News Column

"Embedding Nanoparticles in Thermoplastic Polymers" in Patent Application Approval Process

August 29, 2014



By a News Reporter-Staff News Editor at Drug Week -- A patent application by the inventors Tofail, Syed (Limerick, IE); Zeglinski, Jacek (Limerick, IE); Cronin, Patrick (Limerick, IE); Podbielska, Halina (Wroclaw, PL); Dworniczek, Ewa (Wroclaw, PL); Tiernan, Peter (Limerick, IE); Franiczek, Roman (Wroclaw, PL); Buzalewicz, Igor (Wroclaw, PL); Wawrzynska, Magdalena (Wroclaw, PL), filed on March 16, 2012, was made available online on August 14, 2014, according to news reporting originating from Washington, D.C., by NewsRx correspondents (see also University Of Limerick).

This patent application is assigned to University Of Limerick.

The following quote was obtained by the news editors from the background information supplied by the inventors: "Sterilization of textile materials is typically conducted by consumers and service providers (e.g., hospitals, nursing homes and hotels) using a conventional aqueous immersive laundry process or dry cleaning methods. Conventional laundering requires relatively large amounts of water, and the articles are subject to fading and deterioration after repeated washes. Dry cleaning processes rely on non-aqueous solutions for cleaning However, the large amounts of solvents and the need for dedicated dry cleaning operations make this form of cleaning inconvenient and expensive. Additionally, while the conventional and dry cleaning processes may be effective to remove body soils, dirt and/or stains, they do not effectively sterilize the fabric articles or textiles, posing a public health problem in hotels, inns, and particularly in hospitals, clinics and nursing homes, where visitors and indwellers are less immune to infectious microbes.

"Recent advances in textile technology have produced textiles having microbiocidal agents incorporated in or on the surface of the fabric article or textile. For example, metal based inorganic compounds such as silver (Ag), zinc oxide (ZnO) or titanium dioxide (TiO.sub.2) can be utilized as microbiocidal agents and have been adapted for incorporation on or in a variety of different substrates and surfaces. Such inorganic compounds have been incorporated within melt spun synthetic fibers in order to provide fabric articles which antimicrobial characteristics. This method incorporates these antimicrobial compounds into the bulk of the melt-spun fibres. As microbial attack initiates and continues mostly on the surface and the subsurface region of textiles, bulk incorporation of antimicrobial compounds by using e.g. melt spinning is a inefficient method as it rarely keeps the antimicrobial agent at the surface.

"A contact with solid surfaces provides microbes a favorable environment to grow and spread. A method that kills microbes on contact will make effective microbiocidial surface. Attempts have been made to apply such metal-based microbiocidal agents on the surfaces of fabrics, with little success from a durability standpoint. For example, spray methods and dip-coating techniques have been utilized to apply inorganic compounds to fibers prior to or after weaving or knitting. However, such techniques are not wash-durable, resulting not only in a loss of antimicrobial properties after a few washes, but also an increase in environmental pollution due to the elution of loose microbiocidal agents into the effluent. Moreover, the poor adhesion characteristics of such metal-based compounds to fabric articles or other textiles can pose a serious health risk to individuals wearing or in direct contact with such articles.

"The major difficulty in surface incorporation of microbiocidal agents into textiles lies in the adhesion and binding of these agents to the surface of the textiles. Textile fibres are made of either natural or synthetic polymers or a blend of these two.

"It is known in the art that some of the natural and synthetic polymers used in textiles are thermoplastic in nature i.e. they deform when heated.

"While techniques have been used to improve the adhesion of these inorganic compounds to the surface of textiles, e.g. by chemical functionalization of the textile surface with organic molecules, or by modification of a polymer surface by physical means (e.g., low temperature, high pressure plasma treatments) they still suffer from poor durability due to the problem associated with binding of inorganic microbiocidal agents to textile surfaces. Such techniques are therefore unsuitable in industrial textile applications due to the level of expense and environmental pollution.

