development of natural fiber reinforced composite materials using … · 2014. 5. 16. · than that...

Development of natural fiber reinforced composite materials using a loosing technique and mechanical properties

T. Matsuoka1, K. Sakaguchi1, H. Fujita2, H. Yamamoto3 & M. Kurasaka4 1Department of Mechanical Engineering, Doshisha University, Japan 2Hyogo Prefectural Industrial of Technology, Japan 3Graduate Student, Doshisha University, Japan 4Toppan Printing Co., Ltd, Japan

Abstract

A method of molding composite materials with a loosing technique was developed, and the tensile properties of the composite materials were investigated. This molding method was developed to obtain a higher fiber content and to increase the interfacial area between fiber and resin. Polypropylene/polyethylene (PP/PE) fibrous resin and cotton fibers were used as raw materials, and the composite materials were made by an injection molding and a hot-press molding with loosing cotton fibers and loosing PP/PE fibrous resin. It was clarified that the tensile strength of loosing fiber reinforced composite materials was drastically improved by the vacuum hot-press molding. It was also shown that the tensile strength of the composite material increased to about 50MPa at a fiber content of 30wt.% due to the improvement of interface adhesion state. Keywords: card machine, loosing fiber, cotton fiber, polypropylene/poly-ethylene fibrous resin, Injection molding, hot-press molding, tensile properties.

1 Introduction

In recent years, the environmental problem in an earth scale is emphasized in various fields, and an importance is attached to development of material with few environmental burdens or material with easy recycling also in plastic

High Performance Structures and Materials II, C.A. Brebbia & W.P. De Wilde (Editors)© 2004 WIT Press, www.witpress.com, ISBN 1-85312-717-5

industry. Especially, the glass fiber and the carbon fiber have been used as reinforcement for many of conventional fiber reinforced plastics (FRP), and, since the disposal is not easy for such FRP, the development of FRP that harmonized with environment is demanded [1]. From such a viewpoint, some researches [2, 3, 4] have been studying to use the natural fiber, which it has a moderate mechanical property and is a green material, as a reinforcement of the conventional FRP. However, since generally the strength of natural fiber is lower than that of the glass fiber etc., it is necessary to product a green composite with higher fiber content and longer fiber length in order to obtain a natural fiber reinforced composite material (it is henceforth described as NfRP) with high strength. Therefore, it is important to develop a new creative technology for the composite material that fills these demands.

A method of molding a composite material with using loosing technique was developed in this study. This loosing technique is possible to distribute a fiber uniformly by loosing fibers using a card machine. Moreover, a method of producing high strength NfRP was investigated and the usefulness of the loosing technology was also investigated on pointing the possibility of increasing adhesion area of the fiber/resin interface and increasing fiber content. Furthermore, mechanical properties of NfRP produced this method are searched.

2 Materials and the experiment method

2.1 Materials The polypropylene/polyethylene fiber (Chisso Corp.;ESC) and the polypropylene / acid denaturation polyethylene fiber (Chisso Corp.;INTACK) were used as the matrix resin. These resin are written as PP/PE and PP/APE, respectively. Both fibers have two-layer structure with a core part (PP (melting point: 160℃)) and a skin part (PE (melting point: 130℃)). These two kinds of fibrous resin were used in order to investigate an influence of the adhesive difference in the fiber/resin interface on the strength property of Loosing NfRP. The cotton fiber (raw cotton) grown in Egypt was used as reinforcement and the mean fiber length is 30mm and the mean tensile strength is 516MPa. 2.2 The production method of composite material 2.2.1 The loosing method The loosing of the fibrous resin and the cotton fiber or these mixtures was performed by using a card machine in this research. A card machine is one of the spinning machines, and it can distribute the fibers uniformly, make a sheet-like fiber and arrange fibers to one direction (the loosing direction) with using a card machine.

