Abstract … 16 [626532]

CONTENTS
Abstract ………………………………………………………………………………………………… 16
2.1 Introduction …………………………………………………………………………………….. 16
2.2 Recycling of PUF ……………………………………………………………………………. 26
2.3 Conclusion ……………………………………………………………………………………… 46
Keywords ……………………………………………………………………………………………… 47
References …………………………………………………………………………………………….. 47 CHEMICAL RECYCLING OF
POLYURETHANE FOAMS: A REVIEW
AJAY VASUDEO RANE 1* , ABITHA V. K. 2, K. KANNY1, and
SABU THOMAS 2
1Department of Mechanical Engineering, Durban University of
Technology, Durban, South Africa
2School of Chemical Sciences, Mahatma Gandhi University, Kerala,
India
*Corresponding author. E-mail: [anonimizat] CHAPTER 2

16 Engineering Technologies for Renewable and Recyclable Materials
ABSTRACT
The fate of polymers in nature seems to present an inconsistent problem
at times; most polymers are designed and manufactured to resist environ-
mental degradation (photodegradation, hydrolysis, oxidation, biodegrada-
tion, etc.) but are used for protective and/or structural purposes. Increasing
awareness of solid waste management problems has led to the insist for
polymers that do not have an unsafe collision on the environment during
any part of their life cycles. The corresponding recycling of carbon,
hydrogen, and nitrogen elements as well as of energy through reprocessing
and biological and chemical conversion should be taken advantage of in
polymer design. Recycling is a crucial area of research in Green Polymer
Chemistry. Various developments in recycling are driven by environmental
concerns, interest in sustainability and desire to decrease the dependence
on nonrenewable petroleum-based materials. Polyurethane foams (PUF)
are widely used due to their light weight and superior heat insulation as
well as good mechanical properties. As per survey carried out by Polyure-
thane Foam Association, 12 metric tonnes of PUF are discharged during
manufacturing and/or processing and hence recycling of PUF is necessary
for better economics and ecological reasons. Hence we propose a write u p
describing various methods to recycle PUF.
2.1 INTRODUCTION
/g21/g17/g20/g17/g20/g3 /g42/g53/g40/g40/g49/g3/g55/g40/g38/g43/g49/g50/g47/g50/g42/g60
“The good solve today’ s problems, the great design today’ s world to
avoid tomorrow’ s issues .”
Green Chemistry is not a novel branch of science; i t is a new-fangled
philosophical approach, all the way through applica tion and extension of
the principles of Green Chemistry is capable of to contribute to sustain-
able developments. Chemistry was once viewed as a g round of innovation
resulting in break troughs and modern convenience b ut now is viewed by
many as a fouling the planet earth. 1,2 Green Chemistry encourages envi-
ronmentally conscious behavior and reduces and prev ents pollution and
destruction of planet; it involves process of recyc ling and use of renewable
resources for energy. Green Chemistry is the design of chemical products

Chemical Recycling of Polyurethane Foams: A Review 17
and processes that reduce or eliminate the use and/ or generation of hazardous
substances, it creates new ways to make desired mat erials via different
feedstock’s, different pathways, identifies desired performance characteris-
tics and create new materials. Green Chemistry prov ides a technical solu-
tion to many environmental problems. Green Chemistr y is effective due to
design stage, an effort starting at the molecular l evel lets you design out the
hazardous properties and design environmentally app ropriate features. It is
upto us to live up to our greatness in order to dre am, design, and realize a
truly sustainable world. The modern understanding o f sustainability began
with the United Nations World Commission of Environ ment and Devel-
opment’s report “Our Common Future” also known as the “Brundtland
Report .” The Brundtland Commission described Sustainable Development
as development that meets the needs of the present wit hout comprising the
ability of the future generations to meet their own needs .14 The definition
does not give us many clues or supply much practica l guidance as how to
implement sustainable development or move toward su stainable develop-
ment activities, but it does provide us with a powe rful aspiration. It has
been upto society collectively and upto us as indiv iduals to develop guid-
ance and tools that will help us to design systems and processes that have
the potential to achieve the type of development de scribed in the defini-
tion of sustainable development. By using the term phase triple bottom
line (Fig. 2.1 ) Elkington tried to highlight the need to consider t he intricate
interrelationship among environmental, social, and economic aspects of
human society and the world. In a way, sustainable development can be
seen as a very delicate balancing act among the thr ee factors and not always
with a strong one to one relationship. 6,8
FIGURE 2.1 Phase triple bottom line.

18 Engineering Technologies for Renewable and Recyclable Materials
Coupling technological innovations with policies an d strategies is not
VXI¿FLHQWWREULQJDERXWWKHNLQGRIFKDQJHWKDWLV QHHGHGWROHDGVRFLHW\
WRZDUGPRUHVXVWDLQDEOHSUDFWLFHV7RLQÀXHQFHSHRS OHWRPDNHFRQWLQXHG
changes in the face of pervasive, persistent, and p rolonged resistance, we
QHHGWRXVHDOOWKHVSKHUHVRILQÀXHQFHDWRXUGLVS RVDO,QÀXHQFLQJLVDQ
essential part of driving sustainability; as we hav e seen that the achievement
of greater sustainability would not happen through people working in isola-
tion and requires the dealings and partnership of m any years ( Fig. 2.2 ). 14
FIGURE 2.2 Development of green chemistry.
/g21/g17/g20/g17/g21/g3 /g55/g43/g40/g3/g20/g21/g3/g51/g53/g44/g49/g38/g44/g51/g47/g40/g54/g3/g50/g41/g3/g42/g53/g40/g40/g49/g3/g38/g43/g40/g48/g44/g54/g55/g53/g60
The most important aims of Green Chemistry were defined in 12 prin-
ciples. The number 12 is highly significant and symbolic like the 12
months of the year as the complete sum of the most important things that
we have to do to accomplish a multiple task. Green Chemistry has to cove r
a broad spectrum of chemical and technological aspects in order to offer
its alternative vision for sustainable development. 16 Green Chemistry had
to implement fundamentals ways to reduce or to eliminate environmental
pollution through dedicated, sustainable prevention programs. Green
Chemistry must focus on alternative, environmentally friendly chemicals
in synthetic routes but also to increase reaction rates and lower reacti on
temperature to save energy. Green Chemistry looks very carefully on reac-
tion efficiency, use of less toxic solvents, minimizing the hazards of feed
stocks and products, and reduction of wastes. Anastas, an organic Chemist
working in the office of Pollution Prevention and Toxins at EPA, and John
C Warner developed the 12 principles of Green Chemistry in 1991. These
principles can be grouped into “ Reducing risk ” and “Minimizing the Envi-
ronmental Footprint .” 39

Chemical Recycling of Polyurethane Foams: A Review 19
• Principle no. 1— Prevention : It is better to prevent than to clean
or to treat afterwards (waste or pollution). This is a fundamental
principle. The preventative action can change dramatically many
attitudes among the scientists developed in the last decades. Most
of the chemical processes and synthetic routes produce waste and
secondary toxic substances. Green Chemistry can prevent waste
and toxic by-products by designing the feed stock’s and the chem-
ical processes in advance and with innovative changes.
• Principle no. 2— Maximize synthetic methods, Atom Economy : All
synthetic methods until now were wasteful and their yields were
between 70% and 90%. Green Chemistry supports that synthetic
methods can be designed in advance to maximize the incorporation
of all reagents used in chemical processes into the final product.
The concept of Atom Economy was developed by Barry Trost of
Stanford University. It is a method of expressing how efficiently,
how a particular reaction makes use of the reactant atoms.
• Principle no. 3— Less hazardous chemical use : Synthetic methods
should be designed to use and generate substances that possess little
or no toxicity to the environment and public at large.
• Principle no. 4— Design for safer chemicals : Chemical products
should be designed so that they not only perform their designed
function but are also less toxic in the short and long terms.
• Principle no. 5— Safer solvents and auxiliaries : The use of auxil-
iary substances such as solvents or separation agents should not be
used whenever possible. If their use cannot be avoided, they should
be used as mildly or innocuously as possible.
• Principle no. 6— Design for energy efficiency : Energy requirements
of chemical processes should be recognized for their environmental
and economic impacts and should be minimized. If possible, all
reactions should be conducted at mild temperature and pressure.
• Principle no. 7— Use of renewable feedstock : A raw material or
feedstock should be renewable rather than depleting whenever
technically and economically practicable. For example, oil, gas,
and coal are dwindling resources that cannot be replenished.
• Principle no. 8— Reduction of derivatives : Use of blocking groups,
protection/deprotection, and temporary modification of physical/
chemical processes is known as derivatization , which is normally
practiced during chemical synthesis. Unnecessary derivatization

20 Engineering Technologies for Renewable and Recyclable Materials
should be minimized or avoided. Such steps require additional
reagents and energy and can generate waste.
• Principle no. 9— Catalysis : Catalytic reagents are superior to stoi-
chiometric reagents. The use of heterogeneous catalysts has several
advantages over the use of homogeneous or liquid catalysts. Use of
oxidation catalysts and air is better than using stoichiometric quan-
tities of oxidizing agents.
• Principle no. 10— Design for degradation : Chemical products
should be designed so that at the end of their function they break
down into innocuous degradation products and do not persist in the
environment. A life cycle analysis (beginning to end) will help in
understanding its persistence in nature.
• Principle no. 11— Real-time analysis for pollution prevention :
Analytical methodologies need to be improved to allow for real-
time, in-process monitoring and control prior to the formation of
hazardous substances.
• Principle no. 12— Inherently safer chemistry for accident preven-
tion : Substances and the form of a substance used in a chemical
process should be chosen to minimize the potential for chemical
accidents, including releases, storage of toxic chemicals, explo-
sions, and fires.
• Five main foci emerge from these 12 principles, namely ,15
1. less,
2. safe,
3. process-oriented,
4. waste-reducing, and
5. sustainable.
• All five key words could be grouped and written as 15 :
1. Uses fewer chemicals, solvents, and energy.
2. Have safe raw materials, processes, and solvents.
3. Process should be efficient, without waste, without derivatiza-
tion, and should use catalysts.
4. Waste generated should be monitored in real time and should
degrade.
5. All chemicals, raw materials, solvents, and energy should be
renewable or sustainable.