"A number of metal-based microbiocidal agents owes there anti-microbial actions due to surface interactions with microbes either directly through penetration or indirectly through the generation of antimicrobial species such as nascent oxygen, hydroxyl or peroxy ion produced as a result of photocatalytic activity.

"In many cases, these metal based microbiocidal agents are nanoparticles i.e. at least one dimension of these nanoparticles (height, width or length) is smaller than 100 nm (10.sup.-7 m).

"It is known in the art that such a smaller dimension enormously increases the surface area in nanoparticles. Nanoparticles are also known to possess extraordinary and otherwise impossible crystal structures, morphology and physic-chemical properties such as photocatalytic properties, photoluminescence, high yield point, superior electronic conduction, superhydrophobicity etc. Nanoparticles, due to their enormous surface area, may also possess very high surface energy and activity, which often forces them to form clusters or aggregates. While the effective surface area reduces if nanoparticles aggregates or clusters, it can be still much higher than that available e.g. from their micro-size counterparts.

"It is usually the frontal surface of a textile product exposed to the ambient environment that is more prone to the growth and spread of microbes. Paradoxically, this frontal surface is also exposed to photons from sunlight or any suitable artificial light source, which can more effectively cleanse the textile surface through photocatalytic actions, for example. The microbiocidal actions take place at the surfaces of these metal based microbiocidal agents, which means that a higher amount of surface area exposed to the ambient will result in a larger extent of surface reactions to kill microbes.

"Currently, most techniques to produce inorganic compound-based antimicrobial finishes or surface coatings on textiles yield a relatively thick, often continuous, two-sided coating on the textile product. A continuous coating of microbiocidal agents on textiles is unnecessary due to the colloidal nature and finite size of microbes during their planktonic stage of growth during which the action of microbiocidal action is most effective. It also has the limitation of resulting in a weaker interface due to the inherent difficulty in achieving a strong bonding with the textile surface over a large area. A thick coating accentuates this problem by further weakening the interface due to the mismatch of elastic properties between harder metal-based microbiocidal agents and the soft and compliant textiles matrix. This increases the risk of dislodgement of microbiocides during use and cleaning operations. It also significantly reduces the surface area of the microbiocide that would have been otherwise available to kill bacteria.

"Application of microbiocidal agents on both sides of a textile product is also less meaningful if the microbiocidal action takes place on the surface that is exposed to the stimulus (e.g. a photon from a light source) that is responsible for the microbiocidal action."

In addition to the background information obtained for this patent application, NewsRx journalists also obtained the inventors' summary information for this patent application: "The present invention provides polymeric materials having microbiocidal nanoparticles embedded within a single surface layer of the polymeric material. The embedding process described herein provides superior adhesion and binding of nanoparticles to the polymer surface. The superior binding significantly reduces the risk of dislodgement of nanoparticles during use, washing or care thus minimizing the risk as an environmental or a health hazard. A strong bonding is achieved by utilizing the thermoplastic nature of the polymer in modifying its surface without adversely affecting the bulk properties such as compliance, appearance or durability. Additionally, the embedding process of the invention significantly reduces the amount of nanoparticles required for efficient killing of microbes by incorporating the nanoparticles only on a single surface of the polymeric material. The invention results in a one-sided, non-continuous distribution with separated nanoparticles, which do not form any thick film or coating on the surface and as such reduces the risk of flaking or delamination of coatings that can arise from a thicker coating. The invention thus provides a safe, durable, environmentally safe, inexpensive and industrially scalable technique for producing antimicrobial polymeric textiles using microbiocidal nanoparticles.

"In one aspect, the invention provides a polymeric material having one or more nanoparticles embedded in a surface layer of a single surface of the material, the surface layer having a thickness less than or equal to the diameter of the nanoparticle.

"The nanoparticle can be in a micellar, a colloidal or a sol-gel state that may or may not contain another microbiocidal agent. In one aspect e.g. the nanoparticle possesses microbiocidal property. In another aspect, the nanoparticle is or contains an inorganic compound, such as a metal or a metal-based formulation, which has microbiocidal properties. Examples of such inorganic compounds include, without limitation, gold, copper, zinc, iron, silver, titanium, a rare earth element, or a combination thereof, and their compounds with oxygen, sulfur, chlorine, fluorine, bromine, iodine, nitrogen and phosphorus. In a particular aspect, the microbiocidal agent is a photocatalytic agent that is activated by radiation with a wavelength or a distribution of wavelengths (X) ranging from near infrared radiation (700 nm <.lamda.

