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Cuttlebone as reinforcing filler for natural rubber
European Polymer Journal 44 (2008) 4157–4164
Contents lists available at ScienceDirect
European Polymer Journal journal homepage: www.elsevier.com/locate/europolj
Short communication
Cuttlebone as reinforcing filler for natural rubber Sirilux Poompradub a,*, Yuko Ikeda b, Yota Kokubo b, Takeshi Shiono b a
Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Phatumwon, Bangkok 10330, Thailand Graduate School of Science and Technology, Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan b
a r t i c l e
i n f o
Article history: Received 19 November 2007 Received in revised form 30 July 2008 Accepted 16 September 2008 Available online 22 September 2008
Keywords: Cuttlebone Natural rubber Reinforcing filler Biomass Calcium carbonate
a b s t r a c t Cuttlebone was proved to be a biomass for new reinforcing filler for natural rubber (NR). The cuttlebone particles were obtained by crushing cuttlebone and followed by sieving. Density and crystal structure of the cuttlebone were 2.70 g/cm3 and an aragonite form of CaCO3, respectively. The surface area and average diameter of the cuttlebone particles were measured and the reinforcement effect as filler for NR was investigated. The cuttlebone particles did not prevent a peroxide cross-linking reaction of NR, and mechanical properties of peroxide cross-linked NR filled with cuttlebone particles were found to be comparable with those of peroxide cross-linked NR filled with commercial CaCO3 filler. Presence of chitin on the surface of the cuttlebone particles was speculated to result in a good interaction between cuttlebone particles and NR, which may be ascribed to the mechanical properties of cuttlebone filled NR samples. Crown copyright Ó 2008 Published by Elsevier Ltd. All rights reserved.
1. Introduction Natural rubber (NR) is one of the important elastomers and widely utilized to prepare many rubber products. NR is often reinforced by incorporation of filler to improve its mechanical properties: modulus, hardness, tensile strength, abrasion resistance and tear resistance, and so on [1]. Reinforcing fillers most often used are carbon black and silica (SiO2) [2,3]. Calcium carbonate (CaCO3) is also utilized as filler for rubber. Efficiency of the reinforcing filler depends on several factors such as particle size, surface area and shape of filler. Recently, there has been a growing interest in the use of renewable resources such as bamboo [4] and wood [5] or products like rice husk [6], chitin [7], and coir [8,9] as fillers for polymers. Benefits of these fillers include low cost, light weight, biodegradability and so on [10]. In Thailand, fishermen harvest cuttlefish for food. Skeleton of cuttlefish is removed during cooking, which results in large amounts of waste products of cuttlebone. Can we * Corresponding author. Tel.: +66 2218 7518; fax: +66 2255 5831. E-mail address: [email protected] (S. Poompradub).
use the cuttlebone as a new biomass? Since cuttlebone is mainly composed of CaCO3 and chitin [11], cuttlebone may be used like CaCO3 and chitin. Application of CaCO3 in industries has been significantly grown for over the last 30 years. CaCO3 particles have been utilized as filler to give specific properties for rubber products and to reduce the costs of products in rubber industry. Chitin, on the other hand, has been focused as a biomass from crab and shrimp shells [11]. For rubber, chitin powder was reported to show a reinforcement effect in vulcanized NR composites [12]. Thus, the aim of this study is to characterize the cuttlebone particles and to investigate effect of the filling on the mechanical properties of peroxide cross-linked NR. Outline of the preparation of cuttlebone particles is shown in Fig. 1. One of the applications of cuttlebone as a biomass is reveled by comparing with commercial CaCO3 filler. 2. Experimental 2.1. Materials Ribbed smoked sheet (RSS) No.1 was used as the raw NR. Dicumyl peroxide (DCP) was used as a curing re-
0014-3057/$ - see front matter Crown copyright Ó 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2008.09.015
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(2h) was varied from 0° to 100° using the scanning speed of 2°/min. XPS analysis was performed on metal plates using a JPS9010MC/SP X-ray Photoelectron Spectrometer (JEOL, Japan) using MgKa. Nhe excitation energy was 40 kV and 10 mA. The degradation temperature was determined by thermogravimetric analysis using a Thermal Analyzer Ver 2.40 (Rigaku Ltd., Japan). The sample of ca. 100 mg was placed in a platinum pan and heated up to 1000 °C under air at a heating rate of 10 °C/min. The true volume was measured by a Multipycnometer (Yuasa Ionics Co., Ltd., Japan). Then, the density was determined. The measurements were performed at least five times and the mean value was reported. The Brunauer–Emmett–Teller (BET) specific surface area was estimated by a ASAP 2020 surface area and porosity analyzer (Micromeritics Instrument Group, USA), and the particle size distributions were determined with LA-920 (HORIBA Ltd., Japan). Characteristics of the cuttlebone particles and commercial CaCO3 filler (Silver W) are summarized in Table 1. 2.3. Preparation of peroxide cross-linked NR filled with cuttlebone particles DCP of 2 phr was mixed with NR and filler on a two-roll mill at room temperature. The filler contents were 0, 10, 20, 40, 80 and 100 phr. Peroxide cross-linking was then carried out at 155 °C for 30 min to mold into sheets of 1-mm thickness. As reference samples, peroxide cross-linked NR filled with commercial CaCO3 filler (Silver W) were also prepared by the same method. Sample codes of ‘‘CTB-XX” and ‘‘SV-XX” show peroxide cross-linked NR samples filled with cuttlebone particles and with commercial CaCO3 filler, respectively, where XX shows the amount of particles. NR0 is a reference sample without any particles. 2.4. Characterization of peroxide cross-linked NR filled with cuttlebone particles
Fig. 1. Outline for preparation of cuttlebone particles.
