FLAME-RETARDANT MATERIALS

Abstract: The invention pertains to flame-retardant material prepared from hydrates of polymers that can be used for the manufacture of flame-retardant materials, such as composites, fabrics, non-wovens, films, foams, and paper, with a significant improvement with respect to the non-hydrated materials. Preferred are hydrates of hydroxy-containing polymers, and more preferably fully hydrated rigid rod polymers, in particular fully hydrated PIPD fibers.

Description: FLAME-RETARDANT MATERIALS The invention pertains to flame-retardant materials, and to the use of said materials for the manufacture of flame-retardant composite material, non- woven material, fabric, film, foam, or paper. It is known that some synthetic polymers are suitable for the manufacture of flame-retardant materials. Polymers with recognized flame-retardant properties are, for instance, Twaron® (p-aramid), PIPD (poly{2,6- diimidazo[4,5-b:4',5'-e]pyridinylene-1 ,4-(2,5-dihydroxy)phenylene}; formerly known as M5), and other rigid rod polymers such as PBO (poly-p- phenylenebenzobisoxazole). Fibers of these materials can be used to make composites, non-wovens, fabrics, films, foams, paper, and other materials for use as flame-retardant materials with low heat release and long ignition times. These materials constitute a considerable improvement over older materials, which are high-weight materials or are toxic (such as asbestos). Nevertheless, there is still a need for further improvement It has now been found that spun fibers, films, foams, and injection-molded articles prepared from hydrates of polymers can be used for the manufacture of flame-retardant materials with a significant improvement over non-hydrated fibers, films, foams, or articles. Although the principle of the present invention applies for all types of polymers, the fibers, films, foams, or injection-molded articles are preferably made of hydrates of hydroxy-containing polymers, more preferably hydroxy- containing rigid rod polymers, and, even more preferably, of hydrates of PIPD. Rigid rod polymers based on pyridobisimidazole have been described, int.al., in US-A-4,533,692. PIPD rigid rod polymers have been described in WO 94/25506. The invention now provides, preferably, flame-retardant materials of a rigid rod polymer in which at least 50% of the recurring groups corresponds to the formula: Preferably, at least 50% of the rigid rod polymers according to the present invention is composed of recurring groups of pyridobisimidazole-2,6- diyl(2,5-dihydroxy-p-phenylene), while in the remaining groups the 2,5- dihydroxy-p-phenylene is replaced by an arylene which may be substituted or not and/or the pyridobisimidazole is replaced by benzobisimidazole, benzobisthiazole, benzobisoxazole, pyridobisthiazole, and/or pyridobis- oxazole. Preference is given in that case to polymers at least 75% of the recurring groups of which is made up of pyridobisimidazole-2,6-diyl(2,5- dihydroxy-p-phenylene), while in the remaining groups the 2,5-dihydroxy-p- phenylene is replaced by an arylene which may be substituted or not and/or the pyridobisimidazole is replaced by benzobisimidazole, benzobisthiazole, benzobisoxazole, pyridobisthiazole, and/or pyridobisoxazole. In the case of partial replacement (up to 50% at most) of the 2,5-dihydroxy-p-phenylene, preference is given to a compound which is left after removal of the carboxyl groups of an arylene dicarboxylic acid such as isophthalic acid, terephthalic acid, 2,5-pyridine dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-diphenyl dicarboxylic acid, 2,6-quinoline dicarboxylic acid, and 2,6-bis(4-carboxyphenyl)pyridobisimidazole. For the making of one- or two-dimensional objects, such as fibers, films, foams, tapes, composites, and the like, the polymer of the present invention is brought to the form of its hydrate by spinning of a solution of the polymer in a suitable solvent (for instance, polyphosphoric acid) into water or dilute phosphoric acid, made into a film or foam in the presence of water by methods common in the art, or brought to the form of its hydrate by injection-molding the polymer into water. After spinning the fibers are not or only partially dehydrated and, preferably, are used as such without undergoing any dehydrating heat treatment at all. The hydrate content of the fiber, film, foam, or injection-molded article is >10 wt.%, preferably >20 wt.%, at 21 °C and 65% RH (relative humidity). The polymer can maximally contain one molecule water per hydroxy group (for PIPD 21.4 wt.%), and for fibers, films, and foams usually somewhat more because of water contained in the voids (for PIPD the maximum total water content is up to 25 wt.