INVESTIGATION OF THE WOOD/ PHENOL-FORMALDEHYDE ADHESIVE

232 Pages·2002·2.18 MB·English

INVESTIGATION OF THE WOOD/ PHENOL-FORMALDEHYDE
ADHESIVE INTERPHASE MORPHOLOGY

By

Marie-Pierre G. Laborie

A Dissertation Submitted to the Faculty of Virginia Polytechnic Institute
and State University
in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY
in
Wood Science and Forest Products

Approved by:

Charles E. Frazier, Chairman
Wolfgang G. Glasser
Frederick A. Kamke
Eva Marand
Thomas C. Ward
Alan Esker

February 1, 2002
Blacksburg, Virginia

Keywords: Wood /Adhesive Interphase, Glass transition, Cooperativity Analysis,
Solid -State NMR

Copyright 2002, Marie-Pierre G. Laborie
INVESTIGATION OF THE WOOD/ PHENOL-
FORMALDEHYDE INTERPHASE MORPHOLOGY

by
Marie-Pierre G. Laborie
C.E. Frazier, Chairman
Wood Science and Forest Products
ABSTRACT

This work addresses the morphology of the wood/ Phenol–Formaldehyde (PF)
adhesive interphase using yellow-poplar. In this case, morphology refers to the scale or
dimension of adhesive penetration into wood. The objective is to develop methods for
revealing ever smaller levels of wood/resin morphology. Dynamic techniques that are
commonly utilized in polymer blend studies are investigated as potential methods for
probing the wood/ adhesive interphase morphology. These are Dynamic Mechanical
Analysis (DMA) and solid state NMR using CP/MAS. PF resin molecular weight is
manipulated to promote or inhibit resin penetration in wood, using a very low or a very
high molecular weight PF resin.
With DMA, the influence of PF resin on wood softening is investigated. It is first
demonstrated that the cooperativity analysis according to the Ngai coupling model of
relaxation successfully applies to the in-situ lignin glass transition of yellow-poplar and
spruce woods. No significant difference in intermolecular coupling is detected between
the two woods.
It is then demonstrated that combining simple DMA measurements with the
cooperativity analysis yields ample sensitivity to the interphase morphology. From
simple DMA temperature scans, a low molecular weight PF (PF-Low) does not influence
lignin glass transition temperature. However, the Ngai coupling model of relaxation
indicates that intermolecular coupling is enhanced with the low molecular weight PF.
This behavior is ascribed to the low molecular weight PF penetrating lignin on a
nanometer scale and polymerizing in-situ.
i
On the other hand, a high molecular weight resin with a broad distribution of
olecular weights (PF-High) lowers lignin glass transition temperature dramatically. This
plasticizing effect is ascribed to a small fraction of the PF resin being low enough in
molecular weight to penetrate lignin on a nanoscale, but being too dispersed for forming
a crosslinked network.
With CP/MAS NMR, intermolecular cross-polarization experiments are found
unsuitable to probe the angstrom scale morphology of the wood adhesive interphase.
However, observing the influence of the PF resins on the spin lattice relaxation time in
the rotating frame, HT1r , and the cross-polarization time (TCH) is useful for probing the
interphase morphology. None of the resins significantly affects the cross-polarization
time, suggesting that angstrom scale penetration does not occur with a low nor a high
molecular weight PF resin. However, the low molecular weight PF substantially
modifies wood polymer HT1r , indicating that the nanometer scale environment of wood
polymers is altered. On the other hand, the high molecular weight PF resin has no effect
on wood HT1r . On average, the high molecular weight PF does not penetrate wood on a
nanometer scale. Interestingly, the low molecular weight PF resin disrupts the spin
coupling that is typical among wood components. Spin coupling between wood
components is insensitive to the high molecular weight PF. Finally, it is noteworthy that
the two PF resins have significantly different T1r ‘s in-situ. The low molecular weight
resin T1r lies within the range of wood relaxations, suggesting some degree of spin
coupling. On the other hand, the T1r of the high molecular weight PF appears outside the
range of wood relaxations. Spin coupling between the high molecular weight resin and
wood components is therefore inefficient.
The CP/MAS NMR and DMA studies converge to identify nanometer scale
penetration of the low molecular weight PF in wood. On the other hand, the high
molecular weight PF resin forms separate domains from wood, although a very small
fraction of the PF-High is able to penetrate wood polymers on a nanoscale.
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Il faut bien quel qu’en soit le prix,
faire un peu de musique
avec cette vie unique.

