A. A. Popov

Environmentally friendly films based on poly(3-hydroxybutyrate) and poly(lactic acid): A review

A review of data on the thermo, photo-, and biodegradation of compositions of synthetic polymers with poly-3-hydroxybutyrate and poly(lactic acid) is presented. The influence of these polymers on the thermal, microstructural, and rheological properties of mixtures is examined. The destruction of pure biopolymers, as well as compositions thereof with polyethylene, poly-(3-hydroxybutyrate-co-3-hydroxyvalerate), and polycaprolactone is studied.

Effect of external influences on the structural and dynamic parameters of polyhydroxybutyrate-hydroxyvalerate-based biocomposites

The EPR probe, DSC, and WARDX methods are applied to study the molecular dynamics and structure of 3-hydroxybutyrate-3-hydroxyvalerate copolymer (PHBHV, 5 mol %) and its mixtures with segmented polyester urethane (SPEU) upon ozone oxidation and hydrothermal treatment. It is shown that time-limited (3 and 5 h) treatment of the mixed compositions with water at 40°C has no noticeable effect on the dynamics of rotation of the probe (EPR) and the crystallinity of PHBHV (DSC). However, hydrothermal treatment at 70°C causes an increase in the molecular mobility of the probe in the system, accompanied, according to XRD and DSC analyses, by increases in the degree of crystallinity and density of PHBHV crystallites. The temperature of fusion of mixed compositions also increases. During ozonation, the mobility of the probe slows gradually in PHBHV all the time, whereas in mixed compositions, a slowdown is observed only up to 3 h of oxidation time, after which, up to 5 h of ozonation, the mobility increases, along with decreases in the fraction of the amorphous phase and in the density of the crystallites.

Probe mobility dynamics, crystal structure, and isotope exchange in PHBV and SPEU blend compositions

176 Biodegradable compositions based on natural polymers in combination with synthetic polymers offer an alternative to individual polymers. Blending is expectable to endow the composition with some new physicochemical characteristics that are not intrinsic to its individual components. Innovation technologies employ biodegradable systems for the targeted trans port of drugs and for the manufacture of environmentally friendly construction materials and packaging [1, 2]. Due to the unique combination of thromboresistance and mechanical characteristics, segmented polyether urethanes (SPEUs) are widely used in diverse fields of engineering and biomedicine as construction and functional materials. However, dimethyl isocyanate– based SPEUs are well known to have low biodegrada tion rates. This is a positive factor where long opera tion times are required, but may be considered as a limitation for short times of use. The lifetime of a sys tem can be tailored by blending SPEUs with other biopolymers, such as polyhydroxyalkanoates [3]. Poly(3 hydroxybutyrate) (PHB), a representative poly hydroxyalkanoate, combines useful properties with some undesired properties, namely, high costs and fra gility. These limitations are eliminated by PHB copol ymers with 3 hydroxyvalerate (PHBV) and composi tions with other biomedical polymers, in particular, with chitosan [4]. Varying the component ratio of the PHBV–SPEU composition and thereby influencing the morphology and crystallinity, one can manufac ture composition materials with diversified physico chemical characteristics, such as permeability, water solubility, destruction mechanism and destruction rates, and others. An efficient way to evaluate the states of amor phous and crystalline phases in polymers and polymer blends is a combination of dynamic and structural techniques. In this study, the dynamic techniques used are electron probe microanalysis, ESR, and deuterium isotope exchange. The structural techniques used are wide angle X ray diffraction and differential scanning calorimetry (DSC). Such a combination of structural and dynamic characteristics allows a more complete ascertainment of the structural evolution of PHBV– SPEU blends in an aqueous medium, preceding the hydrolytic decomposition of the polymer system, in the range of small times (hours). The subject matter of this study was blend compo sitions based on a PHBV biodegradable natural copoly mer (from Tianan) and SPEU (from BASF Elastog ran). The characteristics of the individual components were as follows: for SPEU: Mw = 2.29 × 10 5, Mn = 5.3 × 104, and ρ = 0.97 g/cm3; and for PHBV: Mw = 2.4 × 10 5, Mn = 1.5 × 10 5, and ρ = 1.25 g/cm3. The component ratio in PHBV–SPEU blends was varied in the follow ing sequence (wt/wt): 60 : 40, 50 : 50, and 40 : 60. Polymer films were prepared by evaporating a solvent (chloroform or tetrahydrofuran) from polymer solu tions on glass surfaces. Molecular mobility was studied by a spin probe method with determination of the correlation time τ, which characterizes the rotation mobility of the TEMPO probe, using a conventional ESR procedure [5]. DSC studies were carried out on a Netzsch DSC 204 F1 analyzer in an inert (argon) atmosphere with a heating rate of 10 K/min. X ray dif fraction was measured from film samples in transmis sion geometry on a Bruker Advance D8 diffractometer (CuK α radiation). The IR spectra of deuterated films were recorded on a Bruker IFS 48 FTIR spectropho tometer with a resolution of 2 cm–1 using 256 scans for each spectrum. X ray diffraction measurements showed high crys tallinities of PHBV and PHB samples [4]. The X ray diffraction patterns of PHBV films show at least five reflections corresponding to an orthorghombic lattice PHYSICAL CHEMISTRY

