what do you mean a composite plate here? Are you using any resin as a matrix?
If you just want to have a mat with natural fibre , you can use the compression molding method to do it. I hope you can have something like that in house. Put some fibre in the mold and try to contribute them evenly in the mold. Then you can apply a medium pressure for few mins. The pressure depends on your fibre, but you can test and adjust later.
If you want to make a composite plate, you need to know which kind of resin you are going to use. Then the fabrication method will depend on what you have chosen.
For a thermoset resin such as epoxy, you can easily fabricate composite plates using hand lay-up or Vacuum Assisted Resin Transfer Molding (VARTM). For the hand lay-up, you just need to fabricate your mold be it is rectangular or square, then you have to determine the volume fraction of the fiber because it affects the mechanical properties. For short fiber composites, an optimum fiber length has to be adhered to, since the fiber length affects the mechanical behavior whereas for uni-directional composites (long fibers), it's advisable that the fibers are in tension as possible for you to fabricate a sound laminate. If you are using VARTM, you will need a mold, vacuum bagging accessories and a vacuum pump. The VARTM will produce quality laminates compared to hand lay-up whereby you have to deal with microvoids arising from air bubbles trapped in your structure. Don't forget to treat the fibers so as to enhance the fiber-epoxy bonding. Until then good luck in the natural fiber composite world.
I used to use kenaf fibre, sometimes it's called "hemp fibre", with poly(phenol formaldehyde) in the past. I used compression molding method to fabricate the composite panel for mobile house. The fibre I used was treated to increase its mechanical properties and the bonding to the matrix
I would also have to recommend using a Vacuum Infusion method, as I have seen in previous work that compression molding techniques result in high void content and somewhat inconsistent properties. The infusion process must be tailored specifically for your chosen fibers and matrix, you can refer to my groups paper on adapting the process for jute fibers with epoxy matrix.
And to reiterate other responders, proper compatibilizing of the fibers to the matrix via chemical treatment is crucial to making sound and reliable materials, and there is much literature available on many different types of treatments specific to different fiber types, most notably alkali treatment and silane coupling, among many many others.
Thanks for your information, could you please send me your groups paper on adapting the process for jute fibers with epoxy matrix. ([email protected]) I will thankful you help.