Starch and Dextrin Based Adhesives - Article

Trends & Innovations New s Editorials R&D Highlights Patent WatchMaterials & Solutions Articles Training & Education Channels Com m unity Pulse New sletters Open Innovation Market Reports Industry Events Glossary Thomas Schroeder 8 8 Share 0 Like 1 0 More Starch and Dextrin Based Adhesives SpecialChem - May 12, 2004 According to you, what is the basic use of a sealant? To form a protection barrier To seal tw o substrates together To fill gaps or holes Edward M. Petrie, Memb er of SpecialChem Technical Expert Team. Introduction Raw Materials Manufacture of Starch Adhesive Manufacture of Dextrin Adhesives Additives and Modifiers Common Applications and Formulations Introduction An extremely large and well-known class of adhesives is based on starch and dextrin. These play a very large part in industrial production, especially the packaging industry. Starch and dextrin are principally used for bonding paper products. Most corrugated boxboard for making cartons is bonded with starch based adhesives, and other porous substrates can be easily joined with these versatile adhesives. Starch and dextrin adhesives are readily available, low in cost, and easy to apply from water dispersion. They are considered to be the least expensive class of paper packaging adhesive. Formulated starch and dextrin adhesives can be applied hot or cold. These adhesives are generally provided to the end-user as powder and mixed with water prior to use to form a relatively thick paste. Starch and dextrin cure by the loss of moisture. Since these adhesives cure to a thermosetting structure, they have excellent heat resistance. Another significant advantage is their very slow curing rate allowing ample assembly time. Disadvantages include poor moisture resistance and mold growth. Although starch and dextrin have been used as adhesives for many decades, there are several important reasons why these natural adhesives will not be entirely replaced by synthetic products. The following advantages ensure that they continue to fill particular niches in the market place. 1 Availability is good and cost is relatively low Quality is stable Good adhesion to cellulose and many porous substrates Insoluble in oils and fats Non-toxic and biodegradable Heat resistant This article will review the raw materials that go into starch and dextrin adhesives, the methods of adhesive manufacture, and the additives that are commonly used in formulations for improvement of specific properties. Finally, the common applications and formulations of starch and dextrin based adhesives will be reviewed. Article - Trends in Plastic Surface Modifications to Improve Adhesion Article - Carbon Nanotubes Improve Conductivity of Adhesives Article - Formulating w ith Polyurethane Prepolymers Article Keeping Low -isocyanate Emission Polyurethane Adhesives Flow ing Exploiting VAE Technology offers Water-based Adhesive Advantage Starch and Dextrin Based Adhesives SEBS for High Performance Hot Melts POSS – Nanoreinforcement of Structural Adhesives Raw materials Both starch and dextrin (dextrin is starch which is processed further) are considered carbohydrate polymers, and they come from basically the same sources. Starch is a natural polymer, a polysaccharide, derived from the seeds, roots, and leaves of plants. Only a few plants yield starch in sufficient quantity to be economical. These are corn, wheat, potato, rice, tapioca, and sago. The quality of the starch must be high to produce high quality adhesives. Starch is made up of two molecules: amylose and amylopectin. Amylose consists of long helical chains, and amylopectin has a branched structure. Starch does not have a uniform composition. Its molecular structure and amylose / amylopectin ratio vary according to plant source. Thus, the processing characteristics and end properties will vary similarly. The most important methods of differentiation between starches are the molecular weight of the amylose fraction and the ratio of amylose to amylopectin. While amylopectin can be supplied in cold water soluble form, amylose is insoluble. Amylose can be dissolved with strong alkali, by cooking with formaldehyde, or by cooking in water at 150-160 °C under pressure. Upon cooling or neutralization such amylose dispersions will form firm gels at concentrations higher than 2% and precipitate at concentrations lower than 2%. Amylose fractions are never truly soluble in water and in time will form crystalline aggregates by hydrogen bonding - a process known as retrogradation or setback. Retrogradation is the cause of viscosity instability in certain starch based adhesives. The amylopectin is more soluble and less prone to retrogradation. The percent of amylose in various starches and their resulting properties are summarized in Table 1. Corn Wheat Rice Tapioca Potato Sago Source Gelation Tem p, °C Am ylose, % Seed Seed Seed 3-35 25 3-8 19 Root 5-35 20 Root Pith Granule Diam eter, Microns 5-26 28 15-100 10-70 59-68 60-67 25 26 Opinion Space - Do you think that starch and dextrin based-adhesives w ill play a larger part in the future of Adesives & Sealants industry? Share your opinion now on this hot topic w ith other SpecialChem4Adhesives members! 