Development and characterization of silicone/phosphorus modified epoxy materials and their application as anticorrosion and antifouling coatings

Epoxy resin is chosen for our present study owing to its exceptional combination of properties such as easy processing, high safety, excellent solvent and chemical resistance, toughness, low shrinkage on cure, good electrical, mechanical and corrosion resistance with excellent adhesion to many substrates. This versatility in formulation made epoxy resins widely applied for surface coatings, adhesives, laminates, composites, potting, painting materials, encapsulant for semiconductor and insulating material for electric devices. There are numerous paint/coating systems based on epoxy resin available for corrosion and fouling prevention. They however are not completely satisfactory in field applications, where high corrosion, fouling and flame resistance are required. The demand for epoxy resin as corrosion/fouling resistant coatings is restricted mainly due to its inferior characteristics like poor impact strength, high rigidity, and moisture absorbing nature besides inadequate flame retardant properties. It is for this reason that silicones and phosphorus-based compounds are used as modifier in this work by intercrosslinking network mechanism (ICN) to obtain epoxy resin with desired properties ideally suitable for field applications for preventing corrosion and fouling with flame retardantancy. The present work involves the development of solvent free silicone/phosphorus modified epoxy coating systems, since solvent free coating systems are widely used for numerous applications due to their lower cost per unit film thickness, freedom from fire and pollution hazard and ability to provide better performance. For the development of coating systems, epoxy resin (X) serves as base material, hydroxyl terminated polydimethylsiloxane (HTPDMS) as modifier, γ-aminopropyltriethoxysilane (γ-APS) as crosslinking agent and dibutyltindilaurate (DBTDL) as catalyst. Polyamidoamine (A), aromatic amine adducts (B) and phosphorus-containing diamine (C) were used as curing agents. The study also describes the evaluation of corrosion resistant behaviour of unmodified epoxy and siliconized epoxy coatings by potentiodynamic polarization method, electrochemical impedance spectroscopy (EIS), salt-spray and antifouling tests. The results are discussed.     

Cold Crystallization of PLLA Studied by Simultaneous SAXS and WAXS

Summary: The cold crystallization process of initially amorphous poly(L ‐lactic acid), PLLA, with two different molecular weights, during a heating at 2 °C/min, was investigated by DSC and time‐resolved simultaneous SAXS and WAXS, using synchrotron radiation. Equatorial scans of the isotropic 2D‐SAXS patterns showed that the average Bragg long period (L_B) of PLLA samples was approximately constant with the development of cold crystallization up to a temperature that corresponded to a melt/re‐crystallization process that took place before the nominal melting peak seen by DSC. L_B values were found to be higher for the high molecular weight material. This was in accordance with the higher melting temperature observed in the high molecular weight PLLA that implied the existence of thicker lamellae. WAXS results showed that the molecular weight did not apparently affect the crystal form and the final degree of crystallinity of PLLA. The Avrami parameters from WAXS and DSC were consistent, showing that the non‐isothermal cold crystallization of the two PLLA samples corresponded mainly to a three‐dimensional growth, although an imperfect crystallization process was involved at early times. The crystallization rate of PLLA, observed both by WAXS and DSC, decreased with increasing molecular weight.

SAXS profiles of PLLA2 as a function of temperature. The inset shows the 2D‐SAXS pattern obtained at 180 °C.     

Relationship between crystalline structure and mechanical behavior in isotropic and oriented polyamide 6

Polyamide 6 (PA6) isotropic films and oriented cables were prepared by compression molding or by consecutive extrusion and cold‐drawing. These samples were isothermally annealed in the 120–200°C range and were then subjected to tensile tests at room temperature. Synchrotron wide‐angle X‐ray scattering (WAXS) and small‐angle X‐ray scattering (SAXS) patterns were obtained before and after mechanical failure. These data were related with the mechanical properties of the respective PA6 samples. The annealing of isotropic PA6 resulted in an increase in the Young's modulus (E) and yield stress (σ_y) values, which was attributed to the observed proportional reduction of the d‐spacings of the intersheet distances in both the α‐PA6 and γ‐PA6 polymorphs. Analysis of the WAXS and SAXS patterns of isotropic PA6 after break allowed the supposition of structural changes in the amorphous phase, with these being better pronounced with increasing annealing temperature; this made the samples less ductile. In oriented PA6 samples, annealing resulted in a drastic increase in the E and σ_y values accompanied by a phase transition from γ‐PA6 to α‐PA6 and a well‐pronounced reduction in the intersheet distances of both polymorphs. The stretching of the oriented samples led to an additional γ‐to‐α transition, whose extent was also related to structural changes in the amorphous phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2242–2252, 2007     

Preparation and properties of polyamide‐6‐based thermoplastic laminate composites by a novel in‐mold polymerization technique

In this work, a method for preparation of polyamide‐6 (PA6) based laminates reinforced by glass fiber‐ (GFL) or polyamide‐66 (PA66) textile structures (PL) via reactive injection molding is disclosed. It is based on in‐mold anionic polymerization of ε‐caprolactam carried out at 165°C in the presence of the respective reinforcements performed in newly developed prototype equipment whose design concept and operation are described. Both composite types were produced for reaction times of 20 min, with conversion degrees of 97–99%. Initial mechanical tests in tension of GFL samples displayed almost twofold increase of the Young's modulus and stress at break values when compared with the neat anionic PA6. The improvement was proportional to the volume fraction V_f of glass fiber fabric that was varied in the 0.16–0.25 range. A 300% growth of the impact strength was registered in PL composites with V_f of PA66 textile of 0.1. Removing the surface finish of the latter was found to be a factor for improving the adhesion at the matrix–fiber interface. The mechanical behavior of GFL and PL composites was discussed in conjunction with the morphology of the samples studied by optical and electron microscopy and the matrix crystalline structure as revealed by synchrotron X‐ray diffraction. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40083.     

