ArticlePDF Available

An Insight on the Chemistry of Epoxy and Its Curing for Coating Applications: A Detailed Investigation and Future Perspectives.

Authors:
  • Central Institute of Petrochemicals Engineering and Technology BHUBANESWAR
  • Central Institute of Petrochemicals Engineering and Technology (CIPET) , Bhubaneswar

Abstract and Figures

This article is aimed to focus on the developments in the polymeric materials used for coating with special importance to epoxy. A detailed discussion commencing from epoxy derived from both petroleum and plant resources, classification and its application have been elaborated along with various types of curing agents and some potential greener UV-curing techniques used in coating technology. Also detailed discussion on the future perspectives of the polymers in coating has been presented, which may be useful in framing-up the future of polymers from renewable resources via greener route.
Content may be subject to copyright.
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=lpte20
Download by: [Kungliga Tekniska Hogskola] Date: 09 May 2016, At: 22:37
Polymer-Plastics Technology and Engineering
ISSN: 0360-2559 (Print) 1525-6111 (Online) Journal homepage: http://www.tandfonline.com/loi/lpte20
Insight on the Chemistry of Epoxy and Its Curing
for Coating Applications: A Detailed Investigation
and Future Perspectives
Sukanya Pradhan, Priyanka Pandey, Smita Mohanty & Sanjay Kumar Nayak
To cite this article: Sukanya Pradhan, Priyanka Pandey, Smita Mohanty & Sanjay Kumar Nayak
(2016) Insight on the Chemistry of Epoxy and Its Curing for Coating Applications: A Detailed
Investigation and Future Perspectives, Polymer-Plastics Technology and Engineering, 55:8,
862-877, DOI: 10.1080/03602559.2015.1103269
To link to this article: http://dx.doi.org/10.1080/03602559.2015.1103269
Accepted author version posted online: 05
Nov 2015.
Submit your article to this journal
Article views: 54
View related articles
View Crossmark data
POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING
2016, VOL. 55, NO. 8, 862–877
http://dx.doi.org/10.1080/03602559.2015.1103269
Insight on the Chemistry of Epoxy and Its Curing for Coating Applications:
A Detailed Investigation and Future Perspectives
Sukanya Pradhana,b, Priyanka Pandeya, Smita Mohantya,b, and Sanjay Kumar Nayaka,b
aCentral Institute of Plastics Engineering and Technology (CIPET), Chennai, Tamil Nadu, India; bLaboratory for Advanced Research in Polymeric
Materials, Central Institute of Plastics Engineering and Technology, Bhubaneswar, Odisha, India
ABSTRACT
This article is aimed to focus on the developments in the polymeric materials used for coating with
special importance to epoxy. A detailed discussion commencing from epoxy derived from both
petroleum and plant resources, classification and its application have been elaborated along with
various types of curing agents and some potential greener UV-curing techniques used in coating
technology. Also detailed discussion on the future perspectives of the polymers in coating has
been presented, which may be useful in framing-up the future of polymers from renewable
resources via greener route.
GRAPHICAL ABSTRACT
KEYWORDS
Bio-based; coating; curing;
epoxy
Introduction
Polymeric materials are rapidly replacing conventional
material used in coating applications. Polymer-coating
materials comprise of a polymer coat and a substrate
adhered to each other through a specific coating process.
This combination allows incorporating additional
properties into the system. Polymer coat contributes
toward the impermeability of liquids, gases, and dust
particles. In some applications the coats also introduce
antimicrobial properties, enhance conductivity, and
provide shielding from electromagnetic interference/
radio frequency interference. They can also be used for
modifying the decorum of the surface of application
[1]
.
Epoxy resins, owing to its excellent chemical,
corrosion resistance, outstanding adhesion properties,
low shrinkage, and low price, are being widely used in
various coating applications. Also the property of cured
epoxy coating depends on curing agent and curing pro-
cess as well. These curing agents are cross-linking agents
CONTACT Sukanya Pradhan pradhan.sukanya2@gmail.com Central Institute of Plastics Engineering and Technology (CIPET), TVK Industrial Estate,
Guindy, Chennai, 600032, Tamil Nadu, India.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lpte.
© 2016 Taylor & Francis
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
which are labile hydrogen compounds such as acids,
anhydrides, amines, etc.
[2]
.
This article reports about various epoxy and curing
agents and methods. A comparative aspect of other
available materials and epoxy resin has been also dis-
cussed. Furthermore an in-depth analysis about the type
of epoxy material is presented; subsequently the advan-
tage of bio-based epoxy over other available polymer
has been reported. Also a detailed discussion about
types of curing techniques has been reported wherein
various types of UV-curing methods and its advantages
over conventional techniques have been elaborated.
Polymeric materials in coating
Alkyds, polyesteramides (PEAs), polyester polyethera-
mides, polyurethanes, polyols, and epoxies are the
common use polymeric constituents for coating.
Alkyds
Alkyd resins are commonly used in coating and paint
industry due to ease of application in changing environ-
mental condition. It has been introduced in the 1930s as
binders for paints. The first alkyd resin was synthesized
in the mid-1920s by Kienle
[3]
who combined the already
known technology for producing polyester resins based
on glycerol and phthalic anhydride. Several papers, pub-
lished by Hofland, describe alkyd emulsion paint for-
mulating techniques. Alkyd resins are branched
polyesters that are obtained by reacting dicarboxylic
acids or anhydrides and polyols such as glycerol or pen-
taerythritol, and long-chain unsaturated monocar-
boxylic fatty acids derived from natural oils
[4]
. Alkyd
paints have dominated the architectural coating market
for a long period until the appearance of polymer dis-
persion or the so-called latex paints. Though some
new polymeric compositions have replaced the alkyds,
wood and metal application alkyd paints enjoy the
majority of the application. One of the components
used in alkyds, namely glycerol, is a by-product of a
chemical process to produce biofuels thus it has become
increasingly abundant
[5]
.
These factors together have triggered extensive devel-
opment on traditional alkyds as well as on the develop-
ment of a new type of coating systems emerging from
the alkyds. Some of the main issues for traditional
alkyds are reduction of drying times, new drier systems
as a replacement for cobalt driers, reduced dark
yellowing, and improved film properties.
Polyesteramides
Polyesteramides are modified alkyds containing repeat-
ing ester and amide units in their backbone and possess
improved properties over alkyds such as hardness, ease
of drying, water vapor resistance and resistance to
chemicals, in particular, alkalis
[6]
. The synthesis of veg-
etable oil (VO) PEA generally involves high reaction
temperature and time and occurs in the presence of
solvents
[7]
.
To reduce the preparation time and temperature of
PEA, recent studies cover the microwave-assisted syn-
thesis of PEA. The synthesis overall requires 4 min of
time in comparison to the conventional methods which
required 2–6 h
[8]
. Waterborne microwave processed cas-
tor oil-based PEA/(preformed) ZnO nanoparticle com-
posite, which has potential to be used as a nano drug
vehicle
[9]
. In a study reported by Pawan et al. synthesis
of cottonseed oil-based PEA and its modification with
vinyl acetate, which was used as a polymeric binder in
coating application, were investigated
[10]
. The blend of
PEA resin and asphalt cement results in better blend
coating properties compared to virgin asphalt and PEA
used separately. Chemical tests indicated that the coating
blends offered good coating resistance when exposed to
a salt spray environment for 500 h, and mechanical test-
ing indicated very good properties with respect to
adhesion, flexibility, gloss, and scratch hardness
[11]
.
Anticorrosive varnish can be made for industrial
application from modified PEA resins by partial
replacement of hydroxy ethyl fatty acid amide with
polyethylene glycol (PEG400). The properties evaluated
for the modified resins showed good physical, mechan-
ical properties, and the film resistance toward water,
acid, and alkali was improved. The incorporation of
the modifier (PEG400) in the PEA molecule increased
the corrosion resistance
[12]
.
Polyetheramides
The PEtA contains ether and amide groups in its back-
bone, which provides adhesion and chemical resistance
of the coatings. PEtA can also be combined with an
isocyanate to synthesize polyetheramide (PEtA)
urethane which allows the curing to occur at ambient
temperature. Acrylates of PEtA coatings exhibit
improved drying properties, impact resistance,
flexibility, and hardness
[13]
.
Though the combination of ether and amide func-
tional groups in a single backbone allows PEtA to smash
PEA in coating performance, yet it supports the world
of coatings and holds enormous scope for exploration
and applications. Alam et al. reported another possible
method of introducing anticorrosive properties into
the PEtA system is to treat the PEtA resin prepared
from N,N-bis(2-hydroxy ethyl) soybean oil fattyamide
and bisphenol A with toluene-2,4-diisocyanate in differ-
ent weight percent which led to the formation of
POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING 863
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
urethane-modified polyetheramide (UPEtA) resins
[14]
.
A UPEtA can also be developed by the condensation
polymerization reaction of N,N-bis(2-hydroxy ethyl)
Jatropha oil fatty amide and hydroquinone
[15]
.
Hence, UPEtA may find application as an eco-
friendly corrosion protective coating and may be used
effectively at an elevated temperature.
Polyurethanes
Polyurethanes (PUs) are a very important class of poly-
mers that exhibit many desirable characteristics for their
diverse applications in coatings, adhesives, sealants,
elastomers, and plastics. Several researchers have used
VO amide diols and polyols, which have been used as
starting materials for PU synthesis along with aliphatic
and aromatic isocyanates
[16,17]
. Gao et al. and Baolian
et al. in two different study focused and emphasized
on the synthesis and characterization of waterborne
PU
[18,19]
. Microwave-assisted preparation of zinc incor-
porated polyurethaneamide coatings cured at ambient
temperature through moisture and auto-oxidative cur-
ing process showed good physicomechanical and cor-
rosion resistance performance
[20]
.
Cardanol derived from cashew nut shell liquid
(CSNL) is one such renewable material which has
reactive phenolic group and aliphatic double bond that
could be tailor-made to produce novel functional mate-
rials for polymer and coating applications. In a study
reported by Moeini et al.
[21]
it was modified by simple
one step ring opening reaction to produce polyols with
different number of functionalities. Cardanol modified
auto-oxidizable polyurethane dispersions was success-
fully prepared by prepolymer process with low particle
size and good viscosity and noticeable bio-based content.
The cross-linking in the film showed improvement in the
film properties such as hardness, water resistance, and
solvent resistance. The polyurethane coatings prepared
from CSNL-based polyols showed good mechanical per-
formance with respect to hardness, impact, tensile, and
flexibility properties. The excellent chemical resistance,
good thermal stability, and anticorrosive performance
suggested that the coatings could be suitably applied
on metal substrates for high end applications
[22,23]
.
The advantage of PU coatings is that they generally
show curing or drying at ambient temperature. In case
where a coating material shows high-temperature cur-
ing or drying (>100°C), it is treated with an isocyanate
to lower down its curing temperature from elevated to
ambient temperature
[24,25]
.
Polyols
Polyols generally consist of long aliphatic chains with
various functional groups principally hydroxyls, double
bonds, active methylene groups, and often –OCH
3
, –Cl,
–Br, –OCOH, and oxirane ring
[26]
.
The pure bio-based polyols have 100% “greener”
content. The properties of vegetable oil polyol-derived
PU depend on the number, distribution, site of hydro-
xyls, level of unsaturation in the fatty triester chains
of the parent polyol, type, position and structure of
isocyanates, and urethane content of the final PU. The
presence of hydroxyl groups is associated with extensive
hydrogen bonding in polyols as evident by spectral
studies. Hydroxyl groups impart good adhesion
between the coating material and the substrate.
Linseed oil and grapeseed oil polyol PU coatings
have shown anticorrosion as well as antibacterial
behavior
[27,28]
. Zhong et al. reported that novel coatings
with excellent properties have been formulated from
novel SO phosphate ester polyols which were success-
fully incorporated into solventborne- and waterborne-
baked coatings. Coatings were produced with improved
adhesion, low VOC, excellent impact resistance, good
hardness, milder curing conditions, and lower cost
[29]
.
