Utilization of Agricultural Wastes in the Manufacture of Composite Boards

Growing concern for waste minimization led the construction industry to consider the use of agricultural waste in the production of building materials. The Philippines, being an agricultural country produces considerable amount of agricultural waste. As of 1999, generation of 40 million metric tons of agricultural wastes was documented by the Department of Energy (Baconguis 2008). This includes wastes from sugarcane, coconut, corn, rice and logs. If such waste is not be utilized, it will cover a large area of landfill. Thus, the idea of using agricultural wastes as a renewable resource became an optimistic option to minimize this waste. Different types of agricultural waste are viable for a wide variety of products including paper, textiles, other fibrebased materials and wood-based panels such as fibreboards and particleboards (Magundayao et al. 2006; Macatangay 2010).

Strength properties as well as other characteristics suited for their intended uses or application for various construction materials are prescribed by the Philippine National Standard (PNS). These are approved by the Bureau of Product Standards. PNS requirements for particle boards are shown in Table 1.
I n B a t a n g a s S t a t e U n i v e r s i t y, t h e Department of Civil Engineering conducted independent studies on the utilization of agricultural wastes available in the province. These studies focused on the use of corn husks, peanut shells and banana sheath as main components of composite boards.

Corn Husk
As of 2008, approximately 2,490,000 hectares of land in the Philippines were utilized for corn production area (Philippines Agriculture 2003. Farmers typically leave husks and stalks behind in the fields as waste materials. According to Ohio State University, approximately 50 percent of the weight of the total corn plant is residue, consisting of stalk, leaf, cob and husk. In fact, 10% of dry matter residue came from corn husk (Myers 2009).
Corn husk is 80%-87% cellulose material. Its tensile properties show that corn fibre has the unique advantage of moderate strength but with higher toughness, low modulus and higher elongation (Reddya & Yang 2005) which makes it comparable to existing fibres used for the production of fibreboard.

Peanuts Shell
Peanuts are very popular in the Philippines but not much attention is given to this crop for research and development. Almost 35,000 metric tons are harvested each year (Palomar 1998). The shells, which are biodegradable and absorbent, can be utilized as animal food filler, absorbents, or carriers for pesticides or fertilizers, although they are often simply landfilled (Bieak & George 2003;"Hulls" AgTech 2002).

Banana Sheath
As of 2004, 5.9 million farm households were depending on banana as their source of income. Banana is still the leading fruit crop in terms of area, volume and value of production. The national average yield is 9.4 tons per hectare while corporate plantations produce 40 tons per hectare. It is a widely grown fruit in the country, planted as a component of farming system or as a main crop in large plantations in Mindanao. It is an important source of income for small farmers who constitute 80% of the banana growers (Rivera 2004).
Banana has different plant parts that could be good sources of various industrial products, aside from its fruit, its main product. The plant's psuedostem or trunk contains fibre that can be manufactured into rope, sack and mat. Pablo (1975) cited in his study that banana stalk is a potential source of material for the production of boards.

OBJECTIVES
This study aims to present the characteristics of composite boards produced using agricultural waste. Specifically, the study aims to:

MATERIALS AND METHODS
Each of the materials was collected from the locality: corn husks were gathered from Alitagtag, Batangas; peanut shells from peanut butter manufacturing industry in Batangas City; banana stalks were harvested from a small scale banana plantation in Batangas. These materials were sorted cleaned and dried.
Different binding agents were used in the composite boards. Corn husk fibreboard used waste plastics as binding agent while for the peanut shell particle board and banana sheath fibreboard, urea formaldehyde (UF) was used.
Banana fibres were extracted from the trunks which were soaked in water for a week, by pounding using a wooden mallet. The fibres were air dried for one full day. A set of comblike row of pins were used to separate the fibres. For five minutes the fibres were oven dried at 100°C then cut into 5 cm long pieces before mixing with UF and shaped into 300 mm by 300 mm mat. For each mat 1000 gm of fibres were used with 500 gm of powder UF mixed with 250 gm of water.
Peanut shells were sun dried until they became brittle and crushed using an electric food processor. Mats were formed from a mixture of 720 grams of crushed peanut shells and 133 grams of UF with 12% resin content.
Corn husks were sun dried for three days at approximately 30°C -35°C temperature and then cut into about 5 mm wide and 40 mm long pieces and mixed with dry plastic strips of the same size. A 40% -60% proportion by weight was considered in forming the 30 cm × 30 cm × 1.2 cm boards.
The moulded mats were separately placed in the Type VH2-749 Kitagawa hot press machine for about 20 minutes at a temperature of 150°C to achieve a thickness of 12 mm. Before testing, the boards were set aside for approximately three days then cut into 5 cm × 5 cm specimen sizes. A 5-ton Shimadzu Type RH10 Universal Testing Machine was used to test the modulus of rupture, internal bond strength and nail head pull through of the specimens.      Baños, Laguna, Philippines for the production of composite boards. This is also where the production and test procedures were done for the three boards.
Each board utilized different proportions of binding agents. Table 2 shows the proportioning of materials and the binding agent used.

