Progress 10/01/02 to 09/30/06
Outputs
The objective of this year project was to use cold plasma technique to entrap poly(acrylic acid) (PAAc) into cellulose structure (Whatman filter paper) for the generation of novel composite materials with applications in the area of heavy metal removal from water. Generation of entrapped PAAc and poly(4-vinyl pyridine) (PVP) macromolecular complex structures (salts) has also been evaluated. One of the prevalent contaminates in our water supply are metal ions that come from a wide variety of sources including abandoned hard rock and coal mines, highways and large parking lot runoff, and natural erosion of minerals. Most methods to remove metal ions from solution are expensive. It has been shown, however, that cellulose, wood and bark are somewhat effective in removing metal ions from water. Cellulose can also be modified, greatly increasing its metal ion sorption capacity. Whatman filter (pure cellulose) paper along with 25% PAAc solution (Mw= 240,000) and poly PVP (Mw=
60,000) were used for the generation of composites. PAAc was transferred into the cellulose structure using a water based solution and entrapped by heat and/or argon non-equilibrium, low pressure plasma treatment. The PAAc/PVP macromolecular complex formation was accomplished exposing the PAAc structure entrapped ito the cellulose network, to a PVP solution. All RF-plasma treatments were performed in a capacitive coupled; 45 KHz plasma reactor. The copper ion concentrations were analyzed using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP). Plasma parameters used for the experiments were: Power: 200 W; Plasma gases: Argon; Samples: Whatman filter paper soaked in PAA and Whatman filter paper soaked in PVP; Plasma treatment times: 5, 10 and 15 minutes; Base pressure: 50 mTorr; Pressure in absence of plasma: 200 mTorr; Pressure with plasma: 204 mTorr. The noncompetitive adsorption of copper ions by cellulose/PAAc composites was investigated and demonstrated. Survey and
high resolution ESCA-data proved that both PAAc and PVP polymers were successfully retained in the cellulose network (Whatman filter paper) by covalent connection (ester bond formation), argon plasma-enhanced crosslinking-enhanced entrapment and ionic forces (PAAC/PVP complexes). ICP data collected from the modified cellulose samples show that the most efficient removal of copper ions from water were produced by the cellulosic substrates that incorporated PAAc macromolecules as result of the thermal treatment (50%) and those generated by a consecutive argon-plasma exposure (72 %). It was also found that PVP-containing samples exhibited a modes copper ion-removal (6%) process.
Impacts
The results of these investigations will open up novel ways for the non-equilibrium, low pressure plasma-enhanced synthesis of advanced natural products-based composite materials for the design and development of efficient filter systems for the removal of heavy metals from contaminated water.
Publications
- V. Totolin, S. Manolache, R.M. Rowell, and F.S. Denes, Removal of Cu+2 Ions from Solution Using Cellulose - Poly (acrylic acid) and Poly (4-vinyl) Pyridine Based Materials that were Deposited Using Plasma Technique, Journal of Natural Fibers, (Submitted: April 2006).
