Title of Invention

PROCESS FOR MANUFACTURING FLAME RETARDANT REGENERATED FIBRE

Abstract

A process for making flame retardant and glow proofed cellulose fibres/filaments by adding soluble salt of silica such as sodium silicate to a viscose in a proportion of 15 to 60% of SiO2 on cellulose basis by weight, extruding the blended viscose containing mixture so obtained into an acidic spin bath such as herein described, and spun at a ripening index of 12-12˚ H, stretching, regenerating and after reating (fire proofing the resulting staple fibre or filaments.

Full Text

FORM 2 THE PATENTS ACT, 1970 ( 39 of 1970 ) & The Patents Rules, 2003 -PROVISIONAL / COMPLETE SPECIFICATION ( See section 10 and rule 13 ) 1, Title of the Invention : PROCESS FOR MANUFACTURING FLAME RET ARDANT REGENERATED FIBRE 2. Applicant(s) : Name, Nationality address ; BILA RESEARCH INSTITUTE FOR APPLIED SCIENCES, ofBirIagram-456 331, Kagda (Madhya Pradesh), India. An Indian Institute. 3. Preamble to the description ^RQVlSIQNAb : T-fie4oUQwing--spocificatten describes-the invention* COMPLETE : The following specification particularly describes the invention and the manner in which it is to be performed. FIELD OF THE INVENTION This invention relates to a process for manufacturing flame retardant cellulosic fibres. This invention further relates to a process for manufacturing flame retardant regenerated cellulosic fibre by incorporating a soluble salt of silica in viscose, in particular flame resistant cellulosic fibre which is also resistant to smoldering and glow. BACK6R0UND OF THE INVENTION The world demand for inherently flame resistant synthetic fibres has increased sharply over the last few years. This trend is a result of increasing safety awareness of the population specially in highly developed and industrialized countries. Consequently, a number of special process technologies have been developed to produce combustion resistant textiles by finishing or dope additive techniques. In general the flame retardant chemicals are selected from the faiaily of compounds of phosphorous, antimony, sulphur, halogens etc. However, many of these are not eco—friendly due to their hazardous nature. Sandoa-Switzerland had developed a series of Pyrophosphate compounds as flame resistant additives. Gut of these, Sandoflam 5060 (,2"-oxybis C5,5-dimethyl~l,3,2—dioKaphosphorinane3-2,2"~disulphide> was found to be very suitable for producing 2 flame retardant viscose fibre with a dose of 20% on cellulose. However the cost of this chemical is very high and thus the process becomes highly cost intensive. More over the fibre containing this compound on burning produces toxic gases. On the other hand, the fibres containing silicon dioxide are considered out standing in their fire resistant characeristics. Such fibres are manufactured by number of methods. In some method, silica (Si02)fibres are prepared by dry spinning method from a water glass solution as described in US Patent4786017, US Patent 4332601 and Pol. Patent 88193- These methods produce the fibres of silicon dioxide but do not contain the natural or synthetic polymers like cellulose. In another disclosure, in SB Patent 106427, where sodium silicate is mixed with viscose (cellulose xanthate solution) and regenerated in to cellulose embedded with silicic acid. The fibres manufactured in this method contained large amount of silica and are further given a heat treatment in a muffle to convert it in to a porous sintered fibres of Si02 - The cellulosic fibres containing silica, as produced in above method shows serious disadvantages when given an alkaline treatment. In alkaline washing treatment the silica content disssolves out and the flame retarding effect is nullified after sowe washings. To overcome these problems, a process in US Patent 5417752 is described where the silicon dioxide alkaline solution is mixed 3 with viscose solution and the polysilicic acid is precipitated during the regeneration process. The fibres are further treated with sodium aluminate to attach aluminum ions to the polysilicic acid molecules. This treatment converts the polysilicic acid into aluminum silicate which is quite insoluble and thus withstand the washing treatments. The fibre of this invention shows very good flame retarding effect when Si02 +Al2O content is above 30% in fibre. Although these fibres show very good flame retarding characteristics as well as high L01(Limiting Oxygen Index) value, it