WO2023214221A1

WO2023214221A1 - Composition and making of self-forming, continuous-release antimicrobial air gel

Info

Publication number: WO2023214221A1
Application number: PCT/IB2023/053507
Authority: WO
Inventors: Yue Tak LAI; Jong Hong Lee
Original assignee: Chiaphua Industries Ltd
Priority date: 2022-05-05
Filing date: 2023-04-06
Publication date: 2023-11-09

Abstract

A composition and making of self-forming, continuous-release antimicrobial air gel is consists of at least one hygroscopic agent, at least one water absorbent and at least one gaseous-biocide-releasing salt which is sealed stored; when it is unsealed, the moisture in air trigger the gel to continuous-release biocide by the hydrogen ion.

Description

COMPOSITION AND MAKING OF SELF-FORMING, CONTINUOUS-RELEASE ANTIMICROBIAL AIR GEL

This invention describes the preparation method and formulation thereof for a self-activating, sustained release-killing antimicrobial and odour-mitigating gel.

Microbial proliferation is the most common reason for malodour and allergen generation in households. Prolonged exposure to malodour can cause depression, nauseous, and other mental health problems. Uncontrolled microbial proliferation also deteriorates the household hygiene which may cause detectable chronic illness and discomforts.

Apart from routine cleaning, gaseous biocides are good alternative to tackle microbial proliferation due to their air penetration unto hard-to-reach surfaces. Aqueous chlorine dioxide is well studied biocide commonly used in water treatment. In gaseous form, chlorine dioxide is also a rapid and effective wide spectrum biocide and can be deployed against bioweapons such as anthrax.

Chlorine dioxide has a rapid half-life due to its highly reactive nature, making it safe for unmanned large-scale gaseous deployments, as long as followed by a 15-minute aeration. However, chlorine dioxide’s high reactivity, short half-life and high toxicity is also the reason why it is challenging to using chlorine dioxide in sustained disinfection. Sustained continuous generation of low-dose chlorine dioxide can be a solution to tackle this problem.

Koji Abe et al. (US8603355B2, US20100086493A1, US8545898B2) [1] [2] [3] taught us that continuous generation of chlorine dioxide can be achieved by addition of pH adjuster. The continuous chlorine dioxide generating solution can then be converted into various forms by blended into gellant or foaming agents. However, the drawback of the mentioned article is that the chemicals require to be separated during transportation and storage. The ingredients then require end-users to mix the chemicals at end use site, posing operational hazard to non-trained personnel. Upon mixing, a sudden surge of chlorine dioxide is also released upon activation which further imposes hazard on end-users.

This invention tackles the problem by producing a self-forming, self-activating and continuous release gaseous chlorine dioxide air gel. It can be employed to improve sanitary conditions and relief malodour problems in confined spaces.

The present invention proposes a sustained gaseous biocide release gel with composition consists of at least one hygroscopic agent, at least one water absorbent and at least one gaseous-biocide-releasing salt. Acidity moderator, i.e. pH buffering salts, can be included in the composition to regulate the release rate of gaseous biocide. This composition of ingredient is to be stored in a sealed container until intended use.

Detail of the present invention is as follow:

A self-forming, gaseous-biocide-releasing gel, comprising the following ingredients:

at least one hygroscopic agent, at least one water absorbent agent and at least one stable gaseous-biocide-releasing salt;

the composition of ingredients is stored in a sealed container;

unsealing the sealed container when used, the hygroscopic agent draws moisture from the air and the water absorbent agent absorbs the moisture to dissolve the gaseous-biocide-releasing salt; the gaseous-biocide-releasing salt is activated to release biocide by the hydrogen ion.

Furthermore, the hygroscopic agent is selected from: zinc nitrate, copper nitrate, calcium chloride, magnesium chloride, zinc chloride, iron(III) chloride, potassium magnesium chloride, potassium carbonate, potassium phosphate, ammonium ferric citrate, ammonium nitrate, potassium hydroxide, sodium hydroxide, water harvesting nanotubes, and any combination thereof.

