Enhancement of plant roots through polymer infusions for use in soil stabilization

Soil stabilization is an engineering problem faced throughout the world. Many methods have been developed to address this problem, but each method has inherent drawbacks, mainly the need for large amounts of excavation. This research project was undertaken to investigate the efficacy of infusing polymer into plant root systems for soil stabilization. A hybrid of two conventionally used soil stabilization techniques, vegetation and geotextiles, is created by infusing a thermoset epoxy into the plant without any need for excavation work. Through this process, the advantages of both techniques can be utilized while eliminating the major drawbacks of each individual method. Infusion pressures, microscopy imaging, volume and mass change measurements, thermo-gravimetric analysis, tensile testing, and soil testing were conducted to characterize the effects of infusing polymer into the plant material.

Polymer infusion pressures were recorded and analyzed for pressure values corresponding to visual effects during the infusion process. It could be determined that polymer required a minimum of 70-140 kPa of pressure until it was first observed emitting from the tip of the severed primary root. Associated plateauing of the pressure curve could be observed at these pressures.

Staining and fluorescent analysis was conducted on infused and non-infused cross-sections of plant material. It was determined that polymer was flowing through the xylem vessels (water transport vessels) and vascular tissue of the plants. Volume and mass measurements of stem material taken before and after infusions demonstrated increases of 120% ± 17% and 90% ± 15%, respectively. These increases would provide a composite structure of 54% ± 4% polymer and 46% ± 4% plant material by volume or 46% ± 4% polymer and 54% ± 4% plant material by mass. Mass measurements before and after infusions on root sections with lateral roots removed showed mass increase of 53% ± 12% providing a composite structure of 34% ± 5% polymer and 66% ± 5% plant material by mass. Thermo-gravimetric analysis on the infused lateral roots provided a composite structure of 59% polymer and 41% plant material by mass.

Tensile testing of infused lateral roots provided an average tensile strength increase of 107% and a Modulus of Elasticity (Young's Modulus) increase of 92%. The tensile strength increase was observed over the entire strain range of the roots, providing a significant impact on overall tensile strength. While the soil testing did not show any improvement, modeling provided a maximum possible increase of soil shear strength of 485%. The considerable increases in the mechanical properties of the plant-polymer composite over the non-infused plant roots are very beneficial for soil stabilization. By infusing the plants with polymer, biodegradability of the plant material can potentially be reduced significantly. All of these effects make this hybrid technique of soil stabilization a viable option that should be further researched.