is observed that the fabrics/ropes or bales made from these fibres show after glow behaviour i.e. they glow spontaneously without flame. Another major drawback of sodium aluminate treatment is that when the fibre mass comes in contact with the sodium aluminate solution, some of the aluminates get precipitated in the form of alumina tri hydrate (Al2O3 3H2 O)ch is insoluable in water or alkali. The conent of these precipitates increases during the circulation of the solution and a major portion is carried over by the fibre mats. These precipitates adhere on the presssing rollers and thus making the movement of fibre mats difficult. The precipitate carried over by the fibre mats get dried in the dryers and they spread as a dust in nearby zone making the working atmosphere inconvenient and unfreindly. This also 4 indicates the poor stability of the sodium aluminate in the stock solution. The dust problem is also observed in down stream processing of fibres. It is also observed that the loading of Si02 on cellulose basis should be above 40% for getting acceptable flame retarding effect when flame proofing is done with sodium aluminate*.This higher loading of SiO2 in the fibre reduces the fibre strength to a proportion of SiO2 causing the weak fibre production. Further, the consumption of sodium silicate in the known art is quite high as it needed about 40% SiO2 on cellulose weight basis to produce FR-fibre with sodium aluminate as fire proofing compound. OBJECTS OF THE INVENTION It is therefore an object of this invention to propose a process for manufacturing flame retardant cellulosic fibres containing silica compound which has better fire resistant and anti-glow properties. It is a further objection of this invention to propose a process for manufacturing fibres which is dust free and eco-friendly. Another object of this invention is to propose a process for manufacturing fibres whereby the strength of the fibres is increased. 5 Yet another object of this invention is to propose a process for manufacturing fibres which is cost-effective. These and other objects and advantages of the invention will be apparent from the ensuing description. DESCRIPTION OF THE INVENTION Thus according to this invention is provided a process for making flame retardant and glow proofed cellulose fibres/filaments by adding soluble salt of silica such as sodium silicate to a viscose, extruding the blended viscose containing mixture so obtained in to an acidic spin bath stretching, regenerating and after treating the resulting staple fibre or filaments. It is surprisingly observed that if the SiOz containing fibre is treated with poly-aluminum ions, the Silicon dioxide molecules get attached with poly-aluminum ions to form a cross-linking net work. This net work enhances the flame resistant characteristic of fibre and thus prevents the smoldering and after glow effect. The viscose preparation is carried out by any known conventional process such as described in Indian Patent 173872 or Indian Patent 183477, where the cellose pulp is treated with 18-19% sodium hydroxide solution to convert it into alkali-cellulose which is further shredded after removing the excess of alkali. 6 The shredded alkali-cellulose is aged to involve depolymerisation of cellulose molecules to a desired level of 300-350 DP (Degree of polymerisation). Aging is carried out in an atmospheric oxygen o for a period of 3-5 hours at 40-46 C. The aged alkali-cellulose is then reacted with 30-36% carbon disulphide on cellulose weight basis to form sodium cellulose xanthate. This xanthate is further dissolved in dilute sodium hydroxide solution in a dissolver equipped with stirrers and cooling arrangements for a period of o 2-3 hours. The temperature in the dissolver is kept below 20 C. The solution of sodium cellulose xanthate is known as viscose. The viscose composition is maintained as 7—10% cellulose, 4—6.5% sodium hydroxide, 60—70 seconds of ball fall viscosity (hereinafter described as B.F.). The alkaline solution of sodium silicate can be added at any stage after completion of dissolution of cellulose xanthate, viz. i. In the dissolver after completion of dissolution of sodium cellulose xanthate. ii. After filtration of viscose. iii. Prior to spinning at spinning machine by injection method. However it is preferable to incorporate the sodium silicate solution in the dissolver before filtration and mix well so that the sodium silicate gets uniformly mixed in the viscose. The concentration of sodium silicate solution before mixing in 7 viscose should be in the range of 18-20% as SiO2. The higher con¬centration of silicate should be diluted with 10-15% NaOH solution to get 18-20% SiO2 -It is also preferred to filter the sodium silicate solution to remove any impurities or precipitated silica. 