Progress 09/01/08 to 08/31/09
Outputs
OUTPUTS: There are potential environmental and economic advantages in making composites of microfibril cellulose (MFC) and starch. To investigate, starch-MFC films were produced from both cooked and uncooked starch (separately) and MFC. The properties of starch-MFC films were determined versus starch level with physical, thermal, mechanical, and optical analysis. A series of experiments were conducted to understand how the exchange of water with ethanol, used as a pore preserving step in making SMCF materials, affected the dimensional properties of the starch material during and after processing. SMCF were prepared from molded aquagels of cooked corn starch that were subjected to ethanol exchanges with different time intervals (6, 12, or 48 hrs) and number of exchanges (1, 2, or 3) and then air dried. To study the transformation of water-swollen starch into precipitated starch foam in ethanol, the volume of the starch material was measured in the wet state after each exchange and after final air drying. Sodium trimetaphosphate (STMP) has been commonly used to cross-link food grade starches via phosphorylation reaction. STMP is cited as an efficient cross-linking agent is a solid of low toxicity with no reports about the adverse effects on humans. A combination of substitution and cross-linking can provide stability against acid, thermal, and mechanical degradation of starch and delay retrogradation during storage. However, the conventional procedures of starch phosphate preparations are time-consuming and require many steps to achieve the desired degree of chemical bonding. The objective of this part of the work was to study and understand the mechanisms of starch phosphorylation and cross-linking by a one-step reaction and foam formation process of supercritical fluid extrusion (SCFX). Investigation of the effects of NaOH concentration and supercritical carbon dioxide (SC-CO2) injection on the physicochemical and morphological characteristics as well as the 31P NMR spectroscopy of extruded starch phosphates was the main focus of this part of the study. Starch blend comprising (by weight) 40% native and 60% pre-gelatinized wheat starch was mixed with 9% (starch basis) STMP at ambient temperature and extruded at 60-70 deg C with 0.1 M (pH 8.0) or 0.2 M (pH 11.0) NaOH solution and 0-1.5% (dry feed) SC-CO2. In-barrel moisture content was maintained at 55% (dry feed) and the average specific mechanical energy (SME) input for the process was 50 kJ/ kg. Physicochemical and morphological characteristics of extruded starch phosphates were evaluated and compared with unextruded and extruded starch controls. Paper materials were produced with SMCF based particles as well as with conventional calcium carbonate as a filler and the mechanical and optical properties tests versus filler level. Also, starch particles were produced by impinging a jet of starch solution into an ethanol bath and the particles evaluated with scanning electron microscopy. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The cooked starch-MFC composite films showed higher density, stronger tensile strength, lower moister content, lower brightness, and lower opacity with increased starch level. The uncooked starch composites showed the opposite trend with starch level. The uncooked starch material had inferior mechanical properties and superior optical properties relative to the cooked starch composites. High contact angles near 80 degrees and high water repellency were obtained by adding high levels of cooked starch, due to the type of starch, a very inexpensive commercial starch used for sizing paper. Dimensional changes that occur in swollen starch aquagels as water is replaced by ethanol are critical. As water is replaced by ethanol, it was observed that the starch material contracted with the greatest contraction during the first ethanol exchange. The contraction during air drying decreased with decreased water content just before air drying, presumably due to less pore collapse of the stiffer cell walls on drying. Interestingly, the minimum density of 0.37 g/cc SMCF was for the 12 hour exchange time, not the longest exchange time. Evidence of a skin-core morphology included SEM images as well as dimensional instability data on dried samples. The results indicate that SMCF of low density with fewer tendencies to deform during drying does not necessarily require extremely long exchange times. For starch phosphorylation and cross-linking by a one-step extrusion and reaction process (SCFX), the degree of substitution (DS=0.05) and phosphorus content (P=0.92%) was highest with 0.2 M NaOH, indicating the highest level of cross-linking. Cross-linking of starch at the highest pH was evidenced by lower water solubility and 31P NMR spectroscopy results. Introduction of phosphate cross-links into the starch restricted the molecular structure mobility, leading to an increase in the gelatinization temperature (by up to 8 deg C). SC-CO2-based expansion provided light weight materials having the density in the range we previously reported for starch foams. Incorporation of 1.5 % (db) SC-CO2 yielded the highest cross-linked starch foam expansion with microporous structure. SEM images indicate that large pores were found in the center of the extrudates, whereas the smaller pores tended to be toward the edge of the extrudates. Paper products produced with starch filler exhibited about a 10% increase in mechanical properties relative to the same paper with equal amounts of calcium carbonate filler. The brightness of the starch filled paper decreased about 2 % points and the opacity decreased about 8% points relative to calcium carbonate filled paper. It was determined that impinging a jet of cooked starch solution from a fine nozzle into an ethanol bath with modest processing conditions could produce starch particles. The particles were similar in size as the uncooked starch granules. The particles had a surface morphology different than the original starch granules, but did not reveal a well-developed SMCF morphology. To develop a SMCF morphology, increased cooking time or temperature is required.
