A.M. Grande

Review of current strategies to induce self-healing behaviour in fibre reinforced polymer based composites

Abstract This paper addresses the various strategies to induce self-healing behaviour in fibre reinforced polymer based composites. A distinction is made between the extrinsic and intrinsic healing strategies. These strategies can be applied at the level of the fibre, the fibre/matrix interface or at the level of the matrix. It is shown that the degree of healing depends on the type of damage and the testing mode used and examples are given both for extrinsic and for intrinsic healing systems. The conclusion is drawn that self-healing in fibre reinforced composites is possible yet unlikely to become a commercial reality in the near future.

Self-repairing systems based on ionomers and epoxidized natural rubber blends.

The development of materials with the ability of intrinsic self-repairing after damage in a fashion resembling that of living tissues has important scientific and technological implications, particularly in relation to cost-effective approaches toward damage management of materials. Natural rubbers with epoxy functional groups in the macromolecular chain (ENR) and ethylene-methacrylic acid ionomers having acid groups partially neutralized with metal ions possess self-repairing behavior following high energy impacts. This research investigates the self-repairing behavior of both ENR and ionomers during ballistic puncture test on the basis of their thermal and mechanical properties. Heterogeneous blending of ionomers and ENR have also been used here as a strategy to tune the thermal and mechanical properties of the materials. Interestingly, blends of sodium ion containing ionomer exhibit complete self-repairing behavior, whereas blends of zinc ion containing ionomer show limited mending. The chemical structure studied by FTIR and thermal analysis shows that both ion content of ionomer and functionality of ENR have significant influence on the self-repairing behavior of blends. The mobility of rubbery phases along with its interaction to ionomer phase in the blends significantly changes the mending capability of materials. The healing behavior of the materials has been discussed on the basis of their thermal, mechanical, and rheological tests for each materials.

Characterization of self-healing polymers : From macroscopic healing tests to the molecular mechanism

Over the last few years, several testing methods have been introduced for the detection and quantification of autonomous and thermally stimulated healing in polymers. This review summarizes some of the most prominent state-of-the-art techniques for the characterization of polymer healing occurring at the microscopic and macroscopic levels during the repair of damage such as scratches, cracks, or ballistic perforations. In addition to phenomenological investigation of the self-healing process, a range of physical characterization techniques have been explored for elucidation of the underlying healing mechanism at the molecular or polymer network level. The present state of visual methods, spectroscopic techniques, scattering techniques, and dynamic methods is described. A short outlook is provided, discussing the future challenges and expected new trends in the characterization of self-healing polymers.

Monitoring Network and Interfacial Healing Processes by Broadband Dielectric Spectroscopy: A Case Study on Natural Rubber

Broadband dielectric spectroscopy (BDS) is introduced as a new and powerful technique to monitor network and macroscale damage healing in an elastomer. For the proof of concept, a partially cured sulfur-cured natural rubber (NR) containing reversible disulfides as the healing moiety was employed. The forms of damage healed and monitored were an invisible damage in the rubber network due to multiple straining and an imposed macroscopic crack. The relaxation times of pristine, damaged, and healed samples were determined and fitted to the Havriliak-Negami equation to obtain the characteristic polymer parameters. It is shown that seemingly full mechanical healing occurred regardless the type of damage, while BDS demonstrates that the polymer architecture in the healed material differs from that in the original one. These results represent a step forward in the understanding of damage and healing processes in intrinsic self-healing polymer systems with prospective applications such as coatings, tires, seals, and gaskets.

Effect of curing on the mechanical and healing behaviour of a hybrid dual network: a time resolved evaluation

In the present work we show the effect of the crosslinking degree on the mechanical and healing behaviour of a healable thermoset dual-network polymer. A hyphenated rheological test (i.e. simultaneous rheology and FTIR) was used to follow the effect of the curing process on the mechanical behaviour in relation to the underlying chemical reactions. The effect of curing on the bulk properties and the polymer interfacial healing was studied using gap closure kinetics and a fracture mechanical test. The increased crosslinking density at longer curing times led to a more temperature-stable polymer network with significantly higher mechanical properties (elastic modulus and strength at break). It was found that the damage closure kinetics decrease with the curing degree but the ultimate interfacial healing efficiency does not. The results here reported highlight the effect of the crosslinking density on the kinetics of damage closure with a low impact on the maximum interfacial healing efficiency as long as the amount of reversible bonds remains constant.

