K. V. S. N. Raju

Polyurethane conductive blends and composites: synthesis and applications perspective

The objective of this review is to describe the important progress made in the area of synthesis and applications of conducting composites/blends derived from polyurethanes as host material. Polyurethane is one of the most useful polymeric materials with multiple functional applications. The pristine polymer is an insulator and conductivity can be imparted by blending or compositing with conductive materials such as conducting polymers, carbon black, CNTs, and graphite/graphene. The resulting conductive composites are useful as sensors, corrosion-resistance paints, electrostatic dissipaters, EMI shielders, and many others. The review discusses various methods to obtain such conductive polyurethane composites and their intended or demonstrated applications.

The impact of 1,2,3-triazoles in the design of functional coatings

In recent times 1,2,3-triazole rich molecules have gained much importance in the field of polymer and material science because of their excellent properties like strong anti-microbial and anti fouling nature of the triazole ring along with easy synthetic procedures and exceptionally high yield of end product. Generally these molecules are synthesized by azide–alkyne click reaction and this chemistry has potential application in the functionalization of a wide range of inorganic moieties like metal oxide nanoparticles, carbon nanotubes etc. to develop hybrid nanocomposites for high performance materials. Based on the previous reports, this particular review article provides a comprehensive overview of the application of 1,2,3-triazoles in the design of various high performance organic coatings such as anti-corrosive, anti-microbial, self-healing, hybrid nanocomposite, bio degradable etc.

Anti-microbial and anti-corrosive poly (ester amide urethane) siloxane modified ZnO hybrid coatings from Thevetia peruviana seed oil

The utilization of renewable resources for the development of organic coatings is a viable means of creating alternatives to petroleum-based chemicals which are not eco-friendly. This paper reports the synthesis of polyesteramide–urethane–silica–zinc oxide hybrid coatings from Thevetia peruviana seed oil (TPSO). The periphery of ZnO nano-particles is modified with 3-aminopropyltrimethoxysilane to prepare silica grafted ZnO composite particles. The TPSO based polyesteramide was reacted with 4,4′-diisocyanatodicyclohexylmethane in presence of siloxane modified ZnO to obtain –NCO terminated polyesteramide–urethane–silica ZnO prepolymer. These hybrid pre-polymers were casted on tin foil and cured under atmospheric moisture to obtain eco-friendly, moisture cured polyesteramide–urethanes–silica–zinc oxide hybrid coating films. The synthesized polyester and polyurethane formation was confirmed by using FT-IR and NMR spectroscopic techniques. The resultant hybrid coating films were characterized by using FT-IR, TGA, DSC, SEM, corrosion resistance and microbial resistance. Results confirm that with increase of siloxane modified ZnO content in the polyurethane matrix thermal stability, glass transition temperature and corrosion resistance improved. The antibacterial activity shows that the hybrid films exhibit excellent resistance towards Escherichia coli and Staphylococcus aureus. The salt spray test on coated panel samples show good corrosion resistance properties.

Controllable synthesis of biosourced blue-green fluorescent carbon dots from camphor for the detection of heavy metal ions in water

A robust method for the synthesis of fluorescent carbon dots (C dots) from camphor, which provides an insight into the mechanism of C dot formation, is reported. Camphor is a biosourced hydrocarbon, which contains an hexagonal ring arranged like an open book. Burning of camphor leads to the formation of soot, which comprises graphitic domains. The soot when treated with piranha solution disintegrates into smaller domains leading to the formation of C dots with a size distribution of ∼1–4 nm. The C dots obtained were carboxyl terminated which was confirmed from the infrared spectroscopic measurements. The D and G bands at ∼1314 cm−1 and ∼1586 cm−1, respectively, found using Raman spectroscopy and the peaks at 25.01° found using X-ray diffraction of C dots confirm the presence of graphitic domains. Photoluminescence studies were carried out which reveal exceptional fluorescence in the as prepared C dots. Interestingly the quantum yield is found to be around 21.16%, which is significantly higher than the values reported in previous papers. The current study deals with the sensing of metal ions. Heavy metal cations such as Cd2+ and Hg2+ were used to check whether they affect the fluorescence properties of C dots. It was found that other metal ions like Cu2+, Fe2+ and Zn2+ also quenched the fluorescence of C dot with a different quenching profile.