agent. Cuttlebone was obtained from waste stock at commercial processor in Samutsakorn province. Samples were washed in plain water several times and left to dry under the sun. Then, the cuttlebone was crushed and sieved with a 25 lm-mesh sieve. Commercial CaCO3 filler without any surface treatment (Silver-W, Shiraishi Kogyo Ltd., Japan) was used as a reference. The cuttlebone particles and CaCO3 filler were dried at 120 °C for 2 h before use. 2.2. Characterization of cuttlebone The cuttlebone particles and the commercial CaCO3 filler were characterized by a RINT 2200/PC X-Ray Diffractrometer (Rigaku Ltd., Japan) using CuKa. The filament was operated at 40 kv and 40 mA. The diffraction angle
Network chain density (m) of all samples was determined by a micro-compression method [13,14] using a TMA60 Thermo Mechanical Analyzer (Shimadzu Co., Japan). Size of the samples was ca. 1 2 2 mm. At
Table 1 Characteristics of cuttlebone particles and commercial CaCO3 filler (Silver W) Sample
Average particle size (lm)
BET Density Composition (%) surface (g/cm3) CaCO3 Organic area (m2/ component g)
Cuttlebone particles
19.5
5.6
2.70
3.1
6.8
2.71
Commercial CaCO3 filler (Silver W)
92 8 (Aragonite form) 100 0 (Calcite form)
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least, three samples were measured and the mean value was reported. Tensile measurement was conducted using a tensile tester Autograph (Shimadzu Co., Japan). The sample was cut into a ring shape. Outside and inside diameters
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of the sample were 13.7 and 11.7 mm, respectively. All samples were stretched at room temperature (ca. 25 °C) at the tensile speed of 100 mm/min. The measurements were carried out at least five times and the mean value was reported.
Fig. 2. XRD patterns of (a) cuttlebone particles and (b) commercial CaCO3 filler (Silver W).
Fig. 3. TGA thermogram of cuttlebone particles.
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Dynamic mechanical properties were measured by using a Rheospectolar DVE-V4 (Rheology Co. Ltd., Japan). The size of each sample was 25 5 1 mm. The
measurement was carried out from 100 to 80 °C at a constant frequency mode of 10 Hz, an oscillation amplitude of 0.02%, a heating rate of 2 °C/min and a detecting
Fig. 4. Wide scan XPS spectra of (a) cuttlebone particles (b) commercial CaCO3 filler (Silver W).
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step of 2 °C. A tensile mode was used and applied static force was automatically controlled. Scanning electron microscopy (SEM) was conducted by using a JSM-6400 scanning electron microscope (JEOL, Japan) at the voltage of 15 kV after being coated with gold. Cross-sections of the samples were prepared by cutting just after freezing in liquid nitrogen. 3. Results and discussion 3.1. Characterization of cuttlebone particles Fig. 2 a and b show the XRD patterns of cuttlebone particles and commercial CaCO3 filler (Silver W), respectively. Their XRD patterns showed different crystalline peaks. Crystal of cuttlebone was found to be an aragonite form of CaCO3, while that of Silver W was a calcite one [15,16]. In natural minerals and rocks, most of CaCO3 possesses a calcite crystal form, which is a hexagonal–rhombohedral shape. An aragonite crystal form is also detected in nature, which is an orthorhombic shape. Density of cuttlebone particles and Silver W were 2.70 and 2.71 g/cm3, respectively. Cuttlebone was composed of CaCO3 of 92% and an organic part of 8%, which were determined by TGA. The thermogram of cuttlebone particles is shown in Fig. 3. The degradation of cuttlebone occurred in two steps. In the first step, the decomposition of organic material took place at ca. 300 °C and reduced the weight of 8%. In the second step, the decrease started at ca. 650 °C and ended at ca. 825 °C with a weight loss of ca. 40%. This decrease is ascribed to the burning of CaCO3 to produce calcium oxide (CaO) and carbon dioxide (CO2). In order to investigate the composition of the organic part in the cuttlebone surface, cuttlebone particles and commercial CaCO3 filler (Silver W) were subjected to XPS analysis. Their XPS spectra are shown in Fig. 4. In the XPS spectrum of cuttlebone particles, carbon C1s, calcium Ca2p1/2, calcium Ca2s and oxygen O1s were detected together with nitrogen N1s. The binding energies for each element were C1s from graphite and C1s from
