PRODUCTION OF SYNTHETIC ADHESIVE FROM CASSAVA STARCH

 

PRODUCTION OF SYNTHETIC ADHESIVE FROM CASSAVA STARCH

THE DEPARTMENT OF CHEMICAL ENGINEERING

DEDICATION 

This work is dedicated to God Almighty, the giver of life, wisdom and good health for his infinite mercy, guidance and providence throughout the project. 

ABSTRACT

Wet extraction method was used to extract starch from cassava tubers. As a result of the development of several formulas, the highest quality was achieved. The formulations were made using a gelatinization technique, and the grade of the ingredients utilized was varied. The following tests were performed on the formulations: - PH determination; the PH of the formulated adhesive is 6.8, which is quite equivalent. The formulations' solid/moisture content is 19.4 percent and 82.2 percent, respectively, while the standard is 15-30 percent and 65-85 percent. The developed adhesive has a tack duration of 16 minutes, which is equivalent to the industry standard of 15 minutes. The shelf life of the prepared adhesives has exceeded two months and is still appropriate, indicating that it may be comparable to market shelf life. Finally, the compositions' wettability was comparable to that of commercial adhesives.

CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND OF STUDY

Cassava, a relatively obscure crop in the old world before to the discovery of America, is quickly assuming the role of world savior, as it is now growing throughout the tropical world. It is now only second to potato as the most significant starchy root crop for food and industry in the tropics. It's eaten raw or cooked in Nigeria, and it's used to make garri, starch flour and a variety of other items (Tonukari, 2004; Grace, 1977). The current drive towards earning foreign exchange from cassava products in Nigeria had raised more awareness on the importance of the crop.

However, most processing enterprises do not efficiently utilize the secondary product (cassava starch and milk) from the product of garri (the most important food item made from cassava in Nigeria). These items are simply drained without any consideration for their use, particularly in rural areas. It is in the light of this and the fact that this cassava is readily available that these studies were conducted to investigate the possible utilization of cassava starch as a binding material (adhesive).

An adhesive is a substance capable of binding materials together via surface adhesion and sustaining the designed load requirement without deformation or failure (Anonymous, 1982). Adhesives exist in a variety of forms, liquid paste, film, powder, granules and in solid forms, materials being fastened together by adhesives are called substrates. Adhesive materials have been used successfully in a variety of applications for centuries, not until the demands were made for major advancement in adhesive technology, as a result in availability of metals in large volumes and the introduction of plastics, rising needs to join this diversity of materials became a problem. Adhesives are now more vital than ever in our daily lives, and their utility is continually expanding. People now routinely entrust their fortunes and lives to adhesively bonded structures and barely think about it, but researchers are interested in learning more about adhesives and adhesive bonding.

There are two essential characteristics that anadhesive must have in order to be effective. Theadhesive must be capable of impacting adequate bondbetween the two materials by principle of resistance to load shear, which implies creep static or time independent deformation under sustained load(Foschi, 1977). Other desired requirements are ease of application, reasonable setting time, resistance to moisture, aging, heat and fungal attack, non-staining and gap filling(Knight, 1984). Although the primary effect of solidified adhesives in pore spaces may be minor, cassava-based adhesives might be easily manufactured from by-products that would otherwise be discarded, providing a distinct economic benefit. Adhesives work by forming a bond between the adhesive and the product to be adhered. Cassava starch has a fine, silky texture and is non-staining and non-poisonous which makes cassava adhesives a desirable choice particularly for domestic uses and most non-structural utilization of adhesives(FOA, 1983).

The use of starch as an adhesive, on the other hand, has a number of drawbacks. It is important to note that starch-based adhesives are made possible by starch's capacity to gelatinize at a specific temperature. The starch is hydrolyzed to form a gel, paste, or solution during the gelatinization process. Degraded or transformed starch, such as dextrose, is also used in starch-based adhesives. The most important of these is the stability of the product over time, hence very short pot-life. Adhesives generally found its applications in industries and starch-based applied in packaging labeling, leatherworks, binding of books etc. essentially adhesives especially the synthetic types found their application in components needed to make many products such as aircraft, corrugated cartons, plywood, automobiles, envelopes, stamps, etc. The main objective of this study, therefore, is the development of conditions that could ensure the stability of adhesives produced from cassava starch

1.2 PROBLEM STATEMENT

The research project is

“Production of synthetic adhesive from cassava starch”

Adhesive sold in the market are made of conventional organic materials operating with forces to bind or bond two surfaces together. In this project, it is wished to produce adhesive from local raw materials such as cassava starch to compare its bond strength with adhesives or glues sold in the market.

1.3AIM OF STUDY

1.     The goal of this research is to look at the qualities of Cassava starch for the production of adhesives as a potential career path in chemical engineering.This is a good notion since the time has come when we should not rely only on foreign technology for all of our needs; instead, we should aim for self-sufficiency in terms of economics by employing abundant raw materials, such as cassava which is surplus in the south eastern part of the nation.

