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 Preparation of bamboo fiber polymer composite by Vacuum Injection Molding technique and some properties of composite material Received 16 August 2007 Nguyen Hoang An1, Ta thi Phuong Hoa2, Bui Chuong2 1International Training Institute for Materials Science 2Polymer Centre, Hanoi University of Technology summary This paper presents the result of research on equipment development of vacuum injection molding technique for preparation the chopped bamboo fiber polymer composite and some properties of obtained composite material. For the vacuum injection molding technique, firstly the dry fibers were plated in the mold. Then the mold was closed by the vacuum bag, the air inside the mold was sucked out by a vacuum pump, due to the difference of the pressure in side and outside the mold, the polymer liquid was transferred to the closed mold and impregnated the bamboo fiber. The polymer used in this research was unsaturated polyester and epoxy resin. The obtained composite materials were evaluated by measuring some mechanical properties, such as tensile strength, compressive strength, and flexural strength according to ASTM standards. I - Introduction Man-made fibers (such as glass fibers and carbon fibers) are widely used as reinforcing materials in fiber reinforced plastics. Although these materials have high mechanical properties, drawbacks consist of the high costs, the fact that they are non-degradable and that they can cause skin irritation during processing. Natural fibers (jute, flax, sisal, hemp, bamboo etc.) show many advantages. They have a low density, are from a renewable resource, cause no skin irritation and have low costs. At present, the research on natural fiber reinforced plastics has attracted many scientists [1, 3, 4]. Properties of some common natural fibers are presented in table 1. They show that the density of bamboo fibers is much lower than of other fibers. The specific mechanical properties (properties per unit weight) in combination with the abundance of low cost, bamboo fibers in Vietnam make these fibers very attractive for application in composites. Some commercially important fiber sources are present in table 2 [2], which show an annual large amount of bamboo to be supplied in to the world. This research expects good possibilities for the use of bamboo fibers in fiber reinforced composites. Beside the research on the natural fiber, in order to limit the effect of man-made fibers and the organic substance on the human and environment and improve the property of composite material, the research on the new preparation technique is also concerned. Some closed molding techniques have been developed such as Resin Transfer Molding (RTM), Vacuum Injection Molding (VIM)…. In this research, the VIM technique was developed to prepare the polymer composite. 214 Table 1: Physical properties of some natural fibres [1, 2] Specific gravity, g/cm3 Bamboo 0.8 Flax 1.5 Hemp 1.48 Jute 1.46 Sisal Ramie 1.5 Glass 2.58 Steel 7.85 Tensile strength, MPa 400 780 690 550 580 870 2400 450 E modulus, GPa 15 70 70 20 38 44 73 210 Elongation at failure, % 9 1.40 1.60 1.80 2.50 2.00 3 Specific tensile strength, MPa/g/cm3 500 520 466 377 580 930 57 Specific stiffness, GPa/g/cm3 19 47 47 14 29 28 27 Table 2: Commercial important fibre sources [2] Fibre source Wood Bamboo Cotton lint Jute Kenaf Flax Sisal Roselle Hemp Coir Ramie Abaca Sunn hemp Species (>10,000 species) (>1250 species) Gossypium sp. Corchorus sp. Hibiscus cannabinus Linum usitatissimum Agave sisilana Hibiscus sabdariffa Cannabis sativa Cocos nucifera Boehmeria nivea Musa textiles Crorolaria juncea World production (103 tones) Origin 1,750,000 Stem 10,000 Stem 18,450 Fruit 2,300 Stem 970 Stem 830 Stem 378 Leaf 250 Stem 214 Stem 100 Fruit 100 Stem 70 Leaf 70 Stem II - Experimental 1. Materials Bamboo fibers are supplied by Foundation for European Development Assistant (EMDA) in the chopped fiber form, with less than 30 mm in length and less than 1 mm in width (figure 1). The unsaturated polyester, epoxy resin and other chemical compounds for the polymerization of resins are the commercial products widely used for composite materials. 