WO2020165825A1

WO2020165825A1 - Flexible polyurethane foam having antibacterial properties and process for the production thereof

Info

Publication number: WO2020165825A1
Application number: PCT/IB2020/051189
Authority: WO
Inventors: Fabrizio DONDANA
Original assignee: Donchi's Foam Sl
Priority date: 2019-02-14
Filing date: 2020-02-13
Publication date: 2020-08-20
Also published as: EP3924410A1; IT201900002137A1

Abstract

The present invention relates to a flexible polyurethane foam having antibacterial properties and a process for the production thereof. The production process according to the present invention comprises the following sequential phases: a. providing a flexible polyurethane foam; b. applying onto the surface of said flexible polyurethane foam an antibacterial composition comprising at least an aqueous dispersion of silver nanoparticles; c. evaporating the water of said aqueous dispersion in order to fix said silver nanoparticles onto the surface of said flexible polyurethane foam and obtain said flexible polyurethane foam having antibacterial properties.

Description

FLEXIBLE POLYURETHANE FOAM HAVING ANTIBACTERIAL

PROPERTIES AND PROCESS FOR THE PRODUCTION THEREOF

Declaration

The project which has led to the present patent application has been conducted on the Italian territory and developed in collaboration with the Department of Chemistry and the Department of Life Sciences and System Biology of the University of Turin, by carrying out research and development activities at the laboratories of the University of Turin in the city of Turin, in accordance with the collaboration agreements entered into by the Applicant and the respective departments of the University of Turin.

Field of application

The present invention relates to a flexible polyurethane foam having antibacterial properties and a process for the production thereof. Said flexible polyurethane foam having antibacterial properties is particularly suitable for use in manufactured articles such as pillows, mattresses and mattress covers.

Prior art

Flexible polyurethane foams are cellular polymeric materials that, due to their high versatility and low production cost, find application in many fields, particularly in the home furnishing industry (e.g. pillows, mattresses, etc.) , the automotive industry (seat paddings, sound-proofing panels, etc.) and the building industry (e.g. thermal insulating panels).

Viscoelastic flexible polyurethane foams (also known as "memory foam") are becoming increasingly widespread especially in the home furnishing field. These foams, the structure of which is of the open-cell type (or prevalently of the open-cell type) , are characterized by a slow and gradual recovery of their initial shape following compression . Viscoelastic foams can therefore adapt themselves to the profile of the bodies with which they come in contact, attenuate the energy transferred by an impact, and absorb sound energy . These properties make viscoelastic polyurethane foams particularly suitable for use as paddings (e.g. cushions, pillows, mattresses and, in general, supporting elements for the human or animal body) , shoe soles or inserts, anti-injury protective elements, and soundproofing elements.

Within such applications, the products incorporating flexible polyurethane foams (whether viscoelastic or not) are often required to have also antibacterial characteristics. This requirement is especially felt, for example, for pillows, mattresses and mattress covers, since such products are particularly susceptible to contamination by microorganisms that may cause several inconveniences to the user, in particular allergy problems.

In the current state of the art, in order to confer antibacterial properties on cushions, pillows and mattresses it is known to cover such products with textiles (e.g. sheets, pillow slips, etc.) having a textile structure with a very closely woven weft, i.e. a textile structure that attempts to limit the passage of the undesired microorganisms (e.g. mites), but not of their bacteria, and thus the contamination of the underlying foam. This solution solves the contamination problem only partially, in that those microorganisms which cannot go through the covering textile are however permitted to proliferate on its surface.

In an attempt to overcome this problem, it is also known in the art to use textiles having antibacterial properties. Such textiles are obtained by chemically treating the covering fabric or the yarn employed for producing it, e.g. with compositions based on metal compounds, such as silver, zinc or copper compounds. Nevertheless, antibacterial textiles have, due to their very nature, weft dimensions that are bigger by one order of magnitude than those of bacteria, and require rather complex and costly preparation processes. Moreover, since such textiles are periodically washed, their antibacterial efficacy decreases progressively over time .

The Applicant has now found that the above- mentioned and other drawbacks of the state of the art, which will become more apparent in the following description, can be overcome, at least partly, by applying a colloidal aqueous dispersion containing silver nanoparticles onto the surface of a flexible polyurethane foam. The application of said dispersion allows fixing onto the foam surface silver particles having nanometric dimensions (e.g. 5-100 nm) , which can exert an effective antibacterial action against many types of contaminant and allergenic microorganisms. The use of a dispersion of silver particles of nanometric size ensures a homogeneous distribution of such particles on the surface of the cellular polymeric matrix, and hence a uniform antibacterial effect throughout the surface.

