Effect of Varying Alkyl Chain Length on Thermal Decomposition Temperature of Zinc(II) Xanthates and its Impact on Curing of Epoxy Resin

Article abstract of DOI:10.1002/zaac.201500639

Linear and branched zinc(II) xanthates with varying alkyl chain length were synthesized and characterized by ¹H NMR, ¹³C NMR, and IR spectroscopy, as well as elemental analysis. Zinc sulfide as the final decomposition product upon thermal annealing of zinc(II) xanthates was confirmed by XRD analysis. Cure time for epoxy resin composite at various temperatures was analyzed employing zinc(II) xanthates (5 % mass) as latent cure catalysts. XRD investigation of the cured epoxy resin including zinc(II) xanthates upon thermal annealing revealed the presence of ZnS in-situ in the composite matrix, indicating the in-situ thermal decomposition of zinc(II) xanthates as probable mechanism for curing. Thermogravimetric analysis was performed to investigate the thermal decomposition temperature trend of zinc(II) xanthates. A parallel trend was observed correlating the thermal decomposition temperature trend of zinc(II) xanthates and the order of curing catalytic efficiency utilizing zinc(II) xanthates. In the case of linear alkylzinc(II) xanthates with an increase in the alkyl chain length, both thermal decomposition temperature and the cure time were enhanced. In contrast, in case of branched alkyl chain zinc(II) xanthates with increasing alkyl chain length show decreasing thermal decomposition temperature as well as cure time.

Full text of DOI:10.1002/zaac.201500639

Journal of Inorganic and General Chemistry
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ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
DOI: 10.1002/zaac.201500639
Effect of Varying Alkyl Chain Length on Thermal Decomposition
Temperature of Zinc(II) Xanthates and its Impact on Curing of Epoxy Resin
Tarun Chand Vagvala,*[a] Shyam Sudhir Pandey,[a] Suvratha Krishnamurthy,[b] and
Shuzi Hayase*[a]
Keywords: Zinc(II) xanthates; In-situ; Catalyst; Epoxy resin; NMR spectroscopy; IR spectroscopy
Abstract. Linear and branched zinc(II) xanthates with varying alkyl
mechanism for curing. Thermogravimetric analysis was performed to
investigate the thermal decomposition temperature trend of zinc(II)
chain length were synthesized and characterized by 1H NMR, 13C
NMR, and IR spectroscopy, as well as elemental analysis. Zinc sulfide xanthates. A parallel trend was observed correlating the thermal de-
as the final decomposition product upon thermal annealing of zinc(II) composition temperature trend of zinc(II) xanthates and the order of
xanthates was confirmed by XRD analysis. Cure time for epoxy resin
curing catalytic efficiency utilizing zinc(II) xanthates. In the case of
composite at various temperatures was analyzed employing zinc(II) linear alkylzinc(II) xanthates with an increase in the alkyl chain length,
xanthates (5% mass) as latent cure catalysts. XRD investigation of the both thermal decomposition temperature and the cure time were en-
cured epoxy resin including zinc(II) xanthates upon thermal annealing hanced. In contrast, in case of branched alkyl chain zinc(II) xanthates
revealed the presence of ZnS in-situ in the composite matrix, indicat-
ing the in-situ thermal decomposition of zinc(II) xanthates as probable
with increasing alkyl chain length show decreasing thermal decompo-
sition temperature as well as cure time.
