Preparation of bamboo fiber polymer composite by Vacuum Injection Molding technique and some properties of composite material

Journal of Chemistry, Vol. 45 (5A), P. 214 - 220, 2007<br /> <br /> <br /> Preparation of bamboo fiber polymer composite<br /> by Vacuum Injection Molding technique<br /> and some properties of composite material<br /> Received 16 August 2007<br /> Nguyen Hoang An1, Ta thi Phuong Hoa2, Bui Chuong2<br /> 1<br /> International Training Institute for Materials Science<br /> 2<br /> Polymer Centre, Hanoi University of Technology<br /> <br /> <br /> summary<br /> This paper presents the result of research on equipment development of vacuum injection<br /> molding technique for preparation the chopped bamboo fiber polymer composite and some<br /> properties of obtained composite material. For the vacuum injection molding technique, firstly the<br /> dry fibers were plated in the mold. Then the mold was closed by the vacuum bag, the air inside<br /> the mold was sucked out by a vacuum pump, due to the difference of the pressure in side and<br /> outside the mold, the polymer liquid was transferred to the closed mold and impregnated the<br /> bamboo fiber. The polymer used in this research was unsaturated polyester and epoxy resin. The<br /> obtained composite materials were evaluated by measuring some mechanical properties, such as<br /> tensile strength, compressive strength, and flexural strength according to ASTM standards.<br /> <br /> <br /> I - Introduction the abundance of low cost, bamboo fibers in<br /> Vietnam make these fibers very attractive for<br /> Man-made fibers (such as glass fibers and application in composites.<br /> carbon fibers) are widely used as reinforcing Some commercially important fiber sources<br /> materials in fiber reinforced plastics. Although are present in table 2 [2], which show an annual<br /> these materials have high mechanical properties, large amount of bamboo to be supplied in to the<br /> drawbacks consist of the high costs, the fact that world. This research expects good possibilities<br /> they are non-degradable and that they can cause for the use of bamboo fibers in fiber reinforced<br /> skin irritation during processing. Natural fibers composites.<br /> (jute, flax, sisal, hemp, bamboo etc.) show many<br /> Beside the research on the natural fiber, in<br /> advantages. They have a low density, are from a<br /> order to limit the effect of man-made fibers and<br /> renewable resource, cause no skin irritation and<br /> the organic substance on the human and<br /> have low costs. At present, the research on<br /> environment and improve the property of<br /> natural fiber reinforced plastics has attracted<br /> composite material, the research on the new<br /> many scientists [1, 3, 4].<br /> preparation technique is also concerned. Some<br /> Properties of some common natural fibers closed molding techniques have been developed<br /> are presented in table 1. They show that the such as Resin Transfer Molding (RTM),<br /> density of bamboo fibers is much lower than of Vacuum Injection Molding (VIM)…. In this<br /> other fibers. The specific mechanical properties research, the VIM technique was developed to<br /> (properties per unit weight) in combination with prepare the polymer composite.<br /> <br /> 214<br />  Table 1: Physical properties of some natural fibres [1, 2]<br /> Specific Tensile E Specific tensile Specific<br /> Elongation<br /> gravity, strength, modulus, strength, stiffness,<br /> at failure, %<br /> g/cm3 MPa GPa MPa/g/cm3 GPa/g/cm3<br /> Bamboo 0.8 400 15 9 500 19<br /> Flax 1.5 780 70 1.40 520 47<br /> Hemp 1.48 690 70 1.60 466 47<br /> Jute 1.46 550 20 1.80 377 14<br /> Sisal 580 38 2.50<br /> Ramie 1.5 870 44 2.00 580 29<br /> Glass 2.58 2400 73 3 930 28<br /> Steel 7.85 450 210 57 27<br /> <br /> Table 2: Commercial important fibre sources [2]<br /> World production<br /> Fibre source Species (103 tones) Origin<br /> Wood (>10,000 species) 1,750,000 Stem<br /> Bamboo (>1250 species) 10,000 Stem<br /> Cotton lint Gossypium sp. 18,450 Fruit<br /> Jute Corchorus sp. 2,300 Stem<br /> Kenaf Hibiscus cannabinus 970 Stem<br /> Flax Linum usitatissimum 830 Stem<br /> Sisal Agave sisilana 378 Leaf<br /> Roselle Hibiscus sabdariffa 250 Stem<br /> Hemp Cannabis sativa 214 Stem<br /> Coir Cocos nucifera 100 Fruit<br /> Ramie Boehmeria nivea 100 Stem<br /> Abaca Musa textiles 70 Leaf<br /> Sunn hemp Crorolaria juncea 70 Stem<br /> <br /> II - Experimental<br /> <br /> 1. Materials<br /> Bamboo fibers are supplied by Foundation for European Development Assistant (EMDA) in<br /> the chopped fiber form, with less than 30 mm in length and less than 1 mm in width (figure 1).