Nicolas Bouvier

A ma mère,
Modèle d’un certain grain de folie,

A mon père,
Modèle du plus fort, du plus beau et surtout du plus intelligent,

A mes soeurs,
Modèles chacunes à leur façon,

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ACKNOWLEDGEMENTS

When one starts a Ph.D., one has little appreciation of the road to follow.
However, never can one find and follow its road without the guidance and support of
teachers, colleagues and friends. I would like to spend some time thanking the teachers
colleagues and friends that have been on my road and have helped me walk to its end.
Dr. Charles Frazier, my advisor and committee chair, has provided me with the
scientific guidance and encouragement to find my personal interest in research. These
five years of work in his group have been an astonishing experience. There have been
the most fulfilling and thrilling hours of my student career but also some of the darkest
hours. I am especially thankful of his patience and trust during the completion of part of
this research on the other side of the Atlantic.
I would like to express my gratitude to my committee members, Dr. Wolfgang
Glasser, Dr. Frederick Kamke, Dr. Eva Marand and Dr. Thomas Ward for assisting me
and sharing their knowledge and enthusiasm in many occasions during the course of this
work. I am especially indebted to Dr. Wolfgang Glasser for introducing me to Dr.
Lennart Salmén. Without his kind support, the viscoelastic research presented in this
dissertation may not have seen the day. Dr. Alan Esker has agreed to serve on my
committee in several occasions. I am thankful for his time and constructive insight on
my work.
The viscoelastic studies presented in this dissertation have been performed at the
Swedish Research Institute for Pulp and Paper (STFI) in Stockholm. I am indebted to Dr.
Lennart Salmén for sharing his time, facilities and expertise with me. The work of
Lennart Salmén will remain for me a model of one’s most thorough, rigorous and
dedicated contribution to a particular aspect of wood science. I am also grateful to Ann-
Mari Olsson and Joanna Hornatowska for their technical assistance and kindness.
Working among Anna, Federica, Jesper, Martin, Maggan and Suzanne has been a
wonderful experience.
The NMR studies have been performed in the department of Chemistry at
Virginia Tech. The technical assistance of Tom Glass for the CP/MAS NMR studies is
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gratefully acknowledged. Dr. Robert Schmidt and Dr. Reginald Mbachu at Dynea are
also acknowledged for their assistance in molecular weight analysis.
Warm thanks also go to the students, staff and faculty in Wood Science and at the
Center for Adhesive and Sealant Science. Nikki Robitaille has been my labmate and
friend during my graduate career. It has been a pleasure to share many hard working
hours and free time with her.
Friends and family, here and there, have been part of this work. In many
occasions they have provided the moral support necessary for the completion of this
work. Without the friends from all countries and cultures I have had a chance to
appreciate, my stay in Blacksburg would not have been such a rich experience. I am
especially indebted to Laurence who supported me in many ways during the writing
period. I am also thankful for the friends at home that have remained my friends years
and kilometers apart. I hope they will forgive my absence in those numerous occasions
when one expects friends to be at one’s side.
Last but not least, the project of earning a Ph.D. degree would never have come to
my mind without the guidance, support and model of one of my former professors. Dr.
Tony Pizzi has exerted a decisive influence on the course of my life. He first inspired
“my fire” for wood science and chemistry through being my teacher, through his
dedication to science and through his incredible enthusiasm. I cannot thank him enough
for affecting so positively the course of my life.

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TABLE OF CONTENTS

ABSTRACT i
ACKNOWLEDGEMENTS iii
TABLE OF CONTENTS vi
LIST OF FIGURES ix
LIST OF TABLES xvi

I BACKGROUND 1
CHAPTER. I.1. INTRODUCTION 2

CHAPTER. I.2. PHENOL-FORMALDEHYDE RESINS 11
I.2.1 SYNTHESIS OF RESOLE PREPOLYMERS 11
I.2.2 SYNTHESIS CONDITIONS AND PREPOLYMER PROPERTIES 17
I.2.3 PF RESIN CURE 20

CHAPTER. I.3. VISCOELASTIC PROPERTIES OF POLYMERS 26
I.3.1 INTRODUCTION 26
I.3.2 DYNAMIC MECHANICAL ANALYSIS 27
I.3.3 TEMPERATURE DEPENDENCE OF POLYMER PROPERTIES 32
I.3.4 GLASS FORMATION THEORIES 35
I.3.5 VISCOELASTIC PROPERTIES OF WOOD 50
I.3.6 CONCLUSIONS 57

CHAPTER. I.4. CP/MAS NMR OF POLYMERS 58
I.4.1 INTRODUCTION 58
I.4.2 NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY-BASIC CONCEPTS 59
I.4.3 SOLID STATE NMR TECHNIQUES 62
I.4.4 CP/MAS NMR, A PROBE OF POLYMER BLEND MORPHOLOGY 66
I.5 REFERENCES 77
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II DYNAMIC METHODS 88
CHAPTER. II.1. INTERMOLECULAR CP AT THE WOOD/PF INTERPHASE 89
II.1.1 INTRODUCTION 89
II.1.2 LAB-SCALE SYNTHESIS OF PARAFORMALDEHYDE 92
II.1.3 PREPARATION OF A CONTROL 13C PF RESIN 103
D/H
II.1.4 INTERMOLECULAR CP EXPERIMENTS AT THE WOOD/PF INTERPHASE 106
II.1.5 CONCLUSION 113
II.1.6 REFERENCES 114

