Release of carbon nanoparticles of different size and shape from nanocomposite poly(lactic) acid film into food simulants

Abstract

Poly(lactic) acid (PLA) film with 2 wt% mixed carbon nanofillers of graphene nanoplates (GNPs) and multiwall carbon nanotubes (MWCNTs) in a weight ratio of 1:1 with impurities of fullerene and carbon black (CB) was produced by layer-to-layer deposition and hot pressing. The release of carbon nanoparticles from the film was studied at varying time-temperature conditions and simulants. Migrants in simulant solvents were examined with laser diffraction analysis and transmission electron microscopy (TEM). Film integrity and the presence of migrants on the film surfaces were visualised by scanning electron microscopy (SEM). The partial dissolution of PLA polymer in the solvents was confirmed by swelling tests and differential scanning calorimetry (DSC). Nanoparticle migrants were not detected in the simulants (at the LOD 0.020 μm of the laser diffraction analysis) after migration testing at 40°C for 10 days. However, high-temperature migration testing at 90°C for 4 h provoked a release of GNPs from the film into ethanol, acetic acid and oil-based food simulants. Short carbon nanotubes were observed rarely to release in the most aggressive acetic acid solvent. Obviously, the enhanced molecular mobility at temperatures above the glass transition and partial dissolution of PLA polymer by the food simulant facilitate the diffusion processes. Moreover, shape, size and concentration of nanoparticles play a significant role. Flexible naked GNPs (lateral size 100-1000 nm) easily migrate when the polymer molecules exhibit enhanced mobility, while fibrous MWCNTs (> 1 μm length) formed entangled networks on the film surfaces as the PLA polymer is partly dissolved, preventing their release into food simulants. The impurities of fullerenes and CB (5-30 nm) were of minor concentration in the polymer, therefore their migration is low or undetectable. The total amount of released migrants is below overall migration limits.

PLA/Graphene/MWCNT Composites with Improved Electrical and Thermal Properties Suitable for FDM 3D Printing Applications

“…Thermal conductivity and diffusivity of GNP nanocomposites were improved by the addition of graphene nanoplatelets by 181% and 214%, respectively. Thermal transport in obtained PLA/GNP composites is a thriving area of research thanks to graphene's extraordinary heat conductivity properties and its In our previous studies [50][51][52] it was found that the PLA is still biodegradable and, only if there is a burning of composites (T < 850 • C), residual ash contains an amount of graphite and carbon nanotubes, creating concerns about environmental pollution and damage. A quantitative and qualitative risk assessment has been carried out in two cases-so-called "bad practices" (not in compliance with safety measures) and "good practices" (subject to modern safety measures).…”

Release of Graphene and Carbon Nanotubes from Biodegradable Poly(Lactic Acid) Films during Degradation and Combustion: Risk Associated with the End-of-Life of Nanocomposite Food Packaging Materials

“…By contrast, during ultra-strong dynamic migration test [20] the release of nanoscale size particles (100 -1000 nm) from the GNP/MWCNT/PLA composite film is higher (0.5-0.7 number %) compared to (0.1-0.2 number %) nanoparticle migrants that was observed during the strong static migration test in the three food simulants, 3% acidic acid, 10% and 50% ethanol. The larger size nanoparticle migrants (1 -10 microns) were found also in higher amount (3 -5 number %) during the ultra-strong migration test, compared to 1-2 number % for the strong static test.…”

“…The characterization of such release provides critical information for environmental nanoobject exposure from biodegradable nanocomposites. In our previous studies [19][20][21], we have investigated the release of GNP and MWCNTs from the composite film GNP/MWCNT/PLA in alcoholic and acid food simulants, high temperature migration conditions, such as: (i) strong static migration test (with heating at 90 o C for 4 hours); and (ii) ultra-strong dynamic migration test (heating at 90 o C for 4 hours followed by subsequent storage for 10 days at 40°C, including dynamic treatment for 1 min daily). The strong static and ultra-strong dynamic migration conditions were set accordingly with the prescription in EU Regulation 10/2011 (EU 2011) [28] and literature sources [29,30] for migration of polymer films in food simulants.…”

“…At the strong static migration test [19,20], we have observed that large graphene nanoplatelets (GNP) of about 100-1000 nm in length and a few nanometers in thickness indeed migrate from the poly(lactic) composite film, GNP/MWCNT/PLA, into food simulants. We have assumed that heating above the glass transition temperature enhance the dynamics of polymer molecules and facilitate the diffusion of graphene nanoplatelets from PLA film into food simulant.…”

“…Release during service life of MWCNT-based composites is projected to be quite low and composed of polydisperse fragments with only a small fraction of free MWCNTs [15][16][17]. Studies for the release of graphene from food packaging materials into food are very scare [19][20][21].…”