Progress 11/01/01 to 10/31/05
Outputs
Investigations in our lab indicated that co-steam exploding wood chips and plastic produced a mulch that has excellent fiber-to-plastic interfacial properties. In addition, we have shown that this fiber mulch can be used to produce panels using compression molding without the addition of compatibilizers or binders. Our studies indicate that steam explosion can increase interfiber bonding and reduce internal voids in composite products. Binderless boards using steam exploded natural fibers have also been produced.
Impacts
Utilization of steam explosion pre-processing improves conversion efficiency by increasing the range of usable raw materials. Utilization of the resulting mulch for fabrication of composite boards results in biodegradable products from a renewable resource. Thermoplastic composites such as those we have crafted are also recyclable through melting and reforming. Product properties are generally as good as, or in some cases, better than traditional products. They offer improved flexural and yield strength, which has allowed natural fiber plastic composites to be competitive with more traditional products. Binderless wood fiber composites from steam exploded fibers have been shown to have greater dimensional stability than conventional materials. Recycling of wood waste and mixing these with plastics by fiberization and thermal molding promises to improve the sustainability of agricultural resources and to extend the use of renewable materials. By producing a natural
fiber for a binderless fiber-plastic composite for the ever-increasing market, the limitation related to interaction is removed. Through utilization of co-steam explosion, we will improve the interaction properties of natural fibers while simultaneously fiberizing the material. This is an important and cost-efficient step toward recycling, recovery, and production of bio-based industrial products.
Publications
- Renneckar, S., R.K. Johnson, A. Zink-Sharp, N. Sun, and W.G. Glasser. 2005. 13C NMR and dynamic mechanical analysis of co-refined wood and polypropylene. Composite Interfaces. 12(6):559-580.
- Renneckar, S., A. Zink-Sharp, A. Esker, and W.G. Glasser. 2005. Novel Methods for Interfacial Modification of Cellulose Reinforced Composites. In: Cellulose Nanocomposites: Processing, Characterization, and Properties. K. Oksman and M. Sain, Eds. ACS Symposium Series. American Chemical Society. Washington, DC.
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Progress 10/01/03 to 09/30/04
Outputs
Our research goals are to characterize a process that combines wood and plastic waste into binderless composites using steam explosion for fiberization and modification. Steam explosion is a process that creates a fibrous mulch from woody materials through a combination of thermochemical and mechanical action. Our previous work has confirmed that steam explosion is a viable method to refine wood chips and plastics into a uniform material that can either be compression molded or used in a random wetlay process to form composite materials. Recently we have established that improvements can be made to steam explosion technology, and determined optimal material formulations for interfacial bonding, the single physiochemical phenomenon that most researchers working in the arena are striving to achieve. Oak wood chips were steam exploded in the presence of commercial plastics and regenerated cellulose fiber (lyocell). Through extensive testing, optimum conditions were
determined for steam explosion parameters. For microscopy, the plastic materials were tagged with substances easily recognized in appropriate optical and analytical methods. A variety of analytical techniques were used to examine the steam exploded materials, the initial components, and compression molded composites. Mechanical and sorption studies of compression molded composites were completed. We have found evidence through FT-IR spectroscopy of extractions that co-steam explosion does not change the chemical makeup of extracted wood components (hemicellulose and lignin). However, the chemical makeup of the polypropylene was changed slightly with lignin-like components. Lignin present within the polyolefin after alkali extraction of the xylene filtrate suggests a free radical mechanism in the modification of the wood fiber surface. Through this project we have contributed a method for determining the amount of thermoplastic by weight associated with the thermoplastic in the
mixture. We can also conclude that a uniformly distributed modified wood fiber can be created if a high melt flow index plastic is used in the steam explosion process. Initial tests show that using short lyocell fibers and steam exploded wood fiber in a polypropylene matrix have superior modulus and strength properties.
