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SCHOOL OF MATERIALS AND MINERAL RESOURSES ENGINEERING

ENGINEERING CAMPUS

UNIVERSITI SAINS MALAYSIA

Academic Session 2011/2012

SEMESTER II

EBP 216/2

Polymer Engineering Laboratory

(Makmal Kejuruteraan Polimer)

Experiment Number : EXPERIMENT 2

Experiment Title : PHENOL-FORMALDEHYDE (RESOL) PREPARATION

Date of Experiment : 14 MEI 2012

Date of Submission : 21 MEI 2012

Name : MINCE LEONG YEN SHEE

Group Number : GROUP 3

Lab Report Examiner : DR. RAZAINA

Instructor : Ms. SARA

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EBP 216/2 Polymer Engineering Laboratory - Academic Year: 2011/2012

Lab Report Rubric

Student Name : MINCE LEONG YEN SHEE

Matric No. : 109445

Group : 3

Experiment No. : 2

Experiment Date : 14 MEI 2012

Submission Date : 21 MEI 2012

CONTENT

Category Points Marking Description Categorystotal points

Remark

Briefintroduction

about theexperiment

(choose one type of

point from thepreceding column)

0 No introduction

For these first 3 categories, lecturersonly have to choose options given in

the second column, i.e. 0, 5 or 10marks.

5Poor introduction with insufficient references

or acknowledgement to sources cited

7 Introduction adequate but unoriginalcomposition with fair number of references

10 Well written introduction with originalcomposition and reference or

acknowledgement to sources cited

Total = 10%

Objective(choose one type of


0 No objective

5 Objective present

Total = 5%

Experimental(choose one type of


0 No experimental details

5 Incomplete experimental details

From this category onwards lecturersare given freedom to mark but

according to weightage given in thesecond column for each row ,

For example;

Marks for the:1st row = 13/152nd row = 11/153rd row = 16/20

Total marks for R&D category would

be 40/50

Lecturers can use the supplementarymarking rubric to give marks to these

categories and synchronize themaccording to weightage given in the

second column

10 Complete experimental details

Total = 10%

Results andDiscussion(stated in the

preceding column isthe total points for

this category)

15 Communication of experimental results

15 Interpretation of experimental results

20Ability of presenting and discussing

experimental results in an effective way, i.e.easy to understand

Total = 50%

Conclusion(stated in the


this category)

10 Conclusion highlights of results and theirsignificance

Total = 10%

Language(stated in the


this category)

5Ability to relay technical information with

relatively simple statement

Total = 5%

Format andpunctuality(stated in the


this category)

10Compliance to standard technical report (e.g.

graph & table labeling, content, etc.) andsubmission date

Total = 10%

Total (100%)

CONTENT

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Experiment 2

PHENOL-FORMALDEHYDE (RESOL) PREPARATION

Abstract

Phenolic resins are a family of polymers and oligomers composed of a wide range of

structures based on the various reaction products of phenols with formaldehyde. In this

experiment, we synthesized phenol-formaldehyde resin and investigated its curing

properties. To be able to do that, we have to observe the changes in every stage that occur

throughout the experiment. Its changes of physical appearance such as its colour changes

as well as its stickiness (viscosity) throughout different stage was observed and analyzed.

Other than that, we also checked the solubility of the product in alcohol to indicate the

non-occurrence of crosslink in the product. Generally, the product dissolved in alcohol at

initial stage but as time move on, the cross-linkage formed in the product causing the

immiscible of resin in the solvent.

Keywords: oligomer, phenol-formaldehyde resin, curing, crosslink

1.0 Introduction

Resins are polymers made by repeatedly linking discrete molecules (monomers)

together to form chains or networks. Phenolic resins are oligomers (polymers with a few

repeating units) synthesized by repeatedly linking phenolic (hydroxy-aromatic)

monomers with aldehyde chemicals. Phenolformaldehyde (PF) resins are thermosetting

polymers, which are widely used in many fields. One such application is as wood

adhesives for the manufacture of wood-based composites, including plywood, oriented

strand board (OSB), and fiberboard. [1]The oligomers from alkaline polycondensation

between phenol and formaldehyde (PF) are excellent adhesive resins for wood lamination

(plywood, oriented strandboard, veneer lumber). [2]

