Research Grants/Fellowships/SBIR

1999 Progress Report: Aqueous Processing of Biodegradable Materials from Renewable Resources

EPA Grant Number: R826117
Title: Aqueous Processing of Biodegradable Materials from Renewable Resources
Investigators: McCarthy, Stephen P.
Current Investigators: McCarthy, Stephen P. , Koroskenyi, Balint , Zhang, Jinwen
Institution: University of Massachusetts
Current Institution: University of Massachusetts - Lowell
EPA Project Officer: Richards, April
Project Period: November 1, 1997 through October 31, 2000 (Extended to December 31, 2001)
Project Period Covered by this Report: November 1, 1998 through October 31, 1999
Project Amount: $300,004
RFA: Technology for a Sustainable Environment (1997) RFA Text |  Recipients Lists
Research Category: Nanotechnology , Sustainability , Pollution Prevention/Sustainable Development



The main objective of this project is to obtain useful commercial intermediate products such as fibers, films, and foams for bulk applications in areas like packaging from naturally available abundant raw materials, starch, chitosan, and konjac, which are inherently biodegradable and environmental friendly. The main focus will be finding potential alternatives for the petroleum-based conventional polymeric materials that are a major concern for environmental pollution today. Also, this investigation will attempt to design the conversion processes to cause minimum impact on the environment in terms of utilization of harmful chemicals, energy, and water. The conversion of raw material to product will mainly involve using aqueous processing techniques such as extrusion and film casting from solutions. Necessary postprocessing treatments can be subsequently carried out to make the products water resistant.

Polysaccharides possess reasonable physical properties that can be exploited in a number of applications. Their structure allows them to be chemically modified in such a manner that they can become water soluble. In this state they can be converted into the desired form?film, fiber, coating, and foam using conventional processing techniques. However, once the products are obtained, they have to be water resistant to be useful in any application. Again, their ability to readily undergo chemical reaction can be advantageous to impart this quality. Part of this study also will be on utilizing other biodegradable polymers in conjunction with these polymers.

Different approaches have been attempted to process polysaccharides into useful forms. The food industry has long been processing the most common and abundant polysaccharide, namely, starch, to obtain various food products. Popular examples include puffed rice or corn, wafers, or bread (similar to polymer foams); and noodles and pasta (similar to extruded thermoplastic). The physical and chemical transformations occurring during these conversion processes are well understood and documented.

Melt Processing of Starch: In recent years, great interest has been generated in exploiting these natural products to substitute some synthetic materials due to growing environmental concern. Starch is typically plasticized, destructured, and/or blended with other materials to form useful mechanical properties. For instance, in the loose-fill packaging application, foamed polystyrene is being widely substituted by starch foams that are readily biodegradable upon disposal. These expanded products have a closed cell pore structure and densities ranging from 0.01 to 0.1 g/cm3 and are produced by extrusion of a composition containing starch and a synthetic polymer in minor fraction (1). Starch foam in the form of loose-fill or continuous sheet is obtained as follows: raw starch is premixed with 25 to 50 weight percent water and fed into an extruder capable of imparting intensive shear and operating at high temperature (higher than the boiling point of water, i.e., 150-180?C). Under these conditions of shear and temperature, starch breaks down, loses its crystallinity, and gets plasticized with water, resulting in a homogenous amorphous mass. When this gelatinized starch/water mixture exits the extruder, the water that is present in the mass at a temperature higher than its boiling point expands into steam due to a sudden drop in temperature, and the foam is formed. The structure of the foam depends on several parameters, namely, molecular weight, moisture content, head pressure, temperature, extent of gelatinization, or presence of another plasticizer or a polymer (2-5). The amount of moisture present in the final product, which depends on the ambient humidity, strongly influences the physical properties of the starch foam. Addition of another plasticizer (such as glycerol) or a polymer (such as polyvinyl alcohol) imparts more reproducible properties to starch foam. Layers of foam sheets thus produced can be bonded together to obtain a laminate assembly into three-dimensional structures (6). Warner-Lambert/Novon has developed starch-based materials, which are almost totally starch. Fertec in Italy produces starch and vinyl alcohol copolymer blends with starch contents greater than 60 percent under the trademark Mater-Bi. These materials are available in commercial grades suitable for blown film, injection molding, blow molding, thermoforming, and extrusion. They are reported to be significantly moisture resistant and totally biodegradable.

