Advanced Materials Research Vol. 747 (2013) pp 375-378 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.747.375
Cogon Grass Fiber-Epoxidized Natural Rubber Composites Chaiwat Ruksakulpiwat1,a, Wasaphon Wanasut1, Apikiat Singkum1, and Yupaporn Ruksakulpiwat2,b 1
Departments of Chemistry, Faculty of Science, KhonKaen University, KhonKaen 40002, Thailand 2
School of Polymer Engineering, Institute of Engineering, Suranaree University of Technology, NakhonRatchasima 30000, Thailand a
[email protected], b
[email protected]
Keyword: Cogon grass Fiber, Epoxidized Natural Rubber, Bio-filler, Natural Rubber Composites
Abstract. This research shows a great potential of cogon grass fiber to be used as a reinforcement in epoxidized natural rubber composites. The thermal and mechanical properties of cogon grass fiber-epoxidized natural rubber composites were studied. The chemical treatment of cogon grass fiber to be used as a reinforcing filler was revealed. Effects of fiber treatment method and treatment time of cogon grass fiber on thermal properties of the fibers and their composites were elucidated. The addition of cogon grass fiber into epoxidized natural rubber (ENR) improved the mechanical properties of the composites.The result indicated that alkaline treatment followed by acid treatment of cogon grass fiber led to an increase in thermal decomposition temperature and mechanical properties of the composites more than that without acid treatment. With increasing the amount of fiber, tensile strength of ENR composites were significantly increased while elongation at break was insignificantly changed. ENR with the addition of 4-Amino-6-hydroxy-2-mercaptopyrimidine monohydrate as coupling agent (ENRC) was shown to have higher tensile strength, modulus at 200% elongation and elongation at break than ENR. Improved mechanical properties were also obtained in ENRC composites compared to those of ENR composites. Introduction Natural rubber (NR) posses many good properties, such as high strength, outstanding resilience, and high elongation at break. However, NR has low tensile modulus at low elongation. This drawback has been improved by various methods. The addition of reinforcing fibers into NR has been widely used to improve its mechanical properties. Natural fibers are among interesting fillers to be used in polymer composite due to their low cost, light weight, high specific modulus, renewability and biodegradability. Examples of natural fibers which have been used in polymer composite are vetiver grass, jute, flax, hemp and sisal fibers [1-3]. However, natural fiber reinforced NR generally exhibits lower elongation at break. This may be due to the low compatibility between the fiber and the matrix. Epoxidized natural rubber (ENR) is a modified natural rubber which has higher polarity than NR. This may lead to higher compatibility between natural fiber and ENR as a matrix. Cogon grass (Imperata cylindrica) has been ranked as one of the ten worst weeds of the world. In tropical and subtropical regions around the globe, this aggressive, rhizomatous perennial is generally considered a pernicious pest plant due to its ability to successfully disperse, colonize, spread, and subsequently compete with and displace desirable vegetation and disrupt ecosystems over a wide range of environmental conditions. So the study of using cogon grass fiber as a filler in composites is highly challenging which can help to eliminate and make use of this versatile plant. Moreover, in Thailand, cogon grass has been used as a material for roof. Thus, it is expected to have good weather resistant. The aim of this work is to investigate the potential of cogon grass fiber to be used in ENR composites. The effects of teatment method and treatment time of cogon grass fiber as well as the fiber contents on mechanical properties of cured ENR composites were examined.
