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Synthesis and characterization of polymers from cashewnut shell liquid: a renewable resource
European Polymer Journal 36 (2000) 1157±1165
Synthesis and characterization of polymers from cashewnut shell liquid: a renewable resource V. Synthesis of copolyester H.P. Bhunia a, A. Basak b, T.K. Chaki a, G.B. Nando a,* a
Rubber Technology Centre, Indian Institute of Technology, Kharagpur 721302, India Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
b
Received 11 February 1999; received in revised form 25 May 1999; accepted 21 June 1999
Abstract A novel copolyester was synthesized by solution polycondensation of terephthaloyl chloride with 4-[(4-hydroxy-2pentadecenylphenyl)diazenyl] phenol (HPPDP) and 1,4-butane diol. The monomer (HPPDP) has been synthesized from 3-pentadecenyl phenol, a renewable resource and a by-product of the cashew industry characterized earlier [1]. The copolyester was characterized through elemental analysis, 1 H-NMR, IR, and UV spectroscopy. Dilute solution viscosity of its solution was also determined by viscometry. The intrinsic viscosity Z was 0.98 dl/gm. The melting temperatures of the copolyester were 63 and 1278C as observed from Dierential Scanning Calorimetric (DSC) studies. Thermogravimetric analysis show that degradation commences at 2908C in nitrogen atmosphere. Wide-angle X-ray diraction study of the copolyester indicates absence of any crystallinity, whereas DSC studies indicate the presence of two melting peaks. Thus, it is presumed that the copolyester has short range crystallinity. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Cardanol; Copolyester; Thermal decomposition
1. Introduction In recent years, the synthesis of polymers from renewable resources has attracted considerable attention of research workers throughout the world because of the escalating price of petrochemicals and high rate of depletion of the natural mineral resources. This necessitates a look at the renewable natural resources that can serve as alternative feedstocks for monomers
* Corresponding author. Fax: +91-3222-55303. E-mail address: [email protected] (G.B. Nando).
of the polymer industry. In this respect, cashewnut shell liquid (CNSL), an agricultural by-product of the cashew industry, holds considerable promise as a source of unsaturated hydrocarbon phenol, an excellent monomer for polymer production. CNSL occurs as a reddish brown viscous ¯uid in the soft honeycomb structure of the shell of cashewnut, a plantation product obtained from the cashew tree, Anacardium oxidentale. Many researchers have investigated its extraction [2±4], chemistry and composition [5±10]. The CNSL contains four major components namely, 3-pentadecenyl phenol (cardanol), 5-pentadecenyl resorcinol (cardol), 6-pentadecenyl salicylic acid (ana-
0014-3057/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 9 ) 0 0 1 7 1 - 8
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cardic acid) and 2-methyl, 5-pentadecenyl resorcinol (2-methyl cardol). The CNSL and cardanol are in use in the manufacture of special phenolic resins for coatings, lamination and as friction materials [11±13]. In general, polymers from CNSL and cardanol have been prepared either by condensation with electrophilic compounds, such as formaldehyde, or by chain polymerization through the unsaturation in the side chain using acid catalysts, or functionalization at the hydroxyl group and subsequently oligomerization to get functionalized prepolymer. Mishra and Pandey [14] investigated the kinetics of the alkali catalyzed formaldehyde condensation of cardanol. Cardanol was functionalized with both orthophosphoric acid and oligomerized, the resulting prepolymers act as multifunctional additives [15±18]. Recently, Saminathan [19] reported the main-chain liquid crystalline polymer containing a phenyl azo group of cardanol. Cardanol was oxidized with phase transfer catalyzed permanganate and the oxidized product 8-(3-hydroxy phenyl) octanoic acid was copolymerized with p-hydroxy benzoic acid to produce a thermotropic liquid-crystalline copolymer [20]. Though there are a few attempts on synthesis, chemical modi®cation and functionalization of cardanol and its polymers, studies on detailed investigations on the structure and properties and the characterization of the products are limited. Recently, the authors have synthesized a series of polyurethanes [1,21] from 4-[(4-hydroxy-2-pentadecenyl-phenyl)diazenyl] phenol (HPPDP) derived from cardanol and a polyether by modifying cardanol with epichlorohydrin and polymerizing through ring opening polymerization [22]. This paper reports the synthesis and thermal characterization of copolyester by solution polymerization of terephthaloyl chloride with HPPDP and 1,4butane diol. The monomer, HPPDP was synthesized from cardanol which acts as a renewable resource in the synthesis of the polymer.
