Abstract
Use of multi-wall carbon nanotubes (MWCNTs) in external layers (A-layers) of ABA-trilayer polypropylene films was investigated, with the purpose of determining intrinsic and extrinsic factors that could lead to antistatic behavior of transparent films. The incorporation of 0.01, 0.1, and 1 wt % of MWCTNs in the A-layers was done by dilution through the masterbatch method. Masterbatches were fabricated using isotactic polypropylene (iPP) with different melt flow indexes 2.5, 34, and 1200 g/10 min, and using different ultrasound assist methods. It was found that films containing MWCNTs show surface electrical resistivity of 1012 and 1016 Ω/sq, regardless of the iPP melt flow index (MFI) and masterbatch fabrication method. However, electrostatic charge was found to depend upon the iPP MFI, the ultrasound assist method and MWCNT concentration. A percolation electron transport mechanism was determined most likely responsible for this behavior. Optical properties for films containing MWCNTs do not show significant differences compared to the reference film at MWCNT concentrations below 0.1 wt %. However, an enhancement in brightness was observed, and it was attributed to ordered iPP molecules wrapping the MWCNTs. Bright transparent films with low electrostatic charge were obtained even for MWCNTs concentrations as low as 0.01 wt %.
Highlights
Polymer-based packaging films are widely used in the food industry to preserve all kinds of foods, such as cookies, bread, meat, beverage liquids, etc
The internal layer type B consisted of raw material of polypropylene and the external layers type A were fabricated with polypropylene homopolymer and multi-wall carbon nanotubes (MWCNTs) at 0.01, 0.1, and 1 wt %, using the masterbatches described above with an appropriate dilution ratio
The surface resistivity of samples containing MWCNTs decreased with respect to the reference film, and fall within 1012 to 1016 Ω/sq, without a clear tendency with respect to the masterbatch fabrication method, with the melt flow index (MFI) of isotactic polypropylene (iPP) used to prepare the masterbatch or with the final MWCNT concentration on the A-layers of the films
Summary
Polymer-based packaging films are widely used in the food industry to preserve all kinds of foods, such as cookies, bread, meat, beverage liquids, etc. One of the polymers used in an extensive manner in the fabrication of packaging films is isotactic polypropylene (iPP) and its copolymers with polyethylene, due to its low cost, good mechanical properties and excellent optical properties [1]. These types of polyolefins possess a non-polar structure showing hydrophobic behavior. Once on the film surface, the hydrophilic end attracts water molecules forming a low resistance antistatic layer (1010 –1012 Ω/sq) Due to their migrating nature, additives are totally expelled from the film, the antistatic effect is hindered or abates over the time. There is an industrial need for the development of new non-migrating antistatic additives in polymer carriers that are capable of maintaining the antistatic effect over longer periods of time [4]
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