<br /> The unsaturated polyester, epoxy resin and other chemical compounds for the<br /> polymerization of resins are the commercial products widely used for composite materials.<br /> <br /> <br /> 215<br />  Figure 1: Chopped bamboo fibres Figure 2: Schematic of Vacuum injection<br /> molding technique<br /> <br /> 2. Fabrication of composite samples epoxy resin.<br /> The schematic of principle of VIM 3. Preparation of testing specimens<br /> technique is presents in the figure 2. Based on<br /> The testing specimens are prepared<br /> this principle, the technique has been developed<br /> according to ASTM standards or ISO standards.<br /> successfully in the laboratory to prepare the<br /> The shape and dimensions of specimens are<br /> polymer composite sample of bamboo fiber and<br /> shown in table 3.<br /> the unsaturated polyester resin as well as the<br /> <br /> Table 3: Dimensions of testing specimens<br /> Standard Length, mm Width, mm Thickness, mm Shape<br /> Tensile ISO 527 150 20 6 Dog bone<br /> Flexural ASTM D 790 130 12.7 6 Bar<br /> Compression ASTM D 695 25.4 12.7 12.7 Rectangle<br /> <br /> III - Results and discussion VIM in short description: the bamboo fiber<br /> must be placed on a mold that will define the<br /> 1. The VIM technique final shape. Mold and fibers will be covered by<br /> Based on the principle of VIM technique as a vacuum bag, which under vacuum will closely<br /> show in figure 2, we had developed successfully fit the fibers and presses them down to the mold<br /> this technique for preparing the bamboo fiber by the force of the surrounding air pressure.<br /> composite. The picture of experiment with VIM Resin is fed to the fiber package by a hose and<br /> technique is showed in figure 3. as long as the pressure inside the resin reservoir<br /> is higher than the pressure inside the vacuum<br /> In order to use the atmospheric pressure as bag the resin will be forced through the fibers.<br /> the press force to the dry fiber, the vacuum bag During the resin transfer, the vacuum<br /> has to be flexible. installation must be left in operation to ensure a<br /> The fraction of fiber in composite material pressure difference is maintained. To make sure<br /> is depended on the vacuum level, the viscosity all fibers are wetted the resin hose should be<br /> of resin liquid, and the nature of fiber and placed opposite to the vacuum connection and<br /> polymer resin. bleeder material will guide the resin too hard to<br /> 216<br /> reach places. The size of the product is governed In order to create the composite plate for<br /> only by the size of the mold, the size of the measuring the mechanical property, the steel<br /> production room and the capacity of the vacuum plate was used as the mold. The polypropylene<br /> installation. A practical note is though that all film was used as the vacuum bag. A resin trap<br /> fibers must be wetted before the resin becomes was used to avoid the resin coming the vacuum<br /> hard. pump, the model of resin trap is showed in<br /> figure 4.<br /> <br /> <br /> Pressure gauge<br /> meter<br /> <br /> <br /> <br /> <br /> To vacuum<br /> pump<br /> <br /> <br /> <br /> Resin trap<br /> <br /> <br /> <br /> Figure 3: Picture of VIM technique in laboratory Figure 4: Model of resin trap<br /> <br /> <br /> In our experiment, the vacuum level was maintained at -0.9 atm by controlling the valve<br /> system. The fraction in the weight of bamboo fiber in the epoxy based composite and unsaturated<br /> polyester resin is around 30 and 32%, respectively. It means that, the volume fraction of bamboo<br /> fiber in the epoxy based composite and unsaturated polyester resin is around 38 and 41%,<br /> respectively.<br /> The picture of surface of bamboo fiber composite (figure 5) shows good, there are no void<br /> can be seen by naked eye.<br /> <br /> <br /> <br /> <br /> Figure 5: Picture of bamboo fiber composite<br /> surface after preparing by VIM technique<br /> 217<br />  When a force is applied on the specimen, the specimen may be fractured. The fracture may<br /> occur at the defect material area of specimen. Normally, the defect area in the polymer composite<br /> material is the void. These void can be observed by SEM image.