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<p>AMI has identified an unmet market need for an antimicrobial coating applicable to modular conveyor belts and other high-risk polymer surfaces in food processing. To address the need, AMI has created a product development plan to achieve the following goals at the end of the comprehensive commercialization effort (SBIR phase III):- Development of a process for application of a potent, safe, durable, and cost effective antimicrobial N-halamine coating to existing or new polyethylene or polypropylene components of modular conveyor belts. Coating will be capable of deactivating bacteria such as L. monocytogenes and S. enteritidis in 60 minutes or less (6 log reduction), and coating will retain at least 50% of its original active chlorine for more than 6 months. It is highly desirable that the coating is field or on-site applicable.- Confirmation that the treatment is safe, FDA approved, and minimally impactful on performance (load and speed capacity), durability, and chemical resistance of treated product.- Achievement of a cost target of less than $10 per square meter (about 1/3 of current antimicrobial treatments).The phase I effort is a key part of satisfying the over-arching goals and is designed to provide proof of concept.The objectives will focus on the following:
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<br>Objective 1: Optimize plasma treatment parameters to maximize polyethylene surface activation such that a high degree of covalent crosslinking between the polyethylene surface and initial N-halamine monolayer is achieved. Minimum target is 8% nitrogen atomic concentrationas demonstrated by XPS analysis.
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<br>Objective 2: Optimize layer-by-layer and crosslinking in order to achieve an antimicrobial performance of 99.9% kill rate in less than 60 minutes against gram positive and gram negative bacteria as defined above.
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<br>Objective 3: Verify that surface chlorine is stable in simulated meat-contact conditions and <2% active chlorine "leaches" from treated material.
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<br>Objective 4: Verify that material properties (tensile strength, Shore D hardness, surface roughness, and fatigue) of treated samples are retained within 90% of unmodified samples.
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Objective 5: Determine the relationship between antimicrobial performance and abrasion wear, and demonstrate that anticipated field abrasion life exceeds 12 months in typical RTE production.</p>
<p>Task 1. Determine the optimal plasma treatment parameters necessary to achieve maximum surface activation.PE samples will be initially cleaned. Once cleaned, samples will be dried with compressed nitrogen and dried overnight in a desicator. Next, treatment time, power, and chamber pressure will be systematically varied in order to maximize surface activity. Six samples of each configuration will be treated. Water contact angle measurements will be recorded.
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Task 2. Determine the crosslinking between PE and the initial N-halamine bilayer. Verify that the bond density achieved meets design requirements of not less than 8% atomic nitrogen.A PBS solution of 1% (w/w) melamine plus crosslinker EDC with NHS at concentrations of 50 mM and 5 mM respectively will be prepared. Samples activated using the optimized plasma treatment determined in task 1 will IMMEDIATELY be submerged and shaken for 2 hours at 150 rpm. FTIR analysis will initially be used to assess relative bonding levels. Final samples will be sent to an external testing lab for XPS analysis to confirm nitrogen percentage of at least 8%.
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Task 3: Determine the appropriate frequency for use of carbodiimides to achieve acceptable crosslinking of LBL bilayers.In this task, we will prepare six samples, each with 1, 2, 4, and 6 N-halamine bilayers prior to an EDC/NHS crosslinking step. Steps will be as follows:1. Plasma treat samples as according to optimized method determined in task 1.2. Prepare a 1% melamine PBS (pH 7.4) solution and submerge samples immediately after treatment. Shake at 150 rpm for 5 minutes and rinse with copious DI water.3. Repeat step 2 with 5% solution of PAA (w/w) and PBS.4. After application of 1 melamine/PAA bilayer, separate 6 of the samples for crosslinking treatment. Submerged in a solution of 50 mM EDC and 5 mM NHS and shake at 150 rpm for 2 hours. Dry with compressed nitrogen and store in a dry container.5. Repeat steps 2, 3, & 4 for remaining samples as appropriate to develop 6 samples each with 1, 2, 4, and 6 N-halamine bilayers plus 1 crosslinking step.6. Transform melamine into N-halamine compounds by chlorinating in 1% household bleach solution (6% sodium hypochlorite) for 30 minutes.We will evaluate the level of N-halamine crosslinked in each of the coated samples by determining active chlorine content.
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Task 4. Determine number of bilayers and crosslinking steps necessary to achieve targeted active chlorine of 32μg/cm2.We will prepare sets of 3 samples with varying N-halamine bilayers up to a maximum of 24 using the optimized processes established in task 3. These samples will be chlorinated and analyzed using FTIR. Finally, the active chlorine content will be determined using the iodometric titration procedure described in task 3. Samples of the formulation with the least number of bilayers that exceed the active chlorine target of 32μg/cm2 will be noted.
