The investigation of physical and mechanical properties of wood plastic composites (WPC)
Stanisław Zajchowski*, Cezary Gozdecki**, Marek Kociszewski** *Akademia Techniczno-Rolnicza w Bydgoszczy, Katedra Chemii i Technologii Polimerów, ul. Seminaryjna 3, 85-326 Bydgoszcz **Akademia Bydgoska im. Kazimierza Wielkiego, Instytut Techniki, ul. Chodkiewicza 30, 85-064 Bydgoszcz
Quarterly No. 3, 2005 pages 45-50
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abstract The investigation into wood polymer composites containing Malen P, S-901 and wood flour content of 0÷60% was carried out. Wood flour was obtained using a grinder constructed by us that makes it possible to receive milling characterized by high bulk density and distribution uniform with regard to grain size with a vestigial share of powdery fraction (Fig. 1). Particles of 200 to 500 μm size were mixed with polypropylene and moulders in a form of little paddles and beams were obtained by means of injection moulding. The paddle-like moulders were 150 mm long and had two sections: 4x10 mm and 10x10 mm. In order to better relate the composites examined to the properties of wood-based materials, a supplementary board with a moulding mortise of 140x30x20 mm size that makes it possible to obtain beams corresponding with regard to shape and height to the samples used in the investigations into wood-based materials. The basic physical and mechanical properties, that is density, linear shrinkage, water absorption, tensile strength, impact, and toughness were determined for all the materials examined. The obtained properties were related to the content of wood flour in a composite. An advantageous effect of wood flour on linear shrinkage was demonstrated (Fig. 2). It was found out that when the content of a filler increases, the value of shrinkage decreases linearly, reaching the value of 0.2% for the composite containing the wood flour content of 60%. For all the moulders obtained density was determined, that to a considerable degree depends on the wood flour content (Fig. 3). Despite the fact that the density of both components of the composite is lower than 1 g/cm3, the density of the composite increases with the growth of the wood flour content, and at the content of approximately 50% even exceeds 1 g/cm3. The modification of propylene with wood flour also affects a noticeable tendency to water absorption, but it is, however, insignificant when compared to water absorption of pine-wood, MDF or particle board (Figs 4, 5). The results of tensile strength measurements of the wood plastic composites (WPC) (Fig. 6) showed that the tensile strength strongly depends on the cross-section of a sample at the same wood flour content in them. For all tests tensile strength decreases from the value of 31 MPa for Malen itself, to the value of 3.7 and 10 MPa for the composites containing 60% of wood flour. Similarly, the increase in the wood flour content affects the impact strength of the composite (Fig. 7). The increase of the content of a filler reduces the value of impact strength that at over 50% of its content does not change, but even shows a tendency to grow. However, the values of impact strength at the same wood flour content but with different sections considerably differ. The examinations of the toughness of WPC showed that this parameter is dependent on the level of wood flour content (Fig. 8). It was observed that the composite each time had much higher toughness that wood-based materials compared (Fig. 9). It was found out that on the one hand the obtained WPCs can be compared with polymers and evaluated by using methods elaborated for them. On the other hand, the high level of wood flour content in composites enables to compare them with the properties of wood and wood-based materials of a MDF or particleboard type. The comparison was also made, resulting in a conclusion that it is necessary to work out research methods that are representative for both WPCs and woodbased materials. Key words: wood plastic composite, WPC, physical properties, mechanical properties