Thermal degradation of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) in nitrogen and oxygen studied by thermogravimetric-Fourier transform infrared spectroscopy

STRUCTURE AND PROPERTIES OF THERMOPLASTIC PSEUDO-INTERPENETRATING POLYMER NETWORKS BASED ON NATURAL POLY-3-HYDROXYBUTIRATE AND NATURAL RUBBER

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.

Upgrading cardoon biomass into Polyhydroxybutyrate based blends: A holistic approach for the synthesis of biopolymers and additives

Cardoon, Cynara cardunculus L. represents a biorefinery crop with a great potential in the bioplastic field. This work investigates the valorization of different cardoon components into high added value products, finally recombined into novel upgraded bioplastics. Bioprocesses for Polyhydroxybutyrate (PHB) and medium-chain-length Polyhydroxyalkanoates (mcl-PHA) production were set up starting from root inulin and seed oil respectively, highlighting the effect of process conditions on polymer properties. The ternary blend, in which the PHB polymer matrix was added with mcl-PHA and epoxidized cardoon oil, evidenced a synergic effect of both additives in modulating PHB structural and thermal properties, promoted by the physical interaction occurring among the components. This proof-of concept frames the paper in the holistic approach of circular economy applied to bioplastic production.

Isolation and optimization of extracellular PHB depolymerase producer Aeromonas caviae Kuk1-(34) for sustainable solid waste management of biodegradable polymers

Bioplastics, synthesized by several microbes, accumulates inside cells under stress conditions as a storage material. Several microbial enzymes play a crucial role in their degradation. This research was carried to test the biodegradability of poly-β-hydroxybutyrate (PHB) utilizing PHB depolymerase, produced by bacteria isolated from sewage waste soil samples. Potent PHB degrader was screened based on the highest zone of hydrolysis followed by PHB depolymerase activity. Soil burial method was employed to check their degradation ability at different incubation periods of 15, 30, and 45 days at 37±2°C, pH 7.0 at 60% moisture with 1% microbial inoculum of Aeromonas caviae Kuk1-(34) (MN414252). Without optimized conditions, 85.76% of the total weight of the PHB film was degraded after 45 days. This degradation was confirmed with Fourier-transform infrared spectroscopy (FTIR) and Scanning electron microscope (SEM) analysis. The presence of bacterial colonies on the surface of the degraded film, along with crest, holes, surface erosion, and roughness, were visible. Media optimization was carried out in statistical mode using Plackett Burman (PB) and Central Composite Design (CCD) of Response Surface Methodology (RSM) by considering ten different factors. Analysis of Variance (ANOVA), Pareto chart, response surface plots, and F-value of 3.82 implies that the above statistical model was significant. The best production of PHB depolymerase enzyme (14.98 U/mL) was observed when strain Kuk1-(34) was grown in a media containing 0.1% PHB, K₂HPO₄ (1.6 gm/L) at 27 ℃ for seven days. Exploiting these statistically optimized conditions, the culture was found to be a suitable candidate for the management of solid waste, where 94.4% of the total weight of the PHB film was degraded after 45 days of incubation.

Poly(3-Hydroxybutyrate)-Based Nanoparticles for Sorafenib and Doxorubicin Anticancer Drug Delivery

Dual drug-loaded nanotherapeutics can play an important role against the drug resistance and side effects of the single drugs. Doxorubicin and sorafenib were efficiently co-encapsulated by tailor-made poly([R,S]-3-hydroxybutyrate) (PHB) using an emulsion-solvent evaporation method. Subsequent poly(ethylene glycol) (PEG) conjugation onto nanoparticles was applied to make the nanocarriers stealth and to improve their drug release characteristics. Monodisperse PHB-sorafenib-doxorubicin nanoparticles had an average size of 199.3 nm, which was increased to 250.5 nm after PEGylation. The nanoparticle yield and encapsulation efficiencies of drugs decreased slightly in consequence of PEG conjugation. The drug release of the doxorubicin was beneficial, since it was liberated faster in a tumor-specific acidic environment than in blood plasma. The PEG attachment decelerated the release of both the doxorubicin and the sorafenib, however, the release of the latter drug remained still significantly faster with increased initial burst compared to doxorubicin. Nevertheless, the PEG-PHB copolymer showed more beneficial drug release kinetics in vitro in comparison with our recently developed PEGylated poly(lactic-co-glycolic acid) nanoparticles loaded with the same drugs.