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Progress 01/01/05 to 12/31/05
Outputs
The objective of this year project was to use cold plasma technique to improve properties of phenolic-bonded aspen fiberboards. Medium density fiberboard is usually manufactured without any chemical or physical treatments to the fiber. However, it is possible to modify the fiber prior to board formation by heat, chemical and enzyme treatments to greatly improve performance of the finished product. Covalent bonding of desired functionalities to specific natural and synthetic substrate surfaces is a key element for the development of "within-interphase" molecular interaction, which is required for the preparation of advanced composites. Cold-plasma chemistry offers novel solutions, not only in the area of functionalization of even the most inert organic and inorganic polymeric substrates but it also opens up new routes for heterogeneous (solid/gas)-dry-chemistry mediated reaction mechanisms, by taking advantage of both the neutral and charged active species coexistent
in the discharge. Extractives on the surface of the fiber may influence fiber bonding so experiments have been done using both non-extracted and solvent extracted fibers. Aspen has a very low content of extractives; however, a part of its extractive components is located on the fiber surfaces, and due to the fact that plasma-enhanced modifications are par essence surface reaction mechanisms, the effect of these extractives on inter- and intra-fiber bonding was evaluated. The ultimate goal of cold plasma modification of fibers is to use this technology to bond fibers together without the use of any added adhesive. Board manufacture and testing were carried out at FPL-Madison according to standard procedures, and testing results were compared to control samples run in the absence of plasma treatment. All plasma-enhanced surface modification of aspen fibers were performed in an original, rotating, 13.56 MHz, low pressure, cylindrical, glass plasma reactor, and the ammonia- and
oxygen-plasma treatments of virgin and extracted aspen fiber samples have been successfully accomplished. Survey and high resolution ESCA and ATR-FTIR data resulting from non-modified and modified Aspen fiber surfaces indicate that regardless of the nature of the plasma gases additional oxygen-based polar functionalities were surface-implanted onto the discharge-exposed substrates. It was demonstrated that removing the extractives from the surface of aspen fibers results in a 20 percent decrease in the relative surface atomic carbon concentration and in a proportional increase in oxygen content, and that the influence of extractives on the cold-plasma treatment is significant. Thickness swelling of the non-extracted and extracted aspen fiberboards was decreased in the oxygen-plasma treated samples, while little effect was observed in the ammonia-plasma exposed boards. Oxygen plasma treatment of the non-extracted and extracted fiber resulted in the highest dry strength of the
fiberboards whereas O2 plasma treatment of the non-extracted fiber resulted in the highest wet strength. Ammonia-plasma treatment of the extracted aspen boards also resulted in a significant increase of the strength values.
Impacts
The results of these investigations will open up novel ways for the design and development of advanced natural products-based composite materials using plasma-derivatized renewable and biodegradable precursor components.
Publications
- V. Totolin, S. Manolache, R.M. Rowell, and F.S. Denes, Application of Cold Plasma to Improve Properties of Phenolic-Bonded Aspen Fiberboard, Journal of Natural Fibers, (Submitted: 2005).
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Progress 01/01/04 to 12/31/04
Outputs
Generation of wood fibers-based, biodegradable composite-materials, such as particle and fiber boards, using only disposable, cheap and renewable natural ingredients, is still a challenge for many science laboratories throughout the world. Our investigations target the design and development of cellulose fibers-based particle and fiber board composite materials with superior mechanical and reduced moisture absorption characteristics, using non-equilibrium RF-plasma surface-modified cellulose fibers and lignin particles. The plasma-functionalization of fibers and lignin particles was performed in an original, rotating, cylindrical plasma reactor. The semi-cylindrical electrodes are located outside and in the close vicinity of the glass reactor surface. Plasma-gases like argon, oxygen and ammonia were used for the implantation onto cellulose fiber and lignin particle surfaces of polar functionalities. The efficacy of formation of oxygen- and carbon-based polar
functionalities during ex situ reaction of argon-plasma-induced free radicals with oxygen and moisture under open laboratory conditions, is compared with the generation of similar surface groups resulting from oxygen-plasma-generated functionalities. It has been demonstrated earlier in C-PAM/BSE/UW laboratories that ammonia plasma environments mainly lead to the generation of imine groups due to the electron-impact-induced molecular fragmentation. This behavior is also in good agreement with bond energy values, and was also substantiated by molecular conformational, computer aided calculations that clearly suggest that plasma-mediated molecular fragmentation of ammonia result in addition to nitrogen atom-incorporation, mainly to the formation of imine charged and neutral particles. The nascent imine groups are instantly converted in the presence of moisture into carbonyl groups. Accordingly, RF plasma surface-modification experiments (treatment time: 5, 10, and 15 minutes, RF power:
100 W, pressure in the reactor: 200 - 300 mTorr) were carried out on cellulose fiber and lignin particle surfaces using, argon-, oxygen- and ammonia-RF plasma environments and fiber-board samples were prepared adapting well known, conventional hot-pressing technique at the Madison - Forest Products Laboratory facilities. Survey and high resolution XPS data and results from differential attenuated total reflectance, Fourier transform infra red spectroscopy (D-ATR-FTIR) evaluations indicate that all plasma treatments resulted in the formation of various surface densities of C=O and C-O-C functionalities, and smaller amounts of -COOH groups. The highest carbonyl-group concentrations in addition to nitrogen atom-incorporation are associated with the ammonia plasma. It has also been shown that plasma-modified-lignin-based composites might open up a novel way for the development of dimensionally stable board materials regardless of the relative humidity values of the surrounding
environments. Investigations are under way in our laboratories to understand the reaction mechanisms that can lead to the use of minimal amounts of plasma-modified lignin for the generation of the best quality fiber boards.