Conventionally synthetic polyols derived from
petroleum-based products have been used for coating
application. However, the growing environmental
concern has fostered the utilization of renewable
resource-based materials in various applications.
Epoxies
Epoxies are the resins that come under the category of
“thermoset” family of resins, along with polyester, sili-
cones, urethanes, melamines, acrylics, and phenolics.
Epoxies once cured cannot be melted by the application
of heat. This makes epoxies unique among other plastics
like polyethylene, vinyl polypropylene, etc., which can
be melted and molded over and over again. The most
commonly used synthetic epoxy resin is the diglycidyl
ether of bisphenol A (DGEBA).
The epoxy resins used in adhesive formulations vary
from aliphatic resins having simple, low molecular
weight to aromatic resins which are complex and multi-
functional. Due to the property of reusability the epoxy
resins are used in the “potting and casting” process to
form rigid, lightweight, and foamy structures with good
insulation properties. These can be produced by chemi-
cal reaction and by incorporating a prefoamed filler in
the liquid system
[30]
to produce laminated epoxy insula-
tions. Sheets of woven glass, paper, and polyaramid fab-
ric or cotton prepregnated with the B-stage epoxy resins
are laminated in large multiple pattern presses to make
hard and rigid materials in the form of sheets, rods, and
tubes. Copper clad glass or polyaramid fibers for printed
circuit boards used in the electronics industry is also
crafted out of these resins. Because of these improved
864 S. PRADHAN ET AL.
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
properties these resins also have a significant role to
play in the automotive, electronics and advanced aero-
space applications.
Advantages of epoxies over all other polymeric
materials in coating
Epoxy has the capacity of adhesion firmly to most of the
materials including metals, concrete, glass, ceramics,
stone, wood, leather, etc. These are flexible; highly
resistant to chemical solvents; and ambient moisture
due to their long hydrophobic chains, excellent electri-
cal insulating properties, and minimum shrinkage on
curing which provides good dimensional stability. They
are well known for high tensile, flexural, and modulus
properties. Utilization of VO epoxies in coatings would
reduce our dependence on petro-based chemicals and
would also minimize the cost of coatings and paints
without affecting their performance and service life.
About 100% “greener” content in the pure bio-based
epoxies also makes it environment-friendly.
Petro-based and bio-based epoxy
At present there are several vegetable oils available
worldwide such as canola oil, castor oil, corn oil, cotton-
seed oil, linseed oil, rapeseed oil, soybean oil, etc., out of
which some are edible. Apart from their conventional
use as a food ingredient, vegetable oils are also being
utilized as an extensive raw material in various applica-
tions, particularly as the chief ingredient in paint and
coating due to their inherent biodegradability, low cost,
easy availability, and enhanced environmental benefits.
These innate properties of vegetable oils make them a
very significant resource for the purpose of research
and development, since polymers derived from biologi-
cal origin are being used in numerous industrial appli-
cations including paints, coatings, adhesives, and
biomedicines. The production of synthetic polymeric
materials from renewable resources meets the 7th prin-
ciple of 12 principles of Green Chemistry that contri-
butes to sustainability in chemistry
[31]
. The proposed
framework of these principles has been a guide for
many advances in this field. However, they were not
meant to be 12 independent goals, but quite an inte-
grated cohesive system of design. Only through the
application of all the principles one can hope to reach
a truly sustainable process.
Nowadays, there is a growing interest to produce
vegetable oil-based biopolymers. These bio-based poly-
mers have many advantages compared with polymers
prepared from petroleum-based monomers. They are
biodegradable and, in many cases, cheaper than
petroleum-based polymers. As a consequence, most
industrial applications for the resulting epoxy materials
remain limited to nonstructural applications like coat-
ings. Still, interesting developments remain to be carried
out with epoxy prepolymers and curing agents based on
vegetable oils. Several researchers have investigated the
synthesis and mechanical characterization of networks
based on epoxidized vegetable oil epoxy monomers
using various approaches.
Even though the synthetic polymers show excellent
performance properties and competitive price, a
demand for bioplastics has been rapidly increased
because most of the petrochemical materials are not
biodegradable.
Advantages of bio-based epoxy over petro-based
epoxy
The primary risk associated with epoxy use is often
related to the hardener component. Amine hardeners
in particular are generally corrosive but may also be
classed toxic and carcinogenic or mutagenic. Aromatic
amines present a particular health hazard, but their
use is now restricted to specific industrial applications,
and safer aliphatic or cycloaliphatic amines are com-
monly employed. Epoxy use is a main source of occu-
pational asthma among users of plastics. Petro-based
epoxy resins cause skin sensitization and photosensiti-
zation. Hands, arms, face, and throat sensitization has
been reported with epoxy systems. Cases of photosensi-
tivity and photodermatitis to epoxy resins were reported
by Herbert and Kaidbey
[32]
. The adverse reaction caused
by an epoxy system may be due to the base epoxy resin,
curing agents, diluents, or other constituents in epoxy
formulations. Sensitization due to epichlorohydrin
(ECH) and biphenyl A has been reported by a number
of workers
[33,34]
. Reactive diluents were also found to
cause contact allergy. Reactive diluents in epoxy systems
have been reported as strong sensitizers in guinea pigs
and humans
[3537]
.
The bio-based epoxies are superior to other systems
in many aspects, but the matter of concern is its partial
dependency on readily available renewable feedstock—
vegetable oils or other natural sources. This raises the
issues related to environmental concerns and also the
cost factor of the system. The high price of fossil oils
makes the availability of the fossil-based resins more
expensive as compared to renewable resources. The
nontoxicity, nondegradability, domestically abundancy,
nonvolatility, and biodegradability makes the VO-based
epoxy the most sought alternative to fossil oil-based
resins. The yield of these plant-based resins is also
competent to fossil fuel-derived products.
POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING 865
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
This review work concerns the polymeric materials
in the coating, classification of epoxy resin used for
coating application with special importance to bio-
based epoxy and curing agent. The different types of
curing agents and techniques generally used are also
discussed.
Epoxy resins and its types
Epoxy resins are oxirane-containing oligomers. These
resins are heat-setting resin made by the chemical bond-
ing of smaller molecules into larger ones. In 1927,
Schrade reported the first preparation of resins from
ECH. Later in 1936, Castan produced a low-melting,
amber-colored ECH–bisphenol A resin which was
reacted with phthalic anhydride to produce a thermoset.
In 1939, Greenlee explored the ECH–bisphenol A syn-
thesis route for the production of new resins for coating
applications.
Commercially, the first resin was the reaction pro-
duct of ECH and bisphenol A produced in 1947. Now-
adays a wide variety of epoxy resins are available.
Epoxy resins fall into two types based on their mol-
ecular structure and applications, namely the glycidyl
epoxy and nonglycidyl epoxy. These can be further div-
ided into three types on the basis of their structure: gly-
cidyl ether, glycidyl ester, and glycidyl amine (Fig. 1).
Glycidyl epoxies
These are prepared through a condensation reaction of
appropriate dihydroxy compound, dibasic acid or a dia-
mine, and ECH.
Glycidyl ether
Glycidyl ether of epoxy resin is the most common class
of epoxy resin formed from the condensation reaction
between 2 mol of ECH and 1 mol of bisphenol A. It is
the first high-molecular weight commercial epoxy resin
and most widely used known as DGEBA. The conden-
sation reaction occurs in two steps. In the first step,
the formation of chlorohydrins intermediate occurs
and the conversion of the intermediate to glycidyl ether
forms in the second step. The base NaOH has an impor-
tant impact in the formation of the intermediate and to
balance the acid (HCl) formed.
Physicochemical properties. The properties of the
epoxy resin depend on the extent of reaction. The
knowledge of the mechanism and cure kinetics is neces-
sary for assigning structure, property relationships. The
viscosity of the epoxy resin depends on the molecular
weight distribution of the polymer. It increases with
the increase in equivalent weight that results in solid
resin at room temperature. Cross-linking densities can
be lowered by increase in fracture toughness to a small
extent. These resins are generally used in solution form
for coating application and as granular molding com-
pounds. The functional group of the epoxy resin decides
the thermomechanical behavior of the resin. Increase in
epoxy functionality increases the cross-linking density
and thus forms a rigid molecule. Hence, multifunctional
epoxies have a glass transition temperature higher than
difunctional epoxy even after cured with the same hard-
ener. It can be further classified into different categories
on the basis of the structure of the phenol-containing
molecule and the number of phenol groups per
molecule.
Some specific examples. Diglycidyl ether of bisphenol
A. It is the most common and key class of glycidyl
epoxy resin. These resins are transparent and colorless
which are available in the form of various grades dis-
tinguished on the basis of viscosities range from 5 to
14 Pa at 25°C. On storage at ambient temperature it
has a strong tendency to form crystals.
DGEBA has been modified with maleated depoly-
merized natural rubber (MDPR) to improve the mech-
anical properties. The addition of MDPR to DGEBA
results in an increase in the elongation at break. It has
also been found that the impact strength values of
epoxy/MDPR blend of ratio 99/1 and 98/2 are higher
than the values of unmodified epoxy
[38]
.
Qi et al. reported that the effect of different types of
nanoclay on the mechanical properties of DGEBA was
studied under different conditions. The elastic modu-
lus property and fracture toughness were significantly
improved to a certain extent of the addition of clay
content. Many studies have been studied on the mor-
phology and cure kinetics of DGEBA-based epoxy
resin. The curing mechanism of modified DGEBA-
based epoxy resin with CTBN and acylonitrile copoly-
mer by using anhydride as hardener was studied. It
was found that the addition of liquid rubber did not
change the curing mechanism process which can be Figure 1. Classification of epoxy resin.
866 S. PRADHAN ET AL.
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
explained due to increase in viscosity and dilution
effect. The addition of liquid rubber at a higher weight
percent decreases the reaction rate and the extent of
conversion
[39]
.
Studies by Akbari et al. on toughening of epoxy resin
with functionally terminated reactive liquid rubber
revealed that DGEBA can be toughened with CTBN
using aromatic amine as hardener. Although the mech-
anical properties like tensile and flexural strength
showed reduction but the impact strength increased
with higher concentration of CTBN
[40]
.
Phenol novolacs. Novolac resins are suitable inter-
mediates for the synthesis of polyglycidyl ether resins.
The novolac-based epoxy resins (Fig. 2) are synthesized
by the reaction with ECH in the same process as the
bisphenol A-based resins. The number of glycidyl
groups per molecule in the resin is dependent on the
number of the phenolic hydroxyls in the starting novo-
lac, the extent to which they are reacted, and extent to
which the lowest molecular weight species are polymer-
ized during synthesis. Theoretically, all the phenolic
hydroxyls may be reacted. But in actual practice, selec-
tive epoxidation offers an advantage when the novolac
contains more than three phenolic hydroxyls. If com-
plete epoxidation is accomplished, steric factors will
prevent the reaction of some of the epoxy groups dur-
ing cure. The glycidyl ethers of novolacs are commer-
cially important because of their high functionality
property
[41]
.
Cresol novolacs. Cresol novolac is one of the kinds of
aromatic glycidyl ethers. It can be obtained from a
two-step process. A polyphenol is produced by the
combination of cresol and formaldehyde in the first
step followed by the generation of a corresponding
epoxy after its reaction with ECH. The highly cured
glass transition temperature and the excellent tempera-
ture resistance are the most significant and interesting
characteristics of such resins. Montero et al. have
revealed that the O-cresol novolac epoxy network with
high concentration of the novolac compound exhibits
high T
g
(good toughness) and low water absorption
property. But the flame retardance property has been
found to be of inferior degree than the corresponding
phenolic materials
[42]
.
