and a method for its production

This invention relates to flexible polyurethane foam with reduced flammability and a method for its production, wherein the foam is modified to improve useful properties and fire resistance of the porous polymer.

Increasing demands are placed to the foamed polyurethanes regarding their functional, mechanical properties and fire resistance. Therefore, the interest in obtaining and modification of the polyurethane foams continues to increase. In recent years, much emphasis was placed on the modification of polyurethanes and other polymers using environmentally friendly compounds - containing no halogen, antimony oxide or melamine cyanurate. A very important aspect of the polyurethane foam synthesis are their functional properties, and fire resistance in many cases. One of the most important issues while reducing the flammability of the polyurethane foam is to minimize the dripping phenomenon that causes the spread of fire. In order to improve the selected properties of the porous polyurethane, the matrix of polymer is modified with additive and/or reactive additives of various kinds. In the last half-century, special attention is paid to polymers with the addition of nanofillers. Very often silicon-containing compounds are used as nano additives. Properly conducted modification of the polyurethane foams with such compounds may allow to improve their useful, mechanical and other properties. In addition, an accurate selection of synergistically acting system of industrial flame retardants and modified silicate, as well as, properly designed and prepared modified polyurethane foam may have an increased flame resistance.

The publication of the article "Flammability reduction of flexible polyurethane foams via carbon nanofiber network formation" Poiym. Adv. TechnoL 2008. 19, 588-595 Zammarano M. et al, showed that the addition of carbon nanofibers to the industrial flame retardants system may allow to reduce the dripping phenomenon during samples combustion. A major disadvantage of that modified polyurethane is the use of bromine-containing environmentally unfriendly compounds as flame retardants.

In turn, in the publication of the article "Heat release and structural collapse of flexible polyurethane foam" Polymer Degradation and Stability 2010, 95, 11 15-1122 Kramer R.H. et al, the obtaining of the flexible polyurethane foam comprising phosphate flame-retardants was described. The resulting foam was characterized by lower efficient heat of combustion, lower flammability and a lower rate of heat release during combustion than the sample not containing flame retardants. The disadvantage of this known polyurethane foam is also the use of halogenated flame retardants in its formula.

From the invention publication No. WO 2015013226 Al and US 2007221892 Al modified, flexible polyurethane foams, characterized by increased flame resistance are known. A disadvantage of those known solutions is the addition of compounds containing halogen in their structure.

It is also known from the publication of the invention No. WO 2015050691 Al, the method for the obtaining the polyurethane foams with a clearly increased flame resistance. However, the toxic melamine cyanurate was added to the foam, and in addition, those polyurethane foams are foamed with fluorine-containing compounds.

In the patent publications and the scientific literature no solutions for improving the useful properties and flame resistance of the flexible polyurethane foams, containing as modifiers only halogen-free environmentally friendly compounds, including nanofillers, were found. According to the invention, a flexible polyurethane foam with reduced flammability, as the addition of at least one linear polyol with a diisocyanate, containing a nanofiller, is characterized in that as a nanofiller it contains a halloysite organically modified with melamine-formaldehyde adduct, wherein the said modified halloysite is in the form of grains fragmented to micrometric sizes.

Preferably, the flexible foam comprises a halogen-free flame retardants system with a various action mechanism, wherein the said system comprises the nanofiller and at least one additive flame retardant in the form of ammonium phosphate and/or boric acid.

According to the invention, a method for production a flexible polyurethane foam with reduced flammability comprising a nanofiller, and the foam is obtained from reaction of the polyol masterbatch of at least one linear polyol with a diisocyanate, in the presence of a polymerization catalyst, and in the presence of the surface tension reducing agents and water as a blowing agent, is characterized in that an organically modified and mechanically fragmented halloysite is used as a nanofiller, wherein the halloysite is previously modified with melamine-formaldehyde adduct, obtained with a molar ratio of melamine to formaldehyde from 1 : 1 to 1 : 4.

Preferably the melamine-formaldehyde adduct for modification of halloysite is prepared by heating a compound of melamine with formaldehyde in a molar ratio of melamine to formaldehyde of 1 : 2 under reflux condenser, at temperature near the boiling point of the compound, and the reaction is continued to obtain a water tolerance of the resin of 1 : 4. During the modification of halloysite the melamine-formaldehyde adduct is introduced into the halloysite as an aqueous solution and is mixed with it at elevated temperature to obtain a homogeneous compound, and then it is dried and fragmented into a product with micrometer-sized grains.

Further advantages are obtained when a halogen-free flame retardants system with a various action mechanism is introduced to the polyol masterbatch, 80 comprising the said nanofiller and at least one additive flame retardant in the form of ammonium phosphate and/or boric acid. The foam polyol masterbatch is prepared by mixing 50 ÷ 98% by weight of a polyol having a hydroxyl number of LOH = 20 ÷ 80 mg KOH/g, 2 ÷ 10% by weight of a foaming agent, 0.5 ÷ 8% by weight of a surface tension reducing agent, and 1 ÷ 10% by weight of a modified

85 halloysite, and 0.1 ÷ 40% by weight of additive flame retardants, preferably 1 ÷ 40% by weight of ammonium phosphate and/or 0.1 ÷ 10% of boric acid.

The polyol masterbatch is prepared in a multi-stage homogenization of polyol, foaming agents, foam stabilizers and flame retardants. In turn, the polyurethane foam is obtained in the reaction of diisocyanate, polyol masterbatch

90 and catalyst addition.

