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Self-Healing Shape Memory Polymer Coatings for Chemical/Biological Protective Clothing


OBJECTIVE: To develop and prepare self-healing shape memory polymer coatings which contain embedded nano-capsules of bi-component reactive chemicals for use in Chemical/Biological (CB) protective clothing. DESCRIPTION: Soldiers"personal safety is compromised when CB protective uniforms become torn. This topic seeks to develop coatings to self-seal or heal a textile material. Technology applications include enhancing fielded uniforms such as the Joint Service Lightweight Integrated Suit Technology (JSLIST) and the Uniform Integrated Protective Ensemble (UIPE) future increments as well as multiple individual clothing and equipment (CIE) items. There are two known approaches for in situ clothing repair: (1) Interaction of reactive chemical species encapsulated in nano-capsules which are pre-embedded in the coating, and (2) Application of an external force (e.g., increased temperature and/or pressure, etc.) to torn clothing as in a simple laundering procedure for supramolecular polymer coatings. [Reference 1] This topic will focus on the first approach, and solicits technical efforts to develop solutions to self-seal the tears on soldier"s clothing. This topic is also open to other novel solutions addressing the technical innovation sought. Past work on self-healing polymers has shown that it is possible to produce microcapsules (10 to 100 micrometers) containing reactive chemicals for use in self healing polymer systems; [References 2 to 5] however long term stability of the catalyst is a possible issue, and micro-size capsules (50 micrometers plus) are not suitable for coating applications. [Reference 1] In more recent studies, nanocapsules (100-500 nanometers) were found to provide sufficient interfacial area when incorporated into a polymer coating to significantly improve self-sealing efficiency. [Reference 6] Furthermore, self-healing epoxy coatings, with two compartmentalized reactive species (a modified amine and epoxy, respectively) embedded within the coating was demonstrated. [Reference 7] The two reactive species were encapsulated prior to being embedded in the polymer coating using emulsion polymerization. Shape Memory Polymer (SMP) [Reference 8] materials are another complementary approach to past self-healing systems by functioning as responsive matrix carrier for the bi-component reactive nano-embedded capsules. This is due to the matrix ability to adjust its molecular structure to restore (i.e., remember) a polymer coating to the original state (prior to the damage event) thus minimizing flaws such as torn gaps. Coatings should have comparable physical characteristics as that of virgin (un-torn) polymer coatings after the self healing process occurs. They should not adversely affect the performance of the protective ensemble. The following are selected key performance goals/metrics for coating applied to textile materials and protective clothing. Tensile/Tear Strength (FTMS191A TM5034; at break): Warp:>200 lb; fill:>125 lb; Elongation>35%. Abrasion Resistance (FTMS191A TM3884):>5000 cycles. Stiffness (FTMS191A TM5202):<0.01 lb. Dimensional Stability (FTMS191A TM2646): Unidirectional Shrinkage<3%. Durability (FTMS191A TM 2724): Pass after 5 laundering cycles without tear gap(s) reopening. Weight (FTMS191A TM 5041):<0.1 oz/sq. yd of added weight to the self-healed area. Thickness (FTMS191A TM 5030):<25 m (micrometers) of added thickness to the self-healed polymer. Colorfastness (FTMS191A TM5605): Minimal to no visual (color) changes to self-healed tears. Air Permeability (FTMS191A TM5450):<0.2 cu. ft of air/min./sq. ft (i.e., minimal to no significant changes.) Chemical Warfare Agent (CWA) simulant permeation resistance (NSRDEC In-house test method):<10 g/sq. m/24 h. PHASE I: Develop a series of self healing coating materials to demonstrate feasibility. Identify successful candidates using methodology described in the key performance goals. Analyses shall include parameters listed above. Successful coatings shall have comparable characteristics of base polymer coating (i.e., flexible, and durable, etc.), and will not degrade the current performance metrics of fielded clothing systems, and