18-20% SiO2 in the silicate solution is maintained to keep the viscose viscosity nearly same to that of pure viscose. Lower concentration of SiO2 will reduce the viscose viscosity whereas higher concentration may result into increased viscosity and gelling problems. The concentration of SiO may change for a viscose of other composition. The process of manufacturing flame retarding fibre, begins with the blending of alkaline solution of sodium silicate and viscose in proportion to keep the concentration of silicon di oxide SiO2 to about 15-60% by weight on cellulose, preferably 20-50% by weight, the content of cellulose is about 6-12%, preferably 7-9% and the NaOH concentration is about 5-10% preferably 6-8% by weight. All components measured are as dry weight basis. Optionally, the viscose composition may contain viscose additives such as condensate product of glycols and amines in the range of 0.1—1.0% on cellulose basis for proper xanthation reaction and ease of filtration. 8 The composition of blended solution of sodium silicate and viscose (hereinafter described as blended viscose) is in the range of 6-9% cellulose, 6-8% NaQH, 3-4% SiO2 , 2-4-2.8% CS2 and 4S-60 second B.F. viscosity. All components are based on blended viscose basis by weight. The blended viscose of sodium silicate and viscose is properly filtered, deaerated and ripened. The ripening of blended viscose is an important parameter since the polymeric silica precipitates only when the regeneration of fibre is slow. By extensive experimentation it is found that the ripening index (R I) of above 14°H (Hottenroth Index, by ammonium chloride method) is suitable for a viscose of present invention. The lower Rl of viscose shows reduced loading of silica in the fibre indicating that the silica gets dissolved out in the regeneration or washing zones. The R.I of the viscose at spinning is maintained between 12-22°H, preferably by 14-18°H. The well ripened viscose is transformed in to a desired shape like fibre or filaments by spinning technique. The metered quantity of blended viscose is passed through spinnerets of 50- 100 microns hole diameter into an acidic spin bath. The precipitation of cellulose and silicon dioxide takes place in the same manner as normal viscose. A solid polymer of silicon dioxide and cellulose in the form of filament is formed when the blended viscose comes in contact of acidic spin bath. The acidic spin bath contains 105-150 g/l sulphuric acid, preferably 110-140 g/l sulphuric acid, 250-380 g/l sodium sulphate, preferably 300-360 g/l sodium sulphate, 6-20 g/l, preferably 6-12 g/l aluminium sulphate or zinc sulphate at a temperature of 35-55, preferably 40-50 °C. The commercially available sodium silicate contains 25-32% Si02 and the preferable range of molar ratio by weight of,Sj02.: Na2O is 1.8-2.5 for the present invention. The sodium silicate solution must be therefore diluted to about 18-20% as Si02 by adding 10-15% sodium hydroxide solution. The diluted sodium silicate solution should be filtered through a cotton cloth/ cotton pad or some other suitable filter media. The concentration of 18-20% Si02 in sodium silicate before adding in viscose is preferable to maintain the viscosity of viscose to its original state. Thespinning is carried out with a spinnerets having 5000-40000 orifices with 50-100 micron hole dia. The immersion depth of spinneret in the spin bath is to be kept 50-60 cm for proper precipitation of silicon dioxide in polymeric form in the fibre matrix. The regenerated tow from the spin bath is stretched between take up godet and stretching roller to about 40-70% in air, preferably 50-6554. After stretching the tow is drawn into cutter where they are cut into desired length for example 30-120 HMD.1 The cut fibres are regenerated in acid bath of 5-30 g/1 sulphuric o acid at 70-100 C and washed with water. After this washing stage the treatment of poly-aluminnium ions as fire proofing agent according to this invention can be carried out. The poly—aluminium ions will then react strongly with the surface of polymeric silica to form a