Chemical Recycling of Polyurethane Foams: A Review 21
The history of polyurethanes (PU) started in the 1930s in Germany
when Otto Bayer proposed using diisocyanate and diol for preparation of
PDFURPROHFXOHV7KH¿UVWFRPPHUFLDO38EDVHGRQKH[DPHWK\OHQHGLLVR –
cyanate and butanediol, had similar properties to polyamides and is sti ll
XVHGWRPDNH¿EHUVIRUEUXVKHV+RZHYHUIDVWJURZWKRIWKHSURGXFWLRQ
and expanded application range started in the 1950s with the building of
WROXHQHGLLVRF\DQDWH7',DQGSRO\HVWHUSRO\ROSODQWVIRUÀH[LEOHIRDPV
However, the real jump in applications came with the introduction of pol y-
ether polyols in foam formulations. Today, PU are about the sixth largest
polymer by consumption, right behind high-volume thermoplastics, with
about 6% of the market. The largest part of the urethane application is i n
WKH¿HOGRIÀH[LEOHIRDPVDERXWULJLGIRDPVDERXWZKLOH
28% are coatings, adhesives, sealants, and elastomers applications. PU
are a broad class of very different polymers, which have only one thing in
common—the presence of the urethane group ( Fig. 2.3 ).
FIGURE 2.3 Urethane group.
The number of these groups in a polymer can be relatively small
compared with other groups in the chain (e.g., ester or ether groups in
elastomers), but the polymer will still belong to the PU group. Varying t he
structure of PU, one can vary the properties in a wide range. PU are formed
by reaction of polyisocyanates with hydroxyl-containing compounds,
most frequently during processing. By selecting the type of isocyanate and
polyols, or combination of isocyanates and combination of polyols, one
can tailor the structure to obtain desired properties. For this, however, i t is
necessary to know the relationship between the structure and properties.
7KHÀH[LELOLW\WRWDLORUWKHVWUXFWXUHGXULQJSURFHVVLQJLVRQHRIWKHPDLQ
advantages of PU over other types of polymers. Urethane groups form
strong hydrogen bonds among themselves and with different substrates.
Strong intermolecular bonds make them useful for diverse applications
in adhesives and coatings, but also in elastomers and foams. 18 One of the
great advantages of PU arises from the high reactivity of isocyanates,

22 Engineering Technologies for Renewable and Recyclable Materials
which can react with a number of substances having different functional
groups. This allows polymerization at relatively low temperatures and in
short times (several minutes). One group of polymers, which is condition-
ally treated as urethanes, is polyurea, because urea is often formed during
urethane production. Urea is formed in the reaction between isocyanates
and amines. The urea group is similar to the urethane group, except that i t
has two –NH– groups ( Fig. 2.4 ), and can form more hydrogen bonds than
the urethane group.
FIGURE 2.4 Urea group.
/g21/g17/g20/g17/g22/g3 /g54/g60/g49/g55/g43/g40/g54/g44/g54/g3/g50/g41/g3/g51/g56
The basis of PU chemistry is the high reactivity of isocyanate s . They react
under mild conditions with all compounds that contain “active ” hydrogen
atoms . These are mainly alcohols (OH group) but also amines. When the
isocyanate group (NCO) reacts with alcohols, amines, carboxylic acids,
and water, urethane, urea, and amide linkages are formed ( Fig. 2.5 ). PU
are usually classified as engineering polymers characterized by the pres-
ence of the carbamate group (–O–CO–NH–). The major route for the
preparation of PU is the reaction between a diisocyanate and a hydroxyl-
rich compound with at least two hydroxyl groups, according to following
reaction.
FIGURE 2.5 Polyurethane synthesis by reaction of diisocyanate and diol.
In Figure 2.5 , R can be an aliphatic, cycloaliphatic, or polycyclic group.
Of the different diisocyanate used, the most common are methylene-
4,4'-diphenyldiisocyanate, toluene 2,4-diisocyanate, and hexamethylene

Chemical Recycling of Polyurethane Foams: A Review 23
diisocyanate. Likewise, low-molecular weight hydroxyl-terminated poly-
esters or polyether’s are typically employed as dihydroxyl compounds. 18
/g21/g17/g20/g17/g23/g3 /g53/g40/g38/g60/g38/g47/g44/g49/g42/g3/g48/g40/g55/g43/g50/g39/g54
Recycling is a crucial area of research in Green Polymer Chemistry and
developments in recycling are driven by environmental concerns, interest
in sustainability, and desire to decrease dependence on petroleum-based
materials. Sustainability refers to the development that meets the needs of
present without comprising the ability of future generations. Polyurethane
foams (PUF) are widely used due to their light weight and superior heat
insulation as well as good mechanical properties. However, large quanti –
ties of PUF are discharged during manufacturing/processing as a waste
and hence recycling of PUF is necessary. Recycling allows the wastes t o
be reintroduced into the consumption cycle, generally in secondary appli-
cations because in many cases, the recycled products are of lower quality
than the virgin ones. Recycling must be applied only when the amount of
energy consumed in the recycling process is lower than the energy required
for the production of new materials. Plastics can be recycled using two
different approaches: mechanical and feedstock recycling. In the first case,
the plastics are recycled as polymers, whereas in the second, plasti c wastes
are transformed into chemicals or fuels. 13
PU recycling methods can be categorized into four groups, namely,
primary, secondary, tertiary, and quaternary recycling. There is also a so
called “zero-order” recycling technique, which involves the direct reuse
of a PU waste material. There are many other terminologies used for these
recycling categories. 25
• Primary recycling : Primary recycling, also known as reextrusion
is the oldest way of recycling PU. It refers to the “in-plant” recy-
cling of the scrap materials that have similar features to the original
products. This process ensures simplicity and low cost, but requires
uncontaminated scrap, and only deals with single-type waste,
making it an unpopular choice for recyclers.
• Secondary recycling : Secondary recycling, also known as mechan-
ical recycling, was commercialized in the 1970s. It involves sepa-
ration of the polymer from its contaminants and reprocessing it to

24 Engineering Technologies for Renewable and Recyclable Materials
granules via mechanical means. Mechanical recycling steps include
sorting and separation of wastes, removal of contaminants, and
reduction of size by crushing and grinding, extrusion by heat, and
reforming. The more complex and contaminated the waste is, the
more difficult it is to recycle mechanically. Among the main issues
of secondary recycling are the heterogeneity of the solid waste and
the degradation of the product properties each time it is recycled.
Since the reactions in polymerization are all reversible in theory,
the employment of heat results to photooxidation and mechanical
stresses, causing deterioration of the product’s properties. Another
problem is the undesirable gray color resulting from the wastes that
have the same type of resin, but of different color.
• Tertiary recycling : Tertiary recycling, more commonly known as
chemical recycling, involves the transformation of the PU polymer
chain. Usually by means of solvolytic chain cleavage, this process
can either be a total depolymerization back to its monomers or a
partial depolymerization to its oligomers and other industrial chem-
icals. Since PU is a polymer with functional ester, ether groups, it
can be cleaved by some reagents such as water, alcohols, acids,
glycols, and amines. Also, PU is formed through a reversible poly-
condensation reaction, so it can be transformed back to its monomer
or oligomeric units by pushing the reaction to the opposite direc-
tion through the addition of a condensation product. These low-
molecular products can then be purified and reused as raw materials
to produce high-quality chemical products. Among the recycling
methods, chemical recycling is the most established and the only
one acceptable according to the principles of “sustainable devel-
opment, ” defined as development that meets the needs of present
generation without compromising the ability of future generations
to meet their needs (World Commission on Environment and Devel-
opment, 1987), because it leads to the formation of the raw mate-
rials (monomers) from which the polymer is originally made. In
this way, the environment is not surcharged and there is no need for
extra resources for the production of PU .14
Chemolysis is true depolymerization applicable to the recycling
of PU and other polyaddition materials as well as to condensa-
tion polymers such as polyesters (e.g., PET) and polyamides (e.g.,
nylon). In this type of treatment, the molecules are broken down

Chemical Recycling of Polyurethane Foams: A Review 25
into smaller building blocks, which may then be reassembled into
polymers suitable for use in quality applications similar to those for
which the original components were employed. Because it delivers
high-grade products that largely retain their original properties and
functionality, chemolysis offers an attractive alternative to mechan-
ical recycling and the recovery of petrochemical feedstock’s or
energy.
For chemolysis of PU ( Fig. 2.6 ), it is preferable to process
feedstock of known composition in order to obtain consistent
and predictable regenerated products. Water (hydrolysis), glycols
(glycolysis), and amines (aminolysis) typically serve as reagents to
break the urethane bonds. The resulting liquid can be used as such,
or the individual components separated. Several options exist for
IXUWKHUUHSURFHVVLQJ7KHVHPD\LQYROYHSXUL¿FDWLRQDQGFKHPLFDO
processing before use in PU applications. 13
FIGURE 2.6 Chemolysis of polyurethanes.
• Hydrolysis, Aminolysis, and Glycolysis is a process whereby the
PUF is reacted with water under pressure at elevated tempera-
ture. Hydrolysis produces the original polyether polyols together
with diamines, which are the hydrolysis products of the original