62-72 58-64 68-78 49-70 Therefore. Finally add preservative and other additives as required. A starch suspension at pH 8-10 is treated with hypochlorite (5-10% Cl based on starch) for a long enough time to produce the desired viscosity. These treatment methods include: alkali treatment. such as sodium hydroxide. If sufficient alkali is added. Starch solids may range from 20-30%. However. An acid is then added to stop this swelling process short of complete gelatinization. Suspensions with a higher amylose / amylopectin ratio will have a higher viscosity. two-container process as indicated in Table 2. Heat w ith live steam to 71°C. Starches prepared in this manner are often known as thin-boiling or high-fluidity starches. Gradually empty content of upper tank into the low er tank w ith efficient mixing and agitate until viscosity is consistent. Crosslinkers and special starches may be used to impart waterresistance. and borax is finally added. allow to dissolve 2-3 mins and add 500-600 lbs starch and suspend uniformly. The gelation temperature can be lowered by the addition of an alkali. When preparing such single container adhesives. so base must be added to maintain the pH for optimum reactivity. The main features of the single container starch system is that: . and to stop the swelling at the correct stage to ensure that the required viscosity is achieved. In this process. Oxidization of starch is usually obtained by treatment with aqueous alkaline hypochlorite. they are often used for the sizing and coating of printing papers. Because of the low color. Sodium hydroxide is used to lower the gelation temperature and borax to increase the tack. In the first. acid treatment. the starch can be induced to gel at room temperature.Am ylose. lower viscosity. 100 lbs corn starch follow ed by 17 lbs caustic soda in 3 gal w ater. Above 15% starch solids content. the oxidized starch has greater tack and adhesive character and. This was introduced in the 1930s for the purpose of producing an adhesive for corrugated boxes. and the adhesive is produced by control of the temperature and the time of stirring. salts (usually the chlorides of metals such as calcium. Acid is liberated during the reaction. % 28 25 19 20 25 26 Table 1: Properties of Commercial Starches Most starches contain 20-30% by weight of amylose although certain specialty types can have as little as 0% or as high as 80%. is often used in adhesive applications. Dried oxidized starch is generally whiter than unmodified starch. to the starch suspension. If the concentration of the starch is above 7% then the cooked paste is very viscous and difficult to pump. In this form the starch is not a true solution but a colloidal suspension. Upper Tank (Carrier Starch) Low er Tank (Suspended Starch) Table 2: Stein-Hall Tw o-Container Process for Starch Based Corrugating Adhesive 3 The high viscosity cooked starch paste serves as a carrier to prevent the starch granules in the slurry portion from settling out. starch granules first swell and then burst open with a resulting thickening of the suspension. The temperature at which this thickening of the suspension occurs is called the gelation temperature. a solution of caustic soda is added to a slurry of starch to swell the starch granules uniformly until they reach the required adhesive viscosity. the granules gelatinize. These granules must be opened through processing to obtain adhesive bonding. When the adhesive is applied and heated to above its gelatinization temperature. the suspended starch should gelatinize immediately on contact with the heated fluting rolls and develop instant tack at 60-70°C. For most starches in pure water. caustic soda is added to the starch suspension and later on in the process the product is neutralized with acids. In the second and primary method. gelation occurs between 57 and 72°C (see Table 