2.     Comparison of synthetic adhesive from cassava starch to that of potato starch and yam starch

1.4 SCPE OF STUDY

The design project is within the boundaries of Chemical Engineering processes and does not delve into specific areas like electrical engineering, mechanical fabrications and management.

Hence, the design project focuses on the following chemical process engineering principles and assumptions;

·       Extraction of starch from cassava tubers

·       The selection of best process route.

·       The selection of the best separation technique needed to perform the project.

·       Cost estimation of the production for economical use.

·       Possible plant design for the synthesis of the adhesive

1.5 LIMITATION OF STUDY

The design project is limited to the following area of consideration:

i.          Non-availability of required materials within school environment

ii.          Inadequate funding experienced during the production and information acquiring

iii.          Lack of constant power supply due to failure of generation plant

CHAPTER TWO

LITERATURE REVIEW

2.1 CASSAVA STARCH (TAPIOCA)

Starch is one of nature's most plentiful compounds, a renewable and virtually limitless resource. Grain or root crops are used to make starch. Starch is mostly utilized as a food, but it can also be easily transformed chemically, physically, and biologically into a variety of valuable items. To date, starch has been used to make food, paper, textiles, adhesives, beverages, confectionary, pharmaceuticals, and building materials. Cassava starch has many remarkable characteristics, including high paste viscosity, high paste clarity, and high freeze-thaw stability, which are advantageous to many industries.

FIGURE 2.1

2.1.1 PRODUCTION OF CASSAVA STARCH

Cassava starch is produced primarily by the wet milling of fresh cassava roots but in some countries such as in the South East Asia, it is made up of dried cassava chips. Cassava is primarily made up of starch. Tubers that are mature and of good grade contain about 25% starch. Per 100 kg of cassava roots, roughly 60% starch and 10% dry pulp can be recovered from dry cassava chips.

In certain places, fresh tubers are processed during the season while dry chips are processed during the off-season. Preparation (peeling and washing), rasping/pulping/grating, purification (starch washing), dewatering and drying, and finishing are the five primary phases of starch extraction from fresh cassava roots (milling and packaging).

Figure 2.1 Process route showing the production of cassava starch 

From the figure above (fig 2.1), we can see the various process route involved in production of cassava starch, and they are detailed as follows;

Sorting and Weighing:

The tubers are sorted to determine which roots are fit for production. After that, the tubers are weighed.

Peeling: Due to the uneven shape of cassava roots, human peeling was used to avoid the significant peeling loss associated with mechanical peelers.

Washing: The peeled root is rinsed with enough drinkable water to remove sand, dirt, and other contaminants.

Grating:  To make cassava mash, the root is grated.

Detoxification: To remove the poisonous hydrogen cyanide present in cassava, the mash is mechanically detoxified in a mash agitator for a period of time. 

 Dewatering: To prepare for the drying procedure, the moisture level of the mash is mechanically decreased to around 50%.

Granulation:  A hammer mill is used to breakdown the dewatered cake into fine granules.

Drying: To produce cassava flour of the necessary quality, the granulation step is followed by the drying process.

Milling: The flour obtained is milled to the desired particle size.

2.2 STARCH AND MOLECULAR STRUCTURE

2.2.1 STARCH

This is an important part of the glue. It's a carbohydrate, specifically a high molecular weight polysaccharide, with the empirical formula ()n, where n is a huge but unknown number.  Polysaccharides are sugar polymers having hydroxyl groups that allow them to form a paste with water. Starch is made up of two molecular constituents: amylose, which is a straight chain, and amylopectin, which is a branched structure.

           Starch is a carbohydrate that is found in plants' roots, seeds, and stems. It is the second most abundant carbohydrate source after cellulose. Although starch is ubiquitous in plants, only a few sources are numerous enough to make starch extraction commercially viable. Potatoes, corn, tapioca, arrow root, rice, sorghum, sago, wheat, and waxy maize are some of these sources. A variety of processes are used to remove naturally occurring starch from the seed, as in corn, wheat, waxy maize, sorghum, and rice, from the root, as in tapioca, potato, and arrow root, or from the stem, as in sago. Cleaning the plant material is normally followed by grinding, soaking, washing, sieving, and filtering the cake before drying and grinding it. In this form, starch is a white powder, and the naked eye can't tell the difference between plants. In alcohol, most solvents, and cold water, all starches are insoluble. A dilute solution of iodine stain starch blue to bluish red.  Under the microscope, the starch appear as cellular or granular material with shapes varying with the botanical origin.

2.2.2 MOLECULAR STRUCTURE OF STARCH

The primary difference in molecular structure that the various plants produce for their specific needs is related to granular differences. Starch and cellulose, the two main carbohydrates of plant origin, are quite similar in molecular structure. Both are glucose polymers that occur naturally. The glucose units are joined by - 1, 4 – glycoside linkages to form cellulose straight chain molecule, and 1, 4 – glycoside linkages bond the straight chain starch molecules know as amylose, there are branched starch molecules, known as amylopectin.  The branches are formed occasionally in tree like fashion from the 1, 6 -glucoside linkages in a normal 1, 4 – glucoside straight chain polymer.

