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Development of Green Composites from Furfuryl Palmitate Ershad Mistri,† N. R. Bandyopadhyay,† Santi Nath Ghosh,‡ and Dipa Ray*,§ School of Materials Science and Engineering, Bengal Engineering and Science UniVersity, Shibpur, Howrah 711103, India; Department of Chemical Technology, UniVersity of Calcutta, 92 A.P. C Road, Kolkata 700009, India; and Department of Polymer Science & Technology, UniVersity of Calcutta, 92 A.P. C Road, Kolkata 700009, India
Renewable materials like furfuryl alcohol, palmitic acid, and jute were used for the first time to develop green biocomposites. Furfuryl ester of palmitic acid was prepared by enzymatic route and was used as the matrix material for developing green composite materials. The Diels-Alder reaction was carried out between furfuryl palmitate and maleic anhydride which resulted in a new material. Crystal growth was observed on Diels-Alder reaction along with a noncrystalline, semisolid part. The Diels-Alder product was characterized by nuclear magnetic resonance (NMR), IR, optical microscopy. Jute reinforced composites were prepared by solvent impregnation method followed by compression molding. The resulting composites were tested for their mechanical properties and the fiber/matrix bonding was investigated under SEM. Introduction There is a growing urgency to develop novel biobased materials and other innovative technologies that can unhook widespread dependence on fossil fuel. The majority of polymeric materials are derived from petroleum feed stocks, which will be depleted in the next 50 years. The limitation of the petroleum resources and their environmental disadvantages combined with the huge demand for polymers make the use of alternative renewable resources for these materials quite attractive. Eco-friendly biocomposites from plantderived fibers and vegetable oil-derived polymers (biopolymer) are novel materials of the twenty-first century and would be of great importance to the materials world, not only as a solution to growing environmental threat but also as a solution to the uncertainty of petroleum supply.1,2 The best examples of biopolymers based on renewable resources are cellulosic plastics, polylactides (PLA), starch plastics, soybased plastics, and so forth. Plant oils are suitable starting materials for polymers because of their abundance, the rich chemistry that their triglyceride structure provides, and their potential biodegradability. Although the use of plant oils in the polymer field as coatings is very old and well studied,3,4 but the research in the preparation of structural plastics from plant oils is rather new. Li et al. recently prepared thermosetting polymers by cationic polymerization of a variety of oils, including fish, tung, and soybean oil, with petroleum-based comonomers such as styrene, divinyl benzene, and dicyclopentadiene in the presence of boron triflouride diethyl etherate as the initiator.5-7 Polymers ranging from rubbers to hard plastics were obtained. However, long chain fatty acids, which are the major constituents of vegetable oils, can also be used for producing green polymer matrix. The major advantage of using fatty * To whom correspondence should be addressed. Tel: +91-033-2350 1397. Fax: +91-033-2351 9755. E-mail: roy.dipa@ gmail.com. † School of Materials Science and Engineering, Bengal Engineering and Science University. ‡ Department of Chemical Technology, University of Calcutta. § Department of Polymer Science & Technology, University of Calcutta.
acid is that these are renewable resources. S.K. Ghosh et al. recently prepared a series of high solid alkyd polymers from soya oil fatty acid and dehydrated castor oil fatty acid.8 Preeti Lodha et al. studied thermal and mechanical properties of environmentally friendly “green” plastics from stearic acid modified-soy protein isolate.9 Mats Johansson and co-workers successfully synthesized and polymerized a radiation curable hyperbranched resin based on epoxy functional fatty acids.10 Alam et al. developed ambient cured polyamine amide resins by the condensation polymerization reaction of oil fatty amide diol (N,N-bis 2-hydroxy ethyl linseed oil fatty amide) and o-phenylene diamine.11 Guncem Gultekin et al. successfully prepared fatty acid-based polyurethane films for wound dressing applications.12 Issam and his co-worker recently synthesized a new alkyd resin by reacting glycerol, phthalic anhydride, and mono fatty acid in the presence of calcium oxide as a catalyst.13 The Diels-Alder (DA) cycloaddition reaction is one of the most important reactions in organic chemistry, since it enables the formation of two carbon-carbon bonds in a specific manner to form a cyclic (bicyclic) product. A substantial amount of work has been published concerning fabrication of Diels-Alder based polymers. The pioneering work of Stevens and Jenkins tackled the