Thermal behaviour and adhesive properties of some cyanoacrylate adhesives with increased heat resistance

Cured adhesive layers produced from ethyl-(ECA), allyl-(ACA), and allyloxyethyl-(AOECA) 2-cyanoacrylates were studied by means of thermogravimetry and differential scanning calorimetry. Polymer films of ECA-based adhesive compositions comprising various amounts and types of 2-cyano-2,4-pentadienoic acid (CPDA) esters were also examined. The influence of the modifier type, as well as the chemical structure of the cyanoacrylates used, was followed upon the glass transition temperatures (T_g) and the rates of thermal degradation of the corresponding polymers. In the case of cured adhesive mixtures containing unsaturated CPDA esters and when poly(ACA) and poly(AOECA) were studied, a significant increase of their heat resistance was established, as compared with poly(ECA). This fact was explained with the formation of three-dimensional structure of the polymer film due to crosslinking reactions. A different course and character of these reactions were found comparing the thermal behavior of poly(ACA) and cured compositions containing unsaturated CPDA esters. A good agreement was found between data from the thermal analyses and the tensile shear and impact strength tests. It was shown that the modification of ECA with unsaturated CPDA esters is a possible way of increasing the heat resistance of the basic adhesive. © 1993 John Wiley & Sons, Inc.     

Preparation,structural development,and mechanical properties of microfibrillar composite materials based on polyethylene/polyamide 6 oriented blends

The preparation of microfibrillar composites (MFCs) based on oriented blends of polyamide 6 (PA6) and high‐density polyethylene (HDPE) is described. By means of conventional processing techniques, the PA6 phase was transformed in situ into fibrils with diameters in the upper nanometer range embedded in an isotropic HDPE matrix. Three different composite materials were prepared through the variation of the HDPE/PA6 ratio with and without a compatibilizer: MFCs reinforced by long PA6 fibrils arranged as a unidirectional ply; MFCs containing middle‐length, randomly distributed reinforcing PA6 bristles; and a nonoriented PA6‐reinforced material in which the PA6 phase was globular. The evolution of the morphology in the reinforcing phase (e.g., its visible diameter, length, and aspect ratio) was followed during the various processing stages as a function of the blend composition by means of scanning electron microscopy. Synchrotron X‐ray scattering was used to characterize selected unidirectional ply composites. The presence of transcrystalline HDPE was demonstrated in the shell of the reinforcing PA6 fibrils of the final MFCs. The impact of the compatibilizer content on the average diameter and length of the fibrils was assessed. The influence of the reinforcing phase on the tensile strength and Young's modulus of the various composites was also evaluated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cold crystallization of poly(ethylene naphthalene-2,6-dicarboxylate) by simultaneous measurements of X-ray scattering and dielectric spectroscopy

The isothermal cold crystallization of poly(ethylene naphthalene-2,6-dicarboxylate) was investigated by simultaneous small and wide angle X-ray scattering and dielectric spectroscopy (DS). By this experimental approach, simultaneously collected information was obtained about the specific changes occurring in both crystalline and amorphous phases during crystallization, namely about the chain ordering through wide angle X-ray scattering, about the lamellar crystals arrangement by means of small angle X-ray scattering, and about the amorphous phase evolution by means of DS. The results indicate that average mobility of the amorphous phase suffers a discontinuous decrease upon passing from the primary to the secondary crystallization regime. We interpret these results assuming that the restriction to the mobility of the amorphous phase occurs mainly in the amorphous regions between the lamellar stacks and not in the amorphous regions within the lamellar stacks.     

Optical biosensor for catechol determination based on laccase-immobilized anionic polyamide 6 microparticles

This work presents the preparation, optimization, and testing of an enzyme-based optical biosensor for catechol determination. The sensing area is attached to a glass support and contains: anionic polyamide 6 (PA6) porous microparticles supporting laccase from Trametes Versicolor, embedded in a Pebax® MH1657 polymer binder that contains the optical indicator dye 3-methyl-2-benzothiazolinone hydrazone (MBTH), responsible for the optical transduction. The catechol analyte, after its enzymatic oxidation, forms o-benzoquinone that can be detected by oxidative coupling with MBTH giving rise to a colored product. The latter can be quantified measuring the UV/VIS absorbance at 500 nm. The PA6 microparticles performed as useful laccase carriers reaching high immobilization yields of up to 99.8% and preserving the enzyme catalytic activity. This permitted the preparation of a new biosensor presenting a detection limit of 11 μM and responding linearly to up to 118 μM of catechol. Biosensor applicability was tested in spiked natural water samples from river and spring. The recovery rates observed were in the range of 97–108% that proves the good accuracy of the proposed biosensor.