CaCO3 centering at 284.2 and 289.8 eV, respectively, O1s from CaCO3 centering at 531.9 eV, and Ca2p1/2, Ca2p3/2 from CaCO3 centering at 350.8 and 347.3 eV, and N1s from organic component centering at 398.3 eV [17]. Similar XPS spectrum was also obtained for commercial CaCO3 filler (Silver W) except a peak of nitrogen N1s. The signal of nitrogen N1s suggests the presence of organic part on the surface of cuttlebone particles. Birchall et al. [11] reported that one of the main components of cuttlebone is chitin and chitin is covalently linked to protein components in cuttlebone. Thus, the organic part on the surface of cuttlebone particles is speculated to be chitin. The identification of the organic part is necessary and will be reported in the future. The average size and BET surface area of cuttlebone particles were measured for discussing their reinforcement effect for rubber, and they were 19.5 lm and 5.6 m2/g, respectively, as shown in Table 1. 3.2. Effect of cuttlebone particles on peroxide cross-linking of NR Network chain densities of peroxide cross-linked NR filled with and without cuttlebone particles are summarized in Table 2 with the results of peroxide cross-linked NR filled with commercial CaCO3 filler (Silver W). It is clear that the network chain densities of all samples were in same order. With the increase of the amount of cuttlebone particles, the network chain density became larger as well as the samples filled with Silver W, although the increase of the former was a little smaller than that of the latter. These results show that the cuttlebone particles did not prevent the peroxide cross-linking reaction of NR. 3.3. Effect of cuttlebone particles on mechanical properties of peroxide cross-linked NR Table 2 shows the results of tensile measurement for all samples. The moduli increased by increasing the filler loading from 20 phr in the both series. This phenomenon
Table 2 Properties of peroxide cross-linked NR filled with cuttlebone particles or commercial CaCO3 filler (Silver W) Sample code
ma 104 (mol/cm3)
M100b (MPa)
M300c (MPa)
TBd (MPa)
EBe (%)
E’ at 25 °Cf (MPa)
Height of tand peak
Tan d peak (°C)
NR-0 CTB-10 CTB-20 CTB-40 CTB-80 CTB-100 SV-10 SV-20 SV-40 SV-80 SV-100
1.43 1.45 1.48 1.51 1.56 1.56 1.47 1.59 1.69 1.79 1.96
0.7 0.7 0.8 1.0 1.6 1.9 0.7 0.8 1.0 1.5 1.8
2.1 2.0 2.3 3.0 4.4 4.5 2.2 2.6 3.0 4.1 5.2
7.0 (±0.05) 11.2 (±0.06) 11.3 (±0.08) 13.2 (±0.07) 12.5 (±0.06) 7.5 (±0.06) 11.4 (±0.04) 11.5 (±0.02) 11.0 (±0.04) 8.4 (±0.03) 8.8 (±0.07)
575 635 615 615 580 500 616 596 579 511 490
1.5 1.6 1.8 2.3 3.8 4.5 1.5 1.8 2.1 3.0 4.5
2.7 2.5 2.4 2.4 2.2 1.9 2.7 2.4 2.3 2.3 1.8
50.2 50.3 50.3 48.3 48.2 48.2 50.2 50.2 50.1 50.2 48.0
a b c d e f
(±0.01) (±0.00) (±0.01) (±0.00) (±0.03) (±0.03) (±0.01) (±0.01) (±0.00) (±0.01) (±0.01)
Network chain density. Stress at 100% elongation. Stress at 300% elongation. Tensile strength at break. Elongation at break. Storage modulus at 25 °C measured by DMA.
(±0.02) (±0.01) (±0.03) (±0.02) (±0.03) (±0.01) (±0.04) (±0.03) (±0.02) (±0.01) (±0.02)
(±3) (±6) (±6) (±2) (±8) (±7) (±3) (±0) (±3) (±1) (±2)
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is ascribable to reinforcing effects of cuttlebone and Silver W. The reinforcement effect by cuttlebone particles was found to be comparable with that of Silver W. Generally, the smaller the size of filler is, the larger the reinforcement effect of the filler becomes. In this study, however, the average size of cuttlebone particles was about six times larger than that of Silver W, but the reinforcement effect is comparable with that of Silver W. Probably, the presence of organic component such as chitin is speculated to give a good reinforcement effect of cuttlebone particles to NR. The interaction between the organic part of cuttlebone and NR must be large, which is supported by SEM observation. In Fig. 5, the SEM images of cross-sections of cuttlebone filled NR samples with different filler loadings are shown, where the white/bright spots representing filler
particles were dispersed in the NR matrix (black-toned color). It is worth noting that many cuttlebone particles seem to be covered with NR, and the boundary between the cuttlebone and NR is not so sharp comparing with that between Silver W and NR. This trend was more significantly detected in the samples with the high contents of cuttlebone particles. The interaction between cuttlebone and NR through the organic part on the surface of particles must be stronger than that between Silver W and NR to give the specific SEM images of cuttlebone filled samples. The more direct evidence will be investigated in the near future. Tensile strength at break (TB) increased with increasing filler loading up to 40 phr and decreased by further loading. This trend was also observed in commercial CaCO3 (Silver W) filled NR samples, although the maximum of
Fig. 5. SEM images of peroxide cross-linked NR filled with cuttlebone particles and commercial CaCO3 filler (Silver W).