2. Experimental 2.1. Materials Technical-grade CNSL of Indian Standard speci®cation IS:840 (1964) [23] was obtained from Cashew Development Corporation, Quilon, Kerala, India. Cardanol was obtained by double vacuum distillation of CNSL. The chemicals sodium nitrite, p-aminophenol (AR, S.D. Fine Chem. India) and 1,4-butane diol, terephthaloyl chloride (MDI, E.Merck, India) were used as received without puri®cation. The solvents namely, dimethyl formamide (DMF), dichlorobenzene, dimethyl sulfoxide (DMSO), (Merck, India) and chloroform, methanol, acetone, (SRL, India) were
Scheme 1.
dried by standard methods [24,25] and vacuum distilled. 2.2. Synthesis of HPPDP from cardanol The monomer synthesis (Scheme 1) was carried out according to the modi®ed procedure of Pansare et al. [19,26]. The detail procedure has been reported earlier [1]. The red dye HPPDP was then puri®ed by column chromatography on silica-gel (60±120 mesh) using chloroform as eluent. Solvents were removed and the product recrystallized from a methanol±water mixture. Yield was 17.6 g (80%); colour: reddish-green and mp 130±1388C. 2.3. Synthesis of the copolyester The copolyester was synthesized according to the modi®ed procedure of Thammongkol et al. [27]. A 1000 ml three-necked round bottom ¯ask was equipped with a magnetic stirrer bar, a re¯ux condenser, a thermometer,and a nitrogen inlet tube. The copolyester was prepared by taking a 4 : 1 : 5 molar ratio of HPPDP to 1,4-butane diol to terephthaloyl chloride. These monomers were charged into a ¯ask and then dissolved in dichlorobenzene. The polymerization reaction was carried out under vigorous stirring and re¯uxed at 190±1958C for 24 h. Nitrogen was used to drive the reaction forward to product formation by removing hydrogen chloride generated. After the reaction, the mixture was allowed to cool for about an hour. A ®ne grey precipitate was formed. The mixture was then poured into a ¯ask containing acetone to coagulate the polymer and was stirred for 3 h. The precipitate was isolated by vacuum ®ltration and washed several times with acetone, deionized water, and methanol. The polyester was dried in vacuum oven at 1208C for 48 h. The polymerization reaction is shown in Scheme 2.
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Scheme 2.
2.4. Characterization Characterization of the HPPDP and copolyester were carried out through elemental analysis (Heracus CHN-rapid analyser), IR spectrophotometer (model: Perkin±Elmer-843), and UV visible spectroscopy (model: Shimadzu UV-300). 1 H-NMR and 13 C-NMR spectra were recorded by a Bruker 200 MHz and the chemical shifts were reported in ppm units with tetramethylsilane as internal standard. Chloroform (CDCl3) was used as solvent for recording NMR spectra. The thermal measurements were performed in a DuPont 9000 Thermal analyser employing a 20 ml/min ¯ow of dry nitrogen as purge gas for the sample and reference cells and liquid nitrogen as coolant. The intrinsic viscosity of the polymer was determined at 358C in CHCl3 by using Ostwald viscometer. Wide angle X-ray diraction study (WAXS) was carried out with a Philips wide-range X-ray diractometer (model PW1840) using monochromatic CuKa radiation l 1:5402 AÊ) at zero background using a silicon 811 background from diraction angle 10±908.
3. Results and discussion The cardanol was recovered from CNSL by direct double vacuum distillation (5±10 mm of Hg) in the temperature range of 180±2408C and has been characterized by the authors earlier [1]. Cardanol is basically a monoene metasubstituted phenol i.e., cardanol having empirical formula C21H29O. 3.1. Characterization of the polyester The yield of the copolyester was 78%. The el-
emental analysis results showed values of 72.5% carbon, 6.45% hydrogen and 3.2% nitrogen for the copolyester. Theoretical values are 73% carbon, 6.7% hydrogen and 3.6% nitrogen, respectively. The absorption band at 337 nm in the UV spectra (Fig. 1) is related to the n 4 p transition of azo (± N1N±) unit of the copolyester. It has been observed that on exposing the copolyester sample for 1 h in UV light and studying under UV spectroscopy does not make any change in the spectrogram. Fig. 2 shows the IR spectrum of the copolyester. The two intense peaks at 1790 and 1746 cmÿ1 are indicative of the presence of two dierent ester structures in the polymer. This establishes the formation of a copolyester during the polymerization. The IR spectrum also shows C±O ester stretching at 1075, 1174, and 1260 cmÿ1. The absorption peak at 2925 cmÿ1 represents asymmetrical aliphatic C±H stretching and the peaks at 2852 cmÿ1 represent symmetrical C±H stretching. The aromatic ring >C1C< stretching vibrations occurs at 1602, 1587, 1554 and 1528 cmÿ1. These peaks are in good agreement with the literature values [28]. The peaks around 2360 cmÿ1 are due to C±O stretching of carbon dioxide in the atmosphere as this is also observed in the background scan. Fig. 3 shows the 1 H-NMR spectrum of the copolyester which is recorded in deuterated chloroform. The broad resonance centered around d8:5 ppm represents protons on the terephthaloyl ring. The peak appearing in the range of d7:2±7:8 represents the aromatic protons of HPPDP compound, while the signals at d4:5 and 3.2 ppm represent the methylene protons in Ph± CO±O±CH2± and Ph±CO±O±CH2±CH2± moiety, respectively. The ole®nic protons appeared as a multiplet in the range d5:30±5:36 (2H). The broad signal at d2:52 could be attributed to the ±CH2±Ar (2H) and
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Fig. 1. UV spectra of cardanol, HPPDP and copolyester. (ÐÐÐ) cardanol, (- - -) HPPDP, (± ±) copolyester.