This invention relates to the flexible polyurethane foam with reduced flammability and the method for producing such foam, comprising a developed within the invention, modified halloysite as nanofiller. The polyurethane foams with those nanofillers are characterized by lower density than the foam containing 95 no additives. Moreover, the addition of that nanofiller results in the substantial elimination of drips during application of the flame to the foam. In addition, the foams containing the system of halogen-free flame retardants operating synergistically and the said nanofillers are characterized by an increased flame resistance.

The tests conducted in developing the present invention aimed at obtaining a flexible polyurethane foam, characterized by good functional properties and an increased flame resistance. During the works on the flame retardancy improving, the focus was primarily on minimizing the dripping phenomenon. During testing, a particular attention was paid to environment-friendly commercial flame retardants such as ammonium polyphosphate, boric acid, triethyl pyrophosphate, tribytyl polyphosphate, zinc borate, expanding graphite, melamine and nanofillers. After conducting numerous tests and modifications a foam containing a new nano-additive - modified halloysite inhibiting the dripping during the material combustion was obtained. The porous polyurethane was characterized by the 110 apparent density lower than the unmodified foam. Furthermore, due to adding to the polyurethane a nanofiller with appropriately selected flame retardants, a significant increase in the fire resistance of the obtained foam was achieved. During the preparation of those foams a proper selection of additives and method of homogenization of the composition was important.

115 The invention is illustrated by the examples that are not limiting the scope thereof.

Example 1

Preparation of the modified halloysite

A compound of the melamine with formalin neutralized to pH = 8.0 ÷ 8.5 120 in a molar ratio of the melamine to the formaldehyde of 1 : 2 is refluxed at temperature near the boiling point of the mixture. The reaction is conducted to obtain the resin water tolerance of 1 : 4. The modified halloysite is prepared by mixing the previously prepared melamine-formaldehyde adduct and unmodified halloysite at a mass ratio of 4: 1. The resulting mixture is allowed to stand for 24 125 hours at room temperature. The compound is then dried in an oven for 4 hours at 110 °C. The dried halloysite is ground in a ball mill and then screened through a sieve having a mesh of 80 μm.

Preparation of the polyol masterbatch

The polyol masterbatch is prepared by mixing the following ingredients: 130 93% of Rokopol 3600 polyol having a hydroxyl number of LOH = 45 ÷ 50 mg KOH/g; 1.9% of silicone oil having a viscosity of <50 mPas, 2.3% of distilled water, 2.8% of modified halloysite. The compound is homogenized for 50 min in a high shear mixer with a turbine stirrer rotation speed of 5000 min ^"1 . The masterbatch is then triturated for 5 minutes with a high shear cylinder-cylinder 135 type mixer providing shear rate of -1500 s ^-1 . To 68.7 g of so homogenized polyol masterbatch are, 30.7 g of 4,4' diphenylmethane diisocyanate with the trade name Isonate M 340 and 0.6 g of catalyst of 1.4 diazodicyklo[2.2.2.]octane (DABCO) are added and then stirred vigorously for several seconds and then poured into a mold. The foam rise time was of 63 s and the drying time was of 234 s. The so

140 obtained polyurethane foam (Al in Table 1) is characterized by a density lower than the foam (AO in Table 1) which contains no additives. During the attempt of combustion of the resulting porous polyurethane, inhibition of the dripping phenomenon observed for the reference sample AO, can be noted. The main use of this type of foam is production of upholstery materials, especially for seats in

145 public transport vehicles or passenger cars.

Table 1. Useful properties of the resulting Al polyurethane foam and AO reference porous polyurethane

Example 2

150 Preparation of the modified halloysite

The modified halloysite is prepared according to the formula provided for in Example 1.

Preparation of the polyol masterbatch

The polyol masterbatch was received in several stages. In the first stage, 155 95.2% of Rokopol 3600 polyol having a hydroxyl number of L _OH = 45 ÷ 50 mg KOH/g and 4,8 % of the modified halloysite were stirred for 50 min in a high shear mixer with a turbine stirrer with the rotation speed of 5000 min ^-1 . The compound was then ground for 5 minutes with a high shear cylinder-cylinder type mixer providing shear rate of 1500 s ^-1 . To the so obtained compound constituting 160 90.1% of the polyol composition - 1.7% of silicone surfactant, 2.2% of distilled water, 1.7% of boric acid and 4.3% of ammonium polyphosphate were added. The masterbatch was ground for 5 minutes with a high shear cylinder-cylinder type mixer providing shear rate of 1500 s ^-1 . To 70.4 g of so homogenized polyol masterbatch, 29.0 g of 4,4' diphenylmethane diisocyanate with the trade name

165 Isonate M 340 and 0.6 g catalyst of 1.4 diazodicyklo[2.2.2.]octane (DABCO) are added and then stirred vigorously for several seconds and then poured into a mold. The foam rise time was of 98 s and the drying time was of 440 s. The resulting polyurethane foam (A2 in Table 2) is characterized by a considerable increase in the oxygen index as compared to unmodified polyurethane foam (AO). During

170 combustion of the resulting porous polyurethane, minimization of dripping phenomenon was observed in comparison to AO reference sample. The main application of this type of foam is production of upholstery materials, especially for seats in public transport vehicles or passenger cars.

Table 2. Useful properties of the resulting A2 polyurethane foam and AO 175 reference porous polyurethane

The invention may be used in particular in the preparation of the polyurethane foams with reduced density, increased fire resistance and largely eliminated plastic dripping during application of a flame to the foam.