Erosion of the molecular network in the amorphous layers of polyethylene upon high- strain deformation

Samples of linear polyethylene, neat and crosslinked by irradiation with electron beam, were subjected to heavy plastic deformation by plane-strain compression up to the true strain exceeding 2 (deformation ratio λ > 8) at room temperature. Structural studies of deformed samples and investigation of long-term strain recovery demonstrated that the deformation of the neat, non-crosslinked HDPE is completely reversible above the melting point of the crystalline phase, provided that the applied true strain does not exceed e = 1.0 (λ = 2.7). At higher applied strains, e > 1, an irreversible deformation component emerged gradually, and at e = 2.1 (λ = 8.2), the permanent, truly irreversible, residual strain was approx. eres = 0.36 (λ = 1.4). In contrast, samples of crosslinked HDPE above Tm exhibited complete reversibility of deformation, irrespectively of an applied strain, and eres ≈ 0. The source of permanent irreversible strain component in neat HDPE is a deformation-induced partial destruction of the molecular network of entangled chains within amorphous interlamellar layers. The principal mechanism found was chain disentanglement, which was supplemented by a very limited chain scission. In the case of crosslinked materials, the dense and relatively homogeneous molecular network appeared robust enough to avoid any damage. Consequently, the strain appeared here fully reversible upon melting of crystalline phase

Naturalne promieniowanie gamma na poziomie morza wokół kontynentu antarktycznego zarejestrowane na południe od równoleżnika 62°

This study presents the results of dosimetry radiation measurement performed in the Antarctic region at the surface of the sea which was conducted between January and March 2018. Over 2 200 records were collected using a portable Gamma Scout Online radiometer during a 72-day voyage circumnavigating the continent of Antarctica. The mean average of the measured radiation dose rate was 0.091 μSvh-1 and varied from 0.052 to 0.193 μSvh-1. These result are above global average dose rate of radiation at sea level (0.031 μSvh-1) and often higher than those recorded on the Antarctic continent. Yet generally our records fall within well recognized latitudinal trend of radiation being higher toward poles. This is results of troposphere begins at lower altitude in Antarctic in comparison to lower latitudes. The origin of this radiation is natural and results from the presence of higher cosmic rays and secondary radiation induced in the atmosphere. The presence of terrestrial radionuclides in the Antarctic environment has a local, secondary influence on the measured values of radiation. The theoretical calculated annual dose equivalent for humans present in Antarctica could often exceed the limit of 1 mSv as recorded for other Antarctic locations yet our results (0.772 mSv per year) do not confirm that.W pracy przedstawiono wyniki dozymetrycznych pomiarów promieniowania, przeprowadzonych przez załogę jachtu Katharsis II, w trakcie 72-dniowego rejsu wokół Antarktydy. Podczas rejsu trwającego od stycznia do marca 2018 roku, za pomocą przenośnego radiometru Gamma Scout Online rejestrowano dawki promieniowania na poziomie morza w odstępach 10-minutowych. Po wstępnej analizie statystycznej uzyskano dane w postaci 2 200 rekordów, które wykorzystano do wnioskowania o rozkładzie promieniowania w rejonie Antarktyki. Średnia zmierzona moc dawki promieniowania wyniosła 0,091 μSvh-1 i wahała się od 0,052 do 0,193 μSvh-1. Wyniki te są powyżej średniej globalnej mocy dawki promieniowania na poziomie morza (0,031 μSvh-1) i często wyższe niż te zarejestrowane bezpośrednio na Antarktydzie. Jednak, generalnie zarejestrowane przez nas dawki promieniowania mieszczą się w dobrze rozpoznanym równoleżnikowym trendzie, w którym promieniowanie jest wyższe w kierunku biegunów. Związane jest to z cieńszą warstwą troposfery w rejonach biegunowych w porównaniu z niższymi, równikowymi szerokościami geograficznymi. Ogólnie pochodzenie tego promieniowania jest naturalne i związane z silniejszą penetracją troposfery przez promieniowanie kosmiczne oraz obecnością promieniowania wtórnego indukowanego w atmosferze. Obecność radionuklidów naziemnych w środowisku Antarktyki ma lokalny, wtórny wpływ na mierzone wartości promieniowania. Teoretycznie obliczony roczny ekwiwalent dawki dla ludzi, w różnych miejscach Antarktydy, może przekraczać limit 1 mSv, natomiast nasze wyniki (0,772 mSv rocznie) tego nie potwierdzają

Deformation Mechanisms of Isotactic Poly-1-Butene and Its Copolymers Deformed by Plane-Strain Compression and Tension

The deformation-induced crystalline texture of isotactic poly-1-butene and its random copolymers with ethylene, developing during plane-strain compression and uniaxial tension, was investigated with X-Ray pole figures, supported by small-angle scattering (SAXS) and thermal analysis (DSC). The crystallographic (100)[001] chain slip was identified as the primary deformation mechanism, active in both compression and tension, supported by the transverse slip system and interlamellar shear. At the true strain around 0.8, lamellae fragmentation and partial destruction of the crystalline phase due to slip localization was observed, much heavier in tension than in plane-strain compression. That fragmentation brought an acceleration of the slip, which ultimately led to a common fiber texture in tensile samples, with the chain direction oriented preferentially along the drawing (flow) direction. Slightly more complicated crystal texture, reflecting triaxiality of the stress field, still with the chain direction preferentially oriented near the flow direction, was observed in compression. Additional deformation mechanism was observed at low strain in the plane-strain compression, which was either interlamellar shear operating in amorphous layers and supported by crystallographic slips or the simultaneous (110)[110] transverse slip operating on a pair of (110) planes. It was concluded that deformation proceeded similarly in both studied deformation modes, with practically the same deformation mechanisms engaged. Then, the plane-strain compression, proceeding homogeneously and preventing cavitation, seems more suitable for studies of the real deformation behavior, not obscured by any unwanted side-effects