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Hemp Fiber-Reinforced Plastic Research and Development

Early in 2019, the Planet-3 team conducted multiple tests to determine if we could construct and form hemp bioplastic and biodegradable plastic using hemp to strengthen pre-existing polymers and reduce the amount of plastic required. The purpose of the test was:

    1. To determine if hemp fiber could be used as a strengthening agent in fiber-reinforced polymers, or FRP, to replace cotton or glass fiber.
    2. To determine if we could feasibly construct the polymer fiber composite out of 50% hemp fiber in order to reduce the total amount of plastic used.

PROJECT DETAILS

CATEGORY: Product Formulation, Equipment Sourcing

SKILLS: Biochemistry, Research and Development, Materials Science, Sustainable Manufacturing

PROJECT LEAD: Taylor Ange

INTRODUCTION

The potential uses for hemp fiber are immense. With its uses in construction, textiles, and even manufacturing of superconductors, hemp offers revolutionary changes to many traditional materials in both construction and application. The uses of hemp fiber in increasingly more sophisticated capacities are becoming more attractive with hemp’s increasing availability. Hemp bast fiber is one of the strongest natural plant fibers commonly available; it’s tensile strength which is much higher than cotton or even jutte, allows hemp fiber to fill the roles that normal fiber used with polymers just cannot. In 2019, Planet-3 did extensive research in using hemp bio-waste from CBD production to create multiple forms of reinforced bio-plastics.

Planet-3's 3D printed hemp bioplastic grinder
A 3D printed hemp fiber reinforced ABS Grinder made by Planet-3 in 2019 for proof of concept.

Planet-3 worked with Blue Marble Biomaterials to develop two different types of hemp plastics with the hope of a) seeing what the feasibility was of making a hemp-based, biodegradable plastic made from polylactic acid, or PLA, derived from hemp inputs. The second goal was to see if the hemp bast fiber would be a good reinforcing agent and filler to other traditional plastics and polymers such as high-density polycarbonate and PLA. Our objective was to establish if hemp fiber would allow for the reduction of polymer in construction to reduce material and environmental cost and to see how the addition of these fibers could act to strengthen the preexisting polymers. Fiber-reinforced polymers are a common construction material in many specialized parts for the aerospace industry to consumer products.

Although the use of these fiber-reinforced polymers is common, the range of plastics and resins used in their construction differs greatly. The fibers used to strengthen these materials are almost always glass or treated cotton fiber. These fibers add a higher degree of shear strength to the plastics’ inherent qualities. As most higher density plastics are also more brittle, the need to strengthen these compounds with a reinforcing material becomes more necessary. Much like concrete, the hard, brittle plastic is very resistant to compression and tension forces, but when submitted to larger amounts of shear force, more brittle hardened plastics are prone to fail. The addition of fiber gives increased rigidity to the substance, much like rebar with concrete. Due to these reinforcing fibers being made of either cotton or fiberglass, the potential forces that these composite materials can endure is less than that of hemp fiber-reinforced polymers.

DIFFERENCES BETWEEN HEMP FIBER AND HEMP HURD

Hemp, or Cannabis Sativa L., stalks are made up of two distinct regions, the outer fibrous layer consisting of “Bast Fiber” and the inner wood core called “Hurd”. The fiber that makes up the epidermis layer is incredibly strong and durable. The hurd is the xylem, an area in the stem where the majority of the nutrients and water is transported to the rest of the plant. The xylem is the highway of the plant’s system and all vascular plants have this in common.

Diagram of the cross-section of hemp stalk
This is a diagram of a cross-section of a cannabis stalk. The epidermis is the smooth outside of the stalk, the bast fibers were what was used in our study, and the hurd is the xylem or the woody interior. Photo credit: Characterization of Chemically Modified Hemp Hurds. Materials 2014

These two parts of the stalk make up the majority of the usable parts of the non-flowering cannabis plant. The fiber is used for a range of different materials, from textiles to industrial goods. The hurd is currently used for hemp-based paper, hempcrete, and as an alternative to traditional composite wood boards.  

