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

Zapalenie mięśnia sercowego związane z zakażeniem Salmonella parathypi C

Myocarditis related to bacterial gastroenteritis is rare, especially in immunocompetent persons. The clinical course of the disease is characterised by non-specific, sparse symptoms, which greatly impedes diagnosis. This paper presents a case of myocarditis in a 39 year-old man with a Salmonella paratyphi C infection. Salmonella infections rarely cause myocarditis, but they should always be considered in cases where myocarditis is suspected and there is no evidence of a viral aetiology.Zapalenie mięśnia sercowego związane z bakteryjnym zapaleniem jelita występuje rzadko, zwłaszcza u osób immunokompetentnych. Przebieg kliniczny choroby charakteryzuje się niespecyficznymi, skąpymi objawami, co znacznie utrudnia diagnozę. W pracy przedstawiono przypadek zapalenia mięśnia sercowego u 39-letniego mężczyzny z zakażeniem Salmonella parathypi C. Zakażenia salmonellą są rzadką przyczyną zapalenia mięśnia sercowego, ale zawsze powinny być brane pod uwagę w przypadkach z podejrzeniem myocarditis w przypadku braku dowodów na etiologię wirusową

Zapalenie mięśnia sercowego związane z zakażeniem Salmonella parathypi C

Myocarditis related to bacterial gastroenteritis is rare, especially in immunocompetent persons. The clinical course ofthe disease is characterised by non-specific, sparse symptoms, which greatly impedes diagnosis. This paper presentsa case of myocarditis in a 39 year-old man with a Salmonella paratyphi C infection. Salmonella infections rarely causemyocarditis, but they should always be considered in cases where myocarditis is suspected and there is no evidenceof a viral aetiology.Zapalenie mięśnia sercowego związane z bakteryjnym zapaleniem jelita występuje rzadko, zwłaszcza u osób immunokompetentnych. Przebieg kliniczny choroby charakteryzuje się niespecyficznymi, skąpymi objawami, co znacznie utrudnia diagnozę. W pracy przedstawiono przypadek zapalenia mięśnia sercowego u 39-letniego mężczyzny z zakażeniem Salmonella parathypi C. Zakażenia salmonellą są rzadką przyczyną zapalenia mięśnia sercowego, ale zawsze powinny być brane pod uwagę w przypadkach z podejrzeniem myocarditis w przypadku braku dowodów na etiologię wirusową

Deformation Instabilities and Lamellae Fragmentation during Deformation of Cross-linked Polyethylene

The effect of the topology of the amorphous phase and phase interconnectivity on the stability of the deformation of semicrystalline polyethylene was investigated. The chain topology was modified by crosslinking the samples with electron beam irradiation. The samples were deformed by plane-strain compression, while the accompanying structural changes were monitored with X-ray and differential scanning calorimetry (DSC). At the true strain around of e = 0.3, the lamellar stacks parallel to the loading direction experienced microbuckling instability, which shortly led to the cooperative kinking of lamellae. Macroscopically, this showed up as the ‘second yield.’ Buckling is driven by the different stiffness levels of the hard and soft layers and their strong connectivity—for given layer thickness, the critical strain for buckling appeared proportional to the stiffness of the amorphous phase. Above e = 1.0, lamellae fragmentation was observed. This resulted from the localization of crystallographic slip, which was triggered by stress concentrations generated at lamellae faces by taut ‘stress transmitter’ (ST) chains. Accordingly, the fragmentation was found to be dependent on the surface fraction of STs at the amorphous-crystal interface: a low concentration of STs resulted in fewer but stronger stress concentrations, which led to earlier slip localization, followed quickly by lamellae fragmentation. The observed instabilities, either lamellae kinking or fragmentation, profoundly influenced the deformation process as well as the resultant structure. Both phenomena relieved much of the structural constraints imposed on deforming lamellae and make further strain accommodation easier

Microbuckling Instability and the Second Yield during the Deformation of Semicrystalline Polyethylene