Phenol-formaldehyde or phenolic resins are typically cross-linkable polymeric

resins made from phenol and aldehydes, usually pure phenol and formaldehyde. Catalysis

is required to synthesize the polymer. When base is used, the materials are known as

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"Resol" and, when acids are used, the materials are known as "Novolac." [4] Novolac is

one of the phenolic resins made under acidic conditions using excess phenol; the acid

catalyzes the reaction of phenol and formaldehyde to form the cross-linkable polymeric

resin. It is widely used for the formation of moulded pieces and articles. [5]

When the reaction is carried out to high conversion, the result is a highly

crosslinked, often black, hard, tough, impervious solid. Under the reaction conditions,

phenol is trifunctional and formaldehyde is bifunctional, hence a network forms. The

usual procedure is to carry out the reaction in two stages, first to partial conversion so

that the material is still processable, and then finishing off the reaction in the mould to

form the final, impervious, cross-linked material. [4]

1.1 Theory

Phenol formaldehyde for formation of resoles involved 3 stages which are:

A Stage (resoles) is an initial step growth polymerization between phenol and

formaldehyde. Phenol and excess formaldehyde react to produce a mixture of methylol

phenols end groups and very dynamic resins, always advancing toward a cured state.These condense on heating to yield soluble, low molecular weight resoles.

The reaction begins when phenol is deprotonated by the base catalyst to form

phenoxide. The negative charge is accommodated by resonance forms with the charge on

two ortho- positions and the para- position of the ring. These three structures cause

phenol to be trifunctional. Next the phenoxide attacks formaldehyde via ortho- or para-

positions. The reaction can proceed at the other active position to become mono-, di-, and

tri-substituted due to the phenol is a reactive molecule. At further reaction, methylene or

ether bridges may produce that resulted from condensation between methylolphenols and

available ortho- or para- positions. Higher temperatures favour the formation ofmethylene bridges.

Figure 1: Formation of phenoxide. [4]

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Figure 2: Reaction at the ortho- and para- position.[4]

Figure 3: Structure of "methylol" compounds, mono-, di-, and tri-substituted [4]

Figure 4: Formation of ether bridge (up) and methylene bridge (down).[4]

B Stage (resitol) on heating, resoles interact among each other and with other

reaction species present in the system producing larger and mildly crosslink resin

molecule which known as resitol. This represents the second stage of condensation. The

molecule weight of the resin now is larger compare with resoles. Thus resitol is insoluble

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in alkali and alcohol, but partially soluble in acetone. Resitol is softened when heated but

become plastic when cooled.

C Stage (resite) further heating of resitol will turn it into fully cured or crosslink

resin known as resite. The C stage resin is totally insoluble and infusible. This stage is a

category as the final stage of phenol formaldehyde polymerization. High molecular

weight of product is formed due to the formation three-dimensional network.

Figure 5: Highly crosslinked, 3-D network resol structure [4]

Characteristics of phenol-formaldehyde resin at various stages

Stage A:

1. Soluble in alcohol

2. Low viscosity

3. Sensitive to low temperature changes

4. A light brown liquid

5. Low molecular weight

6. short and linear of Polymer chains

7. Easy to flow

Stage B:

1. Insoluble in alcohol

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2. Sensitive to high temperature changes

3. Viscosity higher than resoles

4. Rubbery and brown in colour

5. Lower tendency to flow

6. Higher molecular weight compare with resoles

7. Partially cross-linked in the polymer chain

Stage C

1. Three-dimensional network

2. Stable at high temperature

3. Hard and tough solid

4. Insoluble in alcohol

5. Reddish-brown in colour

6. High molecular weight

2.0 Objectives

To synthesize phenol-formaldehyde resin and to investigate the curing properties of

phenol formaldehyde.