The linear starch polymer and the branchud starch polymer are the two primary forms of starch molecules. The size of amylose molecules ranges from roughly 100 to over 1000 glucose units. The molecule of amylopectin is three or more times bigger. The specific features of each starch granule are determined by the size of the molecules and the amount of each kind contained in the granule. Both types are generally produced by plants and are found in them. The majority of starch granules comprise roughly 20-30% amylose type molecules and the rest amylopectin. Only amylopectin molecules are found in the waxy grain's starches. Some unique hybrids resulted in amylose-rich granules.

Figure : Amylose starch molecule

 

Figure ; linear molecular structure of starch

2.3 ADHESIVES

Adhesive is a material capable of fastening two materials together by surface attachment. Adhesive is synonymous to glue, mastic, cement and mucilage.

Adhesive practically implies the broad set of materials composed of organic compounds (mainly polymeric) which can be used to fasten two materials together. 

Generically, adhesives implies any material capable of being fastened by surface attachment, which would include inorganic materials such as Portland cement and solders such as wood’s metal. The materials being fastened together by the adhesive are the adherends and the resulting assembly is the adhesive bonds (McGraw Hill, 1971).

 

 

Figure ; starch based adhesive

2.3.1 CLASSIFICATIONS OF ADHESIVES

Adhesives can be generally classified into inorganic and organic adhesives.

ORGANIC ADHESIVES

The organic adhesives are sub classified into natural and synthetic adhesives. Synthetic adhesives tend to cover most of the adhesives used today in modern world.

Natural Adhesives;

These includes dextrin, animal glue, starch, casein glue, natural rubber resin, etc. Starch and dextrin and derived from low cost readily corn, cassava, potatoes and are used in paper and paper board. Protein glues are made from hide, bone, blood albumin of animals, soy proteins and casein, they are used on woods, sometimes in combination with synthetic resins.

Natural rubber is useful in pressure cases as it has the ability to stick fast to any surface it comes in contact with.

 

Synthetic Adhesives;

Synthetic adhesives have recently gained popularity in various applications due to their increased strength. Thermoplastic resin, vinyl and polyvinyl, cellulose, thermosetting resin, Epoxy, polyester, and other synthetic adhesives are divided into subcategories.

When heated, thermoplastic adhesive softens and hardens as it cools. They can be dissolved in a variety of liquids, including water and organic solvents. When heated, thermosetting adhesives become permanently stiffened and insoluble. Waxes and asphalts, as well as different cellulose compound vinyls and unvulcanized rubber, are among the thermoplastic synthetic adhesives. Multi-wall bags, whose contents must be kept dry, are laminated with asphdt adhesives. Paraffin wax is the primary coating material on paper for bread wraps, and micro crystalline wax, a wax with an exceptionally fine grain structure, is used for laminating food wraps.

Among the cellulose compounds, cellulose nitrate, commonly known as celluloid or pyroxylin, is the oldest synthetic adhesive. It is used in the bonding of wood, as cellulose plastics, as home cement, and in various shoe-making activities.

The most commonly used synthetic rubbers for structural bonding are neoprene and nitrite rubber, which attach particularly effectively to metal and wood, and polyisobutylene and butyl rubber, which are resistant to oxidation.

Many high-speed packaging operations use vinyl adhesives made of polyvinyl acetate or vinyl acetate to replace starch and dextrin. Polyvinyl alcohol, a water soluble and remoistenable material, is used to make flat envelopes, polyvinyl butyral is used to make safety glass adhesive, and polyvinyl other materials are used to make pressure-sensitive labels.

When rubber-based adhesives are applied to a surface, they are flexible, durable, and normally thermoplastic; however, they can be vulcanized to render them insoluble and heat resistant. They're employed in places like leather, vinyl upholstery, and cloth where a flexible bond is desired. They form a strong and robust metallic bond when mixed with phenolic resin.

The cyanoacrylates when are costly, bond many types of surfaces almost instantaneously. Polyamides are used in adhesive hot melt for paper, plastic film and metal foil.

The most common thermosetting adhesives are phenol-formaldehydes, which are particularly helpful in plywood for outdoor use, amino resins such as urea-formaldehyde for interior grades of plywood, and melamine-formaldehyde for wet-strength sheets. Epoxy resin that contain no volatile solvent and have outstanding adhesion to metals glass, ceramics and thermosetting plastics(Edward H et al, 1978)

 

 

2.3.2    PHYSICAL FORMS OF ADHESIVES

Physically, adhesives exist in many forms, these include:

(i)        Liquid of high or low viscosity: Most adhesive formulations are available in this form, either as a solvent dispersion or as an aqueous emulsion with lattices. They are simple to use and allow the user to alter the viscosity.

 

(ii)       Powders: To attain the liquid state, these adhesives must be mixed with a liquid or heated. Some types contain latent catalysts that are activated during cure at a specific temperature. Powder adhesives, in general, are a cost-effective option with a lengthy shelf life.

(iii)      Mastic or Paste: When void fillers and non-slump properties are required, this shape is ideal. It is possible to achieve a wide range of consistency.