Publications
- Patel, S. V., Venditti, R. A., Pawlak, J. J., 2009, The Effect of Processing Conditions and Composition on Starch Microcellular Foam Properties. (Master of Science Thesis Under the direction of Richard A. Venditti and Joel J. Pawlak), North Carolina State University, Raleigh NC.
- Patel, S. V., Venditti, R. A., Pawlak, J. J., 2009, Dimensional Changes of Starch microcellular foam During the Exchange of Water with Ethanol, Bioresources, 5(1), 121-134, 2010.
- Ayoub, A., Rizvi, S. S., 2008, An overview of the technology of crosslinking of starch for non-food applications. Journal of Plastic Film and Sheeting, 25(1), 25-45, 2009.
- Patel, S., Venditti, R. A., Pawlak, J. J., Ayoub, A., Rizvi, S. S., 2008, Development of cross-linked starch microcellular foam by solvent exchange and reactive supercritical fluid extrusion, J. Appl. Polymer Science, 111(6), 2917-2929, 2009.
- Ayoub, A., Rizvi, S. S., 2008, Properties of supercritical fluid extrusion-based crosslinked starch extrudates , 107(6), 3663-3671, 2008.
- Patel, S., Venditti, R. A., Pawlak, J. J., Ayoub, A., Rizvi, S. S., 2009, Effects of processing conditions on starch microcellular foams produced by reactive supercritical fluid extrusion and solvent exchange, 237th ACS National Meeting, Salt Lake City, UT, March 22-26, 2009.
- Ayoub, A., Rizvi, S. S., 2009, Novel environmental friendly process to produce a family of moisture resistant starch based microcellular foams. In: Polysaccharides As a Source of Advanced Materials. Abo/Turku, Finland, September 21-24th 2009.
- Ayoub, A., Rizvi, S. S., 2010, Development of moisture resistant starch-based foams by supercritical fluid extrusion and their characterization. Journal of Applied Polymer Science, in preparation.
- Manoi, K., Rizvi, S. S., 2010, Physicochemical characteristics of phosphorylated cross-linked starch produced by reactive supercritical fluid extrusion. Carbohydrate Polymers, in preparation.
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Progress 09/01/05 to 08/31/09
Outputs
OUTPUTS: In order to meet the objectives and goal, extensive experiments, analysis of the results, and modeling of SMCF materials have been performed. The results have been disseminated in peer-reviewed research journals and at technical conferences at the regional, national and international scale. Some of the activities are described here. For each exercise the products were analyzed for chemical, physical and structural properties. Numbers in front of the activity indicate the year followed by the activity number. 1.1 Starch microcellular foam was produced by supercritical fluid extrusion (SCFX) using native and pre-gelatinized starch mixtures. The starch solution was reacted with epichlorohydrin in a twin-screw extruder in the presence of supercritical carbon dioxide. 1.2 A native corn cooked starch solution was reacted with glutaraldehyde crosslinker and precipitated under shear with ethanol to produce particles. 1.3 SMCF particles (solvent exchange) were produced with Alkyl Ketene Dimer (AKD) wax at different levels by both coating and blending in order to understand if the AKD could impart water resistance to the particles. 2.1 An emulsion of AKD and cooked corn starch was made by mixing AKD with cooked starch and the effects of reaction temperature, starch concentration and pH on the reaction of AKD with starch was determined. 2.2 Starch aquagels were formed by conventional molding and also by an extrusion process. These materials were then solvent exchanged with ethanol under different conditions and dried. Three types of extruded samples were made: (1) extruded starch, (2) extruded starch with crosslinker, and (3) extruded starch with crosslinker and CO2. 3.1 The application of alkyl ketene dimer (AKD) (a sizing agent used to impart hydrophobicity) and polyamide-epichlorohydrin (a crosslinker) to starch in order to develop a hydrophobic SMCF material were explored. 3.2 An alternative system for crosslinking and imparting hydrophobicity was evaluated with an epichlorohydrin crosslinked (EPI) and acetylated (Ac) starch in one continuous supercritical fluid extrusion (SCFX) process. 3.3 SMCF-Wood Fiber composites were created from solvent exchanged aquagels and were heated in a nitrogen atmosphere to form carbon foam structures. 4.1 Composites of microfibril cellulose (MFC) and cooked starch were produced. 4.2 The solvent exchange process effect on the dimensions of starch materials was performed with dimensional measurements made during ethanol exchange processes. 4.3 Starch microcellular foam (SMCF) particles from starch blended with AKD materials was incorporated into paper and the properties of the paper determined. 