26 Engineering Technologies for Renewable and Recyclable Materials
diisocyanate. The various components are then separated in order
to permit their reprocessing and reuse.
• Aminolysis: In aminolysis, the PUF is reacted with amines such
as dibutylamine, ethanolamine, diethanolamine (DEA), lactam, or
lactam adduct under pressure at elevated temperatures. Aminolysis
is still at the research stage and not much has been carried out.
• Glycolysis is a process wherein the PUF is reacted with diols at
elevated temperature (200°C) with cleavage of covalent bonds. The
high-molecular weight, cross-linked, solid PU are broken down to
lower molecular weight liquid products.
Single-phase glycolysis has been optimized by ISOPA members and
independent researchers (e.g., catalyst selection, posttreatment for mini-
mization of the aromatic amine content).
Split-phase glycolysis has been developed up to pilot scale for MD I
ÀH[LEOHIRDPV7KHJO\FRO\VLVSURGXFWVHSDUDWHVLQWRWZRSKDVHV
• Quaternary recycling: Quaternary recycling represents the
recovery of energy content from the plastic waste by incinera-
tion. When the collection, sorting, and separation of plastics waste
DUHGLI¿FXOWRUHFRQRPLFDOO\QRWYLDEOHRUWKHZDVWHLVWR[LFDQG
hazardous to handle, the best waste management option is incinera-
tion to recover the chemical energy stored in plastics waste in the
form of thermal energy. However, it is thought to be ecologically
unacceptable due to potential health risks from the airborne toxic
substances. 25
• the top layer is a flexible foam polyol which after purification can
be used alone to make the same flexible foam again
ƒthe bottom layer, after posttreatment with propylene oxide, can be
converted into a high-quality rigid foam polyol.
2.2 RECYCLING OF PUF
/g21/g17/g21/g17/g20/g3 /g43/g44/g42/g43/g47/g44/g42/g43/g55/g54
The usage of PU materials in daily life as well as industrially has continu-
ously increased over the last 30 years. The amount of PU consumed per
sector in the industrialized countries has increased over this period, while

Chemical Recycling of Polyurethane Foams: A Review 27
the generation of foam wastes has grown at a similar rate. Recycling of
PUF is now an important field in the polymer industry, not just an activit y
born under environmental pressure. The recycling processes include
industrial operations in which secondary materials are reprocessed and/
or monomers recovered for further polymerization; such processes are
termed secondary and tertiary recycling. At present, there are three main
alternatives for the management of polymeric wastes in addition to land
filling: (1) mechanical recycling by melting and regranulation of the used
polymers, (2) feedstock recycling, and (3) energy recovery. Consequently,
feedstock recycling appears as a potentially interesting approach, base d on
the conversion of polymeric wastes into valuable chemicals useful as fuel s
or as raw materials for the chemical industry. The cleavage and degrada-
tion of the polymer chains may be promoted by temperature, chemical
agents, catalysts, etc. The purpose of this work is to describe and revie w
the different alternatives developed for the chemical recycling of PUF
wastes, with emphasis on both the scientific and technical aspect s. Solid
polymeric materials undergo both physical and chemical changes when
heat is applied usually resulting in undesirable changes in the propert ies of
the material. A clear distinction needs to be made between therma l decom-
position and thermal degradation. The American Society for Testing and
Materials defines thermal decomposition as “A process of extensive
change in chemical species caused by heat” and thermal degradation is “A
process whereby the action of heat or elevated temperature on a material,
product or assembly causes a loss of physical, mechanical or electrical
properties.” 9
The alternative methods of polymer recycling consist of the breakdown
of the polymer by reaction with certain chemical agents, leading back to
the starting monomers. These monomers are identical to those used in the
preparation of virgin polymers, hence the polymer prepared from both
depolymerization and fresh monomers are expected to have similar prop-
erties and quality. According to this approach, polymeric wastes are rein-
troduced to the market as polymers, as happens in the case of material
recycling, but without the loss of resin properties typically associat ed with
the mechanical process. Polymer recycling by chemical depolymerization
is the most established method of polymer chemical recycling. Different
chemolysis processes have been applied on an industrial scale for severa l
years. The major disadvantage of chemical depolymerization is that it is
almost completely restricted to the recycling of condensation polymers

28 Engineering Technologies for Renewable and Recyclable Materials
and is of no use for the decomposition of most addition polymers, which
are the main components of the plastic waste stream. Condensation poly-
mers are obtained by the random reaction of two molecules, which may be
monomers, oligomers, or higher molecular weight intermediates, which
proceeds with the liberation of a small molecule as the chain bonds are
formed. Chemical depolymerization takes place by promoting the reverse
reaction of the polymer formation, usually through the reaction of those
small molecules with the polymeric chains. 13
With regard to the chemical recycling of PU, two aspects must be high-
lighted. PU are used to manufacture durable goods, which mean that it
takes several years for these items to be disposed off into the solid w aste
stream. Moreover, PU contain around 4 wt% of N, which may hinder
WKHLUUHF\FOLQJE\R[LGDWLYHWUHDWPHQWVVXFKDVLQFLQHUDWLRQRUJDVL¿FDWLRQ
GXHWRWKHSRWHQWLDOUHOHDVHRIVLJQL¿FDQWDPRXQWVRI12LQWKHJDVHRXV
HIÀXHQWV 13 The most important chemolysis methods so far developed to
reverse the PU polymerization reaction are glycolysis and hydrolysis.
These processes are reviewed next, together with other less widely inves –
tigated treatments like aminolysis.
/g21/g17/g21/g17/g21/g3 /g42/g47/g60/g38/g50/g47/g60/g54/g44/g54
A variety of processes for PU degradation by reaction with different glycols
has been described in the literature. PU glycolysis is usually carried out
with an excess of glycols at temperatures around 200°C and in many cases,
working at atmospheric pressure. After several hours of reaction, the PU
is completely liquefied and depolymerized, with or without catalysts. The
chemistry of the glycolytic reaction has been described by Ulrich et al.37,38
It involves the transesterification of the carbamate group by addition and
reaction with the glycol. These authors verified this scheme by reacting
benzyl phenyl carbamate and ethylene glycol at 195°C, a total conversion
of the former being observed after 3 h according to the reaction shown in
Figure 2.7 . Because water-blown PUF contain diarylurea linkages, due to
the reaction of diisocyanates with water, they also investigated the glyc ol-
ysis of N, N-diphenylurea as a model compound. The results obtained
clearly showed that the urea linkages are also glycolyzed in these reacti on
conditions, indicating that the polyols derived from water-blown PUF will
present amino end groups.

Chemical Recycling of Polyurethane Foams: A Review 29
FIGURE 2.7 Glycolysis of benzyl phenyl carbamate and diphenyl urea.
*O\FRO\VLVKDVEHHQVXFFHVVIXOO\DSSOLHGWRULJLGDQGÀ H[LEOH38)DV
well as to polyisocyanurate foam. The polyols obtained by degradation
are blended with polyols in a proportion of around 50%. These mixtures
can be used in the formulation of new rigid and semirigid foams, which
exhibit properties similar to those of completely virgin foams. However ,
the use of 100% PU degradation polyols is limited by their lower reac-
tivity and higher viscosity compared to virgin polyols. 13 In a recent patent,
glycolysis has been reported to be a feasible chemical recycling met hod
for the degradation of PU/polyurea or polyurea wastes. Conventional alco-
holysis of these polymeric wastes leads to products with a high content of
urea groups and low-molecular weight primary aromatic amines, which
limits their application in the isocyanate polymerization reaction b ecause
the amine groups are much more reactive toward isocyanates than the
alcohol groups of the polyols. These problems have been solved by a two-
stage process: reaction of the polymeric wastes at 200°C with a diol or
polyol [ethylene glycol, diethylene glycol (DEG), hexanediol, glycerol,
etc.] followed by treatment of the alcoholysis products with urea or a
carbamic acid ester. It has been found that this second reaction greatl y
UHGXFHVWKHDPLQHFRQWHQWVRWKDWWKH¿ QDOSURGXFWLVVXLWDEOHIRUUHXVH
in the isocyanate addition polymerization. Today, several industrial plants
based on glycolytic treatment are in operation for the chemical recycli ng
of PU wastes, mainly those generated from the insulation and automo-
tive sectors. Glycolysis process with ethylene glycol, when applied to PU
ZLWKDKLJKFRQWHQWRIXUHDWKDWLVRIÀ H[LEOHZDWHUEORZQIRDPVIRUPV
a polyphasic system whose main components are, together, with the triol ,