Furthermore, the water absorbent agent is selected from: sodium polyacrylate, potassium polyacrylate, polyacrylamide copolymer, poly(ethylene-alt-maleic anhydride), carboxylmethyl cellulose, cross-linked carboxylmethyl cellulose, poly(vinyl alcohol) hydrogel, cross-linked polyethylene oxide, starch-graft-polyacrylonitrile hydrolysate, other metal neutralized polyacrylic acids, starch powder, and any combinations thereof.

Furthermore, the stable gaseous-biocide-releasing salt is selected from: sodium chlorite, other gaseous biocide releasing salt upon trigger, and any combinations thereof.

Furthermore, includes acidity modifiers, pH moderators pH buffers, and/or Non-water absorbent inert spacing materials.

Furthermore, the acidity modifiers, pH moderators pH buffers are: sodium citrate, citric acid, potassium phosphate monobasic, sodium phosphate dibasic, disodium phosphate, sodium acetate, sodium dihydrogen phosphate, imidazole, sodium carbonate, sodium bicarbonate, sodium hydroxide, other acidic salts, other basic salts, and any combinations thereof.

Furthermore, the Non-water absorbent inert spacing materials are: talcum powder, titanium powder, and any combinations thereof.

Furthermore, the gel is a single-mixture by: first adding dry powders of stable biocide-release salt, water absorbent and mixing, then adding hygroscopic agent and mixing.

Furthermore, the gel is a single-mixture by: first adding dry powders of stable biocide-release salt, water absorbent, acidity modifiers, pH moderators, pH buffers, Non-water absorbent inert spacing materials and mixing, then adding hygroscopic agent and mixing.

Furthermore, the gel is divided into:

a bottom layer which comprises at least the hygroscopic agent;

a middle layer which comprises at least the stable gaseous-biocide-releasing salt;

a top layer which comprises at least the water absorbent agent.

Furthermore, the gel is divided into:

a bottom layer which comprises at least the hygroscopic agent;

a top layer which comprises at least the water absorbent agent;

the acidity modifiers, the pH moderators and the pH buffers, the Non-water absorbent inert spacing materials are added in any of above layers.

Furthermore, the gel is divided into:

a bottom layer which comprises at least the hygroscopic agent;

a top layer which comprises at least the mixture of the stable gaseous-biocide-releasing salt, the acidity modifiers, the pH moderators, the pH buffers, and non-water absorbent inert spacing materials.

Upon opening of the sealed container, the hygroscopic agent draws moisture from air. The moisture is then absorbed by the water absorbent and forms a hydrogel structure while at the same time dissolves the biocide-releasing salt and any other salts within the formulation. The stable biocide-releasing salt is then activated by the presence of water molecules or hydrogen ion present introduced by the moisture harvested by the hygroscopic agent. The sustained continuous release of biocide is achieved by the slow supply of hydrogen ion through buffering and delayed water supply achieved by the balance of moisture absorption of hygroscopic agent and water retention of the water absorbent.

The invention is further illustrated in the accompanying drawings as follows.

Fig.1

shows images of Air Gel, (a) before moisture absorption, (b) after moisture absorption and structural integrity is formed.

Fig.2

shows embodiments of a (a) single-mixture gel, (b) layer-by-layer composite gel, and (c)&(d) combinations of the two preparation methods

Fig.3

shows the duration of continuous release by gel examples.

Fig.4

shows the illustration of biocidal test set-up.

The invention describes a gaseous-biocide-releasing and self-forming gel. The invention can also be stored safety without activation and gel-formation until the sealed container is opened and use moisture in air as the reaction trigger. It is achieved by incorporation of dry chemicals, maintain separation of water during transport and storage, and introduction of water into the system through hygroscopic compound. This invention describes a chlorine dioxide generation system with use of sodium chlorite salt, but the system is also not limited to other biocides that can be activated with water or hydrogen ions.

Chlorine dioxide is a gaseous biocide which can be effective at low doses of 0.05ppm against viruses and at 0.01ppm against bacteria. Chlorine dioxide which exists in a stable salt form as sodium chlorite which can be activated into chlorine dioxide gas by the following chemical reaction:

Therefore, by controlling the hydrogen ion supply, the release of gaseous chlorine dioxide can be controlled.

