FORMULATING AND CHARACTERIZING A FORMALDEHYDE FREE AND HIGH-PERFORMANCE STARCH-BASED WOOD ADHESIVE USING PVAC

CHAPTER ONE

INTRODUCTION

1.1 Background of the study

The role of Adhesives in the woods resources is very vital as well as the expansion and development of forest product industry. (Frihart, 2011). The bonding of solid wood and wood particles of various sizes is crucial for producing modern, functional wood products, whether they are used for construction, furniture, or other applications (Stoeckel et al. 2013). Wood has been joined using bio-based adhesives for many years, but in the 20th century, thermosetting adhesives, which were deemed to be more effective and stable for use in humid conditions, gradually superseded them (Frihart, 2015). The three most popular forms of thermosetting adhesives now on the market are isocyanate, phenolic, and amino-based resins. Utilizing these thermosetting adhesives is thought to be more cost-effective and reactive, with quick curing behavior and a wide range of properties once cured. The market has been dominated by these adhesives for years.(Pizzi, 2014).The most significant adhesives under this category in terms of quantity are urea-formaldehyde (UF) resins (Whitfield, 2007). The production of wood-based products, such as particleboard or medium density fiber (MDF) boards for interior applications, uses virtually solely UF-based adhesives because of their low cost raw materials, quick curing, strong dry bond strength, and colorless glue line. UF resins are typically treated with much more expensive substances like melamine, phenol, or resorcinol when products are used in environments with greater humidity levels. The required strength properties, anticipated moisture resistance, intended formaldehyde emission class, and production cost of the finished product are all factors that affect the final adhesive composition that is used. Both PBs and MDF boards, which are the most common applications, require adhesives with relatively high dry strengths, dimensional stability, moderate temperature and moisture resistance, quick curing, and preferably water solubility for easier viscosity adjustment. The final adhesive formula that is employed is influenced by the necessary strength attributes, predicted moisture resistance, intended formaldehyde emission class, and production cost of the finished product. The most typical applications, PBs and MDF boards, call for adhesives with short curing times, water solubility, moderate temperature and moisture resistance, dimensional stability, and reasonably high dry strengths. In comparison to synthetic polymers, starch is one of the most plentiful, renewable, biodegradable, and natural polymers (Le et al., 2010). It has been utilized as an adhesive in a variety of goods, but it also has several drawbacks, including poor water resistance, weak bonding, and decreased durability when compared to traditional adhesives. In order for starch-based wood adhesives to compete with petrochemical-based wood adhesives, various attempts have recently been undertaken to improve the performance of starch adhesives, particularly the stability behavior (Imam et al. 1999; Sin et al. 2010). Gelatinization, a process that involves molecular reactions connected with the heating of starch in the presence of water, is one of the most popular ways to modify starch. When starches are subjected to high temperatures (typically greater than 50 °C) in a sufficient amount of water, the granules absorb water, swell, and rupture because of the disruption of amylopectin double helices (hydrogen bonds dissociation), while amylase preferentially leaches out of the swollen granules. These events are accompanied by a dramatic increase in the system’s viscosity as the granule structure is progressively ruptured (Garcia et al. 2016) and (Ji et al.2017). The cassava starch that will be used in this investigation will be extracted from the roots of subtropical crops, where amylopectin made up 83% of the starch composition and amylose, 17% (Hung et al., 2017). With rising living standards in recent years, cassava starch has steadily replaced grain starches in a variety of uses. The exquisite cassava starch has a limited amount of contaminants. The granules have a 20 m or smaller diameter and are spherical in shape. Cassava starch gelatinizes at a temperature between 58 and 69 °C. Cassava starch is quickly gelled and has a high peak viscosity when it is gelatinized. But if the gelatinization temperature is carefully managed, it is possible to produce a translucent starch paste that can be utilized for the bonding of corrugated board, plywood, and adhesive tape. When polyvinyl acetate is hydrolyzed, polyvinyl acetate (PVAC) is created. It has several advantageous qualities, including strong biocompatibility, outstanding water solubility, chemical resistance, and optical characteristics. One of the most frequently produced synthetic water polymers worldwide is polyvinyl acetate (PVAC) (Sridach et al. 2013). According to Ramaraj (2007) and Kaboorani and Riedl (2011), polyvinyl acetate (PVAC) is frequently dissolved in water and utilized as an adhesive, a sizing and coating agent, as well as tissue scaffolding materials for biomedical applications. Additionally, it is a crucial component of adhesives that can function as protective colloids. Starch and polyvinyl acetate (PVAC) are both polar materials with hydroxyl groups (-OH) in their chemical compositions. These hydroxyls are quite polar and tend to form intermolecular and intramolecular hydrogen bonds, which improve the integrity of PVAC-starch blends (Tang and Alavi 2011).To the authors' knowledge, however, there hasn't been much research done on how PVOH affects the performance of CS-based wood adhesives. The goal of this project is to develop a low-cost, high-performance, formaldehyde-free starch-based wood adhesive using polyvinyl acetate (PVAC) as a production catalyst and cassava starch (CS) as a primary catalyst that is also renewable and biodegradable for the benefit of humankind.

