The Effect Of Grain Size To Physico Mechanic Properties Of Particle Board Based On Rice Husk and Liquid Rubber Compound

Particle board research produced from a number of grain size of Rice Husk and liquid rubber compound has been carried out. First particle board was produced by mixing rice husk with a number of grain size were 10-25 mesh; 25-50 mesh; 50-75 mesh and <75 mesh with liquid rubber compound as much as 45% to form a particle board with size of 5 x 10 x 7.5 cm in length, width and height and then dried. Then the particle board is pressed to get a thickness of 2.5 cm and then carried out the characterization of the MOR, MOE, screw pull resistance, water content and density. The results showed that the best rice husk particle size was obtained at 25-50 mesh grain size. At this grain size, the value of MOR, MOE, screw pull resistance, water content, and density of particle board were 9054,8 g/mm2; 15090 g/mm2; 69 g/mm2; 4,1% and 0,83 gr/cm3 respectively. The results of this study still do not meet the standards according to SNI 03-2105-2006


1.Introduction
Particle board can be made from a variety of wood waste materials that contain lignocellulosic compounds [1][2][3][4].Particle board has many advantages compared to ordinary wood boards due to the size, shape and quality can be adjusted as needed, besides that the materials used can come from a variety of materials which are usually considered waste materials [5][6][7][8].
Rice husk which is a waste material from the rice harvesting process is one of the materials that contains high lignocellulosic compounds so that it has the potential to be used as a base material for making particle board [9][10][11][12][13].Rice husk is very easy to obtain in a number of regions in Indonesia and is a waste material that is usually not used anymore.In this study a liquid rubber compound made from concentrated latex with a number of compound chemicals was used as an adhesive to bond lignocellulosic materials in the manufacture of particle board [14,15].Indonesia is one of the world's main natural rubber producers, so that natural rubber latex, which is the basic material for making liquid rubber compound, is very easy to obtain in a number of regions in Indonesia, so there is no need to worry about the sustainability of the process of making particle board from rice husk with liquid rubber compound adhesive.
So far, research on the use of liquid natural rubber as an adhesive for making particle boards made from rice husks has not been widely carried out, so research on making particle boards made from rice husks and liquid natural rubber adhesives is very interesting to do.
The aim of this research was to study how to make particle board from rice husk using liquid rubber compound adhesive and to study the effect of rice husk grain size on the physico-mechanical properties of particle board to obtain the best grain size that can produce quality particle board.Tests to determine changes in physico-mechanical properties carried out included tests for screw pullout resistance, MOE, MOR, density and water content.

2.Experimental
The research was started by preparing rice husk powder with sizes of 10-25 mesh, 25-50 mesh, 50-75 mesh, and <75 mesh as the main raw material.Then a liquid rubber compound was also prepared by mixing concentrated latex with a number of compound chemicals which included activating agents, process accelerating agents, stabilizers, vulcanizing agents, antioxidants and fillers [15].Then test pieces of particle board with length, width and thickness of 10x5x7.5 cm were made by mixing 69.6 g of rice husk with grain sizes of 10-25 mesh, 25-50 mesh, 50-75 mesh, and <75 mesh with 45 % liquid rubber compound then dried.The next step was pressing to get a thickness of 2.5 cm which is the thickness of particleboard that is widely circulated in the market and then tested the physic-mechanical properties of particle board that has been produce which includes testing MOR, MOE, screw pullout resistance, water content and density according to SNI 03-2105-2006.

MOR test result
The MOR test results for particle board made with a number of rice husk grain sizes are as can be seen in Figure 1.From Figure 1 it appears that the MOR value of particle board made tend greater on finer grain size of rice husk, reaches maximum at grain size of 25-50 mesh and then decreases at finer grain size.This is due to the finer grain size of rice husk, the greater contact surface area so that the interactions that occur between lignocellulose from rice husk and polyioprene from liquid rubber compounds will be more intensive as a result the chemical bonds that occurs will also increase and the resulting particleboard will also be stronger.At a grain size of 25-50 mesh this interaction reaches a maximum so that the resulting particle board has the greatest strength, while at a finer size of 50 mesh the lignocellulose molecules from rice husk that interacting with polyisoprene from liquid rubber compounds are too much than necessary, as a result there is a decrease in the stiffness of particle board made.The MOR value of the optimum rice husk grain size of the particle board made is equal to 9054.8 g / mm 2 .