layer of aluminium silicate which is more stable in alkaline and acidic bath and thus retains in the fibre even after repeated washing. Poly-aluminium ions may preferably be used from poly—aluminum chloride (PAC). The treatment can be carried out with a solution of poly-aluminum chloride at a concentration of 5—50 g/1 as Al2O3 at a o o temperature of 20-60 C preferably 30—50 C for sufficient time. These fibres do not show any glow after removing/extinguishing the flame. There is no problem of precipitate or dust at any stage in the process, thus making the process eco—friendly. Obviously, the treatment of poly—aluminium ions can also be carried out at any suitble stage after the regeneration bath, for example at stretching stage or CS2 recovering stage or after desulphurization stage or when the fibre has been further processed i.e. during dyeing, yarn making or at fabric stage. The 11 method may be used for the production of fibres or filaments in which case the alumina modification is carried out during purifi¬cation after the regeneration of fibres/filaments. The fibres have been tested to assess their performance and the results are provided hereinbelow. Flammability Assessment Test Following arbitrary test method was developed at Birla Research Institute to assess the flame retarding characteristics of fibre which gives reproducible result and is a quicker method to measure the combustion characteristics—both flaming and, glowing behaviour of fibres in the form of rope. Take 1 gm of dry fibre, open it properly and condition it at o 65% RH at 25 C for 2-4 hours. Make a lea of about 12 inches by hand and twist it sufficiently and make a rope of two ply of 6" length. Hang this rope on a supporting rod in a draft free atmos¬phere. Take an acetone burner 12 the total char length after 5 minutes of glowing. Glow char length is determined by subtracting the initial char length from total char length. Assess the flame retarding character of the fibre as belaw:- 1. If rope burns easily 8e flame propagates — Highly flammable/Low to entire length flame resistant 13 2. If rope burns and gets extinguished after removing the flame, measure the initial char length A. If initial char length is 100 + 30 mm - Moderate flame retardant B. If initial char length is 50 ± 20 mm - Good flame retardant C. If initial char length is below 30 mm -- Excellent flame retardant 3. Glowing or smoldering character is determined by measuring the glow char length after 5 minutes of extinguishing the flame. A. If glow char length is 20 - 30 mm -- Poor glow resistant B. If glow char length is 10- 20 mm - Moderate glow resistant C. If glow char length is 1-10 mm - Good glow resistant D. If glow char length is 0-1 mm - Excellent glow resistant The invention is further/described in the following examples, however they are limiting™* * not regarded as-*tesd*ffiii©*rthe scope of invention. EXAMPLE-1 The viscose was prepared in a conventional manner. To a ready viscose, 182 gm of technical grade sodium silicate (water glass containing 20% Si02) per kg of viscose was added and mixed thoroughly. The blended viscose thus containing 40% Si02 on cellulose basis by weight. Before adding the sodium silicate the viscose contained 9.1% cellulose, 5.46% sodium hydroxide and 32.5% CS2 on cellulose basis and had a viscosity of 55 seconds at 20° C by ball fall method (herein after described as BF). After addition of sodium silicate the proportions of content were, 7.7% cellulose, 3.08% Si02, 6.7% NaOH and viscosity of 59 BF. 14 After filtration, deaeration and attaining the blended viscose (viscose-sodium silicate mixture) flow was metered for 3 denier fibre and was spun through a spinneret of 65 hole diameter in the spin bath containing 135 g/l sulphuric acid, 350 g/l sodium sulphate and 8 g/l aluminum sulphate. The temperature of spin bath was 45°C. The spinneret was immersed to the depth of 50 cm in the spin bath. The filaments coagulated in the spin bath were drawn over rollers and stretched between take-up godet and stretching rollers to a length of 57% greater than its original length. The spinning speed was 42 m/min. The tow was then led to a cutter where it was cut in to staple length of 51 mm The cut fibres were regenerated completely in an acidic bath of 20 g/l H2SO4 at temperature of above 90°C and washed with hot water. After this the fibre mat was treated with different concentration of poly-aluminum chloride solution at 40°C