1.1.1 Definition of terms

Starch

This is abundant, renewable biodegradable and inexpensive natural raw materials which is used as a good alternative for synthetic polymer ( le corre et al. 2010). It is the principle form a carbohydrates reserve in green plants, stored in their chloroplast in the form of granules and in their storage organs such as;

The root of cassave plant
The tuber of the potato
The sterm of pith of sago (oil palm) (Baini et al, 2021).
Seed of corn banaan, wheat, sorghum anud rice.

It has the fundamental chemical formula (CH2O), is a granular, supple, and flavorless powder, and is insoluble in both cool water and alcohol (Britannica, 2023). Though depending on the source, the characteristics of starch, such as color, grain size, and shape, might vary. The favorable characteristics of starch that attract researchers' attention to it include its relative affordability, non-toxicity, and polyfunctionality (Gadhave, 2017). Starch is a poler material that can be pulled to other poler substances like cellulose because it has oxygencarbon and oxygenhydrogen linkages (Monteiro et al., 2016).Due to its affinity for the cellulose in wood, starch is particularly useful in the formulation of wood adhesives because it reduces the contact angle between the wood and itself, resulting in the perfect wet ability and the formation of strong adhesive connections. For its potential in a wide range of value-added applications, such as paper production, food processing, cosmetics, and pharmaceutical products, it has drawn considerable commercial and research interest.

1.1.2 Basic constituency of a starch molecule

Figures 2a and 2b show two naturally occurring high molecular weight polymers made of glucose molecules that make up the semi-crystalline molecule known as "granule," or starch (Mehmood, 2019). The substantial variation in the size, shape, and functional qualities of starch granules across and within species is caused by variations in the properties of amylose and amylopectin, as well as how they are structured inside granules (Bertoft, 2017). Gelatinization, an irreversible process, causes starch granule breakage at high temperatures (between 50 and 80) when starch is cooked in the presence of water (Mandala, 2012). Retrogradation is the process of chilling starch after it has been heated in the presence of water, which causes the disordered amylose and amylopectin to gradually reorganize chains into an adhesive, as indicated by literatures, may include;

Selection of starch: the type of starch used in the adhesive formulation depends on the application and the desired properties of the adhesive to be formulated.
Gelatinization of the selected starch: to improve the properties of the strach, it is first gelatinized by heating in water or water based solution. The gelatinization process helps to breakdown the starch granules and makes them more soluble in water.
Modification of starch: depending on the application, the starch may need to be modified to improve it adhesive properties. Different methods exist through which this can be done.
Longer curing time: starch based adhesives typically have a longer curing time compared to synthetic wood adhesive, which can slowdown the manufacturing process. Hence, the molecular structure of amylase and amylopectin, the gelatanisation and retrogradation of starch are represented in fig 1.
Lower heat resistance: starch based adhesives may not be suitable for applications that require high heat resistance as the can breakdown and lose their strength at high temperature.
Limited bonding strength on certain substrate: while starch based adhesives can proved good bonding to may substrate tha4
t may not be effective on certain materials such as metals or plastics.

1.1.3 Modifications of starch based adhesives

Due to the above listed in sufficiencies of starch, it is important to employ efficient methods to modify starch chemically, physically or biologically. This modification can utter the viscosity and solubility of starch enhances other significant properties during the production of starch based adhesives (Wang et al, 2012).

Properties of starch based adhesives that can be modified through formulation variables include;

1.2 The Aims and Objectives of the study

1.2.1 Aims

The aim of the study is to formulate and characterize a Formaldehyde Free And High-Performance Starch-Based Wood Adhesive using PVAC.

1.2.2 The specific objectives of the study are;

To Synthesis starch-based wood adhesive

To determine the Shear strength of the wood used

To determine the thermal stability of the adhesives.

To examine the changes in the chemical structure of the starch adhesive with modification.
To determine the physical and chemical properties of the starch adhesive.

1.3 Scope of study

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