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«CURE KINETICS OF WOOD PHENOL-FORMALDEHYDE SYSTEMS By JINWU WANG A dissertation submitted in partial fulfillment of the requirements for the degree of ...»

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CURE KINETICS OF WOOD PHENOL-FORMALDEHYDE SYSTEMS

By

JINWU WANG

A dissertation submitted in partial fulfillment of

the requirements for the degree of

DOCTOR OF PHILOSOPHY

WASHINGTON STATE UNIVERSITY

Department of Civil and Environmental Engineering

May 2007

To the Faculty of Washington State University:

The members of the Committee appointed to examine the dissertation of JINWU WANG find it satisfactory and recommend that it be accepted.

___________________________________

Co-Chair ___________________________________

Co-Chair ___________________________________

___________________________________

ii

ACKNOWLEDGEMENT

Many years’ effort and the gracious assistance of many individuals converge in this dissertation. I would like to express my sincere appreciation and deep gratitude to my co-advisors, Dr. Marie-Pierre G. Laborie and Dr. Michael P. Wolcott, for their financial support, academic suggestions, and discussion. Thanks also to my committee members, Dr. Armando A. McDonald and Dr. Jinwen Zhang, for their examination of my dissertation and their suggestions.

I would like to extend my appreciation to those faculty, staff, and students who were willing to discuss interesting questions and help me learn instrument operations.

These individuals include: Dr. David P. Harper, Dr. Tieqi Li, Dr. J. Andy Soria, Scott Lewis, Bob Duncan, Janet Duncan, Pat Smith, Dr. Donald A. Bender, Dr. Pizhong Qiao, Dr. Vikram Yadama, Dr. Gregory Helms, and Dr. Dan Mitchell. Thanks also to Judy for always being there to offer help. Graduate and post-doctoral fellows who

accompanied me through this course of study and made daily life interesting are:

Barun Gupta, Sudip Chowdhury, Jun Qian, Melchor Maranan, Eric Rude, Elvie Brown, William Gacitua, Dr. Yu Geng, and Dr. Long (Edward) Jiang.

Finally, I thank my daughter Yun, my son Kai, and my wife, Xingwu for their support and love.

iii

CURE KINETICS OF WOOD PHENOL-FORMALDEHYDE SYSTEMS

Abstract

by Jinwu Wang, Ph.D.

Washington State University May 2007 Co-Chairs: Marie-Pierre G. Laborie and Michael P. Wolcott This project aims to develop kinetic models for chemical and mechanical cure development and correlate chemical and mechanical degrees of cure in order to create a comprehensive cure model that encompasses both of these tasks. With these objectives, the cure processes of two commercial phenol-formaldehyde (PF) resol resins with differing molecular weights were evaluated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) under isothermal and linear heating regimes. For both resins, cure was characterized in the neat state with DSC, in mixtures of PF/wood flour with DSC, and as a bondline between two wood substrates with DMA.

The synergy of DSC and DMA techniques picked up the phase transitions of PF curing processes and characterization were comparable between the two techniques. During a DSC temperature scan, PF resols typically exhibited two exotherms, while in wood/PF mixtures another small exotherm appeared in a lower temperature range, indicating the impact of wood/PF interactions. In contrast, DMA offered a quantitative view of the adhesion mechanics from which the glass transition of uncured resin, gelation, and vitrification points were inferred. An analytical solution was developed to estimate the in situ shear modulus of the adhesive layer

–  –  –

storage modulus and the ratio of maximum to minimum storage modulus were recommended for direct evaluation of wood-PF system.

Model-fitting kinetics of nth order and autocatalytic models can be reasonably applied to the DSC data, while autocatalytic, Prout-Tompkins, and Avrami-Erofeev models have been successfully applied to describe cure development in the DMA. The activation energy of PF curing processes in the neat state was around 85-100 kJ/mol and decreased to 50-70 kJ/mol in the presence of wood. However, it was the model-free kinetics of the Kissinger-Akhira-Sunnose, Friedman and Vyazovkin methods that offered insight into the cure mechanisms of commercial PF resoles and predicted the cure development under isothermal and linear heating regimes for both mechanical and chemical degrees of cure. Mechanical cure development has been correlated with chemical advancement in an empirical equation analog to the Weibull cumulative function. After either mechanical or chemical cure development is characterized, the other can be estimated through connection of the correlation equation between the mechanical and chemical degrees of cure.