4.4 Production of SMCF particles with an atomizer was performed. 4.5 A study of starch phosphorylation and cross-linking by a one-step reaction and foam formation process of supercritical fluid extrusion was performed. The use of an extruder as a chemical reactor offers a larger operational flexibility as a result of the broad range of processing conditions in pressure, shear and temperature, the possibility of multiple injection, controlled residence time, and degree of cross-linking. PARTICIPANTS: This project was a collaboration between investigators Venditti and Pawlak at North Carolina State University and collaborator Rizvi at Cornell University. At North Carolina State University post-doctoral students (El-tahlawy and Lee), graduate students (Patel) and undergraduates (Bolivar, Rutledge, Cibils) worked on the project. At Cornell, post-doctoral research students (Ayoub and Manoi) participated. TARGET AUDIENCES: This project should impact scientists in the field of carbohydrate materials and foams. Applications of the findings may impact the paper, coatings, pigments, and polymer industries. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Overall, this research has provided a better understanding of the relationships between the composition, the processing, the final structure, and the properties of the resulting SMCF materials. Several novel methods and compositions to produce SMCF materials with a variety of properties have been developed. Structural features of the SMCF materials may be controlled by the concentration of crosslinker. Increased crosslinker concentration decreases pore size and decreases particle size when particles are being formed. Increases in crosslinker also decrease the diffusion of water in the SMCF and the equilibrium water content. These crosslinkers can include glutaraldehyde, epichlorohydrin, sodium trimetaphosphate, and Kymene. The addition of low concentrations of waxes (alkyl ketene dimer) increases the water resistance significantly. Particles of high brightness up to 93% ISO can be produced. It has been determined that the method of cooking, method of molding or extrusion, and the method of solvent exchange can significantly impact structure and properties. The addition of acetic anhydride can impact the water resistance of starch foams significantly and indicates that the combination of acetylation and crosslinking (EPI-Ac) is a method to produce solid foam reactively in one step when combined with supercritical fluid extrusion. SMCF-Wood Fiber composites were created from solvent exchanged aquagels. Higher amylose content starches and fiber contents of up to 4% improved the processability of the foam. Heating the SMCF-fiber in a nitrogen atmosphere to temperatures between 350-700 deg C produced carbon foams with a three-dimensional closed cell foam structure with cell diameters around 50 microns and pore walls around 1-3 microns and a water contact angle of 115 degrees. Cooked starch-microfibrillar cellulose (MFC) composite films showed higher density, stronger tensile strength, lower moisture content, lower brightness, and lower opacity as the added starch level increased. The uncooked starch composites showed the opposite trends with starch level. High contact angles near 80 degrees and high water repellency were obtained by utilizing an inexpensive commercial starch used for sizing paper. Dimensional changes that occur as water is replaced by ethanol are critical. As water is replaced by ethanol, the starch material contracts, with the greatest contraction during the first ethanol exchange. The contraction during air drying decreased with decreased starch water content just before air drying, presumably due to less pore collapse of the stiffer cell walls on drying. Evidence of a skin-core morphology included SEM images as well as dimensional instability data on dried samples. The results indicate that SMCF of low density with fewer tendencies to deform during drying does not necessarily require extremely long exchange times. Paper products with starch filler show about a 10% increase in mechanical properties but lower optical properties relative to the same paper with equal amounts of calcium carbonate filler.
Publications
- Patel, S. V., Venditti, R. A., Pawlak, J. J., 2010, Dimensional Changes of Starch microcellular foam During the Exchange of Water with Ethanol, Bioresources, 5(1), 121-134.
- Ayoub, A., Rizvi, S. S., 2010, Development of moisture resistant starch-based foams by supercritical fluid extrusion and their characterization. Journal of Applied Polymer Science, in preparation.
