Technical Field:

The present invention relates to a process for producing fire-retarded blended fibres of cellulose and chlorous polymers.

Background Art:

Cellulose fibres, such as cotton or viscose, are as such highly inflammable and burn fast.

The combustibility of textiles, primarily the extinction properties, can be described by their LOI value (Limiting Oxygen Index). In this method the smallest oxygen content required for the combustion of a material is determined using a blend of oxygen and nitrogen. If the LOI value is clearly higher than the oxygen content of air (21 %) , the combustion will cease by itself. The LOI values of different fibre qualities are given in the following table (L.

Pakkala, Tekstiililehti ("Textile Magazine") No. 3, 1973:

Table 1 .

Fibre LOI

Polyacryloni .trile 18,2

Cotton 18,4

Cellulose triacetate 18,4

Cellulose di .acetate 18,6

Viscose 19,7

Polyester 20,6

Wool 25,2

Modacrylate 26,8

PVC 37,1

Cotton/polyester 50/50 18,0

The combustibility of a fibre blend cannot be determined out of the combustibility of the separate components, but the determination must always be made out of the blend.

Phosphor-, chlorine-, brome-, antimony-, tungsten- or boracium-bearing compounds are used as fire retardants for cellulosic fibres. These compounds are added to the fibre usually in the finishing stage. Brome-bearing organic compounds have also been blended with viscose prior to the spinning of the fibre.

The most common fire retardants for cellulose fibres are:

1. Ammonium phosphates, -sulfate and -halogenides as well as sodium borates

The disadvantage of these substances is their water solubility. The material loses its fire retardant properties after being washed with water.

2. N-methylol-2(dimethylphosponatoyle-)-propionamide and tetrakishydroxy e h lphosphoniumchloride or -sulfate.

Disadvantages of these characteristically stable fire retardants are the expensive chemicals, the multistage fireretardant finishing, the textile's coarse and in¬ flexible touch, lower light and weather resistance. In addition, when heated they develope strong toxins, such as phosphines.

3. Chlorinated carbohydrogen/antimony oxide

Disadvantages of this finishing process applied only to products that are to be used outdoors, are the coarseness and inflexibility of the product as well as its imperme-

ability to air. The use of antimony causes labour safety problems.

4. Tris-dibromepropylphosphate blended with viscose prior to spinning (approx. 15 % of the amount of cellulose)

The disadvantage of these "built-in" fire retardants is their effect upon the crystallization of the cellulose which causes a vigorous decrease in the strength of the fibre. The substance has been found to be mutagenous and its use is forbidden in the USA.

in the production of viscose fibre, such organic polymers that spun into fibres together with cellulose could have advantageous fire retardant properties cannot be dissolved in an aqueous cellulose xanthogenate solution (viscose) (See table 1) .

It has been suggested (Grinshpan, Kaputskii, Savitskaja, Zhurn, Priklad, him. , 5 , 1977, 702) that.e.g. PVC could be added to cellulose that has been dissolved in a blend of nitrogen tetroxide (N-O,) and dimethyl formamide (DMF) and that PVC could be regenerated in the form of fibres together with cellulose. The production of cellulosic fibres out of a N-O _^ /DMF solution of cellulose has, however, proved to be uneconimical and not a single production unit employing this method has been established.

It has also been suggested (FI patent application 800963) that certain chlorous polymers can be added to a dimethyl- sulfoxide (DMSO) /paraformaldehyd (PF) solution of cellulose and that the chlorous polymer could be precipitated together with cellulose as a fibre, the fire resistance of which is at least 21 % based on the LOI value. It has, however, been found that such chlorous polymers that are most inexpensive

O P I

and contain a lot of fire retardant chlorine (such as PVC or PVC/PVAc- blend polymer) do not form a clear, homogenous blend together with cellulose in a DMSO/PF solvent. This causes the disadvantage that in order to obtain a fire re- tardant effect in fibres of aforementioned blends, more of these inexpensive polymers have to be added to the cellulose than such chlorous polymers which, form a clear, homogenous blend with cellulose in a DMSO/PF solvent. When doing so, part of the advantage ^' gained by the use of polymers as fire retardants is lost. Moreover, it has been found that the properties of fibres produced of turbid, inhomogenous solut¬ ions do not fullfil the requirements set on textile fibres.

