METHODS FOR PRODUCING BIOPOLYMERS TECHNICAL FIELD This invention relates to methods for producing polyol compositions and biopolymers, and more particularly, to producing polyol compositions from fermentation residues, food scraps, corn starch and/or agricultural crop residues and using the resulting polyol compositions to produce biopolymers.

BACKGROUND Polyurethane and polyester are synthetic polymers. The annual market for polyurethane in Canada and the United States is about 2.8 million tons. Currently, polyurethane is mainly synthesized from isocyanate and polyols obtained from petroleum resources. Polyester also is derived mainly from petroleum. Petroleum resources are non-renewable and petroleum-based polymers are unfriendly to the environment, and, in some cases, hazardous to human health. Thus, there is a need for a method to produce polymers from renewable resources to ease the environmental impact of, and the dependence on, petroleum-based products.

SUMMARY The invention is based on a method for producing biopolymers from fermentation. residues, food scraps, starch, and agricultural crop residues such as rice, oat or wheat straw, corn fibers, corn stover, bagasse, soy, oat, or sunflower hulls, and beet pulp. As described herein, such materials can be liquefied under mild conditions using liquefying reagents such as cyclic carbonates and polyhydric alcohols to produce a liquefied mixture containing a hydroxyl-rich polyol composition, which can be directly used for producing polymers such as polyurethane and polyester without separation or purification. Polyol compositions produced with methods of the invention can be used to produce flexible and rigid polyurethane foams by reaction with isocyanates, such as diphenylmethane diisocyanate. The foams can be used, for example, as packaging materials or insulating materials in construction. Polyester also can be prepared from polyol compositions by cross-linking the polyols with organic acids (e. g. , citric acid, adipic acid, or sebacic acid) and/or acid anhydrides (e. g., succinic anhydride or maleic anhydride). The polyester can be processed, for example, into films, sheets and fibers, and used as packaging and textile materials.

In one aspect, the invention features a method for producing a polyol composition.

The method includes combining non-woody crop residues (e. g. , rice straw, oat straw, corn stover, wheat straw, pineapple pulp, sunflower hulls, beet pulp, oat hulls, or soybean hulls) with a liquefying agent to form a reaction mixture and liquefying the reaction mixture to produce the polyol composition. The liquefying agent can be a cyclic carbonate such as ethylene carbonate or propylene carbonate. The liquefying agent also can be a polyhydric alcohol such as ethylene glycol, hexanediol, or polyethylene glycol.

The reaction mixture further can include com starch. The liquefying step can include incubating the reaction mixture at about 150°C to 100°C for an amount of time sufficient to produce the polyol composition.

In another aspect, the invention features a method for producing a polyol composition from starch. The method includes combining com starch with a cyclic carbonate to form a reaction mixture and liquefying the reaction mixture to produce the polyol composition.

The invention also features a method for producing a polyol composition that includes combining starch and a cyclic carbonate to form a first reaction mixture, liquefying the first reaction mixture to form a liquefied reaction mixture, combining non- woody crop residues with the liquefied reaction mixture to obtain a second reaction mixture, and liquefying the second reaction mixture to obtain the polyol composition.

Methods for producing biopolymers also are featured. The polyol compositions can be reacted with diisocyanate or with an organic acid or an organic acid anhydride to obtain the biopolymer.

In another aspect, the invention features a method for producing a polyol composition. The method includes combining food scraps or fermentation residues with a liquefying agent to form a reaction mixture; and liquefying the reaction mixture to produce the polyol composition, wherein the liquefying agent is a cyclic carbonate or a polyhydric alcohol.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.

DESCRIPTION OF DRAWINGS FIG. 1 is a graph depicting the effect of temperature on liquefaction of corn stover.

FIG 2A is a graph depicting the effect of the amount of solid on liquefaction of corn stover.

FIG 2B is a graph depicting the effect of time on the liquefaction of corn stover (ethylene glycol/corn stover ratio: 3; catalyst content: 5%; liquefaction temperature: 140°C ; 160°C ; X180°C).

FIG 2C is a graph depicting the effect of the catalyst content on the liquefaction of corn stover (ethylene glycol/corn stover ratio: 3; liquefaction temperature: 160°C ; catalyst content :-3% ;-5% ; x7%).

FIG 2D is a graph depicting the effect of the ethylene glycol/corn stover ratio on the liquefaction (liquefaction temperature: 160°C ; catalyst content: 5%; ethylene glycol/ corn stover ratio :'1 ;-2 ; x3).

FIG 3 is a graph depicting hydroxyl values for starch liquefaction at different temperatures.

FIG 4 is a graph depicting the effect of catalyst dosage on polyols.

FIG 5 is a graph depicting liquefaction rates for starch using propylene carbonate as a liquefying agent and sulfuric acid (SA) as catalyst.

FIG 6 is a graph depicting hydroxyl values for starch using propylene carbonate as liquefying agent and sulfuric acid (SA) as catalyst.

FIG 7 is a graph depicting effect of curing temperature and time on the cross- linking of starch polyol.

FIG 8A and 8B are bar graphs depicting solubility of polyester sheets from starch polyol (8A) and corn stover polyol (8B).

FIG 9A and 9B are bar graphs depicting the physical strength of polyester sheets from starch polyol (9A) and from starch and corn stover polyols (9B).

FIG 10A and 10B are graphs of the biodegradability of polyurethane foams and polyester sheets from starch polyol (1OA) and corn stover (1OB).

