Manufacturing and Characterizing Hemp Biopolymer Composites
Gabriella Fioravanti, Bryce Peckman, Lexi Patania, Lucia Gargano, Maggie Riley, Ron Kander Thomas Jefferson University
After decades of growing restrictions limiting the cultivation of all varieties of Cannabis Sativa, the U.S. Agriculture Improvement Act granted special allowances for the farming of Hemp in 2018. In Pennsylvania, there have been several thousand acres of Hemp grown each year since the bill was passed. After harvesting, industrial hemp is separated into three raw materials: flower, bast fiber, and hurd (shives). The long bast fibers are taken from the outside of the stalk and used in textile applications. The hurd is the woody core of the stalk, containing short fibers traditionally used in low-value applications. In an effort to improve the value of the Hemp crop, alternative uses of the bast and hurd fibers of the plant are being explored.
In partnership with Pennsylvania businesses, Coexist and Eastern Hemp, the Kander Research Group has investigated the use of hemp waste in plastic composite fabrication. The goal was to create and characterize several bioplastic composites of polylactic acid (PLA) and hemp microparticles for manufacturing applications. By comparing plastics with different percent reinforcement and particle composition, we narrowed down candidates for 3D printing and injection molding.
Researchers received hemp waste of varying composition, including fiber, hurd, whole stalks, and one combined hurd and fiber sample. All hemp samples were cryo-ground by local company Air Products and Chemicals, Inc using their proprietary methodology. Resultant particles were sand-like, non-uniform pieces of plant matter ranging from 10s to 100s of micrometers in length and width. PLA powder and ground hemp were compounded together at varying proportions by weight (0, 10, 20, 30, 40, or 50% hemp). Long extruded filaments can be fed into a 3D printer, or chopped into pellets for injection molding.
On a lab scale, the hemp-PLA bioplastics were found acceptable for 3D printing and injection molding applications. We utilized mechanical tests (tensile), thermal tests (TGA, DSC), and optical microscopy to inform our conclusions. The composites exhibited similar thermal and mechanical properties across filler types (hurd/fiber/stalk). Therefore, we suggest using whole stalks in the manufacturing process. This is the most cost and time efficient option, where farmers don’t have to further process waste stalks before they are used to produce bioplastic composites. If a farmer has hurd left over from decortication, that can also be used. Caution should be taken for mixing together batches of decorticated fiber and hurd, as the combined sample yielded the lowest quality composites in this study. Extra attention should be used in cryogrinding mixed samples to get uniform particles.
Moving forward, the group intends to refine their compounding technique and optimize formulas between 5-30% hemp to create a strong-but-flexible composite. We hypothesize that using less than 10% hemp will yield more ductile composites. Increasing filler amount up to 30% hemp lead to an overall improvement in mechanical properties. Composites with over 30% hemp had poor mechanical properties. A low % hemp formula is favorable for 3D printing applications, while a medium % hemp formula is favorable for injection molding. Surface treatment of powders before compounding and a desiccation protocol may be integrated into the manufacturing process to increase particle adhesion with PLA and control moisture content of samples.
3D printing makes it possible to make complex shapes with little waste and less energy. Injection molding of polymers and composite materials is one of the most common manufacturing processes for making industrial and consumer products. The Kander Research Group has successfully advanced the development of an alternative to conventional plastic filaments and pellets that is made of PLA & hemp, a sustainable and biodegradable option produced within a local PA supply‐chain. By connecting local agricultural, manufacturing, and construction businesses, we have created lasting networks in the Industrial Hemp community and created the possibility for new manufacturing jobs. The Kander Research Group looks forward to injection molding and 3D printing with these composites over the next year.
This is a highly abridged version of the Kander Research Group’s findings. Parties interested in the full report or who have questions are encouraged to reach out to Gabriella Fioravanti (firstname.lastname@example.org).