S. Poompradub et al. / European Polymer Journal 44 (2008) 4157–4164
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Fig. 6. Temperature dispersions of storage modulus (E0 ) and tan d of peroxide cross-linked NR filled with cuttlebone particles.
TB appeared in the different amount of loading. Increases of modulus and TB often bring about the decrease of elongation in the filler-filled rubber materials. However, the decrease of elongation of cuttlebone filled NR samples was not detected except the sample with the highest loading of 100 phr of cuttlebone particles to NR. The good mechanical properties of peroxide crosslinked NR filled with cuttlebone particles were also detected in a dynamic mechanical analysis (DMA). The temperature dispersions of dynamic modulus (E0 ) and loss tangent (tan d) of the samples are shown in Fig. 6. The E0 at 25 °C and height and temperature of tan d peak of these samples are summarized in Table 2 with those of commercial CaCO3 (Silver W) filled NR samples. Variations of E0 at 25 °C and tan d peak by the increase of filler were same in both series. E0 at 25 °C increased and tan d peak decreased with the increase of the filler content. The temperatures of tan d peak, which are ascribed to the glass transition temperatures, were almost equal among the samples. These observations mean that the effect of cuttlebone particles on dynamic mechanical
properties of peroxide cross-linked NR is comparable with that of Silver W. Not only the size and surface properties but also the dispersion of cuttlebone particles would bring about the characteristics of the dynamic mechanical properties. 4. Conclusions A potential application of cuttlebone as filler for NR is reported in this study. The cuttlebone particles were prepared by crushing and sieving using a mesh sieve of 25 lm. Cuttlebone was composed of an inorganic part of 92% and an organic part of 8%. The former was CaCO3 of aragonite form and the latter was speculated to be mainly chitin. The density, average size and BET surface area of cuttlebone particles were 2.70 g/cm3, 19.5 lm and 5.6 m2/g, respectively. The cuttlebone did not prevent a peroxide cross-linking reaction of NR using dicumyl peroxide. The mechanical properties of the cuttlebone filled NR samples were comparable with those of commercial CaCO3 (Silver W) filled NR samples. Cut-
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tlebone can be a candidate as a biomass for filler of rubber materials, which is also useful for decreasing the waste products of cuttlefish from the environmental issues. Acknowledgements The authors gratefully acknowledge the financial support of Thailand–Japan Technology Transfer Project and National Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials. We thank also to Prof. Dr. Shinzo Kohjiya and Assistant Prof. Dr. Mali Hunsom for suggestions throughout this work.
References [1] Byers JT. Basic elastomer technology: fillers-B. Non-black. In: Baranwal KC, Stephens HL, editors. Akron: The Rubber Division American Chemical Society; 2001. p. 82–111. [2] Brydson JA. Rubber materials and their compounds. London: Elsevier Applied Science; 1988. [3] Hofmann W. Rubber technology handbook. Munich: Hanser Publishers; 1989. [4] Ismail H, Edyham MR, Wirjosentono B. Bamboo fibre filled natural rubber composites: the effects of filler loading and bonding agent. Polym Test 2002;21:139–44. [5] Vladkova TG, Dineff PD, Gospodinova DN, Avramova I. Wood flour: new filler for the rubber processing industry. IV. Cure characteristics and the mechanical properties of natural rubber compounds filled by non-modified or corona treated wood flour. J Appl Polym Sci 2006;101:651–8.
