WO2016167759A1

WO2016167759A1 - Surface modification of a resin

Info

Publication number: WO2016167759A1
Application number: PCT/US2015/025878
Authority: WO
Inventors: Mrunal R. THATTE; Stanislav E. Solovyov
Original assignee: Multisorb Technologies, Inc.
Priority date: 2015-04-15
Filing date: 2015-04-15
Publication date: 2016-10-20

Abstract

A method of modifying a polymeric surface including a plurality of carbonyl functional groups to permit chemical attachment of an organic compound including a carboxylic acid group, the method including the step of: a) contacting the plurality of carbonyl functional groups with a reducing agent in a first aqueous solution to form a plurality of modified surface functional groups including hydroxyl functional groups. A method of chemically attaching an organic compound including a carboxylic acid group to a polymeric surface, the method including the steps of: a) treating the polymeric surface with an oxidizing agent to form a plurality of carbonyl functional groups on the polymeric surface; b) contacting the plurality of surface carbonyl functional groups with a reducing agent in a first aqueous solution to form a plurality of modified surface hydroxyl functional groups; and, c) contacting the plurality of modified surface hydroxyl functional groups with an esterification reagent and the organic compound in a second aqueous solution to attach the organic compound to the polymeric surface.

Description

SURFACE MODIFICATION OF A RESIN

FIELD OF THE INVENTION

[0001] The invention broadly relates to surface modification of a polymeric resin, more specifically to surface modification of a resin using aqueous solutions, more particularly to surface modification of a resin using aqueous solutions for chemically attaching an organic compound comprising a carboxylic acid to the resin.

BACKGROUND OF THE INVENTION

[0002] The use of organic solvent based solutions for the grafting of radicals to surfaces for subsequent chemical attachment of organic compounds is known in the art. However, such processes may be unacceptable in some circumstances as the presence of organic solvents may negatively impact the acceptability, quality and desirability of a product, e.g., a polymeric film material intended for food packaging applications. Moreover, grafting of radicals limits the substances that may be attached.

[0003] There is a need for a cost effective, environmentally acceptable and safe surface modification. Heretofore, tradeoffs between performance and material selections were required. Thus, there is a long-felt need for an aqueous based method of modifying a polymeric resin for subsequent chemical attachment thereto. The specific chemistries attached to the resin surface can be used for various purposes such as enhanced food preservation, providing a source of an antimicrobial compound or for modification and control of the gaseous atmosphere within a package, generally by adding different functionalities to the food contact surfaces.

BRIEF SUMMARY OF THE INVENTION

[0004] The present invention broadly comprises a method of chemically attaching an organic compound comprising a carboxylic acid to a surface modified resin.

[0005] In an embodiment, the present method includes modifying a polymeric surface to create a plurality of carbonyl functional groups to permit chemical attachment of an organic compound that includes a carboxylic acid. The method includes the subsequent step of: a) contacting the plurality of carbonyl functional groups with a reducing agent in a first aqueous solution to form a plurality of modified surface functional groups including hydroxyl functional groups. [0006] In an embodiment, the present method includes chemically attaching an organic compound that includes a carboxylic acid group to a polymeric surface. The method includes the steps of: a) treating the polymeric surface with an oxidizing agent to form a plurality of carbonyl functional groups on the polymeric surface; b) contacting the plurality of surface carbonyl functional groups with a reducing agent in a first aqueous solution to form a plurality of modified surface hydroxyl functional groups; and, c) contacting the plurality of modified surface hydroxyl functional groups with an esterification reagent and the organic compound in a second aqueous solution to attach the organic compound to the polymeric surface.

[0007] These and other objects and advantages of the present invention will be readily appreciated from the following description of preferred embodiments of the invention and from the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Various embodiments are disclosed, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a depiction of the transformation from an unmodified organic polymer surface to a modified organic polymer surface having a chemically attached or bonded compound comprising a carboxylic acid group;

Figure 2 is a graph showing the measured absorbance of film samples having methyl red immobilized thereon that were prepared without the step of using a reducing agent, e.g., Na₂S₂0₄;

Figure 3 is a graph showing the measured absorbance of film samples having methyl red immobilized thereon that were prepared with the step of using a reducing agent, e.g., Na₂S₂0₄; and,

Figure 4 is a graph showing the differences of measured absorbance of film samples shown in Figures 2 and 3.