DETAILED DESCRIPTION In general, the invention features methods to produce polyol compositions from renewable and inexpensive sources of biomass such as fermentation residues, (e. g., distiller's dried grains (DDG) or distiller's dried grains with solubles (DDGS), food scraps, corn starch or crop residues. These sources of biomass contain hydroxyl groups in their main chemical components (e. g. , starch, cellulose, hemicellulose, and lignin), and therefore can be used as raw materials for making biopolymers. In order to make the hydroxyl groups accessible for biopolymer formation, the biomass needs to be partially degraded. Polyol compositions obtained from such methods can be used to replace petroleum-related resources as feedstock for biopolymer production (e. g., polyurethane or polyester production). Advantageously, the polyol compositions can be used directly for biopolymer production without further separation or purification. Biopolymers produced from the polyol compositions can be formulated such that the polymers are biodegradable.

Methods of Producing Polyol Compositions Methods of the invention include chemically liquefying biomass with liquefying agents to convert the biomass into a polyol composition. As used herein, the term"polyol composition"refers to a composition containing compounds having multiple hydroxyl groups, including five carbon sugars (pentoses) such as arabinose and xylose, six carbon sugars (hexoses) such as glucose, galactose, and mannose, or other hydroxyl-containing compounds in lignin and glucosides formed during liquefaction of starch and cellulose.

Non-limiting examples of biomass suitable for the production of polyol compositions include fermentation residues, food scraps, corn starch, and non-woody crop residues such as pineapple pulp, rice, oat, and wheat straw, com stover, beet pulp, sunflower hulls, oat hulls, and soybean hulls. Fermentation residues include DDG, DDGS, wet cake, and syrups, or other by-products obtained from the production of ethanol for oxygenated fuels or the distillery industry. Food scraps include any food materials or mixtures of food materials. As such, the protein, fat, fiber, and carbohydrate content of food scraps will vary depending on the types of foods present in the food scraps. Corn starch is a polymer of glucose units linked together by a- (1, 4') glycosidic bonds and branch units linked to the main chain by a- (1, 6') glycosidic bonds. Each glucose unit contains three hydroxyl groups.

Most crop residues are generally lignocellulosic materials, which are composed mainly of cellulose, hemicellulose and lignin. Cellulose is a polymer of glucose units linked by p-l, 4'-glycosidic bonds. Hemicellulose refers to a group of polysaacharides that contains various monosaccharide residues of pentoses and hexoses. Lignin is a polymeric material composed of phenylpropane structural units that are crosslinked through ether and carbon-carbon bonds. Lignin contains both alcoholic and phenolic hydroxyl groups.

The biomass can be combined with a liquefying agent such as a polyhydric alcohol or a cyclic carbonate and a catalyst and incubated at an elevated temperature for an amount of time effective to produce the polyol composition. Non-limiting examples of polyhydric alcohols include pentaerythritol, ethylene glycol, and hexanediol. Non- limiting examples of cyclic carbonates includes ethylene carbonate and propylene carbonate. Cyclic carbonates and ethylene glycol are particularly useful when used together as a liquefying agent. Sulfuric acid is a particularly useful catalyst.

Reaction conditions can include temperatures of 100 to 180°C for about 10 minutes to about eight hours and an amount of catalyst ranging from about 0.5% to 3% of the biomass. Since the boiling points of most liquefying agents can be as high as 200°C, the reactions can be performed under atmospheric pressure. For example, corn starch can be liquefied at low temperatures (e. g. , about 100 to 150°C) by incubating for approximately 10 minutes to six hours. The ratio of starch to liquefying agent can range from 1: 1 to 6: 4 (by weight) with the amount of catalyst ranging from about 0.5 to 3% of the starch. Crop residues can be liquefied at temperatures ranging from 140 to 180°C by incubating for 30 minutes to 8 hours. The ratio of crop residue to liquefying agent can range from 3: 10 to 1: 2 (by weight) with the amount of catalyst ranging from about 1 to 10% of the crop residue. Progress of the reaction can be monitored by determining the hydroxyl value, a measure of how many free hydroxyl groups are in the polyol composition, of the mixture.

The extent of liquefaction can be used to control the viscosity and the amount of hydroxyl groups that are accessible for biopolymer formation in the polyol composition.

Thus, process conditions such as reaction temperature and catalyst dosage can be used to tailor properties of the resulting polyol compositions for particular downstream applications. For example, higher amounts of catalyst typically result in polyol compositions having lower hydroxyl values. When a lower amount of catalyst and lower temperatures are used, viscosity of the polyol compositions typically is higher.

Liquefied corn starch can be used to promote the liquefaction of crop residues. In this embodiment, corn starch can be combined with a liquefying agent and a catalyst, as discussed above, and at least partially liquefied before adding the crop residues. It is not necessary to add additional catalyst when adding the crop residues. Liquefaction of the crop residues can be monitored as discussed above.

Methods of Producing Biopolymers The reactivity of hydroxyl groups in biomass sources such as corn starch or crop residues is usually poor due to the hindered accessibility to the functional groups. In liquefied biomass, however, the hydroxyl groups within the biomass become accessible and more reactive to cross-linking chemicals. Thus, the hydroxyl groups within the polyol compositions obtained from liquefying food scraps, fermentation residues, starch, and/or crop residues can react with cross-linking chemicals and used to produce biopolymers.

Polyurethane foams can be produced by reacting a polyol composition with an isocyanate such as diphenylmethane diisocyanate according to known methodology.

Typically, the polyol composition, a blowing agent (to form bubbles), a catalyst, and a surfactant are mixed together before adding the isocyanate. Reaction conditions can be adjusted to control the type of polyurethane that is produced (e. g., flexible, semi-rigid, or rigid polyurethane foam). Polyurethane foams produced with the polyol compositions can be used as packaging, construction and insulating materials, and can be formulated to be biodegradable.

Polyesters can be produced by reacting a polyol composition with multi-functional acids (citric acid, adipic acid, sebacic acid) and/or acid anhydride (succinic anhydride, maleic anhydride) according to know methodology. Flexibility and mechanical strength of the polyesters can be controlled by adjusting the formulation, processing conditions, curing temperature, and time. The polyester can be processed into films, sheets, and fibers, and used as packaging and textile materials. In addition, polyesters can be formulated into adhesives. Polyesters can be formulated to be biodegradable.

