Enzymatic treatment of flax fibre at the roving stage for production of wet-spun yarn

Abstract

In the past few years, an acute shortage of good quality flax has compelled wet-spinners to seek alternative process steps for maintaining consistent quality of bleached yarns. The objective of the current investigation was to develop process recipes for the production of better quality yarn from lower grade fibre supplies. A laboratory method was developed to screen enzyme and chemical formulations, using hanks of fibre in the form of roving. The splitting of fibre, after treatments with ethylene diaminetetraacetic acid (EDTA) at 40 °C and two enzyme formulations containing, pectinases, xylanase and laccase at 40 °C was monitored by a tensiometer to assess tenacity and extension under load. The treatments were compared with an industry standard caustic boil (4% NaOH) treatment at 95 °C. The duration for all process conditions was 3 h. The selected treatments were scaled up in a twin pilot scale unit using rovings, followed by H₂O₂ bleaching and wet-spinning. The resulting yarns were evaluated for tenacity and regularity. The recommended process steps were pre-treatment of fibre with EDTA followed by sequential treatments of a mixture of pectinases and xylanase enzymes and H₂O₂ bleaching. The results of this investigation have shown that laccase enzyme can be used for roving treatment to improve yarn regularity.

Introduction

The quality of dew-retted fibre has declined considerably in the past few years due to unfavorable weather conditions during the growing and retting of flax. During retting fungi and bacteria colonize the stem and degrade pectin by releasing pectinases and hemicellulases. Recently, wet-spinners in Europe have experienced difficulties in optimizing mechanical and chemical processing stages due to a wide range of variation in the quality of available fibre supplies [1]. The mechanical preparation stage consists of blending lines for the hackled fibres, followed by passing through five drawing stages of pin frames to prepare a homogeneous sliver and also to remove short fibres and residual woody tissues. The processed fibres are wound on to plastic bobbins, which is known as roving. The primary objective of chemical treatment of the fibre at the roving stage is to achieve a degree of separation and breakdown of fibre bundles which is sufficient to permit the wet-spinning process, whilst maintaining structural integrity of the roving under tension [2]. During the spinning operation, either insufficient breakdown of fibre due to under treatment, or over-treatment leading to low tensile strength and excessive breakdown will significantly reduce yarn tenacity and regularity. The conventional process steps, consisting of three or four chemical treatments need to be adjusted to respond to available fibre supply [3].

Sharma [4] reported the initial work on the use of polysaccharide degrading enzymes for scouring dew-retted flax rovings and reviews on the role of enzymes for processing flax have been published [5]. The quality of fibre during the mid 1980's was relatively consistent from year to year and wet-spinners probably did not need to use enzymes for processing dew-retted fibre, as the mechanical and chemical processes provided flexibility in the production of a good quality yarn. However, fibre quality from the 2000 crop onwards has declined considerably [1]. Consequently, the industry expressed the need for a more controllable processing system for wet-spinning flax. The screening of treatment formulations needs to be carried out using a reliable laboratory method and for enzymatic treatments, such practical experience does not yet exist. To date there has been little study of the effects of such processes on fibre tenacity, extension and rupture under load. Any attempt to incorporate a novel rove treatment process can only be assessed on the basis of full-scale spinning trials; the results may subsequently reveal correlation with laboratory test data. The aim of this investigation was to develop process recipes, which can be used for spinning high quality yarn using poor to medium grade fibres.