**4. Conclusions**

This study investigated the multiscale analysis of bio-based composite materials made of hemp/PA11 commingled yarns. Understanding the different manufacturing stages and the influence of process parameters on yarn, fabric, and composite properties allows materials to be produced which better fit the final application requirements.

In this work, the hybrid yarns were produced by the wrapping process on a hollow spindle machine by wrapping a thermoplastic PA11 multifilament around an untreated hemp roving in order to produce yarns with sufficient tenacity (allowing them to be woven) and with a fibre content of no less than 40%. This process improves the hemp roving structure, which becomes more compact and less hairy.

At this yarn scale, tensile tests were initially conducted at different test speeds including the speed involved during fabric testing in order to investigate its influence on the mechanical properties, then at different temperatures including a temperature in the range of the glass transition temperature of the multifilament. Results from this test show the dependence of yarn properties on test speed and temperature, which is mainly due to the nature of the multifilament used.

Then, these yarns were used in weaving to produce two different fabrics with approximately the same warp density and different weft densities and weave diagrams. The textile and mechanical properties of these fabrics were determined, and the results show the dependence of these properties on the production parameters: preform properties in terms of maximum load and strain are either balanced or unbalanced between the warp and weft directions.

At the composite scale, tensile strength and stiffness for each structure are almost balanced between the two main directions of the composite plates. In addition, composite made from a satin 6 fabric shows an improvement of its mechanical properties even though at the fabric scale, the twill 6 fabric presented better properties.

The aim of future work will be the testing of other parameters at each scale in order to produce a light structure adapted to the end-use application. Moreover, the thermomechanical behaviour of hybrid yarns and commingled fabrics will be tested across a range of

temperatures, including the melting temperature of PA11, in order to better understand the behaviour of these materials at high temperatures. Thus, the hydrophilic behaviour of these hybrid yarns will be characterised and compared with that of hemp roving [43].

**Author Contributions:** Investigation: C.L.; writing—original draft preparation: C.L.; validation; supervision: M.F., A.R.L. and D.S.; writing—review and editing: M.F., A.R.L. and D.S.; All authors have read and agreed to the published version of the manuscript.

**Funding:** This project was funded by "Bio-Based Industries Joint Undertaking" under the "European Union's Horizon 2020" Research and Innovation Program with Grant Agreement No. 744349— SSUCHY Project and Hauts de France Region.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data are contained within the article.

**Acknowledgments:** The authors gratefully acknowledge the Italian company Linificio and Canapificio Nazionale (LCN) for providing the hemp roving used in this study.

**Conflicts of Interest:** The authors declare no conflict of interest.
