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Nutty research: Almond shells sustainably strengthen plastics

Almond parts diagram
USDA researchers find adding processed almond shells to plastic masterbatches to create containers for packaging proves to be a fruitful idea that improves performance.

The Institute of Food Technologists show held in Chicago mid-July centers on food ingredients and processing flavored with a little packaging. Intriguingly, a Tech Theater presentation sponsored by the Almond Board of California (Modesto, CA) disclosed research and development in using almond shells as an ingredient in plastics for applications including packaging.

Nutty idea? Literally it is, but figuratively it’s not—the shells enhance the plastics’ strength beyond most traditional materials. The shells are being tested as a partial plastic replacement in plastic trays and pallets and other containers and products.

The highly “edutaining” presenter was Bill Orts, research leader, Bioproducts, Western Regional Research Center (Albany, CA) of the United States Department of Agriculture, who responds to PlasticsToday’s questions. Orts credits much of the answers to Zach McCaffrey, almond project research leader, and Lennard Torres, who he describes as “our polymer go-to-guy.”

Let’s start with an overview of your group.

Orts: The team has been working on sustainable agricultural-derived plastics for at least 20 years with a scope well beyond fillers.  We’ve quietly worked with companies like EarthShell, Cargill-Dow (Ingeo), Clorox-Glad, Metabolix, etc., to create sustainable packaging solutions. 

We’ve also been actively involved in creating standards for the industry. My colleague, Greg Glenn, and I have been on multiple standard committees to help establish, for example, ASTM D6400, ASTM D6868 and the USDA Biopreferred Program. Both Greg and I have been active officers in Bioenvironmental Engineering Polymer Society and the Biodegradable Products Institute (New York City)  

We help companies in this area on a regular basis, and those include these Strategic commercial partners that are presently located within the Research Unit (pilot plant) among others: Method Products (San Francisco), provides us with several researchers to develop sustainable packaging solutions for detergents and other products; tire company Bridgestone Americas Inc. (Nashville, TN) collaboration that provided a big grant to make domestic rubber and another big grant from Cooper Tire & Rubber (Findlay, OH) to make greener tires.

In a nutshell, what’s this research all about as it relates to plastics?

Orts: California produces more than 80% of the world's almonds. That leads to the problem that almond growers and shellers must find an outlet for more than one billion pounds of shells every year. Using shells as fillers in polymer composites have multiple advantages over commercial additives, e.g., cost, energy consumption, renewability, biodegradability, landfilling; however, almond shells are hydrophilic, which limits their incorporation into most polymer matrices. Our research is investigating using almond shells as a filler in polymer composites and results have shown we can make stiffer, stronger and more heat-resistant composites compared to the unfilled polymer. We're starting to work with industrial companies to optimize materials to meet their specifications and work towards scaling up.

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The process involves torrefication—what exactly is that?

Orts: Torrefaction is a thermal process where biomass is heated to 200-300 ⁰C in the absence of air and oxygen.  Compared to raw biomass, torrefied biomass is more hydrophobic, making it more chemically compatible with polymer matrix, and more grindable, reducing the energy required to mill to a small particle size.

Torrefied shells are used as filler and strengthener…what materials do the shells replace?

Orts: Common industrial fillers include calcium carbonate, talc and carbon black.

Next: HDT data, levels, performance and applications

What can you tell us about that research that mixes torrefied almond shells with polypropylene?

Orts: We have published a few papers on torrefied almond shell (TAS) polypropylene (PP) composites.

Briefly, TAS-PP increased the heat deflection temperature (temperature where composite softens), and tensile modulus (stiffness), but had lower tensile strength and elongation compared to neat polypropylene. We are currently working with PE with good results, and are optimistic about others.  We haven't worked enough with PET yet.

At what levels are the shells added?

Orts: Currently we're making masterbatch pellets of 30% TAS/70% PP for trials with plastic manufacturers.  Plastic manufacturers can dilute to meet their desirable processing and material properties with maximum 30% filler. Our industrial partners currently don't use fillers.  So, improved properties (and cost) are compared with unblended (neat) polymer.

What are the performance, sustainability and other benefits of this material?

Orts: The benefits of using almond shell as a filler is it reduces amount of petroleum-based plastic, reduces landfill of almond shells, makes better utilization of almond byproducts, etc.  The major disadvantage is that recyclers (such as CalRecycle) will not recycle the composite material.  Recycling facilities can only tolerate a small non-plastic component.  Thus processes will need to be setup to accommodate the new materials.  Fortunately the companies we are working with already recycle their own materials by regrinding and incorporating the material into new products.   

What are the general benefits of a higher HDT polymer?

Orts: Example of a flower pot that is sitting in the sun, but works equally well for recycling bins, trash cans, etc. The flower pot made with torrefied almond shell composite will be able to resist wilting at higher temperature. Results have shown TAS filler can increase HDT by 10-20°C or 18-36°F.  

What are the applications or potential uses for these composites, especially in packaging?

Orts: Numerous plastics applications using extrusion of injection molded parts: flower pots, trays, pallets, bins, cases, containers, computer parts, automotive parts and more.

What have been the results to date? And at what scale?

Orts: Currently the team has presented prototype products to plastics manufacturers and is upgrading to larger scale. This includes adding automation, creating shaped products such as pallets, and collaborating with industrial partners to test market opportunities. 

Lab-scale experiments have been performed manually, and results published in academic journals (e.g. McCaffrey, et al., 2018 submitted; Chiou et al., 2016; Chiou et al., 2015).  The current prototype system produces about 5lb per hour of blended composite resin, but industrial partners are now requesting ton quantities. For example, a collaborator anticipates manufacturing prototype plastic shipping pallets at a small production scale in coming months, so we're working on scale-up and finding commercial services to aid manufacturing.

Companies are interested and we're trying to demonstrate that our materials improve their products at lower cost.

Tell us about the related work done by molder F-D-S Manufacturing.

Orts: Sullivan Grosz is part of the Almond Board’s “Leadership Program” helps us find business opportunities. He has a packaging background and has helped find potential leads—early adopters—in the California packaging industry.  We’ve visited of F-D-S Manufacturing (Pomona, CA) to work on scaling up to commercial level, but the work has been slow. 

Essentially, they would have an interest in the torrefied fillers if it works as well on their industrial machines as it does on our pilot-scale extruder.  However, there’s a big difference between 10 tons per hour vs. 1 bucket per hour.

What’s next?

Orts: Finding an industrial partner wanting to invest in composite manufacturing.  We're on the right path and have several interested companies who we're working with to make prototype parts that are looking forward to trying to make parts incrementally at larger scales. 

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