When processing the stalk, it is the fiber and hurd components of the plant’s stem that are separated and treated depending on the specifications of the end product. For our project, we did not use the hurd for any of the plastic production.

PREPARATION OF THE HEMP FIBER

The struggle in our testing was breaking down the waste biomass to the point that the fiber could be efficiently separated from the hemp hurd. For this, we cleaned and separated out all of the longer stalks of hemp, removing all vegetation, stalks, and stems under 5mm. After all of the stalks had been separated from the rest of the biomass, a decorticator (a machine that operates much like a rolling mill with two rollers rotating in the same direction but at different speeds creating torque on the hemp stalk as it passes through) was used to further separate the bast fiber from the woody interior hurd of the hemp. The end fiber consisted of hemp strands that were 2-12 inches. One of the batches was retted in vinegar and water for 72 hours and then sent through the decorticator. The hemp fiber was then separated into three quality groups; the first being undamaged fibers around 6-12 inches fiber, 3-6 inch undamaged fiber, and less than 3-inch or visibly damaged fibers. Only undamaged fibers from the first group were used in testing.

Hemp in super sacks waiting to be processed into separated hemp flower and fiber
Hemp in super sacks waiting to be processed into separated hemp flower and fiber.

RESULTS

In our test, we conducted six different experiments that consisted of two subgroups. Each subgroup used a different plastic and had three different lengths of hemp fiber mixed into the polymers and both ABS and PETG polymers were used for our tests. Our goal was to use at least half of the amount of plastic usually needed and replace that space with hemp bast fiber. Our second goal was to determine how this compared to a normal 3D printed plastic model and if the fiber created additional strength. 

We conducted both strength and heat tests of all of the samples of hemp-reinforced plastic. Our hypothesis was that, up to a point, the hemp fiber would help the plastic with both internal strength and resistance to heat. The fiber would act like rebar in holding the plastic together under shear forces and would also absorb some of the heat from the heat test and deform at a slower rate. We found that printing with more fiber in the resin resulted in a higher likelihood for impurities to form in the hemp-plastic composite. So we concluded that there must be an optimal ratio of plastic to hemp fiber.  

We successfully printed hemp plastic jars, straws, and grinders made from 50% hemp fiber and 50% ABS. We found that when the molds comprised of 20-30% hemp fiber the resulting products were the strongest and most resistant to breaking and cracking. Molds with over 40% fiber were actually the most fragile, and pure ABS and PETG models were strong but not as strong as the ones with only 25% hemp fiber in them. Part of the test was to determine the deflection temperature of hemp fiber-reinforced polymers compared to standard ABS plastic. The deflection temperature is a measure of a polymer’s ability to bear a given load at elevated temperatures. We introduced the 30% hemp fiber-reinforced ABS jars and 100% ABS jars to 400℉, 600℉, and 800℉ with a load of 10 Ibs. The results of how much deformation was experienced and how fast deformation occurred, demonstrated that the 30% hemp fiber-reinforced jars held up significantly better to the 10Ib load than the 100% ABS jars under heat. We found that although hemp can reduce the amount of plastic used in many common polymers and potentially make the plastic stronger, when the amount of hemp exceeded ~40%, the internal integrity of the plastic was compromised.

Hemp plastic jar with Greenhouse Farmacy sticker and a hemp plastic straw
This hemp plastic jar was another proof of concept Planet-3 constructed to prove that hemp plastic could fill roles in packaging for the cannabis industry. We teamed up with Greenhouse Farmacy to test our jars and see how they worked as compared to conventional plastic and glass jars. Greenhouse Farmacy is dedicated to sustainability and was a great partner for this test.

CONCLUSION

Hemp fiber offers an alternative to traditional fibers in the fiber-reinforced market. Hopefully, as new methods are developed to process and create hemp-reinforced plastics, the presence of more and more plastics using hemp as a reinforcing agent will increase. Even though biodegradable hemp-based PLA is ultimately unfeasible with the presence of more efficient crops like corn or sweet potatoes, this could be another way to cut down on the large amount of waste generated by the plastics industry and also create better, stronger, more environmental plastic products using a part of the cannabis plant that otherwise, would be left to rot.


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