3.0 Experimental

3.1 Materials

a. Phenol (95%)

b. Formalin (37% formaldehyde solution)

c. Sodium hydroxide (40M)

d. Ethanol (95%)

3.2 Apparatus

a. Pyrex reaction vessel

b. Beaker

c. Glass rod

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d. Hot plate stirrer

e. Retort stand and clamp

f. Spatula

g. Glass dropper

h. Measuring cylinder

i. Fume cupboard

j. Thermometer

k. Analytical mass balance

l. Aluminium foil

3.3 Procedure

A resol preparation was done by mixingphenol (10g) with formalin (12ml) in a

reacting vessel followed by addition of NaOH (1ml) at 80C for 1 hour with continuous

stirring. Any physical change of the reacting polymeric resin was noted. After slight

cooling, the upper aqueous layer was decanted. Few drops of the product were dropped in

a beaker of ethanol to check its solubility. Its physical appearance and solubility in

alcohol were noted (A stage). The rest of the product was poured onto an aluminium foilfolded cover.The resin was heated slightly and its physical state was noted by using glass

rod. It melted into a rubbery state (B stage) initially and transformed into a hardened and

infusible state (C stage) finally. At last stage the solubility of the product was tested by

dissolved it in the alcohol solvent again.

Precautious Steps:

1. Phenol and formalin are carcinogenic. Avoid inhaling their vapour and wash with

excess water when they come into contact with skin.

2. Initially, reaction of phenol and formalin is exothermic. Rigorous stirring would

help preventing for any bursting of the reacting mixture. Thus avoid directing the reaction

vessel towards other person.

3. During the weighing of phenol, not only the aqueous shall be taken, the solute

should be taken also.

4. When testing the solubility of resin, ethanol must more than sample.

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5. Make sure to direction test tube is point to away from people to avoid splitting of

chemical solution.

4.0 Result and Discussion

40 M of NaOH was provided in laboratory but the material used in this experiment was

100ml of 5 M NaOH. (Na = 20, O = 16, H = 1)

( )

mlV

V

VMVM

5.12

100540

1

1

2211

=

=

=

Where

1M = Initial Concentration

1V = Initial Volume

2M = Final Concentration

2V = Final Volume

12.5 ml of 40M of NaOH was used to produce 100 ml 5M NaOH.

Procedure Observation IndicationResol preparation The

beaker was hot.

It is

an exothermic

reaction.

Product was subjected to

80oC water bath and

continuous stirred for 1

hour. The solution was

slightly cooled.

2 layers

were formed.

The

upper aqueous layer was

transparent and the lower

layer was light brown in

colour.

Only a

small amount of upper

layer was formed.

This

shows that there is an

increase in viscosity.

The lower layer was tested

with ethanol.

The The

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lower layer was soluble in

ethanol

polymer chains are

short and simple.

There is no cross-link

chain.

The lower layer was

poured onto aluminium

foil folded cover and was

heated slightly.

The

colour intensity of the

solution turned darker and

became sticky resin

Formati

on of obviously air bubble

The

resin slowly hardened with

time and eventually

solidified.

The

heat provided causes

formation of

methylene bridge and

cross-linkage slowly

The

viscosity of the resin

increased upon

heating with time and

becomes rubbery and

then fully hardens.

5. The solubility of final

product was tested with

ethanol.

The

final product was

insoluble in ethanol.

Had a

smooth surface. Did not

contain air bubbles on

surface.

3-D

network of cross-link

is formed throughout

the resin.

Stages of Resol Formation

In the initial stage, phenol is dissolved in formalin (37% formaldehyde solution).

This is due to the formation of hydroxymethyl phenols which known as resoles. Later the

solution added with NaOH which is the base catalyst to deprotonated the phenol

monomer to form phenoxide and then attacked by aldehyde molecule forming methylol

compounds.(Refer to Figure 1,2&3) When the mixture is being subjected to water bath

and continuous stirred in an hour, formation of 2 layers of solution can be observed. The

upper layer refers as water solution while the lower part is considers as resoles.

Condensation takes place with formation of little amount of water molecule that

eliminated as vapour during heating. It is found that the compound is soluble in ethanol

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solvent due to the present of low molecular weight of molecule and less percentage of

crosslink in the compound. This stage of compound is termed as resol or A stage.

The stickiness and viscosity of the resol increases gradually as heat is continuous

supplied to the resol. The colour intensity of the resol becomes darken without formation

of water molecule. When some of the resol is put on a tissue paper, it sticks on it indicate

that its transform in rubbery state. Thus this state is recognized as resitol or B stage.

Resite is formed when the resitol is continuous heated. This is the C stage. This

transformation of stage happens rapidly from rubbery state to fully harden. At this state

the mixture seen to be hardened and turns into reddish-brown colour. The resite resin is

insoluble in ethanol solvent due to the formation of 3-D network that causing a high

molecular weight of resin.

