## 4 Discussion  
Most thermal degradation tests on biomass aim to analyze their potential as biofuels [19; 53]. The study of the basic behavior of materials against thermal degradation and a simple reaction model are sufficient for practical engineering applications [54]. However, in recent years, these investigations have focused on analyzing the synthesis process of polymeric compounds with natural fibers [55; 56; 57; 58]. It has been seen that the weight loss of the fibers during the heating process is due to the deconstruction of cellulose, hemicellulose, and lignin constituents [56; 59; 60]. Currently, most studies on natural fiber-reinforced compounds include thermal characterization using DSC, both for the composite material itself [61; 62; 63; 64; 65; 66] and for the natural fibers [67; 68; 69]. The FTIR analysis method is used to detect characteristic functional groups in the fibers by passing infrared light through the sample fibers [70; 71]. Natural fibers derived from crop residues can be used to reinforce a variety of thermoplastics after being processed and treated through mechanical, thermomechanical, semichemical, and chemical treatments [72]. These treatments modify the lignin content, thus affecting the cellulose and hemicellulose content in the treated fiber [73]. The bulk density of other fibers, such as cotton, jute, sisal, and coconut, is higher than the bulk density of the achira fiber. However, bamboo fiber has a similar density to that of achira fiber [74]. The composition of cellulose, lignin, pectin, and hemicellulose in plant fibers affects their properties. It is a common practice to remove lignin and pectin to enhance the reinforcing effect of natural fibers. Previous studies have shown that flax fiber demonstrated superior thermal resistance among the natural fibers examined, mainly due to its low lignin content of 2%. In comparison, jute had a lignin content of 11.8%, and sisal had a lignin content of 9.9% [75]. The first phase in creating mixtures with polymeric and agro-industrial waste through mechanical recycling is to determine the mechanical and thermal properties of the materials. \"In recent years, chemically recyclable polymers have been designed and developed to manage plastic waste at the end of its useable life\" [76], and including natural fibrous waste within its structures is a good solution to support circular economy (CE) policies. Waste management technologies are evidently one of the most important aspects currently being considered for CE [77]. This helps maximize the properties of the materials. In regard to the fiber moisture content of 11.007% that was found, it is important to note that the presence of moisture in the fibers can affect their use as reinforcement due to the hydrophobic nature of polymeric resins. This diminishes interfacial bonding, resulting in a reduction in the mechanical properties of the composite [78]. Therefore, it is suggested that the fibers undergo chemical or thermal treatment to optimize bonding when used as a reinforcement material with polymeric matrices. The moisture percentage obtained for the achira fiber presents values similar to those found in other studies for banana, pineapple, and sisal fibers [79]. The results of the moisture absorption percentage showed an average of 81.58% for the seven samples. One of the main challenges in using natural fibers in polymeric matrices is their strong polar character, which creates incompatibility with the matrix. Surface treatments, both chemical and physical, can help alleviate this issue while simultaneously reducing moisture absorption. When the fiber has zero moisture, its density (0.64 g/mg) is higher than its saturation point density (0.23 g/m\({}^{3}\)). This suggests that in order to optimize fiber transportation and storage costs, it is preferable for the fiber to have the least amount of moisture possible to optimize space. The results from the TGA test reveal important aspects, including the fiber's hydrophilic character, with a significant retained moisture percentage of 8.8%.