It is important to distribute the cotton fiber uniformly in resin in mixing of the fibrous resin and the cotton fiber. Therefore, the loosing fibrous resin sheet and the loosing cotton fiber sheet were separately made by the card machine before mixing fibrous resin and cotton fiber. The loosing mixture fiber sheet


392 High Performance Structures and Materials II

distributed uniformly could be made by passing a weight rate of loosing fiber sheets to a card machine again at the time of mixture. This loosing mixture was carried out in a parallel direction to a loosing direction. 2.2.2 Molding method The Loosing NfRP was produced by hot-press molding. It is difficult to obtain a required composite plate at once in the hot-press molding, because the volume of loosing mixture fiber increases sharply in molding an experimental plate. Then, a composite plate was produced by three steps, a press process, a dryness process and a molding process. A compression plate is produced by laying some loosing mixture fiber sheets at the first step (fig.1(a)) and, after that, a plate can be obtained through a press process (fig.1(b)). In the press process, the volume of loosing mixture fiber sheets was decreased by a press molding under 135℃ near the melting point of skin part (PE) of matrix at first, and then, the volume was maintained by melting the fibrous resin of skin part on the surface of plate. At the following process, the moisture causing to void was removed by keeping the compression plate in the drying furnace at 105℃ for 10 minutes. And, the compression plate was inserted in the molding with a predetermined dimension and an experimental plate was molded by the hot press process again (fig.1 (c)). The hot-press molding conditions are shown in table1. The loosing NfRP produced by the hot-press molding is described as Loosing NfRP (Hot-press).

Figure 1: Molding process.

Table 1: Hot-press molding condition.

Weight fraction of fiber (%) 30 Molding pressure (MPa) 10 Molding temperature (oC) 210 Molding time (min) 10 Cure condition Quench cure

(a)

(b)

(c)


High Performance Structures and Materials II 393

Table 2: Injection molding condition.

Weight fraction of fiber (%) 30 Screw speed (rpm) 50 Temp. at heating cylinder (oC) 210 Injection speed (mm/s) 100 Injection pressure (MPa) 0

2.3 Experiment method 2.3.1 Static tensile test The static tensile test was performed in order to examine the mechanical property of a loosing fiber reinforced composite material. The test piece was cut to a rectangle as shown in fig.2 from a plate and the test piece left in the dryer for 24 hours was used in the static tensile test. This loosing fiber passed to the card machine is easy to arrange parallel to a loosing direction. Therefore, the test piece was cut out from a plate as the loosing direction corresponds to the tensile direction. The static tensile tests were carried out at the test speed 1mm/min under a room temperature by Instron testing machine (4467 type).

Figure 2: Dimension of tensile test specimen.

2.3.2 Fiber content and void measurement The fiber content and the void content in a composite material affect the strength property greatly. Therefore, these data were measured by using an area method with the cross-sectional observation photograph from the edge-wise direction. The fiber content Vf was obtained from the ratio of the fiber gross area Af (Void gross area Av) to all area A measured from an observed picture.

Vf = Af/A The fiber content and the void content were obtained from the average values of data given from the 250 pictures.

150

90100

15

253025

2.0

6.0

30

Loosing di r ect ion



3 Results and discussion

3.1 Development of a loosing fiber reinforced composite material Non-Loosing NfRP, Loosing NfRP (Injection), and Loosing NfRP (Hot-press) were produced by using PP/PE fibrous resin and a cotton fiber in order to investigate the internal observation and the strength property. The fiber content of these samples was considered as a constant content of 30wt.%. The strength property of these composite materials was evaluated by a tensile test.

The tensile strength and the Young's modulus are shown in fig.3. The Young's modulus can be improved in Non-Loosing NfRP compared with that of PP/PE resin, but the reinforcement effect by a cotton fiber can be not obtained in the tensile strength. On the other hand, the reinforcement effect of a cotton fiber appeared in the case of Loosing NfRP (Injection) and Loosing NfRP (Hot-press) from the result that the tensile strength was increasing by 1.4 times and 1.6 times to that of a PP/PE resin, respectively. The internal observation from a test piece section was carried out. As a result, the fiber rich part exists in Non-Loosing NfRP and it is difficult to distribute a cotton fiber uniformly only in the action of the plasticization mixing part of an injection molding machine. On the other hand, the fiber is distributing uniformly in Loosing NfRP (Injection) and Loosing NfRP (Hot-press). It becomes clear from this result that the composite material, which the fiber distributed well, can be made by mixing a fiber and a fibrous resin with using a card machine in advance. Generally, the fiber becomes a source of a stress concentration in the composite material when the distribution of fiber is not well, and then, a sufficient reinforcement effect cannot be gained [5]. Therefore, the improvement of strength was not found because of not well dispersing of fibers. On the other hand, the improvement of strength in Loosing NfRP (Injection) and Loosing NfRP (Hot-press) appeared because the composite material dispersed fibers well with using a loosing mixture fiber were obtained.