DETAILED DESCRIPTION OF THE INVENTION

[0009] At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the invention. While the present invention is described with respect to what are presently considered to be the preferred aspects, it is to be understood that the invention as claimed is not limited to the disclosed aspects. [0010] Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims.

[0011] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. As used herein, a "chromium (VI) compound" is intended to include any compound that contains chromium metal in the +6 oxidation state. For example, chromium (VI) compounds include but are not limited to salts of chromate, e.g., potassium chromate, and salts of dichromate, e.g., potassium dichromate. Additionally as used herein, a "reducing agent" is intended to include a reagent capable of reducing a carbon-oxygen double bond in a carbonyl group to a carbon-oxygen single bond with insertion of two hydrogen atoms, as a net result, across the double bond being reduced. Furthermore, the reduction described herein could occur in a single or multiple steps. In some embodiments, a "reducing agent" in a first aqueous solution will form a plurality of modified surface functional groups including hydroxyl functional groups. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described.

[0012] The present method applies to substrates that are in-part derived from a petrochemical source. The present method is carried out under all aqueous conditions, i.e., no organic solvent is used. The method uses common chemicals that are commercially available. The method allows for the chemical attachment or bonding of various organic moieties that comprise a carboxylic acid group. The present method provides a novel approach to surface modification of a substrate material, e.g., a plastic substrate, and more specifically thermoplastic films made from common packaging resins including various polyethylenes, polypropylene, polystyrene, polyamides, ethylene-vinyl acetate copolymers and other copolymers of common industrial monomers.

[0013] Substrate materials discussed herein display modified property profiles upon attachment of chemical molecules at their surface. The present method provides for an approach with less process energy requirements than free radical mediated graft polymerization at the surface of a polymer substrate and for use of common chemicals during the process. Due to the solid film/aqueous reagent nature of an embodiment of the present method, the purification steps involved are relatively simple, i.e., merely rinsing a film with water until it is free of contaminants.

[0014] The present method provides a process of modifying a surface comprising a plurality of carbonyl functional groups to permit chemical attachment of an organic compound comprising a carboxylic acid. The method broadly comprises the step of contacting the plurality of carbonyl functional groups with a reducing agent in a first aqueous solution to form a plurality of modified surface functional groups comprising hydroxyl functional groups. In some embodiments, the reducing agent is selected from the group consisting of: an inorganic sulfur compound; a borohydride; a cyanoborohydride; formic acid; an alkali metal salt of formic acid; an alkaline earth metal salt of formic acid; iron powder in combination with acetic acid; zinc powder in combination with acetic acid; and, combinations thereof. In some embodiments, the reducing agent is an inorganic sulfur compound selected from the group consisting of: alkali sulfide; hydrosulfide; polysulfide; thiosulfate; dithionite, also known as hydrosulfite; bisulfite; and, combinations thereof.

[0015] Moreover, the present method may further comprise additional steps before and after contacting the plurality of surface carbonyl functional groups with a reducing agent. In some embodiments, the present method of chemically attaching an organic compound comprising a carboxylic acid group to a polymeric surface comprises the steps of: a) treating the polymeric surface with an oxidizing agent to form a plurality of carbonyl functional groups on the surface; b) contacting the plurality of surface carbonyl functional groups with a reducing agent in a first aqueous solution to form a plurality of modified surface hydroxyl functional groups; and, c) contacting the plurality of modified surface hydroxyl functional groups with an esterification reagent and the organic compound in a second aqueous solution to attach the organic compound to the surface.

[0016] In some embodiments, the present method includes a step of simultaneously exposing the surface to an oxidizing reagent and an ultra-violet (UV) radiation source. The oxidizing reagent may be selected from the group consisting of: ozone; an aqueous solution of potassium peroxymonosulfate; an aqueous solution of potassium persulfate; an aqueous solution of hydrogen peroxide; an aqueous solution of sodium hypochlorite; an aqueous solution of sodium chlorite; an aqueous solution of sodium chlorate; an aqueous solution of sodium perchlorate; an aqueous solution of tert-butyl hydroperoxide; an aqueous solution of sodium perborate; and, combinations thereof, or other compounds that oxidize the surface in the presence of UV radiation. Moreover, in some instances, ambient air containing sufficient oxygen may be used as an oxidizing reagent in the presence of UV radiation. Additionally, other oxygen containing gas mixtures inert with respect to ozone and atomic oxygen may be used as an oxidizing reagent in the presence of UV radiation. In some embodiments, the UV radiation source emits light at wavelengths between about 180 nm and 260 nm. Moreover, the UV radiation source may emit light at a first wavelength of 184.9 nm and a second wavelength at 253.7 nm or other wavelengths that promote the generation of ozone and formation of atomic oxygen.

