A combination of an alkyd resin with a melamine-formaldehyde resin gives a
cured enamel film with the flexibility of the alkyd constituent and the high
chemical resistance and hardness of the melamine resin at the same time. The
melamine resin is a minor constituent and plays the role of a crosslinking
agent. In this paper, alkyd resins of high hydroxyl numbers based on
trimethylolpropane, ricinoleic acid and phthalic anhydride were synthesized.
Two alkyds having 30 and 40 wt% of ricinoleic acid were formulated by
calculation on alkyd constant. Alkyds were characterized by FTIR and by the
determination of acid and hydroxyl numbers. Then synthesized alkyds were made
into baking enamels by mixing with melamine-formaldehyde resins (weight ratio
of 70:30 based on dried mass). Two types of commercial melamine resins were
used: threeisobutoxymethyl melamine-formaldehyde resin (TIMMF) and
hexamethoxymethyl melamine resin (HMMMF). Prepared alkyd/melamine resin
mixtures were cured in a differential scanning calorimeter (DSC) under
non-isothermal mode. Apparent degree of curing as a function of temperature
was calculated from the curing enthalpies. Kinetic parameters of curing were
calculated using Freeman-Carroll method. TIMMF resin is more reactive with
synthesized alkyds than HMMMF resin what was expected. Alkyd resin with 30
wt% of ricinoleic acid is slightly more reactive than alkyd with 40 wt% of
ricinoleic acid, probably because it has the high contents of free hydroxyl
and acid groups. The gel content, Tg, thermal stability, hardness, elasticity
and impact resistance of coated films cured at 150?C for 60 min were
measured. Cured films show good thermal stability since the onset of films
thermal degradation determined by thermogravimetric analysis (TGA) is
observed at the temperatures from 281 to 329?C. Films based on alkyd 30 are
more thermal stable than those from alkyd 40, with the same melamine resin.
The type of alkyd resin has no significant effect on the gel content and the
hardness of film. Hardness of cured film increases with increasing of Tg. The
values of the films elasticity are satisfied for all prepared samples and are
independent on the type of alkyd or melamine resin. The impact resistances of
coated films are very high.
Microencapsulation of butyl stearate with melamine-formaldehyde resin: Effect of decreasing the pH value on the composition and thermal stability of microcapsules