[6] Costa HMD, Visconte LLY, Nunes RCR, Furtado CRG. Mechanical and dynamic mechanical properties of rice husk ash-filled natural rubber compounds. J Appl Polym Sci 2002;83:2331–46. [7] Yang A, Wu R. Enhancement of the mechanical properties and interfacial interaction of a novel chitin-fiber-reinforced poly(ecaprolactone) composite by irradiation treatment. J Appl Polym Sci 2002;84:486–92. [8] Geethamma VG, Kalaprasad G, Groeninckx G, Thomas S. Dynamic mechanical behavior of short coir fiber reinforced natural rubber composites. Composites: Part A 2005;36:1499–506. [9] Rahman MM, Khan MA. Surface treatment of coir (Cocos nucifera) fibers and its influence on the fibers’ physico-mechanical properties. Compos Sci Technol 2007;67:2369–76. [10] Abdelmouleh M, Boufi S, Belgacem MN, Dufresne A. Short naturalfibre reinforced polyethylene and natural rubber composites: Effect of silane coupling agents and fibres loading. Compos Sci Technol 2007;67:1627–39. [11] Birchall JD, Thomas NL. On the architecture and function of cuttlefish bone. J Mater Sci 1983;18:2081–6. [12] Gopalan Nair K, Dufresne A. Crab shell chitin whisker reinforced natural rubber nanocomposites. 2. Mechanical behavior. Biomacromolecules 2003;4:666–74. [13] Kohjiya S, Murakami K, Iio S, Tanahashi T, Ikeda Y. In situ filling of silica onto ‘‘green” natural rubber by the sol–gel process. Rubber Chem Technol 2001;74(1):16–27. [14] Flory PJ. Principles of polymer chemistry. New York: Cornell university press; 1953. [15] JCPDS-International Centre for Diffraction Data. All rights reserved PCPDFWIN 2003; 24:71-2392. [16] Rocha JHG, Lemos AF, Agathopoulos S, Valério P, Kannan S, Oktar FN, et al. Scaffolds for bone restoration from cuttlefish. Bone 2005;37:850–7. [17] Handbook of X-ray Photoelectron Spectroscopy. JEOL: Serving Advanced Technology.
Contents lists available at ScienceDirect
European Polymer Journal journal homepage: www.elsevier.com/locate/europolj
Short communication
Cuttlebone as reinforcing filler for natural rubber Sirilux Poompradub a,*, Yuko Ikeda b, Yota Kokubo b, Takeshi Shiono b a
Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Phatumwon, Bangkok 10330, Thailand Graduate School of Science and Technology, Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan b
a r t i c l e
i n f o
Article history: Received 19 November 2007 Received in revised form 30 July 2008 Accepted 16 September 2008 Available online 22 September 2008
Keywords: Cuttlebone Natural rubber Reinforcing filler Biomass Calcium carbonate
a b s t r a c t Cuttlebone was proved to be a biomass for new reinforcing filler for natural rubber (NR). The cuttlebone particles were obtained by crushing cuttlebone and followed by sieving. Density and crystal structure of the cuttlebone were 2.70 g/cm3 and an aragonite form of CaCO3, respectively. The surface area and average diameter of the cuttlebone particles were measured and the reinforcement effect as filler for NR was investigated. The cuttlebone particles did not prevent a peroxide cross-linking reaction of NR, and mechanical properties of peroxide cross-linked NR filled with cuttlebone particles were found to be comparable with those of peroxide cross-linked NR filled with commercial CaCO3 filler. Presence of chitin on the surface of the cuttlebone particles was speculated to result in a good interaction between cuttlebone particles and NR, which may be ascribed to the mechanical properties of cuttlebone filled NR samples. Crown copyright Ó 2008 Published by Elsevier Ltd. All rights reserved.
1. Introduction Natural rubber (NR) is one of the important elastomers and widely utilized to prepare many rubber products. NR is often reinforced by incorporation of filler to improve its mechanical properties: modulus, hardness, tensile strength, abrasion resistance and tear resistance, and so on [1]. Reinforcing fillers most often used are carbon black and silica (SiO2) [2,3]. Calcium carbonate (CaCO3) is also utilized as filler for rubber. Efficiency of the reinforcing filler depends on several factors such as particle size, surface area and shape of filler. Recently, there has been a growing interest in the use of renewable resources such as bamboo [4] and wood [5] or products like rice husk [6], chitin [7], and coir [8,9] as fillers for polymers. Benefits of these fillers include low cost, light weight, biodegradability and so on [10]. In Thailand, fishermen harvest cuttlefish for food. Skeleton of cuttlefish is removed during cooking, which results in large amounts of waste products of cuttlebone. Can we * Corresponding author. Tel.: +66 2218 7518; fax: +66 2255 5831. E-mail address: [email protected] (S. Poompradub).
