Cardanol based benzoxazine blends and bio-silica reinforced composites: Thermal and dielectric properties

Article abstract of DOI:10.1039/c7nj04506a

In the present work, a novel cardanol based benzoxazine was synthesised by reacting three different amines (aniline (CrAb), N,N-dimethylaminopropylamine (CrDb) and caprolactam modified N,N-dimethylaminopropylamine (CrCb)) with cardanol in the presence of formaldehyde under appropriate experimental conditions. The resulting benzoxazines were characterised for their molecular structure and thermal behaviour using different analytical methods. Among the different systems studied, the tertiary amine derivatives were found to reduce the curing temperature efficiently (CrAb-275 °C > CrDb-265 °C > CrCb-251 °C) and were confirmed by DSC analysis. These cardanol based CrAb benzoxazines were blended with conventional benzoxazines (Bzs) and bismaleimides (BMIs) as binary and ternary systems and their thermal properties were studied. Three different catalysts (4-hydroxy acetophenone, 4-aminophenol, and 4-hydroxyphenyl maleimide) were used to study the effect of lowering the curing temperature. Further, the prepared benzoxazines were reinforced with varying weight percentages (1, 3, 5 and 10 wt%) of bio-silica derived from rice husk to obtain hybrid composites. The dielectric studies of bio-silica reinforced cardanol benzoxazines infer that the values of dielectric constant decreased with increasing wt% of bio-silica. It was further observed that 10 wt% bio-silica reinforced cardanol benzoxazines show the lowest value of dielectric constant of 1.9 at 1 MHz. From the data obtained from the different studies, it is concluded that the blends of cardanol based benzoxazines can be used in the form of sealants, encapsulants, adhesives and matrices in the fields of microelectronics and automobile applications for better performance.

Full text of DOI:10.1039/c7nj04506a

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: H. Arumugam, S.
Krishnan, M. Chavali and A. Muthukaruppan, New J. Chem., 2018, DOI: 10.1039/C7NJ04506A.
This is an Accepted Manuscript, which has been through the
Volume 40 Number
1 January 2016 Pages 1–846
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
Accepted Manuscripts are published online shortly after
New Journal of Chemistry
www.rsc.org/njc
A journal for new directions in chemistry
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

Page 1 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
Cardanol Based Benzoxazine Blends and Bio-Silica Reinforced Composites: Thermal
and Dielectric Properties
A. Hariharan, K. Srinivasan, C. Murthy and M. Alagar*
Centre of Excellence for Advanced Materials, Manufacturing, Processing and
Characterization (CoExAMMPC), Vignan's University, Vadlamudi, Guntur 522 213, India
E-mail: mkalagar@yahoo.com & muthukaruppanalagar@gmail.com.
Abstract
In the present work, a novel cardanol based benzoxazine was synthesised by reacting
three different amines (Aniline (CrAb), N, N-dimethylaminopropylamine (CrDb) and
caprolactam modified N, N-dimethylaminopropylamine (CrCb)) with cardanol in the
presence of formaldehyde at appropriate experimental conditions. The resulting
benzoxazines were characterised for their molecular structure and thermal behaviour by
using different analytical methods. Among the different systems studied, the tertiary amine
derivatives was found to reduce the curing temperature efficiently (CrAb-275 °C > CrDb-
265 °C > CrCb-251 °C) and are confirmed by DSC analysis. These cardanol based CrAb
benzoxazine was blended with conventional benzoxazines (Bzs), bismaleimides (BMIs) as
binary and ternary systems and studied their thermal properties. Three different catalysts
(4-hydroxy acetophenone, 4-aminophenol, and 4-hydroxyphenyl maleimide) have been
used to study the effect of lowering of curing temperature. Further, prepared benzoxazines
were reinforced with varying weight percentages (1, 3, 5 and 10 wt %) of bio-silica derived
from rice husk to obtain hybrid composites. The dielectric studies of bio-silica reinforced
cardanol benzoxazines infer that the values of dielectric constant are decreased with
increasing wt % of bio-silica. It was further observed that, 10 wt % of bio-silica reinforced
cardanol benzoxazines contributes to the lowest value of dielectric constant of 1.9 at 1MHz.
From the data resulted from different studies, it is concluded that the blends of cardanol
based benzoxazines can be used in the form of sealants, encapsulants, adhesives and
matrices in the fields of microelectronics and automobile applications for better
performance.
Keywords: Cardanol, Bio-silica, Benzoxazine blends, Bismaleimide, Curing temperature,
Glass transition temperature, Thermal stability, Char Yield, Catalytic effect, dielectric
constant, biocomposites.

New Journal of Chemistry
Page 2 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
Introduction
The use of natural products for industrial applications is increasing due to the
concern over environmental issues, waste disposal and depletion of non-renewable
resources. Owing to the growing pressure from environmental protection agencies to
reduce the carbon dioxide emissions from fossil fuels, the need for the development of
alternate chemical feedstocks from renewable resources is warranted. Among the different
renewable resources, cashew nut shell liquid (CNSL), is one of the versatile and valuable
industrial raw material used for the production of polymeric materials in the form of
coatings, paints, varnishes, adhesives, sealants, and matrices.1-6 Cardanol is a by-product of
CNSL and has been used to produce phenalkamine low temperature curative for epoxy
coatings and polyols for the production of polyurethanes for different industrial and
engineering applications.7 Recently, Pratibh Sharma and Bimlesh Loch et al. reported the
synthesis of sustainable bis-benzoxazines by using cardanol and PET-derived
terephthalamides.8
Polybenzoxazines are a new class of resinous materials that combines the thermal
and flame retardant behaviour of phenolic resin with excellent processability and wide
design flexibility of advanced epoxy resins.9 Benzoxazine based thermosets exhibit high
glass transition temperature and high modulus, even though they have relatively low
crosslink densities due to strong hydrogen bonding. The high cure temperature required
for benzoxazine polymerization can be reduced by the incorporation of acidic (Phenol, thio-
bisphenol, mercapto dipropionic acid and etc.) and basic ( amines and imidazoles)
catalysts.10-14 In the present work, compounds with tertiary amine group were used as part
of the reactants with a view to reducing the curing temperature of the benzoxazine.
Several studies of cardanol-based benzoxazines have been reported recently. The
benzoxazines from cardanol have lower melt viscosity, which is favorable from a
processing point of view. Benzoxazines that are liquid at room temperature and can
potentially be cured into stiff, high-performance thermosets are of great interest for
applications, such as fiber-reinforced composites, where higher filler loading and faster
curing can be achieved. Cardanol based benzoxazine exhibits good storage stability at room
temperature, low heat release, near-zero shrinkage during curing and low water uptake
which make these polybenzoxazines become more suitable materials for commercial