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Materials and Methods Materials. Epoxidized natural rubber (ENR), dibenzothiazole disulphide (MBTS), tetramethyl thiuramdisulfide (TMTD), zinc oxide, stearic acid and sulfur were purchased from local supplier. Sodium hydroxide (NaOH), sulfuric acid (H2SO4), 4-Amino-6-hydroxy-2mercaptopyrimidine monohydrate as coupling agent, were purchased from Aldrich. First, cogon grass fiber was cut into 7 cm and then washed by water to get rid of dirt. After that it was dried in an oven at 60oC for 24 hours. Alkaline treatment.Cogon grass fiber was then treated with NaOH (concentration of 5 %w/v) at various time (24, 48, 72 hr). The NaOH treated cogon grass fiber was named according to the treatment time and NaOH concentration by using the abbreviation as GBxty. The subscript x was NaOH concentration and y was treatment time. For example, GB5t24 represents treated cogon grass fiber after immersing in NaOH at 5 %w/v concentration for 24 hours. Acid treatment. Acid treatment was performed by immersing GB5t24 into H2SO4 solution at 5% (v/v) concentration at various times (10,15,20 hr). The H2SO4treated cogon grass fiber was designated by GB5t24Atz in which z represented the acid treatment time. All treated cogon grass fibers were washed with water until pH= 7 and then dried in an oven at 60oC for 24 hours. The fiber was ground by a grinder machine and sieved using mesh no. 80. Preparation and testing of composites. ENR or ENR with coupling agent (ENRC) was mixed with cogon grass fiber obtained from various treatments using two roll mills. All compound formulations werelisted in Table 1. The rubber compounds were compression molded using ZEUS 3114 Engineering Model DHP 050 into test specimen at 130 °C for 8 minutes according to the respective cure time determined by MDR. The tensile test was performed according to ASTM D412-98a using a tensile testing machine (Mitutoyo No. 20468). Thermal decomposition patterns of cogon grass fiber and its composites were determined using an thermogravimetric analyzer (Perkin Elmer Instrument Model Pyris Diamond TG/DTA). Each sample was heated at a heating rate of 10 o C/min under a nitrogen atmosphere. Results and Discussion Generally, many researchers have reported that alkaline treatment by using NaOH on natural fibers such as vetiver grass, jute, sisal, hemp, and oil palm fibers can partially remove the hemicellulose, waxes and lignin presenting on the surface of fiber [3,4]. So in this study various NaOH treatment time on cogon grass fiber was performed. From Table 2, (GB5t24) shows higher decomposition temperature than (GB5t48) and (GB5t72). This indicates that longer alkaline treatment time might cause more degradation of fiber. So the fibers after alkaline treatment at 24 hours was choosen to be further treated by acid treatment. It is interesting to point out that the fibers after acid treatment showed higher decomposition temperature about 20 oC than the fiber without acid treatment. From Table 3, all ENR composites show higher decomposition temperatures than ENR. Moreover, ENR composites from acid treated fiber showed higher decomposition temperature than ENR composites from fiber without acid treatment. From Table 4 and Figure 1, it was shown that the addition of cogon grass fiber into ENR, the tensile strength and modulus at 200%elongation of ENR composites were significantly increased compared to that of ENR while elongation at break of ENR composites was slightly changed. The lowest alkaline treatment time (24 hrs) gave ENR composites from alkaline treated fibers with the highest tensile strength and elongation at break. Further improvement in mechanical properties of ENR composites was observed by using the fibers from acid treatment. This may indicate that acid treatment can further break down the composite fiber bundle into smaller fibers. These increase the effective surface area available for contact between fiber and rubber natrix. The addition of 4-Amino-6-hydroxy-2-mercaptopyrimidine monohydrate as coupling agent into ENR led to an increase in tensile strength and %elongation at break. This may be due to the high possibility of the coupling agent that can react with the epoxide group of ENR leading to an increase in crosslinking density. This resulted in the higher tensile strength, modulus at 200%elongation and elongation at break of ENRC compared to those of ENR.
