Proučavanje mogućnosti mikrotalasne polimerizacije monomera na osnovu obnovljivih sirovina

Polylactide belongs to the biodegradable and biocompatible polymers, and degrade to harmless component, lactic acid, which allows their use in various areas. The development of new methods for the synthesis of polylactide can further extend the application of this polymer and makes its use more economical. The use of microwaves in the synthesis of the polymer can reduce the polymerization time of only 10 to 30 minutes and save a large amount of energy. In this paper, polylactide is synthesized in a microwave reactor, using a frequency of 2,45 GHz and a power of 150 W. FITR analysis confirmed the structure of the resulting polylactide and the thermal properties were studied using differential scanning calorimetry.Polilaktid spada u grupu biorazgradivih i biokompatibilnih polimera i može se razložiti na neškodljivu komponentu, mlečnu kiselinu, što omogućava njegovu primenu u najrazličitijim oblastima. Razvoj novih metoda sinteze polilaktida može proširiti područje primene ovog polimera i učiniti njegovu upotrebu ekonomičnijom. Upotreba mikrotalasa u sintezi polimera može skratiti vreme polimerizacije na svega 10 do 30 minuta štedeći veliku količinu energiju. U ovom radu polilaktid je sintetisan u mikrotalasnom reaktoru, koristeći frekvenciju od 2.45 GHz i snagu od 150 W. FTIC analiza je potvrdila strukturu dobijenog polilaktida, a toplotna svojstva su proučavana metodom diferencijalne skenirajuće kalorimetrije.Vrednost temperatura prelaska u staklasto stanje i temperatura kristalizacije dobijenog polimera zavise od molskog odnosa monomera (L-laktida) i katalizatora (kalaj-oktoata)

Ispitivanje toplotnih svojstava nanokompozitnih polimernih materijala na osnovu biljnih sirovina

Environmental friendliness and functionality have made biopolymers one of the most interesting materials today. In order to broadening their application, there is need for improving their poor mechanical and thermal properties by using reinforce effect of inorganic nanoparticles. In this paper, thermal properties of nanocomposites based on poly(lactide) (PLA) and silicon dioxide were investigated using the differential scanning calorimetry (DSC). The obtained results showed that the addition of nanoparticles causes a change in the values of melting and crystallization temperatures of nanocomposites. Significant influence on the glass transition temperature was not observed.Ekološka prihvatljivost i funkcionalnost biopolimera učinila ih je jednima od najtraženijih materijala današnjice. Njihovu veću primenu ograničavaju slaba mehanička i toplotna svojstva. Kako bi se poboljšala primenska svojstva biopolimera oni se kombinuju sa neorganskim česticama gradeći nanokompozite. U ovom radu ispitivana su toplotna svojstva nanokompozita na osnovu poli(laktida) (PLA) i silicijum(IV)oksida. Dobijeni rezultati su pokazali da dodatak nanočestica dovodi do promene temperature topljenja, porasta temperature kristalizacije, pri čemu nije uočen značajan uticaj nanočestica na temperaturu prelaska u staklasto stanje nanokompozita poli(laktida)

Curing kinetics of alkyd/melamine resin mixtures

Alkyd resins are the most popular and useful synthetic resins applied as the binder in protective coatings. Frequently they are not used alone but are modified with other synthetic resins in the manufacture of the coatings. An alkyd/melamine resin mixture is the usual composition for the preparation of coating called 'baking enamel' and it is cured through functional groups of resins at high temperatures. In this paper, curing kinetics of alkyd resins based on castor oil and dehydrated castor oil with melamine resin, has been studied by DSC method with programmed heating and in isothermal mode. The results determined from dynamic DSC curves were mathematically transformed using the Ozawa isoconversional method for obtaining the isothermal data. These results, degree of curing versus time, are in good agreement with those determined by the isothermal DSC experiments. By applying the Ozawa method it is possible to calculate the isothermal kinetic parameters for the alkyd/melamine resin mixtures curing using only calorimetric data obtained by dynamic DSC runs. Depending on the alkyd resin type and ratio in mixtures the values of activation energies of curing process of resin mixtures are from 51.3 to 114 kJ mol-1. The rate constant of curing increases with increasing the content of melamine resin in the mixture and with curing temperature. The reaction order varies from 1.12 to 1.37 for alkyd based on dehydrated castor oil/melamine resin mixtures and from 1.74 to 2.03 for mixtures with alkyd based on castor oil. Based on the results obtained, we propose that dehydrated castor oil alkyd/melamine resin mixtures can be used in practice (curing temperatures from 120 to 160°C)

Synthesis and curing of alkyd enamels based on ricinoleic acid

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

The effects of alkyd/melamine resin ratio and curing temperature on the properties of the coatings

Synthetic resins are used as binders in protective coatings. An alkyd/melamine resin mixture is the usual composition for the preparation of a coating called “baking enamel” cured through functional groups of resins. The effects of the alkyd/butylated melamine resin ratio (from 85/15 to 70/30) and curing temperature (from 100°C to 160°C) on the crosslinking and properties of the coating are presented in this paper. The degree of curing was determined by differential scanning calorimetry. These data were used for the estimation of the degree of crosslinking. The hardness, elasticity, impact resistance, degree of adherence and gloss were also determined. Optimal coating properties could be achieved with an alkyd/melamine resin ratio of 75/25, a curing temperature of 130 °C and a curing time of 30 min