Page 3 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
applications.15,16 These materials also possess the lower dielectric properties because of
their inherent molecular structure.
One of the main disadvantages of cardanol based polybenzoxazines is their
relatively lower crosslink density, which is surprisingly low considering their high stiffness
and Tg compared to that of other thermosets. This can be addressed by improving the
crosslink density of the system by using multifunctional benzoxazines which will improve
their crosslink density appreciably. Another way to achieve higher crosslink density is by
incorporating suitable compatible material with additional polymerizable group e.g.
bismaleimides into the benzoxazine matrix.17-21 Furthermore, the incorporation of
benzoxazines with varying nature and range of dimensions of reinforcements also
significantly improve their thermal, mechanical, thermomechanical, dielectric behavior and
surface properties which in turn more suitable for high performance industrial and
engineering applications.
The silica has attracted a considerable interest in low dielectric property among
thermoset polymers due to its stability towards light and heat. Silica can be easily obtained
in different forms such as mesoporous SBA-15, nano silica, POSS, and silica nanoparticles,
etc.,22-24 However, most of the reported procedure for the synthesis of silica materials
involves using high-cost materials, less stable polymer and low interfacial interaction
between silicon and host matrices, etc., Our research group has stabilised the conditions to
synthesise biosilica with high percentage of silica and carbon content using rice husk as the
raw material.25-28 Silica materials synthesized from rice husk are found to possess the
properties equivalent to the those prepared from another synthetic sources.
In the present work, cardanol based benzoxazine has been synthesized using
paraformaldehyde and different amino compounds, such as aniline, N, N-dimethyl amino
propylamine (DMAPA) and caprolactam (CPL) modified DMAPA, with a view to reducing
the curing temperature of cardanol benzoxazine. Among the cardanol based benzoxazines
synthesised benzoxazine obtained from aniline was incorporated with a different catalyst
to study their influencing effect on curing behavior. Further, it was blended with
conventional benzoxazines (Bisphenol-A and Bisphenol-F based benzoxazines) and
bismaleimides in order to improve their thermal properties. In addition, cardanol based
benzoxazine from aniline was also reinforced with varying weight percentages of biosilica

New Journal of Chemistry
Page 4 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
obtained from rice-husk to improve their thermal and dielectric behavior. Results obtained
from different studies are correlated, discussed and reported.
Experimental
Materials
Cardanol was obtained from Sathya Cashew Products Chennai. Analytical grades of
N, N-dimethyl amino propylamine (DMAPA), caprolactam, 1, 4-dioxane, aniline,
paraformaldehyde, chloroform, ethyl acetate, 4-hydroxy acetophenone, 4-amino phenol,
maleic anhydride, anhydrous Na2SO4 and sodium hydroxide were purchased from SRL and
Spectrochem, India. Bisphenol-A and aniline based benzoxazine (Bz-A)29, bisphenol-F and
aniline based benzoxazine (Bz-F)30 and bismalimides viz; diaminodiphenylmethane (BMI-
M) based bismaleimide and diaminodiphenylsulphone (BMI-S)31, 32 based bismaleimide
were synthesized using the previously reported procedure.
Measurements
1
FTIR spectra were obtained with an Agilent Cary 630 FTIR spectrometer. H NMR
spectra were recorded with a Bruker 400 MHz using dimethylsulfoxide (DMSO-d6) as a
solvent and tetramethylsilane (TMS) as an internal standard. DSC measurements were
carried out using a Hitachi DSC7020 under N2 purge (60 mL/min) at a scanning rate of 10
°C/min. Thermogravimetric analysis (TGA) was carried out with HITACHI STA7000 series
by taking 7 mg of the sample under N2 flow (260 mL/min) and at a controlled heating rate
of 20 °C/min. The dielectric constant was determined with help of an impedance analyzer
(solution impedance analyzer 1260, UK) at room temperature using platinum electrode at a
frequency range of 1MHz. The surface overview of the composite films was identified from
an FEI QUANTA 200F high-resolution scanning electron microscope (HRSEM). Contact
angle measurements were obtained using a Ramehart Inc. goniometer with 5μl of water as
probe liquid.
Synthesis of CPL Modified DMAPA
CPL modified DMAPA was synthesized as per the modified procedure reported
earlier by our research group.9 In a 250 mL two-necked round-bottomed flask equipped

Page 5 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
with a condenser, 100 mL of N-methyl pyrrolidone (NMP), 0.1 mol of caprolactam, 0.1 mol
of DMAPA and 5 mg of alkali hypophosphate catalyst were added. The mixture was allowed
to react at 100 °C for 24 h at inert atmosphere with efficient agitation to facilitate the
completion of the reaction. The product obtained was filtered by separation (85 % Yield).
The schematic representation for the synthesis of CPL modified DMAPA is presented in
Scheme 1.
H
NMP 100 OC,
24h
O
O
N
CH3
CH3
H2N
H2N
N
N
+
N
5
alkali
hypophosphate
H
CH3
CH3
Scheme 1. Synthesis of CPL modified DMAPA
Synthesis of Cardanol Based Benzoxazine
The synthesis of cardanol based benzoxazines (CrAb, CrDb, and CrCb) are shown in
Scheme 2. About 0.2 mol of paraformaldehyde was mixed with 0.1 mol of cardanol under
vigorous stirring and then, 0.1 mol of different amino compounds (Aniline, DMAPA and CPL
modified DMAPA) was added separately in dropwise and the temperature was raised to
100 °C. The stirring was continued for more than 6 h until the mixture turns homogeneous.
The obtained crude product was filtered and washed three times with 2 N NaOH followed
by distilled water. The organic phase was dried over anhydrous Na2SO4 and the solvent was
evaporated in a rotary evaporator.
R
OH
O
N
H2N
-(CH2O)-
R
R1
R1
H
N
N
N
R
5
O
R1
C15H31
C15H29
C15H27
Scheme 2. Synthesis of Cardanol based benzoxazines

New Journal of Chemistry
Page 6 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
Ring Opening Polymerization of Benzoxazine
The thermal ring opening polymerization of cardanol based benzoxazine was carried out
according to the reported procedure.20 A typical procedure for polymerization is as follows:
the respective amine based homogeneous benzoxazine monomer was placed in the oven at
80 °C for 8 h to stabilize and to remove the impurities (moisture and trace of solvent). After
stabilization, the temperature was raised to 280 °C at a heating rate of 20 °C/h. The heating
is continued for another 3 h at 280 °C for the completion of the curing process. At this
temperature, the monomer undergoes ring opening polymerization to form
polybenzoxazine with cross-linked network structure. The ring opening polymerization
mechanism of benzoxazines is presented in Schemes S1 and S2 (Supporting Information).
The process of polymerization was confirmed by FTIR spectroscopy.
Synthesis of Bismaleimides (BMI)
In a three-necked round-bottomed flask, 600 mL of acetone was added to 98.1 g of
(1.0 M) maleic anhydride and 0.5 M of the diaminodiphenylmethane. The mixture was then
stirred for 8 h in the presence of nitrogen atmosphere. After 8 h of stirring, the formation of
a precipitate (bismaleiamic acid) confirms the completion of the reaction. The obtained
precipitate was filtered, washed and dried. The dried amic acid was then treated with 10
mol % of sodium acetate in the presence of 500 mL of acetone. The resultant mixture was
then heated slowly and refluxed. Two equivalent of acetic anhydride was then added to the
refluxing mixture and heating was continued for an additional 8 h or until the formation of
a homogeneous solution. The resulting solution was quenched with 500 ml of ice water to
obtain the precipitate. The precipitate obtained was filtered, dried in a hot air oven and was
used as such in the present work. The same procedure was followed for the synthesis of
diaminodiphenylsulphone based bismaleimide.
Preparation of CrAb/Bz-A, CrAb/Bz-F, and CrAb/BMIs Blends
The 25, 50, 75 wt % of conventional benzoxazines (Bz-A and Bz-F) were mixed
separately with the cardanol-aniline based benzoxazine (CrAb) and then heated at 80 °C to
obtain the homogenous products. The resulting product was poured into a silane treated
glass petri dish and then heated at 120 °C for an hour, to remove the moisture and air. The