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<br>Task 5. Confirm the antimicrobial performance of samples against on L. monocytogenes (gram positive) and E. coli (gram negative).For all cultures, 20 μL of a bacterial suspension will be placed onto the surface of an N-halamine PE sample (ca. 2×2 cm). The sample will then be "sandwiched" using another identical sample to ensure full contact. After the predetermined periods of contact time, the entire "sandwich" will be transferred into 10 mL of a sterilized sodium thiosulfate (Na2S2O3) aqueous solution (0.03 wt %). The mixtures will be vigorously vortexed for 1 min and sonicated for 5 min to separate the samples, quench the active chlorines, and detach adherent cells from the film surfaces into the solution. The resultant solutions will be serially diluted, and 100 μL of each diluent will be placed onto the appropriate agar plates. The same procedure will also be applied to the untreated samples to serve as controls. Viable microbial colonies on the corresponding agar plates will be visually counted after incubation at 37 °C for 24 h.Each test will be repeated three times and the average value calculated.
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Task 6. Confirm the extent of leaching of treated PE materials is below 2% active chlorine.Samples will be prepared in accordance with procedures confirmed in task 5. These samples (n=6) will then be immersed in 10 mL of buffer solution of pH 6.5 prepared by mixing citric acid monohydrate (0.1 M) and sodium phosphate dibasic (0.2 M) and subjected to constant shaking (50 rpm) at 8 oC for 72 hours.After the test time elapses, 1 mL of solution will be extracted and tested with a Beckman DU 520 UV/vis spectrophotometer to determine whether melamine-containing compounds were released from the coating. The liquid sample will next be iodometrically titrated.
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Task 7. Determine the influence of N-halamine coatings on mechanical properties including tensile strength, shore D hardness, surface roughness, and fatigue.For tensile testing, samples will be prepared in accordance with ASTM D638-03, Standard Test Method for Tensile Properties of Plastics. Testing will be competed according to ASTM D638-03 using an MTS Insight Material Testing System. Fatigue strength impact will also be evaluated using the same test setup, but under dynamic load conditions. Hardness testing will also be completed according to ASTM D2240-05(2010), Standard Test Method for Rubber Property--Durometer Hardness. Surface roughness will also comparison between coated and uncoated samples will also be evaluated using handheld tester and FEI Quanta 450 Scanning Electron Microscope also available at the USD GEAR facility.
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Task 8. Evaluate typical wear characteristics of polyethylene modular conveyor belts after known periods of in-service.Actual conveyor belts will be attained from the RTE production facility along with maintenance records. Measurements will be taken systematically along the width and length of each belt to establish relative wear profiles. Maintenance records will then be used to correlate in-service times. Initial wear data will be used to guide abrasion testing as defined in task 8.
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Task 9. Complete Taber abrasion testing on N-halamine treated surfaces and establish a mathematical relationship between abrasion parameters and active chlorine content.Coated samples will be prepared according to procedures confirmed in task 5 and in accordance with ASTM D 4060-95 Standard Test Method for Abrasion Resistance of Organic Coatings by the Taber Abraser. Taber abrasion testing will be performed per ASTM D 4060-95 and wear performance monitored daily. Based on data recorded from task 7, active chlorine content will be tested at strategic intervals to establish a correlation between abrasion performance (wear index, wear cycles per mil) and chlorine levels.
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Task 10. Quantify actual wear of PE belts in an RTE production environment and compare with abrasion testing to predict coating lifecycle. Prior to installation, new belts used to replace specimens evaluated in task 7 will be measured and marked at specified locations along their length and width in order to develop an accurate representation of the as-new condition. These belts will be operated, cleaned, and maintained in the RTE production environment for approximately 90 days. Product volumes and maintenance records will be maintained throughout the in-service period.After the 90 day period, belts will be replaced and remeasured to quantify actual wear performance over time and specific product volumes. By assessing Taber abrasion results vs. chlorine content against actual wear history at known volumes, an initial assessment of durability can be calculated.
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Milestones:Kickoff - week 1Procurement of Supplies - week 3Task 1 Complete - week 6Task 2 Complete - week 9Task3 Complete - week 13Task 4 Complete - week 17Task5 Complete - week 21Task6 Complete - week21Task7 Complete - week25Task8 Complete - week6Task9 Complete - week 29Task 10 Complete - week 31Final Report - week 34</p>