Reply to Comment on “Monitoring Network and Interfacial Healing Processes by Broadband Dielectric Spectroscopy: A Case Study on Natural Rubber”

Das et al. comment our publication on the use of broadband dielectric spectroscopy as a potential tool for monitoring healing processes in natural rubber. They argue that our interpretation of self-healing processes should be handled with care and that critical issues like rubber tackiness and sample fabrication for dielectric experiments were not properly addressed. We agree that tackiness in partially cured rubber does exist and that interpretation of dielectric experiments requires detailed insight into both the processes and the method, but we will try and re-argue below the correctness of our approach as reported in our publication.

Integrated Solutions for Safe Fuel Tanks

The integration of different tools for the prevention of fires or explosions due to impact or bullet damage may significantly improve the safety of fuel tanks. Self-healing polymers have demonstrated their ability to autonomous mending bullet punctures. The results of ballistic tests to check the response of multilayer structures based on self-healing ionomer and aramid fabric or carbon foam are presented in view of their potential employment as safety materials for dangerous liquids containment. Considerations related to the effect of coupling of different materials over self-healing response are discussed. A conceptual solution that integrates self-healing polymers or composites with cellular filler made of wrinkled aluminium foil for fuel tanks is proposed and discussed. Keywords fillers, fuel tanks, impact, self-healing Language: en

Response to Comment on “Turning Vulcanized Natural Rubber into a Self-Healing Polymer: Effect of the Disulfide/Polysulfide Ratio”

Self-Healing Polymer: Effect of the Disulfide/Polysulfide Ratio” Marianella Hernańdez Santana,*,†,‡ Antonio M. Grande,† Sybrand van der Zwaag,† and Santiago J. García† †Novel Aerospace Materials Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands ‡Institute of Polymer Science and Technology (ICTP-CSIC), Juan de la Cierva 3, 28006 Madrid, Spain

Improved Solutions For Dangerous LiquidContainment

The availability of new materials with uncommon characteristics and functionalities gives the opportunity to develop and possibly integrate new conceptual solutions for the improvement of safety in the design and manufacture of containers for critical substances. Numerous examples can be devised where a proper containment of liquid, even after tank damage, is essential with regard to safety issues. Bullet penetration or debris impact of fuel tanks are two relevant examples where specifically designed configuration and materials may significantly improve safety margins. In such situations, deflagration can be activated by sudden variation of internal pressure and temperature or liquid spilling due to wall container perforation. Cellular filler material in the container can remarkably dispel fire heat and limit pressure wave peaks generated by a bullet explosion; moreover, the overall response to impact loads in case of a crash is remarkably improved. Different fillers with particular configurations, ranging from porous structure to expanded aluminium foil, have been tested as tank explosion suppression media with remarkably positive results. In traditional multilayer wall fuel tanks, self-sealing capability can be obtained as a result of swelling or chemical reaction of rubber/foam layer when it comes in contact with the spilling internal liquid. A usual drawback of these materials is the limited resistance to aging which reduces their effectiveness with time. Moreover, the sealing material does not give structural contribution furthermore consistently increasing the weight of the component. Polymeric materials with intrinsic self-healing capability may become a valid alternative to traditional configurations. In this context, ethylene-methacrylic acid based ionomers can be adopted as self-healing layers. The coupling of such selfSafety and Security Engineering V 379 doi:10.2495/ 3 SAFE 0 1 1 34 www.witpress.com, ISSN 1743-3509 (on-line) WIT Transactions on The Built Environment, Vol 134,