Page 7 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
samples were then heated to 220 °C at the heating rate of 20 °C/h and then post-cured at
250 °C for 3 h. The product was cooled to room temperature and subsequently removed
from the petri dish and characterized. The preparation of a copolymer blend of CrAb with
conventional benzoxazines is illustrated in Scheme 3. Similarly, the blends of CrAb/BMI-M
and CrAb/BMI-S were prepared using the same procedure as mentioned above and is
presented in Scheme 4. Furthermore, the schematic illustration of a terpolymer of CrAb
with conventional benzoxazine and bismaleimides is presented in Scheme 5.
R
2R2
N
N
R
2R2
OH
O
O
N
N
N
+
OH
HO
R1
N
O
R1
R2
C15H31
CH3
C15H29
C15H27
R1
H
Scheme 3. Synthesis of a copolymer of cardanol and aniline based benzoxazine with
conventional benzoxazines.
N
R
OH
N
R
O
O
O
O
N
N
O
N
N
+
O
O
O
R1
O
R
N
O
R
S
CH2
R1
R1
C15H31
C15H29
C15H27
Scheme 4. Synthesis of a copolymer of cardanol and aniline based benzoxazine with
bismalimides.

New Journal of Chemistry
Page 8 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
R
2R2
N
N
N
O
N
O
N
O
O
N
+
O
N
O
N
R
O
R1
O
O
O
R
R2
R2
+
O
O
R
R1
R2
S
CH2
HO
N
N
O
C15H31
CH3
C15H29
C15H27
R1
H
O
O
N
N
N
O
N
BMI-M
O
O
O
Bz-F
S
O
O
N
O
N
N
N
O
Bz-A
O
BMI-S
O
Scheme 5. Synthesis of a terpolymer of cardanol and aniline based benzoxazine with
conventional benzoxazine and bismaleimides.
Preparation of Bio-Silica from Rice Husk
The lignin from rice husk is first removed by the acid treatment, which is one of the
most useful routes to remove, wax and oils covering the wall of the surface of natural
fibers. Rice husk was washed repeatedly with distilled water and dried at about 60 °C for 3
h. Dried rice husk was then bleached with conc. HCl to remove the unwanted contaminants
and subsequently washed with water continuously till the pH become neutral. Then, the
product was dried at 60 °C for 4 h and subsequently heated at 600 °C for 5 h in a muffle
furnace, to obtain rice husk ash in which silica (SiO2) is the major component (85 %).

Page 9 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
Silane Functionalization of Bio-Silica (F-Si)
The prepared rice husk ash (biosilica) was then functionalized with 3-
glycidoxypropyltrimethoxysilane (GPTMS) in order to reinforce with benzoxazine. About, 4
mL of GPTMS was stirred with 95% absolute ethanol and 5% deionized water and
sonicated for 20 min. The solution pH was initially adjusted to 4.5 by using acetic acid and
the sonication was continued for an hour. Subsequently, 10 g of bio-silica was added and
the resulting mixture was sonicated for another 2 h and then refluxed for 24 h at 80 °C. The
obtained mixture was then centrifuged and washed with water followed by ethanol and
hexane. The functionalized bio-silica (F-Si) was further dried in hot air oven at 100 °C in
order to remove the moisture (Scheme S4 - Supporting Information).
Preparation of F-Si Reinforced Cardanol Based Benzoxazine.
The synthesis of F-Si reinforced cardanol based benzoxazines (CrDb/F-Si and
CrCb/F-Si) is presented in Scheme 6. In brief, 1, 5, 10 wt % of F-Si were mixed with
cardanol based benzoxazines (CrDb and CrCb) separately and stirred for 1 h to get the
homogeneous product. The resulting product was poured into a silane treated glass petri
dish and then heated at 120 °C for an hour to remove the moisture and trapped air. The
samples were then heated to 240 °C at the heating rate of 20 °C/h and then post-cured at
260 °C for 3 h.
Scheme 6. Synthesis of a copolymer of cardanol benzoxazine with GPTMS functionalized
bio-silica.

New Journal of Chemistry
Page 10 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
Results and Discussion
The molecular structure of cardanol-aniline (CrAb) and cardanol-DMAPA (CrDb and
1
CrCb) based benzoxazines was confirmed by FT-IR and H NMR spectral analysis. The
thermal behavior of the synthesized benzoxazines was studied by TGA and DSC analysis.
Due to the presence of meta-substituted long alkenes/alkyl (15 carbon) chain groups, the
cardanol derived benzoxazines will exist in the liquid form. Consequently, resulted
benzoxazines possess an improved flexibility, good water repellency, and low dielectric
behavior.33 However, the high polymerization temperature, lower Tg and a low char yield
of these benzoxazines restricting their application in many fields. In general, conventional
thermoset resins (bisphenol A and aniline benzoxazine and bismalimide) possesses the
limited water-repellent behavior and high char yield. By blending cardanol based
benzoxazines with conventional benzoxazines (Bz-A and Bz-F) and bismaleimides (BMI-M
and BMI-S) paves the way to overcome such limitations and to obtain optimum properties.
The FTIR spectra of cardanol based benzoxazines are presented in Figure 1a. The
bands appeared at around 1242 cm-1 and 1045 cm-1 were attributed to the asymmetric and
symmetric stretching vibrations of C-O-C bond in the benzoxazine respectively. The peak at
1189 cm-1 obtained due to the asymmetric stretching of C-N-C. Similarly, the appearance of
bands at around 960 cm-1 and 1496 cm-1 correspond to a tri-substituted benzene ring
which confirms the formation of benzoxazine ring. Further, the band appeared at around
3009 cm-1 corresponds to C-H stretching vibrations of the benzene ring. Characteristic
absorption peaks appeared at around 2925 and 2853 cm-1 represent the asymmetric and
symmetric stretching vibrations of CH2 of oxazine ring respectively as well as alkyl side
chain of cardanol moiety. The formation of benzoxazine ring in CrAb was confirmed by the
1
appearance of resonance peaks at 4.58 (Ar-CH2-N) and 5.5 ppm (O-CH2-N) from H-NMR
spectroscopy (Figure S1). The benzoxazine ring of aliphatic amine-based cardanol
benzoxazines (CrDb and CrCb) shows a singlet at 4.0 ppm and 5.0 ppm for Ar-CH2-N and O-
CH2-N respectively (Figure S2 and S3 - Supporting Information).