Glycidyl ester
Physicochemical properties. As compared to bisphenol
A epoxy resin, glycidyl ester of epoxy resin is usually
less viscous, highly reactive, highly adhesive, and has
good-using processability. The cured epoxy resin has
good physical properties, electric insulation, and also
shows particular traces of leakage resistant as well.
Under ultralow temperature ranging between 196
and 253°C cured epoxy resins show higher adhesive
strength than other types of epoxy resin. Moreover, it
also has good surface gloss, transmittance, and good
climate resistance.
Some specific examples.
1. o-Phthalic acid diglycidyl ester
2. m-Phthalic acid diglycidyl ester
3. Tetrahydrophthalic acid diglycidyl ether
Glycidyl amine
Glycidyl amine resins can be formed by reacting ECH
with an amine. For various applications aromatic
amines are generally preferred. These are also available
in various number of grades based on its particle size
and molecular weight.
Physicochemical properties. Glycidyl amine resins pos-
sess excellent temperature resistance due to which it is
used in aerospace composite applications. They also
exhibit outstanding mechanical properties and high
glass transition temperature. These are generally highly
viscous liquids and they behave like semisolids at room
temperature. Though such resins are multifunctional,
they have high epoxy value, high cross-linking density,
and significantly high heat resistant yet these resins also
have disadvantage like brittleness.
Some specific examples. Tetraglycidyl methylene diani-
line: It is the most important resin in this class. These
resins are more expensive than the difunctional
bisphenols and various novolacs as well.
Figure 2. Structure of a novalac-based epoxy resin.
POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING 867
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
TGPAP (triglycidyl p-aminophenol): It consists of
three epoxy groups attached to a single benzene ring.
The mechanical properties and glass transition tempera-
tures approach those obtained with the tetrafunctional
resins. Due to its low viscosity, TGPAP resins are com-
monly blended with other epoxies to modify the flow or
tack of the flowing system without loss of glass tran-
sition temperature. The primary disadvantage is cost
which can be six to eight times that of commodity
bisphenol A resins.
Nonglycidyl
Non-glycidyl ether epoxides are of two types: one of the
types is cyclic aliphatic resins which are closed in struc-
ture with epoxide group in the molecule and the other
having linear structure onto which epoxide groups
attached are called acyclic aliphatic epoxy resins. Vinyl
cyclohexene dioxide, dicyclopentadiene dioxide, etc.,
are some of the commercially available cyclic aliphatic
epoxy resins. ERL-4229 (wpe131-143), ERL-4206
(wpe70-76), and ERL-4299 (wpeISO-210) are commer-
cial grades of cycloaliphatic epoxy resins. Further, three
types of resins can be classified among acyclic aliphatic
resins. They are epoxidized diene polymers, epoxidized
oils, and polyglycol diepoxides. Cationic polymerization
of a bio-based epoxy, epoxidized castor oil initiated by
N-benzyl pyrazinium and quinoxalinium hexafluroanti-
monates (BPH and BQH, respectively) as catalyst has
been reported by Park et al.
[43]
. Polyglycol diepoxides
are used as flexibilizers in commercial epoxy resins.
Commercially epoxy resins are marketed under the
trade names Araldite, DER, Epi-Cure, Epi-Res, Epikote,
Epon, Epotuf, etc.
Other epoxy resins
Chiral epoxy resins
Generally epoxy resins are optically inactive. But studies
by Hartwig et al. have revealed that using a chiral mono-
mer as starting material or inserting a chiral unit into a
commercially available epoxy through chemical modifi-
cation
[44]
, optically active resin can be obtained. Ratna
et al.
[45]
studied the modification of epoxy with optically
active L-leucine, which was modified by replacing the
NH
2
group with –Cl to get S-2-chloro,4-methyl penta-
noic acid (CMPA) using the dizonium salt reaction
scheme
[47]
. When CMPA is attached to an epoxy
through the reaction between the –COOH group of
CMPA and the epoxide group of the epoxy resin, the
modified resin shows optical activity in the uncured
and cured state.
Liquid crystalline epoxy resins
Liquid crystalline epoxy resins (LCERs) are a unique
class of epoxy resins that are formed upon curing of
low molecular weight, rigid rod epoxy monomers with
aromatic amine curing agents, resulting in the retention
of a liquid crystalline (LC) phase in the three-
dimensional cross-linking networks
[48]
. Compared with
conventional amorphous epoxy resins, LCERs exhibit
improved thermal and mechanical properties because
of the presence of a rigid and ordered liquid crystalline
phase
[49]
. So they are regarded as self-reinforcing
materials. The main reason for the development of this
new class of materials comes from both technological
and theoretical implications. They have great potential
in applications such as polymer matrices in high-
performance composites. Several research groups have
investigated the properties of LCERs prepared from
different epoxy monomers, including thermal
properties
[50,51]
, dynamic mechanical properties,
fracture toughness moisture resistance, and response
to external fields
[52]
. In a study reported by Su and cow-
orkers
[53]
it was concluded that the physical and chemi-
cal properties of epoxy resin-based dental restorative
composite can be greatly improved by incorporating
liquid crystalline epoxy resin biphenyl (BP) into the
nanocomposite. Studies by Kessler and coworker
[54]
revealed that the LCER systems are more resistant to
permanent creep deformation compared to the non-
LCER system. It means the presence of a liquid crystal-
line phase can improve creep resistance of the resins.
Liquid crystals were discovered by the Austrian
chemist and botanist Friedrich Reinitzer, who found
that cholesterol benzoate did not melt into a clear liquid
but remained turbid and becomes clear on further heat-
ing. This particular point at which transition occurs is
called as clearing point. For this reason, in addition to
the common states of aggregation, the liquid crystalline
state was established. The German physicist Otto Leh-
mann coined the term liquid crystal which is formed
mostly by rod-like molecules. They are sometimes
addressed as mesomorphic phases and the materials
that can form such phases are called mesogens. A liquid
crystal is orientated or likewise an anisotropic liquid.
This means that the molecules are oriented preferably
in a fixed direction. Such an anisotropic fluid is a
nematic liquid crystal. A new type of thermotropic
liquid-crystalline (LC) polyester was introduced by
Nagata et al.
[46]
, which has got the ability of forming
nematic phase in a wide range of temperature. A liquid
crystal which is more similar to a solid is a smectic
phase. Here the molecules are arranged in layers, but
within the layers the molecules have no fixed positions.
868 S. PRADHAN ET AL.
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
Suitable epoxide monomers are based on biphenyl moi-
eties
[55]
. Monomers for liquid crystalline epoxide resins
are shown in Figure 3. Liquid crystalline polymers
(LCPs) have potential as multifunctional, environmen-
tally friendly coatings for aerospace, and overcoming
the disadvantages of current materials.
The first investigation on the use of phenylethynyl
terminated LCPs for coating applications was carried
out by Gustavo et al. in which their properties with
commercial LCPs and their applicability for future aero-
space applications has been shown in the study reported
by Guerriero et al.
[56]
.
In a study reported by Kessler et al. referred before,
an epoxy monomer of 4,4-diglycidyloxybiphenyl (BP)
was synthesized and cured with a tetrafunctionalamine,
sulfanilamide to produce novel LCERs which showed
that BP is not a liquid crystalline epoxy monomer itself
and an irreversible crystal transition exists in the tem-
perature range of 120–140°C. It was concluded that cure
temperature has a great influence on the formation and
development of liquid crystalline phase.
Optical resins
In comparison to glasses, plastics have low density, i.e.,
comparative low weight, are fragmentation resistant
and can be easily dyed. Therefore, optical materials made
from organic polymers are attractive for optical elements
such as lenses of eyeglasses and cameras. However, the
refractive index of the standard resins is relatively small.
Therefore, there is a need to use materials with high
refractive index and low chromatic aberration. The intro-
duction of sulfur into the monomers raises the refractive
index. Sulfur-containing resins have a high refractive
index, low dispersion, and a good heat stability
[57,58]
. A
heat curable silicone/epoxy resin composition for high-
brightness LEDs or solar cells has been described by
Taguchi et al. in their study
[59]
. The composition con-
tains a heat-curable silicone resin, triazine-based deriva-
tive epoxy resin, and an acid anhydride. A UV-curable
sealant was synthesized from an epoxy resin with acrylic
acid in the presence of catalyst N,N-dimethylbenzyla-
mine which was solidified by irradiation with UV light
at 365 nm for 8 s which could be used for LCDs
[60]
.
Rubbery epoxy
Instead of liquid rubber, rubbery epoxy-based particles
obtained from an aliphatic epoxy resin can be blended
with an another epoxy resin to act as toughening agents
themselves. One of the limitations of epoxy–CTBN
adducts is their high viscosity; however, there are also
low-viscosity types available. The rubbery epoxy parti-
cles can successfully be applied as a toughening agent
for glassy epoxy matrices. The advantage of these pre-
formed modifiers is the control over the final mor-
phology as the size and concentration of the dispersed
rubber phase can be chosen independently
[61]
. The ther-
mal stability of the glassy and rubbery epoxy matrix is
not significantly affected by the addition of inorganic
and organo-modified clays. Triantafyllidis et.al.
[62]
sug-
gested that both for the rubbery and glassy epoxy nano-
composites with clays an effective organic modifier
should (a) provide the necessary organophilic environ-
ment for the epoxy prepolymer to penetrate the clay gal-
leries and (b) catalyze epoxy ring opening and boost
intragallery epoxy polymerization.
Bio-based epoxy
Any form of lipid that is obtained from plants which
exists in liquid form at room temperature is classified
as a vegetable oil. Vegetable oils are natural products that
are accepted as a rapid biodegradable fluid. They are
materials which are highly adaptable to their circum-
stances and having appropriate reactivity because of
functional groups. Basically each type of oil has the same
structure but functionally differs from one another. This
essentially means that there are many different types of
vegetable oils, each coming from different plants. Oils
extracted from plants have been used since ancient times
and in many cultures. Vegetable oils and fats form part
of a large family of chemical compounds known as lipids.
Vegetable oils are predominantly the triglyceride mole-
cules which are the basic components of most lipids.
Triglycerides are also known by the name triacylglycerol.
In vegetable oil, glycerol molecule is attached to the
three fatty acid chains of unsaturated and saturated fatty
acids. The saturated fatty acids contain only single bond
between two carbon–carbon atoms while the unsatu-
rated fatty acids contain many double or triple bond
between two carbon atoms. Those unsaturated fatty
acids typically contain stearic, oleic, linoleic, and lino-
lenic acids in varying amounts. The functionality
present in vegetable oil is in terms of double bonds thus
Figure 3. Monomers for liquid crystalline epoxide resins.
POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING 869
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
the C ¼C acts as a reaction site for chemical modifi-
cation in vegetable oil. Most of the common oil contains
fatty acids that vary from 14 to 22 carbon in length with
0–3 double bonds per fatty acid.
Curing agents
Amines
Aliphatic amine is a curing agent which is capable of
curing epoxy resin at room temperature. The cured
resin has outstanding properties. It is only the active
hydrogen present in primary amine helps to cure reacts
with an epoxy group to form secondary amine, and the
latter reacts with epoxy group. The role of the tertiary
amine generated is to polymerize the epoxy groups. Ter-
tiary amines are very important as accelerator especially
for acid anhydrides but less used as curing agent. The
amines cured end product has been found highly depen-
dent on the curing speed, amount of hardener loaded,
and the type of epoxy resin.
Aromatic amine due to steric hindrance by the aro-
matic ring slowly cures at room temperature. It has
weaker basicity than aliphatic amine. A modified amine
(ketimine) formed by the reaction between polyamine
and ketone, which acts exactly as a latent curing agent
by absorbing moisture and regenerating amines which
helps in curing at room temperature. The cured resin
has properties almost the same as those of resin cured
by the original polyamine, but its application is limited
to thin films due to the fact that it regenerates ketones,
and its curing speed is slow
[63]
.
