of the other benefits of phenolic paper laminated sheets is that they exhibit impressive temperature resistance. They can withstand both high and low temperatures without compromising their structural integrity or performance. This makes them suitable for use in environments exposed to extreme temperature variations.

Whether used in high-heat industrial processes or in cold storage systems, phenolic paper laminated sheets remain stable and effective. Their ability to perform well under a wide range of temperatures adds to their versatility and makes them a preferred choice for many engineers.

Chemical Resistance

Phenolic paper laminated sheets are highly resistant to chemicals, including acids, alkalis, and solvents. This resistance is beneficial in industries where exposure to harsh chemicals is common. Materials that can deteriorate when exposed to chemicals can lead to failures and safety hazards.

Using phenolic paper laminated sheets helps mitigate these risks. Their chemical resistance ensures that they remain stable and functional even when in contact with aggressive substances. This property extends their application to environments where other materials might fail.

Moisture Resistance

Another notable advantage of phenolic paper laminated sheets is their aversion and resistance to humidity. These sheets do not absorb water, which prevents them from swelling, warping, or degrading over time. This moisture resistance makes them ideal for use in humid or wet conditions.

In applications where moisture exposure is inevitable, such as in marine environments or outdoor settings, phenolic paper laminated sheets maintain their performance and longevity. Engineers can rely on these materials to deliver consistent results, regardless of environmental conditions.

Versatility in Applications

Versatility is one of their most appealing features. Numerous industries can utilize them in a wide range of applications. From electrical and mechanical engineering to aerospace and automotive sectors, these sheets provide solutions to diverse engineering challenges.

Their unique combination of properties, including strength, insulation, and resistance to various environmental factors, allows different fields to tailor them to their specific needs. Engineers can choose use them in custom applications, ensuring optimal performance and efficiency.

Ease of Fabrication

Phenolic paper laminated sheets are also easy to manufacture, which simplifies the fabrication process. An established phenolic resin manufacturer can manufacture phenolic resins for the companies fabricating the laminated sheets. To suit specific applications, other companies may then cut, drill, or shape these sheets with standard tools, making them easy to work with. This ease of fabrication reduces production time and costs, contributing to overall project efficiency.

Their straightforward workability does not compromise their performance. Despite being easy to fabricate, phenolic paper laminated sheets retain all their beneficial properties, ensuring that the final product meets the required standards and specifications.

Cost Effectiveness

Cost is always a significant consideration in engineering projects. Phenolic paper laminated sheets offer a cost-effective solution without sacrificing quality or performance. Their long life span and minimal maintenance requirements translate to lower overall costs.

By electing to use these sheets, engineers can achieve high-performance results while adhering to budget constraints. The initial investment often pays off through reduced maintenance, longer service life, and improved reliability, making them a financially sound choice.

Environmental Impact

Sustainability is becoming increasingly important in engineering practices. Phenolic paper laminated sheets contribute positively to environmental efforts. Their durability and longevity mean less frequent replacements, reducing waste and resource consumption.

Many manufacturers are now adopting eco-friendly practices in the production of these sheets. This includes using renewable resources and minimizing harmful emissions. Engineers who prioritize sustainability can feel confident in choosing phenolic paper laminated sheets as an environmentally responsible option.

Enhancing Performance in Diverse Industries

The benefits of phenolic paper laminated sheets extend across many industries, enhancing performance and efficiency in every field that utilizes them. In the automotive industry, these sheets contribute to lightweight yet strong components. In aerospace, they provide reliable insulation and structural integrity. In electrical engineering, their insulating properties ensure safety and efficacy.

The adaptability and robust performance of these sheets makes them an indispensable material in modern engineering. By leveraging their strengths, engineers can push the boundaries of innovation and design, achieving superior results across various projects.

As you explore innovative materials for your engineering projects, consider partnering with a trusted phenolic resin manufacturer like Capital Resin Corporation. Our commitment to quality and advanced manufacturing techniques ensures that you receive superior phenolic resin that can meet your specific needs. Contact us today to discuss how our products can enhance your applications and contribute to your project&#;s success.

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