Poly(lactic acid) Films Reinforced with TiO<sub>2</sub> and ZnO Nanoparticles: Thermal, Mechanical, Optical, and Phytotoxicity Assessment

Almeida, Mariana Amorim de; Silva, Emerson Oliveira da; Menezes, Lívia Rodrigues de

doi:10.1590/1980-5373-MR-2025-0688

Abstract

Poly(lactic acid) (PLA)-based films containing 0.5 and 1.5 wt% of TiO₂ or ZnO nanoparticles were prepared by solvent casting and evaluated in terms of thermal, mechanical, optical, structural, and ecotoxicological performance, targeting food packaging applications. X-ray diffraction and scanning electron microscopy revealed that low nanoparticle contents promoted partial crystalline ordering and relatively homogeneous dispersion, whereas higher loadings led to agglomeration and reduced crystallinity. Thermogravimetric analysis showed that the incorporation of 0.5 wt% TiO₂ increased the onset decomposition temperature of PLA from 303.3 to 322.8 °C. In contrast, higher nanoparticle contents and all ZnO-containing films exhibited reduced thermal stability and lower glass transition temperatures, with Tg decreasing from 51.3 °C (PLA) to 44.0 °C for PLA15ZnO. Nanoindentation demonstrated a significant increase in nanohardness for all nanocomposites, reaching improvements of up to ~27% compared to neat PLA. Optical analysis showed effective UV-shielding below 400 nm and preservation of visible-light transmittance above ~85% for films containing 0.5 wt% ZnO, whereas higher TiO₂ contents induced pronounced opacity and color changes. Germination assays using lettuce and cucumber indicated concentration-dependent phytotoxic effects for TiO₂, while ZnO showed neutral or slightly positive effects at low concentrations.

Keywords:
Poly(lactic acid); TiO₂NPs. ZnONPs; Food Packaging; Phytotoxicity

Polymeric film composition	Code
1.5 g of PLA + 7.5 mg of TiO₂NP	PLA05TiO₂
1.5 g of PLA + 7.5 mg of TiO₂NP	PLA15TiO₂
1.5 g of PLA + 7.5 mg of ZnONP	PLA05ZnO
1.5 g of PLA + 22.5 mg of ZnONP	PLA15ZnO
1.5 g of PLA	PLA

Sample	T_onset (± 2°C)	T_max (± 2°C)	Total Weight Loss (%)
PLA	303.3	327.6	99.21
PLA05TiO₂	322.8	344.5	98.80
PLA15TiO₂	288.4	314.0	98.62
PLA05ZnO	248.1	274.3	99.06
PLA15ZnO	255.9	277.9	98.99

_Sample	_PLA	_PLA05TiO2	_PLA15TiO2	_PLA05ZnO	_PLA15ZnO
_Xc(%)	_13.2	_42.9	_25.5	_25.9	_7.9