Chemical modification/Reactive processing of starch: The products obtained by simple aqueous processing of starch are highly hydrophilic and readily disintegrate on contact with water, a property that limits their applications. Efforts have been made to improve the moisture resistance by different techniques. One approach is chemically modifying starch. Starch has free hydroxyl groups, which readily undergo a number of reactions such as esterification and etherification. Acetylation of starch with intermediate DS in aqueous media has been disclosed (7). Methods of preparing a number of starch derivatives, including glycosides, graft copolymers with acrylonitrile and acrylamide, and cationic starch by reactive extrusion, have been discussed by Carr (8). Amylose and amylopectin were acetylated following the pyridine-acetic anhydride procedure to obtain thermoplastic starch-based materials with a reinforced hydrophobicity (9). The properties of starch esters with fatty acids for their possible application as environmentally degradable thermoplastics have been investigated. The rheological, thermal, and mechanical properties of a series of fatty-acid esters of high-amylose starch (as well as the effects of adding plasticizer on some selected properties) were evaluated (10). The ester group acts like an internal plasticizer, with an increase in the size of the fatty-acid chain, resulting in greater internal plasticization. Starch has been found to react with polymers containing carboxylic or anhydride groups forming ester links during melt blending (11-13). Grafting of monomers like styrene, acrylonitrile, and caprolactone onto starch also has been attempted (14-16). Grafting of the vinyl monomers onto starch or reactive blending vinyl polymers mentioned above impart some level of hydrophobicity to the resultant product, but upon disposal, only the starch component decomposes due to natural processes leaving behind the synthetic polymer.

Coextrusion of starch and a biodegradable polymer: One of the objectives of the present investigation is to employ the technique of coextrusion or lamination as the commercializable process of choice for producing a product with a water-sensitive polysaccharide sandwiched between two layers of a hydrophobic biodegradable polymer. This technique has been successfully adopted for conventional polymers. Some examples are: top seals for bottle cap liners made from expanded PE laminated to PTFE for packaging aggressive substances (17); coextruded foamed PVC sheet for insulation purposes (18); and laminate comprising a soft polyolefin resin layer, an ethylene-unsaturated carboxylic acid ester-maleic anhydride terpolymer resin layer, and a soft urethane foam resin layer for use in automobiles (19). It is expected that similar sandwiched multilayer products from starch foam and hydrophobic biodegradable polymer could be produced by coextrusion techniques.

Chitosan: Chitin is a naturally occurring polysaccharide derived primarily from shellfish. Chitosan is deacetylated chitin that is swollen with water and dissolves in a water acetic acid mixture. They are biocompatible and biodegradable. Chitosan fibers obtained by wet spinning of chitosan were acetylated, producing regenerated chitin fibers. It was found that, after acetylation, the fibers had an improved thermal stability and tensile strength (20). Crosslinking of chitosan fibers has been demonstrated using epichlorohydrin as a crosslinking agent. The strength of chitosan fibers, especially wet tenacity, is improved by crosslinking (21). It has been shown by IR spectroscopy that the impairment in solubility of chitosan carboxymethyl ether in the form of an internal salt after drying or heat treatment takes place as a result of the formation of amide crosslinks (21).

Pullulan: Pullulan is a microbially produced polysaccharide, a water-soluble extracellular neutral glucan synthesized by a fungus. Pullulan can be solution cast from aqueous media and, with difficulty, it has been processed by conventional melt-processing techniques (22). Plasticizers such as glycerol and ethylene glycol have been shown to reduce the glass transition temperature to below l60?C with the addition of more than 10 percent plasticizer. Modification of pullulan also has been accomplished by acetylation (23).

Konjac: Konjac flour is the generic name of the powdered tuber from Amorphophallus konjac, occurs in a high molecular weight (in excess of 1,000,000 g/mole), and is a polysaccharide classified as a glucomannan. Chemically, it consists of mannose and glucose in a molar ratio of 1.6:1, respectively, with beta 1-3 linkage (24). Konjac flour, in the presence of water, can be thermopressed into sheets below 100?C with rigid and brittle behavior.