30 Engineering Technologies for Renewable and Recyclable Materials
the ethylene glycol solution of the products coming from the interaction
between the aromatic part of the polymer (carbamates and ureas) with
HWK\OHQHJO\FRODQGDVROLGSKDVHZLWKXUHDERQGV,QWKH¿QDOSURGXFWWKH
free isomeric toluene diamine (TDA) is about 1.52% w/w. The glycolysis
process carried out in the presence of hexamethylenetetramine avoids the
formation of a solid phase in the product that presents a low free amine
content, lower than 100 ppm. This product is safe and easy handling,
mainly presents the components required by a material for general use,
ZLWKRXWVHSDUDWLRQRUSXUL¿FDWLRQRIWKHSKDVHVIRUQHZ38 26
In another study, the degradation of PU wastes was carried out with
ethylene glycol, 1, 2-propylene glycol, triethylene glycol, polyethylene
glycol, and DEA and the results of the degradation experiments with
various EG–DEA mixtures was found to be the fastest at a 1:1 EG–DEA
ratio, and it was acceptable even if the ratio of the reactants was 1:6.
Glycolysis in this way results in a two-phase mixture at the end of the
reaction. To identify the upper liquid phase, industrial polyol standards
were used and it was found that this upper liquid phase was the starti ng
SRO\ROLQWKHFDVHRIERWKWKHÀH[LEOHIRDPDQGWKHHODVWRPHU 10
Among the suitable processes, glycolysis, especiall y in two phases,
DOORZVEHWWHUTXDOLW\SURGXFWV,QWKLVVWXG\JO\F RO\VLVUHDFWLRQVRIÀH[ –
ible PUF were conducted in “split-phase” with diffe rent catalysts, in order
to study their activity. DEA, titanium n-butoxide a s well as potassium
and alcium octoate salts, which are novel compounds for this application,
showed suitable catalytic activity. All the catalyz ed processes showed
appropriate activity compared with the noncatalyzed process, allowing the
complete recovery of polyols from the PU matrix. Po tassium and calcium
RFWRDWHVVSHFLDOO\WKH¿UVWKDYHEHHQIRXQGDGYDQ WDJHRXVIRUWKHUHFRYHU\
process. Potassium octoate leads to the complete de gradation of the poly-
meric chain at low reaction time and the recovery o f the polyol in high
concentration. These reaction time and concentratio n are comparable to
those obtained with DEA, the most active catalyst s tudied. Times to reach
complete conversion, chemical properties of the pol yol phase, and its purity
depend on the catalyst employed. The novel catalyst s developed have been
proved to be a worthy and economic alternative to t raditional catalysts. 30,31
,Q DQRWKHU H[SHULPHQW JO\FRO\VLV RI ÀH[LEOH 38) LQ  ³VSOLW SKDVH´ ZDV
conducted with different glycols, in order to study their activity and select
a system to obtain the highest quality recovered po lyol. Times required to
reach complete conversion, chemical properties of t he polyol phase, and
its purity depended on the glycol employed. DEG pro ved to be the most

Chemical Recycling of Polyurethane Foams: A Review 31
suitable glycol to obtain a high purity in the poly ol phase. 29 Glycolysis of
integral skin PUF products with DEG/diethanol amine and NaOH have two
liquid layers—upper and lower phases, which the upp er phase was homo-
geneous polyol that can be reused in the manufactur e of integral skin PUF.
Results calculated from gel permeation chromatograp hy (GPC) analysis
show that upper phase of product has a structure si milar to virgin polyol.
Results collected from quality control of recycled polyol maintained that it
is applicable in a polyol blend for foam formulatio n. 32
In the test of ability, potassium octoate showed a proper performance
as catalyst in the glycolysis of PU wastes. An incr ease in the reac-
tion temperature and catalyst concentration enhance s the degradation
rate; however, this also negatively affects the pro cess by promotion of
secondary reactions and contamination of the polyol phase. As the cata-
lyst concentration is raised, the more polluted is the polyol obtained. The
catalyst of 2.2% seems to be the best choice. Tempe ratures lower than
170°C provide too slow degradation rates, whereas v alues higher than
200°C also promote secondary decarboxylation reacti ons. In this interval,
an increase in the reaction temperature speeds the degradation up mark-
edly. Related to the glycolysis agent amount, the m inimum quantity
required to split the phases has been determined, a s well as the optimal
ratio. Increasing this ratio does not provide any a dditional improvement
of the process and affects economy of the process n egatively. As an incre-
PHQWRIWKHIRDPJO\FROUDWLRODUJHUWKDQGRH VQRWSURGXFHDVLJQL¿ –
cant improvement of the process that proportion can be selected as the
best value to carry out the process. 28
Researchers proposed a system where glycerin was used as a destroying
solvent and sodium hydroxide as the catalyst, respectively. In order to
study the ability of glycerin as a glycolyzing agent and for selecting a
system to obtain high-quality recovered polyol, the effects of various reac-
tion times were investigated and the characterization and comparison of
upper and lower phases were performed. Investigation of the obtained
results from Fourier-transform infrared (FTIR) spectroscopy indicates
that chemical structure of recycled polyol after 1 h and 3 h are too similar
to virgin polyol. Because the vibrations in the spectral regions >3300,
2869, 1455, 1373, and 1109 cm í in virgin polyol are repeated similarly
in the recycled polyol. Except the vibrations at 1617 and 1516 cm í char-
acteristic in the recycled polyol which are corresponding to the bending
vibrations of amine N–H bands originated from the starting isocyanates
as contaminant which slightly has been dissolved in the upper phase.

32 Engineering Technologies for Renewable and Recyclable Materials
Also proton nuclear magnetic resonance ( 1HNMR) and Carbon-13 (C13)
nuclear magnetic resonance ( 13 CNMR) spectra of virgin and recycled
polyols regardless the peaks about 6.6–7.2 ppm in 1HNMR and the peaks
in the region 110–140 ppm in 13 CNMR that are relative to the aromatic
by-products, are quite equal. Also GPC results showed the similarity of
recycled and virgin polyols. Another observation in our study was the
higher hydroxyl value of recovered polyols in comparison with virgin one
due to partial solubility of glycerin in the recycled polyol. According to
the results, glycerin could be used as glycolysis agent to recovering of
KLJKTXDOLW\SRO\ROZKLFKFDQEHUHXVHGIRUSURGXFWLRQRIQHZÀH[LEOH
PUF (Alavi et al., 2007). It is of course possible to convert the waste col d
FXUHÀH[LEOH38)WRDGRXEOHSKDVHGSURGXFWZKLFKLVFRPSOHWHO\DSSOL –
cable in new foam formulation as a portion of polyol blend by mixture
of solvents containing 95% DEG, 5% DEA, and 1% NaOH as the cata-
lyst is a low amine content mixture that is appropriate for PUF rec ycling.
Not being necessary to remove the contamination from waste foams and
SURYLGLQJWKHV\VWHPVIUHHRIFKORURÀXRURFDUERQV&)&VZHUHVRPHRI
other advantages of this research. Large-scaled usage of PUF production
would make huge amount of wastes. Thus, large-scaled glycol treating
would initially run on production waste and is an essential step toward
HQFRXUDJLQJWKHGHYHORSPHQWRISRVWFRQVXPHUZDVWHORJLVWLFVIRUÀH[ –
ible foams. A scaled-up version of the process would be combined with a
EDWFKUHDFWLRQDVDQLQGXVWULDOSODQWIRUFROGFXUHÀH[LEOH38)UHF\FOLQJ
producing a commercially valuable recyclate. By the way, it is necessary
to transfer the result of recycling R&D group works to the PUF producers
sponsored by environmental protecting organization. This implies that
successful recycling via split-phase glycolysis will only be feasibl e with
cooperation or joint development between scrap suppliers, palletiz es, and
process operators, all supported by an organization (Alavi et al., 2007).
5HVHDUFKHUVDWWHPSWHGWRGHYHORSDSURFHVVZKHUHÀH[LEOH38)FDQEH
advantageously treated by two-phase glycolysis in order to recover their
constituent polyols with an improved quality respect to the single-phase
processes. It has been demonstrated that the entire family of commercial
metal octoates shows a certain ability catalyzing glycolysis process.
The octoates have showed different catalytic activi ties according to
their hardness and coordination ability. Hardness c oncept of cations is
UHODWHGWRWKHLUUHVSRQVHOHYHOLQDQHOHFWULFDO¿H OGFRQFUHWHO\LQUHODWLRQ –
ship to the interactions with other atoms and ions. Therefore, it is connected
to their polarizability. It represents how easily a metal ion can be deformed