Bulk 0

40

20

60

Non L-NfRP L-NfRP

0

2.0

4.0

6.0

Tensile strength

Young's modulus

Injection Injection Hot-pressTen

sile

str

eng

th (

MP

a)

Yo

un

g's

mo

du

lus

(GP

a)

Figure 3: Tensile properties of natural fiber reinforced composite materials (30wt.%).



The rate of void in this composite material was measured. Consequently, the rates of void of Loosing NfRP (Injection) and Loosing NfRP (Hot-press) are about 5% and 16.4% to the rate of void of Non-Loosing NfRP being about 1%, and it became clear that many voids is included in Loosing NfRP (Injection) and Loosing NfRP (Hot-press). It is thought that the air left between the loosing fibers at the time of loosing causes to include many voids. And, it is necessary to reduce the void in making the composite material because the existence of void acts as a defect of material. In addition, the resin did not adhere to the fiber surface in using PP/PE resin at all as a result of observing the fiber in the fracture side of test piece after the tensile test (fig.5 (a)) and it was found that the adhesive state of a cotton fiber and the resin was not good. 3.2 Improvement of strength of a loosing fiber reinforced composite

material 3.2.1 Removal of void In the section 3.1, it made clear that many voids have been included in molding a loosing fiber reinforced composite material. Then, the void was removed with using a vacuum hot-press molding. The compression molding effective in improving the strength as shown in the section 3.1 was used in this molding. The fiber content of the composite material made in this molding method was 30wt.%. After that, the composite material not to perform a vacuum molding and that to do so were respectively represented as Loosing NfRP (Hot-press) and Loosing NfRP (Vacuum hot-press).

As a result of measuring the rate of void, the rate of void of Loosing NfRP (Vacuum hot-press) becomes about 3% to the rate of void 16.4% of Loosing NfRP (Hot-press), and then, it is considered to be able to make the rate of void low by vacuum molding.

The tensile strength and the Young's modulus in these materials were shown in fig.4. Many voids existed around the cotton fiber in the case of this composite material. Therefore, it is thought that the reduction of the strength from the nonlinear part became large in the behavior of the stress-strain curve of Loosing NfRP (Hot-press) to progress early the debonding of a fiber / resin interface from the void. The influence of vacuum molding was not seen in the Young’s modulus and was notably seen in the static tensile strength from the result of fig.4. And, the improvement of the strength of Loosing NfRP (Vacuum hot-press) became larger and the tensile strength could be increased by 2.1 times compared with that of the resin. The removal of void is important for increasing the strength of this composite material and it is found that the vacuum hot-press molding is effective.

It was shown from fig.3 and fig.4 that the strength of Loosing NfRP (Vacuum hot-press) became higher compared with that of Loosing NfRP (Injection). And, it is shown from the observation photograph to the test piece flat-wise direction that many shorter fibers existed in the case of Loosing NfRP (Injection) compared with the fiber length of Loosing NfRP (Vacuum hot-press). It is thought as this cause that the fiber length is shorter in mixing a loosing



mixture fiber in the injection-molding and injecting the fiber into metal mold. Moreover, the difference of fiber length is considered to have affected the strength. The observation photograph of a fracture surface is shown in fig.5. Where, the tensile direction is a perpendicular direction to space. Many perpendicular fibers to the tensile direction are seen from fig.5(a) of the fracture side of Loosing NfRP (Injection). On the other hand, many pullout fibers parallel to the tensile direction are seen from fig.5(b) in the fracture side of Loosing NfRP (Vacuum hot-press). A composite material included many fibers perpendicular to the tensile direction was made in injecting the loosing mixture fiber into the die in the case of Loosing NfRP (Injection), and, consequently, it is thought that the last fracture of the Loosing NfRP (Injection) became early compared with the case of Loosing NfRP (Vacuum hot-press) by progressing promptly the debonding of a fiber /resin interface. It is considered from the above result that the compression molding method is effective as the molding method of the loosing fiber reinforced composite materials.

