Wood-plastic composite

Proceedings of the 51st International Convention of Society of Wood Science and Technology November 10-12, 2008 Concepción, CHILE

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Wood-plastic composite

Leandro Shiroma School of Agricultural Engineering, State University of Campinas

Campinas, São Paulo, Brasil

Prof.Dr.Antonio Ludovico Beraldo School of Agricultural Engineering, State University of Campinas

Campinas, São Paulo, Brazil

Abstract Wood is one of the most important raw materials in Brazil, mainly for the industry of construction, packing, furniture among others. In the mechanic process of cutting wood, large volumes of sawdust can eventually pollute the rivers and landfills. There is a great deal for the society to find some rational use for such wastes, like as an energy source to replace the coal, the diesel oil, and enhances its capability in exchange for carbon credits. Following this trend, studies were developed at several countries looking for the reuse of vegetable fibers as reinforcement in thermoplastics matrices, for several industry applications. The objective of this work was to develop a composite from Pinus sp residues and recycled plastics, such as polypropylene (PP) and polyethylene (PE), seeking their use in the manufacture of pallets components. Keywords: Wood, Plastics, Composites, wood-stock, fiber, PP, PE


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Bibliographic Review

Characterization of the residue of saw dust of the manufacturing process of pallets

One wood pallets company, located at the region of Campinas, Brazil, leads daily amount of 100 ton of waste from sawdust. Currently this waste is used as a source of burning energy in industries of this region. Pinus sp is the principal waste wood used as a load of more thermoplastics in Brazil. Its bulk density is between 0.15 a 0.374 kg/m3. Its chemical composition is 50.1% of cellulose, 30.3% of lignin, 9.7% of hemicelluloses and 10% of other substances (CAMARGO, 2006).

Sawdust as reinforcement in thermoplastic (wood-plastic compound)

Thermoplastic composites with sawdust (WPC) have some advantages over the conventional mineral material. They are lighter in compared to the fiber glass = 2.5 kg/m3, CaCO3 or talc = 2.8 kg/m3. Moreover, these materials are less abrasive and not wear the equipment (CAMARGO, 2006). Consumption of composite is very significant in the USA - about 1,170,000 ton of wood-profile extruded plastic was produced. In Europe, consumption was approximately 1,200,000 ton each in 2007. The consumer sectors are furniture, packaging (pallets) and construction (manufacture of terraces, balconies, ceilings, etc.). In the other countries, like Brazil and Chile, consumption still comes up in the cultural barrier that can be broken through an appeal of environmental issues facing marketing (OMEGA, 2007).

Use of waste recycled polypropylene

Thermoplastics modified by vegetable fibers are recent and its melting point should be below the point of degradation of the fibers, usually between 200 to 220 °C (FOREST PRODUCTS LABORATORY, 1999). The polypropylene is a polymer of the same family of polyethylene and differentiated by this one by the presence of radical methyl (CH3) in monomeric unit. The position occupied by methyl radical determines the classification of polypropylene in atatic, sindiotatic, isotatic. The configuration gives the polymer isotatic a greater mechanical strength (SANTOS, 1998).

Use of waste of low density polyethylene (LDPE) recycled

The low-density polyethylene is highly translucent. It is resistant to most chemicals product, except for strong acids, some ketones. Almost half polyethylene produced in recent years has been to the film or plastic film because of its low density, flexibility, high resilience, resistance to wear, resistant to moisture and chemicals (BOLSONI, 2001).


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Materials and Methods

Materials used in the composition of composites

Materials used in the composition of composites

• Sawdust – vegetable waste obtained from Pinus trees, provided by the Industry Woodpack. The material was obtained from a sawmill located at Limeira-SP.

• Polypropylene (PP) and Polyethylene (PE) – recycled materials produced by the company Recicladora de Plástico Brasil - Piracicaba - SP - Brazil

Particle size distribution

Particle size distribution was obtained according to the standard of Brazilian Standardization (ABNT NBR-7217), which defines the mineral particle size distribution, since there is no specifics standard for clusters on the plant origin. Initially, it was weighed 180 g of each dried residue, subjecting them to the screening process using a mechanical shaker of sieves for a period of approximately 5 minutes. A standard series of sieves ABNT was used, with openings of 4.76 mm and 2.38 mm, 1.19 mm and 0.59 mm, 0297 mm and 0149 mm and residue. After the screening, it was obtained the mass of the material retained at each sieve. This procedure was performed with 3 replications.