The invention will be further described in the following examples, which do not limit the scope of the invention described in the claims.

EXAMPLES Example 1-Methods and Materials For Liquefaction of Crop Residues and Starch Corn starch was purchased from the local grocery store and used as feedstock.

Crop residues that were used included pineapple pulp, wheat straw, corn stover, soybean hulls, sunflower hulls, and sugar beet pulp. Table 1 shows the chemical composition of wheat straw and pineapple pulp. "Hot water extractives"include soluble inorganic compounds, tannins, gum, starch, sugar, and coloring matter. The high concentration of the hot water extractives in pineapple pulp is due to its high sugar content. Holocellulose represents polysaccharides (cellulose plus hemicellulose). Pineapple pulp has less ash than wheat straw. The lignin content of pineapple is lower than the lignin content of wood. Its Klason lignin (i. e., lignin obtained after the non-lignin components have been removed with a prescribed sulfuric acid treatment) is lower than that of most agricultural residues, such as rice straw, wheat straw, and corn stover.

TABLE 1 Chemical composition of wheat straw and pineapple pulp Item W71eat straw Pi7zeapple pulp Moisture, % 7. 65 9. 19 Ash, % 7.45 2.10 Hot water extractives, %--17.50 1 % NaOH extractives, %--54. 03 Ethanol-benzene extractives, % 5.51 4.94 Holocellulose, % 72.99 76.14 Klason lignin, % 16.51 8. 14 Fermentation residues used in this study included distillers dried grains with solubles (DDGS), wet cake, and syrup. The food scraps included bread, meat, cheese, cake, and vegetables, etc. Tables 2A and 2B show the composition of DDGS and the food scraps, respectively. Both contain a very high amount of protein and fat, which is a challenge to chemical liquefaction.

TABLE 2A Major components in DDGS Dry Matter 87-93% Crude Protein 26. 8% Crude fat 9.7% Crude fiber 7. 8% TABLE 2B Composition of the food scraps Item Food scrap I Food scrap 2 Moisture, % 9.1 7.8 Ash, % 9.5 11.4 Fat, % 4.8 1.9 Protein, % 5.3 3.1 Total carbohydrate, % 70 75.6 others, % 1.3 0.2 Experimental Setup and procedures of liquefaction : The lab apparatus used for liquefaction contained a heater, a temperature controller, a flask, and a motor-driven stirrer. Because of the high boiling point of the liquefying reagents, the liquefaction was operated under atmospheric pressure. No pressure vessels were required.

The liquefaction procedure was performed as follows. Liquefying reagent and catalyst were added to the flask and heated. For liquefaction of crop residues, ethylene carbonate and a small amount of ethylene glycol (about 10%) were used. For liquefaction of cornstarch, ethylene carbonate, propylene carbonate, and polyhydric alcohols such as ethylene glycol, poly (ethylene glycol), glycerol, propylene glycol, butanediol, hexanediol, were used as liquefying chemicals, either alone or in combination. Weighed raw material or starch was then added into the flask, and mixed with the liquefying chemicals. Liquefaction was conducted with continuous stirring under atmospheric pressure. After a preset reaction time, the heater was turned off, and the stirrer kept running until the mixture cooled down. The liquefied mixture (polyols) was collected for later use and analysis. The liquefied mixture was homogenous and was dark in color and thick (viscous).

Determitiatiott of viscosity. Viscosity of liquefied starch or crop residues was determined at 25°C with a Synchro-Lectric viscometer (Model LVT, Brookfield Engineering Laboratories, Inc. , Stoughton, Massachusetts, USA). Spindle and rotational speed were chosen based on the viscosity of the sample. Viscosity was recorded on a scale of 0-100, then converted to mPa s based on spindle number and speed.

Deterxnittizlg lzydroxyl value of tlze polyols : Hydroxyl value, a measure of the number of free hydroxyl groups in the polyol composition, was determined by placing one gram of bio-polyol sample into a 150 ml beaker then adding 10 ml of phthalic anhydride solution (150 g phthalic anhydride dissolved in 900 ml of dioxane and 100 ml pyridine) to the beaker. The beaker was covered with aluminum foil and placed on a boiling water bath for 20 minutes. After cooling, 20 ml of a dioxane/water (8 : 2) solution and 5 ml of water were added to the beaker, then the mixture was titrated with 1 N NaOH to pH 8. 3 using a pH-meter to indicate the end-point. A blank titration was conducted with the same procedure. Hydroxyl values were calculated using the formula below: Hydroxyl value (mg KOH/g) = (B-S)-N x 56.1/W where B-volume of NaOH standard solution consumed in blank titration, ml S-volume of NaOH standard solution consumed in sample titration, ml W-sample weight, g N-equivalent concentration of NaOH standard solution Example 2-Liquefaction of corn stover Corn stover meal is a porous and low-density material with high absorption ability. Corn stover was liquefied as described in Example 1 with ethylene carbonate and the results shown in FIG 1. To achieve a satisfactory liquefaction, the stover meal and the liquefying reagent were thoroughly mixed to prevent carbonization that may occur due to incomplete heating. With increasing temperature, liquefaction rate increased significantly. Temperatures above 160°C were required to achieve a high liquefaction rate, although hydroxyl value decreased with increasing temperature. Without being bound to a particular mechanism, hydroxyl-rich carbohydrates may be decomposed and converted to low molecular weight products, such as organic acids, at high temperature.

Table 3 shows the liquefaction results at various solids level of com stover. When the ratio of stover to liquefaction reagent was below 30: 100, mild stirring was sufficient to produce a smooth and a uniform liquid. When this ratio was increased, it was necessary to more vigorously stir the mixture as the viscosity of the liquefied product increased significantly. For example, corn stover could be completely liquefied at a ratio of 40: 100, but the viscosity was higher than at a lower ratio. When the ratio was over 50: 100, the liquefaction was incomplete because the liquefaction reagent was insufficient to maintain a uniform reaction. Carbonization occurred at this ratio.

