Stem Anatomy of Hemp Strains and Physical Properties of Their Extracted Fibers
Camille Pierre Mentors: Prabha Amarasinghe, and Aruna Weerasooriya College of Agriculture and Human Sciences Introduction: Hemp (Cannabis sativa) is identified as a leading fiber crop1 and has recently been legalized in Texas, however, the research to identify the suitable fiber strains in Texas and methods of fiber extraction are still at infancy. Hemp stem contains bast and hurd fibers, and they differ in types of cells, chemistry, physical properties, and end-usage. Retting is a process that is used to extract fibers and it can be a chemical or microbial or enzymatic approach to dissolve certain cells and pectin surrounding the fibers2. Genotype of hemp is an important factor which determines fiber quality3. Therefore, we used ten hemp fiber strains to achieve three aims: 1) test their anatomical and yield parameters linked to fiber quality and quantity, 2) investigate their mechanical properties, and 3) determine the best retting approach. Here, our hypotheses are that all fiber strains are equally suitable and all retting methods are equally efficient. This investigation provides further insights into fiber cell distribution patterns in various strains, and pros and cons of retting approaches. Materials and Methods: Hemp strains cultivated in the Prairie View A&M greenhouse were used for this research. Ten accessions were selected based on number of branches and plant heights, and their voucher specimens were prepared. In anatomical studies, cell distribution of each strain was determined using cross-sections of stems stained with methyl greenCongo red4.Cell layers responsible for bast and hurd fibers were microscopically measured. To test the retting approaches, three replicates from each strain were used for each treatment. Fresh weights of samples were measured. As the negative control, stems were disinfected with 70% ethanol and immersed in distilled water at 4 °C. Samples were chemically retted pretreating with 0.3% HCl, treated with 7% NaOH at 100 ℃ for one hour and post treated with 1% acetic acid5. Enzymatic retting was performed using a mixture of enzymes (pectinase, cellulase, xylanase, and laccase)6. In microbial retting, three approaches of dew retting, soil retting7 and rotted vegetable liquor retting were applied. All extracted samples of bast and hurd fibers were tested with toluidine blue staining for the purity and retting evenness. Hurd and bast fibers were dried at 80°C for 6 hours and the dry weight was measured. The tensile strength of the bast fibers was measured8. Statistical analyses of the data were conducted using ANOVA on R v3.5 to determine significant differences between accessions for all the traits and to detect differences between strains. p<0.05 was considered to be statistically significant. Results and discussion: We obtained different bast : hurd ratio in cross sections of hemp stems. Białobrzeskie and US031 showed the highest diameter of the cell layer that formed bast fiber. We found distinct bast : hurd fibers. This ratio can vary due to distances between plants, nutrient supply to plants, etc.9. Fibers obtained from chemical, enzymatic, and rotten vegetables were even, pure and bast fibers were easily separable. Soil and rotten vegetable retting are novel retting approaches for hemp. Dew and soil retted samples showed the highest impurities and lowest evenness which also prevented the downstream testing. Chemical retting resulted in the highest bast fiber yield. Therefore, if affordable, chemical retting is the best in terms of yield and extraction time. Retting approach with rotten vegetables showed moderate fiber yield and this is a cheap method. The strain, US031 showed the highest bast fiber yield from all retting methods. Blue genius showed the best strain for hurd fiber yield from all methods. Tensile stress evaluation and counting of the number of bast fibers used for tensile stress testing is still in progress. With this data, thus far, Białobrzeskie showed the highest applied load and Blue genius showed the lowest applied load.
Conclusions: Our results showed differential suitability of fiber strains and different efficacy of retting methods. Hemp strains can be recommended based on bast and hurd fiber utility in industry. If the fiber of interest is bast, US031 is suitable and if the fiber of interest is hurd, Blue genius is suitable. If tensile stress is important, Białobrzeskie is suitable based on results thus far. In the future, fiber properties will be chemically enhanced and the microbial retting will be improved. References: [1] Aliferis, K. A., and D. Bernard-Perron. 2020. Cannabinomics: Application of Metabolomics in Cannabis (Cannabis sativa L.) Research and Development. Frontiers in Plant Science 11: 554. [2] Liu, S., L. Ge, S. Gao, L. Zhuang, Z. Zhu, and H. Wang. 2017. Activated carbon derived from bio-waste hemp hurd and Page 106 retted hemp hurd for CO2 adsorption. Composites Communications 5: 27–30. of 3