Chemical Recycling of Polyurethane Foams: A Review 33
LQWKHSUHVHQFHRIDQHOHFWULF¿HOGWKHVRIWHUWKH FDWLRQWKHPRUHSRODUL] –
able it is. The activity of alkaline an alkaline-ea rth metal octoates is basi-
cally related with their hardness as cation that de termines their potential
for the formation of a metal alkoxylate. In the cas e of transition metals,
the mechanism involves several steps, including the formation of a metal
alkoxylate, coordination insertion of the alkoxide into the urethane group,
and transfer from recovered polyol to glycol. The p resence of signals in
WKH,5VSHFWUXPRIWKHUHFRYHUHGSRO\ROVFRUUHVSRQG LQJWRWUDQVHVWHUL¿FD –
tion carbamates, DEG, and hydrolysis products such as aromatic amines
characteristic of certain paths of the coordination mechanism proposed
demonstrated it veracity. Among the octoates studie d, lithium and stannous
octoates showed a remarkable catalytic activity. Th ey yielded the greatest
quality for the recovered polyol as well as the hig hest decomposition rates. 27
A study was conducted where, PUF was dissolved in a mixture of DEG
and pentaerythritol (PER). PER is a useful choice in recycling processes
because of its OH functional groups and its structural similarity to pol yols.
The solvent system contained DEG/PER as 9/1 ratio. Sodium hydroxide
was used as the catalyst and the optimum reaction time was 4 h. T he
UHJHQHUDWHGSRO\ROSURYLGHGE\3(5DVVLVWHGJO\FRO\VLVRIÀH[LEOH38)
wastes is capable of high-quality foam formulation production. By opti-
mizing the recycling approach, it is possible to replace about 40% of the
virgin polyol by glycolysis product. Although the economic aspects of the
proposed method are of high interest, the environmental pollution reduc-
tion is the main advantage of the studied polyol regeneration approach. 5
It is useful to know that stannous octoate shows a proper performance
as catalyst in the glycolysis of PU wastes, yielding a great quality for
the recovered polyol in the shortest reaction time. Furthermore stannous
octoate also presents the advantage that the catalyst does not need to be
removed from the polyol for using in further foaming. An increase in the
reaction temperature and catalyst concentration enhances the degrada-
tion rate; however, this also negatively affects the process by extent of
side reactions and contamination of the polyol phase. High mass ratios of
glycolysis agent to PUF displace the equilibrium to the glycol substi tu-
tion, promote the phase splitting which allows the obtaining of a polyol-
rich phase, and avoid problems related to agitation due to undissolved
PU portions in the glycol. However, a too large excess of glycol would
imply huge volume equipment requirements and larger amounts of bottom
phase that has to be recycled by distillation. Taking all into considerat ion,

34 Engineering Technologies for Renewable and Recyclable Materials
equilibrium between reaction rates, polyol content in the upper phase a nd
recovered polyol properties must be achieved. 33,34
Further in a process, three phases are obtained: an upper phase which
contains the polyol, a bottom phase which has the s ubproducts of the reac-
tion and the excess of glycol, and a third phase wh ich is in the middle and
it is formed by the unreacted PU. Several factors t hat affect the reaction
have been studied to optimize the yield of obtained polyol. These factors
are the temperature of reaction, the time of reacti on, the catalyst (DEA) to
solvent (DEG) mass ratio, and the catalyst + solven t to PU mass ratio. The
catalyst reduces the reaction time and allows the c omplete breakdown of
the PU chain against the process with a lower quant ity of DEA. Also, a high
catalyst concentration affects negatively the proce ss because the secondary
reactions and the contamination of the polyol phase occur. Increasing the
relative amount of glycol does not provide any addi tional improvement in
the yield of polyol and affects negatively to the e conomy of the process 1.
2.2.2.1 MECHANISM OF DEPOLYMERIZATION USING METAL
SALT AS CATALYST
For transition metal salt catalysts, the activity o bserved cannot be justified
only on the basis of the different electronegativit ies or on the cationic–
ionic ratio. Some of the cations are located in the border of strong and soft
acids and also present some coordination abilities. As mentioned before,
the transesterification takes place by means of a n ucleophilic attack of the
glycol on the carbon of the carbonyl group. For thi s reason, and taking
into account several theories applied to polyester transesterification, it
can be postulated that the glycolysis of PU in the presence of transition
metal carboxylates is not only a result of a simple addition of an alkoxide
but there could be also an intermediate formed by a coordination complex
of the metallic species with the carbonyl group of the urethane, specially
favorable in the case of the stannous salt. In this way, the proposed mech-
anism for catalysts studied would be composed by a three step cycle.
/g21/g17/g21/g17/g21/g17/g20/g17/g20/g3 /g54/g87/g72/g83/g3/g49/g82/g17/g3/g20/g29/g3/g44/g81/g76/g87/g76/g68/g87/g82/g85/g3/g36/g79/g78/g82/g91/g76/g71/g72/g3/g41/g82/g85/g80/g68/g87/g76/g82/g81
The first step corresponds to the reaction of glycol (e.g., DEG) with
the metal octoate, producing a metal alkoxide species and free 2-ethyl

Chemical Recycling of Polyurethane Foams: A Review 35
hexanoic acid shown in Figure 2.8 . This was the starting acid used to form
the octoate salt. In this step, there is equilibrium between alkoxide and
carboxylate; the stabilities of both species being different, whic h in addi-
tion to the great excess of glycol, move the equilibrium to the alkoxide
formation.
FIGURE 2.8 Reaction of DEG with the octoate, producing a metal alkoxide species and
free 2-ethyl hexanoic acid.
/g21/g17/g21/g17/g21/g17/g20/g17/g21/g3 /g54/g87/g72/g83/g3/g49/g82/g17/g3/g21/g29/g3/g38/g82/g82/g85/g71/g76/g81/g68/g87/g76/g82/g81/g18/g44/g81/g86/g72/g85/g87/g76/g82/g81/g3/g68/g81/g71/g3/g40/g91/g70/g75/g68/g81/g74/g72
After the alkoxide formation, in the case of cations with coordination
ability, a coordination of the cation and the carbonyl oxygen atom would
be produced. This interaction decreases electron density in the carbonyl
group, which enhances the nucleophilic insertion of the alkoxide moieties
as in Figure 2.9 . After the exchange, the polyol is released to the reaction
medium in an irreversible way, since the glycol is added in a large exc ess
and polyol molecules are so big that statistics does not allow sub stitution.
This step in the mechanism implies that metal cations able to produce
coordination would improve the process, as does tin.
FIGURE 2.9 Coordination of the cation and the carbonyl oxygen atom/nucleophilic
insertation of the alkoxide moieties.

36 Engineering Technologies for Renewable and Recyclable Materials
/g21/g17/g21/g17/g21/g17/g20/g17/g22/g3 /g54/g87/g72/g83/g3/g49/g82/g17/g3/g22/g29/g3/g36/g70/g87/g76/g89/g72/g3/g54/g83/g72/g70/g76/g72/g86/g3/g53/g72/g74/g72/g81/g72/g85/g68/g87/g76/g82/g81
The third step requires the active species regeneration in order to continue
the transesterification. The regeneration undergoes by a fast intermolec-
ular exchange of the metal alkoxide moiety in the polyol for a proton from
hydroxyl groups of glycol shown in Figure 2.10 . As in the first step, the
interaction between species, concretely cation–polyol and cation–glycol,
is responsible for the equilibrium shift. In the case of using a glycol and a
divalent cation, the substitution yields a more stabile structure if a ring is
formed described in Figure 2.11 ; this means that polyol regeneration would
be enhanced. This fact has also been reported for stannous octoate in ester
exchange reactions with glycol. Depending on the catalyst type (alkaline,
alkaline earth, or transition metal salt), the first step, namely, alkoxi de
formation, or the coordination for the insertion would be promoted. As it
has been observed experimentally, lithium and stannous octoates are the
most active catalysts in good agreement with their greater hardness and
coordination ability, respectively.
FIGURE 2.10 Intermolecular exchange of the metal alkoxide moiety in the polyol for a
proton from hydroxyl groups of glycol.
FIGURE 2.11 Stable ringlike structure formed between the glycol and divalent cation.
/g21/g17/g21/g17/g22/g3 /g43/g60/g39/g53/g50/g47/g60/g54/g44/g54
Hydrolysis is the second most important method of chemical recycling of
PU. Various studies have been published dealing with PU degradation by

Chemical Recycling of Polyurethane Foams: A Review 37
reaction with liquid water (150–200°C) or steam (200–320°C). The hydro-
lytic reaction proceeds as shown in Figure 2.12 .13
FIGURE 2.12 Polyurethane hydrolysis.
3RO\ROVGLDPLQHVDQGFDUERQGLR[LGHDUHWKH¿ QDOSURGXFWVIRUPHGE\
PU hydrolysis. The reaction between the diamine and phosgene allows the
corresponding isocyanate to be formed, whereas the subsequent polym-
erization of this isocyanate and the polyols yields the starting PU again.
Mahoney et al. 24 have described the reaction of PUF and superheated
water at 200șC for 15 min, which leads to TDA and polypropylene oxide.
Hydrolysis of PU and rubber mixtures has been used as a method not
only of recovering valuable chemicals from the PU fraction but also to
separate the polymers because rubber is inert to hydrolysis. The degrada-
tion takes place by contact with saturated steam at 200°C for 12 h. This
SURFHVV PD\ ¿ QG SDUWLFXODU DSSOLFDWLRQV LQ WKH WUHDWPHQW RI UXEEHU38
laminations. The mechanism and kinetics of the reaction of PUF with dry
steam have been investigated by Gerlock et al. 17 using a polyether-based
TDI as starting material. Reaction with steam at temperatures b etween
190°C and 250°C caused the destruction of all urea and urethane link-
DJHVWR\LHOGDKLJKTXDOLW\SRO\ROSURGXFWDOWKRXJKDVLJQL¿ FDQWGLIIHU
ence in reactivity between these two types of linkages was obse rved. The
authors propose that the urethane bonds are rapidly broken by hydrolysis
according to the reaction shown in Figure 2.13 , whereas the urea linkages
undergo a slow thermal dissociation to form the corresponding isocyanate
and amine. Finally, the formed isocyanate is also hydrolyzed, increasing
the yield of TDA. The effect of basic catalysts on these reactions w as
also investigated, a sharp acceleration being observed with the additi on
of sodium hydroxide at levels of about 2.9 mg per 100 mg of foam. The
polyols obtained by this treatment were mixed with virgin polyol in a rat io
RI\LHOGLQJDKLJKTXDOLW\À H[LEOHIRDP 13
A study carried out in which neutral hydrolytic depolymerization of
the PU waste was done using 0.5 L high-pressure autoclave at tempera-
tures of 150°C, 180°C, 200°C, and 240°C, the autogenious pressures of

