Expanding of polylactide

Polilaktid (PLA) je termoplastični biorazgradivi polimer, pri čemu se proizvodnja PLA temelji na prirodnim izvorima kao što su kukuruz ili šećerna trska. Zbog dobrih mehaničkih i drugih svojstava (gustoća, prozirnost, barijerna svojstva) PLA je našao primjenu u industriji pakiranja (boce, kruta plastika, folije). Osim toga, znatan broj radova posvećen je istraživanju ekspandiranog PLA kao alternative za zamjenu ekspandiranog poli(stirena) (PS-E). Ekspandiranje PLA se najčešće provodi pomoću fizikalnih ekspandirajućih agensa kao što su CO2, N2 ili i–butan. Upotreba navedenih fizikalnih agensa za ekspandiranje PLA ograničena je zbog loših reoloških svojstava taline PLA. U ovom radu kao ekspandirajući agens korištene su mikrosfere komercijalnog Expancela. Granule PLA usitnjene su pomoću mlina, a zatim su priređene njihove smjese sa 3, 5 i 7 mas % Expancela te dodatno homogenizrane uz pomoć tresilice. Homogena smjesa prešana je u hidrauličkoj preši na temperaturi od 190 °C u vremenu 8 minuta. Nakon optimizacije uvjeta prešanja, prešanje je provođeno na 180 °C u vremenu 6 minuta. Nadalje, optimiranjem temperature i vremena prešanja smanjena je degradacija uzoraka prilikom prešanja. Kod pripreme ekspandiranih uzoraka ispitivan je i utjecaj punjenja kalupa na strukturu i svojstva ekspandiranog materijala. Jednoliko popunjavanje kalupa postignuto je za uzorke sa 16 g i 18 g PLA, dok uzorci s 12 g PLA nisu u potpunosti popunili kalup.Polylactide (PLA) is a biodegradable thermoplastic polyester, wherein the production of PLA is based on natural sources such as corn or sugarcane. PLA has found application in the packaging industry (bottles, rigid plastic, foil) due to mechanical and other properties (density, transparency, barrier properties). In addition, a considerable number of papers is devoted to the study of expanded PLA which is an alternative for replacement of the expanded poly(styrene) (E-PS). Expanding of PLA is most commonly achieved by physical blowing agents such as CO2, N2 or i-butane. The use of those physical blowing agents for expanding PLA is limited due to poor rheological properties of PLA melt. Expancel microspheres were used as an expanding agent in this work. PLA granules were grinded with mill and then the mixtures were prepared by adding 3, 5 or 7 wt % of Expancel to grinded PLA granules. Mixtures were additionally homogenized with vortex. The homogeneous mixtures were compressed in a hydraulic press at a temperature of 190 °C for 8 minutes. After optimization of the molding conditions, molding was conducted at 180 °C for 6 minutes. Furthermore, by optimizing the temperature and the pressing time during the pressing process, degradation of samples is reduced. During the preparation of expanded test samples, impact of mold filling on the structure and properties of the expanded material was investigated. Uniform filling of mold was achieved for samples with 16 and 18 g of PLA, while the samples with 12 g of PLA did not completely fill the mold