1). and oxidation. Manufacture of Starch Adhesive Heating in water is the simplest method of breaking up the starch granules. The heating process can take one of two forms. starch suspended in cold water is essentially unable to act as an adhesive because the starch is so tightly bound in crystalline regions. Unmodified starches. and zinc) are added to a suspension of the starch in water. low solids content pastes which do not show a stable viscosity with time. On heating in water. In corrugated box manufacture. The process consists of heating the starch slurry to a temperature above the gelation temperature and then quickly drying the starch before retardation can occur. [2] The Stein-Hall system combines the properties of an 8-9% cooked starch paste and a 25% starch slurry in a two-component. followed by neutralization with a base. it is essential to control carefully the concentrations and temperature of the starch slurry and the caustic solution. Single Container or "No-Carrier Process" This entire operation can also be carried out in a one container system where there is no carrier portion of the adhesive. thus. The Stein-Hall Process The first major commercial process for producing starch adhesives was the Stein-Hall Process. agitate 15 min and then dilute w ith 500 lbs of cold w ater To 1520 lbs w ater add 17 lbs borax. The starch paste now has a high viscosity and acts as an adhesive. are in powder form (pregelation) or high viscosity. magnesium. The main process equipment used is a heated-drum drier or hot roll. To 400 lbs w ater add w ith mixing. Because of the amylose fraction. Acid modification is often used when applications require higher solids content but a controlled. Acid modification of starch is achieved by heating the starch at 49-54°C with small amounts of aqueous mineral acid. This tends to give a much thinner solution at the same solids content when compared to unmodified starch. These oxidized or chlorinated starches behave similarly to acid modified starches. several treatments have been developed to provide liquid adhesives that are not subject to retrogradation and have a viscosity and rheology more suitable for many applications. the cooked paste forms an immobile rubbery mass on cooling. such as produced by the steps outlined above. Pregelation starch is produced by physical modification of the starch to impart the ability to form a paste easily in cold water. and a very viscous and tacky paste is produced. They also have good adhesion and machining properties.2%. readily soluble polymer molecules of moderate size.Buff Yellow Dextrin 135-160 8-14 Moderate Very soluble in w ater Good stability Yellow . Common plasticizers include glycerin. Materials of this type are available that give a viscosity of only 1700 cps at 60% concentration. Chemicals such as calcium chloride. copper sulfate at about 0. bag seams. These are used to reduce cost and control penetration into porous substrates. and sulfonated oil derivates lubricate the layers within the dried adhesive and. This means that drying time is reduced and there is little likelihood of mold infection in warmer climates. higher viscosity than Yellow Yellow . and British gums. and laminating. The range of solubilities of dextrin adhesives are advantageous in that there can be formulated a range of solutions of very different viscosities leading to a variety of gel strengths. slip. etc. sorbitol. There are three main types of dextrin adhesives: white dextrins. the starch molecules are hydrolyzed into small fragments.Brow n Table 3: Description of Common Dextrin Adhesives * Solubility depends on exact reaction conditions The British gums are dextrins with the highest molecular weight and they are the strongest adhesives among the dextrins. As adhesives. °C Roasting Tim e. Frequently dextrin adhesives and sometimes starch based adhesives are formulated with borax (sodium tetraborate) to obtain high tack at moderate concentrations and viscosities with good aging characteristics. etc. Table 3 describes the properties of these dextrin adhesives. fluorides. salicylic acid.Less heat is required for bond formation (as the starch granules are already partially swollen) There is less free water Viscosity allows increase in machine speeds and reduction in warped board production Superior storage and shear stability. Organic solvents are sometimes added to improve the adhesion to waxed surfaces. bill posting. Colloid stabilizers such as soaps and sodium chloride are sometimes used to retard the tendency to retrogradation. and