Synthesis, antimycobacterial screening and ligand-based molecular docking studies on novel pyrrole derivatives bearing pyrazoline, isoxazole and phenyl thiourea moieties

We report here the synthesis, antibacterial and antitubercular evaluation of 61 novel pyrrolyl derivatives bearing pyrazoline, isoxazole and phenyl thiourea moieties. Molecular docking was carried out on enoyl ACP reductase from Mycobacterium tuberculsosis using Surflex-Dock, which is one of the key enzymes involved in type II fatty acid biosynthetic pathway of Mycobacterium tuberculosis, an attractive target for designing novel antitubercular agents. Docking analysis of the crystal structure of ENR performed using Surflex-Dock in Sybyl-X 2.0 software indicates the occupation of substituted pyrrolyl derivatives into hydrophobic pocket of InhA enzyme. Compounds 9b and 9d exhibited the highest antitubercular activity almost close to isoniazid (0.4 μg/mL) with a MIC value of 0.8 μg/mL. All other compounds showed the good activity with a MIC value of 6.25-100 μg/mL. The compounds were further tested for mammalian cell toxicity using human lung cancer cell-line (A549) and were nontoxic. Some compounds exhibited inhibition activities against InhA.

Properties of acetoacetylated hydroxylated polyesters based polyurethane coatings

Abstract The structural variation in the hydroxylated polyesters (HPs) backbone due to the presence of different diol moiety and modification of the pendant hydroxyl group with acetoacetyl group as well on use of them in 2K polyurethane (PU) coatings are reported here. The diols studied were neopentyl glycol, 1,4-cyclohexane dimethanol and 1,3-propane diol in combination with adipic acid, isopthalic acid, trimethylol propane in a moderately branched random co-polyester. Acetoacetylation was carried out by using ethylacetoacetate. The HPs were characterised by gel permeation chromatography and differential scanning calorimetry. The potentialities of these HPs in coating formulation have been studied by developing two pack PU clear coats with diphenylmethane diisocyanate. The results indicate that the structural variation of diol and acetoacetylation help in significant reduction of viscosity of HPs that is also reflected in an increase in percent application solids of coatings. The tensile and dynamic mechanical properties of the coating free films along with supported film properties such as adhesion, scratch resistance, flexibility, impact and abrasion were determined. The dynamic data was used to calculate cross-link density (XLD) and elastically effective network chain ( M c ). The results indicate that the structural variation of building block and acetoacetylation are two potential tools to enhance or maintain the coating properties at higher application solids.

Development of moisture cure polyurethane–urea coatings using 1,2,3-triazole core hyperbranched polyesters

This article reports the development of moisture cure polyurethane–urea coatings. The coating has been developed using different generations of novel 1,2,3-triazole core containing hyperbranched polyester polyols (THBP). For the synthesis of THBP, the core molecule, tetra hydroxyl-terminated di-triazole (THTD), has been synthesized by click reaction involving ethylene diazide and 2-butyne-1,4-diol. The polycondensation reaction between the core THTD and 2,2-bis (hydroxymethyl) propionic acid (Bis-MPA) at different mole ratios has been used to get first (THBPG-1), second (THBPG-2), and third (THBPG-3) generations of triazole core hyperbranched polyesters. The structural investigations of these THBPs have been carried out by 1H NMR, 13C NMR, and FTIR spectroscopy. The different generations of THBPs were further reacted with 1-isocyanato-4-[(4-isocyanatocyclohexyl) methyl] cyclohexane (H12-MDI) at OH:NCO ratio of 1:1.2 to get –NCO terminated triazole core hyperbranched polyurethanes. They were cured under atmospheric moisture to get hyperbranched polyurethane–urea coatings and were named as THBPUG-1, THBPUG-2, and THBPUG-3. FTIR has been used to confirm the formation of polyurethane coatings. The TGA and DMTA have been used to determine the thermal stability and dynamic mechanical properties of the coatings, respectively. The corrosion resistance properties of the coatings have been studied by salt spray and electrochemical test. The coatings were also evaluated for microbial resistance. The results indicate that the thermal stability, glass transition temperature, and corrosion resistance properties increase with an increase in generation number of THBPs used for coating development. All three generations of coating films show excellent antimicrobial activity. Based on overall combined structure–property relationship study, these types of coatings will be useful as multifunctional applications in marine and moist environments.