possibility of fabricating a thermally reversible polymer network bearing DA-reactive furan and maleimide pendant groups.14 However, this idea was not exploited until a decade later, when Saegusa and co-workers described the reversible cross-linking of modified poly(N-acetylethyleneimine) bearing either maleimide or furan-carbonyl pendant moieties.15 The authors claimed that mixing the two modified complementary polymers resulted in a highly cross-linked material. Subsequent heating to 80 °C for 2 h in a polar solvent regenerated the two starting linear precursors in quantitative yield. The validity of this work, as well as of later studies of the same system,16 is interesting, partly because furan-carbonyl moieties are not expected to be reactive dienes for the DA reaction. Several early works concerning polymers formed by the DA reaction of bis-furan and bis-maleimide monomers demonstrated the feasibility of such polymerization. However, detailed structural analyses of these polymers were absent and in most
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cases the degree of polymerization (DP) was quite low (10-20).17,18 Noteworthy is the observation by Kuramoto et al. of partial reversibility at 90 °C when the polymer was prepared from di-2-furfuryl adipate and bis-maleimidodiphenyl methane.19 Also, Gousse and Gandini have synthesized and studied a number of low DP polymer systems composed of difuran and bis-maleimide monomers.20 The same group also prepared 2-furfuryl maleimide (FM), and its subsequent DA oligomers. Multifunctional furan and maleimide-based monomers were used to form highly cross-linked polymeric networks. The first system developed, where a tris-maleimide (3M) and a tetra-furan (4F) were allowed to react to form a clear solid DAstep-growth polymer (3M4F).21 An interesting report by Brand and Klapper reported the thermally reversible Diels-Alder polymerization of R,ω-bis(3-furylmethyl)pentaethylene glycol and R,ω-bis(trans-4,4,4 trifluorocrotonylethyl) polyethylene glycol.22 Under inert conditions, the authors were able to cycle the polymerization/depolymerization multiple times. This system was studied in the context of variable viscosity and did not demonstrate remendability in the solid state. In our work, we used the furfuryl ester of palmitic acid as the starting material. This was subjected to Diels-Alder reaction with maleic anhydride (MA). The reaction was monitored and products (FP-MA) were confirmed by NMR and FTIR analysis. This adduct was then used as the macromonomer to develop green composites using jute fibers as the reinforcement. In-situ polymerization took place during the fabrication of composites. The composites were characterized for their mechanical properties, fracture surface analysis and thermal analysis.
Figure 1. (a) Structure of furfuryl palmitate. (b) 3D-Model.
Experimental Section Materials. Jute felts were collected from the local market. Palmitic acid of A.R grade (SD Chemicals) and furfuryl alcohol (SD Chemicals, A.R grade) were used for preparation of furfuryl ester of palmitic acid. Maleic anhydride of A.R grade (Loba Chemie) was used for Diels-Alder reaction with furfuryl ester of palmitic acid. Concentrated ammonia solution of A.R grade was used as the curing agent. Chemical Modification of Fatty Acid. Furfuryl ester of palmitic acid was prepared by enzymatic route from palmitic acid (a fatty acid which can be derived from palm oil) and furfuryl alcohol. Novozyme 435, Candida antartica lipase B immobilized on a macroporous acrylic resin with a water content of 10% (w/w) was a gift of Novozyme India Pvt. Ltd., Bangalore, India. The Palmitic acid and furfuryl alcohol at 1:1 molar ratio were taken in a 1 L round bottomed flask. The reaction was carried out at 60 ( 2 °C in presence of Candida antartica lipase at 5% level on the weight of total acid and alcohol at reduced pressure of 4 mm of Hg and the reaction was continued for 6 h with continuous stirring by a magnetic stirrer bar. The reaction course was followed by determining the acid value of the product as a function of time. After 6 h reaction, the product mixture was filtered off to remove the enzymes and the reaction water was completely removed as the reaction was carried out under vacuum. We started with furfuryl ester of palmitic acid (Furfuryl Palmitate designated as FP). The Diels-Alder reaction was carried out between FP and maleic anhydride (MA) in 1:1 molar proportion which resulted in Diels-Alder adduct (FP-MA). The MA was added to FP, heated to 120 °C temperature, and stirred for 15 min. Then, stirring as stopped and crystal growth was observed immediately. Preparation and Processing of Biocomposite Using Jute Felt As Reinforcement. The biocomposite was prepared by solvent impregnation method using concentrated ammonia as
Figure 2. Mechanism of Diels-Alder reaction between furfuryl palmitate and maleic anhydride.