TABLE 3 Possibility of liquefaction at high corn stover solids Stover/Liquefying Stirring metZ10d Result reagent 30: 100 Magnetic stirrer Unifonn liquefaction, thin liquid 40: 100 Mechanical stirrer Uniform liquefaction, thicker liquid 50: 100 Mechanical stirrer Partial carbonization Note : l 70 °C, 4 hours and 5% catalyst 071 stover.

FIG 2A shows the liquefaction result of corn stover under various ratios of corn stover to liquefying reagent. The increase in hydroxyl value was probably because of high corn stover content. With an increase in solid content, the viscosity of liquefied product increased sharply, with the ratio of 45: 100 being a critical point. If the ratio is increased higher than 45: 100, the liquid will have very high viscosity, and liquefaction may fail.

Sulfuric acid is typically used as a catalyst for liquefaction, with 1-3% of sulfuric acid generally used. Other catalysts, such as hydrochloric acid, phosphoric acid and zinc chloride were also tested to determine if they were suitable as catalysts. As shown in Table 4, these catalysts did not work in the liquefaction of corn stover. After four hours of reaction at 170°C, corn stover was maintained in its original state (particles).

TABLE 4 Liquefaction of corn stover with different catalysts Catalyst Dosage of catalyst Straw/Liquefaction Result (% straw) reagent H2S04 1.5 30: 100 Completely liquefied HC1 2.0 20: 100 Unable to liquefy H3PO4 6.0 20: 100 Unable to liquefy ZnCl2 3.0 30: 100 Unable to liquefy Note : 170'C, 4 hours.

As depicted in FIG 2B, ethylene glycol also was effective in liquefaction of corn stover. FIG 2B shows the effect of liquefaction time on the liquefaction rate at different reaction temperatures. With each increment of liquefaction time, the liquefaction rate increased significantly. In contrast, the liquefaction rate increased with an increase of the liquefaction temperature. In order to obtain the maximum productivity and economic energy supply, further experiments were performed using a liquefaction time of 4 hr and a reaction temperature of 160°C.

The effect of the sulfuric acid catalyst content on liquefaction is shown in FIG 2C.

As can be seen, with each increment of reaction time, the liquefaction rate increased significantly. The optimum catalyst content was 5%. FIG 2D shows the effect of the ethylene glycol/corn stover ratio on the liquefaction rate. As can be seen in FIG 2D, with the increment of reaction time, the liquefaction rate increased slightly at the ethylene glycol/corn stover ratio 1, and increased quickly at the ratio of 3.

Example 3-Pentaerythritol as liquefying chemical Pentaerythritol, a polyhydric alcohol, was used as a liquefying agent for corn stover. Since the melting point of pentaerythritol is as high as 255°C, the liquefied mixtures were in solid state because of crystallization of pentaerythritol at room temperature. To decrease the melting point, a certain amount of ethylene glycol was added as an assistant liquefying reagent. As shown in Table 5, with the addition of ethylene glycol, the melting point of pentaerythritol dropped greatly. Corn stover was successfully liquefied at 160°C for 3 hours. The ratio of liquefying chemicals (pentaerythritol/ethylene glycol = 60: 40) to corn stover was 100: 40. Although the liquefied mixture was solid at room temperature, it became a thin liquid upon heating.

TABLE 5 Change in melting point of pentaerythritol with addition of ethylene glycol Pentaerythritol/ethylene glycol (w/w) Melting point, C 100: 0 255 60: 40 160 50: 50 130 Example 4-Liquefaction of other crop residues Table 6 gives the liquefaction results for other crop residues, including pineapple pulp, soybean hulls, sunflower hulls, and beet pulp. Although these crop residues were liquefied by ethylene carbonate/ethylene glycol (9: 1), more severe conditions were required than for com stover. In other words, more catalyst, longer liquefaction time, and higher temperatures were required to achieve a complete liquefaction.

TABLE 6 Typical conditions for the liquefaction of other crop residues <BR> <BR> <BR> <BR> Residue/Catalyst Temp. Time Hydroxyl value<BR> <BR> <BR> <BR> Crop residues liquefying (% residue) (°C) (hour) (mg KOH/g)<BR> <BR> agent (w/w) Pineapple pulp 30: 100 4.7 160 7. 5-- Soybean hulls 30: 100 8.0 180 3 208.9 40: 100 6.5 180 6 153.7 Sunflower hulls 30: 100 7.7 180 3 240.3 40: 100 8.0 180 3 135.1 Beet pulp 30: 100 7.7 180 3 256.3 40: 100 6.5 180 6 143.9 40: 100 6.8 180 3 162.5 Example 5-Liquefaction of starch with cyclic carbonates Cornstarch was liquefied with ethylene carbonate (as described in Example 1) and the results presented in Table 7. Starch was completely liquefied at 110°C. From this result, it is believed that total liquefaction of starch can be accomplished within one hour under proper conditions, and low-temperature (below 150°C).

FIG 3 shows that starch polyols obtained at low temperatures seem to have more hydroxyl groups. Without being bound by a particular mechanism, the lower hydroxyl values at higher temperatures may be attributed to the complete decomposition of sugars.

TABLE 7 Rates of starch liquefaction (percent) at different temperatures Temperature (°C) Time (min) 110 120 140 160 10 99. 8 40 99.8 99.5 60 99.4 99.8 100 99.7 120 99. 5 99.7 99.8 180 99. 8 99.4 99.8 190 99. 7 240 99.8 270 99. 5 300 99.8 320 99. 5 Table 8 shows the liquefaction rates and hydroxyl values as affected by starch/liquefying ratio and temperature. The results indicate that starch can be completely liquefied at a ratio of starch to liquefying reagent as high as 65: 35 with a satisfactory product. However, at a high ratio of starch to liquefying reagent, catalyst should be properly increased to achieve good liquefaction. At very high ratio, such as 70: 30, carbonization of reactants occurred due to failure of uniformly mixing starch and liquefying reagent, especially when catalyst and temperature were insufficient to facilitate rapid liquefaction of starch.