while that at 2.0 ppm (4H, m) was assigned to the (± CH2±CH1CH±) component of the HPPDP. The groups (±CH2±)n appeared as a singlet at d1:32 (16H), while the terminal ±CH3 group in the side chain gave a triplet at d0:89:
4. Polymer properties The copolyester isolated from the reaction mixture by precipitation in cold acetone was a dark grey powdery material. The properties of the copolyester thus synthesized are shown in Table 1. It is soluble in chloroform at an elevated temperature in the range of 50±608C. It may be cast from its solution into thin reddish ®lms, which are brittle in character. The density of copolyester is 0.62 gm/cm3. The intrinsic viscosity Z is found to be 0.98 dl/gm at 358C, which indicates that the copolyester molecular weight is high.
5. Thermal analysis Fig. 4 shows the thermogravitogram of the copolyester. The heating rate was maintained at 208C/min in air and nitrogen. The experiment was carried out from
room temperature to 6008C. The copolyester has a stability up to 2818C in air after which it commences to degrade. Whereas in nitrogen the degradation commences at 2908C and is rapid. It shows a two stage degradation. During the ®rst stage of degradation the mass loss is around 20% of its original weight, the temperature range being 290±3718C and Tmax occurring at 3258C. The second and ®nal stage of degradation occurs in the temperature range of 371±10008C accounting for the rest 80% weight loss with the Tmax occurring at 4438C. TGA results of the copolyester, HPPDP, the monomer and cardanol the raw material are summarized in Table 2. In general, a polyester derived from aromatic dihydroxy compound has high thermal stability as compared polyesters having an aliphatic chain in their backbone [29,30]. Figs. 5 and 6 show the Dierential Scanning Calorimetric (DSC) thermograms of the copolyester in nitrogen atmosphere at a heating rate of 208C/min. The curve shows a secondary transition at ÿ708C assumed to be the glass transition temperature of the amorphous side chain attached to the aromatic ring of the copolyester and not to the main chain vibrations. The lower glass transition temperature is attributed to long and ¯exible side chain attached to main chain consisting of three to four ±CH2± groups present in a row. The broad melting temperatures for the copolyester
H.P. Bhunia et al. / European Polymer Journal 36 (2000) 1157±1165
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Fig. 2. IR spectrum of the copolyester.
observed at 63 and 1278C may be due to the two dierent structural repeat units present in the copolyester as shown in Scheme 2. The lower melting temperature may be due to 1,4-butane diol structure adjacent to the terephthaloyl group and the higher melting temperature may be due to the HPPDP unit forming the ester. In the ®rst heating, an endothermic peak is observed which vanishes in the second heating cycle due to quenching of the copolyester which disturbs its ordered structure. However, when the polymer is
cooled down slowly, the endothermic peak reappears again during the second heating cycle. This may be attributed to partially crystalline nature of the copolymer. 6. WAXS study WAXS study of the copolyester synthesized from cardanol was carried out using CuK target in the angular range 108 2y)±908 2y). The diractogram
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Fig. 3. 1 H-NMR spectrum of the copolyester.
shows a broad halo commencing from 138 2y up to 358 2y). It shows that the copolyester is amorphous in character. However, DSC records two melting endotherms indicating the presence of order or crystallinity in the polymer. This has been further con®rmed by annealing in nitrogen atmosphere or spontaneously cooling the sample from molten state to room temperature. The degree of crystallinity is lower this time. This implies that there is some de®nite order or partial
crystallinity in the copolyester, which is not detectable by X-ray diraction.
7. Conclusions The following conclusions have been drawn from the aforesaid study:
Table 1 Properties of copolyester State Colour Odour Density Solubility: Soluble Insoluble Intrinsic viscosity Z at 358C Melting temperature (Tm) Glass transition temperature (Tg) Thermal stability (Ti)
Powder Dark grey Odourless 0.62 gm/cc DMF, DMSO, H2SO4, m-cresol HCOOH, chlorobenzene, cyclohexanone, CHCl3, xylene 0.98 dl/gm +63 and +1278C ÿ708C 2908C
H.P. Bhunia et al. / European Polymer Journal 36 (2000) 1157±1165
Fig. 4. Thermogram of the copolyester. (ÐÐÐ) in N2 atmosphere, ( ) in air.
