Microscopic Study on Hemp Bast Fibre Formation

Abstract

Commonly, fibre hemp (Cannabis sativa) is not considered for the production of soft and easy-care textiles. However, initial tests in the textile industry have shown that certain processes allow improvement in the everyday-wear characteristics of hemp textiles. In the framework of the EU R&D project Hemp-sys [QLRT-01-01363] the potential of hemp as a feedstock in textile processing is investigated. Therefore, a detailed study on the effects of agronomy and fibre extraction processing on fibre properties for textile processing has been carried out. To relate the crop growing conditions with fibre quality and productivity it is required that information is obtained on hemp bast fibre formation. At various stages of the plant development the fibre development has been monitored by microscopic techniques. The two distinct bast fibre types occurring in hemp-the so called primary and secondary fibres-show different and independent development. The primary fibres appear earlier in the development in the rapid growth stage and are formed from the primary meristem in the outer layers (phloem). Primary fibres are thick, extremely long and with compact cell walls and small lumen and are present from bottom to top of the plant. In contrast, the secondary fibres are formed in later stages during thickness growth from the secondary meristem. Secondary fibres are thinner, shorter and with higher lignin content than the primary fibres. In early developmental stages secondary fibres only occur at the bottom of the stem. Substantial secondary fibre formation is observed at the start of flowering or when the plants grow taller than 2.25 m and/or thicker than approximately 1 cm. Based upon these observations a selection of conditions can be made for growing and harvesting of hemp to obtain the best quality fibre for textile processing. To produce a crop with maximum amount of primary fibres free from secondary fibres, the recommended practice is to grow hemp at high seed density to avoid thickness growth and to harvest the hemp stems around flowering of the plants.