Aliphatic amines cured epoxy have good bonding
properties and excellent resistance toward water and
some solvents
[64]
. The major disadvantage is skin irri-
tation and its toxicity. Aromatic amines are also highly
resistant to solvents for which they are known to be
good curing agents. Besides this it has good mechanical,
electrical properties, and heat resistance.
Anhydrides
Anhydrides are generally used for their long pot life and
comparatively well-balanced properties. They possess
good mechanical, chemical, and electrical with a less
amount of heat generation. Most of the commonly used
anhydrides are alicyclic anhydrides like methyltetrahy-
drophthalic anhydride, tetrahydrophthalic anhydride,
hexahydrophthalic anhydride, and methylhexahy-
drophthalic anhydride which are also known as princi-
pal curing agents of anhydrides family
[65,66]
.
Studies revealed that resins obtained from epoxidized
vegetable oil and anhydrides can be a good alternate to
petro-based epoxy resins
[67]
.
Polyamides
Polyamide resin, which has been widely used as a curing
agent for epoxy resin, is formed by the condensation
reaction between dimer acid and polyamine and con-
tains reactive primary and secondary amines in its mole-
cules. Polyamide amine reacts with bisphenol A-type
epoxy resin to cure at or below normal temperature with
moderate heat generation. It cures so slowly that it has a
long pot life. As polyamide has high hydrocarbon moiety
in its molecules, it cures epoxy resin into a highly plas-
ticized rigid thermosetting polymer. The cured resin fea-
tures high tensile, compression, and bending strengths,
while it is stiff, strong, and excellent in shock resistance.
Epoxy polyamide coatings are generally used to pro-
tect mild steel structures from corrosive atmosphere due
to their better adhesion over under prepared surface
and effective barrier protection. But the coating has
the ability to disintegrate due to UV radiation and
high-humidity condition. To improve the weatherability
and chemical resistance performance of epoxy polyam-
ide, there is a need to modify it with suitable cross-link-
ing agent. Epoxy polyamide resin has been modified
with different ratio of camphor oil and the physico-
chemical and electrochemical character of this film on
steel in 0.5 M NaCl solution has been studied. It is found
that 5 wt%of camphor oil incorporated epoxy polyam-
ide coating gives maximum protection for the mild steel
surface
[68]
.
Imidazole
Imidazoles are a type of anionic polymerizing curing
agent for epoxy resin. Imidazoles are characterized by
a relatively long pot life, the ability to form cured resin
with a high heat deformation temperature by thermally
treating at a medium temperature (80–120°C) for a
short time, and the availability of various derivatives
having moderate reactivity that improves workability.
For example, imidazole carboxylate, epoxy–imidazole
adduct, metal salt–imidazole complex compounds, and
imidazole that has been reacted with acidic substances
are used as curing agents. All are intended to improve
workability by achieving a high pot life and rapid curing
at a desired temperature (100–180°C) and have been
used in compound resin compositions such as one-part
thermosetting coating adhesives, casting materials, and
filling materials
[69]
.
Polymercaptan
Liquid polymercaptan, which cures at 0 to 20°C, is
attracting attention as a low-temperature curing agent.
870 S. PRADHAN ET AL.
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
It requires to add tertiary amine as an accelerator.
Polysulfide resin has mercaptan groups at its terminals,
but the resin does not have low temperature and fast-
curing properties and is used as a curing agent doubling
as a flexibilizer. Due to its good water resistance,
polysulfide resin has been used in adhesives, sealing
agents, and casting materials
[70]
.
Bio-based curing agent
In recent years, renewable feedstock especially vegetable
oils have seen a great demand on synthesis of curing
agent for epoxy
[71]
. In a recent article reported by
Matharu and Ding it has been crystal clear that curing
agent derived from plant products like modified plant-
based mannich bases, modified oil, polyamidoamine
from rosin and tung oil, bio-based acid and anhydrides,
bio-based phenols, lignin, and terpenes are very much
valuable in the synthesis of epoxy curing agent as it adds
excellent properties to the cured product
[72]
.
Curing techniques
Thermal/UV curing
Ultraviolet curing is the process of changing polymeric
materials from a liquid to a solid form initiated by photo-
initiators. It is an accepted alternative to conventional
drying. The number and variety of applications for
UV-curable inks, coatings, and adhesives continue to
expand at a rapid pace and pose new design challenges
to increase cure efficiency, speed, and the physical proper-
ties of the cured polymer film. The physical properties of
UV-cured materials are substantially affected by the lamp
systems used to cure them
[73]
. The development of the
intended properties, whether a paint, a clear coating, a
varnish, an ink, or an adhesive, can depend on how well
these lamp factors are designed and managed. The four
key factors of UV lamps are as follows: UV irradiance
(or intensity), spectral distribution (wavelengths) of UV,
UV energy (integral of irradiance and time), and infrared
radiation
[74]
. The major advantages of of UV curing are
fast cure, no waste, and low VOC.
Free radical UV curing
The advantages of free radical systems are very fast
cures, and the wide variety of available raw materials
allow formulations to be customized to fit diverse
applications. When a radical photoinitiatior is exposed
to UV radiation, free radicals are formed initiating the
reaction. When the light is removed, polymerization
stops. The nature of this reaction requires a uniform
exposure over the entire area being cured; this can be
a disadvantage if there are shadowed areas. Free radical
formulas may also suffer from oxygen inhibition. Oxy-
gen inhibition retards the cure at the surface and can
leave it slightly wet or tacky
[75]
. This problem can be
minimized by proper selection of the photo initiator
and light source. More sophisticated cure units are
available to displace oxygen with nitrogen to eliminate
the inhibition.
Cationic UV curing
Cationic formulations are composed primarily of
cycloaliphatic epoxies. With the addition of UV light
and a cationic photoinitiator, such as an iodonium or
sulfonium metallic salt, a bronsted acid is generated.
Since this acid is a true catalyst and is not consumed
by the reaction, polymerization will continue when the
light is removed. This can be beneficial to parts with
shadowed areas, as long as these areas receive some
minimum light exposure
[76]
. Usually an epoxide ring
is opened and linked to a polyol.
Thiol-ene UV curing
This is the relevant type of curing. Thiol-ene UV-
curable coating formulations typically contain a prepo-
lymer, reactive diluent, thiol, and photoinitiator. With
the addition of UV light and optionally another photo-
initiator, hydrogens are removed from S–H functional-
ities. At this point, a sulfur-containing charged species is
formed. This species may attack a double bond, a pro-
cess known as thiol-ene coupling. It may also bond with
another sulfur forming an S-S bond
[77]
.
UV-curable powder coating
The use of powder coatings on substrates such as wood
and its derivatives or plastics was not that much
appreciated because of their bad appearance and the
heat sensitivity of the substrates. But during last few
years the improvement of UV technology and its
application techniques have approved the utilization of
powder coatings on an increasing number of substrates.
Studies revealed that the development of epoxy- or
acrylate-based powder coatings can be used at low
temperature. The use of combination of powder coat-
ings and UV-curing technology has the following
advantages: essentially no emission of VOC, fast-curing
speeds, minimal health risk, and independency of the
flow system from the cure system. The first UV-curable
powder coatings on metal substrate were reported for
commercial application. Recently, several publications
POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING 871
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
concerning UV powder coatings have appeared.
UV-curable powder coatings can be cured through both
the cationic and the radical mechanisms. In radical cure
systems various resins such as unsaturated polyester,
polyurethane acrylate, and maleate vinylether have been
used. In the cationically cured systems however, epoxy-
type resins including, bisphenols, novolac-modified
bisphenols, cycloaliphatic epoxides, glycidyl methacry-
lates, and glycidyl acrylics have dominantly been used.
Despite the advantages of these systems, some of their
physical and mechanical properties such as impact
resistance, tensile strength, flexibility, and hardness are
poorer than their thermally cured equivalents
[78,79]
.
Some of these properties have been recently improved
by varying the type and amount of cross-linkers.
UV-curable nanocoating
Polymer nanocoatings consist of nanosized mineral par-
ticles dispersed into a polymeric matrix; among them
polymer–clay nanocomposites are within the most
promising material. In recent years, polymer nanocoat-
ings have attracted great interest because of dramatically
improved properties. The UV-curing technique can be
successfully employed to initiate such polymerization.
In fact the UV curing of multifunctional monomers or
oligomers is well known to guarantee the building up
of polymeric thermoset matrices through a fast and
environmental friendly process. In recent papers,
UV-curing technology has been used to produce rapidly
a polyacrylated/clay nanocomposite at ambient
temperature. The addition of the mineral filler did not
significantly affect the polymerization kinetics at clay
concentrations up to 7 wt%. Waterborne resins, like
water-based epoxy resins, polyurethanes, polyacrylate,
and silicones, are having tremendous potential use
because of its eco-friendly nature and support no use
of solvents. Those resins are dispersed and prepared
in an emulsion form and thus can be easily spread on
substrates. Therefore, nanoparticles well-dispersed in
water can be used to fabricate a water-based composite.
To fabricate an organic/inorganic coating, especially for
scratch resistance through hard coating on a surface,
some nanoparticles have been incorporated into tough
polymer matrices. For example, boehmite, SiO
2
, or
TiO
2
can be broadly used as a filler to resist the shear
or normal stress propagation and dispersed into photo
or thermocurable polymer matrices
[80]
.
Water-soluble UV curing
Water-soluble UV-curable coating is the combination
of UV-curing technology and waterborne systems.
UV-curable waterborne coatings become a better alter-
native corresponding to conventional solvent- and
monomer-based counterparts. Water-based UV coating
can be prepared with a total small amount of higher mol-
ecular weight prepolymers and it does not depend on the
presence of a low-molecular weight monomer
[81]
. The
noticeable merits that water-soluble UV coatings possess
are lower toxicity, coating shrinkage during the curing
process, easy to clean, and can be applied using conven-
tional application equipment. However, the relevalance
of using this coating technique is limited to coating of
table tops, doors, and wood panels as traditional UV
coating. There are certain defects which traditional UV
coatings exhibit such as nonuniform cross-linking of
cured films, high internal stress, and oxygen inhibition
during the curing process. In last few years, research
on UV-curable waterborne polyurethane coatings has
been most extensively carried out. The main interest of
working on this area is its versatility, nonpollution and
nontoxicity, chemical resistance, excellent mechanical
properties including high hardness and gloss, and appli-
cations in flooring and furniture.
Dual cure coating
The dual cure approach results in enhanced adhesion of
UV primers on sheet-molded compound substrates if
the coating procedure and composition are well
designed. Adhesion of UV cure primers is greatly
improved in formulations containing solvent. This is a
result of enhanced wetting and interaction of the solvent
with the substrate
[82]
.
Hybrid organic–inorganic epoxy coatings were
obtained through a dual cure process, which involves
first the fast and efficient photopolymerization of epoxy
rings and then hydrolysis and subsequent condensation
of alkoxy groups of the inorganic precursor. Both the
ring-opening polymerization and the sol–gel reaction
were catalyzed by the photogenerated bronsted acid in
the presence of a sulfonium salt.
