The overall goal of this procedure is to create robust and rigid natural fiber preforms using bacterial cellulose as a binder and to produce renewable hierarchical composites using a conventional composite making process. This is accomplished by first creating a suspension of bacterial cellulose in water. The second step is to disperse the loose short natural fibers into the bacterial cellulose suspension.
Next, the resulting natural fiber bacterial cellulose suspension is filtered to remove the excess water. The final step is to consolidate and dry the filter cake to form a robust and rigid fiber preform. Ultimately, this fiber preform can subsequently be infused with a liquid resin to create high performance bacterial cellulose reinforced natural fiber reinforced renewable composites.
Demonstrating this procedure will be mata, Kang, and C.Prior to starting this procedure, measure the amount of wet bacterial cellulose peles equivalent to 18 grams of dry bacterial cellulose from a predetermined wet to dry mass of bacterial cellulose. Following this, cut the wet bacterial cellulose peles into small pieces of approximately one to two centimeters using a pair of sharp scissors. After cutting, soak the bacterial cellulose peles in one liter of water to hydrate them.
Feed the cut bacterial cellulose peles into a blender and add 300 to 500 milliliters of water so that the blending process goes smoothly. Then blend the les for two minutes. When finished, pour the blended bacterial cellulose into a 15 liter container and add water until the total water volume is 14 liters, giving a bacterial cellulose concentration in water of 0.1 weight per volume percent.
Next, cut 72 grams of loose size fibers into one to two centimeter long fibers and add them into the bacterial cellulose suspension. Gently stir the suspension with a spatula to ensure a homogenous dispersion of sisal fibers in the bacterial cellulose suspension. At this point, fill the sheet former with deionized water until the water level reaches the backing wire.
Place a 50 mesh metal forming wire on the backing wire centered within the sheet mold base close and latch the sheet mold. Then add additional fresh water until the forming wire is submerged in water. Pour the prepared sisal fiber bacterial cellulose suspension into the sheet mold.
Gently stir the suspension with the spatula to ensure that the size of fibers are homogenously distributed throughout the mold. Following this, open the drain valve to drain the water, which will result in the formation of a wet filter cake of sisal fibers and bacterial cellulose on the forming wire. Immediately after the water drains, open the sheet mold and remove the forming wire.
Place the forming wire on a piece of blotting paper. Then place three additional blotting papers on the top of the filter cake, followed by a metal plate. Next, flip the filter cake around with the forming wire.
Now facing the top, remove it and place three additional blotting papers directly on top of the filter cake, followed by a metal plate. Place a 10 kilogram weight on top of the metal plate to press the water out. When the blotting papers are fully soaked, replace them with fresh blotting papers and press the filter cake again using a weight of 10 kilograms.
Once the blotting papers have been replaced one final time, perform a final pressing of one ton in a hot press to consolidate the fiber preform. Heat the hot press up to 120 degrees Celsius to aid the evaporation of residual water. After four hours, reduce the temperature of the hot press to room temperature and remove the preform once it is cooled.
Place pressure sensitive tape around the periphery of the internal and external setup. Following this place, the preform on top of the tooling side, which consists of a non-porous polytetrafluoroethylene or PTFE coated glass release fabric. Cover the preform with a porous PTFE coated glass release fabric, also known as a peel ply, followed by a porous flow medium.
Position the omega tubes at the intended resin inlet and outlet of the vacuum assisted resin infusion or vari setup. Ensure that the omega tubes are placed on top of the porous flow medium to allow for the resin to distribute into the vari setup During infusion, insert the resin feed and outlet tubes into the openings of the omega tubes. Then cover the setup with the fluoro ethylene polymer based bagging Film and seal it using pressure sensitive tape.
Place a metal plate on top of the inner bag where the fiber preform is followed by a piece of breather cloth. Once the resin feed tube has been sealed, position the other end of the resin outlet tube on top of the breather cloth. After identifying the position where the through bag vacuum valve should be, place the bottom piece of the valve on top of the breather cloth.
Place a vacuum bagging film on top of the internal bag and seal it. Then place the plate on the sealant tape to complete the seal. Cut a small X on the vacuum bagging film where the bottom piece of the valve is and screw in the top piece to complete the through bag.
Vacuum valve. Connect the quick connect fitting and apply a vacuum. Then check for vacuum leaks.
Next, prepare the resin by mixing the epoxy and hardener at a weight ratio of 100 to 19. Degas the resin at a reduced pressure to remove all the air bubbles traps during the mixing of the epoxy resin and hardener. Once the very setup is determined to be leakage free, feed the resin via the tubing connected to the omega tube, ensure that the resin is fed slowly, such that it has time to impregnate into the fiber preform.
Allow for the resin to flow out from the resin outlet tube and soak into the breather cloth until no air bubbles can be observed coming out from the outlet tube. Finally, seal the outlet tube and allow the resin to cure for 24 hours at room temperature, followed by a post curing step at 50 degrees Celsius for 16 hours without a bacterial cellulose binder. The short loose sisal fibers are held together only by friction and entanglements between the fibers.
As a result, this preform is loose and not able to support much weight. Shown here is the sisal fiber preform without bacterial cellulose. As the binder with a load applied in three point bending mode, the preform can be seen to be rather loose, and when a load is applied by adding 40 grams of water into the polypropylene cup, the preform starts to deflect severely.
However, when 28%of bacterial cellulose was used as the binder for these short and loose sisal fibers, a rigid fiber preform was manufactured. This preform can withstand the load of a full polypropylene cup weighing 170 grams without any significant deflection. Scanning electron micrographs of a typical bacterial cellulose sisal fiber preform are shown here.
Bacterial cellulose can be seen to be covering the surface of the sisal fibers. This effect is due to the hydrophilic nature of sisal fibers. The hydrophilic nature of sisal fibers absorbs water drawing in the bacterial cellulose that is dispersed in the medium.
Since bacterial cellulose is larger than the pores of natural fibers, they were not able to penetrate into the fibers. Instead, they were filtered against the surface of sisal fibers and to form a layer of bacterial cellulose coating when the fibers were dried. The mechanical performance of these fiber preforms under tension is tabulated here due to the porous nature of the fiber preforms with a porosity of approximately 70%The tensile strength of the preform is not well-defined.
Therefore, the tensile force and the tensile index of the specimen are tabulated. A tensile force and tensile index of 12.1 kilo newton's per meter and 15 Newton's meter per gram was measured respectively when 20 weight percent of bacterial cellulose was used as the binder. However, the tensile properties of neat sisal fiber preforms were not measurable as the fiber preform is loose.
Our technique paved the way for material scientists and engineers to explore the use of nano cell laws in the development of hierarchical high performance renewable composites.