[0017] In some embodiments, the present method includes a step of simultaneously exposing the surface to an oxidizing reagent in an aqueous solution and an ultrasonic energy source. The oxidizing reagent may be selected from the group consisting of: potassium peroxymonosulfate; hydrogen peroxide; calcium hypochlorite; sodium hypochlorite; sodium chlorite; sodium chlorate; sodium perchlorate; sodium perborate; tert-butyl hydroperoxide; potassium peroxydisulfate; and, combinations thereof or other compounds that oxidize the surface in the presence of ultrasonic energy.

[0018] In some embodiments, the present method includes a step of exposing the surface to an aqueous solution comprising an acid and a component selected from the group consisting of: potassium permanganate; eerie ammonium nitrate; a chromium (VI) compound; and, combinations thereof or other compounds that oxidize the surface in the presence of acid. The acid may be selected from the group consisting of: hydrochloric acid; sulfuric acid; nitric acid and, combinations thereof preferably an acid that is not oxidized by the oxidizing agent. Most acids are thought to work to some extent. Moreover, in some embodiments, the aqueous solution further comprises a salt, and the salt may be selected from the group consisting of: a nitrate of an alkali metal; a nitrate of an alkaline earth metal; and, combinations thereof, or any nitrate salt that disassociates in water.

[0019] In some embodiments of the present method, the reducing agent is selected from the group consisting of: an inorganic sulfur compound; a borohydride; a cyanoborohydride; formic acid; a salt of formic acid with an alkali metal; a salt of formic acid with an alkaline earth metal; iron powder in combination with acetic acid; zinc powder in combination with acetic acid; and, combinations thereof. Other reducing agents that can reduce a carbonyl group at the conditions at which the process is carried out may also be used. In embodiments where the reducing agent is an inorganic sulfur compound, the sulfur compound may be selected from the group consisting of: alkali sulfide; hydrosulfide; polysulfide; thiosulfate; dithionite, also known as hydrosulfite; bisulfite; and, combinations thereof. Other inorganic sulfur compounds that can donate electrons at the conditions at which the process is carried out may also be used.

[0020] In some embodiments of the present method, the esterification reagent is selected from the group consisting of: l-ethyl-3-(3-dimethylaminopropyl)carbodiimide; and, l-ethyl-3-(3-dimethylaminopropyl)carbodiimide in combination with N-hydroxysuccinimide.

[0021] In some embodiments of the present method, the surface to be modified is a surface of a substrate selected from the group consisting of: an organic polymer; a resin; a resinoid; a cellulose derivative; a casein material; a protein; and, combinations thereof. Generally, any organic polymer that can be oxidized using one or the methods described herein may be used.

[0022] In some embodiments of the present method, the organic compound is selected from the group consisting of: a dye; an antimicrobial; an organic oxygen absorber; a light absorber; a moisture absorber; an ethylene absorber; a mercaptan or thiol absorber; an ozone scavenger; and, combinations thereof.

[0023] The following general procedures represent some embodiments of the present method. The three embodiments described below in general terms include: 1) film or surface functionalization using an oxidizer and an acid; 2) film or surface functionalization using UV/Ozone treatment; and, 3) film or surface functionalization using ultra-sound techniques.

[0024] Embodiment 1 - Film/Surface Functionalization using an Oxidizer and an

Acid (can be carried out using either of the two methods described below)

[0025] Method 1 :

[0026] Resin film samples, up to 3 mil in thickness, were cut into 1 inch by 1 inch squares. Each functionalization was carried out using four test samples simultaneously functionalized in the same set up. The resin film samples to be functionalized were placed in a 25 mL glass beaker containing a magnetic stirrer. 7.5 mL of concentrated sulfuric acid was added to the beaker, followed by 0.15 g of sodium nitrate. The contents were stirred gently at room temperature for 5 minutes. Next, 0.9 g of granular potassium permanganate was slowly added while continuing to stir the contents of the beaker at room temperature for 3 hours. After the completion of this period, the film samples were removed from the beaker and washed with distilled water three times. The washed films were introduced into a 100 mL beaker containing 50 mL of aqueous hydrochloric acid at a concentration of approximately 36 wt% and the contents were gently stirred for 15 minutes at room temperature. Subsequently, the films were removed, washed three times with distilled water and air dried.

