Abstract
The current development of “Cannabis sativa L.” hemp fibers for technical textiles and biocomposites demands through consideration of the retting process’s effect on fiber quality. Field retting, though crucial, remains insufficiently managed due to its reliance on empirical methods and dependence to weather conditions. This study aims to improve the understanding of the retting process in the case of the “Futura 75” hemp stems harvested at the end of the flowering period and retted in southern France, which is characterized by a dry Mediterranean climate. Various analyses were performed, including color evolution, morphological (optical microscopy), surface (SEM), biological (density of bacterial and fungal community using qPCR approach), and biochemical (solvent extraction and spectro-colorimetry) analyses. The results showed that retting had a major impact on the chemical composition of the fibers, resulting in a significant loss of pectic substances. This result correlated with microscopic observations, which showed the decohesion of fiber bundles during retting. Since an increase in cellulose proportion was observed, this was associated with both the degradation of the non-cellulosic components and an increase in cellulose crystallinity. A color change from green to black during retting, mainly due to microbial colonization was also observed. This result was further supported by the qPCR results, which indicated an increasing presence of bacterial and fungal populations on the hemp stems during the retting process. All the obtained results are statistically analyzed to identify correlations that, in the long term, could eventually lead to the identification of simple indicators to better control the field retting of hemp and obtain stable fiber properties. The statistical findings suggest correlations between variables related to microbial community, pectin degradation, and climatic data throughout the retting process.