Search

The development of self-healing polymeric materials was inspired by biological systems wherein damage initiates an autonomic healing response and can automatically repair the internal cracks/ damages without the need for external intervention. This is a new and fascinating field of research that has the potential to improve service life of the materials. These have attracted the attention of many scientists/researchers due to their wide range of applications. The self-healing materials have been broadly classified in to two categories: (1) extrinsic self-healing materials, wherein, the repairing agent is pre-embedded in to the resin matrix and no human involvement is needed to start the healing process, and (2) intrinsic self-healing materials, which do not have an embedded healing agent and an external-stimuli is essential to initiate the healing process. The current review article summarizes a state-of-art in terms of self-healing ability of the polymeric materials. It also provides comprehensive comparison of healing efficiencies, advantages and challenges for the future development, and potential applications of such materials in numerous fields, such as aerospace, coatings and paints, electronics energy, etc. [ABSTRACT FROM AUTHOR]

Mixtures of tung oil (TO) and 4,4'-bismaleimidodiphenylmethane (BMI) in the molar ratios of 1:3 and 2:3 were cured at 100 °C or 160 °C to produce the cured products (TB13, TB23 or htTB13, htTB23). Fourier-transform infrared spectroscopy of the cured products confirmed that the trans, trans-diene moieties of TO are almost completely consumed for all the cured products; furthermore, the maleimide groups were almost completely consumed for all the cured products, except for TB13. Differential scanning calorimetry results of the cured products revealed that TB13 and TB23 exhibited strong endothermic peaks due to the retro-Diels–Alder (rDA) reaction. The rDA enthalpy change (ΔHrDA) of TB13 was higher than that of TB23, and the ΔHrDAs of htTB13 and htTB23 were considerably smaller than that of TB13 and TB23. The tan δ peak temperatures of the cured products measured by dynamic mechanical analysis were in the range of 55–131 °C and were increased in the order: TB23 < TB13 < htTB23 < htTB13. The 5% weight loss temperatures of all the cured products were higher than 400 °C. Although TB13 and TB23 exhibited self-healing properties upon hot-pressing at 100 and 120 °C, respectively, htTB13 and htTB23 exhibited no self-healing ability. [ABSTRACT FROM AUTHOR]

This article reports a combination of experimental and computational approaches that were used to study the properties of 3D-printed polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS). Both experimental and ab initio structural computations were used to characterize the structural, electronic, optical and mechanical properties of printed packaging products. The 3D- printed PLA and ABS, which were obtained via lab-scale filament extrusion, exhibited tensile strengths of 39.07 and 16.12 MPa, respectively. Theoretical examination of both PLA and ABS was achieved by density functional theory (DFT) approach generated by the Cambridge Serial Total Package (CASTEP) and forcite module in the material studio (MS) software. Norm conserving module was used as the plane wave basis pseudopotential for ABS and PLA energy calculations, ensuring scattering properties of the pseudopotential were correctly reproduced. In all simulations, molecular structures were geometrically optimized using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm. The exchange correlation functionals used in the determination of electronic properties of the polymers were generalized by gradient approximation under Perdew-Burke-Ernzehorf. The calculated band structure of 1.899 and 2.539 eV for PLA and ABS, respectively, and the computed density of states, all suggested poor conductivity for both materials. This phenomenon was supported by the low computed values of the work functions (Φ) 3.364 eV and 4.503 eV, which signified wide separation between the fermi and vacuum level hence reduced charge carriers. Overall, the good mechanical properties of PLA to ABS are in agreement with values obtained in other studies. In particular, PLA is a greener alternative in packaging and biomedical applications since it is derived from renewable resources and can be used in applications requiring biodegradability. [ABSTRACT FROM AUTHOR]

The present work investigated the effects of the zeolite 4A on the flame retardancy and thermal stability of aluminum β-(p-nitrobenzamide) ethyl methyl phosphinate (AlNP) in acrylonitrile–butadiene–styrene copolymer (ABS). The synergistic effect between AlNP and zeolite 4A was assessed with cone calorimeter test (CCT), thermogravimetric measurement (TG), Fourier transform infrared spectroscopy (FTIR) analysis of the gaseous products, and scanning electron microscopy (SEM) characterization of the residues char. Keep the total loading of the additives at 25 wt.%; ABS filled with 22 wt.% AlNP and 3 wt.% zeolite 4A (ABS-AlNP22-A3) reaches a UL94 V0 classification with LOI value of 29.3%. By comparison, ABS with 25 wt.% AlNP alone (ABS-AlNP25) only passes the UL 94 V 1 rating with LOI value of 26.0%. CCT results verify that the zeolite 4A can depress the heat and smoke release of combustion. The peak heat release rate, total heat release, and total smoke release of ABS-AlNP22-A3 are reduced by 13.84%, 14.35%, and 20.4%, respectively, compared to ABS-AlNP25. The TG/FTIR analysis and morphology of the char residues from scanning electron microscopy further demonstrate that zeolite 4A could retard the volatilization of hydrocarbons and promote the char formation in the combustion process of ABS. The mechanism of synergistic effect of the zeolite 4A is proposed based on the experiment and related previous study. [ABSTRACT FROM AUTHOR]