Progress Summary:

Work is being carried out in the following areas: aqueous processing of starch and its blends; lamination of starch foam with biodegradable polymers; chemical modification of chitosan; and fiber production and thermoplastic processing of pullulan and konjac.

Blends of Starch and PVOH
Melt blending: Starch was melt blended with polyvinyl alcohol in the presence of water or a plasticizer. Three steps were involved in the preparation of the PVOH and starch blend: gelatinization, premixing, and blending. During gelatinization, the starch was gelatinized in water contained inside a 3-liter beaker for about 12 minutes at a temperature of 70-80?C under mechanical stirring. The desired level of gelatinization was obtained by adding the starch to cold water at the beginning of the gelatinization, then slowly raising the temperature up to 70-80?C while stirring. The gelatinization may not be complete and uniform if starch is added after raising the temperature up to that value.

Next, the gelatinized starch was premixed with PVOH (without heating) using the Henschel mixer. The premixing caused a temperature rise from ambient to 55-60?C, and the mixing torque went from 0 to 7-10 amps. It took approximately 8 minutes to complete at a speed of 2,200 rpm. By the end of this stage, a rapid rise in both temperature and torque was observed, which was a manifestation of the completion of the premixing.

Finally, the premixed mixture of gelatinized starch and PVOH was blended and pelleted through the Leistritz twin screw extruder for initial trials, and later the blending was done using the Brabender twin screw mixer. The blown film operation was exclusively conducted through the twin screw mixer, equipped with a 1-inch (25 mm) blown film die.

For the initial batch trial studies, the gelatinized starch was blended with a PVOH fine powder in one step conducted in the Haake Buchler torque rheometer. The batch trial study was performed at the very beginning of this investigation, and it was conducted to screen processing conditions, characterize melt flow behavior, and to provide samples for the blend compatibility study.

Study of compatibility and processability: The compatibility and processability of corn starch blend with PVOH were studied using the Haake torque rheometer, the Brabender single screw extruder, the Leistritz twin screw extruder, and DSC.

Initial batch trials were conducted on the Haake torque rheometer at temperatures ranging from 95 to 110?C. The gelatinized starch was added first to the mixing chamber, followed by the addition of the PVOH fine powder. A programmed mixing time of 15 minutes with a rotating speed of 40 rpm was sufficient to complete the mixing operation. The torque generated and the temperature changes were recorded by a microprocessor. Starch contents of 25, 50, and 75 percent (w/w) were studied, with a consistent water content of 50 phr (per hundred parts of resin). The final mixtures were dried and analyzed by DSC.

The Haake batch study was promising and encouraging in terms of apparent compatibility and processability. Subsequently, the Brabender single screw extruder was employed to perform continuous processing of the same blend. In the single screw extrusion, the premixed mixture generated from the Henschel mixer was fed into the Brabender single screw extruder. The extrusion had a temperature profile from feeder to die as follows: Zone 1: 87?C; Zone 2: 91?C; and Zone 3: 95?C. The die pressure was 100 to 300 psi, and the screw speed was 40 to 50 rpm. Feeding was very difficult to achieve due to the semi-viscous aggregated nature of the mixture and due to the non-positive conveyance of a single screw extruder. Obviously, it was imperative to seek a twin screw extruder to accomplish successful feeding. The extrudates were analyzed in the same manner as described above.

A successful continuous extrusion of the blend was finally obtained using an American Leistritz counter-rotating intermeshing twin screw extruder adapted with a strand die. As was expected, the Leistritz twin screw extruder had no difficulty processing the premixed mixture generated from the Henschel mixer, and the extrusion was very stable. A representative temperature profile of the extrusion from feeder to die was as follows: Zone 1: 80?C; Zone 2: 85?C; Zone 3: 90?C; Zone 4: 90?C; Zone 5: 95?C; Zone 6: 95?C; and Zone 7: 98?C. The melt temperature was 98?C, with a screw speed of 65 rpm and a die pressure of 500-600 psi. Twin screw extruders offer two primary advantages over single screw extruders. The first is the positive conveying characteristic mentioned earlier, and the second is removal of volatiles from a built-in vent port. The volatiles were mainly due to excess moisture that had evaporated during the course of extrusion. However, the slightly white-yellow color of the extrudates indicated overcooking of the blend due to a longer residence time. As before, the extrudates were dried and analyzed by DSC.