Property Testing and Analysis
To determine the different characteristics of the specimens produced, the following tests and analyses were conducted. Test procedures were patterned from the Philippine National Standards for Composite Boards (PNS 26). Tests performed are shown below.
Physical properties. The process determines the length, width, thickness, mass and density of the boards. The physical properties were determined using a caliper and an analytical balance.
Modulus of rupture (MOR). The MOR test was performed in order to determine the strength against bending using the Universal Testing Machine (UTM). The specimen's dimensions were taken and then, force was applied using the UTM. The reading from the UTM determined the load capacity of the board.
The MOR, or bending strength, was then obtained using the formula: where, P = Ultimate load (kg); S = Length or span (cm); W = Width (cm); T = Thickness (cm).

Internal bond strength (IB).
Internal Bond is a mechanical property of materials referring to the tensile strength perpendicular to the plane of the board. IB measured the quality of the particle-to-particle bonding.
The IB Test was computed using the formula: Face screw head test (FSHT) / Nail head pull through (NPHT). The FSHT or NHPT determines the capacity of the board to hold a screw. This test was done by fastening two screws from the surface on both sides until it reached the bottom of the board and then subjected to a pulling force from the UTM. The screws were drawn vertically from the sample. The UTM showed the force required to do that. The purpose of using the screw was for its mechanical ability, the ability to pass through a surface just by turning it, making it much better to use than a nail.
Thickness swelling (TS) and water absorption (WA). TS and WA measure the amount of water absorbed by the boards after 24 hours of soaking. The weight and thickness of each specimen were measured before submerging them in water. After soaking, the specimens were then measured again to determine the amount of water absorbed.
TS was determined using the formula: where, T f = Final thickness; T i = Initial thickness.
WA was determined using the formula: For the comparison of the parameters MOR, IB, FSHT/NPHT, thickness swelling and water absorption; the statistical tool used was one tailed t-test, considering average value equivalence or non-equivalence to standard value, upper and lower bound tailed t-test were considered depending on the value of the PNS.

RESULTS AND DISCUSSION
The observed physical properties of the three different boards did not vary significantly. Both the banana sheath and corn husks boards had smooth surfaces while the peanut shell board was slightly rough; all boards reveal the colour of the materials used and were compact with plane surfaces.
For the banana sheath and peanut shell boards, the colour of the raw materials were evident since the binding agent used was colourless. The differing colours of the plastic strips in the cornhusk board dominate although the husk strips are also observed. The mechanical properties of the boards are shown in Table 3 indicating the values obtained from the tests as compared with the PNS specifications for Type 100 particle board and the statistical comparison in graphical form can be seen in Figures.

Banana Sheath Fibreboard
For the average density of 0.6451 g/cc, a 0 p-value for the upper bound tailed t-test was obtained indicating the probability of achieving a value greater than 0.4 g/cc and a p-value of 1.000 for the upper bound tailed t-test was obtained indicating a value not greater than 0.8 g/cc. The statistical results for the density indicated conformance to the PNS in terms of density. The banana sheath board after being soaked in water for 24 hours, obtained an average of 44.66% water absorption which was greater than the maximum amount set by the PNS as depicted on the p-value of 0.016 for the upper bound tailed t-test, an indication of non-conformance to PNS. A consistent average value of 14.29% thickness swelling was obtained, which was below 20%, the maximum set by the PNS for Type 100. In terms of strength, the board resisted an average 55.33 kg of load in the NHPT having a p-value of 0.022 for the upper bound tailed t-test indicating a non-probable equivalence to 30 kg and greater than 30 kg, and a p-value of 0.216 for upper bound tailed t-test indicating probable non-equivalence to 50 kg and not greater than 50 kg. In general, the NHPT for the banana sheath fibreboard conformed to the PNS. The MOR obtained an average value of 213.6 kg/cm 2 , which conformed to the PNS (minimum of 80 kg/cm 2 ) as reflected by 0.019 of p-value for upper bound tailed t-test. However, in the IB test, the banana sheath fibreboard obtained 1.0367 kg/cm 2 less than to the standard minimum value of 2 kg/cm 2 . Based on the statistical results, a probable non-equivalence to 2 kg/cm 2 or not greater than the said value was concluded as depicted by the p-value of 0.996 upper bound tailed t-test indicated a non-conformance to PNS. with the upper limit standard. The IB statistical evaluation obtained a p-value of 0.305 to check for equivalence of the average value to that of the minimum value of the standard. This indicated a probable equivalence to 2 kg/ cm 2 . The MOR indicates a p-value of 0.004 for the lower bound tailed t-test indicated a probability of lesser value with the standard or non conformance to PNS for type 100 boards.

Corn Husks Fibreboard
The corn husks board samples tested had an average density of 0.6867 g/cc with a p-value of 0 for the upper bound tailed t-test for the comparison with the lower limit standard and a p-value of 0 for the lower bound tailed t-test for the comparison with the upper limit standard. The density of the corn husks board conformed to the PNS. As for the WA, an average value     of the average value with that of the minimum standard, and 0.129 for MOR for the one tailed t-test for the evaluation of the equivalence of the average value with that of the minimum standard.
The banana sheath board was very strong against rupture followed by the cornhusk board while the peanut board passed the standard value for the test with only a slight margin. However, with respect to internal bond, the peanut shell board is stronger than the other two. The banana sheath and peanut shell boards had almost the same resistance against nail head and face screw pull through. The corn husks board, when soaked in water did not swell as much as the other two boards, its water absorption falling within the range for Type 100. Only the corn husk-plastic composite boards conformed to standards for all parameters. The peanut shellresin composite boards conformed in density, thickness swelling, IB, and NHPT/FSHT; while, the banana sheath-UF composite boards conformed in thickness swelling, density, MOR and NHPT/FSHT.