Abstract
For many years, the agricultural sector has been indispensable in ensuring adequate food for decades to come. However, the plastic waste generated from this sector is an eyesore, as it tends to have adverse effects on soil properties and the ecosystem at large. In addition, the direct utilization of fertilizers is also a major problem, as they tend not to reach the plants or crops and affects the quality of soil, surface, and underground water. This work focuses on the development of biodegradable polymer composites with potential applications in the agricultural sector. Polymer composites-based on poly(ε-caprolactone) (PCL), poly(butylene-co-adipate terephthalate) (PBAT), poly(butylene succinate) (PBS), and polylactide (PLA) were developed. Different fillers were incorporated in these polymers, and their effects on the material properties, such as rheological, chemical, and crystalline structures, thermal, mechanical, and soil degradation, were evaluated. In particular, hydroxyapatite (HAP), urea, chitin, and cellulose fibers were used during the development of the composites. It is worth mentioning that these fillers, especially HAP, urea, and chitin, are used as fertilizers for crops. PCL-based composites containing HAP and urea as potential materials for the development of mulch films, low-tunnels, nursery bags, and other applications in agriculture were developed. Firstly, HAP was varied in PCL, and the effects of loading on mechanical, morphological, and thermal properties were investigated. The optimal concentration of HAP was found at 3 wt.%. The urea-containing composites were prepared from PCL composites containing 3 wt.% of HAP. The developed urea-based composites showed a decrease in viscosity at low concentrations, whereas an increase in viscosity was noticed with increased urea concentration. The soil degradation of the composites was accelerated with urea loading. An increase in mass loss was observed due to the presence of urea in the composites, which hastened the degradation rate of PCL.
PBS-based composites containing HAP and chitin were also developed. The investigations indicated a reduction in the crystallinity of PBS, while the thermal properties were not significantly affected by the addition of HAP and chitin. However, the increase in the rigidity of PBS was noticed when chitin fibers were incorporated, as observed from the dramatic decrease in the strain at break. However, the composites showed enhanced degradation of PBS in soil. The prepared PBS composites could be essential in the development of small biodegradable plant pots/containers or films, which would not require seedling removal during transplanting. However, the developed composites are not only limited to this application but can also be applied in other fields in agriculture.
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The PBAT composites containing HAP and cellulose were also prepared for application in developing nursery bags, low tunnels, and mulch films. In this case, cellulose was used to increase the degradation rate of PBAT in soil. Further, plastaid-t was used as a dispersing agent to assist with the dispersion of the cellulose fibers. The results proved that, indeed, degradation of PBAT could be controlled by the inclusion of cellulose and plastaid-t. In addition, the tensile strength and toughness were still high. For example, the strain at break was maintained above 500% at cellulose loading of 10 wt.%. Lastly, the PLA/PBS composites containing chitin and plastaid-t as dispersing agents were also prepared. The morphological analysis demonstrated the localization of chitin fibers in the minor PBS phase, whereas, upon the addition of plastaid-t, the fibers migrated to the interface.
Moreover, the increase in toughness was noticed when plastaid-t was included in the neat PLA/PBS blend. However, a dramatic decrease in this parameter was observed, irrespective of the localization of chitin in the blend. The materials showed no significant change after 120 days of burial in soil. Nonetheless, the materials can still be suitable for designing and developing rigid containers such as crates and rigid containers for storage and preservation, packaging, and transportation as part of post-harvesting management in agricultural applications. Overall, different environmentally friendly composites were successfully prepared through melt-processing techniques. The effects of different fillers on the material properties of the selected polymers were thoroughly investigated. The materials showed potential utilization in myriad application fields in the agricultural sector, and they can contribute significantly to minimizing plastic pollution generated in this sector.