Furthermore, since the antibacterial effect is conferred directly on the polymeric material that forms the antibacterial foam, the articles manufactured by using these foams, e.g. pillows, mattresses, mattress covers and cushions, can be covered with conventional, non-antibacterial or non-miteproof textiles, which can thus be washed repeatedly without affecting the antibacterial properties of the articles manufactured from flexible polyurethane foam.

The method for producing antibacterial flexible polyurethane foams is also simple and cost-effective to implement at industrial level.

Summary of the invention

According to a first aspect, the present invention concerns a method for producing a flexible polyurethane foam having antibacterial properties, comprising the following sequential steps:

a. providing a flexible polyurethane foam;

b. applying onto the surface of said flexible polyurethane foam an antibacterial composition comprising at least an aqueous dispersion of silver nanoparticles;

c. evaporating the water of said aqueous dispersion in order to fix said silver nanoparticles onto the surface of said flexible polyurethane foam and obtain a flexible polyurethane foam having antibacterial properties .

According to a second aspect, the present invention concerns the flexible polyurethane foam having antibacterial properties obtained by means of the above method.

According to a third aspect, the present invention concerns a shaped article comprising said flexible polyurethane foam having antibacterial properties .

According to a fourth aspect, the present invention concerns a shaped article chosen among pillow, mattress and mattress cover, comprising a viscoelastic flexible polyurethane foam and silver nanoparticles distributed at least over the surface of said foam to confer antibacterial properties on said article .

For the purposes of the present description and the appended claims, the term "antibacterial" refers to a substance capable of killing microorganisms or inhibiting the proliferation thereof, i.e. with bactericidal and/or bacteriostatic capability .

For the purposes of the present description and the appended claims, the numerical limits and ranges expressed in the present description and in the appended claims include also the mentioned numerical value (s) . Moreover, all values and sub-ranges of a numerical limit or range should be understood to be specifically included as if they had been explicitly mentioned.

In general, the method according to the present invention allows producing flexible polyurethane foams having antibacterial properties . To this end, an antibacterial composition is used which comprises an aqueous dispersion of metal silver particles in colloidal form and of nanometric size.

The aqueous dispersion can be prepared by using the methods known in the art. Preferably, the aqueous dispersion of silver nanoparticles is obtained by reacting at least one water-soluble silver salt, preferably AgN0₃, with at least one reducing agent, preferably NaBH₄, in the presence of water.

If silver nitrate and borohydrate are used, the reaction scheme is the following:

The reduction reaction that produces the silver nanoparticles can be conducted at room temperature

(22 °C) , more preferably at a temperature of approximately 0 °C, and at atmospheric pressure.

Preferably, the concentration of the reducing agent in the reaction mixture exceeds that of the silver salt.

For the reagents AgNO₃ and NaBH₄, the molar ratio NaBH4 /AgNO3 preferably falls within the range of 1.2 to 5, more preferably within the range of 1.8 to 2.5. In particular, it has been observed that when said molar ratio is 2 a particularly stable colloidal dispersion of silver nanoparticles can be obtained.

Optionally, the reaction mixture may comprise at least one surfactant in order to stabilize the colloidal suspension and avoid aggregation of the nanoparticles, which would result in sedimentation thereof. Preferably, the total concentration of said at least one surfactant is in the range of 0.6% to 1.9% in weight with reference to the weight of the reaction mixture.

The surfactant may be an anionic, cationic or amphoteric surfactant, preferably an anionic surfactant. It is also possible to use polyvinylpyrrolidone as a stabilizing agent.

Preferably, the silver nanoparticles have an average diameter in the range of 5 nm to 100 nm, preferably in the range of 10 nm to 50 nm.

For the purposes of the present invention and the appended claims, the average diameter of the nanoparticles in the colloidal dispersion is to be understood as the average hydrodynamic diameter

which can be measured, for example, by using the ISO

22412:2017 method.

Further information about the preparation of a colloidal dispersion of silver nanoparticles which can be used for the purposes of the present invention can be found in the publication S. D . Solomon et al . , Synthesis and Study of Silver Nanoparticles, J. CHEM. ED. 84 No. 2, February 2007, 322-325.