An aminated β-cyclodextrin (NCD) with an amine substitution degree of 16.4 was prepared through the thiol–ene reaction of allylated β-cyclodextrin and cysteamine hydrochloride. The thermal curing reactions of sorbitol polyglycidyl ether (SPE) with NCD, Jeffamine® ED-600 (JA, an aliphatic polyether amine), and adamantylamine (NAD) with a feed epoxy/NH2 ratio of 1:1 and feed NH2 molar ratios of NCD/JA/NAD = 1/1/1 and 1/2/1 produced epoxy-amine networks. The FT-IR and gel fraction measurements for the cured products revealed that polymer networks were formed by the reaction of epoxy and amino groups. The cured product with a higher JA content showed lower glass transition temperature (Tg), tensile strength, and tensile modulus results than those of the cured product with a lower JA content. Compared with the product with lower JA, the product with higher JA exhibited self-healing properties upon treatment at 60 °C. The self-healing driven by the NCD/NAD host–guest interaction was demonstrated as the self-healed sample returned to its original state after immersion in an ethanol solution of NAD. Moreover, the corresponding SPE/NCD/JA and SPE/JA/NAD cured products did not exhibit self-healing capacity. [ABSTRACT FROM AUTHOR]

The reaction of furfurylamine (FA) and 4,4′-bismaleimidodiphenylmethane (BMI) at a molar ratio of 2/1 generated a product (FABMI) mainly composed of 4,4′-bis(2-furfurylaminosuccinimido)diphenylmethane. Mixtures of FABMI, BMI and p-xylylenediamine (XDA) at FABMI/BMI/XDA molar ratios of 1/3/1, 2/4/1, 1/4/1 and 2/6/1 were prepolymerized at 120 °C, hot-pressed at 130–140 °C, and then annealed at 60 °C to produce cured products. The FT-IR analysis revealed that the Michael addition and Diels-Alder (DA) reactions occurred for all the cured products. FABMI-BMI-XDAs with relatively low feed FABMI mass fractions displayed excellent 5% mass loss temperatures higher than 400 °C. The cured product with the highest feed XDA mass fraction exhibited the highest flexural strength, modulus and strain at break among all the cured products. Onset temperatures of the endothermal retro DA reaction for the cured products were in the ranges of 140–150 °C. All the cured products were at least twice healed by the thermal treatment at 150 °C for 20 min and then 60 °C for 48 h. [ABSTRACT FROM AUTHOR]

A novel capsular adhesive was developed using an acrylic binder and poly (urea-formaldehyde) (PUF) microcapsules containing benzoyl peroxide (BPO) as a core material. The synthesis of the PUF microcapsules was optimized through balancing different parameters including the microcapsule core-shell ratio, release percentage (storage stability), filling content, and the reaction yield. The morphological studies of the microcapsules were conducted using optical microscopy and scanning electron microscopy. The FTIR spectra and the microscopic images confirmed the successful formation of microcapsules containing BPO solution. The filling content of the microcapsules was measured using thermo gravimetric analysis (TGA). The optimum core-shell ratio of the PUF microcapsules was selected based on the results obtained from filling content test, release percentage and the reaction yield. Different mixing speeds of the mechanical stirrer up to 800 rpm were examined to obtain the optimum mean diameter of the microcapsules and optimum filling content. The optimal microcapsule sample was obtained at a core-shell ratio of 90/10 and a mixing speed of 450 rpm. A characteristic spherical morphology with an average diameter of 120 μm with no shell wrinkles and no agglomeration was obtained in this sample. In the next step, the capsular adhesive was prepared through loading different PUF microcapsules in acrylic binder. The adhesive was then pre-coated on metallic bolt and set after microcapsule breakage during fixing nuts. The strength of the capsular adhesive at 15 wt.% of microcapsule loading showed a maximum torque of 8.5 N.m. [ABSTRACT FROM AUTHOR]

Mechanically robust and self-healing epoxy composites are highly desired to satisfy the increasing demand of high-performance smart materials. Herein, a dual functionalized epoxy composite (EpF-MWCNT-PA-BM) with self-healing performance based on Diels-Alder chemistry has been investigated. The furfuryl grafted epoxy (EpF) and furfuryl modified MWCNTs (MWCNT-F) are reacted with bifunctional maleimide (BM) and normal anhydride curing agent (PA) to form a covalently bonded and reversibly crosslinked epoxy composite with two types of intermonomer linkage. That is, thermally reversible Diels-alder bonds between the furan groups of both epoxy and MWNCTs with malemide and thermally stable bonds of epoxide and anhydride groups. MWCNTs act as both reinforcer and a healant in the epoxy composite. In this way, the cured epoxy composite possessed not only enhanced mechanical properties but also thermal remendability that enabled elimination of cracks. The latter function took effect as a result of successive retro-DA and DA reactions, which led to crack healing upto 79.82% healing efficiency in a controlled manner through chain reconnection. [ABSTRACT FROM AUTHOR]