US2440562A - Obtaining of ramie - Google Patents

Description

Patented Apr. 27, 1948 OBTAINING OF RAMIE Mark Michael Wise, Mosman, near Sydney, New South Wales, Australia No Drawing. Application June 12, 1944, Serial No. 540,005. In Australia July 29, 1943 2 Claims.

This invention relates to a method of obtaining ramie fibres from green ramie stems. Ramie (rhea ramie or Chinese grass) is the fibre of several varieties of the genus Boehmeria (M. O. Urticaceae). As at present known it is obtained by the decortication and degumming of the white leaved Boehmerza nivea and the greenleaved Boehmerz'a tenacissima.

Ramie fibre is used for making paper, mats and sails, tapestry, tablecloths, damasks, ropes and cords, and also other articles for the textile industry and for silk decoration and otherwise. It is the principal yarn from which gas-mantle fabrics are knitted and woven.

Ramie fibre belongs to that class of fibres known as bast fibres in which the fibres occur between the bark and the inner woody portions, being cemented to each other and to both the bark and the woody portion by a very tenacious gummy substance.

In the case of other bast fibre plants the gummy constituents are usually destroyed by a retting operation, enabling the fibres to be thereafter separated from the other portions. Owing to the exceptional tenacious qualities of the gummy constituents in ramie this method is known to be unsuitable.

It has been the practice among Chinese peasants to strip the bark by hand from the fibre and woody portions of the ramie stems while the stems are still green. This is a laborious process, and, even after the fibres have been obtained, it

is still necessary to treat the fibres to remove this very tenacious gummy substance therefrom. This may be done by repeated washings and kneading by hand, obviously not a commercial proposition, or by heating with strong alkali solutions, The latter process is not satisfactory since it is found that, if the treatment is sufficiently severe to free the fibres from gum, then the ramie fibres are injured, become brittle, and lose their resistance to extension. Furthermore, it is found that enzyme action sets in almost as soon as the bark has been stripped from the fibres and that this enzyme action affects the ramie fibres and renders them brittle.

In United States specification No. 340,514 it has been proposed to steam or steep ramie stems to soften them and then to crush the stalks while wet to partially separate the woody parts from the fibres. Owing to the fact that, evenafter beating the broken stalks, a considerable portion of the woody part was left adhering to the fibre, this prior method required that the partially treated.

It has also been proposed in United States specification No. 2,263,591 to wet or scald ramie stems to remove the outer bark, and then dry the stems and subject them to a tearing or scutching operation. This specification clearly indicates that the inventor considered that a simple drying of ramie stems would render the inner woody portions of the ramie stems sufiiciently brittle to enable the ramie fibres to be separated from the woody matter. A preliminary wetting or scalding step, whose sole purpose was to remove the outer bark of the ramie stems, is stated to be desirable. Even after this treatment, a scutching machine, which tears the fibres from the other constituents, must be used. This method does not overcome the difliculties caused by the particularly tenacious character of the gummy constituents of ramie stems.

None of the prior methods have proved commercially successful owing to the fact that in none of them is the tenacious gummy binding substance present in ramie destroyed or changed without harming the ramie fibres. Until this gummy substance has been destroyed or changed, however, it is not possible to obtain ramie fibres in a state suitable for spinning.

I have discovered that, if green ramie stems are subjected to a prolonged steam treatment at pressures above atmospheric, and at not less than 15 lbs. per square inch gauge pressure, and the treated stems are then dried, the stems may be broken and crushed easily by hand, and the fibre, almost free from gum, readily separated from the woody portions. To obtain this result it is absolutely essential that the ramie stems be in the green state, and that the steam treatment of this invention be followed by the drying stepthis result is not achieved by a. steam treatment followed by a wet crushing step.

In contrast to the prior methods, the present method changes the gummy binding constituents of the ramie stems in such a way as to enable ready separation of the fibres from the other portions of the stem without at the same time injuring the fibres or rendering them brittle. The present method subjects the ramie stems to a prolonged steam treatment of from 1 to 6 hours at pressures well above atmospheric and preferably between 15 and 40 lbs. to the square inch gauge pressure, that is, approximately 30 to 55 lbs. per square inch absolute pressure. This steam treatment causes chemical and physical changes in the gummy constituents binding the the fibres.

3 fibres and other parts together as a result of which it loses its tenacious character and upon drying is converted to a physical state such that upon even mild mechanical treatment it becomes powdery or dust-like and the greater part thereof falls away from the fibres. It is thought that the chemical changes are hydr-olytic in character.

After the steam treatment the ramie stems are dried, causing the aforesaid change in the gummy constituents and the stems are crushed, whereby the bark and woody portions are separated from A simple crushing operation only is required--it is not necessary to employ a scutching operation in which the fibres are torn from the wood and bark. A small part of the changed gummy constituents may remain adhering to the fibres after this crushing operation, but, owing to the fact that they have lost their original tenacious character, can be readily removed from the fibres by washing with water or soap solution. No severe chemical treatment, which would harm the fibres, is necessary to efi'ect this removal of the powdery changed gums.

