Properties of Green Composites based on Polypropylene Reinforced by Bamboo Shoot Culm Sheath Fibers

Journal of Chemistry, Vol. 45 (5A), P. 190 - 195, 2007<br /> <br /> <br /> Properties of Green Composites based on<br /> Polypropylene Reinforced by Bamboo Shoot Culm<br /> Sheath Fibers<br /> Received 16 August 2007<br /> Nguyen Huy Tung1 and Toru Fujii2<br /> 1<br /> Polymer Centre, Hanoi University of Technology - Vietnam<br /> 2<br /> Mechanical Faculty, Doshisha University - Japan<br /> <br /> <br /> summary<br /> Silane and NaOH were used to treatment bamboo shoot culm sheath fiber. After treatment,<br /> the interfacial shear strength of fiber with MAPP increased by 24% and 30% respectively. Alkali<br /> treatment has much effect on bamboo shoot culm sheath fiber than silane treatment. Washing<br /> NaOH treatment bamboo fiber with acetic acid was improved IFSS of bamboo fiber and<br /> polypropylene (PP) and strength of composite PP reinforced by bamboo fiber.<br /> <br /> <br /> I - Introduction micro-droplet test under laboratory condition:<br /> 21±3oC and 60±5%RH. The tensile speed was<br /> In the world and also in Vietnam, the “green 0.5 mm/min. IFSS is calculated by the following<br /> composite” has been paid more and more equation:<br /> attentions because of their properties such as IFSS= Fp/(L1*L2)<br /> cheap, available, bio-degradable [1, 2]. There<br /> were many published papers concerned these Here, Fp is the maximum load to pull out the<br /> materials. However, these papers were only fiber from the matrix. L1 is the embedded length<br /> covered few problems on the natural fibers of the fiber. L2 is the circumference of the fiber.<br /> composite [3]. MAPP resin Paper tab<br /> Blade<br /> Bamboo fibers were treated with isocyanate<br /> silane or sodium hydroxide to improve<br /> interfacial shear strength (IFSS) with maleic<br /> grafted polypropylene (MAPP) matrix. Micro-<br /> droplet test was used to investigate IFSS of<br /> fibers with MAPP. Paper tab will be cut<br /> when testing Adhesive<br /> Bamboo fiber<br /> agent<br /> II - Composite fabrication and Fig. 1: Schematic drawing of micro-droplet<br /> testing method testing<br /> Bamboo culm sheath fiber reinforced<br /> III - Results and discussion<br /> polypropylene (BsFRP) was fabricated using hot<br /> press method at 190oC and 2 MPa. 1. IFSS of bamboo shoot culm sheath fiber<br /> Interfacial strength was determined by using with MAPP<br /> <br /> 190<br />  In composite material, IFSS is an important modification increases the fiber matrix<br /> part on mechanical properties. Because the interaction. These results are agree with several<br /> interface plays a major role in transferring the author’s reports [6 - 8]. The silane coupling<br /> stress from matrix to fiber, it is important to be agent has two types of functional groups. One<br /> able to characterize the interphase and the level group calls hydrolysable alkoxy group able to<br /> of adhesion to properly understand the condense with hydroxyl groups that on the<br /> performance of the composite [4]. bamboo fiber surface. The other group<br /> Fig. 2 shows the increment of IFSS when the (isocyanate group) can interact with MAPP<br /> fiber diameter goes down. In micro-droplet test, matrix. Besides the reaction of silane with<br /> the matrix covered the fiber before it was pulled hydroxyl group of bamboo fiber on the surface,<br /> out. The small diameter fibers have larger the formation of polysiloxane structures might<br /> contact area with matrix than big diameter also occur [9]. According to Mieck et al. the<br /> fibers do. Hence, the IFSS was higher with small application of alkyl-functional silane does not<br /> diameter fiber. In Fig. 3, alkali treatment lead to chemical bonds between the cellulose<br /> improves the IFSS of fiber and MAPP matrix by fibers and the polypropylene matrix. However, it<br /> 25%. NaOH makes the fibers surface roughness seems to be realistic to assume that the long<br /> that allows certain mechanical interlocking. hydrocarbon chains, provided by the silane<br /> NaOH treatment also increase the wetability of application influence the wet ability of the fibers<br /> fiber surface with matrix and this made the and that the chemical affinity to the<br /> increasing of IFSS. In case of silane treatment, polypropylene is improved [10, 11].