(iv)    Film Tapes: There are supported and unsupported types. These forms are limited to smooth surfaces and are distinguished by quick application, minimal waste, and a homogeneous glue-like thickness.

(v)       Granule, Rods, Cubes and other solid forms:  These are convenient forms for ease of application and are for particular application. “solid” types are basis for adhesive solder sticks and hot-metal materials for long shelf life. (Shields J. 1974)

2.3.3    COMPOSITION OF ADHESIVES

The basic components of adhesives irrespective of the type are:

(i)        BINDERS:  The binders serve as a foundation for the adhesives. The binders are in charge of creating adhesive forces that hold two adherents together. A binder is something like starch.

(ii)       SOLVENTS:  These are the media used to disperse the binders into a spreadable liquid. Water is the most common solvent. To achieve the needed solubility in many adhesives based on synthetic resins, rubbers, and even natural gum, a range of organic solvents are required.

(iii)      FILLERS:  These are generally non-adhesive substances that are added to adhesives to increase their working qualities, persistence, and production costs. Calcium carbonate silicate oxide, alumna, or aluminum silicate are examples of common additives to epoxyresin adhesives.

(iv)      PRESERVATIVES:  These are compounds that are added to certain adhesives to slow or stop the growth of microorganisms, either while the glue is being stored, applied, or while the completed bond is being serviced. These agents are typically used in formulations that contain carbohydrates or proteins that are susceptible to mold, fungi, or bacteria, such as flour, starch, casein, or animal protein. The preventatives used are either, sodium benzoate or formaldehyde.

(v)       CATALYSTS:           These are substances that, when added in little amounts relative to the amounts of the major resistance, significantly speed up the core of an adhesive. Catalysts are used to speed up the rate of a specific chemical reaction in the adhesive base when it solidifies in the joint. Ammonium chloride, which is widely used to speed up the coming or cross-linking of proteins, is a good example of a catalyst.

(vi)      THINNERS OR DILVENTS: These are volatile liquids that are mixed into an adhesive to change its consistency and other characteristics. When utilized properly, such liquids are not genuine solvents for the other components, but they are efficient in diluting or thinning the mixture as needed for spray application.

(vii)     HARDENERS:  These are compounds or mixes of substances that are added to an adhesive in order to promote or control the curing reaction by participating in it. Para-formaldehyde, which is widely used with resorcinol-formaldehyde wood adhesives, is an example of a hardener.

(viii)    EXTENDERS: It has some adhesion properties. They're included to cut down on the amount of primary binder needed per unit area, lowering the cost of the actual joints. Wheat flour, for example, can be used to urea-formaldehyde wood adhesive to lower glue line expenses.

(ix)      FORTIFIERS:          They are ingredients that are added to an adhesive binder primarily to strengthen the persistence of the ensuing bond, which is not yet widely accepted. They could be binders or at the very least have a high sticky value. The addition of resorcinol and para-formaldehyde to a urea-formaldehyde wood glue, for example, can improve the weathering resistance of the resulting joints.

2.3.4       PROPERTIES OF ADHESIVES

There are a number of aspects to consider when evaluating an adhesive; these factors refer to the behavior of an adhesive from the time it is made until the time it achieves its ultimate bond.

These factors include:

(i)        VISCOSITY:   The adhesive materials aren't just ordinary liquids. In general, they are made up of a polymer that is usually dissolved in a solvent and often mixed with particles that have different physical or chemical properties. As a result, it's not unexpected that adhesive materials don't show. More than one measurement is required for Newtonian flow and the characterization of ryhlogical features. Many apparatus are used for determining the viscosity of free flow adhesives.  These include the Brookfield viscometer and the stormer viscometer.

 

(ii)       TACK:  This is the property of an adhesive that causes one adhesive-coated surface to stick to another when they come into contact. It's basically the adhesive's stickiness. It is one of the most essential characteristics in establishing an adhesive's viability for specific applications. Tack can change depending on time, temperature, and film thickness.  The instrument used in measuring tack is called tackmeter.

(iii)      BLOCKING: Is an unfavorable adhesive that forms between layers of similar or dissimilar materials when they come into contact, such as when stored under moderate pressure. Adhesives are applied to one or both of the surfaces to be bonded and kept until ready for use or assembly in some applications. It is essential that the coated surface do not bond or block during storage even if subjected to slight contact pressure or minor variations in humidity or temperature.

(iv)      CURING RATE:       Many adhesives require curing be either the application of heat or the addition of catalyst or both, with or without pressure for specified periods of time.

 

(v)       PENETRATION:  An adhesive that penetrates far beyond the surface of the coating material adds nothing to the bonding of the two layers and is therefore wasted. Adhesive costs rise when extensive substrate penetration occurs. Additionally, a starved ‘glue line' or adhesive layer may result, resulting in a wet or soggy product, which could result in warpage, lower production speed, and process delays.

(vi)      COVERAGE:  Is the quality of an adhesive that governs the extent to which a unit weight or volume of glue can be uniformly dispersed over an area to be bonded.

