Preparation and characterization of PLA composites

U ovom radu istraživali su se kompozitni materijali biorazgradivog polilaktida (PLA) ojačani s mineralnim punilima - Schwerspatom (S) i Glimmerom POS (GL). Umješavanjem u Brabender gnjetalici i prešanjem pripremili su se kompoziti s 0,1; 0,5; 1 i 5 mas. % punila, a iz otopine i prešanjem s 0,1 i 1 mas. % punila. Određivala su se i uspoređivala mehanička i toplinska svojstva dobivenih materijala i čistog polimera. Ispitivanjima univerzalnom kidalicom dobiven je uvid u mehanička svojstva pripravljenih kompozita i PLA. Određivana su vlačna čvrstoća, Young-ov modul i prekidno rastezanje. Dinamičko mehaničkom analizom ispitivana su primarna viskoelastična svojstva materijala kao i utjecaj punila na temperaturu staklastog prijelaza polimerne matrice. Toplinska stabilnost uzoraka određivana je termogravimetrijskom metodom, a uvid u fazne prijelaze i temperature faznih prijelaza polimera (matrice) dobiven je diferencijalnom pretražnom kalorimetrijom. Također se određivao kontaktni kut uzoraka s vodom, formamidom i dijodometanom kao testnim kapljevinama, te je računata površinska energija pripravljenih materijala. Karakterizacijom kopompozitnih materijala ustanovljeno je da se dodatkom punila u polilaktid poboljšavaju njegova svojstva. U prisustvu punila polimernoj matrici potrebno je dulje vrijeme za fazne prijelaze što se očitava u pomaku temperatura staklišta, kristališta i tališta na više vrijednosti. DSC analizom ustanovljeno je i smanjenje udjela kristalinične faze dodatkom punila. Punilo povećava nosivost opterećenja polimerne matrice, vidljivo iz porasta modula pohrane. Kompozitni materijali također imaju bolja mehanička svojstva, tj. veći Young-ov modul, rasteznu i prekidnu čvrstoću kao i prekidno rastezanje. Kompozitni materijali toplinski su stabilniji od čistog polimera. Toplinska degradacija počinje na 50 °C višoj temperaturi od čistog polilaktida.This work investigates composites of biodegradable polylactide (PLA) reinforced with mineral fillers - Schwerspat (S) and Glimmer POS (GL). Composites with 0.1; 0.5; 1 and 5 weight % filler were prepared in a Brabender mixer and molded under pressure. Composites with 0.1 and 1 weight % Schwerspat and Glimmer were prepared by solution mixing and molded under pressure. The mechanical and thermal properties of the composites and pure polymer were investigated and compared to each other. An overview of the mechanical properties of PLA and prepared composites was achieved through experiments with an universla testing machine. The tensile strenght, Young's modulus and elongation of the materials were determined. Dynamic mechanical analysis was used to investigate the primary viscoelastic properties of the materials and the effect of fillers on the glass transition temperature of the polymer matrix. The thermal stability of the samples was monitored by thermogravimetric method and insights into phase transition temperature of the phase transition of the polymer (matrix) obtained by differential scanning calorimetry. The contact angles of test liquids (water, formamide and diiodomethane) and free surface energy were also determined. Characterization of the composite materials revealed that the addition of fillers to polylactide improves its properties. In the presence of fillers the polymer matrix needs more time for phase transitions which can be seen in the shift of glass transition, christalization and melting temperatures to higher values. DSC analysis also showed that by the addition of fillers the cristalinity of the polymer lowers. The filler increases the load carrying capacity of the polymer matrix, evident from the increase in storage modulus. Composite materials also have better mechanical properties, ie. higher Young's modulus, tensile and breaking strength as well as elongation. Composite materials are thermally more stable than the pure polymer. Thermal degradation starts at 50 °C higher temperature than the pure polylactide