The thermograms of dry starch and PVOH, and the blends of starch and PVOH processed individually by the Haake rheometer, the Brabender single screw extruder, and the Leistritz twin screw extruder were observed.

Dry starch has a major transition at about 133?C, and the major transition of dry PVOH is observed at about 214?C. When the starch was blended with PVOH, shifts of the major transitions of each individual component took place, depending on how they were blended. The blend processed by the Leistritz twin screw extruder showed a main transition that was intermediate to both of the components. The blend processed through the Brabender single screw extruder gave the least uniformity of mixing, as indicated from the endothermic peak of PVOH. The shape and location of the peak indicates an independent component or existence of an individual phase.

Effect of moisture content upon mechanical properties: Moisture content dramatically affected the completion of starch gelatinization and the mechanical properties and physical aging of the blown films. It is evident that quantitative determination of the effect of moisture content on the blend of starch PVOH is necessary.

The mechanical property measurement was carried out on the Universal Instron testing machine, Model 1137, on ASTM standard specimens that were die cut from the extruded ribbons. The specimens had gauge dimensions of 2.5 inches in length, 0.25 inches in width, and thickness that varied from 0.20 to 0.25 inches. The reported results are an average value of six specimens and aloof the measurements were made at a crosshead speed of 0.5 inches/minute at ambient temperature.

Tensile stress, Young's modulus, and elongation were plotted as a function of moisture content. The blend of regular starch and PVOH yielded superior mechanical properties compared to the blend of waxy starch and PVOH. The tensile strength of the blend with regular starch is much higher than that of the blend, with waxy starch at moisture contents below 15 percent. The elongation of the blend with regular starch increases linearly as a function of moisture within the entire range of moisture content, but the elongation of the blend with waxy starch drops dramatically as the moisture content exceeds 15 percent. Therefore, the regular starch is the preferred starch to be blended with PVOH.

Blown film processing: As was stated in the previous section, the Leistritz twin screw extruder was successfully used to overcome feeding difficulties of the starch and PVOH blend. DSC analysis also demonstrated the high degree of uniformity of the mixing, in terms of melting temperature depressions of the individual components. It was our projected goal to blow film from the starch and PVOH blend. This was done by using a Brabender twin screw mixer.

The blown film extruder could be operated at suprisingly low temperatures and head pressure. Melt temperatures of 97 and 113?C were recorded for the samples containing 25 and 50 weight percent starch, respectively. These temperatures were consistent with the DSC measurements. The gelatinized starch not only significantly reduced the melt processing temperature, but also effectively prevented thermal degradation of PVOH, because bulk PVOH suffers rapid decomposition at temperatures above 200?C.

Blown film mechanical properties: The blown film mechanical properties of samples containing 25 and 50 weight percent starch were determined from standard tensile experiments conducted in a Series IX Automated Materials Testing System 1.0 at a crosshead speed of 0.5 inches/minute at room temperature. The tensile test specimens had dimensions of 3 x 1 x 0.008 inches. Tensile strength, Young's modulus, and elongation are summarized in Table 1, and the mechanical properties of pure PVOH are included for comparison.

From Table 2, it is evident that the sample with 25 percent starch has a higher tensile strength and Young's modulus as compared to the sample containing 50 percent starch, yet it has a lowered elongation. It is believed that these differences in mechanical properties are due to the difference in starch contents. Increased starch content reduced system regularity and degree of packing, hence weakening the film's strength. The higher elongation value found in the later was unexpected because higher starch content usually produces a low value in elongation. It needs to be mentioned that the water percentage initially used for gelatinization was different for these two samples, but the two samples were tested at equal levels of moisture content. Both samples were dried under the same condition; therefore, the amount of water used for gelatinization should not be a significant factor behind the differences in mechanical properties. Instead, the incorporation of 10 percent glycerin as a synergistic plasticizer and 5 percent talc as an antiblocking agent may have physically and chemically imparted more flexibility to the system, thus outweighing the reduction in elongation due to a higher starch content.