TABLE 8 Liquefaction of starch at different ratios of starch to liquefying reagent No. 5 6 7 8 9 Conditions Starch/Liquefying reagent 100: 100 100: 100 60: 40 65: 35 70: 30 Catalyst, % on starch 1 1 2. 5 2 0.86 Temperature, °C 110 120 130 130 125 Liquefaction time, min 240 85 180 180 180 Liquefaction rate, % 99.4 95.1 99.5 97.8 97.6 Hydroxyl value, mg KOH/g 261.5 226.5 131.3 177.1 200.7 Viscosity High High Low Low Carbonized FIG 4 shows the effect of catalyst dosage on liquefaction of starch at reactions conducted at 130°C and a starch to liquefying chemicals ratio of 100: 70. At low catalyst dosage (<1% of starch), liquefaction was slow, and viscosity of the obtained bio-polyols was high. Furthermore, the amount of accessible hydroxyl groups (hydroxyl value) was also low. For example, at a catalyst dosage of 0.7%, the viscosity was as high as 1. 13 x 105 mPa s, and the hydroxyl value was only 298.2 mg KOH/g. With the addition of more catalyst, the viscosity dropped sharply. On the other hand, the hydroxyl value dropped contrarily after reaching a maximum value at 1 % catalyst. This may be due to the decomposition of low molecular products into organic acids.

Similar results were obtained using propylene carbonate as liquefying reagent for starch. FIG 5 and FIG 6 show the liquefaction results of starch with propylene carbonate under conditions of 130°C and a ratio of starch to propylene carbonate (3: 2). Increasing dosage of sulfuric acid can shorten reaction time. The liquefaction rate was above 96% at any sulfuric acid dosage, which is a slightly lower than that in case of ethylene carbonate.

It was also shown that the liquefied starch had a low hydroxyl value at high sulfuric acid dosage probably due to more sugar decomposition, which matches the results of ethylene carbonate.

Example 6-Liquefaction of starch with polyhydric alcohols Ethylene glycol, propylene glycol, butanediol and hexanediol, glycerol and polyethylene glycol (M = 200 and 400) were tested to determine if they were suitable as liquefying agents. As shown in Table 9, polyhydric alcohols are suitable liquefying agents for starch. Of the polyhydric alcohols tested, ethylene glycol, polyethylene glycol 200, and hexanediol were good candidates as these chemicals have higher boiling points, and produced liquefied products with desirable characteristics.

It was observed that some of the polyhydric alcohols resulted in a very viscous polyol composition. For example, poly (ethylene glycol) 400 (average molecular weight 400) produced a viscosity of 2. 6x 105 s, while glycerol gave a viscosity of 5. 2x 104 rnPa-s. Because of the dehydration, butanediol became tetrahydrofuran during liquefaction. As a result, the temperature was unable to rise above 80°C under atmospheric pressure if butanediol was used as liquefying reagent.

TABLE 9 Liquefaction of starch with polyhydric alcohols <BR> <BR> <BR> <BR> <BR> Hydroxyl<BR> Liquefying Temp. Time value Viscosity<BR> Liquefying (% of<BR> <BR> <BR> <BR> <BR> <BR> <BR> reagents (°C) (hr) (mg (mPa#s #10-3)<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> agent (w/w) starch)<BR> KOH/g)<BR> Ethylene 100:80 2 130 15 389.9 2.47<BR> Ethylene 100: 80 2 130 1.5 389.9 2.47 glycol Ethylene 100 : 60 2 130 1.5 372.6 6.20 glycol Ethylene 70 : 30 2 130 2.0 300.5 18.40 glycol Polyethylene 90 : 60 2 130 2.5 216.6 9.43 glycol 200 Polyethylene 60: 40 2 130 2.8 144.2 261.50 glycol 400 Glycerol 60: 40 2 130 2.0 300.2 52.20 Propanediol 60: 40 2 130 2.0 Butanediol 60: 40 2 80* 2.0 Hexanediol 60: 40 2 130 2.0 * Temperature could only reach about 80°C because of the formation of low-boiling-point tetrahydrofuran by dehydration of butanediol during liquefaction.

Example 7-Liquefaction of starch with sorbitol Sorbitol is another poly-alcohol that can be used as a liquefying chemical for starch. Sorbitol can be easily produced from reduction of glucose, while glucose can be obtained from hydrolysis of starch. Liquefaction of starch using sorbitol was conducted according to the conditions given in Table 10. The results showed that (1) starch can be liquefied by sorbitol; (2) addition of small amount of ethylene glycol as a co-liquefying chemical can significantly improve the liquefaction operation, increase the percentage of starch that can be liquefied and decrease the viscosity of resulting polyol; and (3) polyester sheets can also be made from this polyol, but the sheets are slightly brittle.

TABLE 10 Liquefaction of starch with sorbitol Sorbitol, g Ethylene glycol, g Starch, g 30 0 30 25 5 35 24 6 40 Example 8-Starch Polyol Promotes Liquefaction of Corn Stover Since starch was easy to liquefy, and liquefied starch is a mixture of poly-alcohols with different molecular weights, it was determined if liquefied starch could be used to liquefy corn stover, or at least to improve the liquefaction of corn stover. A series of liquefaction were conducted under the conditions listed in Table 11. The liquefaction was completed in two steps. In the first step, only starch was liquefied with full dosage of liquefying reagents (ethylene carbonate and ethylene glycol). Corn stover was then added into the mixture of liquefied starch and residual liquefying chemicals and liquefied in the second step. The results showed that liquefied starch promoted the liquefaction of corn stover. As discussed above, without starch, 100 parts (weight) of liquefying reagent could liquefy about 40-45 parts of corn stover. However, as shown in Table 11, starch promoted liquefaction of corn stover. Eighty parts of liquefying reagent could liquefy 70 parts of starch and then 50 parts of corn stover (total 120 parts of biomass). The total biomass content in the resulting polyol was 60%.