hesiveness, flexibility,[16] low shrinkage, electrical insu-
lation,[17] low cost, and environmental stability.[18] Owing to
high performance properties of cured epoxy resins, they are
extensively employed in several applications such as aerospace
industry,[19] semiconductor encapsulation,[20] adhesives,[21]
coatings,[22] paints,[23] fiber reinforced plastics,[24] automo-
biles,[25] laminates,[26] and other industries.[27]
Curing of epoxy resin is the transformation of epoxy mono-
mer or polymer chains of low molecular weight into a high
molecular weight three dimensional network aided by curing
catalysts.[28,29] Typical curing agents employed for curing are
Lewis bases and acids.[30] The base curing catalysts includes
amines, amine adducts, ketimine, and anhydrides.[31] Metal
halide complexes such as BF3, FeCl3, AlCl3, SnCl4, and ZnCl2
are employed as acid catalysts.[32,33] Premature curing even
under ambient and undesired conditions[34] consequently re-
ducing the pot-life of formulated mixtures[35] is the main draw-
back imposed by the conventional catalysts.[36] To surpass
these limitations latent curing catalysts, which trigger curing
only upon providing threshold external stimuli are favored.[37]
The utilization of latent curing catalysts includes advantages
such as preventing premature curing,[38] elimination of ad-
ditional mixing phase in the production pipeline[39] and one-
pot mixture.[40]
1 Introduction
Metal xanthates are extensively explored as potential metal
sulfide precursors[1] in various applications such as chemical
vapor deposition,[2] fabrication of inorganic semiconductor
layer for organic-inorganic solar cells,[3] photoluminescence
material[4] and metal sulfide thin films.[5] The properties such
as solubility, stability[6] and morphology of the metal sulfide
can be tuned by tailoring the alkyl chain of the metal xan-
thate.[7,8] It is very well reported that metal xanthates upon
thermal annealing yield metal sulfides[9] in a latent fashion by
decomposing following a Chugaev like elimination mecha-
nism.[10,11]
Cured epoxy resins are of significant industrial value.[12]
The versatile nature of cured epoxy resins is the key for their
wide spread demand in the industry. Cured epoxy resins can
be processed to possess properties such as excellent thermal
resistance,[13] high tensile strength,[14] low weight,[15] high ad-
* T. C. Vagvala
E-Mail: tarunchandv@gmail.com
* Prof. Dr. S. Hayase
E-Mail: hayase@life.kyutech.ac.jp
[a] Department of Biological Functions and Systems
Graduate School of Life Science and Systems Engineering
Kyushu Institute of Technology
2–4 Hibikino
In this context, we have recently reported the utilization of
metal xanthate as latent thermal curing catalyst and its underly-
ing mechanism.[41] Since it is previously explained that alkyl
ligand of the metal xanthate exhibits a crucial role in determin-
ing the behavior of metal xanthates. It is pertinent to investi-
gate the effect of modifying the alkyl chain length of metal
xanthates on its thermal behavior and curing catalytic activity.
Wakamatsu-ku, Kitakyushu 808–0196, Japan
[b] Department of Applied Chemistry
Graduate School of Life Science and Systems Engineering
Kyushu Institute of Technology,
2–4 Hibikino
Wakamatsu-ku, Kitakyushu 808–0196, Japan
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201500639 or from the au-
thor.
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was added dropwise and the solution was stirred for about 5 h. The
In this article, we would like to elucidate the effect of alkyl
reaction mixture was evaporated completely and extracted into acet-
one, followed by filtration to remove insoluble impurities. The solution
was again rotaevaporated, dried, and washed with ample diethyl ether
to obtain yellow residue. Yield: 14 g, 72%. 1H NMR (500 MHz,
26 °C, [D6]acetone): δ = 4.34–4.32 (t, 2 H), 1.69–1.38 (m, 2 H), 1.34–
1.30 (m, 6 H) ppm, 0.91–0.88 (t, 3 H) ppm. 13C NMR (125 MHz,
24 °C, CDCl3): δ = 233.37, 71.94, 32.35, 29.66, 26.57, 23.19,
14.22 ppm. IR (KBr): ν˜ = 2953, 2870, 1458, 1380, 1194, 1131, 1040,
919 cm–1. KC7H13OS2: calcd. C 38.9, H 6%, found: C 40.18, H 6.6%.
chain length of zinc(II) xanthate on its thermal decomposition
temperature and its impact on catalytic activity in curing of
epoxy resin composite.
2 Experimental Section
2.1 Materials
Potassium tert-butoxide, carbon disulfide, 1-hexanol, and zinc(II)
chloride were purchased from Wako Japan. 2,2-Dimethyl-3-pentanol
was purchased from Sigma Aldrich, Japan. 3,3-Dimethyl-2-butanol,
2,2-dimethyl-3-hexanol, potassium butyl xanthate, and potassium amyl
xanthate were purchased from Tokyo Chemical Corporation, Japan.
Commercially available ortho-cresol Novolac Epoxy resin
(CNE200ELB65) melting point 65 °C and Novolac phenolic resin
(BRG556) melting point 80 °C used in this work were supplied by
Kyocera Company, Japan.