be feasible for application to clothing/textile in Phase II. Key physical properties such as tear resistance and CWA simulant permeation data will be used as the primary decision criteria for Phase II work continuation. Phase I deliverables: Self-healable SMP coating samples on release glass surface or standalone films, and a technical report documenting concept design, processes and equipment and test data analysis approaches used in the development of novel coatings, as well as literature searches, technical processes, equipment, materials and chemicals used, technical references, etc. (TRL 4 Component and/or breadboard validation in laboratory environment.) PHASE II: Refine self healable SMP coating formulations, produce durable coated textiles, and refine pilot and commercial processes to produce defect-free coated textiles. Key performance metrics identified in the Description section will apply in Phase II. Prototype clothing will be fabricated, and system level testing will be conducted to assess the usability of self-healing textiles. A commercial viability study will be conducted, and commercial partners identified for Phase III. System level testing will include laundering, thermal manikin testing, rain-room testing, etc. Limited field durability testing of self-healing SMP coated clothing will be planned and conducted under NSRDEC guidance. Life cycle and environmental testing of self healing SMP coated clothing will be conducted. Material costs and cost metrics of viable commercialization of self-healing SMP coating technology will be assessed and studied. Deliverables: 100 linear yards of self-healing SMP engineered fabric, and a final test report will be submitted which includes details of the down-selection process of self-healing SMP coatings, technical data, test results of material and system-level testing, evaluation of coated clothing, technical processes for producing novel coatings and coated textiles, commercial viability study, cost metrics, and life cycle and environmental test results. (TRL 5 - Component and/or breadboard validation in relevant environment.) PHASE III: Transition new self-healing coated textile technology to fielded applications such as the All-Purpose Personal Protective Ensemble (AP-PPE), the Joint Chemical Biological Coverall for Combat Vehicle Crewman (JC3), the Integrated Footwear System (IFS) sock, and the JSLIST Overgarment, and dual-use applications such as clothing for chemical handlers, agricultural workers, domestic preparedness emergency responders, anti-terrorism personnel, and medical personnel working in potentially contaminated environment with toxic industrial chemicals and bacterial/viral infected environment. Self-healing shape memory polymer coated textiles will also be ready for transition to the next UIPE increment. (TRL 6 - System/Subsystem model or prototype demonstration in a relevant environment.) PHASE III DUAL USE APPLICATIONS: SBIR contractor and its commercial partners will formalize partnerships and actively seek dual-use applications for novel self-healing SMP coated textiles and protective clothing. Potential applications include commercial clothing for mountaineers, all-weather sport enthusiasts, as well as non-clothing applications. REFERENCES: 1. University of New Hampshire,"Self-Sealing Polymer Coatings for CB Protective Clothing,"NSRDEC Contract #W911QY09C0100, August 2010-Aug 2011. 2. Blaiszik B.J., Kramer, S.L.B, Olugebefola, et al.,"Self-Healing Polymers and Composites,"Annual Review of Materials Research 2010 40, 179-211. 3. White, S. R.; Sottos, N. R.; et al. Nature 2001, 409, 794; Adv. Mater. 2005, 17, 205. 4. Toohey, K. S.; Sottos, N. R.; Lewis, J. A.; et al. Nature Mater. 2007, 6, 581 5. Chen, X.; Wudl, F.; et al. Science 2002, 295, 1698; Macromolecules 2003, 36, 1802. 6. van Benthem, R. A. T. M.; Ming, W.; de With, G. Self-healing polymer coatings, in"Self Healing Materials: An Alternative Approach to 20 Centuries of Materials Science"(van der Zwaag, S.; Ed.), Chapter 7, pp139-159, Springer, 2007. 7. Sundberg, D. C.; Tsavalas, J. G.; Nguyen, J. K. US patent application pending. 8. Diaplex shape memory polyurethane, Cited materials are readily accessible and available as referenced above.
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