Fig. 5. DSC curve of the copolyester.
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Fig. 6. DSC curves of the copolyester; eect of thermal history. (a) (ÐÐÐ) untreated sample, (b) (± ±) heated and quenched sample, (c) (- - -) heated sample cooled slowly.
Table 2 TGA analysis of cardanol, HPPDP and copolyester in nitrogen Components
Ti (8C)
Tmax (8C)
Tf (8C)
Loss (%)
Cardanol HPPDP monomer 1st stage 2nd stage 3rd stage Copolyester 1st stage 2nd stage
200
329
350
100
255 390 545
336 480 Slow
390 545 1000
30 35 98
290 371
325 443
371 1000
20 80
as con®rmed from DSC studies. WAXS studies do not show any gross crystallinity.
Acknowledgements The authors are grateful to the Council of Scienti®c and Industrial Research, New Delhi, for funding this project.
References 1. A novel copolyester has been synthesized by reacting the monomers HPPDP and 1,4-butane diol with the terephthaloyl chloride. 2. The resulting copolyester has high intrinsic viscosity of 0.98 dl/gm, indicating relatively high molecular weight. 3. The thermal stability of the copolyester is higher than those of the monomers. 4. The copolyester is highly stable to UV light. 5. The copolyester is partially crystalline in character
[1] Bhunia HP, Jana RN, Basak A, Lenka S, Nando GB. J Polym Sci, Part A: Polym Chem 1998;36:391. [2] George KV. Improvement of quantity of CNSL obtained by expelling from oil both roasted shells. In: Third Annual Symposium on Plantation Crops Ð Placrosym III, Kerala, 1980. [3] Wilson RJ, Wilson. The market for cashew kernels and cashewnut shell liquid. Report No. G91, Tropical Products Institute, London, 1975. [4] Tyman HP, Johnson RA, Muir M, Rokhgar R. J Am Or Chem Sci 1989;66:553.
H.P. Bhunia et al. / European Polymer Journal 36 (2000) 1157±1165 [5] Wasserman D, Dawson CR. Ind Eng Chem 1945;38:396. [6] Tyman JHP, Wilczynski D, Kashani MA. J Am Oil Chem Soc 1978;55:663. [7] Lloyd HA, Denny C, Krishna G. J Liquid Chromatog 1980;3:1497. [8] Tyman JH. J Chem Soc, Perkin Trans 1973;1:1639. [9] Tyman HP. J Chromatog 1975;111:277. [10] Tyman JHP, Tychopoulos V, Chain P. J Chromatog 1984;303:137. [11] Tyman JHP. Chem Soc Rev 1979;8:499. [12] Menon ARR, Pillai CKS, Sudha JD, Mathew AG. J Sci Ind Rev 1985;44:324. [13] Gedam PH, Sampathkumaran PS. Prog Org Coatings 1986;14:115. [14] Pandey GN, Mishra AK. J Appl Polym Sci 1985;30:969. [15] Pillai CKS, Prasad VS, Sudha JD, Bera SC, Menon ARR. J Appl Polym Sci 1990;41:2487. [16] Menon ARR, Pillai CKS, Nando GB. Kauts Gummi Kunst 1992;45:708. [17] Menon ARR, Pillai CKS, Nando GB. J Appl Polym Sci 1994;51:2157. [18] Menon ARR, Pillai CKS, Nando GB. J Adhesion Sci Tech 1995;9:443.
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[19] Saminathan M, Pillai CKS, Krishn C, Pavithran C. Macromolecules 1993;26:7103. [20] Pillai CKS, Sherrington DC, Sneddon A. Polym Commun 1992;33:3968. [21] Bhunia HP, Nando GB, Basak A. Eur Polym J, in press. [22] Bhunia HP, Nando GB, Chaki TK, Basak A, Lenka S, Nayak PL. Eur Polym J 1999;35:1381. [23] Murty BGK, Menon MC, Aggarwal JS, Zaheer SH. Paint Manuf 1961;31:47. [24] Perrin DD, Armarego WLF, Perrin DR. Puri®cation of laboratory chemicals, 2nd ed. Oxford: Pergamon Press, 1980. [25] Longman. Vogel's testbook of practical organic chemistry, 4th ed. London: ELBS, 1978. [26] Pansare SV, Kulkarni AB. J Indian Chem Soc 1964;41:251. [27] Thammongokol V, Warner SB, Polok MB. J Polym Sci, Part A: Polym Chem 1995;33:189. [28] Socrates G. Infrared characteristic group frequencies. Chichester, UK: Wiley, 1980. [29] Economy J, Storm RS, Matkovich VJ, Cottis SG, Nowak BE. J Polym Sci, Polym Chem Ed 1976;14:2207. [30] Kricheldorf HR, Schwarz G. Polymer 1984;25:520.