[0027] Method 2:

[0028] The resin film samples were placed in a 100 mL capacity glass beaker containing a magnetic stirrer. The beaker was filled with a 50 mL solution of 0.25M potassium permanganate in 0.1N aqueous hydrochloric acid. The contents of the beaker were heated to 50°C for up to 2 hours while being stirred gently. After the completion of a predetermined time of reaction, the film samples were removed from the beaker and washed with distilled water three times. The washed films were introduced into a 100 mL beaker containing a 50 mL aqueous hydrochloric acid solution at approximately 36 wt% and the contents were gently stirred for 15 minutes at room temperature. Subsequently, the films were removed, washed three times with distilled water and air dried.

[0029] The experiment used to perform film functionalization is described below.

[0030] Embodiment 2 - Film/Surface Functionalization using UV/Ozone treatment

[0031] Step 1

[0032] Resin film samples, up to 3 mil in thickness, were cut into the shape of a 1 inch by 1 inch square. Each functionalization was carried out using four test samples simultaneously functionalized in the same set up. The resin film samples to be functionalized were placed in a 90 cm by 15 cm Pyrex® crystallizing dish. The crystallizing dish was filled to capacity with distilled water with the film samples floating to the surface. The crystallizing dish containing the film samples was carefully placed inside the irradiation chamber of a UVO Cleaner, Model 144AX (manufactured by Jelight, 2 Mason, Irvine, CA 92618) such that the top-surface of the liquid inside the crystallizing dish and the film samples floating in it was approximately 3-4 mm away from the UV light assembly source inside the UVO Cleaner.

[0033] Step 2

[0034] With the vents of UVO Cleaner properly discharged to the exhaust, the UVO Cleaner was turned on with the film sample placed inside the irradiation chamber as described above, following proper safety guidelines recommended by the manufacturer of UVO Cleaner. The irradiation was carried out for 30 minutes after which samples were removed, washed three times with distilled water and air dried.

[0035] When chemical reagents were employed in the UV/Ozone protocol above, an aqueous solution of the reagent was used to fill the crystallizing dish instead of distilled water as described above. Examples of reagents included but are not limited to: Oxone - 1 wt%; Oxone - 5 wt%; Oxone - 10 wt%; Hydrogen Peroxide (H₂O₂) - 3 wt%; Hydrogen Peroxide (H₂O₂) - 10 wt%; and, Sodium Hypochlorite (NaOCl) - 5 wt%. In addition, sample films were completely immersed into the chemical reagent solution to the bottom of crystallizing dish by placing a small glass bead on top of each of the film samples.

[0036] The experiment used to perform film functionalization is described below.

[0037] Embodiment 3 - Film/Surface Functionalization using ultra-sound techniques

[0038] Step 1

[0039] Resin film samples, up to 3 mil in thickness, were cut into 1 inch by 1 inch squares. Each functionalization was carried out using four test samples simultaneously functionalized in the same set up. The resin film samples to be functionalized were placed in a 600 mL capacity glass beaker. The beaker was filled with 500 mL of an aqueous solution of a reagent to be tested. Examples of reagents include but are not limited to: Oxone - 1 wt%; Oxone - 5 wt%; Oxone - 10 wt%; Hydrogen Peroxide (H2O2) - 10 wt%; Sodium Hypochlorite (NaOCl) - 5 wt%; Calcium Hypochlorite (Ca(C10)₂) - 5 wt%; and, Potassium Persulfate (K₂S₂O₈) - 10 wt%. The contents of the beaker were subjected to ultrasonic energy by directly introducing an ultrasonic horn (manufactured by Branson Ultrasonics Corp., 41 Eagle Road, Danbury, CT 06813) powered by a Branson Digital Sonifier 250 (also manufactured by Branson Ultrasonics Corp.). The horn was introduced into the beaker at the center such that the tip of the horn was 1 inch away from the bottom of the beaker. The power setting on the sonifier was set to 70% power level without any temperature control. The sonifier was turned on for 30 minutes, after which the film samples were removed from the beaker, washed with distilled water three times and air dried.

[0040] The experiment used to verify film functionalization is described below.

