Formaldehyde: Chemistry, Applications and Role in Polymerization

220 Pages·2012·10.728 MB·English

by  Chan Bao Cheng, Feng Hu Ln

POLLUTION SCIENCE, TECHNOLOGY AND ABATEMENT

F
ORMALDEHYDE

C , A
HEMISTRY PPLICATIONS
R P
AND OLE IN OLYMERIZATION

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POLLUTION SCIENCE, TECHNOLOGY AND ABATEMENT

F
ORMALDEHYDE

C , A
HEMISTRY PPLICATIONS
R P
AND OLE IN OLYMERIZATION

CHAN BAO CHENG
AND
FENG HU LN
EDITORS

New York
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Library of Congress Cataloging-in-Publication Data

Formaldehyde : chemistry, applications, and role in polymerization / [edited by] Chan Bao
Cheng and Feng Hu Lin.
pages cm
Includes bibliographical references and index.
ISBN: (cid:28)(cid:26)(cid:27)(cid:16)(cid:20)(cid:16)(cid:25)(cid:21)(cid:21)(cid:24)(cid:26)(cid:16)(cid:21)(cid:21)(cid:27)(cid:16)(cid:20) (eBook)
1. Formaldehyde. I. Cheng, Chan Bao, 1969- editor of compilation. II. Lin, Feng Hu, 1964-
editor of compilation.
TP248.F6F67 2012
615.9'51--dc23
2012021148

Published by Nova Science Publishers, Inc. † New York
CONTENTS

Preface vii 
Chapter 1 Properties of Urea-Formaldehyde Resins
for Wood-Based Composites 1 
Byung-Dae Park 
Chapter 2 Formaldehyde Emissions from Wood-Based Panels:
Testing Methods and Industrial Perspectives 73 
Luisa H. Carvalho, Fernão D. Magalhães and João M. Ferra 
Chapter 3 Electronic Spectra of Formaldehyde in Aqueous Solution:
The Nonequilibrium Solvent Effect with Molecular Modeling 109 
Quan Zhu and Yun-Kui Li 
Chapter 4 Decontamination of Indoor Air Pollutant
of Formaldehyde through Catalytic Oxidation
over Oxide Supported Noble Metal Nanocatalysts 143 
Changyan Li, Baocang Liu, Yang Liu, Wenting Hu,
Qin Wang and Jun Zhang 
Chapter 5 Indoor Air Monitoring Using Newly Developed Formaldehyde
Sensor Element and Portable Monitoring Device 165 
Yasuko Yamada Maruo 
Chapter 6 Unusual Behavior during the Electrochemical Oxidation
of Formaldehyde 185 
Mark Schell 
Index   199