use the cuttlebone as a new biomass? Since cuttlebone is mainly composed of CaCO3 and chitin [11], cuttlebone may be used like CaCO3 and chitin. Application of CaCO3 in industries has been significantly grown for over the last 30 years. CaCO3 particles have been utilized as filler to give specific properties for rubber products and to reduce the costs of products in rubber industry. Chitin, on the other hand, has been focused as a biomass from crab and shrimp shells [11]. For rubber, chitin powder was reported to show a reinforcement effect in vulcanized NR composites [12]. Thus, the aim of this study is to characterize the cuttlebone particles and to investigate effect of the filling on the mechanical properties of peroxide cross-linked NR. Outline of the preparation of cuttlebone particles is shown in Fig. 1. One of the applications of cuttlebone as a biomass is reveled by comparing with commercial CaCO3 filler. 2. Experimental 2.1. Materials Ribbed smoked sheet (RSS) No.1 was used as the raw NR. Dicumyl peroxide (DCP) was used as a curing re-
0014-3057/$ - see front matter Crown copyright Ó 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2008.09.015
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S. Poompradub et al. / European Polymer Journal 44 (2008) 4157–4164
(2h) was varied from 0° to 100° using the scanning speed of 2°/min. XPS analysis was performed on metal plates using a JPS9010MC/SP X-ray Photoelectron Spectrometer (JEOL, Japan) using MgKa. Nhe excitation energy was 40 kV and 10 mA. The degradation temperature was determined by thermogravimetric analysis using a Thermal Analyzer Ver 2.40 (Rigaku Ltd., Japan). The sample of ca. 100 mg was placed in a platinum pan and heated up to 1000 °C under air at a heating rate of 10 °C/min. The true volume was measured by a Multipycnometer (Yuasa Ionics Co., Ltd., Japan). Then, the density was determined. The measurements were performed at least five times and the mean value was reported. The Brunauer–Emmett–Teller (BET) specific surface area was estimated by a ASAP 2020 surface area and porosity analyzer (Micromeritics Instrument Group, USA), and the particle size distributions were determined with LA-920 (HORIBA Ltd., Japan). Characteristics of the cuttlebone particles and commercial CaCO3 filler (Silver W) are summarized in Table 1. 2.3. Preparation of peroxide cross-linked NR filled with cuttlebone particles DCP of 2 phr was mixed with NR and filler on a two-roll mill at room temperature. The filler contents were 0, 10, 20, 40, 80 and 100 phr. Peroxide cross-linking was then carried out at 155 °C for 30 min to mold into sheets of 1-mm thickness. As reference samples, peroxide cross-linked NR filled with commercial CaCO3 filler (Silver W) were also prepared by the same method. Sample codes of ‘‘CTB-XX” and ‘‘SV-XX” show peroxide cross-linked NR samples filled with cuttlebone particles and with commercial CaCO3 filler, respectively, where XX shows the amount of particles. NR0 is a reference sample without any particles. 2.4. Characterization of peroxide cross-linked NR filled with cuttlebone particles
Fig. 1. Outline for preparation of cuttlebone particles.
agent. Cuttlebone was obtained from waste stock at commercial processor in Samutsakorn province. Samples were washed in plain water several times and left to dry under the sun. Then, the cuttlebone was crushed and sieved with a 25 lm-mesh sieve. Commercial CaCO3 filler without any surface treatment (Silver-W, Shiraishi Kogyo Ltd., Japan) was used as a reference. The cuttlebone particles and CaCO3 filler were dried at 120 °C for 2 h before use. 2.2. Characterization of cuttlebone The cuttlebone particles and the commercial CaCO3 filler were characterized by a RINT 2200/PC X-Ray Diffractrometer (Rigaku Ltd., Japan) using CuKa. The filament was operated at 40 kv and 40 mA. The diffraction angle
Network chain density (m) of all samples was determined by a micro-compression method [13,14] using a TMA60 Thermo Mechanical Analyzer (Shimadzu Co., Japan). Size of the samples was ca. 1 2 2 mm. At
Table 1 Characteristics of cuttlebone particles and commercial CaCO3 filler (Silver W) Sample
Average particle size (lm)
BET Density Composition (%) surface (g/cm3) CaCO3 Organic area (m2/ component g)
Cuttlebone particles
19.5
5.6
2.70
3.1
6.8
2.71
Commercial CaCO3 filler (Silver W)
92 8 (Aragonite form) 100 0 (Calcite form)
S. Poompradub et al. / European Polymer Journal 44 (2008) 4157–4164
least, three samples were measured and the mean value was reported. Tensile measurement was conducted using a tensile tester Autograph (Shimadzu Co., Japan). The sample was cut into a ring shape. Outside and inside diameters
4159
of the sample were 13.7 and 11.7 mm, respectively. All samples were stretched at room temperature (ca. 25 °C) at the tensile speed of 100 mm/min. The measurements were carried out at least five times and the mean value was reported.
Fig. 2. XRD patterns of (a) cuttlebone particles and (b) commercial CaCO3 filler (Silver W).
Fig. 3. TGA thermogram of cuttlebone particles.
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Dynamic mechanical properties were measured by using a Rheospectolar DVE-V4 (Rheology Co. Ltd., Japan). The size of each sample was 25 5 1 mm. The
measurement was carried out from 100 to 80 °C at a constant frequency mode of 10 Hz, an oscillation amplitude of 0.02%, a heating rate of 2 °C/min and a detecting
Fig. 4. Wide scan XPS spectra of (a) cuttlebone particles (b) commercial CaCO3 filler (Silver W).
