Ivica Janigová

Thermal degradation of plasticized poly(3-hydroxybutyrate) investigated by DSC

The thermal degradation of poly(3-hydroxybutyrate) (PHB) in the presence of two plasticizers (glycerol, glycerol triacetate) was investigated by differential scanning calorimetry (DSC). The thermal degradation was studied as a function of the annealing time, temperature and cooling rate after the thermal treatment. PHB thermal degradation proceeds by the random scission of the polymer chain. The presence of glycerol leads to a significant prodegradative effect on PHB presumably due to the alcoholysis reaction, while glycerol triacetate (triacetine) behaved as an almost inert additive from this point of view. Size exclusion chromatography (SEC) confirmed the results obtained by the DSC method. The data lead to the conclusion that DSC is a suitable method for estimation of PHB thermal degradation.

Plasma treatment of particulate polymer composites for analyses by scanning electron microscopy. II. A study of highly filled polypropylene/calcium carbonate composites

Plasma treatment of fracture surfaces from particulate calcium carbonate/polypropylene composites has been shown to have potential as a means for exposing filler particles in the fracture surface, particularly where fracture occurs through the matrix. It has been found that the optimum time of plasma treatment is governed by the nature of the matrix and possibly by the type of filler-matrix bond. This method of exposing filler particles in composite surfaces provides a very convenient aid in the process of characterising filler particle size distributions and composite homogeneity/heterogeneity.

A new route for chitosan immobilization onto polyethylene surface.

Low-density polyethylene (LDPE) belongs to commodity polymer materials applied in biomedical applications due to its favorable mechanical and chemical properties. The main disadvantage of LDPE in biomedical applications is low resistance to bacterial infections. An antibacterial modification of LDPE appears to be a solution to this problem. In this paper, the chitosan and chitosan/pectin multilayer was immobilized via polyacrylic acid (PAA) brushes grafted on the LDPE surface. The grafting was initiated by a low-temperature plasma treatment of the LDPE surface. Surface and adhesive properties of the samples prepared were investigated by surface analysis techniques. An antibacterial effect was confirmed by inhibition zone measurements of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The chitosan treatment of LDPE led to the highest and most clear inhibition zones (35 mm(2) for E. coli and 275 mm(2) for S. aureus).

Synthesis and bioimmunological efficiency of poly(2-oxazolines) containing a free amino group

Novel amphiphilic copolymers on the basis of 2-oxazolines containing a free amino group were prepared. The copolymers were synthesized by the living cationic polymerization of 2-ethyl-2-oxazoline (ETOX) and 2-(4-aminophenyl)-2-oxazoline (APOX). The main goal of this work was the synthesis of water soluble polymer material with the defined number of functional groups necessary for the attachment of proteins and polysaccharides. A high concentration of free amino groups allows immobilization of various biosubstances, e.g. drugs, proteins or polysaccharides. Thermal properties have been studied with respect to the composition of the copolymers. Cytotoxicity and the bioimmunological efficiency of the selected copolymer were studied.

The effect of inorganic additives on the decomposition of poly (beta-hydroxybutyrate) into volatile products

Abstract Inorganic oxides such as CaO, MgO, PbO, PbO 2 , Al 2 O 3 , ZnO and calcium hydride destabilize PHB to an extent dependent on the basicity of the additive which leads to much easier formation of volatile products compared with PHB itself. Of the additives examined, attention has been focused on the reaction of MgO, which leads to significant formation of a considerably more stable product whose maximum rate of decomposition into volatiles is at 670 K (PHB itself decomposes with a maximum rate at 572 K). An interpretation based on the interaction of MgO with PHB end groups has been proposed.

Temperature effect on kinetics of isothermal crystallization of crosslinked filled LDPE—1. Particulate silica with low surface area as a filler

Abstract The kinetics of isothermal crystallization of low density polyethylene (LDPE) crosslinked and filled with low surface area silica was investigated by DSC method. The crosslinking initiated by thermal decomposition of peroxide leads to overall retardation of crystallization. The filling of LDPE with low surface area silica leads to the increasing nucleation. The isothermal crystallization of crosslinked and filled LDPE is affected by nucleation, retardation and formation of preordered structure, all effects acting simultaneously making overall dependences sometimes rather complicated.

The influence of crosslinking on isothermal crystallization of LDPE filled with silica

Abstract The effect of crosslinking on the isothermal crystallization of low density polyethylene filled with three types of silica was investigated at 375 K. The crosslinking initiated by thermal decomposition of peroxide leads to overall retardation of crystallization. The presence of a filler in the polymer matrix results in the two opposing effects of nucleation and retardation. Crosslinking in the presence of a filler leads to the formation of substantial amounts of an immobile phase resulting in rather unexpected effects, explained by combination of nucleation, retardation and pre-ordering of chains. Comparison of the three types of fillers shows that those with large surface area affect the crystallization to the greatest extent.

Avrami equation and nonisothermal crystallization of polyethylene investigated by DSC

Abstract The kinetics of the nonisothermal crystallization of polyethylene (alone and crosslinked with a peroxide or filled with silica) has been analyzed assuming a composed crystallization process (primary and secondary) and Avrami coefficients have been determined for each component of the process. It has been shown that the Avrami coefficient n of the secondary process increases from 1.8 to 3 with an increasing degree of polymer crosslinking, which indicates a continuous change in the mechanism of crystallization. Filler (silica) affects this parameter, especially at a content up to 10wt%, whereas at higher amounts (up to 35 wt%) the crystallization has apparently the same mechanism as in the pure polymer; in the former case the overall rate of the process, however, is lower.

Comparison of one-step and sequentially irradiated ultrahigh-molecular-weight polyethylene for total joint replacements.

Structure and properties of several ultrahigh-molecular-weight polyethylenes (UHMWPEs), which were crosslinked either by standard, single-step irradiation or by newer, several-step irradiation (sequential irradiation), were compared. To verify the results, the same characterization was carried out for commercially available UHMWPE liners made of sequentially irradiated polymer (X3™, Stryker, Mahwah, NJ) and one-step irradiated polymer (denoted as PE-IMC, produced by Beznoska, Kladno, Czech Republic). The structure was studied by a number of spectroscopic, diffraction, thermal, and microscopic methods. Mechanical properties were assessed by small-punch, microhardness and, wear testing. Our results suggested that sequential irradiation followed by annealing did not lead to unusual structure at the molecular or supermolecular level. Consequently, all measured mechanical properties, including wear resistance, were comparable with one-step irradiated UHMWPEs.

Influence of Crosslinking on Surface Hardness of Poly(Methyl Methacrylate)

Abstract The influence of crosslinking on the surface hardness of poly-(methyl methacrylate) sheets examined by means of damping of standard pendulum oscillations as well as on the nonisothermal mass loss is discussed in this paper. Crosslinked poly(methyl methacrylate)s with different crosslink densities were prepared by copolymerization of methyl methacrylate with polyfunctional comonomers of the allyl and vinyl type and by additional crosslinking of poly(methyl methacrylate) by transamination with aliphatic α,ω-diamines. The highest increase in surface hardness, up to 52% of its value for a silicate plate glass standard, was observed for (PMMA-co-DAlP) sheets with 17 to 25 wt% of comonomer. For commercial noncrosslinked PMMA cast sheets, this value is only 27% of the above standard. Comonomers of the allylic type are more suitable than the methacrylic multifunctional crosslinkers. A large portion of the double bonds remains unreacted if a high concentration of multifunctional agent is copolymerized wit...