**3.6. Mechanical and physical properties of bamboo fibers**

of leptodermous cells. The wear rupture of vascular bundles was severe as compared with that of the matrix tissue. This result was opposite to the abrasive wear behavior of N-type specimens in free-abrasive wear conditions, in which the ends of vascular bundles were protruded on the matrix of the abrading surface of N-type specimens, suggesting that vascular bundles of bamboo possessed higher wear resistance than matrix tissue [5]. It was seen to the naked eye that the ends of vascular bundles were darker than matrix tissue after sliding friction, particularly at high velocity or under high load (see **Figure 7d**, **e**, **g**, and **h**). High temperature caused by frictional heat would burn the contacting bamboo surface. The vascular bundles were mainly burned for the N-type. This phenomenon can be observed clearly after grinding a bamboo block (N-type mode) against an abrasive wheel. The burnt material may easily be removed by asperities of the ring surfaces. The interfacial temperature was dependent upon the normal load and, particularly, sliding velocity [29]. Therefore, topographies of the ends of vascular bundles of worn surfaces of N-type

**Figure 7b** shows that the part surrounded by vascular of cellulose fibers (i.e., the center area of a vascular bundle) protruded. This was more obvious at low load and velocity (see **Figure 7a**

**Figure 7.** Worn surface micrographs of N-type bamboo specimens. (a) 60 N, 0.42 m s−1; (b) details of the center area of a vascular bundle in (a); (c) details of leptodermous cell of the lower area of (a); (d) 120 N, 0.42 m s−1; (e) details of a vascular bundle of the center area of (d); (f) details of the center area of the vascular bundle of (e); (g) 60 N, 0.84 m s−1; (h) 120 N,

bamboo specimens varied with the load and velocity.

96 Bamboo - Current and Future Prospects

0.84 m s−1 (the friction direction of the ring was from left to right).

The mechanical and physical properties of bamboo fibers in this study are listed in **Table 2**. From **Table 2**, it can be seen that the elongation at fracture of alkaline-treated bamboo fibers was about 1.2%, the tensile strength was about 56.3 MPa, and the elastic modulus was about 18.6 GPa. However, for untreated bamboo fibers, the elongation at fracture was 1.7%, the tensile strength was 46.7 MPa, and the elastic modulus was 23.3 GPa. It indicated that the tensile strength and elastic modulus were increased by the modification of bamboo fibers. It is because the crystallinity of the alkaline-treated bamboo fiber was increased, which could improve the polarity of molecules and the adhesion strength between the high molecules. The slip produced by destruction of the binding force of molecules was relatively small, so the elongation at fracture was reduced, and the tensile strength and elastic modulus was increased after modification for bamboo fiber.

The stress-strain curve of the alkaline-treated bamboo fibers is shown in **Figure 8**. At the initial stage, the stress was proportional to the strain, which is consistent with the Hooke's Force Law. There was no yield and necking phenomenon, and the stress and strain were very low before breaking. It indicated that the bamboo fiber was a brittle material. The brake pads were basically acted by compression pressure when they work. Hence, the lower tensile strength of bamboo fiber does not have impact on the braking performance of brake pad.

It can be seen from **Figure 9a** that a major part of the fracture surfaces presented brittle failure. Some small molecule impurities on bamboo fiber surface were removed by the alkaline solution that caused the adhesion strength among fibers to be reduced considerably. The fracture of the untreated fiber (**Figure 9b**) showed that the uneven break presented because of the uneven stress that resulted from the bonding of pectin with lignin among the fibers.

The bamboo fibers connected with each other under pressure. The tangential resistance generated in relative sliding is called friction force. The tangential resistance is called cohesive force at the normal press of zero. **Figure 10** shows that the bamboo fibers were assembled, entangled, bonded,


**Table 2.** Test results of mechanical properties of bamboo fiber.

and held tightly together due to the role of cohesive force that is not easy to loose. Therefore, the properties of the friction materials were affected by the friction force and the cohesive force.

Bamboo Wear and Its Application in Friction Material http://dx.doi.org/10.5772/intechopen.69893 99

It can be found from **Figure 11** that the friction coefficients of BFRFMs with 3, 6, and 9 wt.% bamboo fibers were higher than those of the friction materials without bamboo fibers. The friction coefficients of the BFRFMs have significant variations at the test temperature of 250°C. This is because phenolic resin began to pyrolyse, and the bamboo fibers were carbonized gradually when temperature exceeded 250°C. However, the friction coefficient of BFRFMs

It can be seen from **Figure 12** that wear rates of the BFRFMs generally increased with the increase of test temperature since the matrix began to soften, and the bamboo fibers were carbonized with the increase of test temperature. The surface roughness of friction materials containing 6, 9, and 12 wt.% bamboo fibers was high, so the adhesive wear and microcutting wear appeared on the worn surface. This is because the heat fading of the phenolic resin appeared, and the small hard particles formed from some glass fibers separated from the matrix. Plenty of wear debris formed and fell off, so the wear rate of friction materials significantly increased. The wear rate of friction materials containing 3 wt.% bamboo fibers was the lowest. In fact, some voids and grooves formed after the carbonization of the bamboo fibers can contain some other abrasive particles.

The worn surface morphologies of the BFRFMs are shown in **Figure 13**. It can be seen from **Figure 13** that some glass fibers exposed and some did not separate from the matrix. The glass fibers and friction surfaces were supported by the matrix. Some hard particles from the glass

**Figure 11.** Variation of the friction coefficient of the bamboo fiber reinforced friction materials with the temperature.

containing 12 wt.% bamboo fibers decreased with the increase of test temperature.

**3.7. Effect of bamboo fiber on friction performance**

**3.8. Wear surface morphologies of BFRFMs**

**Figure 8.** Test result of tensile stress-strain curve of a bamboo fiber treated with alkaline solution.

**Figure 9.** Morphologies of tensile fracture of (a) the bamboo fiber treated with alkaline solution; and (b) the untreated bamboo fiber.

**Figure 10.** Bamboo fiber assemblies.

and held tightly together due to the role of cohesive force that is not easy to loose. Therefore, the properties of the friction materials were affected by the friction force and the cohesive force.