Sample	$L^{*}$	$a^{*}$	$b^{*}$	$Δ E_{00}^{*}$
I. Green background
background	38.08 ± 2.25^f	-14.32 ± 1.28^a	7.54 ± 0.02^a	—
PLA	46.76 ± 2.78^{d, e}	-8.92 ± 0.97^b	3.86 ± 0.01^b	6.30 ± 0.74^d
PLA05TiO₂	55.90 ± 3.47^b	-6.41 ± 0.36^c	-5.45 ± 0.02^e	15.24 ± 0.59^b
PLA15TiO₂	60.59 ± 3.36^a	-6.13 ± 0.29^c	-7.67 ± 0.03^f	18.28 ± 1.00^a
PLA05ZnO	48.78 ± 3.36^{c, d}	-8.71 ± 0.71^b	3.37 ± 0.01^c	7.20 ± 0.55^d
PLA15ZnO	50.76 ± 2.98^c	-7.09 ± 0.33^c	0.95 ± 0.01^d	9.57 ± 0.48^c
II. Orange background
background	61.18 ± 3.22^d	46.22 ± 2.72^a	52.28 ± 2.42^a	—
PLA	64.81 ± 3.99^c	37.97 ± 2.54^b	35.57 ± 3.86^b	6.16 ± 0.57^d
PLA05TiO₂	68.94 ± 3.01^{a, b}	33.67 ± 2.73^c	20.26 ± 2.26^d	13.76 ± 0.99^b
PLA15TiO₂	72.13 ± 3.20^a	29.13 ± 2.49^d	12.23 ± 1.38^e	18.27 ± 0.20^a
PLA05ZnO	65.39 ± 3.28^c	38.36 ± 2.91^b	35.33 ± 1.05^b	6.38 ± 0.37^d
PLA15ZnO	66.50 ± 2.78^{b, c}	33.75 ± 3.38^c	28.62 ± 2.00^c	9.14 ± 1.07^c
III. Red background
background	46.92 ± 2.33^e	47.66 ± 3.17^a	21.28 ± 1.48^a	—
PLA	52.77 ± 2.79^d	35.58 ± 3.66^b	12.56 ± 0.74^b	6.03 ± 0.09^d
PLA05TiO₂	60.11 ± 3.35^b	27.89 ± 2.65^c	2.05 ± 0.01^d	13.43 ± 0.67^b
PLA15TiO₂	65.31 ± 4.18^a	22.67 ± 3.36^d	-2.81 ± 0.02^e	17.80 ± 0.10^a
PLA05ZnO	54.75 ± 3.65^d	34.46 ± 2.58^b	11.81 ± 0.56^b	7.01 ± 0.28^d
PLA15ZnO	55.87 ± 3.65^{c, d}	29.74 ± 3.51^c	8.07 ± 0.03^c	9.55 ± 0.63^c
IV. White background
background	88.47 ± 3.64^a	1.27 ± 0.03^{a, b}	-2.13 ± 0.02^a	—
PLA	88.72 ± 3.78^a	1.33 ± 0.03^a	-1.94 ± 0.01^{a, b}	0.72 ± 0.38^{a, b}
PLA05TiO₂	88.42 ± 3.23^a	1.15 ± 0.03^{a, b}	-1.37 ± 0.01^d	0.73 ± 0.16^{a, b}
PLA15TiO₂	88.77 ± 3.13^a	0.99 ± 0.01^b	-1.53 ± 0.01^{c, d}	0.70 ± 0.15^{a, b}
PLA05ZnO	88.59 ± 3.41^a	1.40 ± 0.04^a	-1.90 ± 0.01^b	0.30 ± 0.04^b
PLA15ZnO	86.01 ± 3.65^a	1.40 ± 0.03^a	-1.76 ± 0.02^{b, c}	0.92 ± 0.12^a
V. Yellow background
background	82.49 ± 2.72^b	9.49 ± 0.36^{a, b}	67.21 ± 3.72^a	—
PLA	84.78 ± 5.82^{a, b}	9.89 ± 0.45^a	56.65 ± 3.65^b	3.11 ± 0.76^e
PLA05TiO₂	85.78 ± 4.82^{a, b}	8.51 ± 0.46^{b, c}	41.60 ± 2.85^d	7.71 ± 0.65^c
PLA15TiO₂	87.21 ± 3.08^a	7.89 ± 0.44^{c, d}	31.25 ± 1.63^e	11.62 ± 0.65^a
PLA05ZnO	83.84 ± 4.16^{a, b}	7.64 ± 0.34^{c, d}	49.63 ± 2.91^c	4.92 ± 0.66^d
PLA15ZnO	84.65 ± 3.88^{a, b}	6.77 ± 0.42^d	38.55 ± 2.33^d	8.55 ± 0.17^{b, c}

Poly(lactic acid) Films Reinforced with TiO2 and ZnO Nanoparticles: Thermal, Mechanical, Optical, and Phytotoxicity Assessment

Abstract

Poly(lactic acid) Films Reinforced with TiO₂ and ZnO Nanoparticles: Thermal, Mechanical, Optical, and Phytotoxicity Assessment