"The polymeric material preferably contains a thermoplastic polymer. Examples of thermoplastic polymers include, without limitation, cellulose rayon, cellulose acetate, polyester, polyamide, polyurethane, polyurea, acrylic, olefin, aramid, azlon, modacrylic, novoloid, nytril, aramid, spandex, vinyl polymer, vinal, vinyon, or a combination thereof. Alternatively, the polymeric material can be a blend of a thermoplastic polymer and a natural material such as wool, linen, cotton, silk, or a combination thereof.

"The invention also provides a method of producing a nanoparticle embedded polymeric material having at least two surfaces (i.e., two sides), modifying the surface layer of only one of these surfaces at a depth sufficient to receive one or more nanoparticles in the surface layer, and depositing one or more nanoparticles onto the modified surface layer to embed the one or more nanoparticles in the modified surface layer.

"The surface layer is altered at a depth less than or equal to the diameter of the nanoparticles, thereby ensuring that the nanoparticles are distributed within the surface layer, and not deeper.

"In one aspect, the surface layer is modified by thermal, mechanical and/or chemical treatment of the surface layer. For example, the surface layer can be chemically modified by pre-treating the surface layer with a chemical, such as hydrogen peroxide, to facilitate surface incorporation of nanoparticles in subsequent thermo-mechanical treatment i.e. to heat the polymeric material above its softening temperature but below its melting temperature, to a depth less than or equal to the diameter of the nanoparticle(s) to be embedded within.

"The one or more nanoparticles are deposited in a manner such that the nanoparticles are distributed as patches of individual nanoparticles, their clusters or agglomerates across the surface of a single side of the polymeric material and do not form a continuous layer or films or coatings.

"Nanoparticle deposition can take place prior to or after the thermal, mechanical and/or chemical treatment of the surface. For example, the nanoparticles can be deposited by spraying the nanoparticles onto a thermally, mechanically, and/or chemically treated surface layers. The nanoparticles can be sprayed at a velocity sufficient to embed the nanoparticles into the modified surface layer. Alternatively, nanoparticles can be deposited by spraying the nanoparticles onto a surface layer (e.g., after hydrogen peroxide treatment). Sufficient amount of heat is then applied to the surface layer after nanoparticle deposition to soften the surface layer to a depth less than or equal to the diameter of the deposited nanoparticles. Pressure is then applied to the nanoparticle-deposited, modified surface (e.g., using rollers) to facilitate the embedding process. Heat is applied so that it modifies the surface of the polymer only and not the bulk. When the polymer cools, it recovers from its softened state and cringes which provides a stronger bonding due to mechanical interlocking of the embedded particles within the surface.

"The nanoparticle can be a micellar, a colloidal or a sol-gel composition that contains a microbiocidal agent. For example, the microbiocidal agent can be a metal-based formulation that contains an inorganic compound having microbiocidal properties. Examples of such inorganic compounds include, without limitation, gold, copper, zinc, iron, silver, titanium, a rare earth element, or a combination thereof. In a particular aspect, the microbiocidal agent is a photocatalytic agent that is activated by radiation ranging from near infrared radiation to ultraviolet radiation, to visible radiation. Preferably, the photocatalytic agent is a metal-based formulation, such as TiO.sub.2, Ag.sub.2O, Ag--TiO.sub.2, ZnO, Fe.sub.2O.sub.3, ZnFe.sub.2O.sub.4, CeO.sub.2, La.sub.2O.sub.3, Eu.sub.2O.sub.3, or a combination thereof.