Potassium O-2,2-Dimethylhexan-3-yl-dithiocarbonate: Potassium
tert-butoxide (8 g, 71.3 mmol) was dissolved in THF in a nitrogen
atmosphere. The solution was cooled to 0 °C and 3, 3-dimethyl-2-
hexanol (15 g, 10.15 g, 78.2 mmol) was added slowly. After stirring
for 15 min, carbon disulfide (6 g, 78.2 mmol) was added drop wise,
and the solution was stirred for 5 h. The reaction mixture was rotaeva-
porated completely. The yellow solid obtained was dissolved in acet-
one and the solution was subsequently filtered to eliminate insoluble
impurities. The solution was rotaevaporated again and washed with
1
diethyl ether to obtain a yellow powder. (Yield: 7 g, 73%). H NMR
(500 MHz, 26 °C, [D6]acetone): δ = 2.48–2.47 (t, 1 H), 1.95–1.90 (m,
4 H), 1.34–1.32 (d, 9 H), 1.31–1.29 (t, 3 H) ppm. 13C NMR (125 MHz,
24 °C, CDCl3): δ = 235.30, 87.40, 36.28, 33, 20.35, 15.05 ppm. IR
(KBr): ν˜ = 2953, 2870, 1458, 1380, 1194, 1131, 1040, 919 cm–1.
KC9H17OS2: calcd. C 44.2, H 7%, found: C 43.4, H 5.9%.
2.2 Instrumentation
1H NMR was recorded at 26 °C with a JEOL JNM-A500 nuclear mag-
netic resonance spectrometer operated at 500 MHz. 13C NMR spec-
trum was also recorded at 24 °C with a JEOL nuclear magnetic reso-
nance spectrometer at 125 MHz. NMR spectra were measured in deu-
terated solvents using tetramethylsilane as internal reference. All 1H Potassium-O-2,2-dimethylbutan-3-yl-dithiocarbonate and potassium-
shifts are given in parts per millions (s = singlet; d = doublet; t =
triplet; m = multiplet). Infra-red (IR) spectrum was recorded with a
JASCO FT/IR 4100 spectrophotometer using KBr pellet form. Ele-
mental analysis was performed using Yanaco MT-5 elemental analyzer.
Powder X-ray diffraction (XRD) was measured with a Rigaku RINT-
2000/PC X-ray diffraction apparatus. Curing time of the epoxy resin
at various temperatures was studied using Panasonic KT4 temperature
controller. Thermogravimetric analysis was performed with a DTG-60
simultaneous DTA-TG apparatus, Shimadzu.
O-2,2-dimethylpentan-3-yl-dithiocarbonate were synthesized follow-
ing literature reports.[42,43]
Zinc(II)-O-butan-1-yl-dithiocarbonate (1): An aqueous solution of
potassium-O-butan-1-yl-dithiocarbonate (3 g, 16.3 mmol) was added
dropwise to a solution of zinc(II) chloride (1 g, 7.4 mmol), while stir-
ring at room temperature. A white precipitate resulted was collected
by suction filtration and washed with methanol. Yield: 4.9 g, 82.6%.
1H NMR (500 MHz, 26 °C, CDCl3): δ = 4.51–4.49 (t, 2 H), 1.84–
1.79(m, 2 H), 1.50–1.44 (m, 2 H) ppm, 0.97–0.95 (t, 3 H) ppm. 13C
NMR (125 MHz, 24 °C, CDCl3): δ = 229.73, 77.88, 30.34, 19.08,
13.86 ppm. IR (KBr): ν˜ = 2953, 2870, 1458, 1380, 1194, 1131, 1040,
919 cm–1. Zn(II) C10H18O2S4: calcd. C 33, H 4.9%, found: C 34.48,
H 5.2%.
2.3 Synthesis
Zinc(II) xanthates shown in Figure 1 were synthesized from their
respective potassium xanthate precursors.
Zinc(II)-O-pentan-1-yl-dithiocarbonate (2): An aqueous solution of
zinc(II) chloride (1 g, 7.4 mmol) was added to an aqueous solution of
potassium-O-pentan-1-yl-dithiocarbonate (3.3 g, 16.3 mmol) dropwise
and the solution was stirred for 2 h. The precipitate was filtered and
washed with methanol to obtain the desired product as white solid
1
(yield: 5.3 g, 86.1%). H NMR (500 MHz, 26 °C, CDCl3): δ = 4.50–
4.47 (t, 2 H), 1.85–1.81 (m, 2 H), 1.43–1.33 (m, 4 H) ppm, 0.94–0.90
(t, 3 H) ppm. 13C NMR (125 MHz, 24 °C, CDCl3): δ = 229.82, 78.04,
28.06, 27.92, 22.29, 13.93 ppm. IR (KBr): ν˜ = 2950, 2855, 1461, 1220,
1129, 1075, 1028, 946 cm–1. Zn(II) C12H22O2S4: calcd. C 36.8, H
5.6%, found: C 37.6, H 5.6%.