Determination of the mass of the saw dust unit Waste density at air dry condition was determined using a cylindrical glass container with a volume of 11 L. The container was filled by the residues, launched from a height of 10 cm to 12 cm from the top of the container, to complete its total. The area was settled through a metal ruler and then it was weighted the mass of waste contained in this volume. Preparation of the mixture The residue of sawdust and recycled plastics PP and PE were initially dried in an oven for 80 °C for 24 h. The components of the mixture under appropriate proportions as showed in tables 2.1 and 2.2, were homogenized manually in a plastic container.

Table 2.1 – Polypropylene and sawdust ratios. 60:40 70:30 80:20

PP 1.2 1.4 1.6 Sawdust 0.8 0.6 0.4

Total 2.0 2.0 2.0


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Table 2.2 – Polyethylene and sawdust ratios.

60:40 70:30 80:20 PE 1.2 1.4 1.6 Sawdust 0.8 0.6 0.4 Total 2.0 2.0 2.0

The components were fed directly into the funnel of feeding the extruder, being merged, homogenized in the cannon and pushed through the twin screw co-rotational forming continuous yarns that are cooled in a tank with water in recirculation. The pellets are formed in the chopper that pulls the wires into the tank and short form of granules. Extruder parameters are showed in table 2.3.

Table 2.3 - Parameters of the extruder Flow (kg/h)

Rotation (RPM)

Torque (%)

Zone 1 (°C)

Zone 2 (°C)

Zone 3 (°C)

Zone 4 (°C)

Zone 5 (°C)

20 197 45 172 177 181 186 198

The pellets were placed in an oven for 24 hours at 80 °C for drying before the injection to produces the specimens. Data from the injector process are showed in table 2.4.

Table 2.4 - Parameter of the injectors

Speed injection (mm/s)

Time injection

(s)

Pressurepump (bar)

Temperatureinjection

(°C)

Zone 2 (°C)

Zone 3 (°C)

Zone 4 (°C)

40 3 50 182 179 178 164

Traction

The traction test was performed at an universal test device EMIC DL 2000, at the laboratory of Unesp - Botucatu, Campos Julio de Mesquita. The specimens followed the standard ASTM D 638. Five specimens were tested for each ratio.

Flexure

The flexure test was performed at an universal test device EMIC DL 2000, at the laboratory of Unesp - Botucatu, Campus Julio de Mesquita. The specimens followed the standard ASTM D 790-02. Five specimens were tested for each ratio.


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Impact

The impact test was conducted at a Tinius Olsen device, at the laboratory of Unesp - Botucatu, Campos Julio de Mesquita. The specimens followed the standard ASTM 256-97. It was tested 10 specimens for each ratio.

Results and Discussion

The software Statgraphics 4.1 was applied to perform analysis of variance (ANOVA). Average values were compared by Tukey´s Test at 95%.

Particle size distribution

According to the standard Brazilian NBR 7217, the residue of pine can be classified as a fine aggregate, table 3.1.

Table 3.1 - Saw dust size distribution

% Mesh (mm)

Mass Retained (g)

Retained Acumulated. 4.76 1.02 0,57 0,57 2.38 0.49 0,27 0,84 1.19 7.21 4,01 4,84 0.59 72.68 40,38 45,22 0.297 57.10 31,72 76,94 0.149 30.60 17,00 93,94

residue 10.90 6,06 100,00 TOTAL 180.00 100,00

Fineness 3,22

Maximum diameter 1,20 mm

Bulk density of the residue of pine The value of mass unit was found of 170 kg/m3. Impact results According to ANOVA at Table 3.2, the p-value of polymers type (< 0.05) and p-value of material ratios (<0.05) are highly significant. The interaction between the polymers and ratios are also highly significant. Figure 3.1 shows the impact results. According to the comparison of the polymers, there is a significant difference. For this property, polyethylene showed a better performance than polypropylene. For ratio comparison, as


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shown in Figure 3.1, T1 (60% polimer/40% sawdust), T2 (70% polymer/30% sawdust) and T3 trace (80% polymer / 20% of sawdust) are significantly differents. Ratio T3 showed better performance.