Synthesis and characterization of polymers from cashewnut shell liquid: a renewable resource V. Synthesis of copolyester H.P. Bhunia a, A. Basak b, T.K. Chaki a, G.B. Nando a,* a
Rubber Technology Centre, Indian Institute of Technology, Kharagpur 721302, India Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India
b
Received 11 February 1999; received in revised form 25 May 1999; accepted 21 June 1999
Abstract A novel copolyester was synthesized by solution polycondensation of terephthaloyl chloride with 4-[(4-hydroxy-2pentadecenylphenyl)diazenyl] phenol (HPPDP) and 1,4-butane diol. The monomer (HPPDP) has been synthesized from 3-pentadecenyl phenol, a renewable resource and a by-product of the cashew industry characterized earlier [1]. The copolyester was characterized through elemental analysis, 1 H-NMR, IR, and UV spectroscopy. Dilute solution viscosity of its solution was also determined by viscometry. The intrinsic viscosity Z was 0.98 dl/gm. The melting temperatures of the copolyester were 63 and 1278C as observed from Dierential Scanning Calorimetric (DSC) studies. Thermogravimetric analysis show that degradation commences at 2908C in nitrogen atmosphere. Wide-angle X-ray diraction study of the copolyester indicates absence of any crystallinity, whereas DSC studies indicate the presence of two melting peaks. Thus, it is presumed that the copolyester has short range crystallinity. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Cardanol; Copolyester; Thermal decomposition
1. Introduction In recent years, the synthesis of polymers from renewable resources has attracted considerable attention of research workers throughout the world because of the escalating price of petrochemicals and high rate of depletion of the natural mineral resources. This necessitates a look at the renewable natural resources that can serve as alternative feedstocks for monomers
* Corresponding author. Fax: +91-3222-55303. E-mail address: [email protected] (G.B. Nando).
of the polymer industry. In this respect, cashewnut shell liquid (CNSL), an agricultural by-product of the cashew industry, holds considerable promise as a source of unsaturated hydrocarbon phenol, an excellent monomer for polymer production. CNSL occurs as a reddish brown viscous ¯uid in the soft honeycomb structure of the shell of cashewnut, a plantation product obtained from the cashew tree, Anacardium oxidentale. Many researchers have investigated its extraction [2±4], chemistry and composition [5±10]. The CNSL contains four major components namely, 3-pentadecenyl phenol (cardanol), 5-pentadecenyl resorcinol (cardol), 6-pentadecenyl salicylic acid (ana-
0014-3057/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 9 9 ) 0 0 1 7 1 - 8
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cardic acid) and 2-methyl, 5-pentadecenyl resorcinol (2-methyl cardol). The CNSL and cardanol are in use in the manufacture of special phenolic resins for coatings, lamination and as friction materials [11±13]. In general, polymers from CNSL and cardanol have been prepared either by condensation with electrophilic compounds, such as formaldehyde, or by chain polymerization through the unsaturation in the side chain using acid catalysts, or functionalization at the hydroxyl group and subsequently oligomerization to get functionalized prepolymer. Mishra and Pandey [14] investigated the kinetics of the alkali catalyzed formaldehyde condensation of cardanol. Cardanol was functionalized with both orthophosphoric acid and oligomerized, the resulting prepolymers act as multifunctional additives [15±18]. Recently, Saminathan [19] reported the main-chain liquid crystalline polymer containing a phenyl azo group of cardanol. Cardanol was oxidized with phase transfer catalyzed permanganate and the oxidized product 8-(3-hydroxy phenyl) octanoic acid was copolymerized with p-hydroxy benzoic acid to produce a thermotropic liquid-crystalline copolymer [20]. Though there are a few attempts on synthesis, chemical modi®cation and functionalization of cardanol and its polymers, studies on detailed investigations on the structure and properties and the characterization of the products are limited. Recently, the authors have synthesized a series of polyurethanes [1,21] from 4-[(4-hydroxy-2-pentadecenyl-phenyl)diazenyl] phenol (HPPDP) derived from cardanol and a polyether by modifying cardanol with epichlorohydrin and polymerizing through ring opening polymerization [22]. This paper reports the synthesis and thermal characterization of copolyester by solution polymerization of terephthaloyl chloride with HPPDP and 1,4butane diol. The monomer, HPPDP was synthesized from cardanol which acts as a renewable resource in the synthesis of the polymer.