"The polymeric material is preferably a thermoplastic polymer. Examples of thermoplastic polymers include, without limitation, cellulose rayon, cellulose acetate, polyester, polyamide, polyurethane, polyurea, acrylic, olefin, aramid, azlon, modacrylic, novoloid, nytril, aramid, spandex, vinyl polymer, vinal, vinyon, or a combination thereof. Alternatively, the polymeric material can be a blend of a thermoplastic polymer and a natural material such as wool, linen, cotton, silk, or a combination thereof.

"Various aspects, features, objects, advantages, and details of the invention herein disclosed will become apparent through reference to the following description, the accompanying drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

"In the drawings, like structures and items typically are referenced by the same or similar reference numbers throughout the various views. The illustrations in the drawings are not necessarily drawn to scale, the emphasis instead being placed generally on illustrating the principles of the invention and the disclosed embodiments.

"FIG. 1. is a schematic showing different extent of embedding of a spherical nanoparticle into a cooled polymeric surface previously softened by the application of heat: I. point contact adhesion with the weakest bonding with the polymer surface results in the maximum exposed surface area for microbiocidal action II. partial embedding with slightly stronger bonding with the polymer surface but also with a slightly reduced surface area for microbiocidal action than in I III. optimal embedding with optimally stronger bonding with the polymer surface along with smaller but still reasonable surface area for microbiocidal action IV. sub-optimal embedding with much stronger bonding with the polymer surface but with a significantly reduced surface area for microbiocidal action than in I-III and V. Sinking of nanoparticle having the strongest bonding with the polymer surface but there is no surface area exposed for microbiocidal action. [For a spherical nanoparticle, the penetration depth .lamda. is defined by the diameter of the spherical nanoparticle, i.e 0.ltoreq.D.ltoreq..delta.. An optimal combination of maximum exposed surface area for bacteriocidal action and maximum penetration for stronger bonding occurs when .delta. approaches half the diameter of the nanoparticle (D/2). For nonspherical nanoparticles with a long dimension, D and short dimension d, the best combination of surface area and bonding is obtained when .delta. approaches half the shortest dimension (d/2).]

"FIG. 2. shows nanoparticle retention to polymeric materials after 10 & 40 wash cycles (including 1 cycle of pre-wash).

"FIG. 3. is a flow diagram of depicting an exemplary method of incorporating/embedding nanoparticles containing inorganic compounds in a surface layer of a polymeric material.

"FIG. 4. depicts a polymeric material positioned in hot plate compartment for nanoparticle deposition and heat treatment.

"FIG. 5. depicts a Scanning Electron Microscopy (SEM) image of an uncoated (i.e., no nanoparticles) polyester fabric--reference sample.

"FIG. 6. depicts an SEM image of a non-continuous coating of TiO.sub.2 nanoparticles on polyester fabric (one-sided coating).

"FIG. 7. depicts a magnified SEM image of Magnification of the TiO.sub.2 nanoparticles on polyester fabric (TiO.sub.2--white color).

"FIG. 8. represents a schematic of a fully-automatic rig: 1. Feed Roller 2. Cleaning Blowers 3. Pre-Heater 4. Nanoparticle (Ti0.sub.2) spray 5. Nanoparticle (Ti0.sub.2) reservoir 6. Hot Plate and calendar roller 7. Feed rate 8. Rollers 9. Pinch point 10. Waste wash tank 11. Nanoparticle return loop

"FIG. 9. is a longitudinal view of fully-automatic nanoparticle embedding rig.

"FIG. 10. is a 3-D view of the fully automatic nanoparticle embedding rig.

"FIG. 11. is a general view of a prototype fully automatic embedding rig.

"FIG. 12. is a prototype rig assembly displaying stepper motors and nanoparticle delivery system.

"FIG. 13. is a longitudinal view of embedding process, fabric feed roller (left), and nanoparticle spray nozzle (right).

"FIG. 14. is a longitudinal view of the pre-heater and spring loaded hot-plate assembly.

"FIG. 15. presents optimised process parameters using the automatic embedding rig for polymeric materials and nanoparticles.

"FIG. 16. is a bar graph depicting S. aureus (MRSA)--survival on TiO.sub.2 embedded textiles under light (365 nm, GP 1.5 mW/cm.sup.2).