Zinc(II)-O-hexan-1-yl-dithiocarbonate (3): To an aqueous solution
of zinc(II) chloride (1 g, 7.3 mmol), potassium-O-hexan-1-yl-dithio-
carbonate (3.8 g, 15.4 mmol) dissolved in water was added dropwise
while stirring at room temperature. The solid obtained was filtered and
washed with methanol to give white solid (yield: 2.7 g, 76.5%). 1H
Figure 1. Zinc xanthates with linear (1, 2, 3 ) and branched (4, 5, 6)
alkyl chains.
Potassium O-Hexan-1-yl-dithiocarbonate: Potassium tert-butoxide
(10.5 g, 93 mmol, 1.0 equiv.) was dissolved in tetrahydrofuran (THF) NMR (500 MHz, 26 °C, CDCl3): δ = 4.49–4.47 (t, 2 H), 1.85–1.78
in an inert atmosphere (nitrogen). The solution was cooled down to
(m, 2 H), 1.43–1.29 (m, 6 H) ppm, 0.91–0.88 (t, 3 H) ppm. 13C NMR
0 °C, and 1-hexanol (8.8 g, 86 mmol, 1.1 equiv.) was slowly added. (125 MHz, 24 °C, CDCl3): δ = 229.80, 78.04, 31.38, 28.34, 25.52,
After stirring for 15 min, carbon disulfide (6.5 g, 86 mmol, 1.1 equiv.) 22.53, 14.02 ppm. IR (KBr): ν˜ = 2952, 2850, 1459, 1207, 1132, 1064,
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1032, 936 cm–1. Zn(II) C14H26O2S4: calcd. C 40, H 6.2%, found: C
39.7, H 6.05%.
Zinc(II)-O-2,2-dimethylbutan-3-yl-dithiocarbonate (4): Zinc(II)-O-
2,2-dimethylbutan-3-yl-xanthate in the yield of 5.7 g, 83.2% was syn-
thesized according to the literature report.[42] 1H NMR (500 MHz,
26 °C, CDCl3): δ = 4.88–4.92 (m, 1 H), 1.34–1.32 (d, 3 H), 1–0.99 (d,
9 H) ppm. 13C NMR (125 MHz, 24 °C, CDCl3): δ = 228.93, 94.29,
35.06, 25.68, 14.34 ppm. IR (KBr): ν˜ = 2965, 2873, 1462, 1364, 1252,
1129, 1058, 907 cm–1. Zn(II) C14H26O2S4 calcd. C 40, H 6.2%, found:
C 45.7, H 6.9%.
Zinc(II)-O-2,2-dimethylpentan-3-yl-dithiocarbonate (5): To an
aqueous solution of zinc(II) chloride (1 g, 7 mmol), potassium-O-2,2-
dimethylpentan-3-yl-dithiocarbonate (3.71 g, 16 mmol) dissolved in
water was added dropwise while stirring at room temperature. A white
precipitate formed was collected by suction filtration and washed with
methanol. The solid obtained was extracted into chloroform and
recrystallized from methanol to obtain white powder (yield: 6.4 g,
89%). 1H NMR (500 MHz, 26 °C, CDCl3, δ): 4.92–4.98 (m, 1 H),
1.79–1.72 (m, 2 H), 0.96–0.98 (m, 12 H) ppm. 13C NMR (125 MHz,
24 °C, CDCl3, δ): 230.79, 100.56, 35.88, 25.95, 23.20, 10.96 ppm. IR
(KBr): ν˜ = 2965, 2875, 1468, 1367, 1236, 1129, 1056, 902 cm–1. Zn(II)
C16H30O2S4 calculated: C 42.9, H 6.7%, found: C 42.0, H 6.5%.
Figure 2. XRD analysis of zinc xanthates with linear chains 1, 2, 3
and branched chains 4, 5, 6 under investigation after thermal annealing
at 200 °C.
