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Relaxation behavior of polyethylene welded joints

The paper presents results of the investigation of structure relaxation and thermal properties of PE-80 and PE-100 polyethylene hot-tool butt welds. It was found that a weld with the re-crystallized crystalline structure is formed during the welding of dissimilar types of polyethylene. It is shown that within a long period (1 year) the relaxation occurs not only in amorphous but also in the crystalline phase (crystalline α-form transforms into mixed αβ-form), with respective changes in polyethylene properties.

X-ray Study of Structural Formation and Thermomechanical Properties of Silver-Containing Polymer Nanocomposites

The structural organization and thermomechanical properties of nanocomposites prepared from interpolyelectrolyte-metal complex (IMC) involving anionic polyelectrolyte, pectin and AgNO₃, and cationic polyelectrolyte, poly(4-vinylpyridine), have been investigated using the methods of wide- and small-angle X-ray scattering and thermomechanical analysis. It is established that chemical reduction of Ag⁺ ions in the IMC by sodium borohydride results in formation of the nanocomposite based on the "pectin-poly(4-vinylpyridine)" interpolyelectrolyte complex (IPEC) and Ag⁰ nanoparticles as well. At the same time, the level of nanocomposites' structural heterogeneity is substantially enhancing, while effective size of the heterogeneity regions decreases. The nanocomposites IPEC-Ag⁰ prepared are shown much bigger T _g value and enhanced ability for deformation than those for IMC.

(Bio)degradable Ionomeric Polyurethanes Based on Xanthan: Synthesis, Properties, and Structure

New (bio)degradable environmentally friendly film-forming ionomeric polyurethanes (IPU) based on renewable biotechnological polysaccharide xanthan (Xa) have been obtained. The influence of the component composition on the colloidal-chemical and physic-mechanical properties of IPU/Xa and based films, as well as the change of their properties under the influence of environmental factors, have been studied. The results of IR-, PMS-, DMA-, and X-ray scattering study indicate that incorporation of Xa into the polyurethane chain initiates the formation of a new polymer structure different from the structure of the pure IPU (matrix): an amorphous polymer-polymer microdomain has occurred as a result of the chemical interaction of Xa and IPU. It predetermines the degradation of the IPU/Xa films as a whole, unlike the mixed polymer systems, and plays a key role in the improvement of material performance. The results of acid, alkaline hydrolysis, and incubation into the soil indicate the increase of the intensity of degradation processes occurring in the IPU/Xa in comparison with the pure IPU. It has been shown that the introduction of Xa not only imparts the biodegradability property to polyurethane, but also improves the mechanical properties.

Mesoporous hydrogels: revealing reversible porosity by cryoporometry, X-ray scattering, and gas adsorption

Mesoporous poly(2-hydroxyethyl methacrylate-co-ethylene glycol dimethacrylate) networks, with cross-linker contents ranging from 100 to 5 mol %, were prepared using a hard-templating approach. The imbibition of the silica pellets with a monomer/cross-linker mixture resulted in mesoporous gels with a pore size of approximately 10 nm, which corresponds well with the average size of the fumed silica particles (10-11 nm). The highly cross-linked materials showed permanent surface areas of up to 230 m(2) g(-1) and porosities up to approximately 33 vol %. The porosity of the hydrogels was investigated in both dry and water-saturated state by nitrogen sorption, cryoporometry, and small-angle X-ray scattering (SAXS). It is only polymeric materials that contain 50 mol % or more of the cross-linker that showed a significant porosity after evaporative drying. Freeze-drying is able to preserve the porosity also for hydrogels of intermediate cross-linker content, but the pores of the materials of low cross-linker content collapses completely upon solvent removal. The observed critical cross-linker ratio for pore stability compared favorably with a simple estimate of the critical cross-linker density needed to make the material sufficiently stiff to withstand the Laplace pressure during solvent removal. Analysis of the hydrogels in the water swollen state revealed that gels having cross-linker contents down to 5 mol % still possessed mesoporosity. The pores got less defined at very low cross-linker contents, while their size was rather constant at intermediate to high cross-linking densities. Closed pores could be reopened upon swelling, which suggests that the observed pore collapse upon drying may be at least partly reversible.

Structure and relaxation dynamics of poly(amide urethane)s with bioactive transition metal acetyl acetonates in hard blocks

Structural characteristics, thermal transitions and molecular dynamics of selected poly(amide urethane)s with transition metal acetyl acetonates Me(AcAc)(2) (Me = Sn(4+), Zn(2+), Cu(2+), Pb(2+)) as chain extenders, were comparatively investigated using small- and wide-angle X-ray scattering (SAXS, WAXS), differential scanning calorimetry (DSC), and dielectric techniques (dielectric relaxation spectroscopy, DRS; thermally stimulated currents, TSC). We studied the influence of metal chelates on the mixing of the soft-segment (SS) and hard-segment (HS) domains and the related degree of microphase separation (DMS). The reactivity of Me(AcAc)(2) with macrodiisocyanate was found to decrease in the order Sn(AcAc)(2)Cl(2) > Cu(AcAc)(2) > Zn(AcAc)(2) > Pb(AcAc)(2). While Pb(AcAc)(2) shows a higher tendency for crystallisation, both the dielectric and calorimetric results suggest that the corresponding polyurethane has comparatively low DMS. The type of the transition metal has moderate effect on the glass transition temperature and no influence on the shape of the dielectric alpha relaxation signal, indicating weak interactions between metal ions and SS domains. In contrast, structural parameters and the dielectric behaviour of the beta relaxation suggest preference for hydrogen-bonding interactions between Sn(4+) and Cu(2+) metal-chelates and HS domains. The temperature dependence of dc conductivity sigma(dc) is described by the Vogel-Tammann-Fulcher equation and signifies the coupling between the mobility of polymeric chains and charges' motion. It may be expected that the present combination of techniques and particular results with respect to DMS will contribute to the development and testing of novel biodegradation-resistant and antibacterial metal-polyurethanes for biotechnological and industrial applications.