215 Figure 1: Chopped bamboo fibres 2. Fabrication of composite samples The schematic of principle of VIM technique is presents in the figure 2. Based on this principle, the technique has been developed successfully in the laboratory to prepare the polymer composite sample of bamboo fiber and the unsaturated polyester resin as well as the Figure 2: Schematic of Vacuum injection molding technique epoxy resin. 3. Preparation of testing specimens The testing specimens are prepared according to ASTM standards or ISO standards. The shape and dimensions of specimens are shown in table 3. Table 3: Dimensions of testing specimens Tensile Flexural Compression Standard ISO 527 ASTM D 790 ASTM D 695 Length, mm 150 130 25.4 Width, mm 20 12.7 12.7 Thickness, mm 6 6 12.7 Shape Dog bone Bar Rectangle III - Results and discussion 1. The VIM technique Based on the principle of VIM technique as show in figure 2, we had developed successfully this technique for preparing the bamboo fiber composite. The picture of experiment with VIM technique is showed in figure 3. In order to use the atmospheric pressure as the press force to the dry fiber, the vacuum bag has to be flexible. The fraction of fiber in composite material is depended on the vacuum level, the viscosity of resin liquid, and the nature of fiber and polymer resin. 216 VIM in short description: the bamboo fiber must be placed on a mold that will define the final shape. Mold and fibers will be covered by a vacuum bag, which under vacuum will closely fit the fibers and presses them down to the mold by the force of the surrounding air pressure. Resin is fed to the fiber package by a hose and as long as the pressure inside the resin reservoir is higher than the pressure inside the vacuum bag the resin will be forced through the fibers. During the resin transfer, the vacuum installation must be left in operation to ensure a pressure difference is maintained. To make sure all fibers are wetted the resin hose should be placed opposite to the vacuum connection and bleeder material will guide the resin too hard to reach places. The size of the product is governed only by the size of the mold, the size of the production room and the capacity of the vacuum installation. A practical note is though that all fibers must be wetted before the resin becomes hard. In order to create the composite plate for measuring the mechanical property, the steel plate was used as the mold. The polypropylene film was used as the vacuum bag. A resin trap was used to avoid the resin coming the vacuum pump, the model of resin trap is showed in figure 4. Pressure gauge meter To vacuum pump Resin trap Figure 3: Picture of VIM technique in laboratory Figure 4: Model of resin trap In our experiment, the vacuum level was maintained at -0.9 atm by controlling the valve system. The fraction in the weight of bamboo fiber in the epoxy based composite and unsaturated polyester resin is around 30 and 32%, respectively. It means that, the volume fraction of bamboo fiber in the epoxy based composite and unsaturated polyester resin is around 38 and 41%, respectively. The picture of surface of bamboo fiber composite (figure 5) shows good, there are no void can be seen by naked eye. Figure 5: Picture of bamboo fiber composite surface after preparing by VIM technique 217 When a force is applied on the specimen, the specimen may be fractured. The fracture may occur at the defect material area of specimen. Normally, the defect area in the polymer composite material is the void. These void can be observed by SEM image. (a) (b) Figure 6: SEM images of bamboo fiber-epoxy composite specimen (a) in 1 mm scale; (b) in 200 µm scale (a) (b) Figure 7: SEM images of bamboo fiber-unsaturated polyester composite specimen (a) in 1 mm scale; (b) in 200 µm scale The SEM images of fracture bamboo fiber-epoxy composite specimen are shown in figure 6. It shows that there are no void can be observed in both figures 6a and 6b. It means that the obtained composite of bamboo fiber and epoxy resin has good quality. The SEM images of fracture bamboo fiber-unsaturated polyester composite specimen are shown in figure 7. It shows that there are some small voids can be observed in both figures 7a and 7b. The diameter of these voids is around 100 to 150 µm. It is attributed to the vapor of solvent (styrene) of the unsaturated polyester resin. 2. Property of bamboo fiber composite a) Tensile strength 218 ... - tailieumienphi.vn