Disclosure of the invention:

It is an object of the present invention to provide a process for producing blended fibres of cellulose and chlorous polymers the fire resistance of which is at least 21 % based on the LOI value.

The present invention is based on the observation that by using a new solvent of cellulose, a blend of lithium chloride and dimethylacetamide (DMAC) or of lithium chloride and l-methyl-2-pyrrolidone (DOS 30 27 033) certain chlorous polymers can be blended into the cellulose in the solution in such proportions that when the blend is spun into fibres, it yields a product which has considerable improved^ fire- retardant properties in comparison with cellulosic fibres.

Furthermore, it has been proved that even though DMAC and l-methyl-2-pyrrolidone are good solvents of synthetic polymers, chlorous polymers can be blended into a cellu¬ lose solution only in certain proportions. Otherwise the blend will gell and the spinning into fibres is not possible. Table 2 on the next page shows the spinnability of blends of cellulose and some polymers from solutions of LiCl/DMAC and LiCl/MP.

^■ ^0R£ OMPI

German Patent Application DOS 30 27 033 discloses the possibility to blend polyamides, polyesthers, polyethers, chitin and urethanes to LiCl/DMAc or LiCl/MP solutions of cellulose and to manufacture shaped products out of the blends. As it can be seen from the test results presented in Table 2, the above mentioned solutions are not, however, usually spinnable. Thus they are not suitable for preparing fibres according to the invention.

Table 2. The spinnability of blends of cellulose and certain polymers from LiCl/DMAC and LiCl/MP

+ shows that the blend can be spun

- shows that the blend cannot be spun because of its gelli- ness or turbidity

Polymer Blend proportion (cellulose/polymer) 90/10 70/30 50/50 30/70 10/90

Acrylonitrile, methyl- + acrylate and butadiene 77/22/6 blend polymer (Nitrile resin)

Acrylonitrile and styrene - 35/65 blend polymer (SAN)

Acrylonitrile and vinyl- + dene chloride blend poly¬ mer (Modacrylate)

Acrylonitrile and vinyl- + chloride blend polymer (Modacrylate)

Ethylene ^' and acrylic - acid blend polymer and Na- or Zn-ions (Ionomer)

Ethylene and vinylacetate - blend polymer (EVA)

Gelatin

Polymer Blend proportion (cellulose/polymer) 90/10 70/30 50/50 30/70 10/90

Carboxymethyl cellulose (CMC)

-"- -Na salt

Polyacr lates

Polyaeryle amide

Polyacrylic acid (PAA)

Polyacrylic nitrile (PAN)

Polyamide 6 , 6

-"- 11

Polyamide imide .

Polybuteneterephtalate

Polyethyleneterephtalate

Polyethylene (PE)

Polyethylene, chlorinated

-"-, chlorine-sulphonated

Polycarbonate (PC)

Polymethylmethacrylate (PMMA)

Polystyrene (PS)

Polyurethane (PU)

Polyvinyl alcohol (PVA)

Polyvinyl acetate (PVAc)

Polyvinyl chloride (PVC)

Polyvinyl chloride (post- chlorinated (CPVC)

Polymer Blend proportion (cellulose/polymer) 90/10 70/30 50/50 30/70 10/90

Polyvinyl pyrrolidone (PVP)

Wool

Vinyldene chloride and vinylchloride 90/10 blend polymer (PVDC/PVC)

Vinylchloride and vinyl¬ + + acetate 87/13 blend poly¬ mer (PVC/PVAc)

In the method for producing fire-retarded cellulose-based fibres according to the invention, blend polymer of acrylo¬ nitrile and vinyldene chloride (modacrylate) , polyvinyl chloride (PVC) , blend polymer of vinyldene chloride and vinylacetate (PVDC/PVC) or blend polymer of vinylchloride and vinylacetate (PVC/PVAc) is added into a LiCl/DMAC or LiCl/MP solution of cellulose in such a proportion that the solution formed will not gell.