Impacts
Recent research indicates that the combined North American and European market for natural and wood fiber plastic composites was 1.5 billion pounds in 2002 and was valued at $775 million. Not only is there a large and growing market for wood fiber plastic composites, we are producing binderless panels from waste materials. Creating structural panels with binder (adhesives and compatibizers) is the single physiochemical phenomenon that most researchers working in this research area are striving to achieve. Wood fiber plastic composites increase the efficiency of production by reducing waste and increasing the range of usable raw materials. Properties are generally better than traditional products, which has allowed wood fiber plastic composites to be competitive and successful. Investigating wood fiber plastic composites through steam explosion has resulted in significant scientific and technological advancements.
Publications
- Renneckar, S., A. Zink-Sharp, T.C. Ward, and W.G. Glasser. 2004. Compositional Analysis of Thermoplastic Wood Composites by TGA. Journal of Applied Polymer Science. 93(3):1484-92.
- Renneckar, Scott, H. 2004. Modification of Wood and Cellulose Fiber Surfaces with Thermo-plastics by Steam-Explosion. Ph.D. dissertation, Virginia Polytechnic Institute and State University, Blacksburg, VA.
- Johnson, Richard, K. 2004. Wetlaid Cellulose Fiber-Thermoplastic Hybrid Composites - Effects of Lyocell and Steam-Exploded Wood Fiber Blends. M.S. Thesis Virginia Polytechnic Institute and State University, Blacksburg, VA.
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Progress 10/01/02 to 09/30/03
Outputs
Wood-chips and virgin plastic, polyethylene and polypropylene (common thermoplastics in wood-filled thermoplastic composites), were co-refined by steam-explosion. Plastic form (powder, pellets, fibers), quantity, and melt flow index were varied along with reactivity of the atmosphere. The underlying factor to create well-dispersed wood fiber -plastic mixture was using high melt flow index plastics regardless of the form. We have established a method to determine the amount of thermoplastic (by weight) associated with the thermoplastic. The method incorporated analysis of the first derivative of the thermogravimetric curve. This method shows that the thermoplastic associated with wood fiber after steam-explosion is approximate to the original thermoplastic loading. With the use of Fourier Transform infrared (FT-IR) spectroscopy it was found that co-steam-exploded fibers show evidence of polyethylene and polypropylene. Water sorption kinetics indicate initial sorption
rate for the co-steam-exploded material is the same as the steam-exploded wood fibers when it is normalized by the amount of wood fiber present. Hemicelluloses, lignin, and polyolefin were fractionated in a step-wise process for further analysis with microscopy, spectroscopy and thermal analysis methods to understand fundamental changes in the materials. FT-IR spectroscopy indicated that the co-steam-explosion does not change the chemical make-up of extracted wood components (hemicellulose and lignin). However, the chemical makeup of the polypropylene was changed slightly with lignin like components. We have also labeled maleated polyethylene with a fluorescent dye for use within the confocal laser scanning microscope. Work has entailed trying to minimize the autofluorescence from the steam-exploded fiber in order to visualize the fluorescent labeled polyolefin. This problem is currently unresolved. However, a regenerated cellulose fiber was co-steam-exploded with the tagged
polyolefin for use in the confocal laser scanning microscope. Because of the homogenous surface of the cellulose fiber the polyolefin was resolved. We have also viewed the co-steam-exploded fiber with an FT-IR microscope. This microscope shows the spatial arrangement of specific chemical groups of the co-steam-exploded material. Band intensity ratios of the fiber surface suggest that there is plastic spread across the fiber surface. We have also investigated the mechanical and sorption properties of natural fiber reinforced polypropylene composites. Two natural short fiber types, namely steam exploded wood and lyocell, are used as reinforcements in virgin polypropylene. Previous work on the use of steam exploded wood and continuous lyo fibers as reinforcements in cellulose acetate butyrate matrix showed promising results. The present investigation evaluates the effect of short natural fibers, used individually and in various combinations on the mechanical, thermomechanical and
sorption properties of fiber reinforced polypropylene composites.