–  –  –

ACKNOWLEDGEMENT……………………………………………………………iii ABSTRACT..…………………………………………………………………………iv TABLE OF CONTENT……………………………………………………………....vi LIST OF TABLES..………………………………………………………………….xii LIST OF FIGURES..…………………………………………………………………xv Chapter 1 Project Introduction





BACKGROUND

OBJECTIVES

ORGANIZATION OF THE DISSERTATION

REFERENCES

Chapter 2 Quantitative Analysis of Phenol-formaldehyde Resins with 13C-, H-NMR and Gel Permeation Chromatography

Abstract

INTRODUCTION

EXPERIMENTAL

Materials

Acetylation of PF resins

GPC analysis of the acetylated PF resins

H- and quantitative 13C-NMR analyses of the acetylated resins

H- and quantitative 13C-NMR analyses of the neat resins

–  –  –

Molecular weights of the acetylated PF resins by GPC analyses

Chemical structures and molecular weights of the acetylated PF resins by 1H- and C-NMR

Chemical structures and molecular weights of the neat PF resins by 13C- and 1HNMR

Comparison of different methods

CONCLUSION

REFERENCES

Chapter 3 Comparison of Model-fitting Kinetics for Predicting the Cure Behavior of Commercial Phenol-formaldehyde Resins

ABSTRACT

INTRODUCTION

EXPERIMENTAL

Materials

Differential Scanning Calorimetry

Model-Fitting algorithms

RESULTS AND DISCUSSION

PF Cure analysis

Kinetic parameters from model-fitting kinetics

Predicting cure for dynamic conditions

Predicting cure for isothermal conditions

–  –  –

REFERENCES

Chapter 4 Comparison of Model-free Kinetic Methods for Modeling the Cure Kinetics of Commercial Phenol-formaldehyde Resins

ABSTRACT

INTRODUCTION

EXPERIMENTAL

Materials

Differential Scanning Calorimetry

MFK algorithms

RESULTS AND DiSCUSSION

Kinetic parameters from MFK methods

Prediction of dynamic cure of PF resins

Prediction of isothermal cure of PF resins

CONCLUSION

REFERENCES

Chapter 5 The Influence of Wood on the Cure Kinetics of Phenol-formaldehyde Resins

ABSTRACT

INTRODUCTION

EXPERIMENTAL

Materials

–  –  –

Kinetic models

RESULTS AND DISCUSSION

DSC of moist wood

Comparison among different SYP contents

Comparison among wood constituents and species

CONCLUSION

REFERENCES

Chapter 6 Dynamic Mechanical Analyses of Phenol-formaldehyde Bonded Wood Joints

ABSTRACT

INTRODUCTION

OBJECTIVES

EXPERIMENTAL

PF resins

Specimen preparations

DMA and rheology

RESULTS AND DISCUTION

In situ shear modulus development of adhesives

–  –  –

Optimizating DMA derived parameters for directly evaluating a wood-adhesive systems

–  –  –

CONCLUSION

REFERENCES

Chapter 7 Model-fitting Kinetic Analysis of Phenol-formaldehyde Bonded Wood Joints

ABSTRACT

INTRODUCTION

OBJECTIVES

EXPERIMENTAL

PF resins

Specimen preparations

DMA

RESULTS AND DISCUSSION

Characterization of cure development

Activation energy of gelation and vitrification

Sample preparation effects on Tan δ

Mechanical cure development

Model-fitting kinetics

CONCLUSION

REFERENCES

Chapter 8 Kinetic Analysis and Correlation of Mechanical and Chemical Cure Development for Phenol-formaldehyde Resin Bonded Wood Joints

–  –  –

INTRODUCTION

OBJECTIVES

EXPERIMENTAL

PF resin

Specimen preparations

DMA

DSC

RESULTS AND DISCUSSION

Relationship between mechanical cure and chemical cure

Model-free kinetics of the mechanical cure development

CONCLUSION

REFERENCES

Chapter 9 Summary and Conclusions

–  –  –

Table 2.1 Features of the core PF and face PF resins

Table 2.2 Molecular weights of acetylated resins by GPC

Table 2.3 1H-NMR chemical shift of acetylated resins in CDCl3

Table 2.4 Summary of characteristic structures and molecular weights of two acetylated PF resins based on 1H-NMR spectra in CDCl3

Table 2.5 13C-NMR chemical shifts of the acetylated PF resol resin in chloroform-d.