CHAPTER. II.2. COOPERATIVITY ANALYSIS FOR LIGNIN GLASS TRANSITION 116
II.2.1 INTRODUCTION 116
II.2.2 MATERIALS AND METHODS 119
II.2.3 RESULTS AND DISCUSSION 124
II.2.4 CONCLUSION 138
II.2.5 REFERENCES 139

CHAPTER. II.3. TECHNIQUE FOR IN-SITU CURE CHARACTERIZATION 141
II.3.1 INTRODUCTION 141
II.3.2 MATERIALS AND METHODS 141
II.3.3 RESULTS AND DISCUSSIONS 143
II.3.4 CONCLUSION 147
II.3.5 REFERENCES 148
III MOLECULAR WEIGHT DEPENDENCE OF THE WOOD/PF INTERPHASE
MORPHOLOGY 149
CHAPTER. III.1. MATERIALS 150
III.1.1 INTRODUCTION 150
III.1.2 PF RESIN SYNTHESIS AND CHARACTERIZATION 150
III.1.3 PREPARATION OF WOOD /PF COMPOSITES 153
III.1.4 CONTROL SAMPLES 162
III.1.5 CONCLUSIONS 163
III.1.6 REFERENCES 164
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CHAPTER.III.2. PF INFLUENCE ON THE VISCOELASTIC PROPERTIES OF WOOD 165
III.2.1 INTRODUCTION 165
III.2.2 MATERIALS AND METHODS 166
III.2.3 RESULTS 168
III.2.4 DISCUSSION 184
III.2.5 CONCLUSIONS 192
III.2.6 REFERENCES 194

CHAPTER. III.3. PF INFLUENCE ON CP/MAS NMR RELAXATIONS OF WOOD POLYMERS
195
III.3.1 INTRODUCTION 195
III.3.2 MATERIALS AND METHODS 195
III.3.3 RESULTS 197
III.3.4 DISCUSSION 203
III.3.5 CONCLUSIONS 208
III.3.6 REFERENCES 209
IV CONCLUSIONS 210

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LIST OF FIGURES

FIGURE I.1.1. SCANNING ELECTRON MICROGRAPH OF YELLOW-POPLAR, (FROM [2]).......3
FIGURE I.1.2. SCHEMATIC OF WOOD CELL WALL STRUCTURE (FROM [2]).........................5
FIGURE I.1.3. MOLECULAR SCALE MORPHOLOGY OF WOOD POLYMERS............................7
FIGURE I.2.1. REACTIVE PHENOXIDE ION UNDER BASIC CONDITIONS..............................12
FIGURE I.2.2. ELECTROPHILIC AROMATIC SUBSTITUTION OF METHYLENE GLYCOL ON
PHENOL ORTHO (TOP) AND PARA (BOTTOM) POSITIONS............................................13
FIGURE I.2.3. CHELATE RING INTERMEDIATE IN SODIUM HYDROXIDE BASED CATALYSIS
...................................................................................................................................13
FIGURE I.2.4. DI(HYDROXYBENZYLAMINE) (LEFT) AND TRI(HYDROXYBENZYLAMINE)
(RIGHT) INTERMEDIATES IN AMMONIA BASED CATALYSIS OF PF POLYMERIZATION 14
FIGURE I.2.5. HMP DERIVATIVES ....................................................................................15
FIGURE I.2.6. QUINONE METHIDE FORMATION FROM HMPS............................................15
FIGURE I.2.7. CONDENSATION REACTIONS VIA QUINONE METHIDE INTERMEDIATES......16
FIGURE I.2.8. MECHANISM FOR METHYLENE ETHER BRIDGE FORMATION.......................16
FIGURE I.2.9. CROSSLINKING REACTIONS PROPOSED BY MACIEL (AFTER [31])...............21
FIGURE I.2.10. ETHER EXCHANGE BETWEEN PHENOLIC HYDROXYL AND ETHER BRIDGE
PROPOSED BY SOLOMON’S GROUP (AFTER [33])........................................................22
FIGURE I.2.11. GENERALIZED TIME-TEMPERATURE-TRANSFORMATION (TTT) CURE
DIAGRAM, (AFTER [37]).............................................................................................23
FIGURE I.3.1. MECHANICAL ANALOGS, GDE, AND DYNAMIC STRESS-STRAIN VECTORS
FOR AN ELASTIC MATERIAL, A VISCOUS MATERIAL AND A VISCOELASTIC MATERIAL
(ADAPTED FROM [54])...............................................................................................28
FIGURE I.3.2. RELATIONSHIP BETWEEN THE DYNAMIC PROPERTIES IN A DMA
EXPERIMENT..............................................................................................................30
FIGURE I.3.3. GENERALIZED MAXWELL MODEL..............................................................31
FIGURE I.3.4. RELAXATION SPECTRUM AND DYNAMIC MECHANICAL PROPERTIES (AFTER
[54])...........................................................................................................................32
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