Plasticizer Impact on Mechanical Properties

TS twin screw extrusion, IM internal mixer, E single screw extrusion, I injection molding, C casting, MM manual mixing, crosslinked PLA. 

Miscibility is one of the key factors for the successful increase of tensile properties and decrease of Tg. Most literature studies used a maximum plasticizer concentration of 20 wt%, which allowed for the fabrication of a priori fully miscible blends. Correlation between yield stress and plasticizer concentration is a sign of miscible blends, as yield stress can serve as a measurement of macromolecular mobility. Miscibility limits in PLA observed by some authors were 5 wt% DOA measured by DSC, 10 wt% DINCH (by DSC and FESEM), 20 wt% for DBS (DSC) and CMS 15 wt% (DSC). Furthermore, below 10 wt% DOA, Muriaru et al. observed a decrease in the impact strength, explained by the antiplasticization effect. 

One of the advantages of the Fox equation is that it does not contain adjustable parameters. An agreement of experimental data with the prediction supports the conclusion of the high miscibility. Data from different authors are consistent and show that up to 45 wt% of ATBC content in PLA, the Fox equation is applicable. At concentrations equal to or higher than 60 wt%, ATBC phase separation is evidenced in a miscible PLA/ATBC blend of stable composition and a pure ATBC phase. Consequently two Tg values can be measured, where the high temperature transition becomes independent 

Glass transition temperature depression of PLA/ATBC blends as a function of ATBC content. Symbols Data Ref. 60, Data Ref. 72, Data Ref. 58, A Data Ref. 66. The straight line represents the Fox equation, modelled with the parameters given by Ref. 60. 

The main drawback of monomeric plasticizers is their tendency to migrate from the polymer or to be leached out by contacting media. In anticipation of permanence problems caused by monomeric plasticizers, oligomeric 

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