František Lednický

Formation and structure of the epoxy-silica hybrids

The organic-inorganic hybrid interpenetrating network (IPN) composed of an epoxide-amine network and silica was prepared and studied. Formation of the inorganic phase from tetraethoxysilane (TEOS) by sol-gel process was characterized by 29Si n.m.r. spectroscopy, gas chromatography, small-angle X-ray scattering and electron microscopy. Kinetics of the silica structure build-up in the organic matrix, its final structure and morphology depend on the method of IPN hybrid preparation. The large compact silica aggregates, 100–300 nm in diameter, are formed during the one-stage polymerization. The two-stage process with the acid prehydrolysis of TEOS leads to an acceleration of gelation and formation of more open and smaller silica structures: 50–100 nm in diameter. The most homogeneous hybrid morphology with the smallest silica domains of size 10–20 nm, appears in the sequential IPN. The development of the silica structure is restricted by a rigid reaction medium of the preformed epoxide network.

Microdomain structure in polylactide-block-poly(ethylene oxide) copolymer films

Structured surface is an important property of polymer biomaterials for tissue engineering, for its capacity to expose domains with different surface energy and functional groups. For this purpose, amphiphilic A-B-A block copolymers with polylactide (PLA) as A blocks and poly(ethylene oxide) (PEO 3, Mn = 3090; PEO6, Mn = 6110) as B block were synthesized by ring-opening polymerization of either L-lactide (L-LA) or DL-lactide (DL-LA), using poly(ethylene glycol)s as macroinitiators and tin(II) octanoate (Sn(Oct)2) as a catalyst. Differential scanning calorimetry (DSC) and electron microscopy were used to study the phase separation of the hydrophobic (PLA) and hydrophilic (PEO) segments in films made of the copolymers and their blends with high-molecular-weight PLA homopolymers. Hydrophilic (PEO) and hydrophobic (PLA) domains were formed at the polymer film surface due to the separation of phases. The phase separation was affected by the copolymer composition and the stereoregularity of PLA blocks in the copolymers.

Compatibilization of high-impact polystyrene/polypropylene blends

Abstract Effects of three different linear styrene—butadiene block copolymers on morphology and selected mechanical properties of high-impact polystyrene/polypropylene blends were investigated. Scanning and transmission electron microscopy and small-angle X-ray scattering were used for the determination of the blend morphology. Impact strength, elongation at break and flexural modulus were measured for further evaluation of the compatibilizer efficiency. A similar effect on the particle dispersion was found for all three copolymers but both the styrene-terminated multiblocks influence formation of interfacial layer and consequently the related mechanical properties in a much more pronounced way than the diblock. Small-angle X-ray scattering was found to be the appropriate technique for the determination of triblock concentration necessary for covering a given interfacial area (critical concentration).

Morphology, deformation and failure behaviour of homo- and copolyimide fibres ☆: 1. Fibres from 4,4′-oxybis(phthalic anhydride) (DPhO) and p-phenylenediamine (PPh) or/and 2,5-bis(4-aminophenyl)-pyrimidine (2,5PRM)

Abstract The morphology, deformation and failure behaviour of new high-performance polyimide (PI) fibres were examined by scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD) and tensile measurements. PI fibres were prepared from rigid aromatic diamines p -phenylenediamine (PPh) and 2,5-bis(4-aminophenyl)-pyrimidine (2,5PRM) and semi-rigid 4,4′-oxybis(phthalic anhydride) (DPhO) by wet-spinning of the N , N -dimethylacetamide solutions of their precursor poly(amic acids) in coagulation bath followed by thermal imidization at 400°C. The tensile properties and drawability of copolyimide (coPI) fibres were better than those of homopolyimides (homoPI). The improvement in fibre modulus and tensile strength of the coPI fibres can be explained by the microblock structure on the X-ray level and composed morphology on the macro level. Moreover, changes in the supermolecular structure and apparent fibril sizes, character of morphology, quantity of interfibrillar links, which affect the fracture mode were observed with the different composition of coPI.

Crystalline Character and Microhardness of Gamma‐Irradiated and Thermally Treated UHMWPE

Relationships between Vickers microhardness, x‐ray and differential scanning calorimetry (DSC) crystallinity, x‐ray long period, and melting points were determined for ultrahigh molecular‐weight polyethylene (UHMWPE) of various histories (as‐produced, irradiated, annealed, and remelted). It was shown that the microhardness responds very sensitively to both the irradiation conditions (total radiation dose, radiation dose rate) and the thermal treatment (annealing below the melting temperature, remelting). As microhardness reflects the yield point parameters, the results show that not only the total dose, but also the irradiation dose rate has a considerable influence on mechanical properties of UHMWPE. It was demonstrated that neither x‐ray nor DSC results are so sensitive to treatment as the microhardness results. The most important differences in properties were found between remelted samples and those thermally untreated or annealed.