followed by hot water washing. The fibres were further treated with desulf bath containing 0.5-1 g/l NaOH, bleached with sodium hypochlorite and finished with surface active agent in a similar manner as regular rayon. The another portion of cut fibre was also treated with varying concentration of sodium aluminate solution for comparing the fibre properties. The dry fibres were analysed for their ash content and textile properties. Ash in the fibre was determined by igniting the fibre at 750°C for 90 minutes. Ash obtained in this manner was pure silica and if it was treated with PAC or sodium aluminate it also contained certain quantities of AI2O3. The fibre properties are reported in table-1. 15 Table -1 Ash and textile properties of fibres treated with different liquors Treatment Cone, of Temp Denier Cond. Cond. Ash liquor treatment liquor tenacity elongation (g/l) °C g/d % % The above table shows that the treatment with PAC (poly-aluminum chloride) produces similar fibre properties as that of sodium aluminate with marginal lower ash contents. The Table-2 shows the results of flame test. Table - 2 Flame test PAC NaAI02 Poly-aluminum chloride Sodium aluminate Thus, from the above table it is evident that the use of PAC, even at lower concentration of treatment liquor, the fibre shows excellent.flame retarding character as well as excellent glow/ smoldering resistance. Example - 2 Viscose was prepared in a manner as described in example - 1. 132 gm of commercial grade sodium silicate containing 28% Si02 was diluted with 53 gm of 10% NaOH solution to get 20% Si02 in final silicate solution. This solution was filtered and added to 1 kg of ready viscose. Before adding the sodium silicate, the viscose composition was 9.25% cellulose, 5.55% NaOH and the viscosity was 60 second BF. After addition of sodium silicate the contents were, cellulose 7,8%, NaOH 7.02%, Si02 3.12%, all on viscose weight basis. The viscosity was 59 second BF. The viscose and sodium silicate containing mixture was filtered, deaerated and ripened to get R.l. of 15°H. Metered amount of blended viscose adjusted for different deniers was passed through spinnerets of 65 for 1.5-3 denier and 90 for higher deniers to a spin bath containing 130—135 g/J H2SO4, 8 g/l AI2(S04)3 and 350 g/l Na2S04- The temperature of spin bath was 45°C. The tow coming out from the spin bath was led over the godets and stretched in air to 55% between godet and stretching rollers. The spinning speed was 40 m/min. The tow was then cut in to staple length of 51 mm. The cut fibre was treated with 1-2% sulphuric acid at 95°C for complete regeneration of cellulose. After regeneration the fibre mat was washed with hot water and treated with a solution of 20 g/l poly-aluminum chloride (PAC) at 40°C-for attaching poly-aluminum ions to silica content of the fibre The fibre mat was further washed and treated as regular rayon i.e. desulphurising with 1 g/l NaOH, bleached with sodium hypochlorite, finished and dried. These fibres neither produce any dust at dryer or baling stages nor precipitates at treatment / washing stages. Table - 3 shows the properties of fibre produced in example -2. Table - 3 Properties of fibre samples Treatment Fibre Fibre Properties " Flame Liquor Denier Cond. Cond. Ash AI203 Resistant asAl203 Tenacity Elongation (g/l) g/d % % % PAC, 20 1.50 1.52 18.5 30.5 4.8 Excellent PAC, 20 3.16 1.47 20.1 . 31.8 5.1 Excellent PAC, 20 4.5 1.51 21.5 323 5.2 Excellent PAC, 20 6.0 1.58 24.4 33.0 5.3 Excellent PAC, 20 6.9 1.46 24.1 33.5 5.5 Excellent PAC, 20 8.8 1.36 22.9 33.8 5.8 Excellent 18 Example - 3 Staple fibres were prepared in the same manner as described in Example - 1 by mixing varying amount of sodium silicate in the viscose. The cut fibres were regenerated and treated with 20 g/l solution of poly-aluminum chloride (PAC) as AI2O3 at 40°C. Flame resistant test was carried out and results are presented in Table - 4. Table 4 Fibre Properties Sod. Silicate Spin- Fibre Properties Flame Glow As Si02, bath Denier Cond. Cond. Ash Resistant Resistant on cellulose Acid Tenacity Elongation % g/l g/d % % 10 105 3 2.45 20.5 8.3 Poor 20 115 3 2.25 20.8 17.8 Good Moderate Good 25 120 3 1.88 21.2 22.2 -Moderate- Excellent 30 125 3 1.75 21.6 25.7 Excellent Excellent 35 130 3 1.63 22.5 28.1 Excellent Excellent 40 135 3 1.55 23.0 31.5 Excellent Excellent 50 140 3 1.37 25.5 34.6 Excellent Excellent 19 Example - 4 Staple fibres were prepared as described in