2. Experimental 2.1. Materials Technical-grade CNSL of Indian Standard speci®cation IS:840 (1964) [23] was obtained from Cashew Development Corporation, Quilon, Kerala, India. Cardanol was obtained by double vacuum distillation of CNSL. The chemicals sodium nitrite, p-aminophenol (AR, S.D. Fine Chem. India) and 1,4-butane diol, terephthaloyl chloride (MDI, E.Merck, India) were used as received without puri®cation. The solvents namely, dimethyl formamide (DMF), dichlorobenzene, dimethyl sulfoxide (DMSO), (Merck, India) and chloroform, methanol, acetone, (SRL, India) were
Scheme 1.
dried by standard methods [24,25] and vacuum distilled. 2.2. Synthesis of HPPDP from cardanol The monomer synthesis (Scheme 1) was carried out according to the modi®ed procedure of Pansare et al. [19,26]. The detail procedure has been reported earlier [1]. The red dye HPPDP was then puri®ed by column chromatography on silica-gel (60±120 mesh) using chloroform as eluent. Solvents were removed and the product recrystallized from a methanol±water mixture. Yield was 17.6 g (80%); colour: reddish-green and mp 130±1388C. 2.3. Synthesis of the copolyester The copolyester was synthesized according to the modi®ed procedure of Thammongkol et al. [27]. A 1000 ml three-necked round bottom ¯ask was equipped with a magnetic stirrer bar, a re¯ux condenser, a thermometer,and a nitrogen inlet tube. The copolyester was prepared by taking a 4 : 1 : 5 molar ratio of HPPDP to 1,4-butane diol to terephthaloyl chloride. These monomers were charged into a ¯ask and then dissolved in dichlorobenzene. The polymerization reaction was carried out under vigorous stirring and re¯uxed at 190±1958C for 24 h. Nitrogen was used to drive the reaction forward to product formation by removing hydrogen chloride generated. After the reaction, the mixture was allowed to cool for about an hour. A ®ne grey precipitate was formed. The mixture was then poured into a ¯ask containing acetone to coagulate the polymer and was stirred for 3 h. The precipitate was isolated by vacuum ®ltration and washed several times with acetone, deionized water, and methanol. The polyester was dried in vacuum oven at 1208C for 48 h. The polymerization reaction is shown in Scheme 2.
H.P. Bhunia et al. / European Polymer Journal 36 (2000) 1157±1165
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Scheme 2.
2.4. Characterization Characterization of the HPPDP and copolyester were carried out through elemental analysis (Heracus CHN-rapid analyser), IR spectrophotometer (model: Perkin±Elmer-843), and UV visible spectroscopy (model: Shimadzu UV-300). 1 H-NMR and 13 C-NMR spectra were recorded by a Bruker 200 MHz and the chemical shifts were reported in ppm units with tetramethylsilane as internal standard. Chloroform (CDCl3) was used as solvent for recording NMR spectra. The thermal measurements were performed in a DuPont 9000 Thermal analyser employing a 20 ml/min ¯ow of dry nitrogen as purge gas for the sample and reference cells and liquid nitrogen as coolant. The intrinsic viscosity of the polymer was determined at 358C in CHCl3 by using Ostwald viscometer. Wide angle X-ray diraction study (WAXS) was carried out with a Philips wide-range X-ray diractometer (model PW1840) using monochromatic CuKa radiation l 1:5402 AÊ) at zero background using a silicon 811 background from diraction angle 10±908.
3. Results and discussion The cardanol was recovered from CNSL by direct double vacuum distillation (5±10 mm of Hg) in the temperature range of 180±2408C and has been characterized by the authors earlier [1]. Cardanol is basically a monoene metasubstituted phenol i.e., cardanol having empirical formula C21H29O. 3.1. Characterization of the polyester The yield of the copolyester was 78%. The el-
emental analysis results showed values of 72.5% carbon, 6.45% hydrogen and 3.2% nitrogen for the copolyester. Theoretical values are 73% carbon, 6.7% hydrogen and 3.6% nitrogen, respectively. The absorption band at 337 nm in the UV spectra (Fig. 1) is related to the n 4 p transition of azo (± N1N±) unit of the copolyester. It has been observed that on exposing the copolyester sample for 1 h in UV light and studying under UV spectroscopy does not make any change in the spectrogram. Fig. 2 shows the IR spectrum of the copolyester. The two intense peaks at 1790 and 1746 cmÿ1 are indicative of the presence of two dierent ester structures in the polymer. This establishes the formation of a copolyester during the polymerization. The IR spectrum also shows C±O ester stretching at 1075, 1174, and 1260 cmÿ1. The absorption peak at 2925 cmÿ1 represents asymmetrical aliphatic C±H stretching and the peaks at 2852 cmÿ1 represent symmetrical C±H stretching. The aromatic ring >C1C< stretching vibrations occurs at 1602, 1587, 1554 and 1528 cmÿ1. These peaks are in good agreement with the literature values [28]. The peaks around 2360 cmÿ1 are due to C±O stretching of carbon dioxide in the atmosphere as this is also observed in the background scan. Fig. 3 shows the 1 H-NMR spectrum of the copolyester which is recorded in deuterated chloroform. The broad resonance centered around d8:5 ppm represents protons on the terephthaloyl ring. The peak appearing in the range of d7:2±7:8 represents the aromatic protons of HPPDP compound, while the signals at d4:5 and 3.2 ppm represent the methylene protons in Ph± CO±O±CH2± and Ph±CO±O±CH2±CH2± moiety, respectively. The ole®nic protons appeared as a multiplet in the range d5:30±5:36 (2H). The broad signal at d2:52 could be attributed to the ±CH2±Ar (2H) and
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Fig. 1. UV spectra of cardanol, HPPDP and copolyester. (ÐÐÐ) cardanol, (- - -) HPPDP, (± ±) copolyester.