- Manoi, K., Rizvi, S. S., 2010, Physicochemical characteristics of phosphorylated cross-linked starch produced by reactive supercritical fluid extrusion. Carbohydrate Polymers, in preparation.
- Patel, S. V., Venditti, R. A., Pawlak, J. J., 2009, The Effect of Processing Conditions and Composition on Starch Microcellular Foam Properties. (Master of Science Thesis Under the direction of Richard A. Venditti and Joel J. Pawlak), North Carolina State University, Raleigh, NC.
- Ayoub, A., Rizvi, S. S., 2009, Novel environmental friendly process to produce a family of moisture resistant starch based microcellular foams. In: Polysaccharides As a Source of Advanced Materials. Abo/Turku, Finland, September 21-24th 2009.
- Ayoub, A., Rizvi, S. S., 2009, An overview of the technology of crosslinking of starch for non-food applications. Journal of Plastic Film and Sheeting, 25(1), 25-45.
- Patel, S., Venditti, R. A., Pawlak, J. J., Ayoub, A., Rizvi, S. S., 2009, Effects of processing conditions on starch microcellular foams produced by reactive supercritical fluid extrusion and solvent exchange, 237th ACS National Meeting, Salt Lake City, UT, March 22-26, 2009.
- Patel, S., Venditti, R. A., Pawlak, J. J., Ayoub, A., Rizvi, S. S., 2009, Development of cross-linked starch microcellular foam by solvent exchange and reactive supercritical fluid extrusion, J. Appl. Polymer Science, 111(6), 2917-2929.
- Patel, S., Venditti, R. A., Pawlak, J. J., Ayoub, A., Rizvi, S. S., 2009, Effects of processing conditions on starch microcellular foams produced by reactive supercritical fluid extrusion and solvent exchange, 237th ACS National Meeting, Salt Lake City, UT, March 22-26, 2009.
- Ayoub, A., Rizvi, S. S., 2008, Properties of supercritical fluid extrusion-based crosslinked starch extrudates , J. Appl. Polymer Science, 107(6), 3663-3671.
- El-Tahlawy, K., Venditti, R. A., Pawlak, J. J., 2008. Effect of the Reaction Conditions During Modification of Starch with Alkyl Ketene Dimer on the Properties of Starch Microcellular Foam, Carbohydrate Polymers, 73, 133-142.
- Rutledge, A., Venditti, R. A., Pawlak, J. J., Patel, S., Cibils, J., 2008, Carbonized Starch Microcellular Foam-Cellulose Fiber Composite Structures, BioResources, 3(4) 1063-1080.
- Venditti, R. A., Pawlak, J. J., Rutledge, A., Cibils, J., 2008, Cellulose fibers and microcellular foam starch composites. Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, United States, April 6-10, 2008.
- El-Tahlawy, K., Venditti, R. A., Pawlak, J. J., 2008, Effect of the Reaction Conditions During Modification of Starch with Alkyl Ketene Dimer on the Properties of Starch Microcellular Foam, K. El-Tahlawy, R. A. Venditti, J. J. Pawlak, Carbohydrate Polymers, 73, 133-142.
- Patel, S., Venditti, R. A., Pawlak, J. J., Ayoub, A., Rizvi, S. S., 2008, Development of cross-linked starch microcellular foam by solvent exchange and reactive supercritical fluid extrusion. Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, United States, April 6-10, 2008.
- Bolivar, A. I., Venditti, R. A., Pawlak, J. J., El-Tahlawy, K., 2007, Development and Characterization of Novel Starch and Alkyl Ketene Dimer Microcellular Foam Particles, Journal of Carbohydrate Polymers, 69, pp. 262-271.
- Venditti, R. A., El-Tahlawy, K., Pawlak, J. J., 2007, Starch and alkyl ketene dimer microcellular foam particles, 233rd ACS National Meeting, Division of Cellulose & Renewable Materials, March 2007, Chicago.
- Venditti, R. A., Pawlak, J. J., El-Tahlawy, K., 2007, The use of alkyl ketene dimer to develop water resistance of starch microcellular foam particles, International Symposium on Polymers and the Environment: Emerging Technology and Science, Bioenvironmental Polymer Society, October 17-20, 2007.
- Ayoub, A., Rizvi, S. S. H., Patel, S., Venditti, R. A., Pawlak, J. J., 2007, Development of cross-linked starch microcellular foam by reactive supercritical fluid extrusion, International Symposium on Polymers and the Environment: Emerging Technology and Science, Bioenvironmental Polymer Society, October 17-20, 2007.