<br /> the fiber surface was modified and this<br /> <br /> 3.5<br /> 3 a. No<br /> a. Notreat<br /> treat<br /> Interfacial strength, MPa<br /> <br /> <br /> <br /> <br /> b.<br /> b. Treat<br /> Treatwith Silane<br /> with silane<br /> a. 600 `4 00µ m 3<br /> Interfacial strength, MPa<br /> <br /> <br /> <br /> <br /> b. 400 2` 00µ m c.<br /> c. Treat<br /> Treatwith NaOH<br /> with NaOH<br /> 2.5<br /> c. Under 200µ m 2.5<br /> 2<br /> 2<br /> 1.5 1.5<br /> 1 1<br /> 0.5 0.5<br /> 0 0<br /> a b c a b c<br /> Fig. 2: Variation of interfacial strength with Fig. 3: Variation of interfacial strength with<br /> different fiber diameter different treated fiber<br /> <br /> 2. Effect of fiber diameter on tensile strength than these with bigger diameter fiber. During<br /> of bamboo shoot culm sheath fiber the pressing process, small fibers are easily and<br /> reinforced PP (BsFRP) well distributed in the hot matrix. Moreover, the<br /> contact area of small fiber with matrix is larger<br /> The relationship between tensile strength of than that of big fiber. Therefore, unexpected<br /> BsFRP and bamboo fiber is shown in Fig. 4. voids form in fabricating process was reduced<br /> Like IFSS, the tensile strength of BsFRP was and the strength was improved. This can be seen<br /> also affected by the fiber diameter. With small clearly on the SEM observation of fracture<br /> diameter, the tensile strength was higher. It can surface of BsFRP (Fig. 6).There were many<br /> be attributed to that thin fibers are more flexible voids appeared in the composite materials using<br /> 191<br /> fiber diameter from 200 - 600 µm. These voids diameter of fiber decreased. The modulus of<br /> prevent the contact of fiber and matrix. Under BsFRP using under 200 µm diameter fiber was<br /> the outside load, the crack will start from these 5 times higher than that of BsFRP using fiber<br /> void area and make the material fail. The elastic with diameter 400 - 600 µm.<br /> modulus of BsFRP also increased when<br /> <br /> 40 12<br /> a .. 660000 ~`4 0400µ0 m 'm<br /> 35 a. 600 ~ 400 'm<br /> bb .. 440000 ~`2 0200µ0 m µm<br /> Tensile strength, MPa<br /> <br /> <br /> <br /> <br /> Elastic modulus, GPa<br /> 10 b. 400 ~ 200 µm<br /> c.. UUnndde re r2 0200µ0 mµ m c. U nder 200 µ m<br /> 30<br /> 25 8<br /> 20 6<br /> 15<br /> 4<br /> 10<br /> 2<br /> 5<br /> 0 0<br /> a b c a b c<br /> Fig. 4: Effect of fiber diameter on tensile Fig. 5: Effect of fiber diameter on elastic<br /> strength of BsFRP modulus of BsFRP<br /> <br /> <br /> <br /> <br /> 500µ m 500µ m 500µ m<br /> <br /> Fiber 600 400 µm Fiber 400 200 µm Under 200 µm<br /> Fig. 6: SEM observation of fractured surface of BsFRP<br /> <br /> 3. Effect of treatment on strength of BsFRP and improved strength of composite materials.<br /> But the mechanism of these treatments is<br /> The strengths BsFRP using silane and<br /> different. Silane may cover bamboo fiber<br /> NaOH treated fibers are placed in Fig. 7. It is<br /> surface and become linking between fiber and<br /> clear that treatment process improved the matrix by using their different groups. The<br /> strength of composite. NaOH and silane<br /> strength of hydrogen bonding between silane<br /> treatment increased the strength by 25% and<br /> and bamboo fiber surface depends on number of<br /> 20% respectively in comparing to untreated<br /> OH group of cellulose on the fiber surface.<br /> fiber BsFRP. NaOH treatment has more<br /> Bamboo shoot culm sheath is collected from<br /> effective on bamboo shoot culm sheath fiber<br /> young bamboo. Therefore the percentage of<br /> than silane treatment did. The modulus of<br /> cellulose might lower than that of adult bamboo<br /> composite is also increased by about 20% after<br /> culm. So the effect of silane on bamboo shoot<br /> the treatments. Thus, both sodium hydroxide culm sheath fiber was lower than bamboo fiber.