Melt blending of starch with biodegradable polymers: In this study, starch and starch acetate were melt blended in 20 percent weight with polylactic acid (PLA), polycaprolactone (PCL), and cellulose acetate (CA) separately using a counter rotating twin screw extruder (Brabender, Inc.). In the case of CA, 20 percent PEG was used during processing. All the blends were then extruded into films using a 100 mm push-pull sheet die. The thickness of the films was maintained in the range of 5-7 mils by adjusting the speed of take-up unit. Tensile testing of the films was carried out according to ASTM D882 using an Instron 1137 tensile tester. All the films were conditioned for 40 hours. The test was carried out at a crosshead speed of 12.5 mm/minute with a gauge length of 100 mm using film specimen 25 mm wide. Tensile strength and modulus were calculated from the load-elongation curves obtained for 5-7 specimens from each sample. The standard deviation values for yield strength and modulus were found to be within 5 percent. Table 3 shows the strength and modulus of all the blend samples. All the films are opaque, except CA/StAc blend sample, which has a little transparency. By incorporating 20 percent starch and starch acetate in PLA, there is a drop in strength around 30 percent and an increase in modulus by 40 percent. The similar trend is observed in PCL and the starch blend system. The cellulose/starch blend system shows a different trend. By incorporating 20 percent StAc with PEG, strength increases by 25 percent, and there is not much drop in modulus.

Processing of Pullulan
Pullulan by itself is not melt processable without the aid of plasticizers. Upon thermal treatment, pullulan degrades before it flows. The DSC analysis of raw pullulan showed no detectable glass transition from 25 to 210?C, either on first or second heats. In this study, the plasticization of pullulan with water-soluble plasticizers was undertaken to produce a pullulan derivative with a detectable glass transition temperature.

Solvent casting technique: Polymer films were prepared by solvent casting onto glass plates. For pullulan/plasticizer formulations, 1.0 g of purified polymer was dissolved in water (20 mL) along with the appropriate concentration of either ethylene glycol or glycerol (5.0-50 percent) to produce a (5 percent weight/volume) solution. The polymer solution was poured onto the glass plate, making sure that there were no bubbles. Clear and colorless films were obtained. At this time, the films were peeled off and dried under vacuum (l mmHg) at 50?C for 24 hours.

The polymer and plasticizers were dissolved in water under gentle heating to form a 5 percent (weight/v) solution. The plasticizer content ranged from 10 to 50 phr. The films formed were colorless and transparent regardless of plasticizer content. Depending upon the amount and type of plasticizer used, the material properties ranged from brittle to tenacious. The glycerol films with loading of up to 30 phr were extremely tenacious and pliable; however, at 50 phr, the films became extremely tacky, sticking to almost any surface it would come in contact with. These materials show promise as potential candidates for biodegradable adhesives. The pullulan/ethylene glycol films also were tenacious at high plasticizer loading, but were not as tacky as their glycerol counterparts.

The films were then analyzed by DSC and evaluated for any change in their glass transition temperature. Glycerol is a more effective plasticizer than ethylene glycol in producing a greater reduction in the Tg of pullulan overall, and at any particular composition. This result would be expected based on the solubility parameters of both glycerol and ethylene glycol, 33.8 MPa0.5and 29.9 MPa0.5, respectively. The solubility parameter of pullulan was estimated (Krevelin molar attraction constants), and a value of 27.8 MPa0.5 was obtained. This value may be somewhat lower than expected, because the molar constant values for ring structures were not considered. The mode of plasticization for this case can be explained by the plasticization theory. The oxygen or hydrogen of the hydroxyl group of glycerol could easily undergo hydrogen bonding with the appropriate counterpart on the pullulan molecule, or a dipole interaction may be occurring between the polymer and plasticizer, thus disrupting polymer-polymer interactions and introducing polymer/plasticizer interactions. Glycerol depresses the Tg linearly, which would be expected based on its solubility parameter; however, this trend is not observed in the pullulan/ethylene glycol samples. This deviation from linearity may be due to the solubility parameter of ethylene glycol, which is significantly lower than that of glycerol, and there might be a limited amount of miscibility at higher loadings with the polymer. From this graph, a glass transition value for pullulan may be obtained by extrapolating to zero concentration plasticizer. This extrapolated value is 180?C.