Comparison of novolac and resol preparation

Resol Novolac

Formation of resoles is a one-stage process.

All ingredients are mixed together at one

time.

Formation of novolacs is a two-stage process.

First mixture between phenol, formaldehyde,

and acid. Second stage involves the addition of

curing agent.

Basic catalyst (pH more than 7) is used.

For example: NaOH.

Acid catalyst (pH less than 7) is used. For

example acid catalyst: oxalic, sulphuric acids.

Usually but not necessarily, a molar excess

of formaldehyde is used to make resol

resins. Ratio of phenol to formaldehyde is

1 to 1.5 phenol < formaldehyde.

A molar excess of phenol to formaldehyde are

conditions used to make novolac resins. Ratio

of phenol to formaldehyde is 1 to 0.8 phenol >

formaldehyde.

Experience in 3 stages where in :

A stage involved formation of resol.

B stage involved formation of resitol.

C stage involved formation of resite.

Experience in 2 stages where:

A stage involved formation of novolac.

B stage involved formation of resite.

The base catalyst dephotonate the phenol. The acid catalyst photonate the carbonyl group

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of formaldehyde.

Formation of phenoxide at initial

mechanism of reaction.

Formation of methylol derivatives at initial

mechanism of reaction.

Contains methylene bridge (-CH2-) and

ether linkage (-CH2-O-CH2-).

Methylene bridge is formed by theelimination of the water molecule

Formation of ether linkage

Contains methylene linkage (-CH2-).

Formation of methylene bridges in acidic

condition

Self-crosslinking (cure the resin without

incorporation of a cure agent) due to the

methylol groups

Required crosslinking agent such as

hexamethylenetetramine to complete the

curing process

*By manipulating the phenolic to aldehyde monomer ratio, pH, catalyst type,

reaction temperature, reaction time, and amount of distillation, a variety of resin

structures demonstrating a wide range of properties are possible.

5.0 Conclusion

From the experiment, we learned that the synthesis of phenol-formaldehyde undergoes

different stages. The phenol-formaldehyde resin in different stage has its own properties and

difference. The percentage of crosslinking in the phenol-formaldehyde resin in every stage

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varied causing changes in physical and chemical properties such as the solubility in solvent.

The ability of transformation of stage of the phenol-formaldehyde resin gives good abrasive

properties. In addition, factors like phenolic to aldehyde monomer ratio, pH, catalyst type,

reaction temperature, reaction time, and amount of distillation can give different influence

on the mechanism and properties of product. Thus, with the unique apparent of every stage,

the phenol-formaldehyde is suitable for many conditions in term of application.

6.0 Reference

1. Y. Lei, Q. Wu, K. Lian. (2006). Cure Kinetics of Aqueous PhenolFormaldehyde

Resins Used for Oriented Strandboard Manufacturing: Analytical Technique.

Journal of Applied Polymer Science, Vol. 100: pp 16421650. Wiley Periodicals,

Inc.

2. Gardziella, A., Pilato, L. A., and Knop, A. (2000).Phenolic Resins: Chemistry,

Applications, Standardization, Safety and Ecology. New York: Springer.

3. Peter W. Kopf. (2002). Phenolic Resin.Encyclopedia of Polymer Science and

Technology, Vol.7: pp 322-368. John Wiley & Sons, Inc.

4. Chem424 - Synthetic Polymer Chemistry: Phenol-Formaldehyde and Related

Polymers

http://chem.chem.rochester.edu/~chem424/novolak.htm

5. Xu Junming, Jiang Jianchun and Lv Wei. (2010). PREPARATION OF

NOVOLACS USING PHENOLIC RICH COMPONENTS AS PARTIAL

SUBSTITUTE OF PHENOL FROM BIOMASS PYROLYSIS OILS. ChemicalSociety of Ethiopia, 24(2): pp 251-257.
http://chem.chem.rochester.edu/~chem424/novolak.htmhttp://chem.chem.rochester.edu/~chem424/novolak.htm

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Appendix

Figure 6: The mixture of phenol formaldehyde before heated

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Figure 7: Mixture immersed in water bath

Figure 8: Resol solution (Stage A)

Figure 9: Harden phenol-formaldehyde resin (Stage C)

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