MOE test result
The MOE test results of particle board on a number of rice husk grain sizes are as can be seen in Figure 2. From Figure 2 it appears that the MOE value of particle board is tend greater when using rice husk with finer grain size, reaching a maximum value at a grain size of 25-50 mesh and then decreasing again at a finer grain size.This is due to the finer grain size of rice husk, the larger contact surface area of the lignocellulose so that the interactions that occur between lignocellulose of rice husk with polyioprene of liquid rubber compounds will be more intensive as a result, there are also more chemical bonds that occur and so the particle board is more flexible.At a grain size of 25-50 mesh this interaction reaches a maximum as a result the resulting particle board has the greatest flexibility, while at a grain size finer than 25-50 mesh the lignocellulose molecules from rice husks interact with polyisoprene molecules from liquid rubber compounds too much than necessary so that Instead, there is a weakening of the bond that occurs and as a result there is a decrease in the flexibility of the particle board made.The MOE value of the optimum rice husk grain size of the particle board made is equal to 15090 g / mm 2 .

Screw Pullout Resistance Test Results
The pullout resistance of particle board screws test result on a number of rice husk grain sizes are as can be seen in Figure 3.
From Figure 3 it appears that the finer grain size of rice husk, the stronger the particle board made to hold the screw, reaching a maximum value at a grain size of 25-50 mesh and then decreasing at a finer grain size.From the Figure 3 shows that screw pullout resistance of particle board was increased on the decline of grain size of rice husk and reaching the maximum value on the use of grain size of 25-50 mesh then decrease at finer grain size.This is due to the finer the grain size of rice husk, the greater contact surface area of lignocellulose molecules so that the number of chemical bonds formed between lignocellulose of rice husk with polyisoprene of liquid rubber compound also increases and consequently the resulting particle board is also stronger for holding screw.At a grain size of 25-50 mesh, this interaction reaches a maximum so that the resulting particleboard is denser and has the greatest strength to hold the screw, while at a grain size finer than 25-50 mesh, lignocellulose molecules from rice husks interact with polyisoprene molecules from liquid rubber compounds too

MOE (g/mm2)
Grain size (mesh) much than necessary so that a weakening of the bond occurs and as a result a decrease in the strength of the resulting particle board to hold the screw.On the optimum grain size of rice husk, the strength of particle board to hold the screws is 44360 g / mm 2 .

Water Content
The results of water content test at a number of grain size of rice husk was can be seen in Figure 4. From the curve in Figure 4 it appears that initially, the water content of particle board increases at finer grain sizes of rice husk, reaches a maximum at 25-50 mesh grain sizes and then decreases again at finer grain size.This is due to the finer the grain size of the rice husk, the greater the contact surface area of the lignocellulose molecules so that the chemical bonds that occur between lignocellulose molecules of rice husk with polyisoprene of liquid rubber compound become more numerous and tighter and consequently less water molecules can fill spaces between molecules from the particle board made.On the rice husk grain size of 25-50 mesh, the water content of particle board made is 4.1%.

Density
The particle board density test result at a number of rice husk grain sizes are as can be seen in Figure 5. From the curve in Figure 5 it appears that the finer the grain size of rice husk, the higher the density of particle board made.This is due to the finer the grain size of rice husk, the larger the surface area of particle, so that the lignocellulose molecules from rice husk that can interact with the polyisoprene molecules of liquid rubber compounds are also increase so that the chemical bonds that occur are also getting closer and as a result, the value of particle board density made is also getting bigger.At a grain size of 25-50 mesh, the value of particle board density made is 0.83 g/cm 3

Conclusion
The grain size of rice husk greatly affects the physic-mechanical properties of particle board.The best rice husk grain size to produce particle board with the best physico-mechanical properties is 25-50 mesh.At the best grain size of rice husk, the value of MOR, MOE, screw pull-out resistance, water content and density of particle board made were 9054.8g/mm 2 ; 15090 g/mm 2 ; 69 g/mm 2 ; 4.1% and 0.83 gr/cm 3 respectively.The results of this study still do not meet the standards according to SNI 03-2105-2006.However, particle board made from rice husk and liquid rubber compound can be used to meet the needs of boards that do not require high strength and flexibility because they have other advantages, namely being more resistant to water and termites.