[ACS Symposium Series] Emerging Technologies for Materials and Chemicals from Biomass Volume 476 || Emerging Polymeric Materials Based on Soy Protein

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<ul><li><p>Chapter 17 </p><p>Emerging Polymeric Materials Based on Soy Protein </p><p>Thomas L. Krinski </p><p>Protein Technologies International, Checkerboard Square, St. Louis, MO 63164 </p><p>This chapter will describe the chemical modification of native soy protein, a globular protein primarily used as a food source. A review of the past technology will describe the early industrial uses of soy protein and how the protein was modified to alter its function as an adhesive. Current and future directions will show how chemical modification and alteration of protein chain associa-tion can further enhance soy protein polymers function. The past unfavorable attribute of biodegradation of the soy polymer chain may now guide the future of soy polymer derivatives as the need increases for biodegradable polymers from renewable resources. </p><p>Industrial Soy Protein of the Past </p><p>Industrial soy protein used are primarily in the coating of paper and paperboard, with minor areas in water based inks and water based adhesives. The water based adhesives include bottle label adhesives, foil laminating adhesives, and cone/tube winding adhesives. </p><p>Protein Composition and Isolation. The protein present in the soy bean is not a simple singular globulin but a mixed assortment of different types of protein fractions. These fractions consist of: </p><p>Bowman-Birk Trypsin Inhibitor. A globular protein of 2 4M molecular weight that can form dimers and trimers due to high cystine content. </p><p>Kunitz Trypsin Inhibitor. This is another low molecular weight protein (molecular weight of 21M) which possesses disulfide linkages. </p><p>Hemaglutinin. A glycoprotein with a molecular weight of 100-110M without any disulfide crosslinks. </p><p>0097-6156/92/0476-0299$06.00A) 1992 American Chemical Society </p><p>Dow</p><p>nloa</p><p>ded </p><p>by N</p><p>ORT</p><p>H C</p><p>ARO</p><p>LIN</p><p>A S</p><p>TATE</p><p> UN</p><p>IV o</p><p>n A</p><p>ugus</p><p>t 6, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 4, 1</p><p>992 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>92-047</p><p>6.ch01</p><p>7</p><p>In Emerging Technologies for Materials and Chemicals from Biomass; Rowell, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992. </p></li><li><p>300 MATERIALS AND CHEMICALS FROM BIOMASS </p><p>Lipoxygenase. An enzyme with a molecular weight of 102M which can be disassociated into two near equal fragments using guanidine hydrochloride. </p><p>7S Globulin. A large associated polymer of 180-210M molecular weight consisting of nine polypeptide chains. These peptide chains can be disassociated into 2S and 5S subunits at pH 2.0. At neutral and slightly alkaline pH (pH of 7.6), the 7S can dimerize into the 9S fraction. Fully disassociated, the polypeptide chains that make up the 7S have molecular weights in the 20-25M range. </p><p>11S Globulin. A large 330-350M molecular weight associated polymer which easily disassociates into 7S size fragments. These fragments can likewise further disassociate into various smaller subunits capable of associating with one another to form dimers and trimers. </p><p>Urease. An enzyme having a sedimentation fraction equivalent to an 18S form (1). </p><p>Soy proteins are isolated by aqueous alkaline extraction of defatted soybeans. The native protein can be isolated prior to any additional treatment by precipitation at their average isoelectric point of pH 4.5 and separated from the soy sugars and salts. The molecular weight distribution by HPLC in 6 Molar guanidine hydrochloride i s represented in Figure 1. The native protein has an average molecular weight (Mw) of 192,000 daltons. </p><p>Native soy protein i s d i f f i c u l t to work with as an adhesive because the many different globulins disassociate and reassociate as the protein i s solubilized on the alkaline side. Even though the molecular weight of the native protein i s quite high and i t has good adhesive qualities, the problem of solution rheology control