 (vii)    STORAGE LIFE:     When an adhesive is kept at high temperatures for an extended period of time, physical and chemical changes can occur. The storage life of an adhesive refers to the amount of time it may be kept, preferably under controlled circumstances, and still be used.  The storage life of an adhesive can be measured by taking measurements of the adhesive's consistency, binding strength, or both, before and after storage at a specific temperature for a defined amount of time. It is recommended that the adhesive be stored at a temperature that is close to that of real service, so that changes in the adhesive can be seen.  To determine these changes both consistency and bond strength test should be periodically conducted.

(viii)    SHELF LIFE:   The duration between when an adhesive is ready to use and when it is no longer usable is referred to as the shelf life of an adhesive.

2.3.5 CHEMISTRY OF ADHESIVES

The science of adhesion has only been studied extensively in the last ten years. Researchers have released a number of publications that have begun to provide the groundwork for why and how things stick together. Although much progress has been made in understanding how an adhesive adheres to a surface, the following theory is commonly accepted.

ADHESION:

            This is a phenomena in which interfacial forces, such as valence forces, interlocking action, or both, hold two surfaces together. The glue must be liquid and in close contact with the substrates for adhesion to occur.  The bond has more tenacions as the interfacial contact between atoms and molecules becomes closer to electrostatic interaction. The adhesive must displace air and other impurities from the surface in order to produce a strong bind. When the contact angle approaches zero and the following conditions are present, a phenomenon known as "wetting" occurs, the conditions include; the substrate posses a relatively high surface attraction energy; the adhesive has a real affurity for the substrate and the surface tension of the adhesive is low.  For an adhesive to wet a solid surface, it requires a lower surface tension than the solid.  For example polytetraflooethone (PTF) is a ‘non stick’ material because its surface tension is so low that no liquid adhesive has a surface tension low enough to wet it and hence bond to it. Metal adherends are readily wetted by most organic adhesives. When tight contact is created through wetting, the forces of molecular attraction maintain it, and it can be regarded permanent once the adhesive has set or cured. When the adhesive and substrate molecules come together, a multitude of forces are at work, the most important of which are the van Der Waals forces. There are some times reinforced by the attraction forces of primary chemical bonds.  The van De Walls forces can be likened to a magnetic attraction, except in this case, it is the electrical changes that are involved.  Calculations have indicated that the van Der Waal forces alone can produce theoretical bond strengths substantially greater than those observed in practice, with the difference owing to the challenges in creating a perfect joint and stressing it suitably.

            The shift from a liquid to a solid film largely completes the adhesion process. This transition can take the form of a physical change, such as in thermoplastic glue, or a chemical change, such as in thermosetting adhesive. The physical shift to a solid film in thermoplastic adhesive occurs when a molten liquid cools on a cool surface or when the solvent is lost by evaporation and diffusion. Polymerization creates the solid state in thermosetting glue. When heated to form a strongly connected structure, risin intermediates in a partially reacted state may react with other intermediates or complete their reaction.

 

THE BONDING PROCESS

            The adhesive bonding method is applying the adhesive to the adherend and holding it together (typically under pressure) until the glue has hardened to a given degree of strength. Surface treatment of the adherend may be required as a preliminary step, and heat may be required for hardening. Pure liquid, solution, dispersion (including avulsion), paste, fusible solid (particle, rod, etc.) and fusible film are all examples of adhesives (dropping, or no draping). Spray, brush, roller, knife, curtain coated (called cascade gluing) are all options for applying liquids, depending on the rheology of the liquid, Netonian or thixotropic, for example; the application of solid particles is sometimes affected by gravitational flow on to the adherend moving below.  With the adhesive reduse, a unique procedure is used, which in one form needs the application of liquid and solid particles separately; first, a phenolic resin is applied to the adherend, followed by the solid surface. There are four different types of adhesive hardening processes. Although the terms curing, setting, and even drying are all used interchangeably to describe the process of hardening. Curing refers to a chemical process including polymerization and setting that is used to harden emulsion and gelation glues, although drying is more typically utilized with starch adhesives.

The four bonding processes are:

(1)       Evaporation and absorption are used to dry a solvent or dispersion media (a process that usually necessitates are or both adherends being porous).

(2)       Melting a solid involves raising its temperature to the point where it becomes liquid and wets the adherend, then cooling and resolidification.

(3)       Increasing the rate at which a liquid or molten adhesive polymerizes into a solid to build a big structure, usually with the help of a chemical catalyst and commonly aided by heat.

(4)       Reacting two chemicals together to create a bigger molecular structure with repeating chemical units. This entails the addition of a liquid or solid that, while referred to as a hardener or curing agent, is not principally catalytic in nature. In some situations, the use of heat is required.

            Curing is a gradual process with various degrees of cure, but the end state of cure is somewhat arbitrary. Bone and skin glues, starch case in, poty vinyl acetate dispersions, and sodium silicate are some of the adhesives used in the first curing step.  The second method, known as hot melt gluing, is primarily used in packaging.