Zinc(II)-O-2,2-dimethylhexan-3-yl-dithiocarbonate (6): To an aque-
ous solution of zinc(II) chloride (1 g, 7.4 mmol), potassium-O-2,2-di-
methylhexan-3-yl-dithiocarbonate (3.9 g, 16 mmol) dissolved in water
was added dropwise, while stirring at room temperature. A white pre-
cipitate formed was collected by suction filtration and washed with
methanol. The solid obtained was extracted into chloroform and
recrystallized from methanol to obtain slightly yellow powder as titled
compound (yield: 5.6 g, 72.1%). 1H NMR (500 MHz, 26 °C, CDCl3):
δ = 4.99–4.97 (m, 1 H) 1.76–1.74 (m, 2 H), 1.52–1.47 (2H), 1.01–
1.0(d, 9 H), 0.96–0.89 (m, 3 H) ppm. 13C NMR (125 MHz, 24 °C,
CDCl3): δ = 230.72, 99.44, 35.85, 32.22, 25.89, 19.51, 14.15 ppm. IR
(KBr): ν˜ = 2954, 2870, 1461, 1369, 1222, 1130, 1038, 901 cm–1. Zn(II)
C18H34O2S4 calcd. C 45.4, H 7.2%, found: C 44.2, H 6.9%.
3.2 Thermogravimetric Analysis
The comparison of thermal behavior and decomposition
temperature of zinc xanthates by varying alkyl chain was in-
vestigated utilizing thermogravimetric (TGA) analysis in a ni-
trogen atmosphere. The TGA plots of linear and branched
alkyl chain zinc xanthates are presented in Figure 3.
Supporting Information (see footnote on the first page of this article):
1H NMR, 13C NMR of zinc(II) xanthates, and DSC cure study.
3 Results and Discussion
3.1 XRD Analysis of Thermally Annealed Zinc Xanthates
Figure 3. Thermogravimetric analysis of Zinc xanthates with (a) linear
chains 1, 2, 3 and (b) branched chains 4, 5, 6.
XRD was employed to characterize the final product of de-
composition upon thermal annealing. The zinc(II) xanthates
The TGA plot indicates that zinc(II) xanthates are quite
under consideration were thermally annealed for about 15 min stable at room temperature condition. However, upon further
at 250 °C. The sample powders were grinded thoroughly and increasing beyond certain threshold temperature they decom-
subjected to powder XRD investigation. The XRD spectra of pose. This tendency to decompose by providing threshold ex-
thermally annealed products of zinc xanthates are presented in ternal thermal stimuli can be attributed to the latent capability
Figure 2. The XRD pattern observed for 1, 2, 3, 4, 5, 6 zinc(II) of zinc(II) xanthates. All the zinc xanthates under investigation
xanthates as presented in Figure 2 were similar and had dif- showed expected weight loss percentage (ca. 70%) corre-
fraction peaks at 2θ values of 28.6°, 47.6°, and 56.4° corre- sponding to the formation of zinc sulfide.
sponding to the diffraction planes (111), (220), and (311)
The decomposition temperature of zinc xanthates with
respectively.[44] This peak pattern perfectly describes zinc change in alkyl chain showed interesting results. The thermal
blend structure (JCPDS No. 80–0020).[45] Thus XRD analysis decomposition temperature in the case of linear alkylzinc(II)
confirmed the formation of ZnS with a zinc blend structure xanthates varied in the order 1 Ͻ 2 Ͻ 3, indicating that with
upon thermal annealing of 1, 2, 3, 4, 5, 6 zinc xanthates.
increase in alkyl chain length the decomposition temperature
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is enhanced in the case of linear alkyl chain zinc xanthates. der 1 Ͻ 2 Ͻ 3. In contrast the cure time decreased with in-
On the other hand in the case of branched alkyl chain zinc crease in alkyl chain length in the case of branched alkylzinc
xanthates the trend observed is opposite, wherein with increase xanthates following the order 4 Ͼ 5 Ͼ 6. Comparatively 2,2-
in alkyl chain length the thermal decomposition temperature dimethyl-3-hexanylzinc(II) xanthate showed the most effective
decreases as the TGA analysis portrays the thermal decomposi- catalytic property among the zinc(II) xanthates under consider-
tion temperature in the order 4 Ͼ 5 Ͼ 6. Thus the decomposi- ation. This behavior can be explained based on our communi-
tion temperatures trend in the case of linear chain zinc xan- cation,[41] where the mechanism of curing was reported to oc-
thates increased, while in the case of branched alkylzinc xan- cur via the formation of in-situ metal sulfide. The epoxy resin
thates decreased by increment in the alkyl chain length respec- composite including zinc xanthate upon thermal annealing
tively. 2,2-Dimethyl-3-hexanylzinc(II) xanthate relatively yields in-situ catalytically active zinc sulfide, which is respon-
showed the least decomposition temperature among the sible for cure initiation. Since in the case of linear alkyl chain
zinc(II) xanthates under investigation.
zinc xanthates, by increase in alkyl chain length, the thermal
decomposition temperature is enhanced resulting higher cure
time at a given temperature. On the other hand in the case of
branched alkyl chain zinc(II) xanthates the thermal decomposi-
tion temperature was observed to decrease with increment in
alkyl chain length. Therefore with increase in alkyl chain
length decrease in cure time of epoxy composite at a particular
temperature can be observed. In addition, also explains the rel-
atively effective catalysis of 2,2-dimethyl-3-hexanylzinc(II)
xanthates among the zinc(II) xanthates employed in the current
study owing to its comparatively lowest decomposition tem-
perature.