"FIG. 17. is a bar graph depicting S. aureus (MRSA)--survival on TiO.sub.2 embedded textiles in the dark.

"FIG. 18. is a bar graph depicting S. aureus (MRSA)--survival on Ag--TiO.sub.2 textiles under light (365 nm, GP 1.5 mW/cm.sup.2).

"FIG. 19. is a bar graph depicting S. aureus (MRSA)--survival on Ag--TiO.sub.2 textiles in the dark.

"FIG. 20. is a bar graph depicting E. coli (ESBL) survival on Ag--TiO.sub.2 textiles under light (365 nm, GP 1.5 mW/cm.sup.2).

"FIG. 21. is a bar graph depicting E. coli (ESBL)survival on Ag--TiO.sub.2 textiles in the dark.

"FIG. 22. is a bar graph depicting C. albicans--survival on Ag--TiO.sub.2 textiles under light (365 nm, GP 1.5 mW/cm.sup.2).

"FIG. 23. is a bar graph depicting C. albicans--survival on Ag--TiO.sub.2 textiles in the dark.

"FIG. 24. Effect of hot-plate temperature on the bonding to polymeric materials after 10 & 40 wash cycles (including 1 pre-wash cycle).

"FIG. 25. SEM micrographs of TiO.sub.2 nanoparticles incorporated into surface layer of PET fabric. (A)--distribution of TiO.sub.2 nanoparticles in patches on PET surface; (B)--representative magnified image (C) a magnified view of B showing the spacings between different patches of embedded nanoparticles.

"FIG. 26. Effect of starting concentration of TiO.sub.2 in the colloidal suspension on bonding of these nanoparticles to PET.

"FIG. 27. Effect of roller materials on bonding of nanoparticles to PET

"FIG. 28. effect of active temperature (Ta) as a function of the melting and glass transition temperature of the polymeric material

"FIG. 29. the effect of nanoparticle embedding temperature on two commercially available polymeric materials, Cellulose Acetate and Acrylic.

"FIG. 30A-C. Reduction of methicillin resistant (MRSA) Staphylococcus aureus on PET fabric impregnated with (A) 0.15 wt. %, (B) 0.25 wt. %, and (C) 0.50 wt. % of nano-TiO.sub.2. [PET--reference not containing titania, Dark 40' Dark 60'--samples kept in the dark for 40 and 60 min., UVA 40' and UVA 60'--TiO.sub.2-PET samples UVA-irradiated for 40 and 60 min.]

"FIG. 31A-B. Reduction of methicillin resistant (MRSA) Staphylococcus aureus on PET fabric impregnated with (A) 0.15 wt. %, and (B) 0.50 wt. % of nano-AgTiO.sub.2.

"FIG. 32A-B. Reduction of Escherichia coli ESBL (+) on PET fabric impregnated with (A) 0.15 wt. %, and (B) 0.50 wt. % of nano-AgTiO.sub.2. Dark 20' Dark 40'--samples kept in the dark for 20 and 40 min., UVA 20' and UVA 40'--TiO.sub.2-PET samples UVA-irradiated for 20 and 40 min."

URL and more information on this patent application, see: Tofail, Syed; Zeglinski, Jacek; Cronin, Patrick; Podbielska, Halina; Dworniczek, Ewa; Tiernan, Peter; Franiczek, Roman; Buzalewicz, Igor; Wawrzynska, Magdalena. Embedding Nanoparticles in Thermoplastic Polymers. Filed March 16, 2012 and posted August 14, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3535&p=71&f=G&l=50&d=PG01&S1=20140807.PD.&OS=PD/20140807&RS=PD/20140807

Keywords for this news article include: Hospital, Chemicals, Chemistry, Escherichia, Nanoparticle, Photocatalyst, Nanotechnology, Photocatalytic, Hydrogen Peroxide, Staphylococcaceae, Enterobacteriaceae, Gammaproteobacteria, Emerging Technologies, Staphylococcus aureus, Gram-Positive Bacteria, University Of Limerick, Endospore-Forming Bacteria.

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