%). The hydrated fibers, films, foams, and articles are not heat treated and are used as such for the manufacture of composites, fabrics, non-wovens, papers, and the like. Products obtainable from the polymers preferably are made with 100% hydrated polymers. The preparation of the PIPD homopolymer can be carried out by the incorporation, with vigorous stirring, of the salt of 2,5-dihydroxyterephthalic acid and tetraaminopyridine into strong polyphosphoric acid followed by heating (see WO 94/25506). The polymer is then precipitated in water using a spinning arrangement, and washed with an alkaline solution, such as ammonia. The mixture obtained from the polymerization reaction can be used directly for spinning or extrusion into fibers, films, foams, or tapes without any further measures or additions to the mixture being required, and thereafter used in composites, fabrics, and the like. Hence, in a preferred embodiment for making fibers, the polymer is prepared and spun or extruded in one continuous process, Also, films, foams, or tapes can be made directly from the composition, which is obtained from the solution resulting from the polymerization reaction. These objects such as fibers, tapes, foams, or films can be applied either as such and, hence, consist of the polymer of the present invention, or they can be used in combination with similar objects made of another material. In the latter case, products can be made which comprise the objects of the present invention in combination with other materials. Advantageously, the products may be applied as reinforcement material in products which are used at high temperatures, or where the temperature can increase and where flame-retardancy is a required property. Furthermore, the fibers may be cut and used as staple fiber or, when fibrillated, as pulp, for instance, in paper making. The thermal stability and the flame-retardancy of the polymer of the present invention were found to be very good, with very low loss of the mechanical characteristics of the fibers made thereof. The materials of this invention can be applied in fire barrier materials, such as suits worn by firemen and boundarymen aboard ships, battle helmets, flak vests, fire protection blankets, and the like. To demonstrate that the products of the present invention have flame- retardant properties unique to an organic polymer fiber, fibers of the material of the present invention were tested using a Cone calorimeter. This test provides a good indication of several different characteristics, e.g., the peak heat release rate (PHRR), the time to ignition (TTI), the total specific extinction area (SEA), and the fire performance index (FPI). The as-spun yarns prepared from the polymer according to the present invention, which have not received an after-treatment, were found to have superior properties with respect to known non-hydrated polymers. The invention is further illustrated by the following examples: Example 1 Preparation of tetraaminopyridinium dihydroxy terephthalate In degassed water under a nitrogen atmosphere, the following solutions were made: a) 9.91 g of 2,5-dihydroxyterephthalic acid and 6.05 g of NaOH in 140 g of water, by heating with stirring to about 50°C; b) 13.33 g of tetraamino pyridine hydrochloride in 95 g of water, at room temperature. With vigorous stirring and without the introduction of any air b) was added to a), producing a rich yellow precipitate. After further adiabatic stirring for 5 minutes, the slurry was cooled, with stirring, to about 10°C and filtered, washed three times with about 250 ml of degassed water and twice with degassed ethanol, all this without the introduction of air, flushed with nitrogen for 45 minutes, and dried at 0.1 MPa at 50°C for 18 hours to produce 16.56 grams (which corresponds to a yield of 98.2%) salt of tetraaminopyridine and 2,5-dihydroxyterephthalic acid. This salt showed a 1 :1 tetraaminopyridine/2,5-dihydroxyterephthalic acid composition in NMR. It was found possible to polymerize it to very high DP polymer under standard conditions. 185.51 grams of this salt, 1.0 gram of tin powder, 732.41 grams of 84%- polyphosphoric acid, and 124.06 grams of P 2 O 5 were heated in 0.25 hours to 100°C, with stirring, and kept at 100°C for 0.75 hours with stirring at an increasing rate. The slurry was further heated to 140°C in 0.67 hours and kept at that temperature, with stirring, for another 55 minutes. The temperature was further increased to 180°C in 0.33 hours and the slurry was stirred at that temperature for another 2.25 hours, after which the contents of the autoclave were fed to a storage chamber of a polymer extruder. A little polymer was taken from the autoclave to determine the η re ι, which was found to be 31.6. Example 2 The polymer obtained from Example 2 with a polymer concentration of 14 wt.