TABLE 11 Results of co-liquefaction of corn stover and starch Starch, g Corn stover, g Ethylene glycol, g Ethylene carbonate, g 40 30 50 50 40 40 50 50 50 50 50 50 70 50 50 30 50 55 40 60 50 55 60 40 Example 9-Liquefaction Of DDGS, Wet Cake, Syrup, Wet Cake Plus Syrup From Ethanol Production Table 12 shows the liquefaction results of fermentation residues including wet cake, syrup, and wet cake plus syrup from ethanol production. The liquefaction time was longer than that required for starch and non-woody crop residues. The wet fermentation residues could be liquefied without pre-drying, which saves energy.

TABLE 12 Typical conditions for the liquefaction of DDGS, wet cake, syrup, wet cake plus syrup from ethanol production <BR> <BR> <BR> <BR> Sulfuric Liquefy Hydroxyl<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> Sample Temp. Time Liquefaction acid reagent value (g) (°C) (hr) (%) (g) (mgKOH/g) Rate (%) EC 150 100 DDGS 150 4 5 EG 150 270.9 94.6 Etc 100 Wet cake 200 150 6 8 EG 100 301.8 97.8 <BR> <BR> EG 100<BR> <BR> <BR> <BR> Syrup 500 140 8 10 EG 50 226.3 98.9<BR> EG 50<BR> <BR> Wet cake+ 150 5 8 EC 100 178.7 94.6<BR> Syrup 300 EG100 Example 10-Liquefaction of food scraps Table 13 shows that food scraps can be liquefied using ethylene carbonate (EC), although the liquefaction rate was lower than other materials. Without being bound by a particular mechanism, the liquefaction rate may be lower due to the high ash content.

TABLE 13 Typical conditions for the liquefaction of food scraps Sample Temp. Time Sulfuric Liquefy Hydroxyl value Liquefaction (g) (°C) (hr) acid (%) reagent (g) (mgKOH/g) Ratio(%) <BR> <BR> <BR> <BR> EC 50<BR> <BR> <BR> Food scrap 1 150 2.5 2.5 127.7 89.6<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> EG 50<BR> EC 50 Food scrap 1 150 2.5 2.5 101.8 84.8 <BR> <BR> <BR> <BR> <BR> EG 50<BR> EC 50 Food scrap 2 150 2.5 3 96.2 86.7 <BR> <BR> <BR> <BR> <BR> EG 50<BR> EC 50<BR> <BR> <BR> Food scrap 2 150 2.5 3 88.7 82.3<BR> <BR> EG 50 Example 11 - Producing polyurethane foams from bio-polyols A series of polyurethane foams, ranging from semi-rigid to rigid, were prepared from the bio-polyols from pineapple pulp, corn stover, and corn starch. Diisocyanates used in this research included three kinds of MDI (Diphenylmethane diisocyanate, Papi 27, Isonate 181 and Isonate 143L; DOW Chemical Company). The designated amounts of bio-polyols, catalyst, surfactant, blowing reagent, and other additives, if any, were premixed in a paper cup, and then the prescribed amount of diisocyanate was added into the cup and mixed with a high-speed stirrer for about 20 seconds. The mixture was allowed to rise at room temperature. Table 14 gives some example formulas for preparation of polyurethane foams from the bio-polyols. The foam was allowed to cure at room temperature for two days before any analysis was conducted. Properties of the bio- polyols, diisocyanates, formulation and other factors showed significant effects on formation, color, and physical properties of the bio-polyurethane foams.

TABLE 14 Example formulations of polyurethane foams from bio-polyols Raw material of bio-polyols Formulations Foams A. Pineapple pulp bio-polyol, 7 g PEG 400, 1 g Blowing agent, 0.5 g Pineapple pulp Catalyst, 0.2 g Rigid foam Surfactant, 0.2 g B. Papi 27,16 g 1. A. Corn stover bio-polyol, 7 g PEG 400,1 g Blowing agent, 0.4 g Catalyst, 0.2 g Rigid foam Surfactant, 0.3 g B. Papi 27,14 g Corn stover 2. A. Corn stover bio-polyol, 8 g Starch polyol, 2 g Blowing agent, 0.5 g Semi Catalyst, 0.3 g-rigid foam Surfactant, 0.4 g B. Papi 27,20 g 1. A. Starch bio-polyol, 5 g PEG 200, 1 g Blowing agent, 0.5 g Catalyst, 0.15 g Surfactant, 0.25 g B. Isonat 181, 19 g Corn Starch Rigid Foam 2. A. Starch bio-polyol, 7 g Dioctyl phthalate, 0.5 g Blowing agent, 0.8 g Catalyst, 0.3 g Surfactant, 0.3 g B. Papi 27,14 g Example 12-Producing polyester sheets from polyols Polyols also can be used to produce polyester. The hydroxyl groups in the polyols can react with dicarboxylic acids, dicarboxylic acid chloride, and/or carboxylic acid anhydride to produce polyester. Polyester sheets were prepared by cross-linking the polyols with the carboxylic acids and anhydrides listed in Table 15 to fonn a network of polyester. The weighed polyol, cross-linking chemicals and other additives were heated and mixed with stirring. The homogeneous mixture was molded into a container or coated onto a polished plate to form a uniform layer (0.15-0. 75 mm), which was cured at 120°C-160°C for 15 to 120 minutes, based on the formulation and thickness of the sheets.