Applications
The primary use of vegetable oil in coatings is as drying
oil. Drying oils are highly unsaturated oils that will
oligomerize or polymerize when exposed to the oxygen
in air, usually in the presence of a catalyst. The result is
an increase in the molecular weight as a consequence of
cross-linking. This led to the development of renewable
resources based on coating formulations with improved
performance
[83]
. Vegetable oil derivatives as value-
added polymers/monomers have found enhanced appli-
cations as environment-friendly hyperbranched or
872 S. PRADHAN ET AL.
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
waterborne coating materials that offer improved per-
formance and reduction or elimination in the use of vol-
atile organic solvents. Oil coatings are used to finish
wood carving, to stain and finish wood decks, to coat
cedar shingles, and in other applications for which pen-
etration is desired and a slow cure rate is not a signifi-
cant problem. Water-soluble resins, emulsions,
dispersions, latex, and water-reducible resins are all
considered waterborne coatings. The development of
waterborne materials from vegetable oils is the most
challenging task due to the hydrophobic nature of oil
chains. The development of an oil-modified latex tech-
nology tries to reduce the need for a coalescent aid by
incorporation of the oil into the latex resin. After appli-
cation, the oil portion of the resin, which lowers the
glass transition temperature to allow coalescence into
a film and cross-links to produce a hard, durable
finish
[84]
. Acrylated oils are excellent comonomer to
use in the synthesis of the latex. In this way, soybean
oil-based waterborne urethane–acrylic hybrid latexes
were synthesized by emulsion polymerization
[85]
. Graft-
ing polymerization of the acrylate monomers onto the
soybean oil-based polyurethane (PU) network occurs,
leading to a significant increase in the thermal and
mechanical properties of the resulting hybrid latexes.
Other examples of soybean oil-based waterborne PUs
with high performance have been described from
soybean oil-based polyols prepared by the ring opening
of epoxidized soybean oil with methanol
[86]
. Also, a
waterborne PU wood coating based on rapeseed fatty
acid methyl esters
[87]
and a castor oil-based waterborne
PU dispersions cured with an aziridine-based cross-
linker have been reported
[88]
. Also the preparation of
a coating from a waterborne-epoxidized linseed oil
was reported by Shah et al. cited earlier as shown
in Figure 3. Linseed oil is epoxidized and reacted
with diethanolamine to produce a waterborne oil with
hydroxyl groups which were further reacted with
phthalic anhydride leading to a resin with free car-
boxylic acids. The final coating is prepared by curing
a mixture of this resin with a phenol formaldehyde
resin. UV-curable chemistries based upon thiol-ene
functionality offer many advantages such as lack of oxy-
gen inhibition, extremely uniform networks, delayed gel
points and improved polymerization control, reduced
polymerization shrinkage, and reduced stress
[89]
. Veg-
etable oil acrylates from castor oil were blended with a
trifunctional thiol and cross-linked through UV
irradiation
[90,91]
. Thiol-ene-curable coatings which
incorporate vegetable oil macromonomers as prepoly-
mers are useful for applications that require good flexi-
bility throughout the lifetime of the coating, such as coil
coatings, optical fiber coatings, and paper coatings.
Epoxy coating formulations are available as liquid
resins, solid resins, high-molecular weight thermoplastic
resins, multifunctional resins, radiation-curable resins,
and special purpose resins. Epoxies are also used as a
structural adhesive. Wood and other “low-tech” materi-
als are glued with epoxy resin. In the aerospace industry,
epoxy is used as a structural matrix material which is
then reinforced by fiber
[92]
. Typical fiber reinforcements
include glass, carbon, boron, etc.
Future perspectives
Ultraviolet-curing technology is expected to increase its
market share and demand due to its predicted appli-
cation in various fields of industrial technology. As
the time has proved that the demand always keeps shift-
ing from low-grade materials to highly compatible,
reliable, and environmentally sustainable materials, the
same is also happening in the case of UV-cured com-
pletely waterborne polymers. The development of novel
devices and application facilitates the curing of the
three-dimensional structures. Curing of pigmented
coatings and creation of flexible and elastic coatings
Figure 4. Current research trends and future possibilities in epoxy coating technology.
POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING 873
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
are also possible. In fact the whole process of coating
can be changed from the liquid application to prefabri-
cated shapeable coating films. Such modifications can
completely substitute the conventional painting to foil
coatings. Hence, we can expect some day that a brand
new car can be wallpapered rather than painted.
Advantage must be taken of inherent fluidity charac-
teristics of vegetable oils which may result in no VOC
coatings. Use of solvents during processing, formu-
lation, and application of coating may be cut off in
upcoming days by using waterborne epoxy with com-
plete water-based curing agent. Figure 4 provides a
detailed vision on current research trends and future
possibilities in epoxy coating technology on various
substrates (wood, paper, leather, plastics, etc), thereby
making it more reliable and sustainable in the near
future.
Conclusion
Conventionally, the foremost commercial relevance for
epoxidized vegetable oils is their use as plasticizers and
stabilizers. Epoxidized vegetable oils, which can be
categorized as budding future green materials with
indefinite future prospects, are fully explored to create
new opportunities and applications. They are exten-
sively developed and used in bio-industry sectors dur-
ing the past decades which replace its petro-based
counterparts partially due to cost effectiveness and
degradability factor. It is strongly believed that epoxi-
dized vegetable oils have the potential to fully substitute
current petroleum-based materials because of the pres-
ence of oxirane rings on their backbone which exhibits
the driving force to generate an elastomeric network
after being cured properly. Nonedible vegetable oil-
based lubricants are renewable and biodegradable in
nature and do not interfere with the country’s food
consumption demands. Environmental compatibility
has to be checked for all cases where there is inter-
ference taking place in the midst of human and nature.
Nonedible form of vegetable oils can be considered as a
boon for strengthening the rural economy. Due to the
advances in the oleochemistry technology, sustained
availability of vegetable oils and world market demand
the nonfood applications of epoxidized vegetable oils
will eventually gain popularity and are expected to have
a bright future.
The use of VO in paints and coatings is decades old
and well studied. But these days emphasis are being laid
on research pertaining to the modifications of these
materials to bring novel properties, improved perfor-
mance like antimicrobial, biocompatible, biodegradable,
corrosion protective, low or no VOC, architectural,
decorative, electrical insulating, paper packaging, and
self-healing coatings coupled with environment friendli-
ness at affordable costs.
References
[1] Hofland, A. Alkyd resins: From down and out to alive
and kicking. Prog. Org. Coat. 2012, 73, 274–282.
[2] Akovali, G. Thermoplasticpolymers used in textile
coatings. In: G. Akovali, ed., Advances in Polymer Coated
Textiles, Smithers-Rapra: Shawbury, Shrewsbury,
Shropshire, UK, 2012; Chapter 1; pp. 1–2.
[3] Soucek, M.D.; Salata, R.R. Alkyd resin synthesis. In:
Encyclopedia of Polymeric Nanomaterials. Springer-
Verlag: Berlin, Heidelberg, Germany, 2014. DOI-
10.1007/978-3-642-36199-9_278-1
[4] Aligbodion, A.I.; Pillai, C.K. Synthesis and molecular
weight characteristics of rubber seed oil-modified alkyd
resins. J. Appl. Polym. Sci. 2001, 79, 2431–2438.
[5] Johansson, M.K.G.; Guest Editorial. Alkyds for the 21st
century. Prog. Org. Coat. 2012, 73, 273–275.
[6] Mahapatra, S.S.; Karak, N. Synthesis and characteriza-
tion of poly (ester amide) resins from Nahar seed oil
for surface coating applications. Prog. Org. Coat. 2004,
51, 103–108.
[7] Ahmad, S.; Ashraf, S.M.; Zafar, F. Development of
linseed oil based polyesteramide without organic solvent
at lower temperature. J. Appl. Polym. Sci. 2007, 104,
1143–1148.
[8] Zafar, F.; Sharmin, E.; Kashif, M.; Rahman, O.; Pathan,
S.; Khan, M.S.; Ahmad, S. Solvent free microwave
synthesis of Pongamia glabra oil based polyesteramide.
Bhartiya Vaigyanic Evam Audyogic Anusandhan Patrika
2010, 1, 38–42.
[9] Khan, N.U.; Bharathi, N.P.; Shreaz, S.; Hashmi, A.A.
Development of water-borne green polymer used as a
potential nano drug vehicle and it's in vitro release
studies. J. Polym. Environ. 2011, 19, 607–614.
[10] Meshrama, P.D.; Puria, R.G.; Patil, A.L.; Gite, V.V.
Synthesis and characterization of modified cottonseed
oil based polyesteramide for coating applications. Prog.
Org. Coat. 2013, 76, 1144–1150.
[11] Abd El-Wahab, H.; Saleh, A.M.M.; Wassela, M.A.;
Elkady, G.; Khalaf, N.S.; Ahmed, S. Preparation and
evaluation of a new anti-corrosive coating based on
asphalt cement blended with polyesteramide resin for
steel protection. Prog. Org. Coat. 2013, 76, 1363–1368.
[12] Aqeel, S.; El-Wahab, H.A.; Mahdy, A.; El-Hai, F.A.; El-Fat-
tah, M.A. New modified polyesteramide resin for industrial
applications. Prog. Org. Coat. 2010, 68, 219–224.
[13] Akintayo, C.O.; Akintayo, E.T. Synthesis and character-
ization of acrylated polyetheramide based coatings from
Albizia benth seed oil. World Appl. Sci. J. 2010, 11,
1408–1415.
[14] Alam, M.; Sharmin, E.; Ashraf, S.M.; Ahmad, S. Newly
developed urethane modified polyetheramide-based
anticorrosive coatings from a sustainable resource. Prog.
Org. Coat. 2004, 50 (4), 224–230.
[15] Alam, M.; Alandi, N.M. Microwave-assisted preparation
of urethane-modified polyetheramide coatings from
Jatropha seed oil. High Perform. Polym. 2012, 24,
538–545.
874 S. PRADHAN ET AL.
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
[16] Yadav, S.; Zafar, F.; Hasnat, A.; Ahmad, S. Poly
(urethane fatty amide) resin from linseed oil-a renewable
resource. Prog. Org. Coat. 2009, 64, 27–32.
[17] Kashif, M.; Zafar, F.; Ahmad, S. Pongamia glabra seed oil
based poly (urethane–fatty amide). J. Appl. Polym. Sci.
2010, 117, 1245–1251.
[18] Gao, C.; Xu, X.; Ni, J.; Lin, W.; Zheng, Q. Effects of cas-
tor oil, glycol semi-ester, and polymer concentration on
the properties of waterborne polyurethane dispersions.
Polym. Eng. Sci. 2009, 49, 162–167.
[19] Ni, B.;Yang, L.; Wang, C.; Wang, L.; Finlow, D.E.
Synthesis and thermal properties of soybean oil-based
waterborne polyurethane coatings. J. Therm. Anal.
Calorim. 2010, 100, 239–246.
[20] Zafar, F.; Mir, M.H.; Kashif, M.; Sharmin, E.; Ahmad, S.
Microwave assisted synthesis of bio-based metallopo-
lyurethaneamide. J. Inorg. Organomet. Polym. 2011,
21, 61–68.
[21] Moeini, H.R. Preparation and properties of novel green
poly (ether–ester urethane) insulating coatings based on
polyols derived from glycolyzed PET, castor oil and
adipic acid and blocked isocyanate. J. Appl. Polym. Sci.
2007, 106, 1853–1859.
[22] Patel, C.J.; Mannari, V. Air-drying bio-based poly-
urethane dispersion from cardanol: Synthesis and char-
acterization of coatings. Prog. Org. Coat. 2014, 77,
997–1006.
[23] Kathalewar, M.; Sabnis, A.; D'Melo, D. Polyurethane
coatings prepared from CNSL based polyols: Synthesis,
characterization and properties. Prog. Org. Coat. 2014,
77, 616–626.
[24] Ahmad, S.; Ashraf, S.M.; Hasnat, A.; Sharmin, E.; Kamal,
A. Studies on urethane- modified alumina-filled polyes-
teramide anticorrosive coatings cured at ambient
temperature. J. Polym. Mater. 2005, 22, 377–384.
[25] Ahmad, S.; Ashraf, S.M.; Sharmin, E.; Nazir, M.; Alam,
M. Studies on new polyetheramide-butylated melamine
formaldehyde based anticorrosive coatings from a
sustainable resource. Prog. Org. Coat. 2005, 52, 85–91.