The solutions according to the invention contain 10 - 60 % by weight of chlorous polymer or polymers based on the total amount ofcellulose and chlorous polymers in the solution. The chlorous polymer can either be dissolved straight in the cellulose solution or first in a suitable organic solvent which is then mixed with the cellulose solution. Fibers are manufactured out of the obtained clear blend solution by feeding it to a solution in which cellulose and the chlorous polymer precipitate in the form of fibres. This method yields fibre, the LOI value of which is at least 21 % 0 ₂ , and subsequently its fire-retardant properties are consider¬ ably better than those of pure cellulosic fibre.

The invention has the following advantages over the known

methods for fire-proofing of cellulosic fibres:

a) the method yields a product in which the fire-retardant is "built-in" . The blend is homogenous throughout the fibre, b) the fire-retardant does not dissolve in the spin bath when processing fibre, but precipitates completely together with the cellulose fibre. No chemical losses occur, c) the fire-retardants are not water soluble, thus the fire- proofing of the fibre is permanent and will not weaken in washings, d) since the fire-retardants are long-chain polymers, they orientate in the fibre production like cellulose does and do not have as disadvantageous effects on the strength properties of the fibre as the known fire retardants, e) the addition of chlorous polymers to the cellulosic fibre by this method does not effect the pleasantness of the fibre, f) no health hazards are caused by the use of chlorous polymers in the fibres, g) the cheapest chlorous polymers available, such as PVC and PVC/PVAc blend polymer, can be used in the method without rendering the quality worse.

The following examples illustrate some of the advantageous embodiments of the invention.

Example 1 Preparation of a cellulose solution using a LiCl/DMAC solvent

150 g wet prehydrolysed birch sulfate cellulose (water content 65 %) was kept in 1000 ml dimethylacetamide (DMAC) for 24 h. After filtration the cellulose was pressed as dry

_ as possible and was treated for 2 more hours with a new batch of DMAC. Finally the cellulose was pressed to a dry matter content of 25 %. 48,9 g lithium chloride was dis¬ solved in 495 g DMAC at 60 °C. Said cellulose treated with DMAC was added to a LiCl solution of room temperature. The cellulose was dissolved in two hours. The clear solution containing 6 % cellulose was heated to 90 C and was filtrated. The viscosity of the obtained cellulose solution at 23 °C was 420 P.

Example 2: Preparation of a cellulose solution using a

LiCl/MP solvent

52 g air-dry, pre-hydrolysed birch sulfate cellulose was "activated" by keeping it in 1000 ml water for 1 hour. Cellulose which was pressed dry was kept in 1000 ml 1- methyl-2-pyrrolidone for 3 hours, whereafter it was pressed to a dry matter content of 25 % and the treatment was repeated with a dry solvent. The cellulose was then dissolved at room temperature in 544 g lithium chloride/ l-ιtιethyl-2-pyrrolidone solution the LiCl-content of which was 9 %. The obtained clear solution containing 6 % cellu¬ lose was filtrated at 90 C. The viscosity of the solution at 23 °C was 480 P.

Example 3: Preparation of cellulose/PVC (60/40) blend fibres

173 g DMAC solution was blended with a cellulose solution prepared as set forth in example 1. The DMAC solution contained 20 % PVC. The blend was shaken for one hour at room temperature. The viscosity of the obtained clear, high-grade solution at 23 C was 300 P. The solution was fed through the holes (0 0,08 mm) of a spinnerette into water and the fibre bundle was lifted 200 mm through the water

solution up into the rolls where it was washed, brightened and dried. The spinning speed was 20 m/min. The finished fibre felt soft and warm and it had a sufficient strength for use in textiles. The tensile strength of an aerated fibre was 140 mN/tex and of a wet fibre 60 mN/tex. The LOI value of the fabric manufactured of the blend fibre was 24 -

25 % 0_ and it extincted by itself.in air. The LOI value of •<■ J ^' - the cellulose fibre prepared correspondingly was 18 - 19 0„.