Preferably, the total quantity of antibacterial composition applied onto the flexible polyurethane foam is such as to give a concentration of surface-fixed silver nanoparticles in the range of 10 to 500 mg/m², preferably 40 to 300 mg/m². The quantity of antibacterial composition to be applied depends, therefore, on the concentration of the aqueous dispersion of nanoparticles, and can be easily determined by a person skilled in the art.

It has been observed that the presence of silver nanoparticles on the polyurethane foam in such concentrations permits obtaining a substantially constant and long-lasting antibacterial effect .

The Applicant has also observed that, in order to promote the fixation of the silver nanoparticles onto the foam surface, it may be useful to subject the foam, prior to the application of the antibacterial composition, to an activation treatment by means of an atmospheric plasma . The plasma may be a cold plasma, i.e. a plasma in which only a minor fraction of gas molecules are ionized.

The flexible polyurethane foam usable for the purposes of the present invention is of a type known to those skilled in the art and poses no particular limitations as to its composition.

In general, flexible polyurethane foams are the reaction product of at least one multifunctional isocyanate compound and at least one polyol . The cellular structure, whether with open or closed cells, is obtained through the evolution of a gas, called expanding agent, in the reaction mixture during the phase of growth of the polymeric chains.

Typically, the expanding agent is carbon dioxide, generated in situ by the reaction between water molecules and isocyanate groups .

In one embodiment, the flexible polyurethane foam is the reaction product of:

at least one multifunctional isocyanate component ;

- at least one polyol component reactive with said multifunctional isocyanate component;

water .

The multifunctional isocyanate component (also referred to as component B) may be a multifunctional isocyanate compound of the type generally used for the preparation of polyurethanes. The multifunctional isocyanate compound is a compound containing two or more NCO isocyanate groups capable of reacting with the OH hydroxy groups of the polyol to form urethane bonds. The multifunctional isocyanate compound is selected, for example, from: toluene diisocyanate, methylene diisocyanate, and mixtures thereof.

The polyol component reactive with said multifunctional isocyanate (also referred to as component A) may be a polyol compound of the type generally used for the preparation of polyurethanes. The polyol component is a compound containing two or more OH groups reactive with the isocyanate groups of component

A.

The polyol is selected, for example, from: polyester polyol, polyether polyol, and mixtures thereof . Preferably, the polyol is a polyether polyol .

Preferably, the reactive polyol component is a mixture of two or more different polyols.

The reaction mixture may also include other ingredients, such as: catalysts, surfactants, cross linking agents, stabilizers, dyes or pigments, fillers, etc .

The reaction conditions necessary for obtaining a flexible polyurethane foam can be easily determined by a person skilled in the art on the basis of his/her technical knowledge and the prior art.

For example, the production process may be either of the "one-shot" type, i.e. a process wherein the polyol and the multifunctional isocyanate monomer are reacted together with the other components of the reaction mixture (e.g. chain extender, catalyst, surfactants, etc.) or of the "prepolymer" type, i.e. a process wherein the multifunctional isocyanate monomer and the polyol are reacted beforehand to obtain a prepolymer, and then the prepolymer is reacted with the chain extender to give the final polymer .

In a preferred embodiment, the flexible polyurethane foam is a viscoelastic foam, preferably an open-cell viscoelastic foam.

Preferably, the viscoelastic foam has an hysteresis loss, measured with the ASTM D3574 - X6 method, equal to or greater than 15%, more preferably equal to or greater than 25%. As is known to a person skilled in the art, viscoelastic foams are a particular type of foams obtainable by means of an appropriate selection of polyol and isocyanate components, and optionally of auxiliary components .

Some examples of viscoelastic polyurethane foams available on the market and usable for the purposes of the present invention are the CosyPUR® and Elastoflex® foams produced by BASF.

The equipment that can be used for producing the polyurethane foams according to the present invention is conventional equipment known to those skilled in the art .

For example, the flexible polyurethane foams can be obtained by casting or moulding.

In the casting process, the components of the reaction mixture are continuously cast onto a conveyor belt or into a mould (e.g. parallelepiped in shape) to obtain a foam block that, when the reaction is complete, can be cut into articles having the desired dimensions and shape .

In the moulding process, the reaction mixture is injected either at low pressure or at high pressure (e.g.

