Pistachio Shell Powder as an Additive in Molded Pulp Products

Abstract

Molded pulp products (MPP) products can accommodate a variety of fiber types and additives, including agricultural residues. This work showed the industrial scale production of molded pulp food trays made of double lined kraft clipping fibers with the addition of pistachio shell (PS) powder at levels from 5 to 30 wt% and evaluated the mechanical and barrier properties of the trays. The PS powder used to make the trays was ground using an impact mill and a cryo mill to a D50 of approximately 50 microns. Tray compression strength was tested to simulate the wrapping of food trays with plastic wrap. Additionally, the tray material’s basis weight, thickness, density, tensile strength, short span compressive strength, and absorptiveness were determined. The results showed that compared to the control tray sample, the trays containing the cryo-milled pistachio powder had essentially the same engineering properties as the control trays without PS. For the trays made with the impact-milled powder, the tensile strength, bending resistance, and compressive strength increased relative to the control 11.3%, 6.2%, and 13.5%, respectively.  The study demonstrates a method to evaluate the incorporation of alternative materials into pulp molded products.