other applications. The borax is generally added in amounts of up to 10% based on dry starch. hrs Catalyst Concentration Solubility Viscosity Stability Color White Dextrin 120-130 3-7 High 1-95% in w ater* Prone to retrogradation White . Urea. water and fungus resistance. tube winding. calcium carbonate.Tan British Gum 150-180 10-24 Small 1-95% in w ater* Good stability. Thixotropic agents such as bentonite are also often used in certain applications to control viscosity. Property Roasting Tem p. dextrins are used in many of the same applications as starch adhesives. thiourea. The severity of the heat and acid treatment determines the degree of solubility. solids content. They are usually added at about 5-20% based on dry starch. Manufacture of Dextrin Adhesives Dextrin adhesives are manufactured by dry-roasting starch in the presence of an acid catalyst. and phenols. Dextrins are often preferred to starch. Corn starch is commonly used because of its low cost and ready availability. are used as liquefiers to reduce viscosity or as humectants to control open time and speed of drying. which is the basis for classifying dextrins. canary or yellow dextrins. substrate penetration. impart flexibility. are often used in starch and dextrin adhesives at concentrations of 5-50%. Native starches are capable of yielding high degrees of water resistance. which may be necessary for labeling. These types of plasticizers act as a hygroscopic agent to decrease the drying rate of the film. zinc sulfate. The white dextrins have the lowest color of the three. stability. dextrins are soluble in water. Applications include case sealing. The differences are determined by the roasting time and the temperature and amount of catalyst used. Plasticizers are widely used to control brittleness of the glue line and to regulate the speed of drying. guanidine salts. These adhesives will also dissolve in hot water. bleaches. and cost.2-1. and defoamers. Sodium hydroxide is also added to convert the borax to more active sodium metaborate. sodium nitrate. Optimal moisture resistance is obtained through the addition of thermosetting resins. Possible toxic effects must be carefully considered before choosing a preservative. benzoates. and sugar. Finished dextrins are very fine powder varying in color from pure white to brown. Yellow dextrins are the lowest in molecular weight. Here the main function is to give good green strength and to prevent deformation of the core before being fired in the oven. Dextrins are also used as a core binding material in the manufacture of foundry cores. glycols. tack. Unlike starch. which is often a benefit. drying rate. The formulations generally depend on (1) the type of starch and modification as indicated above and (2) the additives employed. hydrogen and sodium peroxide. Through treatments with heat and acid. and then repolymerized into highly branched. but maximum usable solids content is only approximately 25%. polyglycols. titanium dioxide. thus. Additives and Modifiers Properties of starch and dextrin adhesives that can be modified through formulation variables include: viscosity. flexibility. urea. Improved cold water resistance can be obtained with polyvinyl alcohol or polyvinyl acetate blends.. Their molecular weight is intermediate between those of the other two. Mineral fillers such as kaolin clay. such as urea formaldehyde or resorcinol formaldehyde. sodium nitrate.0%. glucose. Plasticizers based on saps. Generally the same additives and processes used for starch adhesives are used for formulating dextrin adhesives. carton sealing. and formaldehyde plasticize by forming a solid solution with the dried adhesive. as they need less or no cooking and much less water to form the paste. Common bleaching agents include sodium bisulfite. . Other additives that are found in starch and dextrin based adhesive include preservatives. and sodium perborate. Commonly used preservatives used to prevent microbial activity include formaldehyde (35% solids) at 0. although other starches are also employed. These formulations can then be further modified as described in the next section. cool to room temperature and add 50% Aqueous NaOH Form ulation B 3 (Can be used for seam s or bottom s) Water Dextrin Heat to 72°C and add Borax Soap Heat to 88°C and hold.2 3. adjust solids to 30% .7 pbw 19.2 76.0 pbw 70. A fraction of the starch needed to formulate the adhesive is gelatinized with aqueous caustic.9 pbw 28.6 3. Normally three adhesives are used in this application: seam. adjust solids to 