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. 2023 Nov 16;15(22):4432.
doi: 10.3390/polym15224432.

Improvement of Water Vapor Permeability in Polypropylene Composite Films by the Synergy of Carbon Nanotubes and β-Nucleating Agents

Glykeria A Visvini  1   2 , Georgios N Mathioudakis  1   3 , Amaia Soto Beobide  1 , Zoi Piperigkou  4 , Aris E Giannakas  5 , Stavros Messaritakis  6 , Giannis Sotiriou  7 , George A Voyiatzis  1
Affiliations

Improvement of Water Vapor Permeability in Polypropylene Composite Films by the Synergy of Carbon Nanotubes and β-Nucleating Agents

Glykeria A Visvini et al. Polymers (Basel). .

Abstract

A notable application of polymeric nanocomposites is the design of water vapor permeable (WVP) membranes. "Breathable" membranes can be created by the incorporation of micro/nanofillers, such as CaCO3, that interrupt the continuity of the polymeric phase and when subjected to additional uniaxial or biaxial stretching this process leads to the formation of micro/nanoporous structures. Among the candidate nanofillers, carbon nanotubes (CNTs) have demonstrated excellent intrinsic WVP properties. In this study, chemically modified MWCNTs with oligo olefin-type groups (MWCNT-g-PP) are incorporated by melt processes into a PP matrix; a β-nucleating agent (β-ΝA) is also added. The crystallization behavior of the nanocomposite films is evaluated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The WVP performance of the films is assessed via the "wet" cup method. The nanohybrid systems, incorporating both MWCNT-g-PP and β-NA, exhibit enhanced WVP compared to films containing only MWCNT-g-PP or β-NA. This improvement can be attributed to the significant increase in the growth of α-type crystals taking place at the edges of the CNTs. This increased crystal growth exerts a form of stress on the metastable β-phase, thereby expanding the initial microporosity. In parallel, the coexistence of the inherently water vapor-permeable CNTs, further enhances the water vapor permeability reaching a specific water vapor transmission rate (Sp.WVTR) of 5500 μm.g/m2.day in the hybrid composite compared to 1000 μm.g/m2.day in neat PP. Notably, the functionalized MWCNT-g-PP used as nanofiller in the preparation of the "breathable" PP films demonstrated no noteworthy cytotoxicity levels within the low concentration range used, an important factor in terms of sustainability.

Keywords: breathability; carbon nanotubes; nanocomposites; nucleating agent; polypropylene.

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Conflict of interest statement

Author Giannis Sotiriou was employed by the company Thrace Polyfilms S.A. and author Stavros Messaritakis was employed by the company Plastika Kritis S.A. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
DSC thermographs of composite films PP/MWCNT-g-PP (0, 0.5, 1.5, 3, 4 and 6 wt.%) quenched in ice water from melt (a) and annealed at 130 °C (b), XRD patterns for these composite films (c,d).
Figure 2
Figure 2
(a) DSC thermographs of pure PP and PP/ (0.3, 1 and 4 wt.%) β-NA films (quenched in ice water from melt and crystallized at 130 °C), (b) XRD patterns for the same films.
Figure 3
Figure 3
DSC thermographs of PP/4%β-NA/MWCNT-g-PP (0, 0.5, 1.5, 3, 4 and 6 wt.%) composite films (a) quenched in ice water from melt and (b) annealed at 130 °C); (c,d) XRD patterns of the corresponding composite films.
Figure 4
Figure 4
Specific water vapor permeability values, Sp.WVTR, for annealed (130 °C) and quenched composite films PP/x%β-NA/y%MWCNT-g-PP.
Figure 5
Figure 5
Effects of MWCNT-NH2 and MWCNT-g-PP on cell viability. Cell viability following 24 h (a) and 72 h (b) treatment of A549 cells with 1, 10, 50, 200, and 500 ug/mL of each MWCNT was assessed with MTT assay. Asterisk (*) indicates statistically significant differences (p < 0.05).
Figure 6
Figure 6
Phase contrast images with crystal violet dye of A549 cells cultured on pre-coated cell culture plates with 1–500 ug/mL MWCNTs.
See this image and copyright information in PMC

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