In this invention, the supply of hydrogen ion is first inhibited by lack of water in the system. Without water, acidic and basic salts cannot ionize to supply hydrogen ion to initiate sodium chlorite activation for safe storage and transport, referring to (a). Upon use, the sealed containers are opened to allow hygroscopic agent to harvest moisture from air to initiate sodium chlorite activation to generate chlorine dioxide. Simultaneously, water harvested is absorbed by water absorbent to further delay water supply towards sodium chlorite for chlorine dioxide activation and to create a hydrogel structure. The hydrogel structure expends and becomes rigid as water is absorbed which also gives structural integrity of the system and can affix to the container without falling when flipped over, referring to (b).

Hygroscopic agent is the primary reaction initiator of the chain reaction system. One or more hygroscopic agent can be used to control the rate of water harvest from moisture. One or more hygroscopic agent can be selected from: zinc nitrate, copper nitrate, calcium chloride, magnesium chloride, zinc chloride, iron(III) chloride, potassium magnesium chloride, potassium carbonate, potassium phosphate, ammonium ferric citrate, ammonium nitrate, potassium hydroxide, sodium hydroxide, water harvesting nanotubes, other metal nitrates, other metal chlorides, their anhydrous and hydrated forms, and any combinations thereof.

Once moisture is harvested from air, the harvested water is then withheld by water absorbent or dissolves the other species within the system. The water absorbent is to slowdown the reaction rate of system activation and also to form hydrogel to give structural integrity of the system. One or more water absorbent can be selected from: sodium polyacrylate, potassium polyacrylate, polyacrylamide copolymer, poly(ethylene-alt-maleic anhydride), carboxylmethyl cellulose, cross-linked carboxylmethyl cellulose, poly(vinyl alcohol) hydrogel, cross-linked polyethylene oxide, starch-graft-polyacrylonitrile hydrolysate, other metal neutralized polyacrylic acids, and any combinations thereof.

Other components, such as pH modifiers and non-water absorbent inert powders can be included into the system to further impede the sodium chlorite activation.

The gel can be prepared as a single-mixture as (a), a layer-by-layer composite as (b), or a combination of the two where water absorbent as (c) or the single-mixture as top layer as (d). While single-mixture can already form a functioning gel, we find that layer-by-layer composite gives better result in term of storage and controlled-release performance.

To prepare a single-mixture gel, dry powders of stable biocide-release salt, water absorbent, pH modifiers (if any) and inerts (if any) are first added together and well-mixed, followed by addition of hygroscopic agent and mixing. Hygroscopic agent is to be added at last because once hygroscopic agent is added, the chain reaction will start and may lead to premature reaction. Example 1 to Example 9 are examples of single-mixture gel prepared under said method.

To prepare a layer-by-layer composite gel, hygroscopic agent is to be placed at the bottom, followed by stable biocide-releasing salt in the middle, and water absorbent at the top. This configuration allows water moisture to be drawn through the whole system. If pH modifier is added, it can be mixed at either the bottom or middle layer. If inert ingredient is added, it can be mixed at either bottom or middle layer, or in between bottom and middle layer. An additional layer of water absorbent layer can also be included between the stable biocide-releasing salt and hygroscopic agent to enhance structural strength. Example 10 to Example 12 are examples of a 4-layer layer-by-layer composite gel prepared under said method.

The performance of the gels is evaluated by the duration of its continuous release. After opened screw cap and exposed to air, the bottle is left to stand upright and allowed time for the hydrogel to form a rigid structure. For Example 1 to Example 9, the rigid structure is obtained after 1 day. For Example 10 to Example 13, the rigid structure is obtained after 3 days. Successful formation of rigid structure is determined by flipping over the bottle and the gel content do not fall within 1 minute. Once rigid structure is achieved, the bottle is maintained upside-down throughout the whole observation period to allow quick escape of the denser-than-air chlorine dioxide gas.