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Moreover, the coupling agent can react with the hydroxyl group of the cogon grass fibers. This led to higher tensile strength, modulus at 200%elongation and elongation at break of ENRC(GB5t24)45 compared to those of ENR(GB5t24)45. Summary Cogon grass fiber was shown to be an effective reinforcing fiber in ENR composites. The alkaline treatment followed by acid treatment of cogon grass fiber gave the fiber with higher thermal decomposition temperature than alkaline treatment alone. With increasing fiber content, tensile strength of ENR composites were significantly increased while elongation at break of ENR composites was not significantly changed. Coupling agent, 4-Amino-6-hydroxy-2mercaptopyrimidine monohydrate, was shown to be effective in improving mechanical properties of ENRC composite compared to ENR composite. Table 1 Compounding formulations Composite names
Fiber type
Fiber weight (g)
(GB5t24) ENR(GB5t24)22.5 (GB5t24) ENR(GB5t24)45 (GB5t24) ENR(GB5t24)60 ENR(GB5t24At10)45 (GB5t24At10) ENR(GB5t24At15)45 (GB5t24At15) ENR(GB5t24At20)45 (GB5t24At20) (GB5t24) ENRC(GB5t24)45 (GB5t48) ENR(GB5t48)45 (GB5t72) ENR(GB5t72)45 ENRC ENR -
22.5 45 60 45 45 45 45 45 45 -
ENR ZnO 150 150 150 150 150 150 150 150 150 150 150
7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5 7.5
Chemical reagents (g) Stearic Coupling TMTD Sulfur acid agent 3 3 3 3 3 3 3 3 3 3 3
4.5 4.5 -
1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5
3.75 3.75 3.75 3.75 3.75 3.75 3.75 3.75 3.75 3.75 3.75
Table 2 Thermal decomposition temperature (Td) , %weight loss and % residue of cogon grass fiber after alkaline treatment and acid treatment at various treatment time. Samples
Td(๐C)
% weight loss
Residue (%)
(GB5t24)
336.3 ๐C
(GB5t48) (GB5t72) (GB5t24At10)
84.59
15.41
๐
68.76
31.24
๐
317.53 C
51.40
48.60
๐
78.49
11.51
๐
317.70 C 341.8 C
(GB5t24At15 )
341.9 C
74.59
15.41
(GB5t24At20)
338.4 ๐C
78.19
11.81
Table 3 Thermal decomposition temperature (Td) and % residue of ENR and ENR composites. Samples
Td of Rubber (๐C)
ENR(GB5t24) 22.5 ENR(GB5t24) 45 ENR(GB5t24) 60 ENR(GB5t48) 45 ENR(GB5t72) 45 ENR(GB5t24At10 )45 ENR(GB5t24At15 )45 ENR(GB5t24At20 )45 ENRC(GB5t24)45 ENRC ENR
389.0 391.0 391.2
392.9 390.4 397.6 396.2 394.5 395.7 394.9 386.3
Td of Grass Fiber (๐C)
Residue (%)
338.3
15.60 10.00 25.40 138.
322.2 318.2 309.7
322.2 342.7 341.2 340.5 342.7 -
9.30 9.20 11.20 11.10 11.80 1.30 7.10
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Table 4 Tensile strength and elongation at break of ENR, ENRC and the composites. Samples Tensile strength(MPa) Elongation at break (%) ENR(GB5t24)22.5
4.75
320.08
ENR(GB5t24)45
4.03
281.73
ENR(GB5t24)60 ENR(GB5t24At10)45
3.34 4.62
235.10 314.61
ENR(GB5t24At15)45
5.15
345.41
ENR(GB5t24At20)45 ENRC(GB5t24)45 ENR(GB5t48)45 ENR(GB5t72)45 ENRC ENR
3.80 4.39 3.39 3.78 4.05 2.94
249.39 366.13 222.48 317.76 347.09 305.70
Figure 1. Stress-strain curve of ENR, ENRC, ENR(GB5t24)45 and ENR(GB5t24At15)45. References [1] P. Juntuek, C. Ruksakulpiwat, P. Chumsamrong and Y. Ruksakulpiwat. Advanced Materials Research. 410 (2012) 59-62. [2] Y. Ruksakulpiwat, J. Sridee, N. Suppakarn and W. Sutapun. Composites: Part B. 239 (2006) 192–200. [3] Y. Ruksakulpiwat, N. Suppakarn, W. Sutapun and W Thommtong. Composites: Part A. 38 (2007) 590–601. [4] J. George, M.S. Sreekala and S. Thomas, Polym Eng Sci. 41 (2001) 1471–1485.