- El-Tahlawy, K., Venditti, R. A., Pawlak, J. J., 2007, Aspects of the Preparation of Starch Microcellular Foam Particles Crosslinked with Glutaraldehyde Using a Solvent Exchange Technique, Carbohydrate Polymers, 67(3) pp. 319-331.
- El-Tahlawy, K., Venditti, R. A., Pawlak, J. J., 2006, Preparation of Starch Micro-Cellular Foam for Filler Applications, Proceedings of the 2006 Progress in Paper Physics Symposium, October 2-5, 2006, Miami, OH.
- Ana I. Bolivar, A. I., Venditti, R. A., Pawlak, J. J., El-Tahlawy, K., 2006, Development and Characterization of Novel Starch and Alkyl Ketene Dimer Microcellular Foam Particles, North Carolina Biotechnology Center Bioseparations and Bioprocessing Development Symposium, Research Triangle Park, NC, October 25-26, 2006
- Venditti, R. A., Pawlak, J. J., El-Tahlawy, K., 2005, Development of a Microcellular Foam Starch Particle as a Replacement for Inorganic Fillers in Paper or Coating Applications, PIRA Fillers and Pigments for Papermakers, Atlanta GA, November 9-10, 2005.
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Progress 09/01/07 to 08/31/08
Outputs
OUTPUTS: The project further investigated the use of additives and process modifications in order to produce SMCF materials that have a highly developed microcellular structure and water resistance in order to function in humid or wet environments. Activity 1. Several very important aspects of the application of alkyl ketene dimer (AKD) (a sizing agent used to impart hydrophobicity) to starch in order to develop a hydrophobic SMCF material were explored. Cooked starch solutions at 8% solids were blended with AKD at several levels from 1 to 3% AKD on dry starch and solvent exchanged to form SMCF. For AKD levels of 2% or less, a well developed SMCF structure was produced with well formed parts but above 3% the materials produced were too brittle to form coherent foams. Increased AKD from 1% to 2% showed significantly increased water resistance, with water contact angles of around 100 degrees attainable. Water swelling and mass loss after soaking in water confirmed that the AKD increased the water resistance of the SMCF. It was also determined that Kymene, a crosslinking agent based on polyamide-epichlorohydrin, decreased the water absorption of the SMCF materials, suggesting the diffusion of water into the SMCF was lower due to the crosslinks introduced. Kymene did not provide additional increases in water contact angle relative to AKD modified SMCF. Activity 2. An alternative system for crosslinking and imparting hydrophobicity was evaluated with an epichlorohydrin crosslinked (EPI) and acetylated (Ac) starch in one continuous supercritical fluid extrusion (SCFX) process. An increase in EPI concentration from 0 to 3 % increased the degree of cross linking as measured by DSC and confirmed by the quantification of the glucose units in the solution after acid hydrolysis. The most prominent feature of the esterified starches was an increased hydrophobicity with the contact angle for the modified starch (3%EPI-15%Ac) increased from 43.1 to 91.7 degrees. The average density of the SCFX extrudates depended on the concentration of SC-CO2 used, the degree of chemical modification achieved by the addition of (EPI) and (Ac), and the nature of the starch (native or pregelatinized). The average cell size in the extrudate determined by scanning electron microscopy was also found to decrease from 150 to 34 microns by the addition of the two reagents (EPI and Ac). The dual-modification (EPI-Ac) of starches was observed to increase hardness and adhesiveness of the extrudates as compared to the unmodified starches. Activity 3. SMCF-Wood Fiber composites were created from solvent exchanged aquagels. Higher amylose content starches and fiber contents of up to 4% improved the processability of the foam. The SMCF structure revealed agglomerates of swollen starch granules connected by a web of starch with pores in the 50-200 nanometer range. Heating the SMCF-fiber in a nitrogen atmosphere to temperatures between 350-700˚C produced carbon foams with a three-dimensional closed