Characterization of Process Parameters of Adhesive Glue Produced from Leguminous Seeds

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1 Characterization of Process Parameters of Adhesive Glue Produced from Leguminous Seeds 1 SADARE, O. O. 2 OKELANA, T.O. and 1 *AFOLABI, A. S. 1 Department of Civil and Chemical Engineering, College of Science, Engineering and Technology, University of South Africa, P/Bag X6, Florida 1710, Johannesburg, SOUTH AFRICA 2 Department of Chemical Engineering, Faculty of Engineering, Ladoke Akintola University of Technology, Ogbomoso, NIGERIA wumioladejo@yahoo.com;tokelana@yahoo.com;*afolaas@unisa.ac.za Abstract: Soy bean and pigeon pea seeds are biodegradable, easily processed, readily available and relatively inexpensive. Owing to the competition in the food chain with soy bean seeds, pigeon pea seeds, because of their resistance to drought and not commonly consumed as soy bean were used to prepare adhesive glue for wood in this study. Analyses such as ph, viscosity, bond strength and moisture content were carried out on the resultant glue samples. The shear strength of the glue was also tested on wood specimens. This study also investigated the effects of calcium carbonate and wood flour fillers on the glue produced. It was discovered that the sample with ordinary soy bean had higher bond strength on wood samples than the glue sample with ordinary pigeon pea. The analyses of results obtained also showed that mixture of defatted soy flour and pigeon pea flour reinforced with calcium carbonate filler showed the highest bond strength. It can therefore be concluded that soybean glue and pigeon pea glue with CaCO 3 filler produced a better alternative for the expensive and importation of glue in the market. Pigeon pea glue can be further modified to meet up with the shear strength of soy based adhesive in the future investigation. Key-Words: - : calcium carbonate, filler, glue, pigeon pea, soy bean, wood flour, wood samples. 1 Introduction Legumes have been grown in various parts of Africa of which the leading producers are Nigeria, South Africa and Tanzania [1]. Examples of leguminous seeds are; soybean, guinea pea, locust bean, pigeon pea and guar oil seed. The seeds of some of these legumes are starting materials for producing casein, adhesives, and plastics [2]. Soybean has been used by many researchers as a source of adhesive [3]. Soy bean (Glycine max) is an annual summer legume also known as soja bean [4]. A number of products are manufactured from soybeans such as, beverages, sausage, binders, diabetes foods, paints and adhesive, which is the aim of this study. Soybean contains 40% protein, 18% fat, 32% carbohydrate, 4.5% ash and 5.5% crude fibre [5]. Pigeon pea (Cajanus Cajan) which is also known as the Congo pea or bean is one of the most important food legume crops of both tropics and sub-tropics [6]. Pigeon pea displays a wide range of disparity for physiological maturity and can adapt to drought easily [7]. Being a legume, it improves soil nutrients through symbiotic nitrogen fixation [8]. It plays a significant role in reducing malnutrition for large number of people all over the world and comprises amino acid like tryptophan, lysine and methionine [9]. The three major regions in the world where pigeon pea is being produced are: India subcontinent, Eastern Africa, and Central America [6]. Pigeon pea seeds are said to be rich in protein with about % which makes them to be considered as raw material for adhesive. They also contain carbohydrate ranging from %, 7.3 fiber, 1.5 fat and 3.45 calories by weight [8]. The fresh green pods and seed of pigeon pea may be eaten like peas and the green leaves as a cooked vegetable. The seeds can as well be pounded into flour and added to soup and stew. However, the seeds of pigeon pea have been used in the production of (local glue) adhesive [6]. Therefore, soybean and pigeon peas seeds were considered in this study to prepare adhesive glue due to their high percentage of protein. New technologies and environmental issues, have led to the discovery of proteins especially soy flour from soybeans as an important adhesive for interior plywood and wood flooring [10]. Presently, most wood industries are interested in ISBN:

2 petrochemical-based and formaldehyde-based adhesives such as, phenol formaldehyde resin and urea-formaldehyde resins in the preparation of wood composites [11]. Although, adhesives produced from them possess high glue strength and high water resistance, but formaldehyde released from wood composites was recently discovered to be poisonous and toxic to humans. These endanger the lives of workers and users of the wood composite. In addition to these, petrochemical-based adhesives are non-renewable, limited and costly [12]. Therefore, the improvement of environmental friendly adhesive from natural agricultural products has awakened noteworthy attention. Most natural adhesives are used for bonding paper, foil and light wood [13]. A simple paste of soybean and pigeon pea is relatively poor adhesive in water, but addition of some chemical reagents will improve the effectiveness of the glue produced [14]. These chemical reagents help to unfold the major protein structures in protein based adhesive without altering the primary structure of the protein. There are different methods that can be used to denature protein. These include exposure to heat, acid/alkaline, or organic solvent, detergent and urea [15]. The most effective treatment is increasing the ph of the soy meal to 11 or higher. Defatted soy flour was given an alkaline treatment by Hettiarachchy et al [16]. The alkaline treatment allows denaturation and dispersion of soy protein in water. This has been discovered to improve the adhesive strength and water resistance of adhesives prepared from soy proteins [16]. Kalapathy et al [17] investigated the effect of some salts such as NaCl, Na 2 SO 4 or Na 2 SO 3 and discovered that at a concentration of 0.1M, these salts reduced the viscosity of proteins with no significance adverse effect on the adhesive strength and water resistance. Low viscosity adhesives allow easy handling and are useful for gluing highly absorbing materials such as dry wood and particle boards [17]. In this study, the bond strength of soy bean was compared to that of pigeon pea, since soy protein can compete with food chain. A relatively high protein legume was developed to replace soy protein based adhesive. Two fillers namely CaCO 3 and wood flour were incorporated into the adhesives. Adhesive fillers have been known to improve the quality, increase quantity or regulate viscosity and reduce tack and blocking to the adhesive [18, 19]. Calcium carbonate is good filler which improves the viscosity and increase the quantity of the glue [19]. Mohsen [19] used carbon carbonate as filler for polyvinyl acetate emulsion for his application as wood adhesive. Different formulations with variable percentage of fillers were prepared and the shear strength of the applied adhesive on wood was measured. It was concluded after 24 hours that the adhesive developed exceptional shear strength [19]. Wood flour was also adopted to increase the quantity of the glue produced. The mechanical properties of polypropylene filled with wood flour were studied by Kokta et al [20]. They concluded that incorporation of suitable filler into the polymer matrix can produce materials which are equally strong and tough [20]. Wood flours are mainly obtained from natural resources; therefore they are attractive fibres for thermoplastic polymers. They are also cheap with low density and high specific properties [21]. Due to their availability, materials fibres offer a real alternative to the reinforcing fibres presently available [22]. Thus, previously wasted wood materials are converted into useful product and this trend will probably accelerate in the future [23]. However, very limited literatures are available on the use of wood flour and CaCO 3 as fillers in soybean based adhesive. Therefore in this study, these two fillers were incorporated into the protein based adhesive and their effectiveness was compared [19]. In this study, CaCO 3 and wood flour were used as filler to improve the quantity of the glue produced from soy bean and pigeon pea to reduce cost, so the glue produced can serve as alternative for the importation of the expensive glue to the country. Many literatures showed that wood flour has been used as fillers in polypropylene, thermoplastic and calcium carbonate filler in polyvinyl acetate, but few work has been done on incorporation of these two fillers in soy protein and pigeon pea adhesives. Therefore, this study was aimed at producing adhesive from legumes such as soybean and pigeon pea. The study also compared the prepared pigeon pea and soy based adhesive prepared by alkali treatment, and incorporated and compared the effect of wood flour and calcium carbonate fillers on the adhesive produced. The shear strength of alkali modified soy bean and pigeon pea adhesives were also investigated. 2 Materials and Methods Soybean and pigeon pea seeds were purchased from open market in the Western region of Nigeria. Analytically graded calcium carbonate, sodium hydroxide pellets, sodium chloride and acetone were purchased from commercial sources. Wood flour (saw dust) was obtained from wood factory as a waste product. ISBN:

3 Soy bean and pigeon pea seeds were dehulled, dried at 80 o C for 25 minutes each and then grinded to obtain soy flour and pigeon pea flour. Both soy flour and pigeon pea flour were defatted using an apparatus called soxhlet extractor. About 80 g each of powdered soybean and pigeon pea was weighed and wrapped inside filter paper. About 350 ml of acetone was measured for 80 g of soybean and 300 ml acetone for 80 g of pigeon pea and put inside the soxhlet extractor until the whole oil has been extracted. After the extraction process the wrapped powdered bean was removed from the glass thimble and air-dried. Different proportions of soybean flour and pigeon pea were weighed into a beaker of 250 ml while 17 ml of distilled water was added and stirred for 2 minutes gently with a stirring rod, 6 ml of NaOH was poured into the mixture and stirred for 3 minutes and finally 6 ml of NaCl solution was added and stirred for 2 minutes. The wood flour was grinded and sieved. Different proportions of soybean flour and pigeon pea flour were weighed into beaker and 2 g of wood flour filler was weighed into each of the flour. All other materials were added to the mixture as in the production of glue above. The same method was used for calcium carbonate filler; hence glue samples A-L were obtained (Table 1). Table 1: Composition of protein flour and fillers in each sample of glue produced Measurement of ph The ph electrode was standardized and calibrated to ensure its accuracy. It was then dipped inside the glue samples and the reading was taken Determination of viscosity A viscometer was used with a measuring cylinder, stop watch and a steel ball. The glue samples were immersed in a measuring cylinder, the height of the cylinder was marked A, and the lower length also was marked B. The steel ball was gently dropped into the glue inside the cylinder and at the same time the stop watch was switched on. The time taken by the steel ball to reach the marked bottom of the cylinder was noted and recorded Effect of temperature on the bond strength of the glue produced The glue samples produced were heated in an oven at varying temperatures of 30 o C 120 o C. Using tensile testing machine to measure the bond strength of the glue samples, the average bond strength was recorded at different temperatures and calculated using the formula (2.1). Bond strength = Applied force (KN) Area (m 2 ) (2.1) Determination of solid and moisture content The glue samples were heated to 160 o C for 1 hour in air oven, after which they were weighed. The percentage of the solid and moisture content of each glue was then determined using the formula (2.2) % Moisture content = Original wt. Dry wt. Original wt. 100 (2.3) % Solid content = Dry wt. Original wt. 100 (2.4) Note: DFS stands for defatted soy flour, PPF for pigeon pea flour, WF for wood flour and CC for calcium carbonate powder. 2.1 Analyses of the adhesive glue samples produced Various analyses such as ph, viscosity, solid and moisture content, and effect of temperature on bond strength were carried out on the adhesive glue samples produced. 2.2 Determination of bond strength on wood samples An oven method was used to determine the moisture content of the wood sample at 120 o C for 1 hour. On each side of a wood sample ( cm) was 8.0% (w/w) protein solution placed and spread on an area of 2 2 cm to give a protein concentration of 2.0 mg/cm 2. Two other wood samples of same size were placed on the glued area and hard-pressed with a load of 5 kg for 2 hours. The glued wood specimens were allowed to dry overnight at room temperature. The resultant specimen was then ISBN:

4 analyzed for shear strength using an Instron testing machine with cross head speed of 2.5 cm/min. 3 Results and Discussion 3.1 Percentage of oil in soybean and pigeon pea flour Table 2 shows the extraction process results of soybean and pigeon pea flours. From the result, it can be observed that soy flour has larger percentage of oil extracted and lower final dried powder weight while pigeon pea flour has the lower oil extracted. This shows that soy flour has higher percentage (29.35 %) of oil than pigeon pea (18.98 %). This is due to the fact that soy bean is an oil seed with high oil and protein as its major products [24]. Table 2: Process of extraction of oil 3.2 Effect of filler on the viscosity of the glue samples Table 3 shows the results of ph, viscosities and solid content of the glue samples. From the result it can be seen that glue samples A and B which are glue samples of soyflour and pigeon pea without filler have the lowest viscosity of kg/ms and kg/ms respectively. samples with highest viscosities are glue samples containing fillers which increased the percentage solid content of the glue. Therefore, this result confirms that fillers actually increased the viscosity of the glue produced as earlier opined by other researchers [18, 19]. 