Physical Modification of PLA for Increasing Its Durability (Polarizing Light Microscopy Study) ^†

The European Strategy for plastic materials in a circular economy underlines the importance of using renewable polymers for long-lasting applications. The purpose of the paper was to increase polylactic acid’s (PLA) durability by controlling its crystalline structure [1,2,3].

The texture of the samples was analyzed in polarizing light with an Olympus BH-2 microscope, equipped with a THMS600 type heating system and a LINKAM TP92 temperature control system. The samples were studied during a heating/cooling cycle performed at a rate of 5 °C/min. The ATR-FTIR spectra needed for the chemical structure analysis was performed on a PerkinElmerSpectrum 100 instrument. The mechanical analysis was performed in a dynamic regime, on a PerkinElmer Diamond DMA instrument.

In the cooling stage of the neat PLA, the gradual formation of birefringent geometric shapes, next to which spherulites appeared, were observed. At 90 °C, fine birefringent texture was formed, similar in characteristics to those of semi-flexible or rigid polymers (Figure 1). PLA reinforced with nucleation agent presents birefringence at room temperature, indicating a highly ordered material. In the case of the polymer with nucleation and reinforcing agents, and because of their effects, a marked decrease in the mobility of the macromolecular chains was observed.

The investigations of morphological changes by FTIR analysis, optical microscopy, and mechanical properties in a dynamic regime prove the increase of the crystallization ability of the modified PLA due to the reinforcing agents.