Changes in the structural parameters and molecular dynamics of polyhydroxybutyrate-chitosan mixed compositions under external influences

Differential scanning calorimetry (DSC), EPR probe analysis, large-angle X-ray diffraction (XRD), and UV spectroscopy are used to study the molecular dynamics and structure of hydroxybutyrate (PHB) copolymer, chitosan, and mixed compositions thereof upon thermal treatment in an aquatic medium. It is shown that, in mixed compositions, starting from 30% PHB, the correlation time increases by an order of magnitude, indicative of a sharp slowdown of the molecular mobility of the probe, and, concurrently, the degree of crystallinity decreases abruptly, as evidenced by DSC and XRD analyses. The diffusion coefficient of rifampicin in mixed compositions also decreases with increasing PHB content. A short-term (1 h) thermal treatment (at 70°C) in water results in an increase in the molecular mobility of the probe in the system. Crystallinity changes in complex ways.

Thermooxidative degradation of blends based on poly(3-Hydroxybutyrate). Specifics of the process

The relationship between the structure and the kinetics of the thermal oxidation of the poly(3-hydroxybutyrate) — ethylene propylene rubber and polyethylene — poly(3-hydroxybutyrate) systems is studied. For the first system containing 30–50 wt % poly(3-hydroxybutyrate), phase inversion is observed, which affects its reactivity. For the compositions with polyethylene, two stages of oxidation manifest themselves: before and after poly(3-hydroxybutyrate) degradation.

Microstructures and supramolecular structures of butadiene-nitrile rubbers: Paramagnetic-probe study

The chain microstructures and supramolecular structures of butadiene-nitrile rubbers are studied by ESR spectroscopy. On the temperature dependences of the rotational mobility (correlation time τc) of paramagnetic probes differing in size (2,2,6,6-tetramethylpiperidine-1-oxyl and 4-benzoate-2,2,6,6-tetramethylpiperidine-1-oxyl), relaxation transitions are observed. It is shown that there is a correlation between the Arrhenius parameters of rotational mobility of radicals and the copolymer composition and that different brands of rubbers differ in microstructure and supramolecular structure.

Nonwoven blend composites based on poly(3-hydroxybutyrate)–chitosan ultrathin fibers prepared via electrospinning

With the use of scanning electron microscopy, differential scanning calorimetry, and electron paramagnetic resonance, the structural–dynamic analysis of ultrathin fibrous matrixes based on poly(3-hydroxybutyrate) and blend composites of this polymer with chitosan is performed. It is shown that the addition of a small amount of chitosan causes change in the morphologies of the matrixes and leads to a marked increase in their melting enthalpies. It is found that the studied fibers contain amorphous regions with various morphologies. The dynamics of the spin probe TEMPO in these regions is investigated, and its change under the influence of increased temperature, an aqueous medium, and ozone is examined. The mechanism controlling the effects of chitosan, temperature, and an oxidative aggressive medium on the structuring of fibers is advanced.

Mechanochemical modification of natural rubber

Thermomechanochemical changes of SVR 3L natural rubber after the treatment in the internal rubber mixer in the self-heating mode were studied. The effect of the molecular mass and content of the gel fraction of natural rubber is shown. Properties of rubber compounds and vulcanized rubber are presented. Taking into account modern requirements, a new alternative technology of obtaining halogenated elastomers based on the solid-phase (mechanochemical) halide modification is created. New halogen-containing natural rubber produced by this technology proves themselves in the conditions of rubber production. New fluorinated natural rubber produced by this technology proves themselves in the conditions of rubber production.

The Structure of Polybutadienes and Butadiene-Acrylonitrile Copolymers

The paramagnetic probe method with the use of free radicals of different dimensions (2,2,6,6-tet-ramethyl-1-piperidinyloxy and 4-benzoate-2,2,6,6-tetramethyl-1-piperidinyloxy) has been employed to study the effect of the isomeric composition of butadiene units in polybutadienes and butadiene-acrylonitrile copolymers on the number and dimensions of ordered structures. The nature of density fluctuations and defective regions, that is, the regions in which the radicals are sorbed, has been ascertained. It has been shown that the ordered regions are composed of stereoregular chain fragments, while defective regions are enriched with butadiene isomers different from those present in prevailing amounts.

Ozone resistance of crosslinked blends of butadiene-acrylonitrile and ethylene-propylene-diene elastomers and interphase interaction in these blends

The relation of ozone resistance to the volume and structure of the interphase layer and the amounts of crosslinks in the interlayer was studied for covulcanizates of butadiene-acrylonitrile rubbers of various polarities with ethylene-propylene-diene (EPDM) elastomers that differed in the comonomer composition and stereoregularity of propylene units. It was shown that the ozone resistance is determined by the compatibility of the components, the interlayer volume and density, the amount of crosslinks in the interlayer, and the strength of the EPDM network.