The term green ramie stems is to be understood as ramie stems which are in, or have been kept in, substantially the same condition as that in which the said stems existed at the time of cut ting thereof. Experiments which have been made show that the method of this invention is not applicable to ramie stems which have been dried, or have dried during storage. The prolonged steam treatment under pressure of this invention will not produce the required changes in the gummy constituents of the ramie stems unless the stems are in the green state. In fact, if stems which have dried out are so steamed and then dried, the whole stem including the fibres becomes brittle and can be readily broken. On the contrary my process results in fibres retaining their original length and in unoxidized condition.

It has also been found that boiling or steaming green ramie stems at atmospheric pressure, or at pressures only slightly above atmospheric, will not produce the chemical and physical changes in the gummy constituents which are essential to the success of the present invention, and it is not until a pressure of the order of 15 lbs. gauge pressure is employed that the said gummy constituents are so altered. Furthermore, even after the steam treatment according to this invention, it is not possible to separate the bark from the fibres by a simple crushing operation unless the stems are dried after the steam treatment and before crushing, which must be efiected whilst they are still dry.

Accordingly, it is an object of this invention to provide a method of producing ramie fibre from green ramie stems which is simple and inexpensive to carry out, and in which the fibres are not rendered brittle, but are recovered in substantially their natural state.

It is a further object of this invention to provide a simple and inexpensive method which will enable ramie fibres to be obtained substantially free from gum and woody matter.

It is a further object of this invention to subject green ramie stems to steam at well above atmospheric pressure for at least one hour and for suflicient time to produce chemical and physical changes in the gummy constituents of the stems, thereafter to dry said stems to cause the gummy constituents to become powder-like when drycrushed, and finall to crush the dry stems as by means of rollers to separate the fibre from the bark and wood of the stems.

If necessary, the fibres may be subjected to further treatment, as by an air blast or willow machine, to remove any minute particles of bark or other substances which may not have been completely removed during the previous crushing treatment.

' The ramie stems for treatment by the method of this invention are preferably cut when the stems have arrived at that stage of maturity which is indicated by the bark having turned to a brown color, or alternatively at that stage which is indicated by the bark of the ramie stems undergoing a change of color from green to brown. It has been found that the ramie fibres are more readily separated from the gums, bark and wood of the stems when the bark has been allowed to change, or is beginning to change, to a brown color,

The out stems, after the leaves have been re moved, are placed in a closed vessel to which steam under pressure may be fed. The stems may be fed as desired to the said closed vessel, but it has been found highly advantageous to feed the stems in a vertical position relatively to the said vessel since a better disintegration of the stems then occurs when the stems are crushed during the third step of the process.

After the ramie stems have been placed in the closed vessel steam at a pressure greater than atmospheric, and preferably at 15 to 40 lbs. per square inch gauge pressure, it is fed to the vessel for'a prolonged period. A suitable time for the steam treatment has been found to be from 1 to 6 hours, the time of treatment decreasing with increase of pressure.

During the steam treatment the -gummy constituent in the ramie stems undergoes a chemical change or changes, thought to be hydrolysis, which is or are essential to the success of this invention and which causes the altered gums to lose their tenacious character.

The steam treated stems are then-dried by exposure to dry atmospheric air or to hot air, or by any other suitable method or means, whereby the chemically changed gums become powder-like upon dry-crushing. The drying operation may take from 8 to 30 hours or longer.

The dried stems are crushed between rollers to separate the fibres from the bark and wood of the stems. wise and if fluted, they may be in two sets, one of which has wide shallow teeth, and the other has narrow deep teeth. A scutching step, which involves tearing of the stems, is not necessary and is not employed.

It may in some instances be desirable to treat immersion in an aqueous saturated solution of' bleaching powder for from 1 to 48 hours, or in a solution of mineral acid and bleaching powder for a shorter period, or by the action of chlorine gas. Other bleaching methods may be used. The fibres are then washed, dried and combed ready for use.

The rollers may be fiuted or other- 5 I claim: 1. A method oi obtaining ramie iibre irom green ramie stems which consists in subjecting the said green stems to the action of steam at well above atmospheric pressure, and at not less than 15 lbs. per square inch gauge pressure, for a prolonged period. not less than one hour, sufiicient to substantially destroy the tenacious character of the gummy constituents of the stems. drying the steam treated stems to cause the changed gummy constituents to become powderlike when dry-crushed, and crushing the dried stems whereby the gummy union is broken and the fibres are substantially separated from the other substances of the dried stems.

2. A method of obtaining ramie fibre from green ramie stems which consists in subjecting the said green stems to the action of steam at a pressure of between 15 and 40 lbs. per square inch.

gauge pressure for between one and six lyurs, drying the steam treated stems. and crushingthe dried stems to separate the fibres from the other substances of the dried stems.

MARK MICHAEL WISE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Number Great Britain (Man 10. 193'!