Figure 3. Optical microscopic image of the crystals formed during Diels-Alder reaction.
the curing agent. The Diels-Alder product was thoroughly mixed with concentrated ammonia solution (10% by weight with respect to weight of FP-MA), which played the role of a curing
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Figure 4. 1H NMR spectra of Diels-Alder product after reaction with maleic anhydride. Table 1. IR Data of the Diels-Alder Product wave number (cm-1)
functional group
1234 1460 1600 1732 1780 and 1848 2850 to 2932 cm-1
“out of plane” C-H deformation C-H deformation CdC stretching frequency >CdO stretching frequency of ester carbonyl group specific anhydride (-CO-O-CO-) peak aliphatic C-H symmetrical and asymmetrical stretching
agent as well as a solvent. A 2% formalin solution was added to it as antifungal agent. Jute felt was used as the reinforcing
Figure 5. Fabrication of the biocomposite.
material to prepare the composite. The jute felts were impregnated with the FP-MA solution and vacuum-dried for 30 min. The FP-MA impregnated jute felts were hot pressed at 145 °C in a compression molding machine using a pressure of 200 MPa. The composite had 70% jute loading and 30% matrix. Characterization. The molecular structures and functionality of the prepared Diels-Alder product (FP-MA) was analyzed by a standard Bruker 300 MHz 1H nuclear magnetic resonance (NMR) spectrometer and a standard Perkin Elmer infrared (IR) spectrometer, respectively. For 1H NMR inspection, the samples were prepared by dissolving ∼20 mg of product in 0.5 mL of
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Figure 6. Prepared biocomposite.
deuterated chloroform. Optical microscopic image of the crystalline DA product was also analyzed by a standard ADCON optical microscope at 10× zoom. Three-point bend tests were performed in an Instron 4303 instrument in accordance with ASTM D790 to measure the flexural strength of the composites. The reported result is mean of five results. Morphological study of the resulting polymer and biocomposite was carried out by using Hitachi S-3400N SEM. The samples were gold coated prior to SEM investigations. TGA/DTA was done with SDT Q600 V8.2 Build 100 in nitrogen environment with a heating rate of 5 °C/min. Results and Discussion Characterization of FP-MA. Palmitic acid is a renewable resource which is derived from palm oil. The free fatty acid
does not contain any double bond or any functional group as a substituent in its side chain and hence, it is unable to take part in any polymerization reaction. To overcome this shortcoming, palmitic acid was first esterified with furfuryl alcohol, so that it can take part in chemical reaction through the furan ring. Furfuryl palmitate (FP) was used as the precursor in this work (Figure 1). FP was subjected to Diels-Alder reaction with maleic anhydride. The probable mechanism of the reaction is shown in Figure 2. A crystal growth (Figure 3) was observed on Diels-Alder reaction along with a noncrystalline, semisolid part. The product was finally obtained as a white powder. The Diels-Alder product (FP-MA) was analyzed with Infrared (IR) spectroscopy and 1H nuclear magnetic resonance (NMR) spectroscopy. Figure 4 illustrates the 1H NMR spectra of FP-MA. Figure 4 depicts that two isomeric compounds were formed during the Diels-Alder reaction, one is endo product (having two β-H) and another is exo product (having two R-H). The NMR analysis of the prepared Diels-Alder product is as follows: 1 H-NMR (CDCl3), δ ) 0.88 (sCH3) [peak 1]; δ ) 1.25 (sCH2s) [peak 2]; δ ) 1.63 (sO-COsCH2s, R to ester carbonyl carbon) [peak 3]; δ ) 2.34(4H,multiplate,two R and two β CH) [peak 4]; δ ) 3.23 and 3.32 (bridgedsCH group) [peak 5]; δ ) 4.55, 4.91, 5.05, and 5.45 (4H, for two isomeric sCO-OsCH2s) [peak ) 6,6′,7,7′]; all of the peaks of position 8 and 9 are furanic ring sCHdCHs peaks. The peak around δ ) 6.36 and 6.39 is probably for the unreacted compound which initially present in the spectra of furfuryl palmitate. The IR spectra (Table 1) of FP-MA showed specific peaks which indicated that Diels-Alder reaction had taken place. The sample exhibited two consecutive bands in the range from 2850 to 2932 cm-1.These peaks might have appeared due to aliphatic C-H symmetrical and asymmetrical stretching. The band
Figure 7. Proposed mechanism of polymerization reaction of FP-MA in presence of ammonia.