[0041] General protocol to evaluate film functionalization using methyl red as an organic dye containing carboxylic acid group:

[0042] Resin films functionalized by one of the methods described above were placed inside a 150 mL glass beaker containing a magnetic stirrer. A 100 mL aqueous solution of 0.115 M sodium dithionite was added to the beaker and the contents were gently stirred at room temperature for 4 hours. The film samples were then removed and washed with distilled water three times. Chemical attachment of Methyl Red via an esterification process was carried out by placing the film samples obtained in the previous step inside a beaker containing 100 mL of distilled water, 0.5 g of N-hydroxysuccinimide, 0.85 g of l-Ethyl-3-(3- dimethylaminopropyl)carbodiimide (EDC) hydrochloride and 0.5 g of methyl red. The mixture was gently stirred at room temperature for 8 hours using a magnetic stirrer. The film samples were then removed and washed three times with distilled water, then placed in a 100 mL solution of 0.20M sodium carbonate and gently stirred at room temperature for 15 minutes. Finally, the film samples were washed three times with distilled water and air dried. Attachment of the dye imparts color to the functionalized film which is indicative of an esterification reaction between methyl red and the functionalized film, where the intensity of film color is a measure of the extent of film functionalization. The greater the extent of film functionalization, the more intense will be the film color due to a greater extent of dye- attachment by esterification reaction.

[0043] Use of reducing agents other than sodium dithionite was attempted but did not provide film samples that produced intense color upon esterification with Methyl Red. Such reducing agents included aqueous solutions of the following reagents at given concentrations: sodium thiosulfate (Na₂S₂0₃) - 0.115M; sodium thiosulfate (Na₂S₂0₃) - 0.25M; Sodium bisulfite (NaHS0₃) - 0.25M.

[0044] As described above, in some embodiments, the present method includes treating a surface with an oxidizing agent in the presence of UV radiation, modifying surface functional groups using an inorganic sulfur compound, and attaching organic moieties from an organic compound comprising one or more carboxylic acid groups to the modified surface functional groups using an esterification reagent. The following example was performed according to this method.

[0045] Example 1

[0046] Step 1 - treatment with an oxidizing agent:

[0047] a) A polyethylene, e.g., low density polyethylene (LDPE), film was directly exposed in ambient air to a UV radiation source irradiating at wavelengths such as 184.9 nm and 253.7 nm for one hour at room temperature. [0048] b) The film was then rinsed with water three times for five minutes each time.

[0049] Step 2 - generation of 'reactive entities' over the surface:

[0050] a) The film was placed in a six weight percent (6 wt%) aqueous solution of sodium hydrosulfite ( a2S20₄) with mechanical agitation at 25°C for two hours. This step generates 'reactive entities' at the surface of the substrate for performing chemical modifications as described herein.

[0051] b) The film was then rinsed with water three times for five minutes each time.

[0052] Step 3 - chemical attachment of organic compounds:

[0053] a) The film was then treated with an organic acid, e.g., a dye comprising one or more carboxylic acid group, and EDC-HCl (l-ethyl-3-(3- dimethylaminopropyl)carbodiimide hydrochloride) at a concentration of 1.6 wt% at room temperature under aqueous conditions at 25°C for four hours in the presence of N- hydroxysuccinimide at a concentration of 1.0 wt%.

[0054] b) The film was then rinsed with water three times for five minutes each time.

[0055] As described above, in some embodiments, the present method includes treating a surface with an oxidizing agent in the presence of an ultrasonic energy source, modifying surface functional groups using an inorganic sulfur compound, and attaching organic moieties from an organic compound comprising one or more carboxylic acid groups to the modified surface functional groups using an esterification reagent. The following example was performed according to this method.

[0056] Example 2

[0057] Step 1 - treatment with an oxidizing agent:

[0058] a) A polyethylene, e.g., low density polyethylene (LDPE), film was suspended in an aqueous solution containing 2 wt% of Oxone® (chemically, potassium peroxymonosulfate), at room temperature with ultrasonic agitation for one hour. The temperature of the solution gradually rose which was not controlled.

[0059] b) The film was then rinsed with water three times for five minutes each time.

[0060] Step 2 - generation of 'reactive entities' over the surface: [0061] a) The film was placed in a six weight percent (6 wt%) aqueous solution of sodium hydrosulfite ( a2S20₄) with mechanical agitation at 25°C for two hours. This step generates 'reactive entities' at the surface of the substrate for performing chemical modifications as described herein.