Afterwards, the presence of chlorine dioxide is measured by using ATI PortaSens II Gas Detector with 00-1004 core. The gas detector is set to have minimum detection of chlorine dioxide at 0.01ppm. The detector inlet is placed right underneath the mouth of the container and any days of positive detection of chlorine dioxide by the detector is recorded.

Referring to , the duration of continuous release by Example 1 to Example 8 are compared. By comparing Example 1 against Example 2 and 5, it demonstrates that reducing hygroscopic agent does not prolong the continuous release of gaseous biocide. It is because according to formulation 1, once sufficient water is present to initiate the reaction, more water is generated throughout the sodium chlorite activation process. Therefore, reducing hygroscopic agent and increasing water absorbent does not prolong the duration of the gel.

Comparing Example 1 against Example 4, it demonstrates doubling the amount of gaseous biocide source, i.e., sodium chlorite, can extend the durability of the gel by prolonging exhaustion to a limited degree.

By comparing Example 1 against Example 3, 6, 7, 8 and 9, it is clearly observed that the more basic salt present, i.e. higher pH value, the longer the gel prolongs, with Example 9 having only basic salt, it obtained the longest duration period of 20 days when compared to its previous examples.

The release rate and duration of release of the biocide of the gel can therefore be fine controlled by the selecting the inclusion of different acidic and/or basic salts and by the amount of the gaseous biocide source added.

Example 10 to Example 12 are prepared layer-by-layer and have similar composition in term of formulation to Example 9. All layer-by-layer gels have significant durability improvement than single-mixture gel and can extend by 33% from 3 weeks to 4 weeks. It is because as the hydroscopic agent is separated from the stable biocide-releasing salt, it takes a longer pathway before sufficient water has reach the biocide layer to fully initiate the sodium chlorite activation. Another advantage of layer-by-layer gel is that by ensuring the outermost layer is water absorbent, the structural integrity is strongest on the outermost layer, provided strongest support.

According to Morino et al., chlorine dioxide is able to eliminate bacteria at 0.01ppm within 2-3 hours. [4] As the chlorine dioxide detector used in data collection in had a minimum detection limit of 0.01ppm, the gel examples in were all able to eliminate bacteria throughout the duration of release.

To evaluate if the air gel can be stored before activation and its performance after storage, Example 13 to Example 17 were stored for 36 days at room temperature, which is longer than the release duration of the gels according to . The vial caps were closed tightly as soon as the ingredients were added to avoid moisture from entering and activating the system. After storage, the vials caps were removed and allowed to stand for sufficient time for aeration (to release any chlorine dioxide build-up during storage, if any) and for activation.

After aeration and activation, the air gels were then individually placed into 35L sealed containers. Inside the containers, a unit of chlorine dioxide detector and an agar plate pre-spread with E. coli were also placed inside the container to monitor chlorine dioxide level and to perform bactericidal test. For control, an empty vial was placed instead of an air gel into the control container.

Referring to , after the containers were closed and sealed, the systems were allowed to stand for 10 minutes. The systems were then opened again to retrieve the agar plates and thus stopping the biocidal action. The chlorine dioxide concentration data were also recorded right before opening the systems. The agar plates were then incubated for a day and enumerated the following day.

Table 1. Concentration of chlorine dioxide released and bactericidal rate of Air Gels

Example number	Measured Chlorine Dioxide Concentration	Bactericidal rate
13	0.06 ppm	97.55%
14	0.14 ppm	100%
15	0.39 ppm	100%
16	0.13 ppm	100%
17	0.07 ppm	100%

Table 1 demonstrates Example 13 to 17 were able to be stored and still achieve high bactericidal activity after activation. Example 17 also demonstrates concentration of chlorine dioxide released can be controlled to be at safety levels (>0.3ppm STEL and >0.1ppm TWA) [7] while maintaining high bactericidal rate.

Examples

Example 1

Sodium polyacrylate (0.4 gram), citric acid (1 gram) and sodium chlorite (1.5 gram) are first mixed by vortex device. Copper nitrate trihydrate (1 gram) is then added into the mixture and further mixed by vortex device.

Example 2

Sodium polyacrylate (0.4 gram), citric acid (1 gram) and sodium chlorite (1.5 gram) are first mixed by vortex device. Copper nitrate trihydrate (0.5 gram) is then added into the mixture and further mixed by vortex device.

