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Phenol formaldehyde resin-Wikipedia

Phenol formaldehyde resin

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Phenol formaldehyde resin

Structure of Bakelite

Identifiers

CAS Number

  • 9003-35-4

ChemSpider

  • none

ECHA InfoCard

100.105.516

Edit this at Wikidata

CompTox Dashboard

(EPA)

  • DTXSID2049713

    Edit this at Wikidata

Except where otherwise noted, data are given for materials in their

standard state

(at 25 °C [77 °F], 100 kPa).

Infobox references

Chemical compound

Phenol formaldehyde resins (PF) or phenolic resins 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 (plastics). 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.

[1]

[2]

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[

edit

]

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.

Xem thêm: Indy

Novolacs[

edit

]

Segment of a

novolak

, illustrating the predominance of cresol subunits and presence of

crosslinking

.

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.

[3]

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.

[1]

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[

edit

]

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

laminated composite lumber

(LCL) are typical applications.

Crosslinking and the formaldehyde/phenol ratio[

edit

]

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.

Xem thêm: Một số cách tính tích phân suy rộng

Applications[

edit

]

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, used in the 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

[4]

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.

Trade names[

edit

]

Tufnol (Novotext) plate

  • Bakelite

    was originally made from phenolic resin and

    wood flour

    .

  • 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.”

    [5]

  • 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.

    [6]

  • Ebonol

    is a paper filled phenolic resin designed as a replacement for

    ebony

    wood in

    stringed

    and

    woodwind

    instruments.

Xem thêm: Cấu trúc have to trong tiếng Anh: Ví dụ và bài tập

Biodegradation[

edit

]

Phenol-formaldehyde is degraded by the white rot fungus

Phanerochaete chrysosporium

.

[7]

See also[

edit

]

  • Urea-formaldehyde

  • Para tertiary butylphenol formaldehyde resin

References[

edit

]

  1. ^

    a

    b

    A. Gardziella, L.A. Pilato, A. Knop, Phenolic Resins: Chemistry, Applications, Standardization, Safety and Ecology, 2nd edition, Springer, 2000

  2. ^

    Wolfgang Hesse “Phenolic Resins” in Ullmann’s Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim.

    doi

    :

    10.1002/14356007.a19_371

    .

  3. ^

    Ralph Dammel (1993). “Basic Chemistry of Novolaks”. Diazonaphthoquinone-based Resists. Int. Soc. Optical Engineering.

    ISBN

     

    9780819410191

    .

  4. ^

    J. G. Ferguson, W. E. Grutzner, D. C. Koehler, R. S. Skinner, M. T. Skubiak, and D. H. Wetherell.

    “No. 1 ESS Apparatus and Equipment”

    . The Bell System Technical Journal. 1964. p. 2417.

  5. ^

    “Smithers Oasis Resource Center”

    . Archived from

    the original

    on 7 April 2008. Retrieved 21 October 2010.

  6. ^

    Godwin, R. (April 2015).

    “What is Tufnol?”

    . ahistoryoftufnol.org.

  7. ^

    Gusse AC; Miller PD; Volk TJ (July 2006). “White-rot fungi demonstrate first biodegradation of phenolic resin”. Environmental Science and Technology. 40 (13): 4196–9.

    Bibcode

    :

    2006EnST…40.4196G

    .

    doi

    :

    10.1021/es060408h

    .

    PMID

     

    16856735

    .

Retrieved from “

https://en.wikipedia.org/w/index.php?title=Phenol_formaldehyde_resin&oldid=1025001927

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