[0062] b) The film was then rinsed with water three times for five minutes each time.

[0063] Step 3 - chemical attachment of organic compounds:

[0064] a) The film was then treated with an organic acid, e.g., a dye comprising one or more carboxylic acid groups, and EDC.HC1 (l-ethyl-3-(3- dimethylaminopropyl)carbodiimide hydrochloride) at a concentration of 1.6 wt% at room temperature under aqueous conditions at 25°C for four hours in the presence of N- hydroxysuccinimide at a concentration of 1.0 wt%.

[0065] b) The film was then rinsed with water three times for five minutes each time.

[0066] As described above, in some embodiments, the present method includes treating a surface with an oxidizing agent, modifying surface functional groups using an inorganic sulfur compound, and attaching organic moieties comprising one or more carboxylic acid groups to the modified surface functional groups using an esterification reagent. The following example was performed according to this method.

[0067] Example 3

[0068] Step 1 - treatment with an oxidizing agent:

[0069] a) A polyethylene, e.g., low density polyethylene (LDPE), film was suspended in a mechanically agitated aqueous solution of potassium permanganate (KMn0₄) at a concentration of 0.25M in 0.1M HCl solution, at 50°C for two hours at atmospheric pressure.

[0070] b) The film was then rinsed with water and placed in an aqueous

36 wt% HCl solution with mechanical agitation at 25°C for fifteen minutes until loss of any coloration, and then rinsed with water three times for five minutes each time.

[0071] Step 2 - generation of 'reactive entities' over the surface:

[0072] a) The film was placed in a six weight percent (6 wt%) aqueous solution of sodium hydrosulfite ( a2S20₄) with mechanical agitation at 25°C for two hours. This step generates 'reactive entities' at the surface of the substrate for performing chemical modifications as described herein.

[0073] b) The film was then rinsed with water three times for five minutes each time.

[0074] Step 3 - chemical attachment of organic compounds

[0075] a) The film was then treated with an organic acid, e.g., a dye comprising one or more carboxylic acid groups, and EDC.HC1 (l-ethyl-3-(3- dimethylaminopropyl)carbodiimide hydrochloride) at a concentration of 1.6 wt% at room temperature under aqueous conditions at 25°C for four hours in the presence of N- hydroxysuccinimide at a concentration of 1.0 wt%.

[0076] b) The film was then rinsed with water three times for five minutes each time.

[0077] In addition to the foregoing examples, the following examples were also performed using variations in the embodiments described above.

temperature for 7 days; then

esterification

H₂S0₄/NaN03/KMn0₄; then S₂0₃ ^2~;

ί η/α η/α - then esterification

H₂S0₄/NaN0₃/KMn0₄; then HSO3^1";

† η/α η/α - then esterification

Ultraviolet (UV)/Ozone; then S₂0₄ ^2~;

† † % - then esterification

Sample was

UV/Oxone; then S₂0₄ ^2~; then

ί ί η/α completely dipped esterification

into the reagent

Sample was

UV/3% H₂0₂; then S₂0₄ ^2~; then

ί ί η/α completely dipped esterification

into the reagent

Sample was

UV/10% H₂0₂; then S₂0₄ ^2"; then

ί η/α η/α completely dipped esterification

into the reagent

Sample was

UV/NaOCl; then S₂0₄ ^2"; then

ί η/α η/α completely dipped esterification

into the reagent

Ultrasonic (US)/Oxone; then S₂0₄ ^2";

† η/α % - then esterification

US/NaOCl; then S₂0₄ ^2"; then

ί % η/α - esterification

US/Ca(OCl)₂; then S₂0₄ ^2"; then

ί % η/α - esterification

US/S₂0₈ ^2"; then S₂0₄ ^2"; then

ί % η/α - esterification

US/10% H₂0₂; then S₂0₄ ^2"; then

ί η/α η/α - esterification

NaOCl; then S₂0₄ ^2"; then esterification ί η/α η/α -

Oxone; then S₂0₄ ^2"; then esterification ί η/α η/α - S2O₈ ^2"; then S2O4^2"; then esterification † n/a n/a -

PE - polyethylene

LDPE - low density polyethylene

PP - polypropylene

PET - polyethylene terephthalate

† - indicates a contributive and affecting result as applicable to the present methods

- indicates a contributive yet non-affecting result as applicable to the present methods n/a - not attempted

Table 1

[0078] The reaction mechanisms shown in Figure 1 depict the transformation from an unmodified organic polymer surface to a modified organic polymer surface having a chemically attached or bonded compound comprising one or more carboxylic acid groups.