[26] Vashist, S.; Shahabuddin, S.; Gupta, Y.K.; Ahmad, S.
Polyol induced interpenetrating networks: Chitosan–
methylmethacrylate based biocompatible and pH
responsive hydrogels for drug delivery system. J. Mater.
Chem. B 2013, 1, 168–178.
[27] Sharmin, E.; Ashraf, S.M.; Ahmad, S. Synthesis, charac-
terization, antibacterial and corrosion protective proper-
ties of epoxies, epoxy-polyols and epoxy-polyurethane
coatings from linseed and Pongamia glabra seed oils.
Int. J. Biol. Macromol. 2007, 40, 407–422.
[28] Akram, D.; Sharmin, E.; Ahmad, S. Development and
characterization of boron incorporated linseed oil
polyurethanes. J. Appl. Polym. Sci. 2010, 116, 499–508.
[29] Zhong, B.; Shaw, C.; Rahim, M.; Massingill, J. Novel
coatings from soybean oil phosphate ester polyols.
J. Coat. Technol. 2001, 73, 53–57.
[30] Stemmelen, M.; Pessel, F.; Lapinte, V.; Caillol, S.; Habas,
J.P.; Robin, J.J. A fully biobased epoxy resin from
vegetable oils: From the synthesis of the precursors by
thiol-ene reaction to the study of the final material.
J. Polym. Sci. Part A Polym. Chem. 2011, 49, 2434–2444.
[31] Anastas, P.; Eghbali, N. Green chemistry: Principles and
practice. Chem. Soc. Rev. 2010, 39, 301–312.
[32] Herbert, A.; Kaidbey, K. Persistent photosensitivity
following occupational exposure to epoxy resins’. Arch.
Dermatol. 1979, 115, 1307–1311.
[33] Rycroft, R.J.G.; Menné, T.; Frosch, P.J. Textbook of
Contact Dermatitis. Second revised and enlarged ed.
Springer-Verglag: Berlin, Heidelburg, Germany, 1995,
pp. 550–554.
[34] Tavakoli, S.M. An assessment of skin sensitisation by the
use of epoxy resin in the construction industry; Research
report 079 Prepared by TWI Ltd. for the Health and
Safety Executive 2003; ISBN 0 7176 2675 X. 2003
[35] Van Joost, T.H.; Roesyand, I.D.; Satyawan, I.
Occupational sensitisation to epichorohydrin (ECH)
and bisphenol-A during the manufacture of epoxy resin.
Contact Dermatitis 1990, 22, 125–126.
[36] Tosti, A.; Guerra, L.; Bardazzi, F. Occupational contact
dermatitis from exposure to epoxy resins and acrylates.
Clin. Dermatol. 1992, 10, 133–140.
[37] Thorgeirsson, A. Sensitisation capacity of epoxy
reactive diluents in the guinea pig. Acta Derm Venerol
(Stockholm) 1978, 58, 329–331.
[38] Dinesh Kumar, K. Modification of (DGEBA) epoxy resin
with maleated depolymerised natural rubber. eXPRESS
Polym. Lett. 2008, 2 (4), 302–311.
[39] Thomas, R.; Durix, S.; Sinturelb, C.; Omonov, T.;
Goossens, S.; Groeninckx, G.; Moldenaers, P.; Thomas,
S. Cure kinetics, morphology and miscibility of modified
DGEBA-based epoxy resin – Effects of a liquid rubber
inclusion. Polymer 2007, 48 (6), 1441–1814.
[40] Akbari, R.; Behesty, M.H.; Shervin, M. Toughening of
dicyanamide-cured DGEBA-based epoxy resin by CTBN
liquid rubber. Iran. Polym. J. 2013, 22 (5), 313–324.
[41] Cadz, V.; Lligadas, G.; Galia, M.; Ronda, I.C. Renewable
polymeric materials from vegetable oils: A perspective.
Mater. Today 2013, 16 (9), 337–343.
[42] de Espinosa, L.M.; Meir, M.A.R. Plant oils: The perfect
renewable resource for polymer science. Eur. Polym. J.
2011, 47 (5), 837–852.
[43] Unnikrishnan, K.P. Studies on the toughening of epoxy
resins. Ph.D.Thesis. Cochin University of Science and
Technology, India, 2006, 11–13.
[44] Hartwig, A.; Mahato, T.K.; Kaese, T.; Wohrle, D. Prep-
aration and properties of cholesteric network polymers
based on liquid crystalline epoxides. Macromol. Chem.
Phys. 2005, 206, 1718–1730.
[45] Ratna, D.; Varley, R.; Simon, G.P. Processing and
chemorheology of epoxy resins and their blends with
dendritic hyperbranched polymers. J. Appl. Polym. Sci.
2004, 92 (3), 1604–1610.
[46] Nagata, M.; Nakae, M. Synthesis, characterization, and
in vitro degradation of thermotropic polyesters and
copolyesters based on terephthalic acid, 3- (4-hydroxy-
phenyl)propionic acid, and glycols. J. Polym. Sci. Part
A Polym. Chem. 2001, 39, 3043–3051.
[47] Samui, A.B.; Ratna, D.; Chavan, J.G.; Deb, P. C. Modifi-
cation of epoxy resin with optically active carboxylic
acid. J. App. Polym. Sci. 2002, 86 (10), 2523–2529.
[48] Billmeyer, F.W. Textbook of Polymer Science, 3rd ed.
Wiley: New York, USA, 1984.
[49] Muzumdar, S.V.; Lee, L.J. Chemorheological analysis of
unsaturated polyester-styrene copolymerization. Polym.
Eng. Sci. 1996, 36 (7), 943–952.
POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING 875
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
[50] Keenan, M.R. Autocatalytic cure kinetics from DSC
measurements: Zero initial cure rate. J. Appl. Polym.
Sci. 1987, 33 (5), 1725–1734.
[51] Pionteck, J.; Richter, S.; Zschoche, S.; Sahre, K.; Arndt, K.
F. Characterization of network formation during cross-
linking of nematic polyesters by PVT measurements.
Acta Polym. 1988, 49 (4), 192–197.
[52] Haberstroh, E.; Michaeli, W.; Henze, E. Simulation of
the filling and curing phase in injection molding of
liquid silicone rubber (LSR). J. Reinf. Plast. Compos.
2002, 21 (5), 461–471.
[53] Hsu, S.-H.; Chen, R.-S.; Chang, Y.-L.; Chen, M.-H.;
Cheng, K.-C.; Su, W.-F. Biphenyl liquid crystalline epoxy
resin as a low- shrinkage resin-based dental restorative
nanocomposite. Acta Biomater. 2012, 8, 4151–4161.
[54] Li, Y.; Kessler, M.R. Creep-resistant behavior of self-
reinforcing liquid crystalline epoxy resins. Polymer
2014, 55 (8), 2021–2027.
[55] Farren, C.; Akatsuka, M.; Takezawa, Y.; Itoh, Y. Thermal
and mechanical properties of liquid crystalline epoxy
resins as a function of mesogen concentration. Polymer
2001, 42 (4), 1507–1514.
[56] Guerriero, G.; Alderliesten, R.; Dingemans, T.; Benedic-
tus, R. Thermotropic liquid crystalline polymers as
protective coatings for aerospace. Prog. Org. Coat.
2011, 70, 245–251.
[57] Cui, Z.C.; Lu, C.L.; Yang, B.; Shen, J.C.; Su, X.P.; Yang,
H. The research on syntheses and properties of novel
epoxy/polymercaptan curing optical resins with high
refractive indices. Polymer 2001, 42 (26), 10095–10100.
[58] Chen, J.S.; Ober, C.K.; Poliks, M.D. Characterization of
thermally reworkable thermosets: Materials for environ-
mentally friendly processing and reuse. Polymer 2002,
43 (1), 131–139.
[59] Taguchi, Y.; Shiobara, T. Heat-curable silicone resin-
epoxy resin composition, and premolded package
molded from same; US Patent 8 237189, Tokyo, JP,
August 7, 2012.
[60] Ma, Q.-L.; Huang, Y.M. Synthesis and properties of UV-
curable sealant for LCD panels. Key Eng. Mater. 2010,
428–429, 345–348.
[61] Jansen, B.J.P.; Tamminga, K.Y.; Meijer, H.E.H.; Lemstra,
P.J. Preparation of thermoset rubbery epoxy particles as
novel toughening modifiers for glassy epoxy resins.
Polymer 1999, 40, 5601–5607.
[62] Xidas, P.I.; Triantafyllidis, K.S. Effect of the type of
alkylammonium ion clay modifier on the structure
and thermal/mechanical properties of glassy and rub-
bery epoxy–clay nanocomposites. Eur. Polym. J. 2010,
46, 404–417.
[63] Jerabek, R.D.; Marchetti, J.R.; Zwack, R.R. Ketimine-
blocked primary amine group-containing cationic
electrodepositable resins; US4017438 A; 12 April 1977.
[64] Nontipa Supanchaiyamat; Hunt, A.J.; Shuttlteworth, P.
S.; Dingh, C.; Clark, J.H.; Matharu, A.S. Bio-based
thermoset composites from epoxidised linseed oil and
expanded starc. RSC Adv. 2014, 4, 23304–23313.
[65] Tan, S.G.; Chow, W.S. Thermal properties,curing char-
acteristics and water absorption of soybean oil-based
thermoset. Express Polym. Lett. 2011, 5 (6), 480–492.
[66] España, J.M.; Sánchez-Nacher, L.; Boronat, T.;
Fombuena, V.; Balart, R. Properties of biobased epoxy
resins from epoxidized soybean oil (ESBO) cured with
maleic anhydride (MA). J. Am. Oil Chem. Soc. 2012, 11,
221–274.
[67] Shah, M.Y.; Sharif, A. Waterborne vegetable oil epoxy
coatings: Preparation and characterization. Prog. Org.
Coat. 2012, 75, 248–252.
[68] Selvaraj, M.; Maruthan, K.; Venkatachari, G. Studies on
enhancement of surface durability for steel surface by
camphor oil modified epoxy polyamide coating. Corros.
Sci. 2006, 48, 4365–4377.
[69] Nontipa Supanchaiyamat; Shuttlteworth, P.S.; Hunt, A.
J.; Clark, J.H.; Matharu, A.S. Thermosetting resin based
on epoxidised linseed oil and bioderived crosslinker.
Green Chem. 2012, 14, 1759–1765.
[70] Yanga, B.; Cuia, Z.; Lüa, C.; Shena, J.; Sub, X.; Yangb, H.
The research on syntheses and properties of novel
epoxy/polymercaptan curing optical resins with high
refractive indices. Polymer 2001, 42 (26), 10095–10100.
[71] Huang, K.; Li, M.; Li, S.; Xia, J.; Zhang, J. Plant oil-based
curing agents for epoxies. In: Khemani, K. and
Schotz, C., ed., Degradable Polymers and Materials:
Principles and Practice, 2nd ed., American Chemical
Society (ACS), 2012, Chapter 14; pp. 225–234.
[72] Ding, C.; Matharu, A.S. Recent developments on
biobased curing agents: A review of their preparation
and use. ACS Sustainable Chem. Eng. 2014, 2 (10),
2217–2236.
[73] Naguiba, M.; Sangermano, M.; Capozzi, L.C.; Pospiec,
D.; Sahreb, K.; Jehnichen, D.; Scheibner, H.; Voit, B.
Non-reactive and reactive block copolymers for tough-
ening of UV-cured epoxy coating. Prog. Org. Coat.
2015, 85, 178–188.
[74] Glockner, P. Basics of radiation curing technology. In:
Glöckner, P., ed., Radiation Curing: Coatings and Print-
ing Inks, Hanover, Germany: Vincentz Network GmbH
& Co KG, 2008, Chapter 2; pp. 17–19.