38 Engineering Technologies for Renewable and Recyclable Materials
75, 160, 220, and 480 psi, and time intervals of 30, 45, 60, and 90 min.
The obtained product was characterized by measuring its amine value. The
optimum amount of catalysts such as zinc acetate and lead acetate was
found to be 1 g. Zinc acetate was more effective catalyst than lead a cetate
for the depolymerization of PUF reaction. On the basis of amine value and
residual weight of the depolymerized product, the velocity constant was
obtained and found to be in order of 10 í min í , and the reaction was found
WREH¿UVWRUGHU1HPDGHHWDO
FIGURE 2.13 Mechanism for hydrolysis of polyether-based toluene diisocyanate
polyurethane.
A successful attempt wherein post-use PUF was degraded in super-
heated water at 423 to 623 K. The yield of TDA, one of the products,
reached near 90%. The hydrolysis conditions—time and temperature were
important and the perfect liquid products could be obtained under the
economic conditions at 523 K for 30 min. TDA was added to the reaction
to investigate the effect on the decomposition of PUF waste. 15
/g21/g17/g21/g17/g23/g3 /g36/g48/g48/g50/g49/g50/g47/g60/g54/g44/g54/g3/g36/g49/g39/g3/g36/g48/g44/g49/g50/g47/g60/g54/g44/g54
PU chemolysis by reaction with ammonia or amines has been described
by Sheratte et al. (1978); he had proposed a process based on PU

Chemical Recycling of Polyurethane Foams: A Review 39
decomposition by various agents. Several examples were provided for
PU degradation with ethanolamine (120°C), ammonia and ammonium
hydroxide (180°C), diethylene triamine (200°C) and other basic reagents.
In all cases the process involves, simultaneously or subsequently, reacti on
with propylene oxide, which allows the different amines obtained to be
quantitatively converted into polyols according to the reaction shown in
Figure 2.14 . The polyols derived from this process were used in the refor-
mulation of new PU by polymerization with the corresponding isocyanate
and were suitable for application in rigid foams.
FIGURE 2.14 Conversion of primary amines into polyols by reaction with propylene
oxide.
An interesting ammonolysis process has recently been developed
based on the reaction of PU with ammonia under supercritical conditions,
which favors both the degradation reactions and separation of the polyols
SURGXFHG7KHÀ RZGLDJUDPRIWKLVSURFHVVLVVKRZQLQ )LJXUH 7ZR
different PU were used as starting materials: a solid elastomer ba sed on
a trifunctional polyethertriol, 1,4-butanediol, and methylene bis(pheny1
LVRF\DQDWHDQGDÀ H[LEOHIRDPZKHUHWKHGLROZDVUHSODFHGE\ZDWHU7KH 
ammonolysis reactions were carried out at 139°C and 140 atm for 120
min, and with a PU/ammonia weight ratio of 1. Under these conditions the
PU conversion was practically total. The ammonolysis reaction transforms
the CO group into urea and the ester groups and derivatives of carboxylic
acids into amides, whereas ether and hydroxyl groups are inert toward
ammonia. 13 Figure 2.16 illustrates the stoichiometry proposed by the
authors for the ammonolysis of the polyether urethane. The diamines and
the diol can be separated by distillation or precipitation. The phosgena tion
of the amine leads to the corresponding diisocyanate, which together with
the polyol and the diol may be used in the recovery of the raw PU.

40 Engineering Technologies for Renewable and Recyclable Materials
FIGURE 2.15 Ammonolysis of PU by treatment with supercritical ammonia.
FIGURE 2.16 Stoichiometry of ammonolysis of polyether polyurethane.
After the reaction, urea is separated by extraction with water, whereas
the polyol remains as a residue in the reactor. Therefore, under supercrit-
ical conditions, the polyether polyols are separated from the mixture at
the same time that the ammonolysis reaction progresses. Watando et al . 40
has proposed a process based on PUF decomposition using DEA in an

Chemical Recycling of Polyurethane Foams: A Review 41
extruder and the resulting decomposed product could be used as an alter-
native virgin polyol in reclaiming PU elastomers. In an experiment by
Fukaya, a reheating process for the products in the chemical recycling of
rigid PUF by an extruder with DEA as a decomposing agent was effective
for improving the product stability. In another experiment by Chuayjuljit,
rigid PUF scrap was depolymerized by aminolysis using diethylene
triamine as a degrading agent and sodium hydroxide as both a reactant and
FDWDO\VWUHVXOWLQJLQƍPHWK\OHQHGLDQLOLQH 11 Kanaya proposed a system
ZKHUHLQ ÀH[LEOH IRDPV ZHUH GHFRPSRVHG E\ DONDQRODPLQHV ZLWKRXW D
catalyst at 150°C and decomposed products were completely separated
into two layers, the upper liquid layer being a polyol and the lower liquid
layer of methylene diphenyl amine. 23 Lee et al. carried out aminolysis of
rigid PU using diethylene triamine and studied the application of amino-
lyzed products as hardeners of epoxy resins. 20,21,41
/g21/g17/g21/g17/g24/g3 /g38/g50/g48/g37/g44/g49/g40/g39/g3/g38/g43/g40/g48/g50/g47/g60/g54/g44/g54
Several promising alternatives have been described for PU chemical
recycling through a combination of treatments. The Ford hydroglycol-
ysis process is a good example of these combined alternatives because
it couples hydrolytic and glycolytic reactions to degrade the PU chains.
This process was developed while trying to solve some of the problems
present in conventional PU glycolysis, in which a complex mixture of
products is obtained, made up of diamines, aminocarbamates, urea linked
aminocarbamates oligomers, glycols, and polyols. The composition is
difficult to predict, hence the properties of the PU produced using this
recycled mixture directly are difficult to control. An alternative is the
separation and purification of the produced polyol, but this is not an
easy task. On the contrary, the product obtained in the hydroglycolysis
process is made up of significantly fewer products, which makes purifi-
cation of the polyols more feasible. Figure 2.17 is a flow diagram of the
Ford hydroglycolysis process. In the reactor, PUF is degraded in the pres-
ence of water, DEG and alkali metal hydroxides at 200°C. When NaOH
is added to the reaction mixture as a catalyst, a cleaner polyol is o btained
due to the absence of carbamates and ureas in the product—they are trans-
formed into amines and alcohols by hydrolysis. After 4 h of reaction, all
the PU is decomposed, yielding polyols, amines, isocyanates, and carbon

42 Engineering Technologies for Renewable and Recyclable Materials
FIGURE 2.17 Ford hydroglycolysis of polyurethane foam.
dioxide. Separation of the products takes place by extraction with hydro-
carbons such as hexadecanes (separation Tank l), which dissolve most of
the polyols. Moreover, phase separation occurs at about 160°C and the
polyols are expelled from the hydrocarbons (separation Tank 2), being
purified by vacuum distillation. Finally, the glycol-rich phase, coming out

Chemical Recycling of Polyurethane Foams: A Review 43
of the first settling tank, is filtered to remove impurities and also vacuum
distilled to separate the amines and DEG, the latter being recycle d back to
the reactor. Variations of this process have been patented by isolation of
the glycolytic and hydrolytic treatments in different steps and/or the use
of steam as hydrolyzing agent. The quality of the polyols produced in this
hydroglycolysis process was evaluated by using them in the formulation
of new PU by partial replacement of commercial polyols. The foam so
produced did not have significantly different physical properties than the
all-virgin foam, even with replacement levels of 50%. 13 In a novel study,
the combination of glycolysis and aminolysis has also been described for
the chemical recycling of PU. Kondo et al .22 have reported the degrada-
tion of both PU and polyisocyanurate foams by reaction with a mixture
of a glycol (DEG, dipropylene glycol, 1,4-butanediol, or 1,5-pentanediol)
and monoethanolamine at around 200°C for 30 min. The liquid product
obtained was used in the production of rigid PUF that, although slightly
brown in color, exhibited properties suitable for application as a heat insu-
lating material. Similarly, a recent work combines aminolysis and hydro-
lysis reactions for achieving PU decomposition. Thus, scrap PU is reacted
with a mixture of DEA and aqueous sodium hydroxide. The simultaneous
attack of these agents on the polymeric chains allows the reaction tim e
to be appreciably shortened. The reaction product, obtained as an emul-
sion, is subjected to a second treatment with propylene oxide in order to
transform the amines and ureas present in the mixture into polyols, giving
a final product which is substantially free of any hydrogen-containing
nitrogen atoms. The polyols produced have been found to be particularly
suitable for the preparation of fresh PU polymer which can be used as an
elastomer or flexible foam.
/g21/g17/g21/g17/g25/g3 /g48/g44/g38/g53/g50/g58/g36/g57/g40/g3/g39/g40/g51/g50/g47/g60/g48/g40/g53/g44/g61/g36/g55/g44/g50/g49
In this study, microwave irradiation has been used as an energy source
for glycolyzing flexible PUF wastes. In order to study the susceptibility
of the foam and select a system to obtain the highest quality recovered
polyol, the reactions were performed in the presence of various basic cata-
lysts and microwave powers. The completion and dissolution of the foam
was measured, the obtained products separated in two split phases, a nd
the recovered polyol in the upper phase was characterized and compared
by virgin polyol by using FTIR, 1HNMR, and 13 CNMR spectroscopic

