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. 2019 Oct 16;11(10):1692.
doi: 10.3390/polym11101692.

The Effect of Titanium Dioxide Surface Modification on the Dispersion, Morphology, and Mechanical Properties of Recycled PP/PET/TiO2 PBNANOs

Eider Matxinandiarena  1 , Agurtzane Múgica  2 , Manuela Zubitur  3 , Cristina Yus  4 , Víctor Sebastián  5   6 , Silvia Irusta  7   8 , Alfonso David Loaeza  9 , Orlando Santana  10 , Maria Lluisa Maspoch  11 , Cristian Puig  12 , Alejandro J Müller  13   14
Affiliations

The Effect of Titanium Dioxide Surface Modification on the Dispersion, Morphology, and Mechanical Properties of Recycled PP/PET/TiO2 PBNANOs

Eider Matxinandiarena et al. Polymers (Basel). .

Abstract

Titanium dioxide (TiO2) nanoparticles have recently appeared in PET waste because of the introduction of opaque PET bottles. We prepare polymer blend nanocomposites (PBNANOs) by adding hydrophilic (hphi), hydrophobic (hpho), and hydrophobically modified (hphoM) titanium dioxide (TiO2) nanoparticles to 80rPP/20rPET recycled blends. Contact angle measurements show that the degree of hydrophilicity of TiO2 decreases in the order hphi > hpho > hphoM. A reduction of rPET droplet size occurs with the addition of TiO2 nanoparticles. The hydrophilic/hydrophobic balance controls the nanoparticles location. Transmission electron microscopy (TEM_ shows that hphi TiO2 preferentially locates inside the PET droplets and hpho at both the interface and PP matrix. HphoM also locates within the PP matrix and at the interface, but large loadings (12%) can completely cover the surfaces of the droplets forming a physical barrier that avoids coalescence, leading to the formation of smaller droplets. A good correlation is found between the crystallization rate of PET (determined by DSC) and nanoparticles location, where hphi TiO2 induces the highest PET crystallization rate. PET lamellar morphology (revealed by TEM) is also dependent on particle location. The mechanical behavior improves in the elastic regime with TiO2 addition, but the plastic deformation of the material is limited and strongly depends on the type of TiO2 employed.

Keywords: PBNANO; blend; morphology; nanoparticles; titanium dioxide.

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Conflict of interest statement

The authors declare no conflict of interest

Figures

Figure 1
Figure 1
Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images and size histograms of the three different types of TiO2 nanoparticles. Hydrophobic samples were negatively stained with phosphotungstic acid for TEM analysis.
Figure 2
Figure 2
(a) Fourier-transform infrared (FTIR) spectra and (b) thermogravimetric analysis TGA curves of commercial hydrophobic (hpho) and TMOS modified nanoparticles (hphoM).
Figure 3
Figure 3
SEM image of PBNANO-2% TiO2.
Figure 4
Figure 4
SEM images of PBNANO-12% containing: (a) hydrophilic (hphi), (b) hydrophobic (hpho), and (c) hydrophobically modified (hphoM) TiO2.
Figure 5
Figure 5
SEM images of PBNANO-hphoM with (a) 3% (b) 7%, and (c) 12% TiO2.
Figure 6
Figure 6
Number average diameter (dn) plotted as a function of total TiO2 content for the PBNANOs prepared in this work with the three types of TiO2 indicated in the legend. PBNANO-0 is the sample without additional TiO2, which contains 2% TiO2, as the rPET employed in this work already had 2% TiO2. So, PBNANO-0 is the 80/20 blend of rPP and rPET without any additional TiO2.
Figure 7
Figure 7
TEM images of PBNANO-hphoM with: (a,d) 3% (b,e) 7%, and (c,f) 12% TiO2.
Figure 8
Figure 8
TEM images of PBNANO-12% containing: (a,d) hydrophilic (hphi), (b,e) hydrophobic (hpho), and (c,f) hydrophobically modified (hphoM) TiO2.
Figure 9
Figure 9
Overall crystallization rate of rPP and the rPP phase within the indicated PBNANOs as a function of crystallization temperature. Solid lines correspond to mathematical fits to the Lauritzen and Hoffman theory [41].
Figure 10
Figure 10
Overall crystallization rate of rPET and the rPET phase within the indicated PBNANOs as a function of crystallization temperature. Solid lines correspond to mathematical fits to the Lauritzen and Hoffman theory [41].
Figure 11
Figure 11
TEM images of 80rPP/20rPET/12% TiO2 PBNANOs containing: (a,b) hydrophilic TiO2 (hphi); (c,d) hydrophobic TiO2 (hpho); (e) and (f) hydrophobically modified TiO2 (hphoM).
Figure 12
Figure 12
(a–c) Comparison between experimental data and the fits to the Avrami equation using the Origin plug-in developed by Lorenzo et al. [32].
Figure 13
Figure 13
Avrami index (n) as a function of crystallization temperature for the indicated samples.
Figure 14
Figure 14
Representative engineering stress–strain curves of PBNANOs tested (a) and appearance of the deformation process zone after tensile tests (b).
Figure 15
Figure 15
SEM micrographs of the fracture process zone after tensile tests of PBNANO-0 (a) PBNANO-hpho (b), PBNANO-hphoM (c) PBNANO-hphi (d).
Figure 16
Figure 16
Mechanical tensile parameters obtained for the materials under study. (a) Elastic modulus (E); (b) yielding stress (σy); (c) deformation at yield (εy) and (d) elongation at break (εb). Horizontal solid lines represent the upper (red) and the lower (blue) limits of the additive mixing law. The dashed lines in (d), represent their respective error bands.
Figure 17
Figure 17
SEM micrographs from fracture surface of: PBNANO-hphoM (a) and PBNANO-hphi (b). The yellow circle highlights the TiO2 nanoparticles that are left attached to the rPP matrix (“bed”) after extraction of a PET droplet.
See this image and copyright information in PMC

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