            A variety of thermoplastic polymers are used in the glue. The third and fourth processes are almost solely used in structural adhesives made of synthetic resins, such as urea, melamine, and phenol formaldehyde, as well as epoxide, polyisocyamate, and polyester. The two polymer adhesive is a type of structural glue that is commonly used in aircraft, hovercraft, and brake and clutch linings. Both of these adhesives are primarily interactive, and process 2 and 3 are regularly used, with process 2 and 4 being used less frequently. Instant stick adhesives, such as pressure sensitive tapes, usually do not require curing and stay tacky liquid. Because a lot of adhesive bonding is used to unite elements of a stress-bearing structure, the most common materials used are wood, metal (especially high alloys), and strong plastics like resin/glass fibre laminate. However, paper is the most commonly glued material, followed by wood, particularly for polywood manufacturing and veneering.

2.3.6       ADVANTAGES AND LIMITATION OF ADHESIVE BONDING

When the adherends are relatively thin, it can be joined by adhesive but cannot be efficiently bolted, riveted, or welded, as opposed to joining by mechanical methods or welding. The advantages of gluing however becomes less as the thickness of the metal increases.

The advantages of adhesive bonding can be summarized as follows:-

(1)             It is a very sensible method of joining since it does not necessitate the removal of valuable elements from the adherend.

(2)             Normally, there isn't much distortion (Distortion is greatest where an adhesive having high shrinkage is needed with thin adherends).

(3)             Other methods of connecting, including as riveting, bolting, nailing, and welding, may not be practicable when one or both adherends are thin. Although the specific strength of a glued joint may be lower than that of a mechanical or welded joint when using thick adhesive, adhesive bonding allows for a considerably broader area to be bonded, providing stress continuity, increased stiffness, reduced stress concentration and less risk of fatigue failure.

(4)             When attaching dissimilar elements, a properly chosen glue will not cause corrosion and may even remove the risk of galvanic action.

(5)             The sealing properties of adhesive may be utilized to provide fluid tightness in fuel tanks.

THE LIMITATION OF ADHESIVE BONDING

(1)             The most significant flaw is the comparatively low heat resistance. This is primarily an issue in structural metal applications, such as high-speed aircraft.

(2)             In some application the electrical resistance of adhesives, it is a huge disadvantage.

(3)             Despite the fact that many synthetic area adhesives have good chemical resistance, some chemicals damage or disintegrate them. However, in many circumstances, there exist substances that are not commonly seen.

(4)             Many adhesives have rather low peel and clearage strength.

(5)             It is necessary to hold part in position until the adhesive reaches a certain degree of strength, this may necessitates the use of clamps, complicated jigs etc.

(6)             Many high-strength adhesives require the use of heat, which, when paired with the necessity for high pressure, may necessitate the use of a heated hydraulic press or autoclave.

(7)             It is difficult to access the quality of the bond because in between the joint cannot be seen

2.3.7       USES OF ADHESIVES

Hot melt adhesives are utilized in corrugated paper production, packaging, book binding, and shoe manufacturing. The most common application of pressure sensitive adhesives is as a tape coating. From electrical tape to surgical tape, these pressure sensitive adhesive pastes offer a wide range of applications. Structural adhesives come in a variety of forms, including liquids, pastes, and 100% sticky films. Epoxy liquids and pastes are widely used adhesive materials, with uses ranging from ordinary industrial to automotive to aerospace and vehicle building. In the construction of aircraft, solid film structural adhesives are commonly employed. Acrylic adhesives are utilized in thread locking procedures as well as minor activities requiring quick cure times, such as electronics manufacturing. The most adhesive is used in the production of plywood and other wood goods. Acrylic adhesives are used in thread locking and other minor tasks that require short cure times, such as electronics fabrication. The majority of glue is utilized in the manufacturing of plywood and other wood products.

CHAPTER THREE 

MATERIALS AND METHODS 

3.1   MATERIALS

3.1.1   FEEDSTOCK

Cassava starch was used in this work as the raw material. 

3.1.2   CHEMICAL AND REAGENTS

The following chemicals and reagents were used in this work;

       i.          Sodium hydroxide pellets

     ii.          Borax

   iii.          Formaldehyde

   iv.          Calcium carbonate

     v.          Distilled water

 

3.1.3   APPARATUSES

The following laboratory equipments were used in this work:

        i.          Hot Water Bath

       ii.          Pipette

     iii.          Conical Flasks

     iv.          Burette

       v.          Beakers

     vi.          Measuring Cylinder

   vii.          Stop Watch

 viii.          Laboratory Oven

     ix.          Digital Viscometer

       x.          Electronic Weighing Balance

 

3.2   METHODS

3.2.1 PRODUCTION OF THE CASSAVA STARCH

Cassava tubers were purchased at Eziobodo market in Owerri west local government area of Imo state. The tuber were debarked and cut into small pieces, allowed to dried for a period of three days, the small chops of cassava was taken to market and grinded into powder form. A mixer was used to puree the debarked tubers. This was sieved with water to make a slurry of starch and gluten, which was separated by allowing the starch to settle and decanting the supernatant gluten liquid.  The method above was developed by (Bussy, D. 1972) and was owing to the fact that starch granules are tiny in comparison to fibrous materials.