Impacts
Wood composite board materials are a very important part of the economy both in Wisconsin and the USA. Composite boards more efficiently utilize wood materials and are extensively employed in home construction. Methods to improve these boards and/or reduce the cost of the composite materials would improve profitablity and keep consumer costs low, thus aiding all segments of the society. An improved adhesive system as explored in this research would produce superior composite boards and a reduced price. The results of these investigations will open up novel highways for the design and development of advanced natural products-based composite materials using plasma-derivatized renewable and biodegradable precursor components.
Publications
- Denes, F. S., Cruz-Barba, L. E. and Manolache, S. 2005. Plasma Treatment of Wood, (Chapter 16), in: R. M. Rowell (Ed), Handbook of Wood Chemistry and Wood Composites. CRC Press. 447-473.
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Progress 01/01/03 to 12/31/03
Outputs
Wood-based composite materials, including particle boards and fiberboards, are produced from disintegrated waste-wood materials. The generation of high quality composite materials is strongly dependent on the adhesion between the wood substrate surfaces and the adhesive materials involved. The main objective of this research is to use a plasma-aided technology for modification of both wood and lignin-particle surfaces, and to generate specific surface functionalities that will enhance adhesion characteristics. Powdery lignin substrates were exposed separately both to argon and formaldehyde plasma environments in a rotating glass, plasma reactor (capacity of the reactor 1L :semi-cylindrical, outside electrodes; frequency of the driving field: 13.56 MHz; RF-power dissipated to the electrodes: 100 W; pressure in the reaction chamber: 200 mTorr; plasma-exposure time: 2 minutes) for the generation of active sites on the particle surfaces (free radicals and aldehyde
functionalities) and reacted under in situ conditions with epichlorohydrin (EC), and consecutively with ethylenediamine (EDA) using ex-situ reactions. The only slight surface modifications noted as a result of argon, formaldehyde, and EC surface-modification reactions (evidenced by survey and high resolution ESCA analysis can be attributed to the presence of similar chemical bonds both in the virgin and modified substrates and to the extremely high specific surface area of powdery lignin. However, the existence of nitrogen atoms in the discharge-generated surface layers of the lignin particles clearly could be identified. In order to enhance the sensitivity of surface-analytical measurements lignin pellets (diameter 13 mm; thickness: 1 mm) were prepared and plasma-treated using the parallel-plate installation, using experimental conditions similar to the surface modification of wood chips. This time, ESCA, Tollens, and fluorescamine-labeling tests exhibited the formation of the
desired functionalities. Wood chips were treated under formaldehyde-plasma environments (driving-field frequency: 40 kHz; RF-power dissipated to the electrodes: 50 W; pressure in the reaction chamber: 250 mTorr; base pressure: 50 mTorr) using a parallel plate, RF static, plasma reactor. It was assumed that the newly created aldehyde surface functionalities could mediate in the next step ex situ reactions that could render improved adhesion. Survey and high resolution ESCA data indicate the presence of C=O/ CH=O (288 eV) functionalities and the Tollens reaction test substantiates the fact that aldehyde groups or alpha-hydroxy-ketones are present on the plasma-modified wood-chip surfaces. Results from recent reactions performed on a higher-capacity (10 L) rotating, glass plasma reactor substantiate the conclusion that the clod plasma technique is an efficient approach for surface modification of lignin and wood substrates. Primary amine functionalities were introduced onto the lignin
particle surfaces and epichlorohydrine will be consecutively attached. Bisphenol-A-based composite materials will be prepared from the plasma-functionalized lignin.
Impacts
Wood composite board materials are a very important part of the economy both in Wisconsin and the USA. Composite boards more efficiently utilize wood materials and are extensively employed in home construction. Methods to improve these boards and/or reduce the cost of the composite materials would improve profitablity and keep consumer costs low, thus aiding all segments of the society. An improved adhesive system as explored in this research would produce superior composite boards and a reduced price.
Publications
- No publications reported this period
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