A Comparative Study of the Effect of Field Retting Time on the Properties of Hemp Fibres Harvested at Different Growth Stages

Brahim Mazian,Anne Bergeret,Jean-Charles Benezet,Luc Malhautier

doi:10.3390/fib7120108

Brahim Mazian, Anne Bergeret + Show 2 more

Open Access

https://doi.org/10.3390/fib7120108

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Abstract

In this study, the comparison of field retting of hemp fibres harvested at different growth stages (beginning and end of flowering, seed maturity) was studied. Regardless of the harvest period, identical evolution of the fibres’ properties was observed during retting. The main difference is the kinetics of this transformation, which depend on weather conditions and the initial state of the fibres after harvesting. Retting leads to a change in colour of the stems and fibres, an increase of the cellulose fraction and a gradual improvement of the fibres’ thermal stability, in relation with a decrease in the non-cellulosic materials. This process induces fibre bundle separation into elementary fibres. A long period (5 weeks) is required for getting the highest mechanical properties of fibres harvested at the beginning and the end of flowering. However, the retting of fibres harvested at seed maturity has to be performed in a short period (1 week) in order to avoid over-retting treatment. If the fibres are over-retted, their quality decreases in terms of structure and mechanical properties.

Highlights

Based on environmental concern, the interest in using the cellulosic fibres has increased in high grade composites in recent years
For beginning of flowering (BF) and end of flowering (EF), the colour of the unretted samples was light green, contrarily to the stems and fibres harvested at seed maturity (SM) that were transformed into yellow
The fibres harvested at BF and EF required 9 weeks to be completely dark grey, while only 3 weeks were needed for the fibres harvested at SM

Summary

Introduction

The interest in using the cellulosic fibres has increased in high grade composites in recent years. Plant fibres issued from hemp (Cannabis sativa L.) are part of these cellulosic fibres which could be used as an alternative of conventional fibres (e.g., glass and synthetic fibres) for manufacturing industry of low cost, low weight composite materials. This attraction of hemp fibres as reinforcement agents in composite is related to their high specific mechanical properties [1,2], their biodegradability [3,4], as well as their low-density [5]. For using these fibres in material composite, a separation of bundle of fibres to individual fibres or smaller fibres bundles is necessary for improving

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