Chemometrics and Related Fields in Python

The Python programing language is becoming a promising tool for data analysis in various fields. However, little attention has been paid to using Python in the field of analytical chemistry, though recent advances in instrumental analysis require robust and reliable data analysis. In order to overcome the difficulty in accurate analysis, multivariate analysis, or chemometrics, has been widely applied to various kinds of data obtained by instrumental analysis. In the present work, the potential usefulness of Python for chemometrics and related fields in chemistry is reviewed. Many practical tools for chemometrics, e.g., principal component analysis (PCA), partial least squares (PLS), support vector machine (SVM), etc., are included in the scikit-learn machine learning (ML) library for Python. Other useful libraries such as pyMCR for multivariate curve resolution (MCR), 2Dpy for two-dimensional correlation spectroscopy (2D-COS), etc. can be obtained from GitHub. For these reasons, a computational environment for chemometrics is easily constructed in Python.

Enhancement of poly(3-hydroxybutyrate) thermal and processing stability using a bio-waste derived additive

Poly(3-hydroxybutyrate) (PHB) is a biodegradable polymer, whose applicability is limited by its brittleness and narrow processing window. In this study a pomace extract (EP), from the bio-waste of winery industry, was used as thermal and processing stabilizer for PHB, aimed to engineer a totally bio-based system. The results showed that EP enhanced the thermal stability of PHB, which maintained high molecular weights after processing. This evidence was in agreement with the slower decrease in viscosity over time observed by rheological tests. EP also affected the melt crystallization kinetics and the overall crystallinity extent. Finally, dynamic mechanical and tensile tests showed that EP slightly improved the polymer ductility. The results are intriguing, in view of the development of sustainable alternatives to synthetic polymer additives, thus increasing the applicability of bio-based materials. Moreover, the reported results demonstrated the feasibility of the conversion of an agro-food by-product into a bio-resource in an environmentally friendly and cost-effective way.

Molecular weight dependence of the thermal degradation of poly(epsilon-caprolactone): a thermogravimetric differential thermal Fourier transform infrared spectroscopy study

The effect of molecular weight on the thermal degradation of poly(epsilon-caprolactone) (PCL) was investigated by thermogravimetric analysis in combination with differential thermal analysis and Fourier transform infrared spectroscopy (TGA/DTA/FT-IR). The measurements were made in the temperature range 40-720 degrees C and it was found that PCL undergoes completely different degradation processes in nitrogen and oxygen atmosphere. Thus, in nitrogen atmosphere low molecular weight (M(n) = 10,000 g/mol) PCL (PCL(10k)) decomposed in a three-step mechanism. The evolved gases detected by FT-IR spectroscopy were identified as epsilon-caprolactone, 5-hexenoic acid, CO(2), and methyl pentanoate and traces of H(2)O. In the case of high molecular weight (M(n) = 80,000 g/mol) PCL (PCL(80k)) only a two-step degradation was observed. By FT-IR spectroscopy 5-hexenoic acid, CO(2), H(2)O, and methyl pentanoate were detected as decomposition products. In an oxygen environment, similar degradation products were detected for the different molecular-weight PCLs. The recorded FT-IR spectra of the evolved gases were identified as CO(2), CO, H(2)O, and short-chain carboxylic acids.

Thermally induced dissociation nature of pure 2-pyrrolidinone via near-infrared correlation spectroscopy analysis

The temperature-dependent dissociation behavior of 2-pyrrolidinone in the pure liquid state was investigated via perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy and two-dimensional near-infrared (2D-NIR) correlation spectroscopy. Absorption bands in the region of 6900-6000 cm(-1) assigned to the first overtones of stretching modes of NH groups provided detailed information about the dissociation process from 25 degrees C to 95 degrees C. On the basis of PCMW2D analysis, the sequence of dissociation events occurring during the temperature variation were elucidated in two temperature ranges (25-60 degrees C and 65-95 degrees C). Specific dissociation order of the hydrogen bond under temperature perturbation was disclosed by 2D-NIR correlation spectroscopy. As temperature increased, the dissociation of larger oligomers occurred firstly with the generation of smaller oligomers, which were then consumed later by the decomposition of hydrogen bonds. The dissociation of stable cyclic dimers occurred mainly at higher temperature through gradually weakened hydrogen-bonding of NH groups.