3.2.2 PRODUCTION OF ADHESIVE FROM CASSAVA STARCH

METHOD

185ml of distilled water was put in a beaker, 12.5g of starch was dissolved in the water, 0.65g of CaCo3 was also added.  To achieve a uniform dispersion, the mixture was completely stored. The beaker and its contents were heated in a bursen flame, and 1.24g of Na0H pellets were added while heating with constant stirring. After a few minutes of continuous stirring, a temperature of 700C was reached, and gelatinization, or the swelling of the starch granules, happened. The temperature was maintained at the same level for two minutes, after which the tick white solution was completely mixed.

            Further stirring increased the adhesive's strength and viscosity to their maximum levels. After removing the beaker from the burner, 0.30g of formaldehyde was added as a preservative.

            The proportions of the various chemicals were changed in consecutive batches to achieve the optimal result. In order to determine the effect of an addition on the adhesive, an additive was occasionally left out. 

3.2.3       pH DETERMINATION

This test was carried out using a digital pH meter. The pH meter was zeroed when the sample was placed in a beaker. The PH electrode was dipped into the sample and the digital display read the value.

3.2.4     DETERMINATION OF TACK TIME

Tack time refers to how long it takes for an adhesive-bonded joint to reach full strength. It differs between materials and is affected by temperature and pressure. This was established by separating a sheet of paper into 2cm by 2cm units and applying a uniform smear of adhesive to the papers before placing them on a wood surface.  To promote maximal wetting and penetration of the adhesive into the adherend, pressure was applied to the surface.

The first paper was readily ripped apart for the first two minutes. This tugging action was carried out until a profound fibre failure was achieved, which corresponded to the adhesive's tack time.

3.2.5    SOLID/MOISTURE CONTENT DETERMINATION

1 gram of adhesive sample was weighed and placed in the oven. The oven was turned on and the temperature was set to 1000 degrees Celsius. The sample was placed in the oven for 45 minutes before being retrieved and weighed again. The formular was used to calculate the solid content of the sample in percentages.

            Weight of sample after drying            x          100      =   solid content

            Weight of sample before drying                        1      

           

The moisture content of the sample expressed in percentage, was determined by the expression:

Moisture content = 100   x   Weight of sample before drying - weight of dined sample

                                                          Weight of sample before drying                                

3.2.6    WET ABILITY DETERMINATION

Weighing 1 gram of glue sample and placing it in the oven The oven was turned on with a temperature of 1000 degrees Celsius. Before being recovered and weighed again, the sample was baked in the oven for 45 minutes. The solid content of the sample was calculated in percentages using the formular. 

3.2.7    STORAGE LIFE DETERMINATION

The adhesive was sealed and stored at room temperature for more than a month and a half

CHAPTER FOUR

RESULTS AND CONCLUSION

4.1 RESULTS

MATERIAL	A	B	C	D
Water Starch Na 0H Ca Co3 Borox Formaldehyde	185ml 12.5g 1.24g 0.65g 0.5g 0.30g	185ml 12.66g 1.24g 0.65g 0.6g 0.32g	183.76mls 12.51g 1.23g 0.64g 0.7g 0.35g	184.34mls 12.36g 1.25g 0.63g 0.8g 0.32g

Table 4.1; 

sample variations in adhesive production 

4.1.1       PH VALUES

The PH value of adhesives is 7.5

The PH value of standard is 8 – 12

FORMULATION	PH VALUES
A B C D	7.8 7.0 6.9 5.6

 

Table 4.2 ; pH value of adhesive

4.1.2       TACK TIME DETERMINATION

FORMULATION	TACK TIME (MINUTES)
A B C D	14 12 18 10

 

Table 4.3; Tack time determination

4.1.3       SOLD AND MOISTURE CONTENT

FORMULATION	MOISTURE CONTENT	SOLID CONTENT
A B C D	79% 82% 88% 83%	20% 17% 11% 18%

 

Table 4.4 ; solid and moisture content of standard adhesive.

4.1.3    WET ABILITY

            After drying for 24 hours and then wetting again, all of the formulations were able to adhere correctly.

4.1.4    STORAGE LIFE

            There were no visible alterations after 2 months of storage, and the product is still usable.

4.2     DISCUSSION

The goal of stabilizing adhesive made from starch is to help solve most of the challenges associated with fastening or holding substances together through surface attachment. The following methods were used in this study: literature review of starch, its chemical, physical, and adhesive qualities. Also classification and application of adhesives as well as its formulations and analysis were investigated.(Eze TC, 1993) and some standard values form the Standard Organization of Nigeria (SON).

Starch was the main component of this glue and functioned as the binder; the additional additives utilized improved the adhesive's working capabilities. The use of starch as an adhesive stems from its ability to reach a specific temperature. Because of its abundance, cassava was chosen as a starch source.  Although starch adhesive has weaker working properties than synthetic competitors, such as a longer tack time and inadequate bonding strength, it nevertheless has a large market demand due to its low material and production costs. The adhesive's viscosity was inversely proportional to the volume of water utilized; the more water used, the less viscous the adhesives were. The viscosity problem is solved by adding borax, which raises the viscosity to the required range.