usually discourages i t s use (2). </p><p>Physico-chemical Treatment of Soy Protein (Caustic Treatment). Native soy protein has been modified using a controlled alkaline heat treatment of the protein while in solution. This processing u t i l i z e s three factors to control the protein reorganization: pH, temperature and time (3). </p><p>Table 1 shows the primary events which occur during physico-chemical treatment. Protein globulins slowly unfold with a minimum of backbone chain cleavage. As the chains unfold, they reorganize or reassociate, this time by hydrophobic/hydrophilic regions, this exposes more potential hydrophilic groups to aqueous contact. </p><p>A portion of the asparagine and glutamine residues are hydrolyzed to the free acids. This increases the anionic character of the protein as seen in the ti t r a t i o n curve of Figure 2. </p><p>Finally, we also achieve some internal chemical crosslinking through the formation of lysinoalanine (LAL). This occurs when the cysteine or serine residues undergo a elimination reaction (Figure 3) in the presence of elevated ph and temperature, forming a dehydroalanyl residue. This residue can then react with lysine amine through a base catalysed reaction achieving potential crosslinking of two independent protein chains. </p><p>Dow</p><p>nloa</p><p>ded </p><p>by N</p><p>ORT</p><p>H C</p><p>ARO</p><p>LIN</p><p>A S</p><p>TATE</p><p> UN</p><p>IV o</p><p>n A</p><p>ugus</p><p>t 6, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 4, 1</p><p>992 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>92-047</p><p>6.ch01</p><p>7</p><p>In Emerging Technologies for Materials and Chemicals from Biomass; Rowell, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992. </p></li><li><p>17. KRINSKI Emerging Polymeric Materials Based on Soy Protein 301 </p><p>6M GUANIDINE HYDROCHLORIDE pH 10 %/Min. TSK-G5000PWxl </p><p>1000 10,000 100,000 1,000,000 10,000,000 </p><p>Molecular Weight </p><p>Figure 1. Native protein Mw distribution. </p><p>Table I. Caustic Treatment (pH&gt;10.5, 40C</p></li><li><p>302 MATERIALS AND CHEMICALS FROM BIOMASS </p><p>Figure 4 shows the molecular weight distribution of a caustic treated protein compared with the native. With an average molecular weight of 150,000 daltons, there i s a marked shift to lower molecular weights as compared with the native protein. </p><p>The physico-chemical treatment step achieves reorganization of the protein globules/chains. Hydrophilic residues are exposed to more aqueous contact, while hydrophobics are buried. Combined with increased anionic character, the treatment greatly reduces the protein globules tendancy to self associate, which changes their rheological function and how they interact when used in coating paper (4). </p><p>Paper Coating Applications The major use of soy protein polymers is in the coating of paper and paperboard. Paper i s coated (Table 2) to improve i t s surface appearance and to make i t whiter and more uniform in color. The coatings impart a smoother surface which accepts ink uniformly without feathering of the ink. </p><p>A paper coating consists of three classes of components (Table 3) . pigment makes up most of the coating weight. The combined use of different levels of protein, latex, and starch provides the adhesive which holds the pigment on the paper surface. </p><p>Coating rheology influences how well the coating can be applied to the paper surface. The hercules rheogram (52% solids, 4400 RPM) of the native protein (Figure 5) has a much higher viscosity than the caustic treated protein rheogram (Figure 6). Physico-chemical treatment reduces not only the internal reactivity of the protein chains but also the reactivity of the protein with pigments such as clay. This leads to more uniform application of the coating to the paper surface with improved overall surface properties. Chemical Modification of Soy Proteins </p><p>Recent technology indicates that chemical modification of some of the amino acid residues can provide the a b i l i t y to design new protein polymers with more specific functionality changes than simple caustic treatment can achieve. Both of these protein modification tools can be combined