100 180 bar) into a mould, thereby obtaining a shaped article of flexible polyurethane foam.

The above techniques are suitable for making shaped articles such as: mattresses, pillows, seat cushions, shoe soles, anti-injury protective elements, and sound- proofing elements .

The antibacterial composition can be applied onto the flexible polyurethane foam by using known techniques commonly employed for the application of liquid coating compositions onto the surface of polyurethane materials. In particular, the antibacterial composition may be applied by spraying, brushing, rolling, or other similar techniques .

Once applied, the liquid phase of the antibacterial composition is evaporated from the surface of the polyurethane foam. Evaporation may occur at room temperature, with the foam whereon the composition has been applied being left to stand. The evaporation of the aqueous liquid phase can be sped up by subjecting the foam to a moderate heat treatment (e.g. 30 70 °C) .

The application of the antibacterial composition onto the surface can be repeated one or more times until the desired concentration of silver nanoparticles is attained.

It has been observed that the application of the antibacterial composition is particularly advantageous on shaped articles obtained by moulding, in that the final article will have more pronounced antibacterial properties, the quantity of antibacterial composition applied being equal, than articles obtained by casting and subsequent cutting.

Without reference to any particular theory, it is believed that such difference in antibacterial performance is at least partly due to the different morphology of the surface of the polyurethane foam subjected to application of the antibacterial composition in the two above-mentioned cases. In articles obtained by moulding, in fact, the external surface that receives the antibacterial composition has a more compact porous structure, with smaller cells, on average, than the cells of the (less compact) porous structure of articles obtained by casting and subsequent cutting . In articles obtained by moulding, the exposed surface is substantially determined by the contact of the foam with the inner surface of the mould. In articles obtained by casting, on the contrary, the exposed surface is an inner surface of the initially cast article, which is exposed after the cutting of the initial cast article .

This unexpected property of moulded articles can be exploited to advantage for the production of pillows and mattress covers, since such articles can be obtained by moulding .

For the above reasons, in a preferred embodiment the antibacterial composition is applied directly onto the surface of a shaped article obtained by moulding, i.e. without said article being previously subjected to cutting operations or other operations than may significantly alter the surface structure of the article .

Detailed description of the invention

The present invention will now be further illustrated by means of the following embodiments.

Example 1 Preparation of a colloidal aqueous dispersion of silver nanoparticles

An aqueous solution of AgNOs 3.7*10^-3 M was prepared by dissolving 12.6 mg of AgNOs into 20 ml of deionized water (at room temperature and pressure) . A reducing solution of NaBH₄ 7.4*10^-3 M was prepared by dissolving 16.8 mg of NaBH₄ into 60 ml of deionized water.

The solution of AgNO₃ was added drop-wise to the reducing solution of NaBH₄, the latter being kept in an ice bath under stirring. At the end of the reaction, a stable yellow-coloured colloidal dispersion was obtained, such colour being indicative of the presence of silver particles of nanometric size. The antibacterial composition thus prepared had a concentration of metal silver of 9*10^-4 M (approx. 0.1 g/i) .

The size of the particles was quantitatively determined by UV-Vis spectroscopy. The UV-Vis spectrum featured a main absorption band at 400 nm (band width at half maximum of approx. 80 nm) . Such a UV-Vis spectrum is typical of aqueous solutions containing silver nanoparticles having an average size of approx. 15 nm (Solomon et al . , Synthesis and Study of Silver Nanoparticles, J. CHEM. ED., Vol. 84, No. 2, February

2007) .

Example 2 Preparation of a viscoelastic polyurethane foam with antibacterial properties In a conventional high-pressure apparatus for the preparation of flexible polyurethane foams, a viscoelastic polyurethane foam was produced by using the commercial products CosyPUR® 5206/159 (polyol component A) and Iso 145/22 (isocyanate - component B) , both produced by BASF Espanola S.L. The chosen component A/component B ratio was 100/40 (parts in weight) . The pressure used for mixing the two components in the injection head in use was 140 bar, at room temperature (25 °C) . Injection occurred in a mould maintained at a temperature of approx. 50 °C, whereon a mould release agent had been previously applied.

The final product was then treated with an antibacterial composition prepared as illustrated in Example 1. To this end, the antibacterial composition (0.1 g/1 of metal Ag) was deposited onto the surface of the polyurethane foam by spraying, in such a quantity as to obtain the deposition of 200 mg/m² of metal Ag.

