Sustainable plastics from agricultural coproducts: Seven things to know

Researchers with the United States Department of Agriculture’s Agricultural Research Service (ARS) Western Regional Research Center (Albany, CA) provide an update to their projects centering on optimizing bioproducts that PlasticsToday most recently reported on in September 2018, California’s going nuts over plastic recycling.

1. What are the exciting new developments with plastics and composites research?

USDA ARS: Several exciting developments on composite research are worth highlighting. One of the goals of the USDA ARS project is to scale-up torrefaction of California-derived biomass, such as almond or walnut shells, which are made into a charcoal-like material to displace carbon black. Commercial utilization of our torrefaction technology (torrefaction is defined in Question 3 below) involves preparing composites for various areas of industry; e.g., automotive parts, shipping containers, pallets, and building materials.

Previously, our studies provided insights into the impact of biomass feedstock characteristics and the level of torrefaction on the overall properties of the composites. The torrefaction concepts that came from this study were based on lab-scale results, which we documented in several scientific journal articles. USDA ARS 2019 Update PQ1Recently, we began a collaboration with Mega Machinery Inc. (Knoxville, TN) and FDS Manufacturing Co. (Pomona, CA) to scale-up from kilograms to kilotons. Our torrefaction/pelleting method is based on a patent-pending process developed at the USDA ARS Western Regional Research Center in Albany, CA. To fund this novel technology, the research team at the USDA helped write a grant with FDS Manufacturing Co. through the Department of Resources Recycling and Recovery (CalRecycle). In May 2019, CalRecycle awarded FDS Manufacturing Co. with $2.9M to help develop the team’s idea.

Another exciting collaboration revolved around using the resins created in the torrefaction/pelleting process to make plastic composites into extruded or molded industrial prototypes. The collaboration resulted in protocols for producing the prototypes.  Two prototypes in particular are being explored for their commercial viability: injection-molded shipping pallets and extruded slip sheets. Injection-molded pallets were prepared in partnership with plastic pallet provider TranPak (Fresno, CA).  The TranPak team utilized various torrefied biomass feedstocks at low concentrations as plastic fillers with post-consumer recycled polypropylene/polyethylene blends. 

Another collaborator, Repsco (Modesto, CA), blended torrefied biomass with recycled plastic to improve mechanical and thermal properties of slip sheets, laminated thin sheets of plastic that are placed under and between shipping pallets to prevent containers from slipping during shipping, as well as to protect the products.  Both projects demonstrated the use of torrefied biomass as a replacement for carbon black in these significant industrial products. Moreover, the project also showed-off the Federal Technology Transfer process whereby bench-top trial-and-error science moves from the laboratory into the commercial realm.

USDA ARS pallet molding at Tranpak
Injection molding of a polypropylene pallet containing 4% torrefied biomass at TranPak (Fresno, CA).

2. What was the focus of the CalRecycle grant?

USDA ARS: CalRecycle offered a grant through the Recycled Fiber, Plastic, and Glass Grant Program, a statewide initiative that was aimed at the reduction of greenhouse gas emissions. The program created financial incentives for industries, particularly located in disadvantaged communities, to invest in technologies to reduce pollution.

In March 2019, Kevin Stevenson, co-owner of FDS Manufacturing applied for a grant along with Mega Machinery through the CalRecycle program. In May 2019, FDS Manufacturing was awarded $2.9M to develop a process for diverting post-consumer, recycled polypropylene and polyethylene to create compounded masterbatch resin pellets. USDA ARS 2019 Update PQ2These resulting pellets will then be used by FDS Manufacturing and other industrial partners to produce commercial products such as pallets, agricultural storage bins, angle boards, and other multi-use products. A projected 4,005 tons of plastic is estimated to be diverted from landfills in this initial pilot study.

By adding torrefied walnut and almond shells, especially to recycled plastics (and less so to virgin plastics), we can increase the tensile and flexural modulus (i.e. stiffness) as well as the heat deformation temperature of the resulting plastics.  For applications like a pallet where a stiff plastic is desirable, using torrefied shells in recycled polypropylene allows the manufacturer to reduce costs because torrefied biomass is cheaper than recycled plastic. We also reduce plastic usage.  Plus, walnut and almond shells are a renewable bio-based filler.

3. What is torrefaction?

USDA ARS: Torrefaction is a thermal process, used most famously to “roast” coffee beans, in which biomass is heated between 200-300 °C in a low oxygen environment.  Three distinct final products are obtained: (1) a permanent gas, composed mostly of CO2 and CO; (2) a condensable liquid, high in water content, but often acidic; and (3) a carbonized solid. The solid has a higher hydrophobicity than the non-torrefied biomass, which means it overcomes issues with water uptake when using most agricultural fibers. Increasing the hydrophobicity of biomass filler through torrefaction improves the overall properties of the composites by improving adhesion of filler to plastic. Thus, torrefied biomass can be considered an attractive, eco-friendly, renewable and low-cost reinforcement filler for recycled, or “waste,” plastics.

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