44 Engineering Technologies for Renewable and Recyclable Materials
methods. All the assayed catalysts showed appropriate activity comp ared
with the noncatalyzed process, allowing the recovery of polyols from
the PU matrix. According to obtained information, potassium hydroxide,
especially, has been found advantageous for the recovery process due to
the reaction performance completely at the shortest reaction time, where as
the reactions performed with zinc acetate in comparison with the other
basic catalysts has longer reaction time, potassium hydroxide and sodium
hydroxide lead to the complete degradation of the polymeric chain at low
reaction time and the recovery of the polyol in high quality. 2
Researchers attempt to carry out glycolysis reactio n of cold cure
ÀH[LEOH38)LQDPLFURZDYHRYHQDWDWPRVSKHULFSUHV VXUH,QRUGHUWR
obtain high-quality recovered polyols via “split-ph ase” condition and
short-reaction times, glycerin and sodium or potass ium hydroxides were
used as solvent and catalysts, respectively. Reacti ons were carried out
at various temperatures, namely, 160°C, 180°C, 200° C, and 220°C.
Decreasing of reaction time was observed by the inc reasing in reac-
tion temperature. On the order hand, microwave irra diation accelerated
the conversion reaction 20–30 times faster than con ventional heating
methods. Hence, microwave can be used as an energy source in glycol-
ysis reactions and their performance was monitored at short time with
simple controlled conditions 3.
,QDQRWKHUH[SHULPHQWWKHFKHPLFDOUHF\FOLQJRIÀH[LEOH38)ZDVWHV
are performed through hydroglycolysis process under microwave irradia-
tion at atmospheric pressure and 160°C. Mixtures of glycerin, water, and
sodium hydroxide are used as hydroglycolysis agent. Water is added at
different ratios containing 5%, 10%, 15%, 20%, 25%, 30%, 35%, and 40%
of solvent system. The effect of water in the foam dissolution rate as we ll
DVZDWHUFRQWHQWRI¿QDOUHFRYHUHGSRO\ROLVLQYHVWLJDWHG$OWKRXJKDGGL –
tion of water as the second reagent in the hydroglycolysis agent slows
foam dissolution (such that only 20% of the foam dissolves after 15 min),
it is a potential low-cost replacement for up to 40% of the glycerin, sinc e
reasonable dissolution times are still achievable (compared with 10 h for
conventional heating). 7+\GURJO\FRO\VLVRIÀH[LEOHSRO\XUHWKDQHUXEEHU
(PUR) foam has been studied under the microwave radiation with glyc-
erol/sorbitol/water mixtures, differing in compositions, and NaOH were
used as glycolysis agents and the catalyst, respectively. An increase in
sorbitol part in the mixture being glycolysis agent prolongs the glycolysis
process. 4

Chemical Recycling of Polyurethane Foams: A Review 45
/g21/g17/g21/g17/g26/g3 /g39/g40/g42/g53/g36/g39/g36/g55/g44/g50/g49
Researchers propose a system in which dimethyl phosphonate is used as
a degrading agent for PU elastomer based on diphenylmethane diisocya-
nate and polyester polyol. The results obtained reveal that the chemica l
degradation proceeds at 142°C without any catalysts. The degradation
products are phosphorus containing oligomers with phosphonate end
groups. These products, directly or after chemical treatment, can be used
for the synthesis of PU with reduced flammability or as additives to poly-
mers improving their fire resistance. It is likely that other diesters (al kyl
and aryl) of phosphonic acid, esters of alkyl(aryl)phosphonate acid, as
well as alkyl(aryl)ester of phosphoric acid, could also participate in the
abovementioned reactions and could also degrade polyesters, polycarbon-
ates, and phosphorylated polyamides. 34 Flexible PUF based on polyester
or polyether polyol and TDI can be converted quantitatively into liquid
form by treatment with triethyl phosphate (TEP) by reaction between the
urethane group and ethoxy groups of phosphoric acid triethyl ester. The
degraded products are phosphorus containing oligourethanes which can
be used as a flame retardant. 35
In another experiment, diethyl phosphonate and tris (1-methyl-2-chlo-
roethyl) phosphate were used as degrading agents for microporous PU
HODVWRPHU'HJUDGHGSURGXFWVFOHDUO\FRQ¿UPWKDWWKHOLTXHIDFWLRQRIWKH
microporous PU elastomer results from the proceeding of exchange reac-
tion between ethoxy groups of diethyl phosphonate or 1-methyl-2-chlo-
roethoxy groups of tris (1-methyl-2-chloroethyl) phosphate and urethane
groups. The rate of the exchange reaction depends on the type of the
ĮFDUERQDWRPRIWKHGHJUDGLQJDJHQWV'HJUDGHGSURGXFWVDUHSKRVSKRUXV
or phosphorus and chlorine containing oligomers. 36
In another study, chemical degradation of used PU was intentionally
PDGH E\ WKH DGGLWLRQ RI ÀDPH UHWDUGDQWV VXFK DV WULVFKORURSURS\O
phosphate (TCPP), TEP, and trimethyl phosphonate (TMP). Final product
obtained after the degradation reaction turned out to be phosphorous
containing oligourethanes. Rigid PUF was produced using the degraded
SURGXFWV DV ÀDPH UHWDUGDQWV 7KH ÀDPPDELOLW\ DQG WKHUPDO VWDELOLW\ RI
recycled rigid PU was investigated. The mechanical properties such as
compressive strength and tensile strength of recycled PU were also
VWXGLHG7KHUHF\FOHG38VKRZVUHGXFHGÀDPPDELOLW\DQGKLJKHUWKHUPDO
stability over virgin PU. Mechanical strength of recycled PU also shows

46 Engineering Technologies for Renewable and Recyclable Materials
DVKLJKDVWKDWRIYLUJLQ38,QRUGHUWRHYDOXDWHÀDPHUHWDUGDQWSURSHU –
ties of the recycled PUF with various amounts of depolymerized product,
heat release rate of the foam was measured by cone calorimeter. Scanni ng
electron micrograph of recycled PU shows uniform cell morphology as
virgin PU. 12
Polyester PUR had attracted attention because of its biodegradability.
There are many reports on the degradation of polyester PUR by micro-
organisms, especially by fungi. Microbial degradation of polyester PUR
is thought to be mainly due to the hydrolysis of ester bonds by esterases.
5HFHQWO\SRO\HVWHU385GHJUDGLQJHQ]\PHVKDYHEHHQSXUL¿HGDQGWKHLU
characteristics have been reported. Among them, a solid-polyester-PUR-
degrading enzyme (PUR esterase) derived from Comamonas acidovorans
TB-35 had unique characteristics. This enzyme has a hydrophobic PUR
surface binding domain and a catalytic domain, and the surface-binding
domain was considered as being essential for PUR degradation. This hydro-
phobic surface-binding domain is also observed in other solid-polyester-
degrading enzymes such as polyhydroxyalkanoate (PHA) depolymerases.
7KHUHZDVQRVLJQL¿FDQWKRPRORJ\EHWZHHQWKHDPLQRDFLGVHTXHQFHRI
PUR esterase and that of PHA depolymerases, except in the hydrophobic
surface-binding region. Thus, PUR esterase and PHA depolymerases are
probably different in terms of their evolutionary origin and it is possible
WKDW385HVWHUDVHFRPHWREHFODVVL¿HGDVDQHZVROLGSRO\HVWHUGHJUD GLQJ
enzyme family. 19
2.3 CONCLUSION
The purpose of chemical recycling is the recovery of polyols, which can
be reused in the production of PUF, by the depolymerization of PUF
scrap. Numerous processes applicable to chemical recovery of PUF have
been proposed including hydrolysis, aminolysis, glycolysis, alcoholysis,
and combinations thereof such as hydroglycolysis. These processes vary
according to the quality of the PU feed that can be used, the quality of the
end products, and the number of purification and washing steps involved.
In hydrolysis, PU are broken down into their original precursors; the base
polyol and an amine, by the application of superheated steam In principle ,
it is possible to separate the amine obtained from the hydrolysis proc ess
and, after purification, use it again as a raw material for the isocyanate

Chemical Recycling of Polyurethane Foams: A Review 47
process. In aminolysis, the PU scrap is chemically cleaved by amines such
as dibutylamine; ethanolamine or lactam are added to the PUF scrap. T he
decomposition of PUF with amines leads to quite a different product mix
than with glycolysis and hydrolysis. Aminolysis converts the urethane
linkages to polyol and disubstituted urea which in turn, breaks down to
yield oligomeric ureas and amines. Aminolysis is not much explored route
for recycling, hence we have proposed aminolysis as a tool to recycle PUF
in chapter ahead. Glycolysis of PU is by far the most promising chemical
recycling route for PUF.
KEYWORDS
•recycle
•polyurethane
•foams
•degradation
•green chemistry
REFERENCES
1. Aguado, A.; Martínez, L.; Moral, A.; Fermoso, J.; Irusta, R. Chemical Recycling of
Polyurethane Foam Waste via Glycolysis. Chem. Eng. Trans. 2011, 24 , 1069–1074.
2. Alavi Nikje, M. M.; Nikrah, M. Microwave-assisted Glycolysis of Polyuret hane Cold
Cure Foam Wastes from Automotive Seats in “Split-Phase” Condition. Polym. Plast.
Technol. Eng . 2007, 46 , 409–415.
3. Alavi Nikje, M. M. “Split-phase” Glycolysis of Flexible PUF Wastes and Application
of Recovered Phases in Rigid and Flexible Foams Production. Polym. Plast. Technol.
Eng . 2007, 46 , 265–271.
4. Alavi Nikje, M. M.; Mohammadi, F. H. A. Sorbitol/Glycerin/Water Te rnary System
as a Novel Glycolysis Agent for Flexible Polyurethane Foam in the Chemica l Recy-
cling using Microwave Radiation. Polimery 2009, 54 , 541–546.
5. Alavi Nikje, M. M.; Tavassoli, K. M. Chemical Recycling of Semi-rigid Polyure-
thane Foams by using an Eco-friendly and Green Method. Curr. Chem. Lett . 2012,
1, 175–180.
6. Alavi Nikje, M. M.; Nikrah, M. Glycerin as a New Glycolysing Agent for Chem-
ical Recycling of Cold Cure Polyurethane Foam Wastes in “Split-phase” Condit ion.
Polym. Bull . 2007, 58 , 411–423.