Page 11 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
CrAb polymer
CrDb polymer
CrAb
CrCb
1242 cm-1
1045cm-1
960cm-1
960cm-1
CrCb polymer
CrDb
1189cm-1
(a)
(b)
4000
3500
3000
2500
2000
1500
1000
5004000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Wavenumber (cm-1)
Figure 1. FTIR spectra of a) Cardanol-Aniline Based Benzoxazine (CrAb), Cardanol-DMAPA
Based Benzoxazine (CrDb), Cardanol-CPL modified DMAPA Based Benzoxazine (CrCb)
b) cardanol based benzoxazines (CrAb, CrDb, and CrCb) after heating at 280 °C for 3h.
FT -IR Analysis for Polymers
The thermal treatment of cardanol based benzoxazines was studied using FTIR
measurements (Figure 1b). The absorption band at 960 cm-1 of oxazine ring disappeared
after thermal curing at 280 °C for 3 h which confirms the occurrence of complete ring-
opening and cross-linking polymerization to form polybenzoxazine. Similarly, the
appearance of an absorption band at 1240 cm-1 indicates the generation of ether bonds
(Figure S4 and S5 - Supporting Information), as a result of the occurrence of Michael
addition reaction between BMI and benzoxazine as shown in Schemes 3-5. The reaction
occurred between the glycidyl functionalized bio-silica and CrAb were also confirmed by
FT-IR spectra and is presented in Figure S6. The peak appeared at 960 cm−1 (O-CH2-N
stretching) indicates the formation of monomeric benzoxazines, and it was disappeared in
bio-silica reinforced benzoxazine matrix which confirms the complete curing reaction
occurred between the benzoxazine matrix and the bio-silica reinforcement. The cleavage of
oxazine ring and the formation of –OH linkage were also confirmed from the formations of
polymeric network structure. The peak appeared at 1095 cm−1 indicates the presence of Si-
O-Si- linkages of asymmetric stretching and symmetric stretching appeared at 817 cm-1 due
to the presence of silica group in the bio-silica.34-36 On comparison of FTIR stretching

New Journal of Chemistry
Page 12 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
patterns of polymeric structure with that of the monomeric structure it clearly
demonstrates that the occurrence of thermal ring-opening polymerization of benzoxazine
is also influenced by the presence of nature of reinforcements.
Thermal Behaviour
Neat Cardanol Based Benzoxazines
The curing behavior of all the synthesized benzoxazine monomers was examined by
DSC analysis at the heating rate of 10 °C/min. Figure 2a shows the DSC thermograms of
cardanol based benzoxazines with different amines. The appearance of exothermic peaks
with regard to the benzoxazines viz; CrAb, CrDb, and CrCb confirm the polymerization
proceeds through thermal ring-opening mechanism (Schemes S1 and S2 - Supporting
information). The curing temperature (exotherm maxima - Tp) of CrAb, CrDb, and CrCb
benzoxazines was observed at 275 °C, 265 °C and 251 °C (Table 1) respectively. In general
curing temperature of aliphatic amine containing benzoxazine curing temperature will be
higher than that of aromatic amine-based benzoxazines.37 However in the present study, it
is reversed, because of inbuilt tertiary amine substitution present in one of the reactants
used for the synthesis of benzoxazine. The lowering of cure temperature may be explained
due to the formation of Zwitterion intermediate followed by the proton exchange in the
case of benzoxazines moiety having tertiary amine constituents. Consequently, the
formation of Zwitterion intermediate reduces the polymerization temperature when
compared to that of aryl amine based benzoxazine. When compared to CrDb and CrCb,
CrCb shows the lowest curing temperature, which might arise due to the presence of
flexible aliphatic linkages.
The thermal stability of cardanol based benzoxazines was studied by
thermogravimetric analysis (Figure 2b) and the results are presented in Table 1. Thermal
stability of polybenzoxazine matrix is one of the important factors to be considered in
device fabrication. TGA provides a valuable data with regard to the thermal stability of
materials, the number of impurities or solvents present and the nature of degradation by
measuring the weight loss at each instant. For the cardanol based benzoxazine with three
different amines (CrAb, CrDb and CrCb), the 5% weight loss was noticed at 381, 376, and
372oC respectively. The maximum degradation takes place at 463, 460 and 458 °C

Page 13 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
respectively. The char yield of CrAb, CrDb, and CrCb based benzoxazine was 8, 6 and 5%
respectively at 800°C. Among the benzoxazines, CrAb has little higher char yield than that
of CrDb and CrCb, due to the presence of arylamine moiety.
100
80
60
40
20
0
CrAb
CrDb
CrCb
CrAb
CrDb
CrCb
(a)
(b)
230
240
250
260
270
280
100
200
300
400
500
600
700
800
Temperature (oC)
Temperature (oC)
Figure 2. DSC and TGA thermogram of cardanol based benzoxazine (a) DSC polymerization
temperature curve of CrAb, CrDb, and CrCb benzoxazine; (b) TGA thermogram of poly
benzoxazine of CrAb, CrDb and CrCb.
Table 1. Thermal Behavior of Cardanol Based Benzoxazines.
Cardanol
based
benzoxazines
Curing behavior
Tp Tf
5%
10%
Tmax
Char
yield
% at
weight weight (oC)
Ti
ΔH
loss
(oC)
loss
(oC)
(oC) (oC) (oC) (mJ/mg)
800oC
CrAb
CrDb
CrCb
238 275 287
243 265 283
242 251 263
31
23
18
381
376
372
419
414
410
461
460
458
8
6
5
Binary Blends of CrAb with Benzoxazine (Bzs) and Bismaleimide (BMI).
Cardanol based benzoxazines can be utilized as a diluent for conventional
benzoxazines (Bz-A and Bz-F) (Scheme 3) and bismaliemides (BMI-M and BMI-S) (Scheme
4) and the resulting blends are expected to improve the processing behavior. Among the
cardanol based benzoxazine systems, aniline derived benzoxazine was found to have a
better thermal stability and thus it was taken as a diluent for conventional benzoxazines

New Journal of Chemistry
Page 14 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
(Bz-A and Bz-F) and bismaleimides (BMI-M and BMI-S). Four different blends were
prepared by blending CrAb (as diluent) with Bz-A, Bz-F, BMI-M, and BMI-S. The thermal
characteristics of the prepared blends were studied and it was observed that all the binary
blends have lower curing temperature than that of parent CrAb (275 °C). The varying ratio
of CrAb benzoxazine with Bz-A 75/25, 50/50 and 25/75 doesn’t show any major change in
curing temperature which was ~231 °C (Table 2). Similarly, the curing temperature for the
blend of different combinations of CrAb with Bz-F (Table 3) also appeared at ~213 °C
(Figure 3a and 3b). A similar trend was also observed in the case of blends of 50/50 ratio of
CrAb with BMI-M and BMI-S and the curing temperatures obtained are 227 °C and 213 °C
respectively (Figure 4a).
CrAb
CrAb
(a)
(b)
CrAb 25 : Bz-F 75
CrAb 50 : Bz-F 50
CrAb 75 : Bz-F 25
Bz-F
CrAb 25 : Bz-A 75
CrAb 50 : Bz-A 50
CrAb 75 : Bz-A 25
Bz A
140 160 180 200 220 240 260 280
100 125 150 175 200 225 250 275
o
Temperature (oC)
Temperature ( C)
Figure 3. DSC thermogram of polymerization temperature of benzoxazine (a) DSC curve of
CrAb/Bz-A blend benzoxazine and (b) DSC curve of CrAb/Bz-F benzoxazine blends.