<br /> <br /> <br /> <br /> <br /> (a) (b)<br /> Figure 6: SEM images of bamboo fiber-epoxy composite specimen<br /> (a) in 1 mm scale; (b) in 200 µm scale<br /> <br /> <br /> <br /> <br /> (a) (b)<br /> Figure 7: SEM images of bamboo fiber-unsaturated polyester composite specimen<br /> (a) in 1 mm scale; (b) in 200 µm scale<br /> <br /> The SEM images of fracture bamboo fiber- shown in figure 7. It shows that there are some<br /> epoxy composite specimen are shown in figure small voids can be observed in both figures 7a<br /> 6. It shows that there are no void can be and 7b. The diameter of these voids is around<br /> observed in both figures 6a and 6b. It means 100 to 150 µm. It is attributed to the vapor of<br /> that the obtained composite of bamboo fiber and solvent (styrene) of the unsaturated polyester<br /> epoxy resin has good quality. resin.<br /> The SEM images of fracture bamboo fiber- 2. Property of bamboo fiber composite<br /> unsaturated polyester composite specimen are<br /> a) Tensile strength<br /> <br /> 218<br />  The tensile strengths and the elastic modules large scatter in values can be seen, which<br /> of composite specimens are shown in tables 4a implies less homogeneity of the bamboo fiber<br /> and 4b. They show a low tensile strength of that was commented in the SEM images of<br /> bamboo fiber composites for both resins. A bamboo fiber.<br /> <br /> Table 4b: Results of tensile property of<br /> Table 4a: Results of tensile property of<br /> bamboo fiber-unsaturated polyester<br /> bamboo fiber-epoxy composite<br /> composite<br /> Specimen ,<br /> max<br /> E-modulus, Strain, Specimen ,<br /> max<br /> E-modulus, Strain,<br /> number MPa MPa % number MPa MPa %<br /> 1 32 913 8.43 1 21 546 5.64<br /> 2 29 816 7.62 2 24 788 6.91<br /> 3 23 890 4.67 3 20 625 6.25<br /> 4 25 804 5.23 4 28 613 7.26<br /> 5 24 722 4.72 5 28 668 7.37<br /> Average 26 837 Average 24 635<br /> <br /> b) Flexural strength<br /> In tables 5a and 5b, the flexural properties of specimens are presented. These properties of<br /> both of composites are good, the flexural strength and the modulus of elasticity are high and the<br /> values show less scatter. The unsaturated polyester specimen is more flexural than the epoxy<br /> specimen is.<br /> <br /> Table 5a: Results of flexural property of Table 5b: Results of flexural property of<br /> bamboo fiber-epoxy composite bamboo fiber-unsaturated polyester composite<br /> Flexural Flexural<br /> Specimen Modulus, Deflection, Specimen Modulus, Deflection,<br /> strength, strength,<br /> number MPa mm number MPa mm<br /> MPa MPa<br /> 1 61 4114 4.37 1 48 2028 7.72<br /> 2 65 4333 4.17 2 47 2777 7.06<br /> 3 56 3972 3.66 3 54 2389 6.22<br /> 4 63 3874 4.39 4 55 2427 7.77<br /> 5 57 3685 3.61 5 51 1851 7.75<br /> Average 61 3996 Average 51 2295<br /> <br /> c) Compressive strength<br /> The compressive strength of the bamboo fiber composites is good (tables 6a and 6b)<br /> especially, the compression property of bamboo fiber-epoxy resin composite.<br /> Figures 6 and 7 also show the gap between the fiber and the polymer matrix after fracture. It<br /> means that the adhesion of bamboo fiber and polymer matrix is not so good, and the further research<br /> <br /> <br /> 219<br /> to modify the surface property of bamboo fiber is necessary to improve the property of bamboo fiber<br /> polymer composite.<br /> <br /> Table 6a: Results of compression property of Table 6b : Results of compression property of<br /> bamboo fiber-epoxy composite bamboo fiber-unsaturated polyester composite<br /> Compr. Compr.<br /> Specimen Modulus, Deflection, Specimen Modulus, Deflection,<br /> Strength, Strength,<br /> number MPa mm number MPa mm<br /> MPa MPa<br /> 1 79 871 2.79 1 59 734 2.44<br /> 2 79 843 2.82 2 53 670 2.64<br /> 3 78 916 2.74 3 55 667 2.64<br /> 4 82 769 3.15 4 53 654 2.51<br /> 5 79 898 2.64 5 53 648 2.62<br /> Average 80 859 Average 55 675<br /> <br /> <br /> IV - Conclusions application in high perform composite products.<br /> <br /> The VIM technique with a soft vacuum bag References<br /> made of polypropylene was successfully<br /> developed for fiber reinforced polymer 1. W. D. Brouwer. Proceeding of the third<br /> composite. The SEM study and mechanical international workshop on materials science<br /> property testing showed that the chopped (IWOMS’99), Hanoi, P. 336 - 340 (1999).<br /> bamboo fiber reinforced unsaturated polyester 2. S. J. Eichhorn et al. 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