Advantages of the using of the poliester resin to manufacturing of the composite materials based on wood flour.

Cerbu, Camelia ; Luca, Dana Motoc ; Ciofoaia, Vasile 等

1. INTRODUCTION

This work analyses the effects of some internal factors such as kind of wood flour or the type of resin, on the mechanical characteristics of the composites resulted by their mixing.

Nowadays, it is known the great interest for recycling of the large amount of wood waste (Kandem et al., 2004) in the form of wood flour, fibres is suitable as a filler for polyolefin matrix composites or for recycled plastics. A published research (Adhikary et al., 2008) shown that the composites made of high-density polyethylene and fir wood flour as filler, treated with coupling agents, could be desirable as building materials.

On the other hand, there were preoccupations concerning the recycling of fibre materials (Bartl et al., 2005) such as the textiles, carpets, composite materials reinforced with fibres etc; the recycling of the CDs / DVDs (Cerbu & Teodorescu, 2009).

Herein, an urea-formaldehyde resin was used to manufacture three kinds of composite materials filled with oak wood flour, beech wood flour or carpinus wood flour. Moreover, a polyester resin Copoly 7233 was reinforced only with oak wood flour to manufacture another composite. The best mechanical characteristics in flexural test were recorded in case of the polyester filled with oak wood flour.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

In the next research, it will try to improve the mechanical characteristics of the composite materials filled with wood flour by additionally reinforcing with E-glass fibres.

2. MATERIALS AND METHODS

The first of all, two kinds of resins (urea-formaldehyde, polyester) were used to manufacture four composite plates having the dimensions 350 x 250 [mm.sup.2] and 4 mm in thickness. The urea-formaldehyde resin Urelit R was reinforced with oak wood flour, beech wood flour or carpinus wood flour. The polyester resin Copoly 7233 was reinforced with oak wood flour. Every time the weight ratio of wood flour was the same 200 g / 500 ml resin. Urelit R urea-formaldehyde resin (***, 2008) is used in wood industry for bordering of the chipboards, pasting of the solid elements.

The plates were kept at room temperature and dried environment for three weeks. Then, the specimens were cut from the plates for the flexural test (three-point method). Figure 2 shows the scheme of loading (SR EN ISO 178, 2001).

LR5K Plus machine manufactured by LLOYD Instruments was used for the flexural test. This is power driven (maximum force [F.sub.max] = 5 kN). The speed of loading was 1.5 mm/min. Before each flexural test of a specimen, the dimensions of its cross-section were accurately measured (0.1 mm).

These were considered as input data in the software program of the machine. The testing equipment allowed us to record pairs of values (force F and deflection v at midpoint of the specimens) in form of files having 100-150 recordings. The testing machine also gave us the results of a statistical calculus for the set of the specimens tested.

3. RESULTS AND DISCUSSIONS

The force-displacement curves (F-v) recorded in case of all specimens tested are shown in the figures 1 and 3, respectively. It may easily observe that the slope corresponding to the linear portions of the F-v curves recorded in case of oak wood flour / polyester composite (fig. 1) is much greater than in case of the composites made of oak wood flour / urea-formaldehyde resin.

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

The experimental results concerning the modulus of elasticity E (fig. 4 and 6) reaffirm the above remarks concerning the best stiffness recorded in case of the oak wood flour / polyester composite. On the other hand, the average value of E recorded in case of reinforcing with beech wood flour is over three times less than the one recorded in case of reinforcing with oak wood flour when the urea-formaldehyde Urelit R is used to prepare the composite materials.

From strength point of view, it may remark that the maximum flexural stress 31.1 MPa recorded in case of oak wood flour / polyester composite (fig. 7) is just about twice times greater than the value 16.9 MPa recorded in case of wood flour / urea-formaldehyde composite (fig. 5). In case of the composites manufactured with urea-formaldehyde (fig. 5), the lowest values of the limit normal stresses a were recorded in case of the beech wood flour / urea-formaldehyde resin.

4. CONCLUSIONS

Among the composite materials tested, the one made of polyester resin reinforced with oak wood flour is the best from both stiffness and strength point of view.

[FIGURE 5 OMITTED]

The mechanical characteristics are also affected by the kind of species of wood the wood flour is made of.

Taking into account the recycling necessity of the large quantity of wood wastes, none the less that the values of mechanical characteristics are smaller, the composite materials tested could be used only to manufacture products that are not strength members (boards in construction, furnish ornaments, carcasses etc.).

5. ACKNOWLEDGEMENT

The research described within the present paper was possible owing to a national scientific project exploratory research, Project ID_733 / 2008 whose funds were supported by Ministry of Education and Research of Romania.

6. REFERENCES

Adhikary, K. B.; Pang, S. & Staiger, M. P. (2008). Dimensional stability and mechanical behaviour of wood-plastic composites based on recycled and virgin high-density polyethylene (HDPE). Composites: Part B, 39, 2008, pp. 807-815, ISSN 1359-8368

Bartl, A.; Hackl, A.; Mihalyi, B.; Wistuba, M. & Marini, I. (2005). Recycling of fibre materials. Process Safety and Environmental Protection, 83 (B4), 2005, pp. 351-358, ISSN 0957-5820

Cerbu, C. & Teodorescu, H. (2009). Bending behaviour of the composite materials made by recycling of the CDs and DVDs, In: Proceedings (ISI) of The World Congress on Engineering WCE 2009, vol. 2, pp. 1753-1756, ISBN 978988-18210-1-0, London, 1-3 july, 2009, IAENG Publisher

Kamdem, D. P.; Jiang, H.; Cui, W.; Freed, J. & Matuana, L. M. (2004). Properties of wood plastic composites made of recycled HDPE and wood flour from CCA-treated wood removed from service, Composites: Part A, 35, 2004, pp. 347-355, ISSN 1359-835X

SR EN ISO 178 (2001). Plastics. Determination of flexural properties, European Committee for Standardization, Brussels, 2001

***(2008) http://www.viromet.ro--Material data sheet Urelit[R]R, S.C. VIROMET S.A., Victoria (Romania), Accesed on: 2009-03-12

Fig. 6. Values of Young's modulus E in case of the specimens
manufactured with Copoly 7233 polyester resin

Specimen 1 2656.6

Specimen 2 2815.2

Specimen 3 2499.4

Specimen 4 2432.0

Specimen 5 2642.1

Average
value: 2609.1 MPa

Table made from a bar graph.

Fig. 7. Maximum values of flexural stress [sigma] in case of the
specimens manufactured with Copoly 7233 polyester

Specimen 1 28.4

Specimen 2 31.0

Specimen 3 32.8

Specimen 4 30.7

Specimen 5 32.4

Average
value: 31.1 MPa

Table made from a bar graph.