Page 15 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
CrAb 50 : BMI-M 50
CrAb 50 : BMI-S 50
CrAb 50 : Bz-F 50
CrAb 50 : Bz-A 50
CrAb 100 : Bz-A : 100 : BMI-M 50
CrAb 100 : Bz-A : 100 : BMI-S 50
CrAb 100 : Bz-F : 100 : BMI-M 50
CrAb 100 : Bz-F : 100 : BMI-S 50
(a)
(b)
140
160
180
200
220
240
260
75
100 125 150 175 200 225 250
Temperature (oC)
Temperature (oC)
Figure 4. DSC thermogram of polymerization temperature of benzoxazine (a) DSC curve of
CrAb/BMIs blends and (b) DSC curve of CrAb/Bz/ BMI blends.
Table 2. Thermal Behavior of CrAb/Bz-A Benzoxazine Binary Blends
Weight
ratio of
CrAb/
Bz-A
Curing Behavior
Tp Tf
Tg
5%
10%
Tmax
Char
yield
% at
LOI
(oC) weight weight (oC)
Ti
(oC)
ΔH
(oC) (oC) (mJ/mg)
loss
(oC)
loss
(oC)
800oC
100/0
75/25
50/50
25/75
0/100
238
163
159
158
158
275 287
232 273
231 276
231 276
223 276
31
-
96
108
138
176
381
383
389
383
330
419
419
414
405
352
461
454
446
443
425
8
21
22
23
25
29
156
228
239
288
12
14
19
28
Table 3. Thermal Behavior of CrAb/Bz-F Benzoxazine Binary Blends
Weight
ratio of
Curing Behavior
Tg
5%
10%
Tmax(oC) Char
yield
LOI
(oC) weight weight
CrAb/BzF
loss
(oC)
loss
(oC)
% at
Ti
Tp
Tf
ΔH
800 oC
(oC) (oC) (oC) (mJ/mg)
100/0
75/25
50/50
25/75
0/100
238 275 287
156 214 272
156 213 270
155 213 272
146 211 275
31
-
86
106
141
180
381
391
382
387
312
419
422
419
412
345
461
461
457
450
440
8
21
22
23
27
28
164
206
244
267
12
14
23
26

New Journal of Chemistry
Page 16 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
The maximum degradation temperature obtained for varying the weight percent
o
ratios of CrAb/Bz-A for 75/25, 50/50 and 25/75 is 454, 446, and 443 C respectively. The
results are presented in Table-2 and Figure 5a. The char yield of benzoxazine blend
CrAb/Bz-A with different ratio of 75/25, 50/50, 25/75 is 12, 14 and 19% respectively.
Similarly, CrAb/Bz-F based blends also possess the value of char yield for the ratio
CrAb/Bz-F ratio of 75/25, 50/50, 25/75 is 12, 14 and 23 % respectively (Table 3 and
Figure 5b). The blends of cardanol based benzoxazine CrAb with BMI-M and BMI-S exhibit
better thermal stability than that of neat benzoxazine. The maximum degradation
temperature obtained for CrAb/BMI-M blend of 75/25, 50/50, 25/75 is 454, 472 and 467
oC respectively. The char yield of CrAb/BMI-M blend with a ratio of 75/25, 50/50 and
25/75 wt % is 14, 24 and 20% respectively. Similarly, the maximum degradation
temperature obtained for CrAb/BMI-S blend of 75/25, 50/50, 25/75 is 455, 461 and 456 oC
respectively. For CrAb/BMI-S blend with ratios of 75/25, 50/50 and 25/75 possess the
char yield of 12, 31 and 23% respectively. Among the different ratios studied the 50/50
blends of both BMI and CrAb show the maximum thermal stability than that of other ratios
(Table 4 and Figure 6a & 6b).
110
(a)
(b)
100
80
60
40
20
0
100
90
80
70
60
50
40
30
20
10
0
CrAb
CrAb
CrAb 25 : Bz-A 75
CrAb 50 : Bz-A 50
CrAb 75 : Bz-A 25
Bz- A
CrAb 25 : Bz-F 75
CrAb 50 : Bz-F 50
CrAb 75 : Bz-F 25
Bz-F
100
200
300
400
500
600
700
800
100
200
300
400
500
600
700
800
o
Temperature (oC)
Temperature ( C)
Figure 5. TGA thermogram of poly CrAb/Bzs; (a) TGA thermogram of copolymer of
CrAb/Bz-A;(b) TGA thermogram of copolymer of CrAb/Bz-F.

Page 17 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
110
(a)
(b)
100
80
60
40
20
0
100
90
80
70
60
50
40
30
20
10
CrAb 25 : BMI-S 75
CrAb 50 : BMI-S 50
CrAb 75 : BMI-S 25
CrAb 25 : BMI-M 75
CrAb 50 : BMI-M 50
CrAb 75 : BMI-M 25
100
200
300
400
500
600
700
800
100
200
300
400
500
600
700
800
o
Temperature (oC)
Temperature ( C)
Figure 6. TGA thermogram of poly CrAb/BMIs; (a) TGA thermogram of copolymer of
CrAb/BMI-M; (b) TGA thermogram of copolymer of CrAb/BMI-S.
The glass transition temperature (Tg) of cardanol based polybenzoxazines was
studied by DSC analysis. The Tg of cardanol based polybenzoxazine cannot be predicted in
DSC analysis, due to low Tg value of the system after curing. Whereas in the case of binary
blends of CrAb with conventional benzoxazines (Bz-A, Bz-F), the value of Tg increased with
the increased amount of incorporation of conventional benzoxazine (Tables 2 and 3). For
CrAb/Bz-A with blend ratios of 75/25, 50/50 and 25/75, the Tg values were found to be 96,
108 and 138 °C respectively. A similar trend was obtained for CrAb/Bz-F blends of 75/25,
50/50 and 25/75 and the values are 86, 106 and 141 °C respectively.
Table 4. Thermal Behavior of CrAb/BMI-M and CrAb/BMI-S Benzoxazine Binary Blends.
Binary
Samples
weight
ratio
CrAb/ BMI-M
10% Tmax Char LOI
weight weight (oC)
CrAb/ BMI-S
10% Tmax Char LOI
weight weight (oC) yield
5%
5%
yield
% at
800oC
14
loss
(oC)
364
loss
(oC)
396
loss
(oC)
364
loss
(oC)
398
% at
800oC
12
75/25
454
23
455
22
50/50
25/75
366
366
399
399
472
467
24
20
27
26
333
356
367
392
461
456
31
23
30
27

New Journal of Chemistry
Page 18 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
Ternary blends of CrAb with benzoxazine (Bz-A, Bz-F) and bismaleimide (BMI-M,
BMI-S).
Based on the binary blend results, the ratio of CrAb to Bz-A and Bz-F for the ternary
system was kept as constant i.e 100 % and the ratio of bismaleimide was varied (Table 5).
In the case of ternary systems {(CrAb 100 : Bz-A 100 : BMI-M 50), (CrAb 100 : Bz-A 100 :
BMI-S 50), (CrAb 100 : Bz-F 100 : BMI-M 50) and (CrAb 100 : Bz-F 100 : BMI-S 50)} the
curing temperature was found to be reduced significantly with respect to CrAb and the
values are 214, 199, 212 and 203 °C respectively whereas that of the neat matrix exhibits a
Tp value of 275 °C (Figure 4b). Among the ternary systems, blend of CrAb/Bz-A/BMI-S
found to possess the lowest curing temperature than that of other blends and the values
are presented in Figure 4b. From the data resulted, it was observed that the ternary system
contributes to the lowering of curing temperature efficiently than that of binary blends and
neat matrices.
The blend of benzoxazines with BMIs ternary blends was found to possess better
thermal stability than that of other binary blends. This may be explained due to the
formation of ether linkage as a result of Michael addition reaction occurred between the
hydroxyl group of polybenzoxazine and an olefinic group of bismalimides. For example, the
ternary blends of CrAb/Bz-A/BMI-M with wt % ratios of 100:100:25, 100:100:50 and
100:100:75 showed a gradual improvement in char yield with values of 16, 22 and 38%
respectively andthe maximum degradation temperatures obtained for the above ternary
blends are 460, 463 and 465 °C respectively (Figure 7). Similarly ternary blends of
CrAb/Bz-A/BMI-S, CrAb/Bz-F/BMI-M and CrAb/Bz-F/BMI-S with ratios of 100:100:25,
100:100:50 and 100:100:75 show good thermal properties, and the results obtained are
presented in Tables 5 and 6. Among the different ratios of ternary blends, the blends with a
ratio of 100:100:75 possess the highest thermal stability than that of neat matrices and
other binary blend systems. The data obtained for different ternary blend systems are
presented in Tables 5 and 6.