27-28% and add Preservative Form ulation B 3 (Insoluble adhesive w hich should be used w ithout delay) Water White dextrin Soap 17. Cross paste adhesives are used for the manufacture of multiwall bags.2 Urea-formaldehyde Cook w ith live steam to 95°C. Starch based adhesives are also commonly used for bag manufacture.01 0. This is blended with a concentrated suspension of unmodified starch granules. Generally mineral fillers are added to this adhesive so that it does not bleed through the paper.7 pbw 39.6 0.Common Applications and Formulations The majority of starch and dextrin adhesive are used in the paper and textile industries.0 0. and it generally has greater tack. The bottom adhesive is made from a more viscous paste. Upon subsequent exposure to heat. Some of the most common applications for these adhesives are described below. Typical formulations for seam and bottoming adhesives are shown in Table 5 and 6. Initially in bag production the paper is formed into a long tube with a side-seam adhesive.2 0.2 0.0 1.0 0.8 Cook to 93°C for 20-30 mins. The paste is applied cold to the corrugated flutes and the liners. forming a strong bond.3 49.7 5.03 1.0 25.0 4. hanging pastes.1 0. borax to speed gelatinization. dilute w ith cold w ater. Bottom pastes are normally composed of white dextrins or starch. the starch granules swell and burst. and bottoming. and a small quantity of preservatives as a mold inhibitor.4 67. and add Ammonium chloride Table 5 : Typical Side-Seam Adhesives for Paper Bags Form ulation A 4 Water Starch Borax Preservative Soap Form ulation B 3 (Can be used for seam s or bottom s) Water Starch Dextrin Soap 67. The viscosity and solids content of these adhesives are relatively low.4 25. Application Fiberboard cases including corrugated boxes and solid board Paper bags Cartons Wallpaper.2 7. The principal end uses of starch and dextrin adhesive are shown in Table 4.4 pbw 6. Form ulation A 4 Water White dextrin (94% solids) White dextrin (13-15% solids) Borax Preservative Antifoaming agent Cook to 85°C for 20-30 mins. sizes and binders Cigarette manufacture Bottle and jar labeling Other labeling and gum tape Plasterboard production Tube w inding and lamination Envelope manufacture Book binding Starch Dextrin X X X X X X X X X X X X X X X X X X X X Table 4: Principal End-Uses of Starch and Dextrin Adhesives Most corrugated boxboard for making cartons is bonded with starch based adhesives. Generally they are made from high soluble white dextrin or acid modified starch. cross-pasting. (See Table 1) A typical starch adhesive formulation also includes bentonite as a thixotroping agent. .M. cool to 48°C. K. 2. humidity resistant adhesives.025 (1936).. cool to 60°C.2 0.W. U. Carton sealing adhesive require a low and stable viscosity. Water White dextrin Clay Urea Borax Cook to gel 54. Baumann. Mittal. Chapter 22. Chapter 10. and add Corn syrup Table 9 : Formulation of Remoistening Adhesive 4 65. D.0 0.2 1. Marcel Dekker.Soap Heat to 88°C. A.V. Yellow dextrin (95% soluble) Water Tributyl phosphate Heat to 88°C for 30 min. 2nd ed. I.557 (1940). Applied Science. Water White dextrin Preservative Borax Antifoaming agent Cook to 85°C for 20 mins. Join SpecialChem Expert Team : Write Articles / Answer Technical Requests / Conduct Online Training Courses. and add 50% Aqueous NaOH 11.3 Table 6 : Typical Bottom Adhesives for Paper Bags Laminating adhesives must exhibit high tack. several processes have been employed.5 6. A typical formulation is shown in Table 7. labels. and Conner. London. dextrin adhesives are used in certain applications where low cost must be achieved. Pizzi and K.12 Table 8 : Typical Formulation for Carton Sealing: 42% Solids. This generally requires that the formulation contain acid modified starch or high soluble white and yellow dextrins to allow high solids contents.051. 3. W. Patents 2. Another process uses a solvent deposition of the adhesive where a cold water soluble dextrin is suspended in an organic solvent.2 1. 7. Handbook of Adhesives.212. the tape or label substrate with dried adhesive is run over a bar to produce microcracks in the adhesive layer.2 0. "Starch Based Adhesives". 2003. but poor water resistance. "Adhesives Based on Starch". sodium nitrate. 