The present invention relates to filters, particularly for air conditioners, air purifiers or masks, consisting of a textile fibre support subjected to an anionisation treatment.

The filters of the invention able to retain viruses such as SARS-Cov2.

State of the art

Coronaviruses are responsible for a variety of respiratory diseases, from the common cold to serious illnesses such as Severe Acute Respiratory Syndrome (SARS). Coronaviruses are round in shape and have a diameter of about 100 nanometres. Transmission from one individual to another occurs through drops or droplets emitted during breathing and, more markedly, following coughing or sneezing. The finest droplets (< 5 microns) form an aerosol that can be dispersed over distances of several metres.

During the recent Covid- 19 pandemic, caused by the SARS-Cov2 coronavirus, the risk of infection was demonstrated in air-conditioned public places where air currents emitted by air conditioners were able to spread infected droplets to distances far greater than those recommended (1-2 metres) for the so-called social distancing (Lu J, Gu J, Li K, et al, 2020. Emerging Infectious Diseases. 2020;26(7): 1628-1631).

High efficiency air filters (HEP A) that effectively remove 99.7% of particles down to the size of 0.3 microns are mostly used in air conditioning and purification systems in laboratories, healthcare facilities and commercial aircraft. These filters are also expensive and require frequent and costly maintenance.

WO 2012123446 and DE 202020101788 disclose filter materials, particularly in the form of masks, comprising an anionic surfactant.

Anionising treatments of textile fibres have also been disclosed in JP H02 80665, US 6 149 549, JP 6 216574 and in JP H09 78451, but for purposes other than particle filtration efficiency.

There is therefore a need for filter systems that are also suitable for domestic or small-scale installations and for the production of protective masks, which are inexpensive, efficient and capable of selectively retaining viral particles.

Description of the invention

It has now been found that a satisfactory solution to the above problems can be provided by treating textile fibres of natural or synthetic origin with appropriate anionisation processes, without resorting to the use of anionic surfactants.

It is hypothesised that filters made of negatively charged materials on the surface are able to bind viral particles, particularly from coronaviruses such as SARS-CoV2, by mimicking the glycosaminoglycan receptors used by the virus for binding to the cell membrane (Brenna OV et al. Int J Immunopathol Pharmacol. 2020 Jan-Dec; 34:2058738420966078).

However, the validity of the invention should not be understood as being linked to the actual testing of this hypothesis.

An anionisation treatment is any chemical treatment that introduces anionic groups such as carboxyl, sulphonic or similar groups to the fibre. The treatment may result in a modification of chemical functionalities present in the structure of the fibre, for example as a result of oxidation or hydrolysis processes, or may involve a reaction with appropriate compounds containing anionic functionalities.

The invention therefore relates to air disinfection filters comprising a textile fibre support subjected to anionisation treatments which do not include the use of anionic surfactants.

Examples of textile fibres which may be used according to the invention include cotton, linen, wool, nylon or silk.

In case the textile fibre is cotton or linen, the anionisation treatment can be carried out by oxidation, for example with hydrogen peroxide, sodium hypochlorite, nitric acid or peracetic acid. This introduces carboxyl groups (anionic at physiological pH) by oxidation of the C6 alcohol group of the glucose unit in a quantity sufficient for the purpose and such that the structure of the fabric is not mechanically impaired.

In case the textile fibre is nylon, silk or wool, the anionisation treatment can be performed by partial hydrolysis with diluted HC1 and/or by reaction with a polymeric polyanhydride, e.g. GANTREZ® AN 119, with formation of amide bonds with the free amine groups and formation of carboxyl groups by hydrolysis of the anhydride (Arecchi A et al., Anal Bioanal Chem. 2010 Dec;398(7-8):3097-103).

In the case of nylon, nylon polyamide with 2500 mesh size 125 pm treated by hydrolysis with diluted HC1 is particularly suitable.

The filters of the invention can be easily adapted to existing filtration and air conditioning systems, used in civil environments (homes, schools, cinemas, theatres, restaurants), transport facilities, in environments at risk of contamination such as hospitals, nursing homes and healthcare facilities in general. The filters of the invention can be installed, for example, at the air outlet or splitter of commercial air conditioners.

Textile fibres that have undergone the anionisation treatment can also be used for the manufacture of protective face masks for personal use.

The filters of the invention are inexpensive, require no special maintenance, can be easily replaced and have demonstrated high efficiency in reducing viral load in closed environments, thus preventing viral infections, particularly those induced by SARS-Cov2.

The following examples illustrate the invention in more detail.

Example 1

A sample of mercerised cotton fabric was treated by boiling in a 4% sodium hypochlorite solution for 30 minutes. After long rinsing with deionised water and drying, the fabric is ready for use.

To determine the degree of substitution in carboxyl groups, a colorimetric method can be used, such as the spectrophotometric evaluation of a residual unabsorbed methylene blue solution.

Example 2

A tissue sample treated as in Example 1 was placed instead of an ordinary filter in an air-conditioning unit in a closed room and put into operation after a suitable number of individuals had been in the unit for 8 hours. The tissue was then carefully removed and wetted with PBS (phosphate buffered saline pH 7 containing 0.15 M NaCl). A piece of the filter was placed in a syringe and squeezed, and the resulting solution, collected in a test tube, was tested for the presence of viral material (Sars-Cov-2) by means of an antigenic test for detecting the presence of the virus.