Andrzej Pawlak

Characterization of scrap poly(ethylene terephthalate)

Abstract The goals of the investigation were: to indicate the methods of characterization of recycled polymers, to show general tendencies in properties deterioration and characterize recyclates on Central Europe and European Community markets. The properties and composition of scrap poly(ethylene terephthalate) from several sources were characterized by: TGA, DSC, FTIR, tensile properties, dynamic viscosity, intrinsic viscosity and thermo-oxidative stability. We found that all PET regrinds contained admixture of other polymers (0.1–5 wt%). The presence of more than 50 ppm PVC makes PET worthless for advanced application as film forming, because it catalyzes the hydrolysis and reduces the strength of material. Although the individual flakes of recycled PET show almost unchanged molecular characteristics and properties, the processed regrinds always exhibit worse properties. Partial restoration of recycled PET properties can be achieved by careful working, removing the dust fraction and by proper drying. The difference between studied PETs results from different applied recycling procedure. Admixtures of polymers without compatibilizer always deteriorate tensile properties. Various levels of stability of polymer viscous flow during film and tape extrusion were observed, depending on composition of recycled PET from various sources. Microgels were observed in all samples during film extrusion.

Effect of negative pressure on melting behavior of spherulites in thin films of several crystalline polymers

The melting behavior of spherulites in thin films of isotactic polypropylene, poly(ethylene oxide), poly(methylene oxide), and poly(ethylene adipate) crystallized isothermally at various temperatures has been studied by polarized light microscopy. The local increase of melting temperature in regions surrounding cavities and multiple boundary points, dependent on the crystallization temperature, was observed in all studied polymers. In pockets of occluded melt an arising negative pressure lowers an equilibrium melting temperature; hence, decreases an undercooling, which results in the increase of lamellae thickness and their melting temperature. The elevation of melting temperature and the negative pressure buildup depend on the polymer and the crystallization temperature.

Ataxia telangiectasia heterozygotes and patients display increased fluidity and decrease in contents of sulfhydryl groups in red blood cell membranes.

In red blood cell membranes of ataxia telangiectasia mutated (ATM) homozygotes and heterozygotes, decreased values of the corrected fluorescence anisotropy and the anisotropy parameter were found, indicating increased fluidity and decreased microviscosity, respectively. These changes in membranes were accompanied by a decrease in SH-groups and an increase in malondialdehyde (MDA) contents. The content of MDA both in homozygotes and in heterozygotes exceeded roughly threefold the respective control values. Decreased content of GSH in red blood cells was found only in ATM homozygotes. The change most specific for the ATM gene appears to be the increase in fluidity, since only this parameter displays the proportionally greater changes in ATM homozygotes compared to ATM heterozygotes. The observations presented here may indicate that the ATM gene is expressed in precursors of red blood cells and deficiency of normal AT gene function may produce the changes which persist in circulating cells.

Effect of the route of benzo[a]pyrene administration on sister chromatid exchange and DNA binding in bone marrow of mice differing with respect to cytochrome P450 1A1 induction

The effects of the route of benzo[a]pyrene administration on sister chromatid exchange (SCE) and B[a]P diol epoxide (B[a]PDE)-DNA adducts formation in bone marrow cells of Ah responsive (C57BL/6; B6) and Ah non-responsive (DBA/2; D2) mice were determined. Animals were treated intraperitoneally (i.p.), intragastrically (i.g.) or topically with two 100 mg/kg doses of benzo[a]pyrene 24 h apart and killed 96 h after the first treatment. Significant increase in the frequencies of SCE and the level of B[a]PDE-DNA adducts as measured by synchronous fluorescence spectrophotometry were detected in D2 mice as compared to B6 mice. The route of administration had little effect on SCE levels in bone marrow cells in D2 mice. In B6 mice higher levels of SCE were observed following i.p. administration as compared to i.g. or topical administration. In both strains the highest level of B[a]PDE-DNA adducts was formed after i.p. administration of B[a]P. We conclude that the i.p. route of B[a]P administration is the most effective in inducing SCE and B[a]P-DNA adducts formation. SCE induction does not correlate linearly with the amount of B[a]PDE-DNA adducts formed in these cells after administration of the above dose of B[a]P.

Photoelastic studies of residual stresses around fillers embedded in an epoxy matrix

A photoelastic method was used to investigate the residual stresses in thermoset matrices during curing and cooling generated around spherical and high shape ratio fillers modelled by glass beads and glass or carbon fibers,respectively. Two types of reactive systems were selected: i/ based on a stoichiometric mixture of epoxy prepolymer and diamine comonomers -polycondensation-; ii/ based on a mixture of epoxy prepolymer and an anhydride -chain polymerization-. A mapping of the residual stresses was obtained after curing process and after hydrothermal aging. From such a method, the location of the maximal stresses and the extend of residual stresses field can be discussed as a function of the geometry of the inclusions, the nature of the matrix, and the aging. The photoelastic method can be effective for various types of fillers and polymer matrices in order to select the proper associations of components for composite materials.

Polish variant of glucose-6-phosphate dehydrogenase (G-6-PD lublin)

SummaryA new, favism-inducing variant of glucose-6-phosphate dehydrogenase in erythrocytes is described in a Polish family. The enzyme activity has been 0–4% of normal. The enzyme displayed normal heat stability, electrophoretic mobility 105–110% of normal, Km for NADP: 16–22 μM, Km for G-6-P: 26 μM, and the utilization of 2-deoxy-G-6-P: 2–3%.