<br /> and silane are modified bamboo fiber surface<br /> 192<br /> On the other hand, sodium hydroxide (NaOH) the excessive sodium hydroxide after treatment.<br /> modified bamboo shoot culm sheath fiber by NaOH treated bamboo shoot culm sheath<br /> dissolving hemi cellulose and lignin and cleaned fibers were put in a 0.01% acetic acid solution<br /> the fiber surface. After NaOH treatment, for 2 hours. Then fibers were washed with water<br /> bamboo fiber surface were rough. Fibers carefully. Clean fibers were dried at 80oC for 2<br /> themselves are more flexible because some hours.<br /> lignin was extracted. Hence, PP matrix was<br /> more easily to penetrate into fiber during The strength of BsFRP using NaOH and<br /> material fabrication. This explains the reason acetic acid treated bamboo fiber was measured.<br /> why BsFRP had higher tensile strength after From the results in Fig. 9, the IFSS is increase by<br /> treatment with sodium hydroxide. 25% after clean excessive sodium hydroxide with<br /> acetic acid. The tensile strength and modulus are<br /> Although the strength of BsFRP was also increased by 25% (Fig. 10 and 11). Thus,<br /> improved when applying sodium hydroxide NaOH stayed inside fiber after treatment has<br /> treatment was applied, it is still low in much effect on strength of BsFRP. The SEM of<br /> comparing to other materials. The reason might fractured surface of BsFRP (Fig. 12) also<br /> be that there is sodium hydroxide stay inside indicates the improvement of interphase in<br /> bamboo fiber after washing by fresh water. This BsFRP. Voids was reduced and fibers were well<br /> excessive sodium hydroxide becomes barrier to distributed in matrix. According to these results<br /> prevent fiber contact with matrix. Therefore, in above, bamboo shoot culm sheath fibers can be<br /> this study, we try to use acetic acid to neutralize used in some application as bamboo fiber.<br /> <br /> 40 7<br /> a. N o tr e at a . N o tr e a t<br /> 35 6 b . T r e a t w ith S ila n e<br /> Tensile strength, MPa<br /> <br /> <br /> <br /> <br /> b . T r ea t w i th S ilan e<br /> Elastic modulus, GPa<br /> <br /> <br /> <br /> <br /> c. T re a t w ith N a O H c . T re a t w ith N a O H<br /> 30 5<br /> 25<br /> 4<br /> 20<br /> 3<br /> 15<br /> 2<br /> 10<br /> 5 1<br /> 0 0<br /> a b c a b c<br /> Fig. 7: Effect of surface treatment on tensile Fig. 8: Effect of surface treatment on elastic<br /> strength of BsFRP modulus of BsFRP<br /> 4 .5 a . N o tr e a t<br /> 4<br /> a. N o trea t 40<br /> Interfacial strength, MPa<br /> <br /> <br /> <br /> <br /> b . T reat w ith N a O H b . T r e a t w ith N a O H<br /> c . T re a t w ith N a O H<br /> 3 .5 c. T re at w ith N aO H 35<br /> Tensile strength, MPa<br /> <br /> <br /> <br /> <br /> + A c e tic A c id<br /> + A c etic A c id<br /> 3 30<br /> 2 .5 25<br /> 2 20<br /> 1 .5 15<br /> 1 10<br /> 0 .5 5<br /> 0 0<br /> a b c a b c<br /> Fig. 9: Variation of interfacial strength of alkali Fig. 10: Effect of alkali and acetic anhydride<br /> and acetic anhydride treated fiber treatment on tensile strength of BsFRP<br /> <br /> 193<br />  a. N o treat<br /> 8 b. T reat w ith N aO H<br /> c. Treat w ith N aO H<br /> 7<br /> <br /> <br /> Elastic modulus, GPa<br /> +A cetic A cid<br /> 6<br /> 5<br /> 4<br /> 3<br /> 2<br /> 1<br /> 0<br /> a b c<br /> Fig. 11: Effect of alkali and acetic anhydride treatment on elastic modulus of BsFRP<br /> <br /> <br /> <br /> <br /> 500µ m 500µ m 500µ m<br /> <br /> <br /> Untreated NaOH treated NaOH + acetic acid treated<br /> <br /> Fig. 12: SEM observation of fractured surface of BsFRP<br /> <br /> IV - Conclusions References<br /> <br /> 1. IFSS of bamboo shoot culm sheath fiber 1. C. M. Chen, H. C Chen, M. Tracy and Y.<br /> with MAPP was improved after treating Liao. Bonding moso bamboo with<br /> with silane or alkali. copolymer resins made of biomass residue<br /> 2. Alkali treatment has much effect on extract with phenol and formaldehyde,<br /> bamboo shoot culm sheath fiber than silane Forest Products Journal, Vol. 50, 9B, P. 70 -<br /> treatment has. 74 (2000).<br /> 3. Bamboo shoot culm sheath fiber can be use 2. T. 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