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Transcript of EBP 216 Exp 2
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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
point from thepreceding column)
0 No objective
5 Objective present
Total = 5%
Experimental(choose one type of
point from thepreceding column)
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
preceding column isthe total points for
this category)
10 Conclusion highlights of results and theirsignificance
Total = 10%
Language(stated in the
preceding column isthe total points for
this category)
5Ability to relay technical information with
relatively simple statement
Total = 5%
Format andpunctuality(stated in the
preceding column isthe total points for
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)