3.3 Effect of alkaline treatment on the ph value of glue samples The ph result in Table 3 shows that the alkaline treatment of protein adhesive maintained the ph of the glue samples at 11 and above [16]. The glue sample A shows the highest ph value of followed by D and C, and respectively, while the addition of filler slightly reduces the ph value of the glue. Glue samples I and L show the least ph values. 3.4 Effect of filler on percentage solid and moisture content Fig. 1 shows the percentage solid and moisture content results of the samples. From this Figure, it is seen that the percentage solid content in control glue sample A (SBF) is higher than the percentage solid content in glue sample B (PPF). An increase in percentage solid content is noticed in glue samples I L. Therefore, it can be deduced from this observation that filler reduced the moisture content and increased the percentage solid content of the glue. Table 3: ph, viscosity and % solid content of glue samples A - L Fig. 1 Effect of filler on the percentage moisture and solid content of glue However, glue sample J has the highest viscosity value of kg/ms followed by glue sample I with viscosity value of and then K, kg/ms. These three glue 3.5 Effect of temperature on the bond strength of glue produced Table 4 shows the effect of temperature on the bond strength of each sample of glue produced. From the result in Fig. 2, it can be seen that glue A L ISBN:

5 decreased as temperature increased from 30 o C- 120 o C. However, bond strength of glue samples K and L increased as the temperature increased from 30 o C to 120 o C. This result shows there is thermal stability with glue samples K and L even at increased temperature. Table 4 Effect of bond strength at different temperatures reinforcement agent than wood flour filler. The result also shows that glue samples K, a mixture of DSF: PPF (4:6) with 2 g of calcium carbonate (CC) and glue L is a mixture of PPF and CC in ratio 8:2. It can therefore be deduced that the combination of both protein adhesive produced better bonding property than when only PPF was used with calcium carbonate filler. Comparing glue samples H and L, though PPF had poor bond strength even with wood flour filler, but a great improvement was achieved in bond strength when calcium carbonate was used as the filler. Fig. 3 Determination of bond strength on wood specimen (Bond strength measured in kn/m 2 ) Fig. 2: Effect of temperature on bond strength of glue samples A-L (Temperature (T o C) and bond strength in kn/m 2 ) 3.6 Determination of bond strength of the glue samples on wood specimen Fig. 3 shows that glue sample K had the highest bond strength of 5.27 kn/m 2, then glue sample L with bond strength of 4.52 kn/m 2. Comparing glue sample A (alkaline modified defatted soy flour, DSF) to glue sample B (alkaline modified pigeon pea flour, PPF), the result shows that glue A shows better strength on wood specimen better than glue B. This shows that DSF is a better glue than PPF on wood. Glue samples G and H show low bond strength with no significant difference between the two of them. These two glue samples of different proportions of DSF and PPF as shown in Table 1 were reinforced with wood flour. However, the glue samples with highest bond strength (K and L) were reinforced with calcium carbonate filler. This result shows that calcium carbonate filler is a better 4 Conclusion In this study, the possibility of improving the bond strength of adhesive glue produced from soybean and pigeon pea seeds were studied by treating them with alkaline and incorporating CaCO 3 and wood flour fillers into them. It was observed that soybean glue showed a better strength than pigeon pea glue. However, CaCO 3 filler addition to pigeon pea glue produced increase in bond strength on the wood specimen. The mixture of soybean and pigeon pea glue reinforced with CaCO 3 filler produced the best bond strength. Increase in thermal stability was also observed with this glue sample when compared to the control samples without fillers. Therefore, these results indicated that the mixtures of defatted soy flour and defatted pigeon pea flour reinforced with CaCO 3 filler can serve an alternative for the importation of expensive glue in the market. It can also be concluded that calcium carbonate is a better reinforcing filler than the wood flour. ISBN:

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