Synergistic effect of TiO2 nanoparticles and poly (ethylene-co-vinyl acetate) on the morphology and crystallization behavior of polylactic acid

Abstract

The impact of adding ethylene vinyl acetate copolymer (EVA 80) and 1 wt% TiO₂ nanoparticles on the morphology and crystallization behavior of poly(lactic acid) blends was investigated using DSC, SEM, and POM. Thermal analysis revealed the enhancement of crystallinity of PLA in the presence of TiO₂ and higher EVA 80 content in the blend. The PLA and EVA 80 components showed compatibility, as evidenced by the shift of the glass transition temperatures of the PLA phase in the blend to lower values compared to neat PLA. The lower temperature shift of the cold crystallization of the PLA and the formation of the small spherulites of the PLA in the blends indicated that the EVA 80 and TiO₂ act as a nucleating agent for crystallization. The non-isothermal crystallization parameters of the composites were evaluated using Avrami's modified model, the MO approach, and Friedman's isoconversional method. The Avrami's modified rate constant (K) and the effective activation energy values significantly increased with the incorporation of EVA 80 and TiO₂ nanoparticles. Furthermore, the thermogravimetric analysis (TGA) showed improved thermal stability of PLA by adding EVA 80 and TiO₂.

Keywords: DSC; Effective activation energy; MDSC; Modified Avrami; POM; Poly(ethylene-co-vinyl acetate); Polylactic acid (PLA); SEM; With vinyl acetate content 80 (EVA80).

Scheme 1

XRD pattern for produced TiO₂ calcinated at 500 °C.

Scheme 2

TEM micrograph for TiO₂ calcinated at 500 °C.

Figure 1

DSC second heating curves for (a) PLA: EVA80; (b) PLA: EVA80:TiO₂.

Figure 2

TMDSC curves in the glass transition region of the PLA: EVA80: 1 wt% TiO₂; (a) reversing Cp; (b) phase angle.

Figure 3

SEM micrographs for PLA: EVA80: 1 wt% TiO₂.

Figure 4

polarized optical micrograph for PLA: EVA80:TiO₂ after isothermal crystallized at 125 °C for 90 min.

Figure 5

TGA (a) and Drev. Mass loss (b) curves of PLA: EVA80: 1 wt% TiO₂ with a heating rate of 10 °C/min.

Figure 6

non-isothermal DSC different heating curves of PLA: EVA80: 1 wt% TiO₂.

Figure 7

Relative crystallinity, $\text{X}\left(\text{t}\right)$ versus crystallization time for non-isothermally crystallized PLA: EVA80: 1 wt% TiO₂ composites at different cooling rates, dot lines refer to t_0.5.

Figure 8

$\frac{1}{{\text{t}}_{0.5}}$ versus a heating rate for PLA:EVA80: 1 TiO₂ composites.

Figure 9

log(− ln(1 − xt)) versus log(t) for PLA: EVA 80: 1 wt% TiO₂.

Figure 10

$ln\left(\mathrm{\varnothing }\right)$ versus $\text{ln}(\text{t})$ for different $\text{X}\left(\text{t}\right)$ of PLA: EVA 80: 1 wt% TiO₂ composites.

Figure 11

An effective activation energy as a function of relative crystallinity and average crystallization temperature.