while that at 2.0 ppm (4H, m) was assigned to the (± CH2±CH1CH±) component of the HPPDP. The groups (±CH2±)n appeared as a singlet at d1:32 (16H), while the terminal ±CH3 group in the side chain gave a triplet at d0:89:
4. Polymer properties The copolyester isolated from the reaction mixture by precipitation in cold acetone was a dark grey powdery material. The properties of the copolyester thus synthesized are shown in Table 1. It is soluble in chloroform at an elevated temperature in the range of 50±608C. It may be cast from its solution into thin reddish ®lms, which are brittle in character. The density of copolyester is 0.62 gm/cm3. The intrinsic viscosity Z is found to be 0.98 dl/gm at 358C, which indicates that the copolyester molecular weight is high.
5. Thermal analysis Fig. 4 shows the thermogravitogram of the copolyester. The heating rate was maintained at 208C/min in air and nitrogen. The experiment was carried out from
room temperature to 6008C. The copolyester has a stability up to 2818C in air after which it commences to degrade. Whereas in nitrogen the degradation commences at 2908C and is rapid. It shows a two stage degradation. During the ®rst stage of degradation the mass loss is around 20% of its original weight, the temperature range being 290±3718C and Tmax occurring at 3258C. The second and ®nal stage of degradation occurs in the temperature range of 371±10008C accounting for the rest 80% weight loss with the Tmax occurring at 4438C. TGA results of the copolyester, HPPDP, the monomer and cardanol the raw material are summarized in Table 2. In general, a polyester derived from aromatic dihydroxy compound has high thermal stability as compared polyesters having an aliphatic chain in their backbone [29,30]. Figs. 5 and 6 show the Dierential Scanning Calorimetric (DSC) thermograms of the copolyester in nitrogen atmosphere at a heating rate of 208C/min. The curve shows a secondary transition at ÿ708C assumed to be the glass transition temperature of the amorphous side chain attached to the aromatic ring of the copolyester and not to the main chain vibrations. The lower glass transition temperature is attributed to long and ¯exible side chain attached to main chain consisting of three to four ±CH2± groups present in a row. The broad melting temperatures for the copolyester
H.P. Bhunia et al. / European Polymer Journal 36 (2000) 1157±1165
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Fig. 2. IR spectrum of the copolyester.
observed at 63 and 1278C may be due to the two dierent structural repeat units present in the copolyester as shown in Scheme 2. The lower melting temperature may be due to 1,4-butane diol structure adjacent to the terephthaloyl group and the higher melting temperature may be due to the HPPDP unit forming the ester. In the ®rst heating, an endothermic peak is observed which vanishes in the second heating cycle due to quenching of the copolyester which disturbs its ordered structure. However, when the polymer is
cooled down slowly, the endothermic peak reappears again during the second heating cycle. This may be attributed to partially crystalline nature of the copolymer. 6. WAXS study WAXS study of the copolyester synthesized from cardanol was carried out using CuK target in the angular range 108 2y)±908 2y). The diractogram
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H.P. Bhunia et al. / European Polymer Journal 36 (2000) 1157±1165
Fig. 3. 1 H-NMR spectrum of the copolyester.
shows a broad halo commencing from 138 2y up to 358 2y). It shows that the copolyester is amorphous in character. However, DSC records two melting endotherms indicating the presence of order or crystallinity in the polymer. This has been further con®rmed by annealing in nitrogen atmosphere or spontaneously cooling the sample from molten state to room temperature. The degree of crystallinity is lower this time. This implies that there is some de®nite order or partial
crystallinity in the copolyester, which is not detectable by X-ray diraction.
7. Conclusions The following conclusions have been drawn from the aforesaid study:
Table 1 Properties of copolyester State Colour Odour Density Solubility: Soluble Insoluble Intrinsic viscosity Z at 358C Melting temperature (Tm) Glass transition temperature (Tg) Thermal stability (Ti)
Powder Dark grey Odourless 0.62 gm/cc DMF, DMSO, H2SO4, m-cresol HCOOH, chlorobenzene, cyclohexanone, CHCl3, xylene 0.98 dl/gm +63 and +1278C ÿ708C 2908C
H.P. Bhunia et al. / European Polymer Journal 36 (2000) 1157±1165
Fig. 4. Thermogram of the copolyester. (ÐÐÐ) in N2 atmosphere, ( ) in air.