example-1 and regenerated fibres were treated with varying concentration of fire proofing agents. The fibres were converted into non-woven fabrics of 200 gm/m2 and LOI was determined according to standard IS-13501 method. The results are reported in Table - 5. Table-5 Limiting Oxygen Index Value Treatment Liquor Ash Fibre quality Grammage LOI g/l % Den x mm g / m2 0 (w/o treatment) 27.0 1.5Dx51 200 26.7 0 (w/o treatment) 26.5 3D x 51 200 25.7 10g/IPAC 29.5 3D x 51 200 34.5 20 g/l PAC 31.0 3D x 51 200 36.6 30 g/l PAC 31.4 3D x 51 200 39.2 40 g/l PAC 32.0 3D x 51 200 40.0 20 g/l NaAI02 30.0 3D x 51 200 30.0 30 g/lNaA102 31.5 3 D x 51" 200 31.5 40 g/lNaAIC-2 33.5 3 D x 51 200 34.0 Example - 5 Staple fibre of 3 denier x 51 mm was prepared in the same manner as described in example-2. The fire proofing was carried out with different compounds of soluble aluminum salts. The ash content and flammability characteristics were evaluated. The results are presented in Table - 6. Table - 6 Fire proofing trials with different aluminum compounds Cone, of fire S. Ash Flame Glow Fire Proofing Agents proofing No. % Resistant Resistant agents (g/l) 1. Control (w/o fire proofed) - 27.0 Moderate Poor 2. Aluminum Sulphate 40 27.0 Moderate Poor 3. Sodium Aluminate 40 33.5 Excellent Moderate 4. Poly-aluminum Chloride 40 32.5 Excellent Excellent 5. Poly-aluminum Chloride 20 31.5 Excellent Excellent Above table shows that the ash content and flame/glow resistant characteristics of non-fire proofed (i.e. control) and that of aluminum sulphate treated fibres are same. The ash content is 27% in both cases. The flame resistant and glow resistant properties are also almost same indicating that aluminum sulphate does not show any fire proofing effect on silica containing fibres. The ash content of sodium aluminate treated sample is 33.5% and that of PAC treated sample is 32.5%. Although the sodium aluminate treated fibre shows excellent flame retarding character but is inferior in glow resistant properties than PAC. This is evident that PAC is better flame retarding as well as glow resistant agent than sodium aluminate. Example - 6 Sodium silicate blended viscose was prepared in the same manner as described in example-1 containing 40% Si02 on cellulose basis. The blended viscose was filtered, deaerated and spun at varying ripening index (R.I.). The regenerated fibre was treated with PAC as fire proofing agents of 20 g/l concentration at 40°C and NaAI02 of 40 g/l at 60°C. The fibre was further conventionally treated with desulphuring and bleaching baths and finished with lubricating agents. The ash and flame resistant properties were measured and reported in Table-7. 21 Table - 7 : Effect of spinning R.I. on flame retarding properties of fibre The above table indicates that the polymeric form of silica (which is less soluble in after treatment and washing liquor) is precipitated only at higher R.I. i.e. above 14°H. At lower Rl, a major part of silica is washed out showing that the silica precipitated below 14°H is soluble form. This is also indicative with ash content and flame tests. Therefore, the ripening index of blended viscose at the time of spinning is an important parameter of the present invention. 7. The process as claimed in claims 1 and 6 wherein the soluble silica compound is sodium silicate and fire proofing agent is poly—aluminum ions. 8. A process as claimed in claims 1 & 7,wherein the poly-aluminum ions are supplied from poly—aluminum chloride. 9. The process as claimed in claim 6 wherein the silicon dioxide containing fibre/ filaments are after treated with poly-aluminum chloride solution containing 5—50 g/1 as Al2 O3 preferaby 10-30 g/1 Poly—aluminum chloride as Al2 03 • 10. A method of making flame/glow retandant fibres/filaments, substantially herein before described with reference to examples. Dated this 25th day of FEBRUARY 2005

Documents:

219-mum-2005-abstract(11-12-2006).doc

219-mum-2005-abstract(11-12-2006).pdf

219-mum-2005-cancelled pages(11-12-2006).pdf

219-mum-2005-claims(granted)-(11-12-2006).doc

219-mum-2005-claims(granted)-(11-12-2006).pdf

219-mum-2005-correspondence(22-8-2008).pdf

219-mum-2005-correspondence(ipo)-(18-10-2006).pdf

219-mum-2005-form 1(28-2-2005).pdf

219-mum-2005-form 18(22-8-2005).pdf

219-mum-2005-form 2(granted)-(11-12-2006).doc

219-mum-2005-form 2(granted)-(11-12-2006).pdf

219-mum-2005-form 3(28-2-2005).pdf

219-mum-2005-petition under rule137(18-10-2007).pdf