2500-3500 cps 3 Adhesive for tapes. A. 2. M. Bauer.. However. cool to 57°C. slow drying. References: 1. and non-curling behavior. or urea is often added at 30-50% of the dextrin to increase solids and to control open time.H. The adhesive must also meet the requirements of the laminating equipment. Dextrins and converted starches are often used for bonding labels.102. When this suspension is applied to paper and dries. Adhesives and Adhesion. and similar applications required noncurling ability and they should be nonblocking under humid conditions. high solids starch based jelly gums represent tacky.0 pbw 8. Foil laminations require resin based adhesive for adhesion and water resistance. In bottle labeling.9 0. ed. White dextrin is often used in this application. which will swell and produce the required tack on contact with water.0 Table 7 : Typical Formulation for a Laminating Adhesive 4 Today most paperboard cartons are sealed with liquid glues or hot melt adhesive.1 To prevent curling. Allen.01 0. Dextrin formulations are used where high concentration and speed are required. adjust to 25% solids.G.Jun 07.7 5.. envelopes. and add Preservative 0. Vol.S. A formulation for a remoistening adhesive that is often used for envelopes is given in Table 9. Marketing / Sales at Hi-Tech Starches Thanks alert moderator | add y our reaction . These are generally preferred because of their high speed of operation and ability to bond strongly to many different substrates. "Carbohydrate Polymers as Adhesives".. 2011 posted by Nilesh Lakhani.L. Lazarus. Jarow enko. 4.D..7 pbw 32. 2. New York. 1983. Chapter 12. 1977. van Nostrand Reinhold.6 pbw 20. They have good adhesion to polyethylene and treated polypropylene. Handbook of Adhesive Technology. New York. hold 20 min. Certain tape and label adhesive also must be capable of rewetting or remoistening. Sugar. it leaves behind discrete particles of adhesive. low permeation of the substrate. A formulation for a white dextrin adhesive for carton sealing is provided in Table 8. Alkaline starch types yield excellent adhesion to aluminum foil and good heat resistance... Define your expertise and apply here! SpecialChem4Adhesives Members Reactions Great thing .2 13. and they must set quickly. In one process.937 (1937). was very helpfu. . alert moderator | add y our reaction 5 .Don’t post discriminatory or commercially-oriented message(s) We reserve the right to remove some comments not aligned w ith this charter. Looking forward to see more advanced articles & e training on the subject alert moderator | add y our reaction Excelent Comprehensive Overview on Starch based adhesives .A.Site Map .Oct 11.SpecialChem Portal Copyright © 2011 SpecialChem S.Applied/ Form ulation/ Product developm ent Thanks for sharing this excellent information. 2011 posted by PAWAN KAYAL.Jul 15.Aug 22.Applied/ Form ulation/ Product developm ent at Vinayak Packaging This would certainly expand to understand specialization in starch based adhesive. R&D . alert moderator | add y our reaction Very good but brief . I am very interested in uses with ureaformaldehyde polymers in several applications.Dec 18.Applied/ Form ulation/ Product developm ent at Interquim S. It would have been better if it include new developments in Dextrin making and new starch based adhesive through extrusion technology.Be courteous .RSS . R&D . Thanks very much alert moderator | add y our reaction Rate this Document Select info you would like to be published with your Reaction: Title of your Reaction Name Thomas Schroeder Scholle Chemical Co Your Reaction Company Job Department R&D . . 2009 posted by ANOOP GUPTA. alert moderator | add y our reaction Is a very interesting review.Basic Research All this information is a consise starting point for develoment of especialties in starch or dextrines adhesives. Corporate Managem ent at stardex Article summarises all the basic formulations. R&D . Open information permit use it in industrial process and increase of starch consumption. 2009 posted by om ar vera. Technical Service/ Custom er Assistance at bOMBAY SILICATE WORKS A to Z of Starch and Dextrine Based adhesives . 2010 posted by rajesh patel.Be concise (you’ll have better chances to be read by other Members!) .alert moderator | add y our reaction Helpfull and Informative . Keep it up alert moderator | add y our reaction Excelent open information . 2010 posted by Anthony D’Souza. R&D . 2010 posted by Bhaskar Reddy. Gives insight in to adhesives.Forgot your UserID / Passw ord? .Applied/ Formulation/ Product development Advice: . 2009 posted by Jose Lenin Ortiz Mongui. narrated in very informative way.A. About SpecialChem . Production / Manufacturing at aneri industries good alert moderator | add y our reaction Good knowledge based information .May 19.Jan 23.Terms and Conditions .Jul 28.About SpecialChem4Adhesives Contact Us .