Table 3.2- Analysis of Variance for impact - Sum of square Type III.

Font Sum of square GL Average

square Coefficient-

F P-

Value EFECT A:polymers 75102.3 1 75102.3 299.93 0.0000 B:ratios 99390.4 2 49695.2 198.46 0.0000 Interaction AB 32460.7 2 16230.3 64.82 0.0000 Residue 13020.7 52 250.398 TOTAL (CORRECTED) 223367 57

Figure 3.1 - Impact Test.

Traction Results According to ANOVA table 3.3, the p-value of polymers types (<0.05) and the p-value of ratios (<0.05) are highly significant. The interaction between the polymers and ratio are also highly significant. Figure 3.2 shows the traction results. According to the comparison of polymer types, there is a significant difference, and the PP shows a better performance than PE. According to the comparison of the ratios, as shown in Figure 3.2, T1 (60% polymer/40% sawdust), T2 (70% polymer/30% sawdust) and T3 (80% polymer/20% sawdust) are significantly different. Ratio T3 shows a better performance.


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Table 3.3 - Analysis of Variance for traction - Sum of square Type III.


square Coefficient-

F P-Valor

EFECT A:polymers 1.27717E6 1 1.27717E6 32074.24 0.0000 B:ratios 10127.6 2 5063.81 127.17 0.0000 Interaction AB 5267.59 2 2633.8 66.14 0.0000 Residue 955.661 24 39.8192 TOTAL (CORRECTED) 1.293527E6 29

Figure 3.2 - Traction Test.

Flexure results According to ANOVA, (table 3.4), the p-value polymers (<0.05) is highly significant, but the p-value ratios (> 0.05) is not. Figure 3.3 shows the flexure results. According to the comparison of polymers types, there is a significantly difference. For this property PP shows a better performance. According to the ratio comparison, as showed in Figure 3.3, T1 (60% polymer/40% sawdust), T2 (70% polymer/30% sawdust) and T3 (80% polymer/20% sawdust) are not significantly different.


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Table 3.4 - Analysis of Variance to flexion - Sum of square Type III


square Coefficient-

F P-Valor

EFECT A:polymers 23310.5 1 23310.5 607.8 0.0000 B:ratios 25.3424 2 12.6712 0.33 0.7216 Residue 997.155 26 38.3521 TOTAL (CORRECTED) 24333.0 29

Figure 3.3 - Flexion Test.

Conclusions With respect to the recycled plastic type it can be concluded that polypropylene (PP) presented a better performance in relation to the polyethylene. The ratio T3 (80% of recycled polymer and 20% of sawdust by weight) showed a better performance for manufacturing pallets components. To manufacturing pallet boards, which is a piece that needs to bear loads and presents some flexibility, can be concluded that the ratios studied in this work did not interfere in the bending property. The recycled polypropylene (PP) was more suitable for this application. For the next steps, an assessment of accelerated aging and natural decay is necessary to verify the composite performance in relation to conventional wood pieces. Biodegradability test, mainly fungi resistance, is also an important point to consider. The development and use of other types of recycled plastic is also an important point for reducing the cost of products.


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References

Camargo, A. S. 2006. Compósito de polipropileno reforçado com farinha de madeira para aplicações em produtos moldados por injeção. Itatiba, SP.

Omega, C. 2007. Perfiles Extruídos de Madera Plástico. Santiago, Chile. http://www.corfo.cl/rps_corfo_v57/OpenSite/Corfo/Centro%20de%20. Documentación/Estudios/Estudios_doc/Estudio_Perfiles_Extruidos_Madera_Plástico01.pdf

Santos, D. G. 1998. Efeito do uso de compatibilizante no processamento e produção de fios da blenda PET/PP.Campinas, SP.

Bolsoni, E.2001. Estuda da Reprocessabilidade do polietileno de baixa densidade.Campinas, SP.

Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material. Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,Forest Products Laboratory. 463 p.

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Wood-plastic composite