cell foam structure with cell diameters around 50 microns and pore walls around 1-3 microns and a water contact angle of 115 degrees. PARTICIPANTS: Dr. Venditti and Pawlak at North Carolina State University are the principal investigators. Dr. Rizvi is a collaborator who is directing research at Cornell University under a sub-contract. At NCSU, Sameer Patel, a MS student has been active in performing laboratory research and in the production of manuscripts and presentations. Undergraduate students Andy Rutledge and Andy Cibils have participated in laboratory research and generated a publication and presentations on this project. At Cornell a post-doctoral researcher, Dr. Ali Ayoub, has conducted laboratory and pilot plant experiments and participated in the preparation of manuscripts and presentations. TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Activity 1. The results confirm previous findings that the addition of AKD can significantly increase the water resistance of SMCF materials. An optimum AKD level in the range of 1 to 2% has been observed and the improved performance of AKD after curing was realized. The use of a crosslinking agent, polyamide-epichlorohydrin, decreased the water swelling of SMCF indicating a decreased water diffusivity of the crosslinked SMCF but did not decrease the water contact angle relative to AKD alone treated SMCF. Activity 2. The results indicate that the addition of acetic anhydride can impact the water resistance of starch foams significantly and suggests that the combination of acetylation and crosslinking may be a powerful tool to produce solid foam reactively in one step when combined with supercritical fluid extrusion. Our finding clearly demonstrates the positive effects of dual modification on the structure and the pore size distribution of solid foams. Further research is needed to more precisely quantify the processing parameter and the sequence of a dual modification strategy on the final structure and morphology of starch-based foams. Activity 3. It has been shown that the use of fibers to reinforce the starch based composites during processing into microcellular foams is beneficial. Addition of up to 4% by weight of wood based fibers improved the uniformity and foam structure of the final materials. It is of significant interest to further develop fiber-SMCF composites as a high specific surface area material produced from sustainable materials. The carbonization of such composites is also a very promising area of research. In total, these three activities continue to promote the concept that SMCF materials can compete with non-renewable industrial materials in pigment, absorbent, catalyst, and other applications in which high specific surface area is important.
Publications
- El-Tahlawy, K., Venditti, R. A., Pawlak, J. J., 2008. Effect of the Reaction Conditions During Modification of Starch with Alkyl Ketene Dimer on the Properties of Starch Microcellular Foam, Carbohydrate Polymers, 73, 133-142.
- Rutledge, A., Venditti, R. A., Pawlak, J. J., Patel, S., Cibils, J., 2008, Carbonized Starch Microcellular Foam-Cellulose Fiber Composite Structures, BioResources, 3(4) 1063-1080.
- Ayoub, A., Rizvi, S. S., 2008, An overview of the technology of the crosslinking of starch for non-food applications. Journal of Plastic Film and Sheeting, accepted, March 2008.
- Patel, S., Venditti, R. A., Pawlak, J. J., Ayoub, A., Rizvi, S. S., 2008, Development of cross-linked starch microcellular foam by solvent exchange and reactive supercritical fluid extrusion, J. Appl. Polymer Science, in press, November 2008.
- Venditti, R. A., Pawlak, J. J., Rutledge, A., Cibils, J., 2008, Cellulose fibers and microcellular foam starch composites. Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, United States, April 6-10, 2008.
- Patel, S., Venditti, R. A., Pawlak, J. J., Ayoub, A., Rizvi, S. S., 2008, Development of cross-linked starch microcellular foam by solvent exchange and reactive supercritical fluid extrusion. Abstracts of Papers, 235th ACS National Meeting, New Orleans, LA, United States, April 6-10, 2008.