Deformation instabilities, such as microbuckling or lamellar fragmentation due to slip localization, play a very important role in the deformation of semicrystalline polymers, although it still not well explored. Such instabilities often appear necessary to modify the deformation path and facilitate strain accommodation in an energy-minimizing manner. In this work, microbuckling instability was investigated using partially oriented, injection-molded (IM) samples of high-density polyethylene, deformed by a plane-strain compression. Deformed samples were probed by SEM, X-ray (small- and wide-angle X-ray scattering: SAXS, WAXS), and differential scanning calorimetry (DSC). It was found that microbuckling instability, followed quickly by the formation of lamellar kinks, occurred in high-density polyethylene (HDPE) at a true strain of about e = 0.3–0.4, mainly in those lamellar stacks which were initially oriented parallel to the compression direction. This phenomenon was observed with scanning electron microscopy, especially in the oriented skin layers of IM specimens, where a chevron morphology resulting from lamellae microbuckling/kinking was evidenced. Macroscopically, this instability manifested as the so-called “second macroscopic yield” in the form of a hump in the true stress–true strain curve. Microbuckling instability can have a profound effect on the subsequent stages of the deformation process, as well as the resulting structure. This is particularly important in deforming well-oriented lamellar structures—e.g., in drawing pre-oriented films of a semicrystalline polymer, a process commonly used in many technologies

Plastic Deformation of High Density Polyethylene with Extended-Chain Crystal Morphology

Samples of polyethylene with extended-chain crystal morphology, obtained by crystallization under high pressure, were subjected to uniaxial compression to various strains. Accompanying structural changes were analyzed using scanning electron microscopy. At the true strain of e = 0.2–0.3 the microbuckling instability was observed in longitudinally loaded lamellae, resulting in the formation of angular kinks. This induced a rapid reorientation of the lamellae, facilitating their further deformation by crystallographic slip. Microbuckling instability was found to occur earlier than in samples with folded-chain crystal morphology (e = 0.3–0.4) due to a smaller ratio of the amorphous to crystalline layer thickness. SEM observations demonstrated that the microbuckling instability begins with small undulation in long lamellae. Sharp angular lamellar kinks develop from the initial undulation through intense plastic deformation by crystallographic slip along the chain direction. The same slip system was found to operate throughout the kink, including the tip region as well as both limbs. In contrast to thin folded-chain lamellae that often undergo fragmentation during deformation, the thick extended-chain lamellae deform stably by chain slip and retain their continuity up to high strains, e > 1.6. This stability of deformation is related to the large thickness of extended-chain lamellae

Deformation of Poly-l-lactid acid (PLLA) under Uniaxial Tension and Plane-Strain Compression

The ability of PLLA, either amorphous or semicrystalline, to plastic deformation to large strain was investigated in a wide temperature range (Td = 70–140 °C). Active deformation mechanisms have been identified and compared for two different deformation modes—uniaxial drawing and plane-strain compression. The initially amorphous PLLA was capable of significant deformation in both tension and plane-strain compression. In contrast, the samples of crystallized PLLA were found brittle in tensile, whereas they proved to be ductile and capable of high-strain deformation when deformed in plane-strain compression. The main deformation mechanism identified in amorphous PLLA was the orientation of chains due to plastic flow, followed by strain-induced crystallization occurring at the true strain above e = 0.5. The oriented chains in amorphous phase were then transformed into oriented mesophase and/or oriented crystals. An upper temperature limit for mesophase formation was found below Td = 90 °C. The amount of mesophase formed in this process did not exceed 5 wt.%. An additional mesophase fraction was generated at high strains from crystals damaged by severe deformation. After the formation of the crystalline phase, further deformation followed the mechanisms characteristic for the semicrystalline polymer. Interlamellar slip supported by crystallographic chain slip has been identified as the major deformation mechanism in semicrystalline PLLA. It was found that the contribution of crystallographic slip increased notably with the increase in the deformation temperature. The most probable active crystallographic slip systems were (010)[001], (100)[001] or (110)[001] slip systems operating along the chain direction. At high temperatures (Td = 115–140 °C), the α→β crystal transformation was additionally observed, leading to the formation of a small fraction of β crystals