Synthesis and properties of siloxane-crosslinked polyurethane-urea/silica hybrid films from castor oil

A novel hybrid diol (HD) crosslinker has been synthesized with hydrolyzable –Si–OR groups from 3-amino propyl trimethoxy silane and 3-glycidoxy propyl trimethoxy silane. Its chemical structure was confirmed by Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy to introduce it as a crosslinker in the castor oil, a renewable resource, to develop functional organic inorganic hybrid coatings. A series of castor oil-based organic–inorganic hybrid materials were prepared from castor oil, isophorone diisocyanate, and the different weight percentages of synthesized HD. Dynamic mechanical thermal analysis, thermogravimetric analysis, differential scanning calorimetry, and the universal testing machine were employed to characterize the hybrid films. The measured properties were found to be strongly influenced by the weight ratio of HD to the castor oil-based polyurethanes. The glass transition temperatures (Tg) for the cured hybrid films were found to be 26–72°C. Antibacterial activity, in vitro hydrolytic degradation, and swelling properties of the hybrid films have been studied. The cured hybrid films exhibited excellent antibacterial activity, which was enhanced with addition of the HD. The alkoxy silane-crosslinked castor oil-based coatings have shown better mechanical and viscoelastic properties in comparison to the control (uncrosslinked castor oil-based polyurethane-urea) coatings. The results showed that the weight percent of the HD is the main factor that controls the thermal, antimicrobial, mechanical, swelling, and degradation properties of these hybrid films.

Cure, viscoelastic and mechanical properties of hydroxylated polyester melamine high solids coatings

This paper presents the effects of diol structure and acetoacetylation on cure, viscoelastic and mechanical properties of hydroxylated polyesters (HPS)/ hexamethoxymethylmelamine (HMMM) clear coatings. Acetoacetylation of HPs is a potential tool for researchers to get the equivalent or superior performance at higher application solids than their base counterpart. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analyzer (DMTA) and Thermo Gravimetric Analysis (TGA) have been utilized to study the cure, cure and viscoelastic behavior and thermal stability of the coatings respectively. The crosslink density (XLD) and elastically effective chain length between crosslinks (Mc) of the coating films has also been determined. Furthermore, the mechanical film properties such as tensile properties, adhesion strength and hardness were measured and related to chemical composition. The results indicate that the combined analysis helps in correlating the structure property relationship with end use properties.

Graphitic nanoparticles from thermal dissociation of camphor as an effective filler in polymeric coatings

We report an easy synthesis of uniformly-sized water soluble graphitic-carbon nanoparticles (CNP) from the soot obtained by the incineration of camphor. The soot was characterized by X-ray diffraction (XRD) and Raman spectroscopy which reveal the presence of graphitic domains in the obtained nanoparticles. Scanning electron microscope (SEM) images display uniformly sized CNPs of about ∼50 nm. The camphoric soot was then oxidized with a piranha solution to decorate the CNP surface with a carboxyl group. This presence of carboxyl groups was confirmed by the CO stretching at 1720.17 cm−1 in the Fourier transform-infrared spectroscopy. Following the surface treatment, CNPs were reacted with diisocyanate to form amide linkages, which were exploited in the fabrication of CNP–polyurethane hybrid composite material (CNP–PU). Minuscule incorporation (0.1, 0.5 wt%) of CNP into polyurethanes showed a magnificent improvement in the overall thermo-mechanical properties of the CNP–PU as compared to neat polyurethane films. From the XRD analysis of CNP–PU it is evident that incorporation of CNPs enhances the crystallinity of the resultant composite. Proper dispersion of CNPs into the polyurethane matrix was noticeable in the SEM images of the composite.