Curing of poly(furfuryl alcohol) resin catalyzed by a homologous series of dicarboxylic acid catalysts: Kinetics and pot life

Curing kinetics and pot life are two vital characteristics for the application of poly(furfuryl alcohol) (PFA) resin because of the complexities both in the resin composition and curing mechanisms involved. However, few reports have provided a complete picture of PFA curing behavior. In this research, the effect of the addition of catalysts on the pot life and curing behavior of a PFA resin were evaluated. A homologous series of dicarboxylic acids [i.e., oxalic acid (OX), succinic acid (SU), and adipic acid (SA)] were used as the catalysts. Rheometric and nonisothermal differential scanning calorimetry (DSC) measurements and headspace gas chromatography/mass spectrometry analysis were carried out at 0, 6, and 24 h after the addition of the catalyst. The relaxation exponent (n), gel stiffness (S), and gel strength (A_F) of the prepared compositions were calculated with the Winter and Chambon and Gabriele rheological models. Furthermore, the curing kinetics were evaluated by the fitting of nonisothermal, multiple‐heating‐rate models. The DSC measurements showed a higher curing degree for samples containing OX catalyst compared to their counterparts containing either SU or AD. The rheometric findings supported an increased stiffness, gel strength, and curing development of the resin in the presence of OX compared to samples containing SU or AD. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44009.     

The adhesion properties and corrosion performance of differently pretreated epoxy coatings on an aluminium alloy

The influence of various blends of hexafluorozirconic-acid (Zr), polyacrylic-acid (PAA) and polyacrylamide (PAM) pretreatment on the performance of an epoxy coated aluminium substrate was investigated and compared to that of a so-called chromate/phosphate conversion coating (CPCC).Adhesive-strength of epoxy coated substrates was evaluated using pull-off and tape tests. Salt spray, humidity chambers and EIS were employed to characterize corrosion performance of coated substrates with different initial surface pretreatments. Among the Zr-based formulations, PAA/Zr and PAA/PAM/Zr showed the best adhesion strength, while the later revealed a good corrosion performance as well. However, CPCC pretreated sample was still superior in these aspects.     

Adhesive strength of powder coated aluminium substrates

Adhesive strengths of differently pretreated powder coated aluminium substrates were evaluated using the pull-off and the tape tests in the dry and wet conditions. Various accelerated test chambers were employed to evaluate the corrosion behaviour of the samples. Scanning electron microscopy (SEM), with energy dispersive X-ray analysis (EDX) were also employed to the better understanding of the nature and morphology of the differently pretreated aluminium substrates prior to and after the accelerated tests.

Accelerated tests and wet adhesion measurements showed that the degreased samples demonstrated a better performance than Polyacrylic acid (PAA) treated samples. The chromate/phosphate conversion coating (CPCC) treated samples gave the best performance and the Polyacrylic acid/ hexafluorozirconic acid treated samples (PZr) gave marginally second best performance in anti-corrosive behaviour.

Based on the results obtained from the different experiments, it is argued that these studies may provide sufficient evidence to show that hydrolysis may destroy interface bonds between PAA and aluminium substrate. Moreover, SEM/EDX analysis, suggest that, the thin PAA polymeric layer was replaced by a crystalline, thick hydrated oxide layer, when samples were exposed to humid conditions.     

Adhesion performance of an epoxy clear coat on aluminum alloy in the presence of vinyl and amino-silane primers

The influence of amino and vinyl-silane-based treatments on the performance of an epoxy coated AA 1050 aluminum has been studied. The surface energy of the silane treated samples was determined using static contact angle measurement. Chemical interactions between the silane layer and aluminum substrates were also examined using FTIR-ATR spectroscopy. Pull-off adhesion was used under wet, dry and recovery conditions. The contact angle measurements showed a relative increase in the surface free energy of the silane treated specimens. For specimens treated with silane solutions below the IEP of aluminum, adhesion strengths were higher than those for pHs higher than IEP. This may suggest that an acid–base interaction occurs between the negatively charged silanol species and the positively charged AA surface. FTIR revealed two modes of interaction, one between silane and Al³⁺ (Si–O–Al), and the other indicative of a siloxane network (Si–O–Si). Thickness measurement showed that the silane layer is 100–200 nm thick indicating that the silane formed at the surface is not a monomolecular layer. Direct pull-off adhesion measurements of silane treated samples showed a significant improvement in initial bond strength compared with degreased aluminum substrates. However, those silane solutions having pHs higher than 8.4 showed inferior adhesion in comparison to those having lower pHs. The adhesion improvement was maintained, to some extent, after exposure to salt spray cabinet. In spite of good dry, wet and recovery adhesion, silane treated surfaces are not comparable with chromated AA aluminum in terms corrosion resistance.     