Impacts
This research has shown that co-steam-explosion is a viable method to refine wood and plastic to a uniform material that can either be compression molded or used in a random wet-lay process to form composite materials. The co-steam-explosion process has the potential to make new materials from recycled wooden pallets and plastic waste. This research shows that a uniformly distributed modified wood fiber can be created if a high melt flow index plastic is used in the steam-explosion process. This research is expected to introduce new short fiber reinforced plastic composites, particularly with the combination of chopped lyocell and steam exploded wood fibers in a synthetic thermoplastic. Results of mechanical properties tests of lyocell reinforced polypropylene without binder have shown substantial promise so far and it is anticipated that their combination with steam exploded wood will lead to considerably low cost composites with superior properties.
Publications
- Esker, A., Becker, U., Jamin, S., Beppu, S., Renneckar S., and Glasser, W.G. 2003. Self-Assembly Behavior of Some Co-and Hetero-Polysaccharides Related to Hemicelluloses. In Hemicelluloses: Science and Technology; Gatenholm, P. and Tenkanen, M., Eds.; ACS Symposium Series 864. American Chemical Society, Washington DC, pg. 198-219.
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Progress 10/01/01 to 09/30/02
Outputs
The surface modification for improved interaction with thermoplastic polymers has been studied using steam explosion in the presence of polyethylene. A 3.8 liter (one-gallon) experimental steam exploder has been assembled and tested which consists of a multi-speed auger-type stirring mechanism, a port to control the atmosphere prior to steam-explosion, and heater coils surrounding the pressure vessel. The steam-exploder is connected to a boiler that has an upper temperature limit of approximately 237C. The resulting fibers were characterized by thermal analysis, optical and electron microscopic techniques as well as by IR mapping. The results suggest the creation of a polymer coating on the wood fiber surface. The surface modification was evaluated by a modified thermogravimetric analysis (TGA) technique that assays the moisture pick up during exposure to water vapor. Moisture gain and the rate of moisture gain varied significantly with polymer presence. FT-IR
spectroscopy revealed chemical changes of the steam-exploded material that was reflected in the sorption study. For the co-steam-exploded wood and polyethylene there was a reduction of hydroxyl absorption and an increase in methylene absorption. This means the surface is less polar reducing interactions with water. Future experiments will incorporate varying the reactivity of the atmosphere in the vessel prior to the induction of steam to control the degree of fiber modification. In addition, confocal laser scanning microscopy will be applied to locate and characterize the assembly of the thermoplastic on the fiber surface.
Impacts
Improvements in the interfacial adhesion of wood fiber-plastic composites have enormous implications. The 181,437 metric ton market for fiber-reinforced composites could possibly be elevated to a much higher level if long term stability and rheological properties of these composites could be improved significantly. Such improvements are being observed in our project. Already, binderless wood fiber composites from steam exploded fibers have been shown to have greater dimensional stability than conventional materials. Recycling of wood, wood waste, and mixtures of wood and plastic film, by fiberization and thermal moulding promises to improve the sustainability of renewable resources and to extend the use of renewable materials. We will improve the interaction properties of wood fibers at the same time as we fiberize the wood. This is an important and cost-efficient step toward recycling. Now, not only virgin wood fiber can be used, but also recycled wood and plastic
that ordinarily would be headed for the landfill will be utilized in products.
Publications
- Seavey, K. C., I. Ghosh, R. M. Davis, and W. G. Glasser. 2001. Continuous Cellulose Fiber-Reinforced Cellulose Ester Composites. I. Manufacturing Options. Cellulose 8(2), 149-159.
- Seavey, K. C., and W. G. Glasser. 2001. Continuous Cellulose Fiber-Reinforced Cellulose Ester Composites.II. Surface Modification and Consolidation Conditions. Cellulose 8(2), 161-169.
- Franko, A., Seavey, K. C., and W. G. Glasser. 2001. Continuous Cellulose Fiber-Reinforced Cellulose Ester Composites. III. Commercial Matrix and Fiber Options. Cellulose 8(2), 171-179.
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