[0079] It should be appreciated that the oxidation mechanisms described herein between an organic material, e.g., a hydrocarbon, and a transition metal oxidant are a subject of study in the scientific community and such mechanisms are not well understood in several cases including permanganate oxidation. The oxidation mechanism is generally considered to be a radical or an electron transfer process. The reduction mechanisms typically involve a transfer of electron or a hydride within a solvent cage depending on the reagent used. The reduction mechanisms may also involve, as with sulfur-based reagents, an oxidative addition of a sulfur compound followed by a simple hydrolysis of the carbonyl-sulfur adduct.

[0080] Results of various experiments are shown in Figures 2 and 3. In each figure, the lengths of time the film samples were exposed during an oxidative step with potassium permanganate (KMnC^), are shown on the X-axis, i.e., 15 minutes to 3 hours, the various wavelength ranges measured are shown on the Y-axis, i.e., 510 nm - 520 nm, 510 nm - 530 nm and 500 nm - 540 nm, and the maximum absorbance due to the immobilized methyl red over the film surface by method described here for wavelength range measured is shown on the Z-axis. UV-Vis measurements reported here were performed using Newport OSM-400 UV/VIS-U spectrophotometer with a Newport LSM-DT-S UV-VIS source (Newport Corporation, 1791 Deere Avenue, Irvine, CA 92606). Figure 2 shows the results of immobilization of methyl red when the film samples were not exposed to a reducing agent such as a2S20₄. Figure 3 shows the results of immobilization of methyl red when the film samples were exposed to a reducing agent such as a₂S₂0₄. Figure 4 shows the differences in absorbance between the experiments shown in Figures 2 and 3. As can be seen in Figure 4, exposure to a reducing agent generally improves the immobilization of methyl red to the surfaces of the film samples, and in particular improves the performance of immobilization during periods of shorter exposure of the film samples to potassium permanganate, e.g., periods of 15 minutes to 75 minutes. An industrial process utilizing surface functionalization steps disclosed here can benefit from the shorter times required for an effective surface functionalization when using a reducing agent, such as sodium hydrosulfite, compared to when no reducing agent is utilized.

[0081] The present disclosure sets forth an all aqueous process to afford polymers, compounded materials and commodity plastics the ability to chemically attach or bond with organic chemicals and reagents in a controlled manner by introducing readily accessible surface functional groups.

[0082] Thus, it is seen that the objects of the present methods are efficiently obtained, although modifications and changes to the methods should be readily apparent to those having ordinary skill in the art, which modifications are intended to be within the intent and scope of the methods as claimed. It also is understood that the foregoing description is illustrative of the present methods and should not be considered as limiting. Therefore, other embodiments of the present methods are possible without departing from the intent and scope of the present methods.

Claims

CLAIMS What Is Claimed Is:

1. A method of chemically attaching an organic compound comprising a carboxylic acid group to a polymeric surface, the method comprising the steps of:

a) treating the polymeric surface with an oxidizing agent to form a plurality of carbonyl functional groups on the polymeric surface;

b) contacting the plurality of surface carbonyl functional groups with a reducing agent in a first aqueous solution to form a plurality of modified surface hydroxyl functional groups; and,

c) contacting the plurality of modified surface hydroxyl functional groups with an esterification reagent and the organic compound in a second aqueous solution to attach the organic compound to the polymeric surface.

2. The method of modifying a polymeric surface of Claim 1 wherein the step of treating the polymeric surface with an oxidizing agent comprises:

al) simultaneously exposing the polymeric surface to an oxidizing reagent and an ultra-violet (UV) radiation source.

3. The method of modifying a polymeric surface of Claim 2 wherein the oxidizing reagent is selected from the group consisting of: ozone; an aqueous solution of potassium peroxymonosulfate; an aqueous solution of potassium persulfate; an aqueous solution of hydrogen peroxide; an aqueous solution of sodium hypochlorite; an aqueous solution of sodium chlorite; an aqueous solution of sodium chlorate; an aqueous solution of sodium perchlorate; an aqueous solution of tert-butyl hydroperoxide; an aqueous solution of sodium perborate; and, combinations thereof.