Page 19 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
Table 5. Thermal Behavior of CrAb/Bz-A/BMI-M and CrAb/Bz-A/BMI-S Benzoxazine
Ternary Blends.
Ternary
Blends
weight ratio
CrAb/Bz-A/ BMI-M
5% 10% Tmax Char LOI Tg
(oC) weight weight (oC) yield
CrAb/Bz-A/ BMI-S
Tg
5%
10% Tmax Char
LOI
(oC) weight weight (oC)
yield
% at
loss
loss
(oC)
% at
loss
(oC)
loss
(oC)
(oC)
800
800oC
oC
100/100/25 127
100/100/50 149
100/100/75 179
384
390
392
410
413
413
460 16
463 22
465 38
24 132
26 154
33 182
371
385
387
402
412
417
436
438
443
15
28
34
24
29
31
(a)
(b)
100
80
60
40
20
100
80
60
40
20
0
CrAb 100: Bz-A100 : BMI-M 25
CrAb 100: Bz-A100 : BMI-M 50
CrAb 100: Bz-A100 : BMI-M 75
CrAb 100 : Bz-A 100 : BMI-S 25
CrAb 100 : Bz-A 100 : BMI-S 50
CrAb 100 : Bz-A 100 : BMI-S 75
0
100
200
300
400
500
600
700
800
100
200
300
400
500
600
700
800
(c)
(d)
100
80
60
40
20
0
100
80
60
40
20
0
CrAb 100 : Bz-F 100 : BMI-M 25
CrAb 100 : Bz-F 100 : BMI-M 50
CrAb 100 : Bz-F 100 : BMI-M 75
CrAb 100 : Bz-F 100 : BMI-S 25
CrAb 100 : Bz-F 100 : BMI-S 50
CrAb 100 : Bz-F 100 : BMI-S 75
100
200
300
400
500
600
700
800
100
200
300
400
500
600
700
800
Temperature (oC)
Temperature (oC)
Figure 7. TGA thermogram of poly CrAb/Bz-A/BMIs; (a) TGA thermogram of copolymer of
CrAb/Bz-A/BMI-M; (b) TGA thermogram of copolymer of CrAb/Bz-A/BMI-S. (c) TGA

New Journal of Chemistry
Page 20 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
thermogram of copolymer of CrAb/Bz-F/BMI-M; (d) TGA thermogram of copolymer of
CrAb/Bz-F/BMI-S.
Table 6. Thermal Behavior of CrAb/Bz-F/BMI-M and CrAb/Bz-F/BMI-S Benzoxazine
Ternary Blends
Ternary
blends
weight ratio
CrAb/Bz-F/ BMI-M
10% Tmax Char LOI Tg
(oC) weight weight (oC) yield (oC) weight weight (oC) yield
CrAb/Bz-F/ BMI-S
Tg
5%
5%
10% Tmax Char LOI
loss
loss
% at
loss
loss
% at
(oC)
(oC)
800oC
(oC)
(oC)
800oC
100/100/25 126
100/100/50 158
100/100/75 183
350
356
357
393
395
395
450
451
461
22
29
34
26 135
29 162
31 179
387
399
399
418
428
423
436
440
445
21
30
36
26
30
32
Compared to the binary blend systems, the Tg value of ternary blend systems with
the different percentage combinations of BMI and benzoxazines are founded to be higher.
For example, the blends of CrAb/Bz-A with 75 % of BMI-M and BMI-S showed the
maximum Tg values of 179 and 182 °C respectively. In the cases of CrAb/Bz-F/BMI-M (183
°C) and BMI-S (179 °C) blends, a similar trend was noticed and the values are presented in
Table 6. The Tg values obtained for the different combination of ternary blends are
presented in Tables 5 and 6. From the data resulted, it was observed that the increasing Tg
values for the polymer blends are an indication for the formation of high crosslinking
density which in turn results in an enhanced thermal stability with improved char yield.
The TGA graph of all the benzoxazines and their blends are presented in Figures S7-S10
(supporting information).
Further, the catalytic effect on curing behavior of the prepared blends was studied,
using different phenolic compounds as catalysts. From the data resulted, BMI-S and BMI-M
based ternary blends exhibit similar curing and thermal stability behavior. Thus, we have
taken the blend of BMI-S, to study the catalytic effect. The blend of BMI-S was incorporated
with three different catalysts (10 wt %) separately such as 4-hydroxyphenyl maleimide
(HPM), 4-Aminophenol (AP) and 4-hydroxy acetophenone (HAP) and their catalytic
efficacy was studied. In general, it was reported that the phenolic group can reduce the

Page 21 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
cure temperature [38] of the benzoxazines. The catalytic effect on cure temperature of
100:100:50 blends of CrAb/Bz-A/BMI-S and CrAb/Bz-F/BMI-S was studied by
incorporating 10 wt% of HPM, AP and HAP catalysts separately. It was observed that 10
wt% incorporation of HPM, AP, and HAP with CrAb/Bz-A/BMI-S, reduces the cure
temperature effectively. The value of Tp for 10 wt% incorporation of HPM, AP and HAP
with CrAb/Bz-A/BMI-S are 192 °C, 187 °C and 173 °C respectively (Table S2 and Figure
S11). In the case of CrAb/Bz-F/BMI-S, the values of Tp are 195°C, 178 °C, and 168 °C
respectively. From the data obtained, it is concluded that the incorporation of 10 wt% of
HAP reduces the Tp values more efficiently than that of other catalysts. The details of
catalytic mechanism related to cure behaviour of benzoxazines is presented in Scheme S3
(supporting information). Further, it was also noticed that there was no significant
variation in the values of Tg and char yield. It is explained that the presence of amine, active
methyl and maleimide groups in the catalysts will also undergo Michael addition reaction
during the curing process. These types of catalysts will also reduce the curing temperature
without altering the char yield.
Flame retardant property
The thermogravimetric analysis provides the valuable information about the flame
retardant behavior, in addition to thermal stability. The Limiting Oxygen Index (LOI) value
can be calculated using the value of char yield from TGA and is substituted in Van Krevelen
and Hoftyzer relation (equation 1) [39, 40].
LOI = 17.5 + 0.4 CR
---- equation (1).
where CR is the percentage char yield of polymer remaining at 800 °C. In general, the
polymer with more than 21 of LOI value is a good flame retardant material and it is
experimentally proved that the materials with highest LOI values possess the superior
flame retardant property. The LOI values of the cured binary and ternary blends were
calculated from their respective char yield. These values are found to be higher than that of
the conventional benzoxazines, which contributes to enhanced flame retardant
characteristics of the material. The LOI values calculated for different blends are presented
in Tables 1-7.

