Properties of hemp and flax fibres cottonised by chemical modification.

Blascu, Vasile ; Vrinceanu, Narcisa

Abstract: This paper presents the effect of chemically modifying hemp and flax hackling noil on the physical/mechanical and chemical properties of the fibres. As a result of treating hemp and flax-hackling noil with the emollients preparation Pektochem, the technical fibre bundles undergo separation into smaller units.

Key words: flax noil, emollient, cottonised hemp fibre, cottonised flax fibres

1. INTRODUCTION

All technical hemp and flax fibres, including the hackling noil, occur as compact bundles of elementary fibres that are characterised by a high degree of lignifications of both their cell walls and the intermediate lamellae that cement the elementary fibres into bundles [Blascu, 2007] [Bla[degrees]cu, 2006] [Malcomete, 2000] [Blascu, 2007] [Blascu, 2007]. The conventional methods of cottonising the technical bast fibres have been for many years directed towards improving the spinning properties of cottonised flax and hemp. [Blascu, 2007] [Blascu, 2007] [Blascu,1997]. That is why, improvement of the cottonising process was directed toward modifying the chemical composition of the bast fibre so as to improve its separation, flexibility and softness.

2. EXPERIMENTAL

After numerous laboratory experiments, it was found that a level of hydrolysis of the intermediate lamellae ensuring sufficient separation of the technical hemp and flax fibres could be attained through:

--increasing the emollients preparation concentration of the chemical-modifying bath; introducing pre-scouring of the technical hemp and flax fibres prior to the chemical-modifying treatment in order to soften the pectinous gums (which cement the fibre bundles) and facilitate their enzymatic hydrolysis; increasing the time of exposure to emollients preparation of the technical hemp and flax fibres while it is being subjected to pre-scouring. To develop a suitable technology, four commercial-scale variants of chemical modification based on the laboratory-scale results were prepared and tested. All variants were tested using a single lot of hemp hackling noil with a linear density of 4.2 tex and a mean length of fibres of 274 mm and a single lot of flax hackling noil with a linear density of 3.6 tex and a mean length of fibres of 261 mm. The sequence of technological operations in the individual variants is presented in Table 1. The final phase of the chemical-modifying process comprised the following operations: rinsing; application of softening agents; centrifuging, and drying. Evaluation of the results of chemically modifying the technical hemp and flax fibres was based on analysis of:

--changes in the linear density, length and chemical composition of the fibres; the effect of carding the chemical-modified hemp and flax fibres on the properties; changes in the structure of hemp-fibre and flax-fibre bundles after their biological modification and carding.

The physical/mechanical and chemical properties of the hemp and flax fibres were tested at the laboratories of the Textile Fibres in Technical University of Jassy. The carding experiments were performed on a TURBO-type Octir flat card, with permanent flats and saw-tooth clothing. The changes in structure of the hemp and flax fibres bundles were examined under a JSM-5200 LV (JEOL) scanning microscope. The pictures were imaged and recorded.

3. RESULTS AND DISCUSSION

Changes were noted in the linear density and length of the fibres and in the structure of the elementary fibre bundles. The changes in the fibre properties following modification are presented in Table 1 and Table 2. The changes in technical hemp and flax fibres due to the chemical modifications can be seen in Figures 1-6, which show microscopic images of the surface and cross-sections of the fibres before and after modification. Post-modification changes, photomicrographs of variant IV are shown, as in this variant the changes in fibre length and linear density were the greatest. The changes in fibre properties after flat carding compared to the changes directly following biological modification are presented in Figures 7 and 8. On the other hand, hemicellulose and (to some extent) pectin are the primary components of the binding substance of the elementary bast fibres, while lignin plays the part of a stabiliser and screen for other fibrogenous substances. Laboratory analyses of the chemical composition of hemp fibre before and after modification in Variants III and IV showed that the level of cellulose was the highest, and that of hemicellulose, pectin and lignin the lowest. In the variants mentioned, cellulose content was increased by 6.4%, while hemicellulose was reduced by 27.6-27.78%, lignin by 17.87-22.77%, and pectin by 98.37%. Sensory tests showed the chemically modified hemp and flax fibres to be soft and flexible.

4. FIGURES

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

6. CONCLUSION

The chemical modifications of hemp and flax consists in the the emollients preparation Pektochem separating, by its chemically action, the compact fibre bundles of hemp and flax into smaller units that can be further separated in the mechanical processing operations; chemical modification of the technical hemp fibre reduces its linear density by 40%, and its mean length is reduced 5 times compared to the input length; Chemical modification of the technical flax fibre reduces its linear density by 30%, and its mean length is reduced 4 times. After flat carding, the chemically modified hemp fibre reaches a mean linear density of about 1.7 tex and a mean length of about 27 mm. Following chemical modification, the chemical composition of the hemp fibre is changed to a degree that indicates a good capability for spinning. There is a slight increase in cellulose content, while the content of the cementing vegetable substances is reduced: hemicellulose by 24%, pectin by 86%, and lignin by 20%.

7. REFERENCES

Blascu, V. (2007) Textile Fibres (in Romanian), Ed. Performantica, ISBN 973-973-730-346-2, Iasi.

Blascu, V. (2006) Physico-Chemistry and Properties of the Textile Fibres (in Romanian), Ed. Performantica, ISBN 973-973-730-287-7, Iasi.

Malcomete, O.; Bla[degrees]cu V.& Homutescu, J. (2000) Textile Fibres (in Romanian), Ed. Acad. "Gh. Zane", ISBN 973-98070-6-2, Iasi.

Blascu, V. (2007) Physico-Chemistry and Properties of the Textile Fibres. Laboratory's Technique for Investigations, (in Romanian) Ed. Performantica, Iasi.

Blascu, V. (2007) Textile Fibres. Laboratory's Technique for Investigations (in Romanian), Ed. Performantica, ISBN 978-973-730-344-8, Iasi.

Blascu, V. (1997) Specially Methods for Investigation of the Textile Raw Materials, Ed.BIT--CARTEX, ISBN 973-96414-5-8, Iasi.

Figure 7. Mean length of hemp fibre before and after
chemical modification and after flat carding

 before and after after flat
 modification carding

before 4.3
 modification
variant I 3.74 1.80
variant II 2.78 1.52
variant III 2.7 1.5
variant IV 2.64 1.40

Note: Table made from bar graph.

Figure 8. Mean linear density of flax fibre before and
after chemical modification and after flat carding.

 before and after after flat
 modification carding

before 274
 modification
variant I 67 34
variant II 61 33
variant III 56.8 34.4
variant IV 40.4 34.4

Note: Table made from bar graph.

Table 1. Sequence of operations in chemical modification of
hemp and flax hackling noil

Variant I Variant II Variant III Variant IV

-Treatment -Treatment
with 2% with 3%
emollients emollients
preparation preparation
Pektochem Pektochem
bath bath

-Removal of -Removal of
bath bath

-Scouring -Scouring
with use of with use of
detergents detergents

-Final -Final
operations operations

Table 2. Linear density and length of fibres of hemp hackling
noil before and after application of various variants of
chemical modification

 Before
Parameter Unit modification After modification variant

 I II III IV

Mean linear tex 4.2 3.24 2.78 2.7 2.54
density of
fibre

 Nm 238.1 308.6 359.7 370.4 393.7

Reduction of % 0 22.9 33.8 35.7 39.5
linear density

Mean fibre mm 274.0 67.0 61.0 56.8 48.4
length

Reduction of % 0 74.4 77.7 79.3 82.3
fibre length