Biostability of synthetic polymer materials – polyethylene, polypropylene and polycarbonate – in the conditions of Surgut

The paper is devoted to the study of biostability of polyethylene, polypropylene and polycarbonate in the conditions of Surgut after their presence within a year in different types of soils swamp-podzolic soil, culturosem and urbanozem. The studied types of soils differ in their chemical composition urbanozems are saturated with bases, have a slightly alkaline reaction, they also contain an excess of lead content due to their close location to highways. In the studied soils bacterial microflora prevails over mycoflora, the amount of heterotrophic and lithoautotrophic microflora in urbanozems is especially high, which is due to the high anthropogenic load on these soils. For seeds and seedlings of wheat and radish the stimulating effect of these soils was revealed. Micromycetes isolated from the surface of polypropylene and polyethylene pipes are typical soil saprotrophs that can act as biodestructors of polymers. In the field experiment all the materials under study are biostable, and there was a slight change in the color of the cross-linked polyethylene sample. In the laboratory experiment certain instability of all the materials under study was revealed; their gradation in terms of mushroom resistance (from resistant to unstable) is as follows: low-density polyethylene, polypropylene random-heat-resistant copolymer, polycarbonate, cross-linked polyethylene. The nature of damage to low-density polyethylene (polyethylene film) is superficial, which corresponds to the literature data.

Acoustic emission description from a damage and failure scenario of rotomoulded polyolefin sandwich structure subjected to internal pressure for storage applications

The aim of this paper is to study the damage mechanisms in a sandwich polymer structure that contains three layers: two polyolefin skins and the foam core (skin–foam–skin). Specific tests on structure associated with the acoustic emission (AE) technique and tomographic observations (RX) are used to identify the damage. Initially, a conventional tensile test was performed to correlate the acoustic emission with the initiation of plasticity and damage to a polyethylene sample. The results obtained are close to those observed in other studies and it is possible to separate the signal from cavitation and propagation of necking. The technique is then employed to capture the rupture of a polymer skin on a multilayer rotomoulded structure (bottle). Tests were carried out on this bottle under internal water pressure. Three tests are performed with more or less early interruptions in order to identify the first damage and understand their evolution. Different quantities (average frequency, RA value, etc.) are observed in order to quantify and understand the perceived damage. With the AE/RX correlation and mechanical behaviour, a scenario of structural damage is proposed.

Investigations Regarding the Thermoplastic Resistance Evaluation with Simulated Imperfections

The thermoplastic polymer components are used in new domains and the evaluation of their characteristics in specific conditions represents a new actuality domain. The experimental program realized on polyethylene sample pipes type PE 80, SDR 11 GAS, Æ160x15.5 mm had the objective to present the imperfection noxiousness of the geometric configuration, respectively the different dimensions and to define the influence of those to the safety in exploitation of the transport networks and to the industrial distribution of the fluids under pressure (water, natural gases, etc). A hybrid TT-IRT test method is used, combining the tensile test (TT) and the Infrared Thermography (IRT) method. The temperature distribution of the material is monitored under loading conditions with different rates. The noxiousness of the geometric discontinuity is analyzed by the local losses of resistance following the local heating in the imperfection areas. The results obtained are used in design calculus for the materials quality levels in specified safety conditions for the fluids transport networks.