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High Performance Polyolefin - Wood Fiber Composites
HIGH PERFORMANCE POLYOLEFIN - WOOD FIBER COMPOSITES
M.-T. Ton-That1, J. Denault2, F. Perrin3, and K. C. Cole4
Industrial Materials Institute, National Research Council Canada, 75 bd de Mortagne, Boucherville, Quebec, Canada
J4B 6Y4 – 1*Minh-Tan.Ton-That@cnrc-nrc.gc.ca; 2Johanne.Denault@cnrc-nrc.gc.ca; 3
Florence.Perrin@cnrc-nrc.gc.ca; 4Kenneth.Cole@cnrc-nrc.gc.ca
Abstract - In this work, wood fiber composites based on neat and recycled polypropylene (PP) were fabricated by melt processing. Different formulations involving various reinforcement contents, different types of coupling agents, different types of reactive additives, and an impact modifier were developed. The reinforcements were in the form of wood sawdust and shavings. The samples were prepared by extrusion followed by injection molding. The tensile, flexural and impact performance were characterized and all composites showed superior mechanical properties when compared with the pristine matrix. The mechanical performance of the wood composites was also evaluated before and after conditioning in water for 1 and 7 days. Results indicate that the composites resist humidity very well. The results also demonstrate the effect of formulations on the performance of the recycled composites.
Introduction
Although the pioneering work in wood-filled thermoplastic composites was done in the 1970s [1-3], they are still undergoing substantial development even today. Wood plastic composites are gaining market share because of their advantages over wood and metal in terms of longevity, appearance, life-cycle cost, and value. They are attractive, insect- and rot-resistant, and paintable, while they can be made to have a wood look. In addition, they are stiffer and cheaper than plastic products while at the same time they can be worked, cut, glued and fastened with the same screws or nails as wood.
At this stage in the technology, the processing of wood thermoplastic composites has been well explored. However it is essential that the wood reinforcement be dried well before compounding with the polymer matrix in order to avoid degradation and formation of bubbles/voids. Several different approaches have been developed to meet this requirement but each of them poses different challenges. A sound approach using chemical principles to resolve the drying problem and improve the wood composite performance was developed by Got et al. [4]. In general, the humidity and wood acidity are absorbed/neutralized with/by basic oxides, such as CaO, during processing. As a result no drying of wood is required and degradation is limited. However, according to the authors the amount of calcium oxide must be carefully calculated so that the water of the wood cellulose filler becomes finally 2-5% by weight, otherwise the composites will become very sensitive to humidity. Since humidity in wood varies from one location to another, the method disclosed in this patent is difficult to apply as the correct humidity of the wood is not always easy to
determine. In addition, the use of CaO requires surface treatment of the CaO. This paper presents a method to overcome wood humidity and improve the mechanical properties of the wood composites in which the basic oxide filler is used without surface treatment.
Experimental
Two reground recycled polypropylenes PP1 and PP2 were obtained from Novoplas (Quebec, Canada). Virgin PP6100 SM (PP-a) was supplied by Montell. High melt flow index PP (PP-b) was provided by Unicolor (Quebec, Canada). Coupling agents (CA) based on maleic anhydride (MA) grafted polypro-pylene, such as Epolene-43 (E43) (Mn = 9,100; ~ 4.81 wt% of MA), Epolene-3015 (E3015) (Mn = 47,000; ~ 1.31 wt% of MA), and Epolene-3003 (E3003) (Mn = 52,000; ~ 0.71 wt% of MA), all from Eastman Chemicals, were used in this study. Different spruce sawdusts (<2% moisture) were provided by JER Envirotech (Canada). Calcium oxide CaO and aluminum oxide were supplied by C. P. Hall Company and Malakof Industries Inc. respectively.
The composites were prepared by a twin-screw Extrusion Spec W&P 30 mm having L/D = 40, speed = 150-175 rpm, Tmax = 185°C. Samples were molded by injection at T = 200°C. All samples contained 40 wt% wood particles and 2 wt% coupling agent.