4. The method of modifying a polymeric surface of Claim 2 wherein the oxidizing reagent is ambient air.

5. The method of modifying a polymeric surface of Claim 2 wherein the UV radiation source emits light at wavelengths between about 180 nm and 260 nm.

6. The method of modifying a polymeric surface of Claim 5 wherein the UV radiation source emits light at a first wavelength of 184.9 nm and a second wavelength at 253.7 nm.

7. The method of modifying a polymeric surface of Claim 1 wherein the step of treating the polymeric surface with an oxidizing agent comprises:

al) simultaneously exposing the polymeric surface to an oxidizing reagent in a third aqueous solution and an ultrasonic energy source.

8. The method of modifying a polymeric surface of Claim 7 wherein the oxidizing reagent is selected from the group consisting of: potassium peroxymonosulfate; hydrogen peroxide; calcium hypochlorite; sodium hypochlorite; sodium chlorite; sodium chlorate; sodium perchlorate; sodium perborate; tert-butyl hydroperoxide; potassium peroxydisulfate; and, combinations thereof.

9. The method of modifying a polymeric surface of Claim 1 wherein the step of treating the polymeric surface with an oxidizing agent comprises:

al) exposing the polymeric surface to a third aqueous solution comprising an acid and a component selected from the group consisting of: potassium permanganate; ceric ammonium nitrate; a chromium (VI) compound; and, combinations thereof.

10. The method of modifying a polymeric surface of Claim 9 wherein the acid is selected from the group consisting of: hydrochloric acid; sulfuric acid; nitric acid; and, combinations thereof.

11. The method of modifying a polymeric surface of Claim 9 wherein the third aqueous solution further comprises a salt.

12. The method of modifying a polymeric surface of Claim 1 1 wherein the salt is selected from the group consisting of: a nitrate of an alkali metal; a nitrate of an alkaline earth metal; and, combinations thereof.

13. The method of modifying a polymeric surface of Claim 1 wherein the reducing agent is selected from the group consisting of: an inorganic sulfur compound; a borohydride; a cyanoborohydride; formic acid; a salt of formic acid with an alkali metal; a salt of formic acid with an alkaline earth metal; iron powder in combination with acetic acid; zinc powder in combination with acetic acid; and, combinations thereof.

14. The method of modifying a polymeric surface of Claim 13 wherein the reducing agent is the inorganic sulfur compound selected from the group consisting of: alkali sulfide; hydrosulfide; polysulfide; thiosulfate; dithionite; bisulfite; and, combinations thereof.

15. The method of modifying a polymeric surface of Claim 1 wherein the esterification reagent is selected from the group consisting of: l-ethyl-3-(3- dimethylaminopropyl)carbodiimide; and, l-ethyl-3-(3-dimethylaminopropyl)carbodiimide in combination with N-hydroxysuccinimide.

16. The method of modifying a polymeric surface of Claim 1 wherein the polymeric surface is formed from a substrate selected from the group consisting of: an organic polymer; a resin; a resinoid; a cellulose derivative; a casein material; a protein; and, combinations thereof.

17. The method of modifying a polymeric surface of Claim 1 wherein the organic compound is selected from the group consisting of: a dye; an antimicrobial; an organic oxygen absorber; a light absorber; a moisture absorber; an ethylene absorber; a thiol absorber; an ozone scavenger; and, combinations thereof.

18. A method of modifying a polymeric surface comprising a plurality of carbonyl functional groups to permit chemical attachment of an organic compound comprising a carboxylic acid group, the method comprising the step of:

a) contacting the plurality of carbonyl functional groups with a reducing agent in a first aqueous solution to form a plurality of modified surface functional groups comprising hydroxyl functional groups.

19. The method of modifying a polymeric surface of Claim 18 wherein the reducing agent is selected from the group consisting of: an inorganic sulfur compound; a borohydride; a cyanoborohydride; formic acid; a salt of formic acid with an alkali metal; a salt of formic acid with an alkaline earth metal; iron powder in combination with acetic acid; zinc powder in combination with acetic acid; and, combinations thereof.

20. The method of modifying a polymeric surface of Claim 19 wherein the reducing agent is the inorganic sulfur compound selected from the group consisting of: alkali sulfide; hydrosulfide; polysulfide; thiosulfate; dithionite; bisulfite; and, combinations thereof.