Phase structure, composition and orientation of PC/PSAN blends studied by Raman spectroscopy, confocal Raman imaging spectroscopy and polarised PA-FTIR spectroscopy

Polycarbonate(PC)/ poly(styrene-co-acrylonitrile)(PSAN) blends were investigated by Raman and confocal Raman imaging spectroscopy, revealing the existence of two-phase (PC-rich and PSAN-rich) microdomain structure. This structure is coarser in blends with comparable component contents. During cold drawing the microdomains are strongly extended. As follows from polarised photoacoustic FTIR spectroscopy, a substantial orientation of PC chains occurs, as opposed to PSAN chains which orient only slightly.

Investigation of heterogeneous nucleation Using the induction time of crystallization: 1. Theory of induction time

The theory of the induction time was developed which is applicable to experimental studies of the early stages of the heterogeneous crystallization of polymers which is applicable to the evaluation of the effects of the surfaces of a dispersed component. The aspects of the epitaxial and nonepitaxial nucleation on the background of the induction time theory is discussed. The model of the formation of the heterogeneous nucleus was proposed as a basis for the induction time theory.

Reactive compatibilization of polyolefins using low molecular weight polybutadiene

Compatibilization of polyolefins using a combined system consisting of a low molecular weight liquid polybutadiene (l-PB) and a free radical initiator has been investigated. Binary blends LDPE/HDPE and LDPE/PP as well as ternary blends LDPE/HDPE/PP were prepared by reactive blending in the chamber of a Brabender Plasticorder. Transmission electron microscopy has been used for determination of phase structure of the final blends. Tensile impact strength of these materials, as the main criterion of compatibilization efficiency, was determined by a standardized method. A significant improvement in tensile impact strength of the compatibilized blends and considerable changes in their morphology have been found. The increase in tensile impact strength was apparently attained due to formation of effective linkages between main polymer components with the help of polybutadiene chains, providing good adhesion at the interface. Because the permanent thermoplasticity of these materials has been proved by repeated processing, any stable network based on covalent bonds in these blends cannot be considered. The used procedure shows to be a promising way for the recycling of commingled polyolefin waste as well as for the preparation of special polyolefin blends from virgin polymers. Die Kompatibilisierung von Polyolefinen mit einem kombinierten System bestehend aus einem niedrigmolekularen, flussigen Polybutadien und einem Radikalinitiator wurde untersucht. Durch reaktives Blenden in der Knetkammer eines Brabender-Plasticorders wurden sowohl binare Blends LDPE/HDPE und LDPE/PP als auch ternare Blends LDPE/HDPE/PP hergestellt. Die Phasenstrukturen der Blends wurden mittels Transmissionselektronenmikroskopie bestimmt. Die Zugschlagzahigkeit als Hauptkriterium fur der Kompatibilisierung dieser Materialien wurde nach einer normierten Methode gemessen. Eine signifikante Verbesserung der Zugschlagzahigkeit und erhebliche morphologische Anderungen der kompatibilisierten Blends wurden beobachtet. Der Anstieg der Zugschlagzahigkeit wird offensichtlich durch die Bildung wirksamer Bindungen zwischen den polymeren Hauptkomponenten unter Mitwirkung von Polybutadienketten erreicht, was eine gute Oberflachenadhasion zur Folge hat. Weil die Blends auch nach mehrmaligem Verarbeiten noch thermoplastisch waren, kann die Bildung eines stabilen Netzwerks mit kovalenten Bindungen ausgeschlossen werden. Das hier vorgestellte Verfahren ist ein vielversprechender Weg sowohl zur Aufarbeitung von Polyolefin-Mischabfallen als auch zur Herstellung spezieller Polyolefin-Blends aus Neumaterial.

Ultrathin sectioning of polymeric materials for low-voltage transmission electron microscopy

The relief in ultrathin sections is interpreted as one of the reasons for the image contrast observed in low-voltage transmission electron microscopy. In order to clarify this, processes taking place in the course of ultrathin sectioning were monitored using a polymeric material composed of hard matrix and soft particles (high-impact polystyrene). Volume changes leading to a surface relief were observed both on cut surfaces and in ultrathin sections.

Induction time as a measure for heterogeneous spherulite nucleation: Quantitative evaluation of early-stage growth kinetics

A theory is proposed indicating that the induction time characterizes the nucleation process in polymer crystallization. A microscopic method has been developed to monitor early stages of the spherulite growth. Using the method, based on photometric measurement of the depolarized light intensity during isothermal crystallization from the melt, nonzero nucleation induction time values were found for polypropylene (PP). From comparison of the theory with the experimental results obtained from polypropylene crystallization, it follows that the formation of PP crystal nuclei on admixtures is affected both by the formation of the first crystalline layer and by the size of the critical nucleus.