Tensile properties and un-notched Izod impact resistance were measured according to ASTM D638 and ASTM D256, respectively.
Results and Discussion
The effect of the coupling agent chemistry (molecular weight and grafting amount) on the formulation was
examined. As indicated in Figure 1, in the absence of CaO, E3015 provides greater strength but lower modulus. This can be explained by the fact that E3015 has higher molecular weight, which allows better compatibility with the PP matrix. In the presence of CaO, E43 gives better performance than E3015. E43, which has a high amount of grafting, should allow better interaction with the wood particles and the CaO. The negative effect of the low molecular weight of E43 can be significantly reduced by the reaction between CaO and E43. Thus, all lead to a better improvement in interface and dispersion. Figure 2 shows that E3015 provides better ductility and toughness as a result of its higher molecular weight compared to E43. However, with the incorporation of CaO, ductility and toughness of samples formulated with E3015 were reduced, while those of samples formulated with E43 increased (due to a better chance for chemical reaction between E43 and CaO). At 10 wt% CaO, there is no difference in ductility and toughness between the two formulations.
15 20 25 30 35 40
Fig. 1. Tensile properties of the wood composites with
different compatibilizers.
Fig. 2. Ductility and impact resistance of the wood
composites with different compatibilizers. The effect of the PP type on the formulation was also studied. Figure 3 shows the tensile properties of the composites prepared from recycled PP1, recycled PP2, and pure PP Profax 1274. The positive effect of CaO in the mechanical performance of the wood composites was again confirmed in all three PP matrices.
Fig. 3. Tensile properties of the wood composites with
different PP matrices.
Conclusion
The results show that the presence of basic oxides combined with coupling agent significantly improves the mechanical performance of the wood composites. These oxides absorb the humidity and neutralize the acidity of the wood reinforcement, thus limiting the degradation during compounding. The short-chain coupling agent MAgPP E43 provides a better advantage since it has a higher mobility to impregnate the wood particle surface. The loss in mechanical properties resulting from the short-chain molecules of E43 is limited by the presence of basic oxide fillers. Besides the reinforcing effect, these fillers can react with the MA group of E43 to increase the effective molecular weight of the E43, thus improving the composite performance.
Acknowledgements
The supply of wood fillers by JER Envirotech (Canada) for this project is highly appreciated.
References
1. T. Laufenberg, The Future of Recycled Material Usage in Building Applications: Summary of Conference Viewpoints, Proceedings of the
Conference on The Use of Recycled Wood and
Paper in Building Applications, Madison,
Wisconsin, USA, September 1996, p.155.
2. Wood Handbook - Wood as an Engineering Material, Forest Products Laboratory, Gen. Tech. Rep. FPL-GTR-113, Madison, WI, US Depart-ment of Agriculture, Forest Service, 1999.
3. T. M. Maloney, Terminology and Products Definitions - A Suggested Approach to Uniformity Worldwide, Proceedings of the 18th International
Union of Forest Research Organization World
Congress, Ljubljana, Yugoslavia, September 1986.
4. F. Got, Y. Kasahara, and T. Ishiura, U. S. Patent 6066278, 2000. 1 3 5 7 9 0 - E43 5% CaO - E43 10% CaO - E43 0 - E3015 5% CaO - E3015 10% CaO - E3 015 Str a in at b reak (%) 5 9 13 17 Im p act str e ngth (kJ/m 2) Strain Impact 40wt% sawdust Recycled P R P P-1
10% CaOecylced PP-210% CaOrofax 127410% CaO
Te ns il e st re n gth (MPa ) 1000 2000 3000 4000 5000 6000 Te ns il e m od ulus (MPa ) 40wt% sawdust Strength Modulus 25 27 29 31 33 35 37 39 0 - E43 5% CaO E43 10% CaO - E43 0 - E3015 5% CaO E3015 10% CaO - E3015 T e ns il e s tr e ng th (M Pa ) 3000 3500 4000 4500 5000 5500 Tensile mo dulus ( M P a ) Strength Modulus 40wt% sawdust
