2.4. Characterization methods
Viscosity of the resin solutions at 70 and 80% concentrationswas measured using Brookfield DV III Ultra Programmable Rheometer, Spindle number SC4-27. Fourier transformation infrared (FT-IR) spectra of the high solids alkyd resins as well as their films were recorded on a PerkinElmer Spectrum One spectrometer. Clear films (with and without driers) were applied on KBr pellet uniformly and the absorption spectra of the films were recorded immediately after application of the
film. Molecularweights of the high solids alkyd resinswere measured by gel permeation chromatography (GPC, Model PerkinElmer series 2000) technique at 30 ◦C using THF as a solvent and flow rate of 1ml/min. Drying times of the films were recorded using conventional methods [16]. A commercial thermal analyst Q10 system from TA Instruments was used for differential scanning calorimetry (DSC) at a heating rate of 10 ◦C/min. Thermogravimetry analysis (TGA) was carried out for the
dried films using Thermogravimetry analyzer model PYRIS-1 TGA PerkinElmer US at a heating rate of 10 ◦C/min. Surface topography information of dry films was obtained by using Veeco Instruments AFM (atomic force microscope), operated in contact mode with silicon nitride imaging cantilevers with scan sizes of 10_m×10_m. Impedance spectra were recorded at ambient conditions in 3.5% NaCl using Gamry EIS 300 Impedance analyzer. The resistance of the coating was measured for each of the panel after the weathering test and the impedance values and phase angle profile were used to rank the coatings containing different DPE content. Dupont Impact tester (Model TA 910 S) was used for checking impact resistance of the dry film. A conical mandrel (Braive Instruments Model 1510) was used for the flexibility test as per ASTM D 522. A crosshatch cutter was used for adhesion tests as per ASTM D 3359. Film hardness was measured using pencil and pendulum hardness tester after maturing the film for 7 days at ambient temperature. Specular gloss measurements were performed at 20◦ with a
Micro TRI Glossometer as per ASTM D 523. Acid and alkali resistance of the clear films was determined as
per IS 2932:1993 method [17]. The high solids clear alkyd films were weathered in accelerated condition using Q -PanelsWeathering Tester Model QUV Solar Eyes (QUV B313 lamps) for 500 h. The test procedure involved cyclic exposure to UV irradiation and 100% humidity, 4 h each.