Preparation of thermoplastic pullulan: As mentioned earlier, pullulan is not melt processable without the aid of plasticizers. Thermoplastic pullulan was produced by plasticizing pullulan with ethylene glycol, glycerol, and water. After formulation, these materials were then either injection molded, compression molded, or extruded depending upon their final application.

The torque rheometer's torque and melt temperature were plotted as a function of time. From this plot, we see what would be considered as typical behavior for a polymer-plasticizer pair. First, an initial increase in the torque upon addition of material to the mixing chamber is observed. This is referred to as the loading torque and is associated with physically loading the material into the mixing chamber. As we follow the profile further, a steady increase in the torque is observed until a maximum is reached. At this maximum, the material is now fused. Fusion or the fusion torque is described as the point at which the polymer (solid form) and plasticizer (liquid form) are homogeneously mixed forming a molten plastic. After the fusion point, the torque gradually levels off and reaches a constant value.

Several formulations were produced with various concentrations of plasticizers, yielding different fusion torque data. It was observed that the higher the fusion torque, the lower the processing temperature. Torque data could then be used for viscosity evaluation in other melt processes. As seen in Table 4, with a plasticizer loading of up to 50 percent glycerol, the fusion torque was about seven times lower than that with a plasticizer content of 12.5 percent. This large decrease in torque can be attributed to the large amount of motion now associated with the polymer with the introduction of the plasticizer. The polymer's melt viscosity has now been significantly reduced; thus, an overall reduction in torque is observed. The same trend was evident with the ethylene glycol samples. It should be noted that the material produced from the 100 phr glycerol formulation was so tacky that it stuck to every surface it came into contact with. The 50-phr glycerol sample was very rubbery after removal from the torque rheometer; however, it became extremely brittle upon cooling to room temperature. These materials showed promise for potential adhesive applications because they were so tacky.

Melt blending: Melt blending of the polymer/plasticizer pairs, which included glycerol (Aldrich Chemical Co., used as received, 98 percent), ethylene glycol (Aldrich Chemical Co., used as received, 99 percent), and distilled water was conducted in a Haake torque rheometer equipped with twin screw mixing heads at concentrations ranging from 12 to 50 percent. The torque and melt temperature of these formulations was recorded on a microprocessor. The maximum bowl capacity of the rheometer is 55 cc. The polymer, in the form of a white powder, was dried under vacuum (1 mmHg) at 50?C for 24 hours prior to use. Following this drying procedure, the polymer was introduced to the mixing chamber followed by the plasticizer. The loading torque, fusion torque, and compaction rates were determined as a function of time.

Compression molding: The polymer/plasticizer pairs were dried under vacuum (1 mmHg) at 50?C for 24 hours prior to molding. Samples consisting of 50 percent glycerol and ethylene glycol were too sticky to process. Samples were compression molded at temperatures ranging from 110~140?C using a WAKED Press Model 45-197, and subsequently cooled in a DARED Press Model 45-197 at room temperature (70?F); 1.3 g of the plasticized pullulan was placed in a rectangular mold (50 mm x 25 mm x 0.7 mm), covered with a cut piece of mylar film (90 mm x 75 mm), and covered with an aluminum block (108 mm x 108 mm x 6 mm). All of the samples were preheated for 1 minute, heated under pressure for 2 minutes at approximately 20 tons, and then allowed to cool to room temperature before removal. All samples were placed in a dessicator containing drierite prior to subsequent analysis.

Injection molding: Injection molding was performed on the plasticized pullulan pairs produced from the Haake torque rheometer. The samples were dried and molded into micro tensile-dumbbells using a Model CS-183 Mini Max Molder. The cup temperature was 140?C, and the material was allowed to melt for about 1.5 minutes prior to injection. The material was manually injected into a mold held by a heated clamp kept at a temperature of 95?C. The samples were removed immediately from the hot mold, the flash was trimmed, and the samples placed in a dessicator prior to further characterization.

