The present invention is directed to plant fiber-reinforced biocomposite thermoplastic and/or resin compositions and a method for reinforcing thermoplastic resins. The present invention provides a use for the cellulose portion of a plant material, which is the portion left over after processing the selected plant materials to separate the cellulose in a mechanical process that does not damage the internal molecular structure of the cellulose fraction, enabling the cellulose fraction to chemically bond with the thermoplastic resin to enhance the reinforcement of the resin or thermoplastic biocomposite composition.