Fig. 5. DSC curve of the copolyester.
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H.P. Bhunia et al. / European Polymer Journal 36 (2000) 1157±1165
Fig. 6. DSC curves of the copolyester; eect of thermal history. (a) (ÐÐÐ) untreated sample, (b) (± ±) heated and quenched sample, (c) (- - -) heated sample cooled slowly.
Table 2 TGA analysis of cardanol, HPPDP and copolyester in nitrogen Components
Ti (8C)
Tmax (8C)
Tf (8C)
Loss (%)
Cardanol HPPDP monomer 1st stage 2nd stage 3rd stage Copolyester 1st stage 2nd stage
200
329
350
100
255 390 545
336 480 Slow
390 545 1000
30 35 98
290 371
325 443
371 1000
20 80
as con®rmed from DSC studies. WAXS studies do not show any gross crystallinity.
Acknowledgements The authors are grateful to the Council of Scienti®c and Industrial Research, New Delhi, for funding this project.
References 1. A novel copolyester has been synthesized by reacting the monomers HPPDP and 1,4-butane diol with the terephthaloyl chloride. 2. The resulting copolyester has high intrinsic viscosity of 0.98 dl/gm, indicating relatively high molecular weight. 3. The thermal stability of the copolyester is higher than those of the monomers. 4. The copolyester is highly stable to UV light. 5. The copolyester is partially crystalline in character
[1] Bhunia HP, Jana RN, Basak A, Lenka S, Nando GB. J Polym Sci, Part A: Polym Chem 1998;36:391. [2] George KV. Improvement of quantity of CNSL obtained by expelling from oil both roasted shells. In: Third Annual Symposium on Plantation Crops Ð Placrosym III, Kerala, 1980. [3] Wilson RJ, Wilson. The market for cashew kernels and cashewnut shell liquid. Report No. G91, Tropical Products Institute, London, 1975. [4] Tyman HP, Johnson RA, Muir M, Rokhgar R. J Am Or Chem Sci 1989;66:553.
H.P. Bhunia et al. / European Polymer Journal 36 (2000) 1157±1165 [5] Wasserman D, Dawson CR. Ind Eng Chem 1945;38:396. [6] Tyman JHP, Wilczynski D, Kashani MA. J Am Oil Chem Soc 1978;55:663. [7] Lloyd HA, Denny C, Krishna G. J Liquid Chromatog 1980;3:1497. [8] Tyman JH. J Chem Soc, Perkin Trans 1973;1:1639. [9] Tyman HP. J Chromatog 1975;111:277. [10] Tyman JHP, Tychopoulos V, Chain P. J Chromatog 1984;303:137. [11] Tyman JHP. Chem Soc Rev 1979;8:499. [12] Menon ARR, Pillai CKS, Sudha JD, Mathew AG. J Sci Ind Rev 1985;44:324. [13] Gedam PH, Sampathkumaran PS. Prog Org Coatings 1986;14:115. [14] Pandey GN, Mishra AK. J Appl Polym Sci 1985;30:969. [15] Pillai CKS, Prasad VS, Sudha JD, Bera SC, Menon ARR. J Appl Polym Sci 1990;41:2487. [16] Menon ARR, Pillai CKS, Nando GB. Kauts Gummi Kunst 1992;45:708. [17] Menon ARR, Pillai CKS, Nando GB. J Appl Polym Sci 1994;51:2157. [18] Menon ARR, Pillai CKS, Nando GB. J Adhesion Sci Tech 1995;9:443.
1165
[19] Saminathan M, Pillai CKS, Krishn C, Pavithran C. Macromolecules 1993;26:7103. [20] Pillai CKS, Sherrington DC, Sneddon A. Polym Commun 1992;33:3968. [21] Bhunia HP, Nando GB, Basak A. Eur Polym J, in press. [22] Bhunia HP, Nando GB, Chaki TK, Basak A, Lenka S, Nayak PL. Eur Polym J 1999;35:1381. [23] Murty BGK, Menon MC, Aggarwal JS, Zaheer SH. Paint Manuf 1961;31:47. [24] Perrin DD, Armarego WLF, Perrin DR. Puri®cation of laboratory chemicals, 2nd ed. Oxford: Pergamon Press, 1980. [25] Longman. Vogel's testbook of practical organic chemistry, 4th ed. London: ELBS, 1978. [26] Pansare SV, Kulkarni AB. J Indian Chem Soc 1964;41:251. [27] Thammongokol V, Warner SB, Polok MB. J Polym Sci, Part A: Polym Chem 1995;33:189. [28] Socrates G. Infrared characteristic group frequencies. Chichester, UK: Wiley, 1980. [29] Economy J, Storm RS, Matkovich VJ, Cottis SG, Nowak BE. J Polym Sci, Polym Chem Ed 1976;14:2207. [30] Kricheldorf HR, Schwarz G. Polymer 1984;25:520.