Effects of plasticizers on processability: Dried pullulan was melt blended with various plasticizers using a Haake torque rheometer. Depending upon the amount of plasticizer used, the material had physical characteristics ranging from that of an elastomer to that of a brittle plastic. The following observations can be made. Viscosity decreases only slightly with temperature, and at higher temperatures, water loss may be occurring that produce no effective change in the viscosity. When glycerol is used instead of water, it was observed that glycerol shows a greater dependence of viscosity on temperature.

Lamination and Coextrusion of Starch Foam
Starch foam of 1/16-inch thickness was supplied by Americal Excelsior Co., TX. The foam sheet was used as a substrate in an extrusion coating unit where a biodegradable polymer can be melt coated onto the foam. Presently, polymers such as poly(lactic acid) (supplied by Cargill Co., MN), poly(caprolactone) (Union Carbide), and an aromatic-alliphatic copolyester (supplied by Eastman Chemicals, TN) are being attempted. The main focus in this study is to deposit a thin film of polymer on both sides of the starch foam sheet that can be thermoformed. Coextrusion of starch foam and a biodegradable polymer simultaneously also will be attempted.

Chitosan and Fiber Production
Chitosan (DAC 90 percent) chitosanium pyrrlidone carboxylate and chitosanium lactate were purchased from the Amerchol Corporation, and PVOH was purchased from the Aldrich Chemical Co. The chitosanium pyrrolidone carboxylate and chitosanium lactate are O-modified chitosan containing both amino and carboxyl groups, and show varying solubility in water, dilute acid, and dilute alkali?depending on the degree of substitution. The viscosity of different samples was determined by RVTD-II viscometer. Thermal properties of the sample were tested by Perkin?Elmer TGA. Fibers of chitosan and its derivatives were obtained by using a solution spinning method. The films were cast directly from 1 percent acetic acid solution and washed with 0.05 N ammonium hydroxide solution. All mechanical properties were tested by using universal testing machine. The crosshead speed was 0.1 inches/minute.

Table 5 shows that when chitosan is modified either by N-linking or O-linking, the initial decomposition temperature and decomposition temperature decrease. By comparing chitosan, butyryl chitosan, and hexanoyl chitosan, it is clear that the decomposition temperature decreases when the molecular weight of the modified group increases. Table 6 shows the heat stability of chitosan-Cu++ and chitosanium lactate-Cu++. The result shows that the heat decomposition temperature decreases when the chitosan and chitosanium lactate interact with Cu++ from the complex. It is interesting that when Cu++ is washed out by EDTA water solution, the decomposition temperature increases?but still lower than chitosan or chitosanium lactate. These phenomenon indicate that the inter- and intra-molecular electrostatic repulsion between chitosan chains will cause chains to form a special network that results in the decrease of decomposition temperature. After takeoff of Cu++ by EDTA, the chitosan chains cannot return to the original structure state, and the decomposition temperature is still lower than chitosan.

The viscosity of chitosan and its derivatives are dependent on the molecules and their concentration (Mn of chitosan: 50,000, chitosonium lactate and chitosonium pyrrolidone carboxylate, <30, 000), due to inter- and intra-hydrogen bonding between chitosan chains; the viscosity of chitosan derivatives in 1 percent acetic acid solution increases quickly by increasing its content. The solution becomes gel state when the chitosan derivatives are higher than 5 percent. For the solution spinning, viscosity of solution and pull ratio are very important. When the chitosan concentration and pull ratio are increased, the mechanical properties of wet spun fibers can be increased. In the gel state, the pull ratio of wet fiber is less than 3; it is therefore difficult to get good mechanical properties. To decrease the inter- and intra-hydrogen bonding, the PVOH has been mixed with chitosan derivatives. The incorporation of more than 4 percent PVOH in chitosan solution decreases the viscosity.