New Journal of Chemistry
Page 22 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
Biosilica reinforced CrDb and CrCb.
The thermal degradation behavior of GPTMS functionalized bio-silica (F-Si)
reinforced [27] cardanol based benzoxazines (CrDb and CrCb) are analyzed by TGA (Figure
8). As shown in Figure 8, the value of temperature for 5% weight loss for all 1, 5, and 10 wt
% of bio-silica reinforced with CrDb nanocomposites was found to be more or less the
same (~416 °C). Similarly, the maximum degradation temperature obtained for the
composites are 463, 466, and 470 °C respectively. The thermal stability and char yield of
biosilica reinforced CrDb composites are found to be gradually increased with an increased
weight percentage incorporation of reinforcements (Table 7). The char yield of 1, 5, and 10
wt % biosilica reinforced CrDb systems are found to be 13, 23, and 25% respectively. In the
case of biosilica reinforced CrCb system, the maximum degradation temperature is closer
to biosilica reinforced CrDb system and the values are presented in Table 7. The value of Tg
for varying weight percentages biosilica reinforced (1, 5, and 10 wt. %) CrDb
nanocomposites are 147, 184, and 236 °C respectively. In the case of bio-silica reinforced
CrCb, the Tg value is found to be 139 °C (1 %), 181 °C (5%), and 231 °C (10 %) respectively.
The higher values of Tg obtained for composites may be explained due to the formation of
enhanced network structure between the benzoxazines and functionalized biosilica
reinforcement.
110
(a)
(b)
100
90
80
70
60
50
40
30
20
10
0
100
80
60
40
20
0
CrDb/ 1 wt% F-bio-silica
CrDb/ 5 wt% F-bio-silica
CrDb/ 10 wt% F-bio-silica
CrCb/ 1 wt% F-bio-silica
CrCb/ 5 wt% F-bio-silica
CrCb/ 10 wt% F-bio-silica
100
200
300
400
500
600
700
800
100
200
300
400
500
600
700
800
Temperature (oC)
Temperature (oC)
Figure 8. TGA thermogram of poly CrDb or CrCb/composites; (a) TGA thermogram of
CrDb/F-bio-silica; (b) TGA thermogram of CrCb/F-bio-silica.

Page 23 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
Table 7. The thermal and dielectric behavior of CrDb/F-bio-silica and CrCb/F-bio-silica
composites.
F-Si wt%
with
cardanol
benzoxazine
CrDb
CrCb
Tg
5%
10% Tmax Char LOI
K
Tg
5%
10% Tmax Char LOI
k
(oC) weight weight (oC) yield
(oC) weight weight (oC) yield
loss
loss
% at
loss
loss
% at
(oC)
(oC)
800oC
(oC)
(oC)
800oC
1%
5%
10%
147
184
236
416
416
416
436
436
436
457
458
462
13
23
25
23 3.10 139
27 2.62 181
28 1.92 231
418
418
418
436
436
436
461
463
467
16
18
26
24 3.20
25 2.53
28 1.89
Morphological properties
XRD Analysis
The XRD diffractogram of F-bio-Silica reinforced cardanol based benzoxazines
composites are presented in Figure S12. The appearance of a peak at 2θ = 20° showed the
amorphous nature of F-bio-Silica in CrDb benzoxazine matrix. A similar trend also noticed
in the case of F-bio-Silica reinforced CrCb. XRD pattern confirms the F-bio-Silica
reinforcement with cardanol based benzoxazine matrix. The existence of homogeneous
morphology observed from XRD analysis contributes to an enhanced thermal stability and
improved flame retardant behavior functionalized bio-silica reinforced benzoxazine
composites.
Scanning electron microscopy (SEM) images of the neat CrDb and biosilica
composites are shown in Figure 9. The CrDb based composite material is taken as a
representative sample for SEM analysis. The CrDb matrix forms a homogenous dispersion
without any cracking and voids in the matrix system and thus possesses an improved
thermal properties. Further, the rice husk ash reinforcement imparts the formation of

New Journal of Chemistry
Page 24 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
strong covalent bonding as well as inter cross linking network with CrDb benzoxazine
system, which in turn develops the smooth surfaces.
Figure 9. Scanning Electron Microscopy (SEM) images of (a) neat CrDb, (b) 1 wt%, (c) 5
wt% and (d) 10 wt% F-biosilica incorporated CrDb.
Influence of Water Absorption Dielectric Behavior and Contact Angle of F-Bio-Silica
Based Nanocomposites
The dielectric constant (K) of varying weight percentages (1, 5 and 10 wt %) of F-
bio-Silica reinforced cardanol based benzoxazine nanocomposites are determined using
dielectric spectrometer between 10 Hz to 1MHz and the values are presented in Table 7.
The value of dielectric constant obtained for 1 wt % of F-Si reinforced CrDb benzoxazine is
3.1 at 1 MHz. whereas that of 5 and 10 wt % of F-bio-Silica reinforced CrDb composites are
found to be 2.62 and 1.92 respectively (Figure 10). Similarly, the values of dielectric

Page 25 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
constant obtained for 1, 5 and 10 wt% of F-bio-Silica reinforced CrCb benzoxazine are 3.2,
2.53 and 1.89 at 1MHz respectively. The incorporation of F-Si will results in the reduction
of dipole-dipole interaction within the composite system and contributes to reduce the
value of dielectric constant. The silane functionalized biosilica reinforced benzoxazine
composites with low values of dielectric constant can be used as an effective insulation
material for high-performance microelectronics applications in the form of adhesives
sealants, encapsulants and potting compounds.
The contact angle images of neat CrDb, CrCb and 10 wt % bio silica reinforced
CrDb,and CrCb are given in Figure 11. It can be observed that the reinforced composites
possess the higher values of contact angle when compared to that of neat CrDb and CrCb.
The value of contact angle of neat CrDb is 96o and 10 wt% of F-biosilica incorporated CrDb
is 125o. The value of contact angle of neat CrCb is 97o and 10 wt% of F-biosilica
incorporated CrCb is 137o. The lower affinity of the developed composites indicates the
improvement in the hydrophobic behavior contributed by the functionalized silica (FSi)
reinforcement to organic matrix. This may be due to the long aliphatic chain of cardanol
moiety and less polar nature of Fsi contribute to enhanced contact angle and reduced
dielectric constant. In addition, the intra-molecular hydrogen bonding results in enhanced
water contact angle (decrease in the surface free energy) and the reduction in the dielectric
constant. Consequently, the developed composites with a reduced surface free energy and
enhanced hydrophobic behavior suggest that these materials can be used as an effective
insulation material in humid environments.
4.5
4.0
3.5
3.0
2.5
2.0
1.5
4.5
4.0
3.5
3.0
2.5
2.0
1.5
Neat
Neat
(a)
(b)
CrDb-F-bio-Silica 1 wt%
CrDb-F-bio-Silica 5 wt%
CrDb-F-bio-Silica 10 wt%
CrCb-F-bio-Silica 1 wt%
CrCb-F-bio-Silica 5 wt%
CrCb-F-bio-Silica 10 wt%
2.0x105 4.0x105 6.0x105 8.0x105 1.0x106
Frenquency (Hz)
2.0x105 4.0x105 6.0x105 8.0x105 1.0x106
Frenquency (Hz)