[75] Cho, J.-D.; Hong, J.-W. UV-initiated free radical and
cationic photopolymerizations of acrylate/epoxide and
acrylate/vinyl ether hybrid systems with and without
photosensitizer. J. Appl. Polym. Sci. 2004, 93 (3),
1473–1483.
[76] Golaz, B.; Michaud, V.; Leterrier, Y.; Manson, J.-A.E. UV
intensity, temperature and dark-curing effects in cationic
photo-polymerization of a cycloaliphatic epoxy resin.
Polymer 2012, 53 (10), 2038–2048.
[77] Cornille, A.; Froidevaux, V.; Negrell, C.; Caillol, S.;
Boutevin, B. Thiol-ene coupling : An efficient tool for
the synthesis of new biobased aliphatic amines for epoxy
curing. Polymer 2015, 68, 140–146.
[78] Maurin, V.; Croutxé-Barghorn, C.; Allonas, X. Photopo-
lymerization process of UV powders: Characterization
of coating properties. Prog. Org. Coat. 2012, 73 (2–3),
250–256.
[79] Barletta, M.; Vesco, S.; Trovalusci, F. Effect of the
substrate and interface on micro-scratch deformation
of epoxy-polyester powder coatings. Prog. Org. Coat.
2012, 74 (4), 712–718.
[80] Ribeiro, T.; Baleizão, C.; Farinha, J. Functional films
from silica/polymer nanoparticles. Materials 2014, 7,
3881–3900.
[81] Hwanga, H.-D.; Parka, C.-H.; Moona, J.-I.; Kima, H.-J.;
Masubuchib, T. UV-curing behavior and physical
876 S. PRADHAN ET AL.
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
properties of waterborne UV-curable polycarbonate-
based polyurethane dispersion. Prog. Org. Coat. 2011,
72 (4), 663–675.
[82] Lee, S.-W.; Park, J.-W.; Park, C.-H.; Lim, D.-H.; Kim,
H.-J.; Song, J.-Y.; Lee, J.-H. UV-curing and thermal
stability of dual curable urethane epoxy adhesives for
temporary bonding in 3D multi-chip package process.
Int. J. Adhes. Adhes. 2013, 44, 138–143.
[83] Derksen, J.T.P.; Cuperus, F.P.; Kolster, P. Renewable
resources in coatings technology: A review. Prog. Org.
Coat. 1996, 27, 45–53.
[84] Van De Mark, M.R.; Sandefur, K. Vegetable oils in
paint and coatings. In: Erhan, S.Z. ed. Industrial Uses
of Vegetable Oils, AOCS Press: Champaign, Illinois,
2005, pp. 149–168.
[85] Lu, Y.; Larock, R.C. New hybrid latexes from a soybean oil-
based waterborne polyurethane and acrylics via emulsion
polymerization. Biomacromolecules 2007, 8, 3108–3114.
[86] Lu, Y.; Larock, R.C. Soybean-oil-based waterborne poly-
urethane dispersions: Effects of polyol functionality and
hard segment content on properties. Biomacromolecules
2008, 9, 3332–3340.
[87] Philipp, C.; Eschig, S. Waterborne polyurethane wood
coatings based on rapeseed fatty acid methyl esters. Prog.
Org. Coat. 2012, 74, 705–711.
[88] Xia, Y.; Larock, R.C. Castor-oil-based waterborne poly-
urethane dispersions cured with an aziridine-
based crosslinker. Macromol. Mater. Eng. 2011, 296,
703–709.
[89] Shah, M.Y.; Ahmad, S. Waterborne vegetable oil epoxy
coatings: Preparation and characterization. Prog. Org.
Coat. 2012, 75, 248–252.
[90] Phillips, J.P.; Mackey, N.M.; Confait, B.S.; Heaps, D.T.;
Deng, X.; Todd, M.L.; Stevenson, S.; Zhou, H.; Hoyle,
C.E. Dispersion of gold nanoparticles in UV-cured,
thiolene films by precomplexation of goldthiol.
Chem. Mater. 2008, 20, 5240–5245.
[91] Black, M.; Rawlins, J.W. Thiol–ene UV-curable coatings
using vegetable oil macromonomers. Eur. Polym. J.
2009, 45, 1433–1441.
[92] Vinay, H.B.; Govindaraju, H.K.; and Banakar, P. A review
on investigation on the influence of reinforcement on
mechanical properties of hybrid composites. Int. J. Pure
Appl. Sci. Technol. 2014, 24(2), 39–48.
POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING 877
Downloaded by [Kungliga Tekniska Hogskola] at 22:37 09 May 2016
... e successful incorporation of ER into asphalt materials requires a clear understanding of ER, including each material component and its curing process since behaviors of epoxy-asphalt composite were mostly dominated by epoxy. Pradhan et al. [10] pointed out that epoxy can be divided into glycidyl epoxy and nonglycidyl epoxy based on the molecular structure and applications. e desired properties of cured epoxy can be well controlled through careful selection of ER, curing agent, modifier, component composition, and curing conditions [1,11]. ...
... Epoxy monomers have also been converted from aliphatic or cyclic aliphatic alkenes with peracids. erefore, ERs can be categorized into glycidyl epoxy and nonglycidyl epoxy based on the procedure of their synthesis and the molecular structure [10,19]. Glycidyl epoxy can be further classified as glycidyl-ether, glycidylester, and glycidyl-amine, as shown in Figure 2. Nonglycidyl epoxy can be further divided into aliphatic epoxy with a linear structure and cyclic aliphatic epoxy with a closed structure [19]. ...
... In addition, the reaction of dicarboxylic acids with caustic is generally used to produce diglyceride ester type resins, which is normally less viscous compared to bisphenol A epoxy resin. By reacting ECH with the nitrogen atom of an amine instead of a hydroxyl group, glycidyl amine resin can be obtained [10]. ...
Article
Full-text available
One of the failure mechanisms associated with asphalt paving layers, especially on steel deck bridges, is large permanent deformation, which adversely affects its long-term performance in service. Thus, epoxy resin was introduced in asphalt paving industry to tackle permanent deformation of asphalt mixtures due to its thermosetting nature. In this review, epoxy resin as a dominant component of the epoxy-asphalt composite system was first considered, followed by a discussion on its curing methods and curing mechanism. Furthermore, the physicochemical property and mechanical performance of epoxy asphalt and epoxy asphalt mixture were thoroughly examined. Crosslink density of epoxy asphalt dictates its viscosity and thus the allowable construction time. Phase separation and dispersion of asphalt particles in the epoxy matrix was observed for epoxy-asphalt composite, and it showed superior elastic behavior and deformation resistance capability when compared with conventional asphalt materials. Furthermore, epoxy asphalt mixture exhibited significantly higher compressive strength, much better rutting resistance, and superior durability and water resistance properties. However, its low-temperature cracking resistance was slightly compromised.
... It acts against thermal and chemical degradation [9][10][11]. Although the epoxy resins show excellent anticorrosion, good chemical properties, and improved adhesive properties [12,13], their poor outdoor durability is the cause of concern. Therefore, epoxy hybrids are used extensively in all the industrial sectors. ...
Article
Full-text available
The influence of 3-mercaptopropyltrimethoxysilane (MPTMS)/WC nanoparticles within the neat epoxy (EP) coated mild steel was investigated for its hydrophobic, mechanical and electrochemical properties in the marine environment. The MPTMS modified WC nanoparticles were confirmed by TGA, XRD, SEM/EDX, AFM and TEM to investigate the chemical structure. The electrochemical techniques (EIS, SECM and Polarization) were utilized to investigate the protective properties of the investigated coatings. The FE-SEM/EDX and XRD were carried out to examine the nature of the corrosion products. The water repellent property of EP, EP/WC, EP/MPTMS, and EP-MPTMS/WC coatings was characterized by contact angle measurement (CA). It was found that the coating resistance of the EP-MPTMS/WC nanocomposite is over 41% higher than that of the pure epoxy coating. The coating resistance of the EP-MPTMS/WC coated steel was found to be 5699.76 kΩ.cm² whereas the coating resistance of EP was 1.11 kΩ.cm² even after 240 h exposed to the marine environment. Similarly, the corrosion current density of the EP-MPTMS/WC nanocomposite coated steel obtained by SECM technique was 2.1 nA/cm² in comparison to EP coated steel (14.4 nA/cm²). The results showed that the newly developed EP-MPTMS/WC nanocomposite coating possessed superior corrosion protection and enhanced hydrophobic behaviors (WCA: 144°). The investigated coatings showed profound mechanical properties. Therefore, the compatibility of EP, MPTMS and WC nanoparticles was established by superior hydrophobicity and improved corrosion protection and enhanced mechanical properties. Graphical Abstract
... These two components mixed together in a certain ratio will produce a film with very high adhesion, the paint film has strong toughness, high gloss, abrasion resistance, solvent resistance, good chemical resistance, anti-static. electric, anti-rust, acid-resistant [3,4,5]. ...
Article
Currently, epoxy paint is being widely used in the industry. Nanotechnology can create many small nanometer-sized materials with many applications, it has brought many outstanding properties to epoxy paints. The aim of this study is to investigate the effect of TiO2 nanoparticles in epoxy paint formulation towards metal surface. We created a sample of two-component epoxy paint, part A is epoxy resin, anti-sedimentation, dispersant substance, foam breaking agent, cover substance, solvent, other additives, and part B is a curing agent for epoxy resins. Methods of analyzing the properties of the epoxy paint film are based on Vietnam standards. TiO2 nanoparticles are a good coating substance in epoxy paint. The study results showed that TiO2 nanoparticles have increased the properties of the epoxy paint film, improving the Impact and Glossy of the epoxy paint film. TiO2 nanoparticles increases from 1% to 6% by weight, the impact increased by about 18.75%. (80 to 96 kg.cm), Glossy 600 increased by about 12.79% (80 to 97). Adding TiO2 nanoparticles to epoxy paint has increased Impact and Glossy for the paint film. The higher the rate of TiO2 nanoparticles, the better the properties of the epoxy paint film. Therefore, TiO2 nanoparticles are a good coating in epoxy paint, it improves the properties of the paint film. Because the cost of nanomaterials is higher than that of normal coating materials, the nanomaterial should only be added with a ratio of about 2-5% by weight.
... Epoxies are thermoset resins that once cured cannot be melted again by the application of heat (Pradhan et al., 2016). Epoxylite have strong bonding strength to other materials like metals, good chemical and environmental resistance, good chemical and insulating properties (Uygunoglu et al., 2015). ...
... NIPHUs are an interesting class of polymers based on the formation of 2-hydroxyurethane bonds via the reaction between cyclic carbonates and amines [9,10]. Some researchers [11,12] have proposed vegetable oils as a renewable feedstock that can be advantageously exploited as a reliable source to develop non-isocyanate polyhydroxyurethanes. However, the use of these vegetable oils would compete with food production [1]. ...
Article
Full-text available
The present paper describes a greener sustainable route toward the synthesis of NIPHUs. We report a highly efficient solvent-free process to produce [4,4′-bi(1,3-dioxolane)]-2,2′-dione (BDC), involving CO2, as renewable feedstock, and bis-epoxide (1,3-butadiendiepoxide) using only metal–organic frameworks (MOFs) as catalysts and cetyltrimethyl-ammonium bromide (CTAB) as a co-catalyst. This synthetic procedure is evaluated in the context of reducing global emissions of waste CO2 and converting CO2 into useful chemical feedstocks. The reaction was carried out in a pressurized reactor at pressures of 30 bars and controlled temperatures of around 120–130 °C. This study examines how reaction parameters such as catalyst used, temperature, or reaction time can influence the molar mass, yield, or reactivity of BDC. High BDC reactivity is essential for producing high molar mass linear non-isocyanate polyhydroxyurethane (NIPHU) via melt-phase polyaddition with aliphatic diamines. The optimized Al-OH-fumarate catalyst system described in this paper exhibited a 78% GC-MS conversion for the desired cyclic carbonates, in the absence of a solvent and a 50 wt % chemically fixed CO2. The cycloaddition reaction could also be carried out in the absence of CTAB, although lower cyclic carbonate yields were observed.
