Search results for "Geology"
showing 10 items of 6012 documents
Shear influences on the solubility of LDPE in ethene
1998
Abstract The influence of shear on the demixing pressures of the binary system ethene/polyethene was determined viscometrically in the temperature range 147–195°C up to pressures of 1400 bar at polymer concentrations of 18.4, 22.5 and 27.4 wt%, respectively. Autoclaves were used to prepare the solutions and to measure cloud points for the stagnant system. A high-pressure viscometer was used to perform experiments at shear rates γ up to 1500 s −1 . Under all conditions investigated here the two-phase area grows as γ becomes larger and the demixing pressures increase up to 23 bar. This observation is in contrast to theoretical expectation according to which it should be the one-phase region w…
Mass spectrometrical detection of polymer particles in capsule tissue surrounding joint endoprotheses of polyethyleneterephthalate
1982
Pyrolysis mass spectrometry of synthetic high polymers is described. The method is used to detect polymer wear particles in capsule tissue surrounding endoprotheses with polyethyleneterephthalate parts. An approximation of semi-quantitative determination of the polymer wear will be discussed.
Reprocessing of Poly(Vinyl Chloride), Polycarbonate and Polyethyleneterephthalate
1998
Poly ethyleneterephthalate — PET- and Poly(vinyl chloride) — PVC — are two of the most frequently encountered polymers in post-consumer plastics. In particular, these polymers can be used for manufacturing the same products (bottles, for example) and therefore are often found in the same stream, even when the collection is done with separation. The recycling of PET and PVC is usually carried out by separating them and reprocessing the two homogeneous polymers. Indeed, the heterogeneous recycling of two polymers is at present almost impossible because of many problems: as their melting points are very different, at the processing temperature of PET severe degradation phenomena of PVC take pl…
EVA copolymer based nanocomposites: rheological behavior under shear and isothermal and non-isothermal elongational flow
2006
Abstract Nanocomposites are a very promising new class of polymer composites that exhibit an interesting combination of chemical, physical and mechanical properties. Only small amounts of nanofiller are sufficient to generate great variation of many properties. This work focuses on the rheological properties of poly[ethylene- co -(vinyl acetate)] (EVA copolymer) based nanocomposites in shear and in isothermal and non-isothermal elongational flow. The nanocomposites, at two different filler contents, were prepared in two different extruders and intercalates were obtained for all the samples. The twin-screw compounder is more efficient. The change of rheological properties, both in shear and …
Recycling and Thermomechanical Degradation of LDPE/Modified Clay Nanocomposites
2013
The special features of polymer nanocomposites are continually gaining interest both in academia and in industry. The latter is especially experiencing an increase in interest towards this class of polymer composites, and this is leading to the first concerns about their reprocessing and reciclability. Here, a systematic study on the behavior of LDPE/Cloisite 15A systems upon reprocessing in a single-screw extruder is described, focusing on rheological, mechanical, and morphological properties changes. The investigated systems show a very complex thermomechanical degradation behavior, with the degradation of the clay modifier and different degradation paths involving the polymer matrix; all…
Characterization of monopolymer blend of virgin and recycled polyamide 6
2002
It is a common industrial practice to blend virgin polymer with the same recycled polymer coming from plastic scraps that, in general, has not undergone relevant degradation. In this work, the characteristics of blends of virgin and recycled polyamide have been considered by changing the amount of recycled polymer and the presence of humidity and a stabilizer. Neither dry nor wet stabilized recycled polyamide samples show significant variations of the molecular weight, but the melt Newtonian viscosity of the blends are slightly different from that predicted by an additive rule, despite the same chemical nature of the two components. This holds true even more for the humid unstabilized sampl…
Macro-oriented network of liquid-crystalline polyesters: crosslinking induced by g-irradiation and thermally activated reaction.
2000
Abstract The synthesis of a macro-oriented network from liquid-crystalline polymers, bearing pendant groups with unsaturations, is reported. Virgin polymers are processable to obtain oriented samples, e.g. fibres, which may be crosslinked through thermal activation and/or exposure to γ-radiation. The liquid-crystalline state is “frozen” and the macroscopic anisotropy is preserved even at high temperatures. Compared to virgin fibres, irradiated samples show an enhancement of tensile performances, thus indicating that the main effect of irradiation is crosslinking without significant degradation phenomena.
The role of additives in the recycling of polymers
1998
The main problems in post-consumer plastics recycling are due to the degradation undergone by the polymers during processing steps and by the products during their lifetime and, for heterogeneous recycling, to the incompatibility of different polymers. To reduce the negative effects of the recycling steps, two main ways can be adopted for homogeneous materials: restabilization during the recycling to avoid or at least to slow the degradation and addition of fillers and modifiers capable of improving the performance of thermoplastic polymers without increasing the final cost of the secondary material. In the case of mixed plastics, compatibilization is the necessary step to obtain secondary …
Closed-loop recycling. A case study of films for greenhouses
2010
Abstract The degradation undergone by plastic films used for greenhouse coverage is the main cause of the worsening of the processability, of the mechanical properties and of the durability of secondary materials obtained by their recycling. This means that this secondary material cannot be processed to produce films for the same applications (closed-loop recycling). In this work different strategies are proposed to improve the processability, some mechanical properties and the resistance to photo-oxidation of these secondary materials. In particular, homopolymer blends or multilayer films where the secondary material is used in combination with virgin polymer give the best results.
Time-resolved rheology as a tool to monitor the progress of polymer degradation in the melt state - Part I: Thermal and thermo-oxidative degradation …
2015
Abstract Thermal and thermo-oxidative degradation of polyamide 11 (PA11) in the melt state (T = 215 °C) are studied by resorting to time-resolved mechanical spectroscopy. Such an approach allows to elude the changes in the rheological properties occurring while testing, thus enabling the rigorous study of polymer degradation in the melt state. Different concurrent degradation reactions in oxidative (air) and non-oxidative (N2) environment are promptly guessed by studying the time evolutions of rheological functions. In particular, changes in the zero-frequency complex viscosity reflects changes in the average molecular weight, while the appearance of a yield stress in the complex viscosity …