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The biocomposite was subjected to TGA and DTA analysis, shown in Figure 10. The TG and DTG curves showed three phase degradation (Figure 10a,b). The degradation peaks observed around 270 °C (small hump) and 350 °C were due to the degradation of hemicellulose and R-cellulose present in the jute fibers.24 The peak at 460 °C might be due to the degradation of lignin present in jute fibers and furfuryl alcohol in the matrix.25 The peak at 200 °C could be due to the degradation of matrix. In the DTA curve (Figure 10c), no sharp melting peaks were evident which indicated the presence of extensive hydrogen bonds within the matrix. A strong hydrogen bonding might have occurred between the jute fibers and the matrix also, which restricted the mobility of the polymer molecules.
Figure 8. Flexural strength, flexural modulus, and % breaking strain of the biocomposite.
around 1732 cm-1 was due to CdO stretching frequency of ester carbonyl group. There were two important bands at 1780 cm-1 and1848cm-1 whicharespecificanhydride(-COsO-CO-) peak. The peak around 1460 cm-1 can be attributed to C-H deformation. The small peak around 1600 cm-1 might be due to CdC stretching frequency. A broad peak appeared around 1234 cm-1 which was due to “out of plane” C-H deformation (like wagging and twisting). Characterization of the Biocomposite. A schematic view of the fabrication of biocomposite is shown in Figure 5 and the biocomposite formed is shown in Figure 6. In-situ polymerization of FP-MA took place during the fabrication of the composites and the probable polymerization mechanism of FPMA in presence of ammonia is shown in Figure 7. Flexural properties of the 70% (w/w) jute fiber reinforced biocomposite were observed by flexural test. The flexural strength, flexural modulus, and % breaking strain were observed to be 10.06 MPa, 1349 MPa, and 1.83%, respectively (Figure 8). The presence of the fatty acid chains imparted flexibility in the material whereas furan ring introduced rigidity. The mechanical properties of the prepared composites can be compared with reported mechanical properties of jute reinforced polypropylene composites,23 which showed tensile strength and tensile modulus values of nearly 12 and 600 MPa with 70 wt% jute loading. The mechanical properties of such composites are therefore comparable with reported values and can be enhanced further by suitable modifications. The fracture surface of the biocomposite is shown in Figure 9, parts a and b. The fibers showed good adhesion to the matrix, indicating that such matrices are suitable for natural fibers like jute and allow high fiber loading.
Figure 9. (a,b) Fracture surface of the biocomposite.
Such in situ polymerization of furfuryl palmitate during composite fabrication has been reported for the first time to our knowledge. This shows a new route of green material development from fatty acid and furfuryl alcohol. On the basis of this work, more experimental work will be done in future to maximize the mechanical properties of the composites and to optimize the fabrication processes.
Conclusions Renewable resources like palmitic acid and furfuryl alcohol were used for the first time to prepare bio-based matrix for developing green biocomposites. The Diels-Alder product obtained by reacting furfuryl palmitate with maleic anhydride was used as macromonomer. A good compatibility between the matrix and the reinforcement was observed from SEM micrographs. The presence of palmitic acid imparted flexibility to the material, whereas, furfuryl alcohol imparted some rigidity. This is a new approach of developing a macromonomer from renewable materials like palmitic acid and furfuryl alcohol and converting that into a matrix by in situ polymerization. Effective tailor-made products can be designed to fit the purpose. Mechanical properties can also be enhanced by suitable chemical modifications which will be pursued in future work.
Acknowledgment D.R. is thankful to All India Council for Technical Education (AICTE), Government of India, for granting her a Career Award Project. Authors are thankful to Tanmoy De, Research Scholar, Department of Home Science, University of Calcutta, for preparing the Furfuryl Palmitate.