New Journal of Chemistry
Page 26 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
Figure 10. Dielectric Constant of varying weight percentage of F-bio-silica reinforced
cardanol based benzoxazines (a) CrDb/F-bio-silica (b) CrCb/F-bio-silica.
Figure 11. Water based contact angle of (a) neat CrDb, (b) 10 wt% biosilica incorporated
CrDb, (c) neat CrCb and (d) 10 wt% biosilica incorporated CrCb.
Conclusion
In the present work, a novel cardanol based benzoxazine was synthesized using
formaldehyde and different amino compounds viz., aniline, N, N-dimethyl amino
propylamine (DMAPA) and caprolactam modified DMAPA. The molecular structure of
1
benzoxazines are characterized by FT-IR and H-NMR. Data obtained from DSC analysis, it
was ascertained that the benzoxazine synthesized using an amino compound with the
presence of tertiary amine moiety brings down the curing temperature of benzoxazine
when compared with that of other benzoxazines synthesized in the present work. A binary
blend made using cardanol-benzoxazine and bismalimides possess an enhanced thermal
stability with improved glass transition temperature and char yield. Similarly, ternary
blends prepared using cardanol –benzoxazine with conventional benzoxazine and
bismalimides also exhibit an enhanced thermal stability, glass transition temperature and
char yield with lowered curing temperature. Biosilica derived from rice-husk ash
functionalized with silane derivative reinforced with selected blends of benzoxazine
possess an improved thermal behavior with a lower value of dielectric constant. Results
obtained from SEM analysis indicate the homogenous morphology. Data resulted from

Page 27 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
different studies it is concluded that the blends of renewable source cardanol blend
benzoxazine reinforced with silane functionalized biosilica composites can be used in the
form of adhesives, sealants, and encapsulants for microelectronics insulation applications
for improved performance and enhanced longevity.

New Journal of Chemistry
Page 28 of 29
View Article Online
DOI: 10.1039/C7NJ04506A
Reference
1. L. A. Varghese and E. T. Thachil, Journal of Adhesion Science and Technology, 2004,
18, 181-193.
2. R. Liu, X. Zhang, J. Zhu, X. Liu, Z. Wang, and J. Yan, ACS Sustainable Chem.
Eng, 2015, 3 , 1313–1320.
3. S. K. Shukla, K. Srivastav and D. Srivastav, Materials Research, 2015, 18, 1217-1223.
4. D. Balgude, A. Sabnis, and S. K. Ghosh, European Polymer, 2016, 620-634.
5. M. Kathalewar and A. Sabnis, J. Coat. Technol. Res. 2014, 11, 601–618.
6. L. Yao, Q. Chen, W. Xu, Z. Ye, Z. Shen, M. Chen, J. Appl. Polym. Sci. 2017, 134, 44890.
7. S. .G. Rajeshwari, K. G. Raut, M. V. Badiger, J. Appl. Polym. Sci. 2017, 134, 44920.
8. P. Sharma, B. Lochab, D. Kumar, and P. Kumar, ACS Sustainable Chem. Eng. 2016, 4,
1085–1093.
9. K. Sethuraman and M. Alagar, RSC Adv. 2015, 5, 9607-9617.
10. A. Ruligaj, B. Ali, M. Krajnc, U. "ebenik eXPRESS Polymer Letters, 2015, 9, 647–657.
11. B.S. Rao and A. Palanisamy, Progress in Organic Coatings, 2012, 74, 427–434.
12. J. Q. Sun, W. Wei, Y. Z. Xu, J. H. Qu, X. D. Liu, and T. Endo RSC Adv., 2015, 5, 19048-
19057 .
13. S. Ohashi, J. Kilbane, T. Heyl, and H. Ishida, Macromolecules, 2015, 48, 8412–8417.
14. Y. Xu, Q Ran, C. Li, R. Zhu and Y. Gu, RSC Adv., 2015, 5, 82429-82437.
15. C. Zhang, X. Luo, R. Zhu, H. Ling & Yi Gu, Journal of Adhesion Science and Technology,
2015, 29, 767-777.
16. H. X. Ma, J.J. Li, J. J. Qiu, Y. Liu, and C. M. Liu, ACS Sustainable Chem. Eng., 2017, 5,
350–359.
17. K. S. Santhosh Kumar, C.P. Reghunadhan Nair, R. Sadhana, K.N. Ninan, European
Polymer Journal. 2007, 43, 5084–5096.
18. Y. Wang, K. Kou, G. Wu, A. Feng and L. Zhuo, RSC Adv. 2015, 5, 58821 –58831.
19. G. Wu, K. Kou, L. Zhuo, Y. Wang, J. Zhang, Thermochimica Acta, 2013, 559, 86–91.
20. Y. Wang, K. Kou, G. Wu, L. Zhuo, J. Li, Y. Zhang, Polymer, 2015, 77, 354-360.
21. T. Takeichi, Y. Saito, T. Agag, H. Muto, T. Kawauchi, Polymer, 2008, 49, 1173-1179.
22. K. Zhang, Q. Zhuang, X. Liu, G. Yang, R. Cai, and Z. Han, Macromolecules, 2013, 46,
2696–2704.

Page 29 of 29
New Journal of Chemistry
View Article Online
DOI: 10.1039/C7NJ04506A
23. R. Sasi kumar and M. Alagar, RSC Adv. 2015, 5, 33008-33015.
24. M. R. Vengatesan, S. Devaraju, K. Dinakaran and M. Alagar, J. Mater. Chem., 2012, 22,
7559-7566.
25. D. P. Wong, R. Suriyaprabh, R. Yuvakumar, V. Rajendran, Y.T. Chen, B. J. Hwang, Li. C.
Chen and K. H. Chen, J. Mater. Chem. A, 2014, 2, 13437-13441.
26. K. Kanimozhi, K. Sethuraman, V. Selvaraj, and M. Alagar, Front Chem. 2014, 2, 65.
27. K. Kanimozhi, P. Prabunathan, V. Selvaraj and M. Alagar, RSC Adv., 2014, 4, 18157-
18163.
28. H. Ishida, Y. Rodriguez, Journal of applied polymer science, 1995, 58, 1751–1760.
29. J. Liu and H. Ishida Macromolecules, 2014, 47, 5682–5690.
30. K. Dinakaran, and M. Alagar, J Appl Polym Sci, 2002, 86, 2502–2508.
31. K. Dinakaran, R. Suresh Kumar, M. Alagar J Appl Polym Sci, 2003, 90, 1596–1603.
32. V. Selvaraj, K. P. Jayanthi, T. Lakshmikandhan and M. Alagar, RSC Adv. 2015, 5, 48898-
48907.
33. K. C. Chang, C. H. Hsu, C. W. Peng, Y. Y. Huang, J. M. Yeh eXPRESS Polymer Letters,
2014, 8, 207–218.
34. K. C. Chang, C. H. Hsu, C. W. Peng, Y. Y. Huang, J. M. Yeh, eXPRESS Polymer Letters
2014, 8, 207–218.
35. X. Ji, J. He, J. E. Hampsey, Z. Yang, Q. Hu, and Y. Lu Chem. Mater. 2003, 15, 3656-3662.
36. H. Mahfuz, M. Hasan, V. Dhanak, G. Beamson, J. Stewart, V. Rangari, V. Khabashesku
and S. Jeelani, Nanotechnology 2008, 19, 445702.
37. J. Wang, T.T. Ren Yu-dan Wang, X. He, W. Liu and X. Shen Reactive and Functional
Polymers, 2014, 74, 22–30
38. S. N. Kolanadiyil, M. Azechi and T. Endo, J. Polym. Sci. Pol. Chem. 2016, 54, 2811-
2819.
39. H.H. Hassan, A.F. Elhusseiny, Y.M.A. Elkony and E.S.M. Mansour, Chem. Cent. J. 2013,
7, 13
40. A. Hariharan, S. Kumar, M. Alagar, K. Dinakaran and K. Subramanian, Polym. Bull.
2017. doi:10.1007/s00289-017-2015-1.