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step of 2 °C. A tensile mode was used and applied static force was automatically controlled. Scanning electron microscopy (SEM) was conducted by using a JSM-6400 scanning electron microscope (JEOL, Japan) at the voltage of 15 kV after being coated with gold. Cross-sections of the samples were prepared by cutting just after freezing in liquid nitrogen. 3. Results and discussion 3.1. Characterization of cuttlebone particles Fig. 2 a and b show the XRD patterns of cuttlebone particles and commercial CaCO3 filler (Silver W), respectively. Their XRD patterns showed different crystalline peaks. Crystal of cuttlebone was found to be an aragonite form of CaCO3, while that of Silver W was a calcite one [15,16]. In natural minerals and rocks, most of CaCO3 possesses a calcite crystal form, which is a hexagonal–rhombohedral shape. An aragonite crystal form is also detected in nature, which is an orthorhombic shape. Density of cuttlebone particles and Silver W were 2.70 and 2.71 g/cm3, respectively. Cuttlebone was composed of CaCO3 of 92% and an organic part of 8%, which were determined by TGA. The thermogram of cuttlebone particles is shown in Fig. 3. The degradation of cuttlebone occurred in two steps. In the first step, the decomposition of organic material took place at ca. 300 °C and reduced the weight of 8%. In the second step, the decrease started at ca. 650 °C and ended at ca. 825 °C with a weight loss of ca. 40%. This decrease is ascribed to the burning of CaCO3 to produce calcium oxide (CaO) and carbon dioxide (CO2). In order to investigate the composition of the organic part in the cuttlebone surface, cuttlebone particles and commercial CaCO3 filler (Silver W) were subjected to XPS analysis. Their XPS spectra are shown in Fig. 4. In the XPS spectrum of cuttlebone particles, carbon C1s, calcium Ca2p1/2, calcium Ca2s and oxygen O1s were detected together with nitrogen N1s. The binding energies for each element were C1s from graphite and C1s from
CaCO3 centering at 284.2 and 289.8 eV, respectively, O1s from CaCO3 centering at 531.9 eV, and Ca2p1/2, Ca2p3/2 from CaCO3 centering at 350.8 and 347.3 eV, and N1s from organic component centering at 398.3 eV [17]. Similar XPS spectrum was also obtained for commercial CaCO3 filler (Silver W) except a peak of nitrogen N1s. The signal of nitrogen N1s suggests the presence of organic part on the surface of cuttlebone particles. Birchall et al. [11] reported that one of the main components of cuttlebone is chitin and chitin is covalently linked to protein components in cuttlebone. Thus, the organic part on the surface of cuttlebone particles is speculated to be chitin. The identification of the organic part is necessary and will be reported in the future. The average size and BET surface area of cuttlebone particles were measured for discussing their reinforcement effect for rubber, and they were 19.5 lm and 5.6 m2/g, respectively, as shown in Table 1. 3.2. Effect of cuttlebone particles on peroxide cross-linking of NR Network chain densities of peroxide cross-linked NR filled with and without cuttlebone particles are summarized in Table 2 with the results of peroxide cross-linked NR filled with commercial CaCO3 filler (Silver W). It is clear that the network chain densities of all samples were in same order. With the increase of the amount of cuttlebone particles, the network chain density became larger as well as the samples filled with Silver W, although the increase of the former was a little smaller than that of the latter. These results show that the cuttlebone particles did not prevent the peroxide cross-linking reaction of NR. 3.3. Effect of cuttlebone particles on mechanical properties of peroxide cross-linked NR Table 2 shows the results of tensile measurement for all samples. The moduli increased by increasing the filler loading from 20 phr in the both series. This phenomenon
Table 2 Properties of peroxide cross-linked NR filled with cuttlebone particles or commercial CaCO3 filler (Silver W) Sample code
ma 104 (mol/cm3)
M100b (MPa)
M300c (MPa)
TBd (MPa)
EBe (%)
E’ at 25 °Cf (MPa)
Height of tand peak
Tan d peak (°C)
NR-0 CTB-10 CTB-20 CTB-40 CTB-80 CTB-100 SV-10 SV-20 SV-40 SV-80 SV-100
1.43 1.45 1.48 1.51 1.56 1.56 1.47 1.59 1.69 1.79 1.96
0.7 0.7 0.8 1.0 1.6 1.9 0.7 0.8 1.0 1.5 1.8
2.1 2.0 2.3 3.0 4.4 4.5 2.2 2.6 3.0 4.1 5.2
7.0 (±0.05) 11.2 (±0.06) 11.3 (±0.08) 13.2 (±0.07) 12.5 (±0.06) 7.5 (±0.06) 11.4 (±0.04) 11.5 (±0.02) 11.0 (±0.04) 8.4 (±0.03) 8.8 (±0.07)
575 635 615 615 580 500 616 596 579 511 490
1.5 1.6 1.8 2.3 3.8 4.5 1.5 1.8 2.1 3.0 4.5
2.7 2.5 2.4 2.4 2.2 1.9 2.7 2.4 2.3 2.3 1.8
50.2 50.3 50.3 48.3 48.2 48.2 50.2 50.2 50.1 50.2 48.0
a b c d e f
(±0.01) (±0.00) (±0.01) (±0.00) (±0.03) (±0.03) (±0.01) (±0.01) (±0.00) (±0.01) (±0.01)
Network chain density. Stress at 100% elongation. Stress at 300% elongation. Tensile strength at break. Elongation at break. Storage modulus at 25 °C measured by DMA.
