2. Experimental
2.1. Materials
SOFA (MP Dichem (India) Pvt Ltd.), DCOFA (Jayant Agro Organic
Ltd.), phthalic anhydride (M/S Asian Paints Ltd.), benzoic acid
(BA, Ujwal Pharma Pvt Ltd.) and hypophosphorous acid (HPA,
NEEMC Co.) used to synthesize the alkyd resins were of commercial
grade. Pentaerythritol (PE, M/S Asian Paints Ltd.) used
was of nitration grade. DPE was kindly supplied by Perstorp AB,
Sweden.
o-Xylene (Manish PetrochemPvt Ltd.) and mineral turpentine oil
(MTO—a mixture of saturated aliphatic and alicyclic C7–C12 hydrocarbons
with a maximum content of 25% of C7–C12 alkyl aromatic
hydrocarbons; Bharat Petroleum) were used as solvent. 6% cobalt
octoate (Alpha Chemie), 3% calcium octoate (National Chemical &
Dyes Company) and 18% zirconium octoate (Sunflag Chemicals Pvt
Ltd.) were used as driers. All these materials were used as such
without any further purification.
2.2. Synthesis of resins
Fatty acid technique with solvent process was employed to
synthesize the alkyd resins. The reactionwas carried out in 2-l fournecked
flask equipped with a variable speed stirrer, a thermometer,
nitrogen gas inlet tube and condenser. A Dean and Stark apparatus
was used to remove the water of reaction azeotropically. Concept
alkyds have been synthesized according to the following protocol:
• Fatty acids, PE and/or DPE, phthalic anhydride, benzoic acid (as
chain terminator), hypophosphorous acid and xylene (4% on raw
materials) were charged.
• Heating started. Temperature was raised at the rate of 4 ◦C/min
up to 160 ◦C.
• Further the temperature was raised to 240±5 ◦C at 1◦C/min
increase and maintained until the final acid number of
<12mgKOH/g was achieved.
• The resin was cooled to 160–170 ◦C and diluted with MTO to 80%
solids.
Extent of the reaction was monitored by acid value and viscosity
(Gardner scale) determinations at regular intervals. Heating
was stopped when the acid value of the resin reached below
12mgKOH/g. Nine experimental setswere prepared by varying the
PE and DPE compositions. The detailed recipe and theoretical alkyd
constants are illustrated in Table 1.
2.3. Preparation of dry films
Clear filmswere prepared by diluting the high solids alkyd resins
in MTO and by adding the driers (0.02% cobalt octoate, 0.6% zirconium
octoate and 0.25% calcium octoate on the basis of solid
resin). An amount of 0.2% of methyl ethyl ketoxime was used as
anti-skinning agent.
Clear filmswere applied onmild steel and tin panels using brush
and cured at ambient conditions. The dry film thickness achieved
was in the range of 30–35m. Film performance properties were
measured after 7 days of drying.
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 10m×10m.
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