... Moreover, the development of new water-soluble UV-curable inks, adhesives and coatings is expected to be an important sector of investment for ERs during the next years. This technology presents several advantages when compared with the conventional techniques, including the lower amount of prepolymer involved in the process, as well as, the absence of low molecular weight monomers [246] and reduced amount of volatile organic compounds. The result is the production of materials with a greener profile due to their lower toxicity along with reduced hazardous air pollutants. ...
Article
The urgent need to replace fossil resource-based products is considerably increasing in the past few years, resulting in the search for more sustainable materials, with the aim of reducing the wastes from polymer pollution, solving economic and environmental issues. This is even more relevant in industrial fields, where toxic compounds are the basis of their polymeric formulations. Herein is reported the most relevant advances of epoxy resins (ERs) in the past decade, with great emphasis on the replacement of bisphenol A (BPA), leading to the production of renewable-based ERs with good properties. The synthesis of ERs based on renewable sources, such as vegetable oils, phenolic compounds, sugars and the outcome in the material’s structure is explored within this review. Emphasis is also given to the use of new biobased curing agents and biofillers to enhance the biocharacter of the ERs.
Article
Epoxy was loaded with varying concentrations of fly ash and was characterized for its structural properties using XRD and SEM. The XRD results revealed reduction of crystallinity with increase in filler content indicating that the composites are semi crystalline in nature. The SEM images showed that at lower concentration of filler content, fly ash is uniformly distributed within the epoxy and at higher concentrations of fly ash, agglomerates were observed. Mechanical properties such as tensile and compressive properties were estimated and the results showed that, the composites exhibit enhanced tensile strength and compressive strength for epoxy with 20 wt% fly ash. Flammable properties such as heat release rate, peak heat release rate, time to ignition, CO and CO 2 yields are estimated and reported. Decrease in combustion time, peak heat release rate, time to ignition, CO and CO 2 yields with increase in filler content clearly indicates the superior flammability performance of epoxy composites loaded with fly ash.
Article
Full-text available
Ideal halogen-free instinct flame-retardant waterborne polyurethanes have high flame-retardant efficiency, environmental friendliness, fine compatibility, and good thermostability. Phosphorus flame-retardants are currently widely used in halogen-free instinct flame-retardant waterborne polyurethanes (HIFWPU), especially those with phosphorous–nitrogen co-structures. Phosphorous–nitrogen HIFWPU have become a hotspot because their co-structures provide higher flame-retardance as compared to waterborne polyurethanes. This review introduces three main types of HIFWPU based on composition, performance and application. HIFWPU not only have improved flame-retardance but also satisfy the various requirements for functionality. HIFWPU have been widely developed in textile, furniture, automobile, and aerospace applications.
Thesis
Les matériaux poreux sont d’intérêts en raison de leurs utilisations dans de nombreux domaines du quotidien. Néanmoins, la relation entre leurs propriétés effectives et leurs microstructures poreuses lesquelles sont complexes et dépendantes du processus d’élaboration reste encore mal résolue. De plus, la nécessité actuelle de diminuer la dépendance vis-à-vis du pétrole justifie la demande actuelle pour le développement de matériaux polymériques plus respectueux de l’environnement. Afin de répondre à ces problématiques, cette étude est consacrée à l’étude de la relation microstructures-propriétés à travers le développement de nouveaux matériaux poreux à base de résines époxydes biosourcées pour l’isolation acoustique et thermique dans la construction. La première partie de la thèse concerne l’élaboration et la caractérisation expérimentale de matériaux poreux synthétisés par polymérisation cationique sous irradiation de l’éther diglycidique de résorcinol. Des matériaux macroporeux modèles obtenus à l’aide d’un gabarit de sels frittés ont permis la corrélation au volet modélisation. L’optimisation de la polymérisation sous UV d’une formulation opaque a conduit à des composites résorcinol-terre de diatomée dont les caractéristiques mécaniques, acoustiques et thermiques sont attrayantes et les propriétés de retard au feu significatives. La deuxième partie se concentre sur le développement de méthodes multi-échelles pour la caractérisation numérique des propriétés effectives des résines macroporeuses élaborées. Basée sur la méthode d’homogénéisation asymptotique, ce cadre multi-échelle a permis de montrer l'effet de diverses caractéristiques microstructurales sur le comportement macroscopique des matériaux étudiés.
Chapter
The present work deals with the influence of cryogenic coolants LN2 delivered through holes made on flank surface and rake surface of tungsten carbide cutting tool inserts in turning of super duplex stainless steel (SDSS) using in-house developed cryogenic setup. Experiments were conducted with the cryogenically treated tool, cryogenically treated tool with tempering and cryogenic coolant directly passed through a modified cutting tool insert. Results are compared with dry cutting conditions. The cutting conditions are low feed rate/high depth of cut, medium feed rate/medium depth of cut, and high feed rate/low depth of cut. The material removal rate and cutting speed is kept constant under all three cutting conditions. Microstructural study of the tool as received and cryogenically treated is examined using SEM. The population of harder tungsten carbide phase (gamma phase) is found to be more in the cryogenically treated tool. Due to tempering, the hardness of insert is improved by 8% which in turn increased tool life. By direct supply of LN2 through modified cutting tool increased tool life by 23%, more than the cryogenically tempered tool. There are no appreciable changes in the temperature of the cutting tool under dry cutting and cryogenically treated inserts. However, there is a large difference observed in temperature of cutting tool when LN2 is supplied through a modified insert directly, which in turn yielded high tool life.
Article
Full-text available
The role of the interface on the deformation response in scratch tests of epoxy-polyester films deposited by electrostatic spraying is investigated. A comparative study of the scratch deformation behaviour of films deposited on micro- and macro-corrugated rigid substrates and on ‘soft’ silicon sub-layers is made. Scratch deformation parameters were evaluated by contact gauge inductive profilometry, whilst morphological examinations of the residual scratch patterns were performed by electron microscopy.3-Response models based on a 2-D and 3-D reconstruction of the scratch pattern during the application and after the release of the load were used to perform the deformation response analysis and calculate the key geometrical features of the residual scratch patterns. In particular, the influence on the residual scratch patterns of the applied loads, sliding speeds, contact geometries, and the test modes were looked into.
Book
10. 1. 1. 1 The Purpose of Patch Testing Patch testing is a well-established method of diagnosing allergic contact dermatitis, a delayed type of hypersensitivity (type IV reaction). Patients with a history and clinical picture of contact dermatitis are reexposed to the suspected allergens under controlled conditions to verify the diagnosis. Besides testing patients with hand, arm, face or leg eczema (stasis dermatitis), testing of other types of eczema (atopic, seborrhoeic dermatitis, nummular eczema) is sometimes indicated, especially when the dermatologist suspects contact allergy to prescribed topical medicaments and their vehicles. Apart from its use to confirm a suspected allergic contact dermatitis, the patch test procedure can also be used before recommending alternative corti­ costeroids, skin care products, cosmetics, gloves, etc. in a particular patient. If the patient does not react to the alternatives tested, it is very unlikely that she or he will react to the products in ordinary use. 10. 1. 1.2 Standardization The first patch tests according to present principles were carried out in 1895 [1], but were preceded by some preliminary experiments [2] (see Chap. 1).
Chapter
Use of fatty acids and their derivatives in preparing amine type curing agents for epoxies was explored in this study. Dicarboxylic (C21) acids were prepared through addition reaction of esters of tung oil fatty aids and acrylic acid. The C21 acids were then reacted with polyamines to yield polyamidoamine type curing agents. The flexible hydrocarbon chains of fatty acids were also introduced to the Mannich base type curing agents for improved impact strength. Derivatives of fatty alcohols were used to prepare curing agents for waterborne epoxies. Furthermore, polyamidoamines based on rosin modified dimer fatty acids were also prepared. The properties of epoxies cured with these curing agents were evaluated.
Article
Reactive and non-reactive diblock copolymers based on polyethylene oxide (PEO) and a poly(glycidyl methacrylate) (PGMA, reactive) or polystyrene (non-reactive) block, respectively, are prepared via ATRP and those are incorporated into a cycloaliphatic epoxy matrix. Crosslinking of the matrix is then performed by cationic UV curing, producing modified thermosets. 1H NMR and SEC measurements are carried out and used to analyze the composition, the molar mass and dispersity of the prepared block copolymers. The viscoelastic properties and morphology of the modified epoxy are determined using DMTA and FESEM, respectively. The addition of 4 and 8 wt% of the reactive PEO-b-PGMA block copolymer into epoxy resin has only minor effects on the glass transition temperature, Tg. The reactive homopolymer PGMA significantly increases and the non-reactive block copolymer PEO-b-PS slightly decreases the glass transition temperature of the epoxy matrix. The non-reactive block copolymer PEO-b-PS causes a little decrease in Tg values. The measurement of the critical stress factor, KIC, shows that the fracture toughness of the composite materials is enhanced by inclusion of the non-reactive block copolymer. In contrary, the reactive block copolymer has negative effect on the fracture toughness especially in case of short PEO block. FESEM micrographs studies on the fracture surfaces sustain the microphase separation and the increase in surface roughness in the toughened samples, indicating more energy was dissipated.
Article
A series of thiol-ene UV-curable inorganic–organic hybrid polysilsesquioxanes of various phenyl:methacryloxypropyl and phenyl:mercaptopropyl copolymer compositions were synthesized in one-batch using a base-catalyzed system. These thermoplastic photocurable ladder-like structured materials were examined as scratch-resistant, hard-coating materials on both glass and PET substrates. The unique fully condensed structure of the hybrid polymers allowed for simplified processing and through variation of the organic functional group, films with high transparency, tunable refractive indices in the range of 1.467–1.546, pencil hardness values of 9H, and high nanoindentation modulus were obtained (7 GPa). These scratch-resistant polysilsesquioxanes may provide insight into the different organic functional group compositions which allow for optimal mechanical properties.
Article
Persistent photosensitivity developed in eight men following occupational exposure to hot epoxy resin fumes. The condition was limited to sites the resin contacted. Small doses of ultraviolet-A light (2 to 5 joules/sq cm) evoked abnormal reactions consisting of erythema, edema, and papules in the clinically involved skin. Positive photopatch tests to epoxy resin were observed in four subjects, and to 4,4′-isopropylidenediphenol (Bisphenol A) in all. The photosensitivity is most probably due to photocontact allergy to 4,4′-isopropylidenediphenol or to a closely related chemical. (Arch Dermatol 115:1307-1310, 1979)
Article
Trends in wood coatings are driven to waterborne systems and to renewable resources. Vegetable oils are well known for wood coatings, e.g. alkyds or polyurethane dispersions. In this context, fatty acid methyl esters turn out to be an alternative to technical fatty acids and vegetable oils. High contents of hydrophobic oil-based monomers require a sufficient understanding of the dispersion stability. This study shows the influence of hydrophobic monomers, ionic centers, degree of neutralization, and stirring procedure to the particle size distribution and dispersion stability. Furthermore, the impact of these parameters on the resulting coating film properties was investigated.
Article
Epoxidized soybean oil (ESO) was successfully thermal-cured by using methylhexahydrophthalic anhydride (MHHPA) curing agent, in the presence of tetraethylammonium bromide (TEAB) catalyst of varied concentration (0.3–0.8phr). The polyesterification process of ESO thermoset was proven and supported by Fourier transforms infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy analysis (GC-MS). A possible chemical reaction of the MHHPA, TEAB and ESO was proposed based on the experimental work. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) revealed that there is a positive relationship between the degree of conversion and crosslink density of ESO thermoset with TEAB concentration. The kinetics of water absorption of the ESO thermoset were found to conform to Fickian law behavior.