Example 4: Preparation of cellulose/PVC (80/20) blend fibres

6,5 g PVC pulver was added to a cellulose solution prepared as set forth in example 2 and the blend was mixed at 50 C for 3 hours. The clear solution was filtrated and spun into fibres as set forth in example 3. The LOI value of the obtained fibre was 22 - 23 C and it continued to burn in air very slowly or extincted entirely. The tensile strength of an aerated fibre was 200mN/tex and of a wet fibre 120 mN/ tex.

Example 5: Preparation of cellulose/vinylchloride-vinyl acetate (40/60) blend fibres

78 g of vinylchloride-vinylacetate blend polymer dissolved in l-methyl-2pyrrolidone was added to LiCl/l-methyl-2-pyrro- lidone solution of cellulose prepared as set forth in example 2. The blend was shaken for 2 hours at room temperature and the clear, high-grade blend solution was spun to fibres as set forth in example 3. The obtained white blend fibre was strong enough for use in textiles. The tensile strength of an aerated fibre was 140 mN/tex and of a wet fibre 65 mN/tex. The fabric manufactured of the blend fibre extincted by itself in air after the flame was removed and its LOI value was 27 - 28 % 0- .

Example 6: Preparation of cellulose/vinylidenechloride- vinylchloride (80/20) blend fibres

13 g vinyldenechloride-vinylchloride blend polymer dis¬ solved in l-methyl-2-pyrrolidone was blended with LiCl/DMAC solution of cellulose prepared as set forth in example 1. The clear blend solution was spun to fibres as set forth in example 3. The LOI value of this pleasantly feeling fibre was 23 - 24 % 0_ and it extincted itself in air.

The strength of the blend fibre was satisfactory.

Example 7: Preparation of cellulose/vinyldenechloride- vinylchloride blend polymer/modacrylate (70/20/10) blend fibres

14,9 g vinyldenechloride-vinylchloride blend ply er and 7,4 g modacrylate fibre dissolved in DMAC were blended with a .LiCl/DMAC solution of cellulose prepared as set forth in example 1. The solution was mixed for 2 hours. The obtained clear blend solution was spun to fibres as set forth in example 3. The prepared fibre felt soft and its strength was better than that of the fibre presented in example 6. The blend fibre extincted by itself in air after the flame was removed and its LOI value was 25 - 26 % 0~ .

Example 8: Preparation of cellulose/modacrylate (90/10) blend fibres

5,8 g modacrylate fibre dissolved in DMAC was blended with a cellulose solution prepared as set forth in example 1.

The blend solution was spun to fibre as set forth in example 3. The blend fibre felt pleasant and continued to burn slowly in air after the flame was removed. Its LOI value was 21 - 22 % O _p . The strength of the fibre was good.

OMPI

Example 9: Preparation of cellulose/PVC 60/40 blend fibres using a DMSO/PF solvent

83 g air air-dry, prehydrolyzed cellulose, 83 g paraformal- dehyde and 1100 g dimethylsufoxide were heated in a 2 1 vessel to 120 °C during approx. 1,5 h. The obtained clear solution was kept for further 2,5 hours at 120 C in order to remove excess formaldehyde. The solution was filtered while it was still hot and DMSO and 55,3 g polyvinylchloride was blended with it. The blend was shaken for 2 hours at 70 C. The obtained turbid solution was fed through the perforations of a spinnerette to an aqueous spinning bath. The fibre bundle was streched, washed and dried. The LOI value of the finished fibre bundle was 24 to 25 % 0-. The tensile strength of an aerated blend fibre was 60 mN/tex and of a wet fibre 15 mN/tex, which is not sufficient for textile use.

Example 10: Preparation of cellulose/PVAc 40/60 blend fibres in a DMSO/PF solvent

DMSO and 125 g vinylchloride-vinylacetate blend polymer were blended with a filtrated cellulose solution prepared as set forth in example 9. The blend darkened rapidly, gelled and it was not possible to produce fibres out of it.