(±0.02) (±0.01) (±0.03) (±0.02) (±0.03) (±0.01) (±0.04) (±0.03) (±0.02) (±0.01) (±0.02)
(±3) (±6) (±6) (±2) (±8) (±7) (±3) (±0) (±3) (±1) (±2)
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is ascribable to reinforcing effects of cuttlebone and Silver W. The reinforcement effect by cuttlebone particles was found to be comparable with that of Silver W. Generally, the smaller the size of filler is, the larger the reinforcement effect of the filler becomes. In this study, however, the average size of cuttlebone particles was about six times larger than that of Silver W, but the reinforcement effect is comparable with that of Silver W. Probably, the presence of organic component such as chitin is speculated to give a good reinforcement effect of cuttlebone particles to NR. The interaction between the organic part of cuttlebone and NR must be large, which is supported by SEM observation. In Fig. 5, the SEM images of cross-sections of cuttlebone filled NR samples with different filler loadings are shown, where the white/bright spots representing filler
particles were dispersed in the NR matrix (black-toned color). It is worth noting that many cuttlebone particles seem to be covered with NR, and the boundary between the cuttlebone and NR is not so sharp comparing with that between Silver W and NR. This trend was more significantly detected in the samples with the high contents of cuttlebone particles. The interaction between cuttlebone and NR through the organic part on the surface of particles must be stronger than that between Silver W and NR to give the specific SEM images of cuttlebone filled samples. The more direct evidence will be investigated in the near future. Tensile strength at break (TB) increased with increasing filler loading up to 40 phr and decreased by further loading. This trend was also observed in commercial CaCO3 (Silver W) filled NR samples, although the maximum of
Fig. 5. SEM images of peroxide cross-linked NR filled with cuttlebone particles and commercial CaCO3 filler (Silver W).
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Fig. 6. Temperature dispersions of storage modulus (E0 ) and tan d of peroxide cross-linked NR filled with cuttlebone particles.
TB appeared in the different amount of loading. Increases of modulus and TB often bring about the decrease of elongation in the filler-filled rubber materials. However, the decrease of elongation of cuttlebone filled NR samples was not detected except the sample with the highest loading of 100 phr of cuttlebone particles to NR. The good mechanical properties of peroxide crosslinked NR filled with cuttlebone particles were also detected in a dynamic mechanical analysis (DMA). The temperature dispersions of dynamic modulus (E0 ) and loss tangent (tan d) of the samples are shown in Fig. 6. The E0 at 25 °C and height and temperature of tan d peak of these samples are summarized in Table 2 with those of commercial CaCO3 (Silver W) filled NR samples. Variations of E0 at 25 °C and tan d peak by the increase of filler were same in both series. E0 at 25 °C increased and tan d peak decreased with the increase of the filler content. The temperatures of tan d peak, which are ascribed to the glass transition temperatures, were almost equal among the samples. These observations mean that the effect of cuttlebone particles on dynamic mechanical
properties of peroxide cross-linked NR is comparable with that of Silver W. Not only the size and surface properties but also the dispersion of cuttlebone particles would bring about the characteristics of the dynamic mechanical properties. 4. Conclusions A potential application of cuttlebone as filler for NR is reported in this study. The cuttlebone particles were prepared by crushing and sieving using a mesh sieve of 25 lm. Cuttlebone was composed of an inorganic part of 92% and an organic part of 8%. The former was CaCO3 of aragonite form and the latter was speculated to be mainly chitin. The density, average size and BET surface area of cuttlebone particles were 2.70 g/cm3, 19.5 lm and 5.6 m2/g, respectively. The cuttlebone did not prevent a peroxide cross-linking reaction of NR using dicumyl peroxide. The mechanical properties of the cuttlebone filled NR samples were comparable with those of commercial CaCO3 (Silver W) filled NR samples. Cut-
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tlebone can be a candidate as a biomass for filler of rubber materials, which is also useful for decreasing the waste products of cuttlefish from the environmental issues. Acknowledgements The authors gratefully acknowledge the financial support of Thailand–Japan Technology Transfer Project and National Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials. We thank also to Prof. Dr. Shinzo Kohjiya and Assistant Prof. Dr. Mali Hunsom for suggestions throughout this work.
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