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Progress 09/01/06 to 08/31/07
Outputs
OUTPUTS: The goal of this research is to develop a novel application of starch-based microcellular foam (SMCF), an inherently high specific surface area material, as an opacifying agent in paper, paint and coating applications. SMCF structure is formed only by being dried or processed in such a way to develop a high concentration of voids in the micron range. Activity 1. The production of a hydrophobic SMCF through the addition of an alkyl ketene dimer (AKD) would be a bio-based material with valuable properties for many applications in which high specific surface area, low density and water resistance is important. Pigments for paper and coatings are a potential application. An emulsion of AKD and cooked corn starch was made by mixing AKD with cooked starch at 50 C under a high rate of shear. The effects of reaction temperature, starch concentration and pH on the reaction of AKD with starch and the resulting microcellular foam structure was studied. The starch/AKD foam particles
were characterized by scanning electron microscope, elemental analysis to determine extent of reaction, thermogravimetric analysis, brightness, particle size and water swellability. The apparent viscosity of the starch solution was shown to have a linear relationship with the particle size and the brightness of the particles. The particles under all conditions had a very high brightness. The AKD was able to impart a significant hydrophobicity to the particles relative to starch alone but the water resistance was not great enough to preserve the porous structure when wetted. Activity 2. The objective was to describe how processing conditions and the use of a crosslinking material would affect the SMCF structure, physical and optical properties and moisture related properties. Starch aquagels were formed by conventional cooking and pouring the starch solution in molds and also by an extrusion process. These materials were then solvent exchanged with ethanol and dried. SMCF materials
prepared in molds were produced by a slow solvent exchange (40, 70, 90, three 100% ethanol exchanges at 48 hr) and fast solvent exchange (three 100% ethanol exchanges at 48 hr) at three different cooking extents. Extruded starch samples were processed with the slow and fast solvent exchange. Three types of extruded samples were made: (1) extruded starch, (2) extruded starch with crosslinker, and (3) extruded starch with crosslinker and CO2. Density, brightness, water swelling and mass loss, moisture content and water contact angle were measured. SMCF extruded samples contained large pores (>50 microns) that were produced when the extrudate expanded upon pressure release whereas SMCF molded samples did not have these large pores. SMCF molded samples showed a fine pore structure with a significant amount of pores with size less than 10 microns. The SMCF samples prepared from a mold had significantly lower density and higher brightness than did extruded samples. Crosslinking in the
extruded samples increased the water resistance significantly.
PARTICIPANTS: Syed S. H. Rizvi, Professor of Food Process Engineering, continues to be a collaborator on this project leading the extrusion research. Dr. Ali Ayoub, research associate, of the same department, has been working with Dr. Rizvi on this project.
Impacts
Activity 1. The results indicate that the addition of AKD can impact the water resistance of the SMCF materials significantly. The results showed that further research is needed to more effectively treat the SMCF with AKD. The results also suggest that the combination of sizing via AKD and crosslinking may be a powerful method to increase water resistance levels. Activity 2. The results of activity 2 clearly demonstrate the differences between extruded starch products and molded starch products. Further, this study verifies that the method of cooking, method of solvent exchange and the incorporation of a crosslinking material can significantly impact structure and that the structure alters the physical and moisture related properties of the materials. Both activities results suggest that SMCF materials can compete with non-renewable industrial pigments such as clays, calcium carbonates, and titanium dioxide, with values ranging from $200-800. It is clear from our work
that SMCF has promise in competing at the upper range of the pigment costs. To fully capitalize on this, the water resistance of the SMCF still must be improved.
Publications
- Development and Characterization of Novel Starch and Alkyl Ketene Dimer Microcellular Foam Particles, A I. Bolivar, Richard A. Venditti, Joel J. Pawlak, and Khaled El-Tahlawy, Journal of Carbohydrate Polymers, 69, pp. 262-271, 2007.
- Effect of the Reaction Conditions During Modification of Starch with Alkyl Ketene Dimer on the Properties of Starch Microcellular Foam, K. El-Tahlawy, R. A. Venditti, J. J. Pawlak,, Carbohydrate Polymers, accepted, Nov. 2007.
- Starch and alkyl ketene dimer microcellular foam particles, R.A. Venditti, K. El-Tahlawy, and J.J. Pawlak, 233rd ACS National Meeting, Division of Cellulose & Renewable Materials, March 2007, Chicago.
- The use of alkyl ketene dimer to develop water resistance of starch microcellular foam particles, R. A. Venditti, J. J. Pawlak, K. El-Tahlawy, International Symposium on Polymers and the Environment: Emerging Technology and Science, Bioenvironmental Polymer Society, October 17-20, 2007.
- Development of cross-linked starch microcellular foam by reactive supercritical fluid extrusion, A. Ayoub, S. S. H. Rizvi, S. Patel, R. A. Venditti, J. J. Pawlak, International Symposium on Polymers and the Environment: Emerging Technology and Science, Bioenvironmental Polymer Society, October 17-20, 2007.