Example 3

Sodium polyacrylate (0.4 gram), citric acid (0.5 gram) and sodium chlorite (1.5 gram) are first mixed by vortex device. Copper nitrate trihydrate (1 gram) is then added into the mixture and further mixed by vortex device.

Example 4

Sodium polyacrylate (0.4 gram), citric acid (1 gram) and sodium chlorite (3 gram) are first mixed by vortex device. Copper nitrate trihydrate (1 gram) is then added into the mixture and further mixed by vortex device.

Example 5

Sodium polyacrylate (0.8 gram), citric acid (1 gram) and sodium chlorite (1.5 gram) are first mixed by vortex device. Copper nitrate trihydrate (1 gram) is then added into the mixture and further mixed by vortex device.

Example 6

Sodium polyacrylate (0.4 gram), citric acid (0.32 gram), sodium citrate dihydrate (0.68 gram) and sodium chlorite (1.5 gram) are first mixed by vortex device. Copper nitrate trihydrate (1 gram) is then added into the mixture and further mixed by vortex device.

Example 7

Sodium polyacrylate (0.4 gram), citric acid (0.21 gram), sodium citrate dihydrate (0.78 gram) and sodium chlorite (1.5 gram) are first mixed by vortex device. Copper nitrate trihydrate (1 gram) is then added into the mixture and further mixed by vortex device.

Example 8

Sodium polyacrylate (0.4 gram), citric acid (0.12 gram), sodium citrate dihydrate (0.88 gram) and sodium chlorite (1.5 gram) are first mixed by vortex device. Copper nitrate trihydrate (1 gram) is then added into the mixture and further mixed by vortex device.

Example 9

Sodium polyacrylate (0.4 gram), sodium citrate dihydrate (1 gram) and sodium chlorite (1.5 gram) are first mixed by vortex device. Copper nitrate trihydrate (1 gram) is then added into the mixture and further mixed by vortex device.

Example 10

A pre-mixed mixture of copper nitrate trihydrate (1 gram) and sodium citrate dihydrate (1 gram) is first added into the system as bottom layer. Another pre-mixed mixture of sodium chlorite (1.5 gram) and sodium polyacrylate (0.4 gram) is then added into the system as second layer.

Example 11

Copper nitrate trihydrate (1 gram) is first added into the system as bottom layer. A pre-mixed mixture of sodium chlorite (1.5 gram) and sodium citrate dihydrate (1 gram) is then added into the system as second layer. Sodium polyacrylate (0.4 gram) is the added into the system as top layer.

Example 12

A pre-mixed mixture of copper nitrate trihydrate (1 gram) and sodium citrate dihydrate (1 gram) is first added into the system as bottom layer. Sodium polyacrylate (0.4 gram) is added into the system as a spacer layer. A pre-mixed mixture of sodium chlorite (1.5 gram) and sodium citrate dihydrate (1 gram) is then added into the system as third layer. Another layer of sodium polyacrylate (0.2 gram) is further added into the system as top layer.

Example 13

A pre-mixed mixture of copper nitrate trihydrate (1 gram) and sodium citrate dihydrate (1 gram) is first added into the system as bottom layer. Sodium chlorite (1.5 gram) is then added into the system as second layer. Sodium polyacrylate (0.4 gram) is then added into the system as third and top layer.

Example 14

A pre-mixed mixture of copper chloride trihydrate (1 gram) and sodium citrate dihydrate (1 gram) is first added into the system as bottom layer. Sodium chlorite (1.5 gram) is then added into the system as second layer. Sodium polyacrylate (0.4 gram) is then added into the system as third and top layer.

Example 15

A pre-mixed mixture of copper chloride trihydrate (1 gram) and sodium bicarbonate (1 gram) is first added into the system as bottom layer. Sodium chlorite (1.5 gram) is then added into the system as second layer. Sodium polyacrylate (0.4 gram) is then added into the system as third and top layer.