TABLE 15 Cross-linking chemicals for starch polyol Cross-Result and Formula linking chemicals observation Adipic acid HOOC (CH2) 4COOH Fair sheet, bubbles Sebacid acid HOOC (CH2) 8COOH Not well cross-linleed, sticky, bubbles Terephthalic acid HOOC(C6H4)COOH Weak sheet, brittle, bubbles Terephthaloyl ClOC (C6H4) COCl A lot of bubbles, like foam; chloride brittle Citric acid HOOCCH2 (HOOC) C (OH) CH2COOH Brittle, bubbles Maleic anhydride C4H203 Fair sheet, stiff Succinic anhydride C4H403 Good sheet, flexible Note: OH/COOH = 1 : 1, sheets were cured at 120°C for 4 hours.

Table 16 shows some example formulas for preparation of polyester sheets. The properties such as flexibility and mechanical strength of the sheets are dependent on processing conditions of the polyols, formula composition, curing temperature, and time.

The carboxyl/hydroxyl ratio was generally 1.1-1. 2: 1.

TABLE 16 Example formulas for preparation of polyester sheets from bio-polyols Curing Formulation temperature Sheet source (°C) 1. Corn stover bio-polyol, 15 g Succinic anhydride, 3 g Citric acid, 0.9 g 140 Flexible sheet PEG 400,1. 2 g Additives, 1.3 g Corn stover 2. Com stover bio-polyol, 15 g 140 rubbery sheet Succinic ahydride, 3.8 g PEG 400,1. 3 g Additives, 1.4 g Corn Starch 1. Starch bio-polyol A, 15 g 120 Flexible sheet Succinic anhydride, 3 g Citric acid, 1.0 g PEG 400,1. 2 g Additives, 1.3 g 2. Starch bio-polyol A, 10 g 140 Stiff sheet Succinic anhydride, 2.0 g Citric acid, 0.6 g PEG 400,0. 8 g Additives, 0.8 g 3. Starch bio-polyol B, 10 g 120 Rubbery sheet Succinic acid, 1.7 g Citric acid, 1.0 g PEG 400,0. 8 g Additives, 0.9 g * Starch bio-polyol A was prepared using ethylene carbonate, and starch bio-polyol B using poly (ethylene glycol).

Determinafion of cross-linking extent of polyester. Since completely cross- linked network of polyester is almost insoluble in dioxane/water (8: 2, v/v), the percentage of insoluble residue in dioxane/water was used to evaluate, indirectly, the cross-linking extent of polyester. Weighed samples of cross-linked polyester were put into a flask containing dioxane/water (80: 20, v/v) for 24 hours at room temperature with stirring, then solvent was removed by filtration. The sample was washed with solvent until no black color was left, and then the insoluble residue was dried overnight in an oven at 105°C to determine its weight. The cross-linking extent of polyester was calculated using the following formula: Cross-linking extent (%) = (Wr/Ws) xl00 Where Ws-weight of initial sample Wr-weight of insoluble residue As indicated in Table 15, while the cross-linking reagents were able to react with polyols to form a polyester network, the reagents varied in affecting the properties of the formed polyester. The results of Table 15 show that cyclic anhydrides, such as succinic and maleic anhydrides, were suitable cross-linking reagent for polyols. Since the amount of the water produced by the anhydrides is only half of that by diacids, the polyester sheets cross-linked by anhydrides have less and smaller bubbles. Compared with succinic anhydride, maleic anhydride produces stiffer and less flexible sheets, since the double bond in maleric anhydride makes its molecular not as flexible as succinic anhydride.

Although citric acid has three carboxyl groups and one hydroxyl group, it was not as good a cross-linker as expected. The polyester sheet cross-linked by citric acid appears brittle and foamy.

A small amount of polyhydric alcohols, such as polyethylene glycol, hexanediol and glycerol, greatly improved the strength of the polyester sheet. Succinic anhydride alone can cure the starch or crop residue polyol into a polyester sheet, but the sheet was weak and less flexible. The long-chain polyhydric alcohols (polyethylene glycol and hexanediol) improved the flexibility of polyester sheet, while glycerol (with more hydroxyl groups) was helpful to increase the cross-linking density. Glycerol also functions as a plasticizer to improve the flexibility of polyester sheet. A small amount of citric acid is positive to the strength of the polyester sheet due to a higher cross-linking density.

In addition to cross-linking reagents, the curing reaction of the starch polyol was dependent on curing temperature and time. FIG 7 shows cross-linking results of starch polyol at different temperature and varied curing duration. Cross-linking extent was expressed as the percentage of insoluble residue of cross-linked polyester sheet in dioxane-water (80: 20, v/v), as described above. The results show that at the same temperature, curing extent increases with the extension of reaction time. High temperature enhances the curing reaction. For example, when the sheet was cured at 140°C for 5 hours, the curing extent was less than 70%, while if the sheet was cured at 180°C for 5 hours, the curing extent is near 100%.

Properties of tlzepolyester sheet.

Solubility. Polyester sheets were cut into small pieces of about 3x3 mm.

Weighed polyester pieces were put into flasks containing water or selected solvents, and kept for 8 days at room temperature, then water or solvent was removed by filtration. The samples were washed with corresponding water or solvent, and then dried overnight in the oven at 105°C to determine weight loss. For the solubility of polyester sheets in hot water, alkaline, and acid solution, the samples were refluxed for 6 hours in water, 2M NaOH or 2M H2S04, and then washed with water and dried to determine weight loss.

The solubility of polyester sheets was calculated using the following formula: Solubility (%) = [(Wi-Wf)/Ws] x100 Where W ;-initial weight of sample Wf-final weight of sample after treatment with water, solvents, alkali and acid solution The results depicted in FIG 8A and 8B show that starch and crop residue polyester sheets were stable in cold organic solvents and cold water. Only about 8-13% was dissolved during an 8-day treatment, depending on different solvents (see Table 17). The dissolved contents should represent those of unreacted cross-linking chemicals, residual liquefying reagents, and small pieces not completely cross-linked in the polyester sheet.