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Progress 09/01/05 to 09/01/06
Outputs
The goal of this research is to develop a novel application of starch-based microcellular foam (SMCF), an inherently high specific surface area material, as an opacifying agent in paper, paint and coating applications. SMCF are starch based foams that have been dried or processed in such a way to develop a high concentration of voids in the micron range. Part 1. Starch microcellular foam was produced by supercritical fluid extrusion (SCFX) using native and pre-gelatinized starch mixtures. The starch solution was reacted with epichlorohydrin (alkaline conditions) in a twin-screw extruder in the presence of supercritical carbon dioxide. The relationship between cross-linking density and cell size and their distribution in the foamed extrudates was studied. An increase in the EPI concentration from 0 to 0.5 % increased the degree of cross linking as measured by DSC and confirmed by diffusion coefficients measured by NMR. The diffusion coefficient of cross-linked samples
was observed to be 2.5 times lower than that of a non-crosslinked control. The average cell size of the structure showed a decrease from 147 to 87 micrometers as the concentration of EPI was increased (SEM). The cell size distribution of the cross-linked samples was significantly improved but the total expansion was lowered. Part 2. Another approach has been to generate SMCF using a solvent exchange technique. It was postulated that crosslinking of the starch would inhibit molecular mobility during the solvent exchange process, resulting in a more porous structure. A native corn cooked starch solution was reacted with glutaraldehyde crosslinker and precipitated under shear with ethanol. An increase in the glutaraldehyde from 0 to 15 g /100g starch caused a decrease in particle size and moisture content and an increase in brightness and specific surface area. The smallest average void diameter obtained was 0.182 microns at a 7.5 g /100g starch (SEM). Starch materials having different
viscosity were prepared by acid hydrolysis of the starch to investigate the relationship between starch molecular weight and void structure of the SMCF. Decreasing the starch viscosity decreased the brightness and specific surface area, and increased the particle size, void diameter and moisture content. Part 3. SMCF particles (solvent exchange) were produced with Alkyl Ketene Dimer (AKD) wax at different levels by both coating and blending in order to understand if the AKD could impart water resistance to the particles. Particles with porous structure and high brightness were developed for all combinations of starch and AKD. For the AKD coated particles a minimum amount of AKD charged was needed to develop a high contact angle, low solubility, and low water retention value, higher levels of AKD in AKD coated particles did not further alter these properties. Starch AKD blends did not show any increased resistance to water relative to a untreated control. Further work needs to be
performed to more effectively hydrophobize the starch foams with a combination of crosslinker and AKD.
Impacts
Part I. The results obtained to date indicate, for the first time, that reactive extrusion of starch with EPI with supercritical carbon dioxide as a blowing agent offers a promising new technique to generate microporous foams for use in various applications. This has important environmental impact in that this process does not use organic solvents. Further the economics of the process are expected to be improved relative to a solvent exchange process because there is no need to separate water from solvent, an expensive operation. Part 2 and 3. It has been clearly shown that SMCF can readily be produced in the form of particles with brightness of 93 % ISO. This is without an extensive optimization of the process. To contrast SMCF performance with industrial pigments and fillers, clays typically have brightness values of 70-80%, calcium carbonate of 81-96%, and titanium dioxide of 97%. Clearly, SMCF particles have brightness properties that compete in performance and
cost favorably with many of these non-renewable resources. Low grade fillers cost in the range of $200 and high end pigments around $800. It is clear from our work that SMCF has promise in competing at the upper range of the pigment costs. To fully capitalize on this, the water resistance of the SMCF must be improved.
Publications
- Aspects of the Preparation of Starch Microcellular Foam Particles Crosslinked with Glutaraldehyde Using a Solvent Exchange Technique, K. El-Tahlawy, R. A. Venditti, J. J. Pawlak,, Carbohydrate Polymers, 67(3) pp. 319-331 (2007).
- Development and Characterization of Novel Starch and Alkyl Ketene Dimer Microcellular Foam Particles, A I. Bolivar, Richard A. Venditti, Joel J. Pawlak, and Khaled El-Tahlawy, Journal of Carbohydrate Polymers, accepted 2006.
- Preparation of Starch Micro-Cellular Foam for Filler Applications, Khaled El-Tahlawy, Richard Venditti, and Joel J. Pawlak, Proceedings of the 2006 Progress in Paper Physics Symposium, October 2-5, 2006, Miami, OH.
- Development and Characterization of Novel Starch and Alkyl Ketene Dimer Microcellular Foam Particles, Ana I. Bolivar, Dr. Richard A. Venditti*, Dr. Joel J. Pawlak, Dr. Khaled El-Tahlawy North Carolina Biotechnology Center Bioseparations and Bioprocessing Development Symposium, Research Triangle Park, NC, October 25-26, 2006
- Development of a Microcellular Foam Starch Particle as a Replacement for Inorganic Fillers in Paper or Coating Applications, Venditti, R. A., Pawlak, J. J., El Tahlaway, K. PIRA Fillers and Pigments for Papermakers, Atlanta GA, November 9-10, 2005.
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