48 Engineering Technologies for Renewable and Recyclable Materials
7. Alavi Nikje, M. M.; Nikrah, M.; Mohammadi, F. H A. Microwave-assiste d Polyure-
thane Bond Cleavage via Hydroglycolysis Process at Atmospheric Pressure. J. Cell.
Plast . 2008, 44 , 367–380.
8. Alavi Nikje, M. M.; Nikrah, M.; Haghshenas, M. Microwave Assisted “S plit-phase”
Glycolysis of Polyurethane Flexible Foam Wastes. Polym. Bull . 2007, 59 , 91–104.
9. Beyler, C. L.; Marcelo, M H. Thermal Decomposition of Polymers. In SFPE Hand-
book of Fire Protection Engineering. 2002 , 2, 111–131.
10. Borda, J.; Pasztor, G.; Zsuga, M. S. Glycolysis of Polyurethane Foams and Ela sto-
mers. Polym. Degrad. Stab . 2000, 68 , 419–422.
11. Chuayjuljit, S.; Norakankorn, C.; Pimpan, V . Chemical Recycling of Rigid Polyure-
thane Foam Scrap via Base Catalyzed Aminolysis. J. Met. Mater. Miner . 2002, 12 (1),
19–22.
12. Chung, Y .; Kim, Y .; Kim, S. Flame Retardant Properties of Polyurethane Produced
by the Addition of Phosphorous Containing Polyurethane Oligomers (II). J. Ind. Eng.
Chem . 2009, 15 , 888–893.
13. Clark, J. Feedstock Recycling of Plastic Wastes, 1st Ed., Royal Society of Chemistry:
UK, 1999; pp 31–56.
14. Clark. J.; Macquarrie, D. Handbook of Green Chemistry and Technology , 1st Ed.,
Blackwell Publishing: New Jersey, 2002; pp 1–9, 56–60.
15. Dai, Z.; Hatano, B.; Kadokawa, J.; Tagaya H. Effect of Diaminotoluene on t he
Decomposition of Polyurethane Foam Waste in Superheated Water. Polym. Degrad.
Stab . 2002 , 76 , 179–184.
16. Doble, M.; Kruthiventi, A. K. Green Chemistry and Engineering ; Academic Press,
Elsevier Inc.: London, 2010.
17. Gerlock, J. L.; Braslaw, J.; Mahoney, L R.; Ferris, F. C. Hydrolysis of Polyurethane
Foam Waste. J. Appl. Polymer Sci . 1980, 18 , 541.
18. Hans, R. K.; Oskar, N.; Graham, S. Handbook of Polymer Synthesis , 2nd Ed., Marcel
Dekker: New York, 2004; pp 511–517.
19. Kambe, Y .; Nakajima, T.; Akutsu, S.; Nomura, N.; Onuma, F.; Nakahara, T. M icrobial
Degradation of Polyurethane, Polyester Polyurethanes and Polyether Polyurethanes.
Appl. Microbiol. Biotechnol . 1999, 51 , 134–140.
20. Keesuwan, S.; Chen, J. Recycling of Polyurethane Foam as a Hardener for Epoxy
Resin. J. Sci. Res . 1998, 23 (2), 155–165.
21. Kim, B. C.; Lee, D. S.; Hyun, S. W. Curing Behavior of Epoxy Resin Using Aminol-
ysis Products of Waste Polyurethane as Hardners. J. Ind. Eng. Chem . 2001, 7(6),
449–453.
22. Kondo, O.; Hashimoto, T.; Hasegawa, H. US Patent 4 014 809, 1977.
23. Kanaya, K.; Takahashi, S. Decomposition of Polyurethane Foams by Alkanolamine s.
J. Appl. Polym. Sci . 1994, 51 , 675–682.
24. Mahoney, L. R.; Weiner, S. A.; Ferris, F. C. Hydrolysis of Polyurethane Foam Wast e.
Environ. Sci. Technol . 1974, 8, 135.
25. Mantia, F. P. Recycling of Plastic Materials, 1st Ed. ChemTec Publishing: Canada,
1993; pp 1–14.
26. Modesti, M.; Simioni, I.; Munari, R.; Baldoin, N. Recycling of Flexible Polyurethane
Foams with Low Aromatic Amine Content. React. Funct. Polym . 1995, 26 , 157–165.

Chemical Recycling of Polyurethane Foams: A Review 49
27. Molero, C.; de Lucas, A.; Rodriguez, J. F. Activities of Octoate Salts as Novel Cata-
lysts for the Transesterification of Flexible Polyurethane Foams with Die thylene
Glycol. Polym. Degrad. Stab . 2009, 94 , 533–539.
28. Molero, C.; de Lucas, A.; Rodriguez, J. F. Recovery of Polyols from Flexible Poly-
urethane Foam by “Split-phase” Glycolysis: Study on the Influence of Reacti on
Parameters. Polym. Degrad. Stab . 2008, 93 , 353–361.
29. Molero, C.; de Lucas, A.; Rodriguez, J. F. Recovery of Polyols from Flexible Poly-
urethane Foam by ‘‘Split-phase’’ Glycolysis: Glycol Influence. Polym. Degrad. Stab .
2006, 91 , 221–228.
30. Molero, C.; de Lucas, A.; Rodriguez, J. F. Recovery of Polyols from Flexible Poly-
urethane Foam by ‘‘Split-phase’’ Glycolysis with New Catalysts. Polym. Degrad.
Stab . 2005, 91 , 894–901.
31. Nemade, A. M.; Mishra, S.; Zope, V . S. Kinetics and Thermodynamics of Ne utral
Hydrolytic Depolymerization of Polyurethane Foam Waste Using Different Catal ysts
at Higher Temperature and Autogenious Pressures. Polym. Plast. Technol. Eng . 2010,
49 , 83–89.
32. Nikje Alavi, M. M.; Haghshenas, M.; Garmarudi, A. B. Preparation and Applic ation
of Glycolysed Polyurethane Integral Skin Foams Recyclate from Automotive Wastes .
Polym. Bull . 2006, 56 , 257–265.
33. Simon, D.; Garcia, M. T.; de Lucas, A.; Borreguero, A. M.; Rodriguez, J. F. Glycol-
ysis of Flexible Polyurethane Wastes Using Stannous Octoate as the Cat alyst: Study
on the Influence of Reaction Parameters. Polym. Degrad. Stab . 2013, 98 , 144–149.
34. Troev, K.; Grancharov, G.; Tsevi, R.; Tsekova, A. A Novel Approach to Recycling of
Polyurethanes: Chemical Degradation of Flexible Polyurethane Foams by Triethyl
Phosphate . Polymer 2000, 41 , 7017–7022.
35. Troev, K.; Grancharov, G.; Tsevi, R. Chemical Degradation of Polyurethanes 3.
Degradation of Microporous Polyurethane Elastomer by Phosphonate and Tris(1-
methyl-2-chloroethyl) Phosphate. Polym. Degrad. Stab . 2000, 70 , 43–48.
36. Troev, K.; Atanasov, I.; Tsevi, R.; Grancharov, G.; Tsekova, A. Chemical Degrada tion
of Polyurethanes. Degradation of Microporous Polyurethane Elastomer by Dimethyl
Phosphonate. Polym. Degrad. Stab . 2000, 67 , 159–165
37. Ulrich, H.; Odinak, A.; Tucker, B.; Sayigh, A. R. R. Recycling of Polyurethane and
Polyisocyanurate Foam. Polym. Eng. Sci . 1978, 18 (11), 844–848.
38. Ulrich H. Recycling of Polyurethane and Isocyanurate Foam. Adv. Urethane Sci.
Technol. 1978, 5, 49.
39. Valavanidis, A.; Vlachogianni, T. Green Chemistry and Green Engineering, 1st Ed.
Synchrona Themata, Non Profit Publishing House: Athens, 2012; pp 17–44, 45–60.
40. Watando, H.; Saya, S.; Fukaya, T.; Fujieda, S.; Yamamoto, M. Improving Chemica l
Recycling Rate by Reclaiming Polyurethane Elastomer from Polyurethane Foam.
Polym. Degrad. Stab. 2006, 91 , 3354–3359.
41. Xue, S.; Omoto, M.; Hidai, T.; Imai, Y . Preparation of Epoxy Hardeners from Was te
Rigid Polyurethane Foam and Their Applications. J. Appl. Polym. Sci . 1995, 56 ,
127–134.