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Literature Cited (1) Mohanty, A. K.; Misra, M.; Hinrichsen, G. Biofibres, biodegradable polymers and biocomposites: An overview. Macromol. Mater. Eng. 2000, 276/277, 1–24. (2) Mohanty, A. K.; Misra, M.; Drzal, L. T. Surface modifications of natural fibers and performance of the resulting biocomposites: An Overview. Compos. Interf. 2001, 8, 313–343. (3) Solomon, D. H. The Chemistry of Organic Film Formers; Wiley: New York, 1967. (4) Allen, R. R.; Formo, M. V.; Krishnamurthy, R. G.; McDermott, G. N.; Norris, F. A.; Sonntag, N. O. V. Bailey’s Industrial Oil and Fat Products; Wiley: New York, 1982. (5) Li, F.; Marks, D. W.; Larock, R. C.; Otaigbe, J. U. Fish oil thermosetting polymers: synthesis, structure, properties and their relationships. Polymer 2000, 41, 7925. (6) Li, F.; Larock, R. C. Thermosetting polymers from cationic copolymerization of tung oil: Synthesis and characterization. J. Appl. Polym. Sci. 2000, 78, 1044. (7) Li, F.; Larock, R. C. New soybean oil-styrene-divinylbenzene thermosetting copolymers. I. Synthesis and characterization. J. Appl. Polym. Sci. 2001, 80, 658. (8) Ghosh, S. K.; Syed, H.; Randhir, P.; Gulzar, W. Study of hexafunctional polyol in high solids air-drying alkyd: Improved film performance. Prog. Org. Coat. 2009, 64, 446–453. (9) Lodha, P.; Netravali, A. N. Thermal and mechanical properties of environment-friendly ‘green’ plastics from stearic acid modified-soy protein isolate. Ind. Crops Prod. 2005, 21, 49–64. (10) Samuelsson, J.; Sundell, P. E.; Johansson, M. Synthesis and polymerization of a radiation curable hyperbranched resin based on epoxy functional fatty acids. Prog. Org. Coat. 2004, 50, 193–198. (11) Alam, M.; Ray, A. R.; Ashraf, S. M. Synthesis, characterization and performance of amine modified linseed oil fatty amide coatings. J. Am. Oil Chem. Soc. 2009, 86, 573–580. (12) Gultekin, G.; Oral, C. A.; Erkal, S.; Sahin, F.; Karastova, D.; Ersolmaz, S. B.T.; Guner, F. S. Fatty acid-based polyurethane films for wound dressing applications. J. Mater. Sci.: Mater. Med. 2009, 20, 421–431. (13) Issam, A. M.; Cheun, C. Y. A study of the effect of palm oil on the properties of a new alkyd resin. Malaysian Polym. J. 2009, 4, 42–49, No. 1. (14) Stevens, M.; Jenkins, A. Crosslinking of polystyrene via pendant maleimide groups. J. Polym. Sci. 1979, 17, 3675. (15) Chujo, Y.; Sada, K.; Saegusa, T. Reversible gelation of polyoxazoline by means of Diels-Alder reaction. Macromolecules 1990, 23, 2636. (16) Imai, Y.; Itoh, H.; Naka, K.; Chujo, Y. Thermally reversible IPN organic-inorganic polymer hybrids utilizing the Diels-Alder reaction. Macromolecules 2000, 33, 4343. (17) Tesoro, G. C.; Sastri, V. R. Synthesis of siloxane-containing bis(furans) and polymerization with bis(maleimides). Ind. Eng. Chem. Prod. Res. DeV. 1986, 25, 444. (18) Diakoumakos, C. D.; Mikroyannidis, J. A. Heat-resistant resins derived from cyano-substituted Diels-Alder polymers. Eur. Polym. J. 1994, 30, 465. (19) Kuramoto, N.; Hayashi, K.; Nagai, K. Thermoreversible reaction of Diels-Alder polymer composed of difurufuryladipate with bis-maleimidodophenylmethane. J. Polym. Sci., Polym. Chem. 1994, 32, 2501. (20) Gousse, C.; Gandini, A. Diels-Alder polymerization of difurans with bismaleimides. Polym. Int. 1999, 48, 723. (21) Chen, X.; Dam, M. A.; Ono, K.; Mal, A.; Shen, H.; Nutt, S. R.; Sheran, K.; Wudl, F. A thermally re-mendable cross-linked polymeric material. Science 2002, 295, 1698. (22) Brand, T.; Klapper, M. Control of viscosity through reversible addition of telechelics via repetitive Diels-Alder reaction in bulk. Des. Monomers Polym. 1999, 2, 287. (23) Lee, B.-H.; Kim, H.-J.; Yu, W.-R. Fabrication of long and discontinuous natural fiber reinforced polypropylene biocomposites and their mechanical properties. 2009, 10, 83. (24) Ray, D.; Sarkar, B. K.; Basak, R. K.; Rana, A. K. Thermal behavior of vinylester resin matrix composites reinforced with alkali-treated jute fibers. J. Appl. Polym. Sci. 2004, 94, 123. (25) Guigo, N.; Mija, A.; Zavaglia, R.; Vincent, L.; Sbirrazzuoli, N. New insights on the thermal degradation pathways of neat poly(furfuryl alcohol) and poly(furfuryl alcohol)/SiO2 hybrid materials. Polym. Degrad. Stab. 2009, 94, 908. Figure 10. The thermal analysis curves of the biocomposites: (a) TGA, (b) DTG, and (c) DTA.
ReceiVed for reView March 18, 2010 ReVised manuscript receiVed September 12, 2010 Accepted September 14, 2010 IE101586S