Microencapsulation of 1-methylimidazole using solid epoxy resin: study on microcapsule residence time and properties of the system

In this study for the first time 1-methylimidazole was microencapsulated successfully by solid epoxy resin using solvent evaporation method. Fourier transform infrared spectroscopy, scanning electron microscopy, thermal gravimetric and differential scanning calorimetry were used for characterization of microcapsule and epoxy resin/microcapsule systems. The results revealed that although the solid epoxy shell was in contact with imidazole curing agent for a long time, it still remained as a thermoplastic. The chain length of the solid epoxy resin was grown in anionic polymerization process which led to an increase in the melting temperature from 64 to 78 °C. On the other hand, all epoxy functional groups of the shell did not participate in the curing reaction of resin with core curing agent of the microcapsule. The results showed that by increasing the residence time of the microcapsules, the number of epoxy groups of liquid epoxy decreased slightly but the rate of complex viscosity increase or the rate of curing reaction was increased and the cured epoxy system exhibited a single-phase morphology. On the other hand, in the presence of microcapsules the curing reaction of epoxy resin was successfully carried out and the curing temperature and the onset of viscosity increase or gel time at 120 °C were not more or less affected by sufficiently long contact time of epoxy and microcapsule.     

Thermooxidative reactions of polypropylene wax in the molten state

Thermooxidation of polypropylene wax was investigated in the molten state under an air‐flowing atmosphere. Calorimetric measurements were performed to investigate the effect of the inclusion of 1‐dodecanol as an efficient primary alcohol and to reveal the typical outlines of thermooxidation, that is, the induction time and oxidation rate. The same parameters were obtained and compared on the basis of the Fourier transform infrared (FTIR) peaks of major oxidation products, such as ketones and hydroxyl groups. The results showed that 1‐dodecanol caused a change in the shape of the calorimetric thermogram and also yielded oxidized products with more clarity in color. With the Arrhenius equation, the apparent activation energy was calculated on the basis of the induction time and oxidation rate for carbonyl and hydroxyl groups individually. The obtained apparent activation energy was in agreement with the proposed mechanism based on bimolecular hydroperoxide decomposition involving dodecanol. With FTIR spectroscopy, no changes in the chain helical conformation or double‐bond concentration were observed during oxidation up to 500 min. An acid value of up to 6 mg of KOH per gram was obtained at this time. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Evaluation of the weathering performance of basecoat/clearcoat automotive paint systems by electrochemical properties measurements

The aim of the present study was to investigate the possibility of evaluating the weathering performance of a basecoat/clearcoat automotive paint system through the determination of its electrochemical properties. To this end, the electrochemical properties of a basecoat/clearcoat automotive paint in a 3.5% solution of NaCl in deionized water were measured at different weathering exposure times. A constant phase element (CPE) was used for describing the electrochemical behavior of the coatings under test. The values of the CPE parameters, i.e. Y₀ (the CPE constant) and n (the CPE power) were subsequently correlated to the extent of photo-oxidation (as measured by appearance, surface roughness, FTIR, surface tension and adhesion measurements) of clearcoat at the surface, in the bulk and at the interface between the basecoat and the clearcoat. The result showed that the electrochemical parameters Y₀ and n provide ready means for comparing the weathering performances of basecoat/clearcoat automotive paint systems. Increases in the value of Y₀ together with decreases in the value of n with increasing weathering exposure times suggest increased possibilities for the onset of cracking in the clearcoat itself in addition to its propagation towards the basecoat. Additionally, sudden variations in the values of Y₀ and n are indicative of increases for the clearcoat to peel off.