After application, the aqueous phase of the composition was evaporated by leaving the manufactured article exposed to room temperature.

Example 3 - Antibacterial efficacy test

The antibacterial efficacy of the article made of polyurethane foam of Example 2 was tested (Kirby-Bauer diffusion test) against the following bacterial cultures: Escherichia coli, Staphylococcus aureus,

Pseudomonas aeruginosa and Acinetobacter radioresistens . For this purpose, 100 ml of culture were deposited onto LB-agar plates after a growth up to OD₆₀₀ = 0.5 (approx .

100.000 UFC) and incubated at 37 °C (30 °C for

Acinetobacter radioresistens) for 24 hours.

A sample of antibacterial polyurethane foam of 1cm x 1cm x 5mm in size was deposited onto the culture and kept in contact therewith at 37 °C for 24 hours.

For comparison purposes, each test was also carried out with a sample of the same polyurethane foam not treated with the antibacterial composition (control) .

In all tests carried out, no diffused inhibition halo was observed on either the antibacterial foam samples or the control samples. For the antibacterial foam samples only, the appearance of an inhibition halo was observed in the area of the sample in contact with the culture medium.

This result confirms the efficacy of the antibacterial polyurethane foam according to the present invention. In particular, the antibacterial flexible polyurethane foam according to the present invention is particularly suitable for use as a pillow, cushion, mattress or mattress cover, where an antibacterial action is needed in order to prevent surface contamination following contact with the user' s head or body .

Claims

1. Method for producing a flexible polyurethane foam having antibacterial properties, comprising the following sequential steps:

a. providing a flexible polyurethane foam;

b. applying onto the surface of said flexible polyurethane foam an antibacterial composition comprising at least one aqueous dispersion of silver nanoparticles;

c . evaporating the water of said aqueous dispersion in order to fix said silver nanoparticles onto the surface of said flexible polyurethane foam and obtain said flexible polyurethane foam having antibacterial properties .

2. Method for producing a flexible polyurethane foam according to claim 1, wherein said aqueous dispersion of silver nanoparticles is obtained by reacting a water-soluble silver salt, preferably AgNOs, with at least one reducing agent, preferably NaBH₄, in the presence of water .

3. Method for producing a flexible polyurethane foam according to one or more of the preceding claims, wherein the total quantity of said antibacterial composition applied is such as to obtain a concentration of silver nanoparticles on the flexible polyurethane foam in the range of 10 mg/m² to 500 mg/m², preferably

40 mg/m² to 300 mg/m².

4. Method for producing a flexible polyurethane foam according to one or more of the preceding claims, wherein, prior to said step b, said flexible polyurethane foam is subjected to a surface activation treatment by means of a plasma at atmospheric pressure.

5. Method for producing a flexible polyurethane foam according to one or more of the preceding claims, wherein said silver nanoparticles have an average size in the range of 5 nm to 100 nm, preferably in the range of 10 nm to 50 nm.

6. Method for producing a flexible polyurethane foam according to one or more of the preceding claims, wherein said flexible polyurethane foam is a viscoelastic polyurethane foam.

7. Method for producing a flexible polyurethane foam according to claim 6, wherein said viscoelastic flexible polyurethane foam has a hysteresis loss, measured in accordance with the ASTM D3574 - X6 method, equal to or greater than 15%, more preferably equal to or greater than 25%.

8. Method for producing a flexible polyurethane foam according to one or more of the preceding claim, wherein said polyurethane foam is obtained by mould injection, preferably at high pressure.

9. Method for producing a flexible polyurethane foam according to one or more of the preceding claims, wherein in said step a. said flexible polyurethane foam comprises the reaction product of:

at least one multifunctional isocyanate component ;

water .

10. Flexible polyurethane foam obtained through the method according to one or more of the preceding claims.

11. Shaped article comprising a flexible polyurethane foam according to claim 10.

12. Shaped article according to claim 11, selected from: support element for the human or animal body, preferably pillow, mattress, mattress cover, seat padding, shoe sole, anti-injury protective element ; and soundproofing element.

13. Shaped article chosen among pillow, mattress and mattress cover, comprising a viscoelastic flexible polyurethane foam and silver nanoparticles distributed over the surface of said foam to confer antibacterial properties on said article .

14. Shaped article according to claim 13, wherein said article is a pillow .