Table 2.6 The ratios of phenolic to other aromatic carbons (1:5) and acetyl methyl to acetyl carbonyl carbons (1:1)

Table 2.7 Summary of characteristic structures and molecular weights of two acetylated PF resins based on 13C-NMR spectra in CDCl3

Table 2.8 1H-NMR chemical shift of neat resins in D2O (Woodbrey et al.

1965)......27 Table 2.9 Summary of characteristic structures and molecular weights of two neat PF resins based on 1H-NMR spectra in D2O

Table 2.10 13C-NMR chemical shifts of PF resins in D2O solvent.

Table 2.11 Summary of characteristic structures and molecular weights of two neat PF resins based on 13C-NMR spectra in D2O.

Table 2.12 Comparison of number average molecular weight (Mn) and degree of polymerization (n) of the neat resins by 1H- and 13C-NMR.

Table 2.13 Comparison of number average molecular weight (Mn) and degree of

–  –  –

Table 3.1 Summary of kinetic models, parameters and methods used

Table 3.2 Summary of PF cure peak temperature, degree of cure at peaks in parenthesis and heat of reaction across 4 heating rates*

Table 3.3 Kinetic parameters for the PF-low and PF-high Resins obtained from the model-fitting kinetic methods.

Table 3.4 Mean squared errors of prediction (MSEP) for both dynamic and isothermal conditions at specific degree of cure and data points (in parentheses).

Table 4.1 Mean squared errors of prediction for both dynamic and isothermal conditions at specific degree of cure and data points (in parentheses).

Table 5.1 Summary of DSC features at different southern yellow pine contents.

......99 Table 5.2 Kinetic parameters by the nth order Borchadt-Daniels method for southern yellow pine mixtures

Table 5.3 DSC local peak temperatures (T) at 5 oC/min, activation energies (E) of the peaks by the Kissinger equation, heat of reaction (∆H) and ratio of reaction heat to that of pure PF resin at 35% wood contents.

Table 5.4 Comparison of kinetic parameters by the nth order Borchadt-Daniels method for various wood/PF mixtures at 35% wood contents.

–  –  –

coefficient of variation in parenthesis

Table 7.1 Characteristic temperature (°C) at different heating rates and activation

–  –  –

Table 7.2 Vitrification time (min) and activation energy Ea at different isothermal cure temperatures as determined using the peak time method.

Table 7.3 Summary of models and constants for PF-low bonded wood joints under isothermal temperature

Table 7.4 Summary of parameters for Prout-Tomkins model under isothermal conditions

Table 7.5 Summary of activation energy (kJ/mol) with different methods.

..............173 Table 8.1 Corresponding mechanical and chemical degree of cure at gelation and vitrification points under the linear heating regime for aluminum foil-wrapped PF bonded wood joints.

Table 8.2 Corresponding mechanical and chemical degree of cure at the vitrification points under the isothermal heating regime for foil-wrapped PF bonded wood joints.

Table 8.3 Parameters for the relationship equation of mechanical and chemical cure

–  –  –

Figure 2.1 GPC chromatogram for core and face PF resin obtained from the differential viscometer detector

Figure 2.2 1H-NMR spectra of the acetylated face PF and core PF resins in CDCl3; Ar:

aromatic ring, Ac: acetoxy group

Figure 2.3 13C-NMR spectra of the core and face PF resins in CDCl3 with carbon assignments shown in scheme 2.

Figure 2.4 1H-NMR spectrum of the neat core PF resin in D2O

Figure 2.5 13C NMR spectra of the core and face PF resins in D2O solvent.

GPC has shown that the core PF has a higher molecular weight than that of the face resin......29 Figure 3.1 (a) DSC heat flow (dH/dt) at 2 oC/min and (b) degree of cure (α) for PF-low and PF-high.

The number 1 and 2 designate exotherm peak 1 and peak 2.



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