Increased frequency of chromatid breaks in lymphocytes of heterozygotes of ataxia telangiectasia after in vitro treatment with caffeine

The frequencies of caffeine-induced chromosomal aberrations (CA), mainly chromatid (CdB) and chromosome (CB) breaks, were studied in lymphocyte cultures derived from 6 obligatory heterozygotes and 1 homozygote of ataxia telangiectasia (AT), and from 4 control adult healthy persons. Caffeine (CF, 1 mM) was added at the beginning of the culture. In control cultures exposed to CF the frequency of CB was 1.9% and of CdB 1.3%. In cells of the AT homozygote, the frequency of CdB was 6.8% in the absence and 8.7% in the presence of caffeine, the frequencies of CB being 3.4 and 10.9%, respectively. In AT heterozygous cells treated with CF, CdB increased 13-fold as compared to a less than 3-fold increase in control cells. Comparing the frequencies of CF-induced chromosomal lesions in control and AT heterozygous cells, potentiation factors (Pf) for the effect of 1 AT gene on cell sensitivity to CF (Pf [AT]) were 3.5 for CB, 6.6 for CdB and 5.5 for CA. These data demonstrate that lymphocytes of AT heterozygotes are significantly more sensitive to caffeine treatment in vitro in terms of increased frequency of CdB than normal cells, which may be useful for the diagnosis of carriers of this defective gene.

Polymer Nano-Materials Through Self-Assembly of Polymeric POSS Systems

The self-organization of polyhedral silsesquioxane (POSS) moieties tethered as side groups onto flexible backbones of amorphous siloxanes and poly(1,2-butadiene) was investigated. For comparison, linear oligosiloxanes substituted with POSS units at the chain end (α- or α,ω-functionalization) were examined. The properties of POSS-functionalized materials were studied (SAXS, WAXD, DSC, TGA, and optical microscopy). The formation of organized POSS assemblies was monitored as a function of the structure of the polymer chain, as well as the POSS concentration in the polymer matrix. It was confirmed that the rubbery polymers allow the pendant POSS units to assemble without the competition of the main chain crystallization. Materials with a larger number of POSS groups tend to form lamellar structures. It was found that the process of disintegration of POSS assemblies in siloxanes is thermally driven. The temperature of melting depends on the structure of a POSS assembly, and the time needed for the organized structure recovery from the melt depends on the type of arrangement of POSS-moieties that is to be formed. At a low POSS content besides the POSS assemblies, which are crystallites of nanometric size, larger polycrystalline objects of micrometric sizes are formed. They consist of a greater number of POSS crystallites embedded in the siloxane polymer. Their shapes and sizes are dependent on the polymer structure and the history of the polymer sample.

Measurements of characteristic parameters in polymer composites by means of a micropolariscope

A new method of determining the characteristic parameters in nonhomogeneous polymers is described. The method makes it possible to measure the characteristic parameters for a large region of the sample in a fast and simple way. The measurements are made by means of a modified polarizing microscope, serving as a micropolariscope. Characteristic parameters are determined for epoxy resin with different spherical inclusions: glass, poly(vinyl acetate), and an air bubble. It is concluded that retardation images are related to the type of inclusion. The analysis of characteristic direction images is more complicated because they depend on the position of the inclusion within sample thickness.

Ah locus-associated differences in induction of sister-chromatid exchanges and in DNA adducts by benzo[a]pyrene in mice

The effect of alleles of the Ah locus on the induction of sister-chromatid exchanges (SCE) was studied in C57Bl/6 and in DBA/2 mice treated twice intragastrically with benzo[a]pyrene (BP, 100 or 10 mg/kg b.w.). To measure the changes in the frequency of SCE, 2 protocols were used: in vivo in bone marrow cells after implantation of 5-bromodeoxyuridine (BrdU) tablets and in vivo/in vitro in spleen lymphocytes cultured with BrdU. On day 5 mice were killed and SCEs estimated in bone marrow cells. BP-DNA adducts in bone marrow and spleen were analyzed on day 5 after the same exposure to BP. In the spleen lymphocytes SCE frequencies were analyzed after an additional 48 h of culture. We found that at both doses of BP, the number of SCEs and BP-DNA adducts in bone marrow and in spleen cells was significantly higher in aryl hydrocarbon hydroxylase (AHH)-non-inducible (DBA/2) mice than in AHH-inducible (C57BL/6) mice. Only marginal induction of SCE was noted after the high dose of BP in C57BL/6 mice in bone marrow in vivo, whereas a highly significant increase in the frequency of SCEs was found in splenocytes in the in vivo/in vitro test. The spleen cells contained larger amounts of BP-DNA adducts and demonstrated higher absolute levels of SCEs than bone marrow cells. The sensitivity of both the in vivo/in vitro and the in vivo SCE test is high enough for assessment of Ah locus-linked differences in BP genotoxicity in mice at the prolonged time between treatment and cell preparation. The present data confirm the influence of inducibility of AHH in the intestine on the genotoxicity of BP to distal tissues after oral exposure to BP.