The water-soluble chitosan (50 percent DAC), chitosonium pyrrolidone carboxylate, chitosonium lactate and chitosan/PVOH, chitosonium pyrrolidone carboxylate/PVOH, and chitosonium lactate/PVOH (PVOH content: 5 percent of the chitosan or chitosan derivatives) were wet spun into fibers by conventional method (0.07 N NH4OH solution). The draw ratio achieved only 3 because of strong hydrogen bonding between chitosan chains. Table 7 shows the mechanical properties of fibers of chitosan and their derivatives. It is observed that the tensile strength and modulus of the O-linking modified chitosan derivative have lower properties than chitosan (50 percent DAC). Both strength and modulus decrease when the O-linking modified chitosan mixes with PVOH, whereas the properties get better in chitosan and PVOH. Table 1 shows the physical properties of cast films of chitosan and chitosan derivatives. Chitosan films show better properties than their derivatives.

Processing of Konjac
Work has been initiated recently. Konjac flour will be mixed with different plasticizers for extrusion. An attempt will be made to study the grafting on caprolactone using some lewis acid catalyst. Reactive extrusion will be carried out to make films.

Table 1. Physical properties of the cast films of chitosan and chotosan derivatives.

Thickness (mm)
Tensile strength (MPa)
Elongation (%)
Chitosan (50% DAC)
0.07 + 0.01
40.7 + 8
Chitosanium pyrrolidone carboxylate
0.06 +0.01
29.3 + 12
Chitosanium lactate
0.07 + 0.01
31.5 +10

Table 2. Effect of starch content upon blown film mechanical properties.

Fully hydrolyzed PVOH
Starch content (wt %)
Tensile stress (Psi)
Std. Dev +/-
Young's modulus (psi)
103, 000
97, 660
20, 420
Std. Dev. +/-
12, 280
2, 987
Elongation (%)
Std. Dev. +/-

Table 3. Mechanical properties of starch and its derivatives with biodegradable polymers.

Strength (Mpa)
Modulus (Mpa)

Table 4. Fusion torque and temperature for pullulan/plasticizer pairs formulated in torque rheometer.

Fusion torque (Mg) Temperature (?C)
DD0G78 (100 phr glycerol) 972 110, Td = 217a
DD0G81 (50 phr glycerol) 1325 120, Td = 234
DD0G99 (25 phr glycerol) 7250 110, Td = 248
DDE122 (50 phr ethylene glycol) 1638 100, Td = 210
DDE125 (40 phr ethylene glycol) 2160 120, Td = 228
DDP122 (25 phr ethylene glycol) 8879 110, Td = 237
a: onset of decomposition determined from TGA

Table 5. Moisture content, decomposition temperature of chitosan and its derivatives.

Moisture content (%)
Initial Decomposition temperature (?C)
Decomposition temperature (?C)
Chitosan (90% DAC)
Butyryl chitosan
Hexanol chitosan
Chitosan (50% DAC)
Chitosanium pyrrolidone carboxylate
Chitosanium lactate

Table 6. The decomposition temperature of chitosan-Cu++ and chitosanium lactate-Cu++ complex.

Decomposition temperature (?C)
Decomposition temperature (?C) after treated by EDTA water solution
Chitosan (90% DAC)
chitosan-Cu++ complex
Chitosanium lactate-Cu++ complex

Table 7. Mechanical properties of fibers of chitosan and its derivatives.

Chotosan 50% DAC
Chotosan PC
Chotosan PC/PVOH
Chotosan L
Chotosan L/PVOH
Tensile strength
Tensile modulus

Chitosan L: chitosan lactate, chitosan PC: chitosan pyrrolidone carboxylate

Future Activities:

Co-PIs and graduate students will continue working on this project.


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Journal Articles:

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Supplemental Keywords:

risk management, pollution prevention, green chemistry, life-cycle analysis, alternatives, sustainable development, clean technologies, innovative technologies, renewable, waste reduction, waste minimization, environmentally conscious manufacturing., RFA, Scientific Discipline, Sustainable Industry/Business, Environmental Chemistry, Sustainable Environment, Technology for Sustainable Environment, Analytical Chemistry, Biochemistry, cleaner production, environmentally conscious manufacturing, aqueous processing, alternative materials, konjac, biodegradable materials, innovative technology, polysaccairde, chitosan, plastics, water soluble, pollution prevention, polymer design, cellulose, green chemistry

Progress and Final Reports:
Original Abstract
Final Report