PREFACE

Formaldehyde is a building block in the synthesis of many other compounds of
specialized and industrial significance. It exhibits most of the chemical properties of other
aldehydes but is more reactive. In this book, the authors discuss the chemistry, applications
and role in polymerization of formaldehyde. Topics discussed include the properties of urea-
formaldehyde resins for wood-based composites; electronic spectra of formaldehyde in
aqueous solution; decontamination of indoor air pollutants of formaldehyde through catalytic
oxidation over oxide supported noble metal nanocatalysts; indoor air monitoring using newly
developed formaldehyde sensor elements and portable monitoring devices; unusual behavior
during the electrochemical oxidation of formaldehyde; and an algebraic approach to estimate
the PES of formaldehyde through the study of vibrational excitations.
Chapter 1 - This chapter reviews recent progresses on properties, chemical structure,
thermal curing behavior, hydrolytic stability, morphology, microstructure, crystalline
structure, and modifications of urea-formaldehyde (UF) resin as an adhesive for wood-based
composite panels, particularly by focusing on the parameters related to formaldehyde
emission (FE), such as synthesis reaction pH conditions, formaldehyde/urea (F/U) mole ratio,
and resin modifications.
The reaction pH condition of UF resin synthesis showed that the amount of free
formaldehyde strongly affected the reactivity of UF resin, and also indicated that the weak
acid reaction condition provided a balance between increasing resin reactivity and improving
adhesion strength of UF resins. Solid-state 13C-NMR spectroscopy indicated that the
molecular mobility of cured UF resin increased with decreasing the reaction pH used during its
synthesis. The 13C-NMR spectroscopy showed that UF resins with higher F/U mole ratios
(i.e., 1.6 and 1.4) had two distinctive peaks, indicating the presence of dimethylene ether
linkages and methylene glycols, which give a greater contribution to the FE than that of lower
F/U mole ratio. However, these peaks were not detected at the UF resins with lower F/U mole
ratios (i.e., 1.2 and 1.0). Lowering F/U mole ratio of UF resins as a way of abating FE
consequently requires improving their reactivity. As the F/U mole ratio decreases, thermal
curing behavior of these UF resins such as the gel time, onset and peak temperatures, and heat
of reaction (H) increased, while the activation energy (Ea) and rate constant (k) were
decreased. The results also suggested that as the F/U mole ratio decreased, the FE of
particleboard (PB) was greatly reduced at the expense of the reactivity of UF resin and slight
deterioration of performance of PB prepared. Dynamic mechanical analysis (DMA) results
viii Chan Bao Cheng and Feng Hu Ln
partially explained the reason why UF resin adhesives with lower F/U mole ratio resulted in
relatively poor adhesion performance.
Morphological investigation on UF resins illustrated that the spherical structures in cured
UF resins were much more resistant to the hydrolytic degradation by the acid than amorphous
region. Atomic force microscopy (AFM) images showed two distinctive regions, i.e., hard
and soft phases in cured UF resins. The AFM study suggested that the soft phase was much
more susceptible to the hydrolysis of cured UF resin than the hard phase. The soft phase of
cured UF resins by ammonium chloride was much more easily hydrolyzed than those cured
by ammonium sulfate, indicating that hardener types had a great impact on the hydrolytic
degradation behavior of cured UF resins. For the first time, the presence of thin filament-like
crystalline structures on the fracture surface of cured UF resin was reported. And X-ray
diffraction (XRD) results showed that the crystalline regions of cured UF resins with lower
F/U mole ratio contribute partially to the improved hydrolytic stability of the cured resin.
Chapter 2 - Formaldehyde is an important chemical feedstock for the production of
phenoplast and aminoplast thermosetting resins, by reaction with other monomers (mostly
urea, but also melamine, phenol and resorcinol). These adhesives are mainly used in the
manufacture of wood-based panels: plywood, particleboard, hardboard, medium density
fiberboard (MDF) and oriented strand board (OSB). These products have a wide range of
applications, from non-structural to structural, outdoor or indoor, mostly in construction and
furniture, but also in decoration and packaging. The WBP industry plays an important role in
the global economy and contributes for forest sustainability and carbon sequestration. In
2009, FAO (Food and Agriculture Organization) reported that a total of 260 million m3 WBPs
were produced in the world (Europe 29.7%, Asia 43.9%, North America 18.3% and others
2.5%).
Being economically competitive and highly performing, a major drawback of
formaldehyde-based resins, mostly urea-formaldehyde, is the formaldehyde emission during
panel manufacturing and service life. There are two sources of emission: release of unreacted
monomer, during or after panel production, and long-term resin degradation (hydrolysis). The
formaldehyde content and chemical stability of the resin will therefore affect emission levels.
In addition, external factors like temperature, humidity or air renewal rate will also play a
role. It must be noted that wood itself contributes to formaldehyde emission, since it is a
product of metabolism and decomposition processes. The actual emission level depends
strongly on the type(s) of wood used in panel production.
Due to information considering formaldehyde as potentially carcinogenic to humans, the
implementation of international regulations and requirements for emissions from WBPs has
led to establishment of standard testing methods. Two main groups are considered: chamber
methods (emulating indoor living environments, mentioned in ASTM, ISO and European
standards), and small scale methods, also called derived tests, oriented to industrial quality
control and development. This second group includes commonly used methods, mentioned in
different international standards, like the so-called: perforator (actually a test of potential
formaldehyde emission), flask, desiccator, and gas analysis methods. Correlation between
results from different methods has been a matter of debate, not yet completely elucidated.
Based on different test methods, emission limit standards for WBPs have been issued by
several governmental organizations in Europe, Japan and United States, allowing for product
classification according to emission level. Additionally, limits drawn by major industrial
consumers, like IKEA, have been a defining guideline for WBP producers.