0

40

20

0

2.0

4.0

60 6.0Tensile strength

Young's modulus

Bulk Non-vacuum Vacuum

Ten

sile

str

eng

th (

MP

a)

Young's

modulu

s (G

Pa)

Figure 4: Tensile properties of natural fiber reinforced composite materials

(30wt.%) for two hot-press moldings.

100 m 100 m

(a) Loosing NfRP (Injection) (b) Loosing NfRP (Vacuum hot-press)

Figure 5: Scanning electron micrographs of fracture surface on natural fiber reinforced composite materials (30wt.%) for two moldings.



0

40

20

0

2.0

4.0

(30wt.%)Tensile

Young's modulus

60 6.0

Bulk Composite PP/PE resin

Bulk Composite PP/APE resin T

ensi

le s

tren

gth

(M

Pa)

Yo

un

g's

mo

du

lus

(GP

a)

Figure 6: Tensile properties of natural fiber reinforced composite materials (30wt.%) for two resins.

50µ m 50µ m(a) Cotton/(PP/PE) (b) Cotton/(PP/APE)

Figure 7: Scanning electron micrographs of natural fiber reinforced composite materials (30wt.%) for two resins.

3.2.2 Improvement of interface adhesion state An adhesive badness of a cotton fiber was pointed out in Section 3.1. It is considered that the influence of adhesion state on a strength property becomes large because the adhesion area of a fiber / resin interface is remarkably increased by the loosing mixture. Then, the interfacial adhesion was improved by using PP/APE resin. The composite material of fiber content 30wt.% was also made by the vacuum hot press molding with this resin type. The tensile strength and the Young’s modulus obtained from the stress-strain curve are shown in fig.6. As a result of observing the fiber of the fracture side after an examination, the resin has not adhered to the fiber surface of the sample using PP/PE resin at all (fig.7 (a)). By the way, it became clear that much resin has adhered to the cotton fiber surface (fig.7 (b)) in using PP/APE resin and the adhesion state of cotton / resin interface is improved. Therefore, the adhesion state of a fiber/resin



interface improved in the case of using PP/APE resin. Consequently, the progress of debonding of a fiber/resin interface was delayed and the fall of the slope of a nonlinear part was suppressed with a PP/PE composite material. It made clear from fig.6 that the tensile strength of a PP/APE composite material is possible to raise the tensile strength of the PP/APE resin by about 2.8 times and also to be increased compared with the tensile strength of a PP/PE composite material further.

4 Conclusion

In this research, as a result of investigating the development of the natural fiber reinforced composite material using loosing technology and the raise of its strength, the following conclusions were obtained. (1) A natural fiber reinforced composite material which dispersed fibers well

could be obtained by using the loosing technology. However, it became clear that this composite material have a weak point to include many voids by this product method and have a demerit of the adhesive badness in the interface between natural fiber and resin.

(2) It became clear that a high strength natural fiber reinforced composite material could be produced by means of the removal of void and improvement of interfacial adhesion state with a loosing fiber.

References

[1] T. Kimura, Aim at Environment Friendly Composites. J. Soc. Mat. Sci., Japan, Vol.50, No.10, pp. 1158, 2001.

[2] Y. Okawa, T. Matsuoka, K. Sakaguchi, H. Fujita, Reinforced Plastics, Japan, Vol.48, pp.161, 2002.

[3] Saheb, D. Nabi, Natural Fiber Polymer Composites: A Review, Advances in Polymer Technology, Vol.18, No.4, pp.351-363, 1999.

[4] M. Muenker, Improved Adhesion in Natural Fiber Composites, Kunnststoffe-Plast Europe, pp.29-31, 1999.

[5] The Chemical Society of Japan, Composite Material, Japan Socientific Societies Press, pp.141, 1975.



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