The amount of sodium hydroxide in the formulation is responsible for the adhesive's gelatinization. Sodium hydroxide offers the advantage of lowering the gelatinization temperature, increasing the adhesive's working life, but lowering the adhesive's setting speed. Other ingredients such as calcium carbonate and formaldehyde were crucial in their own right, providing strength to the created glue and a preservative with formaldehyde solution. The thinner, which is an organic volatile liquid, was employed to thin the glue while simultaneously adding sticky characteristics.

During manufacture, it was discovered that formulation D took longer to gelatinize than the others, owing to the absence of sodium hydroxide, which lowers the adhesive's gelling temperature. The viscosity of Formulation C, which has the highest Borax content, is high. The results of the test analysis on the formulated adhesive are provided in the tables above, and the method used to calculate the parameters is shown in Appendix B. The adhesive on the market had a low solid percentage. This suggests that low solid content is a characteristic of the starch – based adhesive.  For the tack time, no standard value is available.

As a result, the tack time must be moderate for the adhesive to be useful. A long tack time may make the adhesive unsuitable, yet a short tack time may indicate that the glue has not penetrated the adherent properly, resulting in an unsatisfactory bond. Despite its limitations, the starch-based glue has seen a significant growth in demand due to its inexpensive cost.

 

CHAPTER FIVE

CONCLUSION AND RECOMMENDATION 

5.1 CONLUSION

The goal of this research project, which was to create a starch-based glue, was accomplished. The most intriguing aspect of it all was that the adhesive was made with over 70% local raw resources.

The test results demonstrate that the glue created in this project has functioning properties that are within the standard range and that it compares favorably to those on the market. The shelf life of starch-based adhesives is not as lengthy as that of synthetic adhesives, and starch, as an organic component, is susceptible to microbial attack over time.

5.2 RECOMMENDATION

I recommend that the work be done with other raw materials that have starch as its natural extractive.

5.3 CONTRIBUTION TO KNOWLEDGE

From this research work, it has been proven that starch from cassava is a good adhesive but not to all surfaces like metals and addition of inorganic chemicals can improve the adhesive strength of it.

REFRENCES

Alphonsus V.P. (1987):          “Adhesives”. Encyclopedia of

Science and Technology. V. 16^th Edition, McGraw

Hill Company New Yrok, Pp. 122 – 123.

 

De Bussy J.H (1972): Natural Organic Materials and

Related Synthesis Products, Materials and

Technology. Volume V. Longman Group Limited. 

London P. 63 – 71.

 

Bikales M.N (1971):   Adhesion and Bonding John Willey

Co. New York P. 20.

 

Edward H. (1993):      New Age Encyclopedia. Volume 1,

Lexicon Publication, Inc. Pp. 65 – 66.

 

Eze T.C (1993):          Production of Gum using Cassava

Tubers as the starting raw material.  Chemical

Engineering Department, I.M.T, Enugu. (An

Unpublished Paper

 

French D. (1950):       Inker’s Chemistry and Industry of

Starch.  Academic Press Inc. New York. P. 165.

 

Kinloch A.J (1987):    Adhesion and Adhesives. Chapman

and Hall Limited, London.

 

Lees W.A (1989):       Adhesive and the Engineer:

Mechanical Engineering Publication Limited,

London Pp. 1, 23 – 25.

 

 

 

Radley, J.A (1968):    Starch and its Derivatives.

Chapman and Hall Limited, London. Pp. 168 – 190

 

Shelds J. (1974):         Adhesive Bonding Oxford

University Press, London Pp. 3 – 5.

 

White, T.A (1987):     “Starch”. Encyclopedia of Science

and Technology. Volume 17, 6^th Edition. McGraw Hill Company New York pp. 326 – 328

APPENDIX B

SOLID AND MOISTURE CONTENTDETERMINATION

 

FORMULATION A

Weight of dish                                                            =          33.74g

Weight of sample                                                       =          1.00g

Weight of sample + dish                                            =          34.73g

Weight of sample + dish after drying                         =          33.92g

 

Weight of sample after drying

       33.92 – 33.74                          =          0.21g

\    Solid content               =          0.21g

\    Moisture content         =          1 – 0.21g   =   0.79g

\    % Moisture content    =          0.79       x   100

                                                         1                  1

                                                       =          19%    

APPENDIX C

STANDARD GLUE SAMPLES AND THEIR CHARACTERISTICS

A         =          PGN Glue

B         =          Stephen Glue

C         =          Polar Glue

TYPES OF GLUE

CHARACTERISTICS	A	B	C
Moisture Content Solid Content   PH Value Tack Time	55%   15% 15%	85%   15% 10%	60%   40% 11%

 

            The above date was obtained from laboratory analysis by (Eze T.C, 1993).

            Some of the standard values available are:

a.         Solid content 15 - 30

b.         PH value 8 - 12

c.         Moisture content 65 – 85%