Example 16

A pre-mixed mixture of anhydrous copper chloride (1 gram) and sodium bicarbonate (1 gram) is first added into the system as bottom layer. Sodium chlorite (1.5 gram) is then added into the system as second layer. Sodium polyacrylate (0.4 gram) is then added into the system as third and top layer.

Example 17

A pre-mixed mixture of copper nitrate trihydrate (1 gram) and sodium bicarbonate (1 gram) is first added into the system as bottom layer. Sodium chlorite (1.5 gram) is then added into the system as second layer. Sodium polyacrylate (0.4 gram) is then added into the system as third and top layer.

Claims

A self-forming, gaseous-biocide-releasing gel, comprising the following ingredients:
at least one hygroscopic agent, at least one water absorbent agent and at least one stable gaseous-biocide-releasing salt;
the composition of ingredients is stored in a sealed container;
unsealing the sealed container when used, the hygroscopic agent draws moisture from the air and the water absorbent agent absorbs the moisture to dissolve the gaseous-biocide-releasing salt; the gaseous-biocide-releasing salt is activated to release biocide by the hydrogen ion.
The gel of claim 1, wherein the hygroscopic agent is selected from: zinc nitrate, copper nitrate, calcium chloride, magnesium chloride, zinc chloride, iron(III) chloride, potassium magnesium chloride, potassium carbonate, potassium phosphate, ammonium ferric citrate, ammonium nitrate, potassium hydroxide, sodium hydroxide, water harvesting nanotubes, and any combination thereof.
The gel of claim 1, wherein the water absorbent agent is selected from: sodium polyacrylate, potassium polyacrylate, polyacrylamide copolymer, poly(ethylene-alt-maleic anhydride), carboxylmethyl cellulose, cross-linked carboxylmethyl cellulose, poly(vinyl alcohol) hydrogel, cross-linked polyethylene oxide, starch-graft-polyacrylonitrile hydrolysate, other metal neutralized polyacrylic acids, starch powder, and any combinations thereof.
The gel of claim 1, wherein the stable gaseous-biocide-releasing salt is selected from: sodium chlorite, other gaseous biocide releasing salt upon trigger, and any combinations thereof.
The gel of claim 1, wherein includes acidity modifiers, pH moderators pH buffers, and/or Non-water absorbent inert spacing materials.
The gel of claim 1, wherein the acidity modifiers, pH moderators pH buffers are: sodium citrate, citric acid, potassium phosphate monobasic, sodium phosphate dibasic, disodium phosphate, sodium acetate, sodium dihydrogen phosphate, imidazole, sodium carbonate, sodium bicarbonate, sodium hydroxide, other acidic salts, other basic salts, and any combinations thereof.
The gel of claim 1, wherein the Non-water absorbent inert spacing materials are: talcum powder, titanium powder, and any combinations thereof.
The preparation of the gel of claim 1, wherein the gel is a single-mixture by: first adding dry powders of stable biocide-release salt, water absorbent and mixing, then adding hygroscopic agent and mixing.
The preparation of the gel of claim 5, wherein the gel is a single-mixture by: first adding dry powders of stable biocide-release salt, water absorbent, acidity modifiers, pH moderators, pH buffers, Non-water absorbent inert spacing materials and mixing, then adding hygroscopic agent and mixing.
The preparation of the gel of claim 1, wherein the gel is divided into:
a bottom layer which comprises at least the hygroscopic agent;
a middle layer which comprises at least the stable gaseous-biocide-releasing salt;
a top layer which comprises at least the water absorbent agent.
The preparation of the gel of claim 5, wherein the gel is divided into:
a bottom layer which comprises at least the hygroscopic agent;
a middle layer which comprises at least the stable gaseous-biocide-releasing salt;
a top layer which comprises at least the water absorbent agent;
the acidity modifiers, the pH moderators and the pH buffers, the Non-water absorbent inert spacing materials are added in any of above layers.
The preparation of the gel of claim 5, wherein the gel is divided into:
a bottom layer which comprises at least the hygroscopic agent;
a top layer which comprises at least the mixture of the stable gaseous-biocide-releasing salt, the acidity modifiers, the pH moderators, the pH buffers, and non-water absorbent inert spacing materials.