% was fed at a temperature of 195°C to a 0.6 m 1 metering pump by means of a 19 mm single screw extruder. The polymer was passed through a 25 μm filter package and subsequently extruded at a throughput of 6.5 mVmin and a temperature of 205°C through a spinneret containing 40 spinning holes of a diameter of 100 μm. Fibers were produced by a dry-jet-wet spinning technique, with water being used as the coagulation medium. The air gap length was 20 mm, the draw ratio in the air gap 4.65. The fibers were wound onto a bobbin, and washed with water for 48 hours, neutralized with ammonia, and washed again. These undried fibers (AS-PIPD) were used as such. Example 3 Between 10.3 g and 11.5 g of a sample of AS-PIPD (PIPD as spun, hydrated PIPD), PIPD (non-hydrated PIPD), PBO-HM (high-modulus PBO), Twaron® (poly(p-phenyleneterephthalamide)), Nomex® (poly(m-phenylene- terephthalamide)), or PVC (polyvinylchloride with the stabilizers Phosflex 41 and zinc borate) was brought into a Cone calorimeter having a heat release of 75 kW/m 2 . The calorimeter has a heating mantle for constant heat transfer to a sample of standard size. A spark plug was used to generate sparks. After a burning time of 5 sec the spark plug was removed. When the sample was extinguished, the spark plug was replaced until the sample burnt again. The PHRR, which gives the maximum heat release, the TTI, which is the time the sample needs from the start of the test to continuously burn, the SEA, which is the total extinction of light measured by a laser and a receiver during the test, and the FPI, which is the fire performance index obtained by the quotient of TTI/PHRR, were measured. The PHRR is a measure for flame retardancy. The lower the value, the better the flame retardancy. The TTI value should be as high a possible. The SEA is a measure for smoke release. A low value is beneficial. The following data were measured: Conclusion: in all respects the hydrated PIPD (AS-PIPD) has better flame- retardant properties than the other non-hydrated polymers. Example 4 In the same manner as described above in Example 3, the PHRR, TTI, SEA, and FPI values for chitosan hydrate were compared with those of chitosan. Conclusion: in most respects the hydrated chitosan has better flame- retardant properties than the non-hydrated chitosan. Example 5 The heat absorption of various PIPD samples was measured with a Setaram C80D calorimeter. An open cell using 1 g of material and a scan rate of 0.2 °C/min yielded scans from 30 to 200°C. The scans show the specific heat as a function of temperature and the absorption of heat due to the evaporation of water from the open cell. The test samples contained AS-PIPD (hydrated PIPD as spun), ASd-PIPD (dried PIPD as spun), HT- PIPD (heat treated partially hydrated PIPD), or HTd-PIPD (heat treated dried PIPD). The higher the heat absorption, the greater the flame-retardant effect. The table lists the absorbed heat: Example 6 The water content of the hydrate of the hydroxy-containing rigid rod polymer was determined as follows: The mass (m b ) of a sample of the material is determined. The sample is then dried at 150°C at <0.133 kPa during 16 to 20 h, after which the dry mass (m a ) of the sample is determined immediately. The water content is then calculated to be 100.(m -ma)/m b %.

Claims: Claims 1. A flame-retardant material comprising spun fibers, film, foam, or injection-molded articles containing a hydrate of a polymer. 2. The flame-retardant material of claim 1 wherein the polymer is a hydroxy-containing polymer. 3. The flame-retardant material of claim 2 wherein the polymer is a hydroxy-containing rigid rod polymer. 4. The flame-retardant material of claim 3 wherein the polymer is PIPD. 5. The flame-retardant material of any one of claims 1-4 wherein the hydrate content is >10 wt.%, preferably >20 wt.%, at 21 °C and 65% RH. 6. The flame-retardant material of any one of claims 1-5 wherein the material is a composite material, non-woven material, fabric, foam, or paper. 7. The flame-retardant material of any one of claims 1-5 wherein the material comprises spun fibers. 8. Use of the flame-retardant material of any one of claims 1-7 for the manufacture of a flame-retardant composite material, non-woven material, fabric, film, foam, or paper.

Inventors: NORTHOLT MAURITS GERHARD, SIKKEMA DOETZE JAKOB, NORTHOLT, MAURITS, GERHARD, SIKKEMA, DOETZE, JAKOB
Applicants: AKZO NOBEL NV, NORTHOLT MAURITS GERHARD, SIKKEMA DOETZE JAKOB, AKZO NOBEL N.V., NORTHOLT, MAURITS, GERHARD, SIKKEMA, DOETZE, JAKOB
Application year: 1998
Main classification: D01F6
IPC codes: D01F6