Thus this trend explains the possible mechanism of curing
of epoxy resin composite including zinc(II) xanthates via for-
mation of in-situ formation of zinc sulfide in the epoxy resin
matrix. Further it can be concluded that cure catalytic property
is determined by the alkyl chain moiety of metal xanthate spe-
cies.
Curing of epoxy resin is an activated process and differential
scanning calorimetric analysis (DSC) is popularly used to
study the cure process.[47] To further confirm the curing of
epoxy resin utilizing zinc(II) xanthate as catalyst upon thermal
annealing. Dynamic DSC study[48,49] was performed for 1:1
(w/w) epoxy/phenolic composite including 5% 2,2-dimethyl-
3-hexanylzinc(II) xanthate as catalyst (Figure S17, Supporting
Information). The curing of epoxy resin employing zinc(II)
xanthate was characterized by its cure exotherm and the
dynamic DSC data was utilized to estimate the activation
energy by Flynn-Wall-Ozawa[50] and Kissinger’s methods[51]
(Appendix 1, Supporting Information).
3.3 Investigation of Epoxy Resin Curing using Zinc(II)
Xanthates
Physical changes of curing involve transformation of melted
epoxy composite in liquid form to a highly viscous glassy state
via highly viscous semi solid. The time when the melted liquid
epoxy composite fully transforms into solid glassy state is re-
corded as the curing time.[46] Lower the cure time at a given
temperature means faster curing process indicating the higher
efficiency of the catalyst under consideration. The cure time
vs. temperature study was utilized to analyze and compare the
curing catalytic property of zinc xanthates. The epoxy resin
composite including the catalyst was placed on a hot plate
maintained at a specific temperature and the time to form com-
plete solid was recorded as cure time. The composite was con-
stantly mixed until the mixture, which initially becomes liquid
due to melting later on upon completion of curing becomes
fully solid. For the presented study a 1:1 (w/w) mixture of
epoxy resin and phenol was homogenously grinded including
5% of corresponding zinc(II) xanthate for performing cure
time study of epoxy resin as a function of temperature. The
curing time was recorded at different temperatures ranging
from 180–200 °C utilizing 5% zinc xanthates and is shown in
Figure 4. There was no significant curing observed until
160 °C. The cure time trend by zinc xanthates with varying
alkyl ligands at a particular temperature showed results in par-
allel to the order of thermal decomposition temperature as re-
vealed by TGA of zinc(II) xanthates under investigation.
3.4 XRD Analysis of Post Cured Epoxy Resins Including
Zinc(II) Xanthates by Thermal Annealing
To further validate our results that the in situ formed ZnS is
responsible for curing of epoxy resin upon thermal annealing
utilizing zinc(II) xanthates catalysts, samples consisting of ep-
oxy composite including zinc(II) xanthates were characterized.
XRD analysis was performed for the thermally annealed cured
epoxy resin samples obtained employing 20% zinc(II) xan-
thates as catalysts. Figure 5 represents the XRD spectra of
thermally annealed zinc(II) xanthates including epoxy resin
composite. The XRD analysis spectra of the cured epoxy resin
including zinc xanthates consisted of similar peaks as pre-
Figure 4. Cure time vs. temperature with 5% zinc xanthates with (a)
linear alkyl chains 1, 2, 3 and (b) branched alkyl chains 4, 5, 6 as
catalysts.
In the case of linear alkylzinc xanthates the cure time in- sented in Figure 2, which confirms the formation of zinc sulf-
creased with increment in alkyl chain length following the or- ide in situ in the composite matrix. In addition to the peaks
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similar to Figure 2 an additional broad amorphous peak was ture of zinc(II) xanthates can be tuned and resulting in control
observed in Figure 5. This peak is explained by the presence over curing catalytic behavior.
of amorphous cured epoxy resin. Thus the presence of zinc
sulfide peaks in the cured epoxy composite matrix clearly indi-
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Received: August 11, 2015
Published Online: November 30, 2015
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