The solubility of polyester in hot water was 3-4 times higher than that in cold water.

Because of the trace of sulfuric acid in the polyester sheet, when it was refluxed in boiling water, the hydrolysis of the polyester was catalyzed by the sulfuric acid. This is the main cause of the higher solubility of polyester sheet in hot water than in cold water.

TABLE 17 Solubility of polyester sheets Solvents Solubility, % Acetone 13.2 Ethyl alcohol 10.7 1, 4-Dioxane 12.2 Benzene 10.7 Chloroform 13.2 Dimethyl fulfoxide 13.3 Acetic acid 12.8 Pyridine 13.1 80% aqueous 1,4-dioxane 8.8 85% aqueous pyridine 8.6 Cold water 8.2 Hot water 33.4 Hot 2M NaOH 100.0 Hot 2M H2S04 70. 0 It is known that esters can be catalytically hydrolyzed under either alkaline or acidic condition. Therefore, when the polyester sheet was refluxed in 2M NaOH or 2M H2SO4 for 6 hours, they were soluble. The solubility was 66% in 2M H2SO4 and 86% in 2M NaOH, respectively. The polyester sheet was more soluble in alkaline solution than in acidic one.

Tensile strength. Tensile strength of the polyester sheets (25 mm sample) was evaluated with a material testing system (Model APEX-T1000, Satec Systems, Inc., Grove City, Pennsylvania, USA) using a loading speed of 5 mm/min. Five tests were conducted for each sample, and the average reported.

FIG 9A and 9B show the tensile strength of polyester sheets from starch and starch and crop residues. For each polyol composition, two samples were evaluated. One was prepared from the polyol produced with ethylene carbonate/ethylene glycol (9: 1) (Sample #1), and to compare, another was made from the polyol produced with 100% glycol (Sample #2). The two samples had similar strength and elongation. Although the sheets were not very strong (about 5 MPa), the strength was acceptable for some applications, such as garden mulch film. iodegradability ofpolyurethaze and polyester. To evaluate the biodegradability of polyurethane foams and polyester sheets, the natural degradation of polymers in soil was simulated in lab. The soil used in this research was a merchandised potting soil. To ensure the presence of desired microorganisms, garden soil collected from outside was mixed into the potting soil. The test samples were buried in the potting soil in flowerpots.

The flowerpots were kept at 25°C in a cultivating room. The samples were watered twice a week. Every month, three samples were taken out, washed with water, dried in oven at 105°C to determine weight loss of the samples. The rate of biodegradation was indicated by the weight loss.

FIG 1 OA and 1 OB show the biodegradability of polyurethane foams and polyester sheets in a lab test over five months. The results show that polymer sheets made from corn stover lost about 82% of their initial weight in 10 months. Polyurethane foams from corn stover degraded more slowly than the polyester sheets. The foam lost about 16% of its initial weight in 10 months. It was also found that the weight loss was much more during the first month than during the following months. Starch polyurethane foam and polyester sheets lost near 5% and 8%, respectively, of its initial weight during first month, but only a few percentage points increase in weight loss was found during the followed months. Polyester sheets from corn stover lost 14.6% of their initial weight during the first month, but only 4.6 and 2.6% during the second and third months, respectively.

Microorganism spots or strains were observable on the surface of the foams and sheets under the microscope. Nematode and acarids also were observable on the surface of samples and in the surrounding soil.

Example 13-Biopolyols as Wood Adhesive The resultant biopolyols described in the above examples can be mixed with the cross-linking chemicals described above to produce a polyester-based wood adhesive with strong adhesiveness properties. Corn stover meal or wood meal (e. g. saw dust) was completely mixed in a given proportion with the bio-polyols and the cross-linking chemicals. The mixture was put in a mold and hot-pressed under a selected pressure and temperature for a given period. Performance of the adhesive was influenced by the curing conditions. Table 18 shows that at low curing temperatures (120°C-130°C), a long time is needed for adhesive curing; at moderate temperatures (140°C-160°C), the curing time needed ranged from 85 to 240 min; at the elevated temperatures (170°C-200°C), a good deal of low molecule substances evaporated in a short time. However, it is known that wood tends to bend seriously at high temperatures because cellulose in the wood is likely to be pyrolyzed at 200°C or above. In the present case, 150°C and 120 min seem to be the optimum curing condition for this new wood adhesive.

TABLE 18 Wood adhesive curing under different conditions 1 2 3 4 5 6 7 8 9 Temp. (°C) 120 130 140 150 160 170 180 190 200 Time (min) 720 410 240 120 85 50 30 15 10 Wt of adhesive (g) 2.345 2.074 2.456 2.402 2.177 2.070 2.253 2.313 2.445 Wt of cured adhesive 1.677 1.536 1.897 1.833 1.679 1.586 1.763 1.843 1.911 (g) Wt loss during curing 28. 49 39.15 22.76 27.86 22.88 23.38 21.75 20.32 21.94 (%) Water absorbed within 7.69 5.27 7.17 6.66 8.76 9.90 9.76 10.91 12.61 10d after cured (%) Acid catalyst residues and acidic materials generated during the liquefaction process produced a high acidity in the biopolyols. In general, a high acidity (pH<3.5) of a wood adhesive may damage wood fibers, resulting in increased water absorption and hence decreased adhesive strength. Borax was used to neutralize the polyol so that its pH was close to that of commercial wood adhesives. The adhesive was cured on non- absorbing aluminum foil and the water content was measured at 0,1, 2,3, 4,5, 6,7, 8, and 17 days after curing. It was determined that the adhesive absorbed water slower than a southern China fir plywood board.

OTHER EMBODIMENTS It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims.

Other aspects, advantages, and modifications are within the scope of the following claims.