to further enhance the protein modification and extend the application. </p><p>In chemical modification of the proteins, we must keep in mind that the hydrophilic amino acids (Table 4) due to their reactivity provide the best targets considering the aqueous conditions under which these proteins are processed (5). </p><p>Specific amino acid residues can be targeted (figure 7), by choosing the proper reaction pH (6). </p><p>Anhydride Reactions. Acid anhydrides reacting with pendant free amine groups can be used to modify the protein. A primary anhydride such as acetic (Figure 8), can be used to react with the amine groups negating their cationic charge. This tends to decrease solution and paper coating viscosities of the soy protein (7). </p><p>The use of di and tricarboxylic anhydrides enables the modification not only to negate the cationic amines, but also to </p><p>Dow</p><p>nloa</p><p>ded </p><p>by N</p><p>ORT</p><p>H C</p><p>ARO</p><p>LIN</p><p>A S</p><p>TATE</p><p> UN</p><p>IV o</p><p>n A</p><p>ugus</p><p>t 6, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 4, 1</p><p>992 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>92-047</p><p>6.ch01</p><p>7</p><p>In Emerging Technologies for Materials and Chemicals from Biomass; Rowell, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992. </p></li><li><p>17. KRINSKI Emerging Polymeric Materials Based on Soy Protein 303 </p><p> R - N , </p><p> / \ C CH 2 _SH I II </p><p> u R ; </p><p> / \ - C C H 2 - O H I II </p><p>OH" </p><p> - CH-CH2-NH(CH2)4-CH / \ </p><p>^ Lysinoalanine </p><p> R C CH2+H2S or 2 0 </p><p>E - C / I II </p><p>OH" 9 . 0 </p><p> / R </p><p>H2N(CH2)4-CH 0 </p><p> I </p><p>Figure 3. Protein crosslinking by lysinoalanine formation. </p><p>0 1000 10,000 100,000 1,000,000 10,000,000 Mo lecu la r Weight </p><p>Figure 4. Protein Mw distribution. </p><p>Table II. Primary Use Paper Coatings General Coating Applied to Paper </p><p> Improved appearance Improved color Improved printing surface </p><p>Dow</p><p>nloa</p><p>ded </p><p>by N</p><p>ORT</p><p>H C</p><p>ARO</p><p>LIN</p><p>A S</p><p>TATE</p><p> UN</p><p>IV o</p><p>n A</p><p>ugus</p><p>t 6, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 4, 1</p><p>992 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>92-047</p><p>6.ch01</p><p>7</p><p>In Emerging Technologies for Materials and Chemicals from Biomass; Rowell, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992. </p></li><li><p>304 MATERIALS AND CHEMICALS FROM BIOMASS </p><p>Table III. Primary Use Paper Coatings Composition (Aqueous) o Pigment </p><p>Clay Calcium Carbonate Titanium Dioxide </p><p> Adhesive Soy Protein Latex Starch </p><p> Minor Additives </p><p>COATING RHEOLOGY OF NATIVE SOY PROTEIN </p><p>S h e a r Ra te </p><p>Shear Stress Figure 5. Native protein rheogram. </p><p>Dow</p><p>nloa</p><p>ded </p><p>by N</p><p>ORT</p><p>H C</p><p>ARO</p><p>LIN</p><p>A S</p><p>TATE</p><p> UN</p><p>IV o</p><p>n A</p><p>ugus</p><p>t 6, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 4, 1</p><p>992 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>92-047</p><p>6.ch01</p><p>7</p><p>In Emerging Technologies for Materials and Chemicals from Biomass; Rowell, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992. </p></li><li><p>17. KRINSKI Emerging Polymeric Materials Based on Soy Protein 305 </p><p>COATING RHEOLOGY OF HYDROLYZED SOY POLYMER </p><p>S h e a r Ra te </p><p>Shear Stress </p><p>Figure 6. Soy polymer rheogram. </p><p>TABLE IV. AMINO ACID COMPOSITION OF SOY PROTEINS </p><p>H Y D </p><p>R </p><p>L I C </p><p>AMINO ACID CYSTEINE PROLINE </p><p>THREONINE </p><p>TYROSINE </p><p>ASPARTIC ACID </p><p>ASPARAGINE </p><p>GLUTAMIC ACID </p><p>GLUTAMINE </p><p>HISTIDINE </p><p>LYSINE </p><p>ARGININE </p><p>SERINE </p><p>} </p><p>} </p><p>MOLE% 0.68 </p><p>6.33 </p><p>4.01 </p><p>2.64 </p><p>11.33 </p><p>18.11 </p><p>SIDE OROVP -CH2SH </p><p>2.19 </p><p>5.50 </p><p>5.56 </p><p>6.34 </p><p> CO-</p><p>- CH (CH^OH </p><p>- C H 2 (5&gt; OH - C H 2 C 0 2 </p><p>- C H 2 C ^ </p><p>NH 2 - C H 2 C H 2 C02H </p><p> - C H 2 C H 2 C^ </p><p>NH 2 -CH 2 ^ </p><p>-CH 2 C H 2 C H 2 C H 2 NH 2 NH </p><p>- C H 2 C H 2 C H 2 N C * ' </p><p> C H 2 OH NH 2 </p><p>Dow</p><p>nloa</p><p>ded </p><p>by N</p><p>ORT</p><p>H C</p><p>ARO</p><p>LIN</p><p>A S</p><p>TATE</p><p> UN</p><p>IV o</p><p>n A</p><p>ugus</p><p>t 6, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 4, 1</p><p>992 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>92-047</p><p>6.ch01</p><p>7</p><p>In Emerging Technologies for Materials and Chemicals from Biomass; Rowell, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1992. </p></li><li><p>306 M A T E R I A L S A N D C H E M I C A L S F R O M B I O M A S S </p><p>replace them with additional acid groups (Figure 9 &amp; 10). The increased anionic character is evident in the t i t r a t i o n curves of Figure 11 where di and tricarboxylic anhydrides were used to modify the soy protein. This type of modification in coatings tends to decrease the viscosity of soy protein even further (Hercules Rheogram in Figure 12). Increased anionic charge on the protein further reduces the associative nature of the protein and increases i t s dispersant nature. A shift to lower average molecular weight (133,000 daltons - Figure 13) occurs due to increased processing time and increased dissociation of the soy globulins. </p><p>Crosslinking Reactions. Soy proteins can be mildly crosslinked through the use of various simple or complex reagents. Using epichlorohydrin (Figure 14), the soy protein molecular weight and solution viscosity can be increased by varying the amount of reagent used. </p><p>A more complex monomer such as methyl acrylamidoglycolate methyl ester (MAGME) which has the a b i l i t y to crosslink both during i n i t i a l reaction and later during application (Figure 15) can be used (8). Under basic conditions, the primary reaction with the protein can occur either at the double bond or at the activated ester. At elevated temperatures, the proton on the amide group i s acidic enough to encourage further crosslinking at the amide nitrogen. This second reaction could occur during the soy polymers use in the coating-drying-calendering of paper. </p><p>Base Catalysed Reactions. Due to the alkaline processing conditions, nucleophilic addition reactions are excellent f i t s for modification of soy protein and can be tailored even to selective amino acid residues, water soluble monomers such as acrylamide (Figure 16) and acrylonitrile provide excellent reactivity with lysine amine groups and sulfhydryl of cysteine. </p><p>Hydroxyacrylates can also be used to modify any free amine groups and add additional hydroxyl residues to the protein (9). In paper coating applications, this allows the protein to hydrate more thus adding water holding to the paper coating as i t i s applied. The runnability of the coating as i t ' s applied to the paper is improved. </p><p>Exotic monomers, such as glycidyl oxypropyl trimethoxy silane, can add a silane ester to the protein amines (10). This modification greatly increases the viscosity of the protein with clay pigments or causes total destabilization of the clay suspension. </p><p>Interpolymer Technology. When soy polymers are used in the coating of paper, a styrene butadiene latex is also used. The increased dispersant action and lower viscosity of the anionic modified soy protein has been used in the preparation of various latices (Figure 17). Monomers can be emulsified by using the soy polymer as the only surfactant. These miscelles can then be polymerized in the presence of the soy polymer resulting in a soy latex interpolymer whose core is stabilized by a "surfactant shell" of soy protein. Figures 18 and 19 show the particle size analysis of such a styrene butadiene latex with an average size of 0.2 micron. This is </p><p>Dow</p><p>nloa</p><p>ded </p><p>by N</p><p>ORT</p><p>H C</p><p>ARO</p><p>LIN</p><p>A S</p><p>TATE</p><p> UN</p><p>IV o</p><p>n A</p><p>ugus</p><p>t 6, 2</p><p>012 </p><p>| http:</p><p>//pubs</p><p>.acs.o</p><p>rg Pu</p><p>blic</p><p>atio</p><p>n D</p><p>ate:</p><p> Dec</p><p>embe</p><p>r 4, 1</p><p>992 </p><p>| doi: 1</p><p>0.1021</p><p>/bk-19</p><p>92-047</p><p>6.ch01</p><p>7</p><p>In Emerging Technologies for Materials and Chemicals from Biomass; Rowell, R., et al.; ACS...</p></li></ul>

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