STRUCTURE AND PROPERTIES OF THERMOPLASTIC PSEUDO-INTERPENETRATING POLYMER NETWORKS BASED ON NATURAL POLY-3-HYDROXYBUTIRATE AND NATURAL RUBBER
Authors:   Institute of macromolecular Chemistry NAS of Ukraine, 48, Kharkivske shose, Kyiv, 02155, Ukraine, GRIGORYEVA O.P. , STAROSTENKO O.M. ,   Institute of macromolecular Chemistry NAS of Ukraine, 48, Kharkivske shose, Kyiv, 02155, Ukraine, GUSAKOVA K.G. ,   Institute of macromolecular Chemistry NAS of Ukraine, 48, Kharkivske shose, Kyiv, 02155, Ukraine, FAINLEIB O.M. ,   Institute of macromolecular Chemistry NAS of Ukraine, 48, Kharkivske shose, Kyiv, 02155, Ukraine
Published: January 2023

Thermoplastic film materials with a structure of pseudo-interpenetrating polymer networks (pseudo-IPNs) were created on the basis of natural semi-crystalline poly-3-hydroxybutyrate (PHB) and natural rubber (NR), the content of the NR was varied from 2 to 40 wt.%. Using the methods of Fourier Transform Infra-Red (FTIR) spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), structure-properties relationships were studied for PHB/NR thermoplastic pseudo-IPNs at different ratios of the components. Significant non-additive increase in mechanical characteristics compared to the individual PHB was found for PHB/NR pseudo-IPNs samples with a low content (up to 15 wt.%) of NR. For the sample with a content of 5 wt.% NR, the greatest increase (~18.4%) in strength at break was fixed (σb ≈ 22.5 MPa); for a sample with a content of 10 wt.% NR, the largest increase (~ 215%) in elongation at break (εb ≈ 48.8%) was observed. By FTIR spectroscopy, it was found that certain changes in the crystal structure of the PHB matrix occurred in the samples of pseudo-IPNs at increasing the NR content; however, no changes in the chemical structure of the components were detected. The SEM method revealed spherical domains of the dispersed elastomeric NR phase distributed in the PHB matrix in the samples of PHB/NR pseudo-IPNs. These observations evidence the microphase separation of the system components due to their thermodynamic incompatibility. It is worth to note that the sizes of the domains of the dispersed elastomeric phase naturally increased from ~10–20 μm for pseudo-IPNs PHB/NR = 85/15 wt.%, up to ~ 100 μm for PHB/NR = 60/40 wt.%. Using TGA method, it is established that PHB/NR pseudo-IPNs samples are characterized by high resistance to thermo-oxidative destruction, which non-additively increases with increasing the NR content. Destruction of PHB/NR pseudo-IPNs samples occur in two main stages: at I stage (Td ~ 240–285 °С) the main weight loss of the samples is occurred due to the destruction of macromolecules of the PHB matrix; at II stage (Td ~ 320–380 °С) the oxidative destruction of NR component takes place. Calculations have shown that with increasing the NR content, the maximum rate of thermo-oxidative destruction of pseudo-IPNs samples decreases compared to the individual PHB by 5–52 % with increasing the NR content from 2 to 40 wt.%. Therefore, it means that their resistance to thermo-oxidative destruction increases. The results obtained by DSC method have shown that the introduction of NR and changes of the components ratio significantly and non-additively affect all the thermophysical characteristics of the samples studied. This indicates a significant restructuring of the microphase (amorphous and crystalline) structure of pseudo-IPNs synthesized due to the interpenetration of the components into the microphases of each other and the formation of mixed PHB/NR microphases with different ratios of the components.