Thermal transfer simulation regarding the rotational moulding of polyamide 11

Simulation of thermal phenomena in rotational moulding is very important to follow the evolution of the temperature in various zones of this process. It was a question of modelling heat gradients developing in rota-tional moulding part. Thermal model tested take into account the temperature change (thermal transfer mecha-nism) of melting and crystallization pseudo-stages (enthalpy method). Series of tests in polyamide 11 (PA11) were carried out by means of rotational moulding STP LAB, and non-isothermal crystallization kinetics of rota-tional moulding PA11 grade are measured and analysed by DSC technique type TAQ20. A result of non-isothermal crystallization of the studied polyamide was confronted with Ozawa model. In order to test the validity degree of enthalpy method (layer to layer), another approach based on Ozawa model has also been used in the case of cooling pseudo-stage. As results, the rotational moulding of PA11 was successfully carried out. The simulation of the fusion and crystallization stages, by application of Ozawa model coupled with enthalpy method gave a good representation of experimental data

Thermal degradation of polymers during their mechanical recycling

This chapter deals with thermal degradation processes occurring during polymer recycling by melt re-processing, i.e. mechanical recycling. Some general aspects of polymer processing are first recalled. Then, thermal degradation mechanisms and kinetics are described, and the main processing methods are compared from this point of view. Temperature-molar mass maps allow to define a processability window and to envisage industrial ways (in particular, the use of processing aids and thermal stabilizers) to widen this window. The end of this chapter is devoted to a case study: PET mechanical recycling by extrusion molding, which is characterized by an especially complex combination of degradation processes

Shape Memory Effect and Properties Memory Effect of Polyurethane

The relationship between shape and properties memory effect, especially viscoelastic properties of polyurethane under study is the main aim of this research work. Tensile tests have been performed in order to introduce 100% of deformation in the polyurethane samples. Under this deformation, stress–relaxation experiments have been performed in order to eliminate the residual stresses. This deformation of the samples has been fixed by cooling. Recovery tests, then, were carried out at different isothermal temperatures that varied from 30 C to 60 C. Viscoelastic behavior has been studied by a biparabolic model and by using the Cole–Cole method. It was shown that this model describes the behavior of the polymer at the different states of shape memory tests. The constants of this model then have been determined. This study leads to a better understanding of the mechanism of shape memory effect. The comparison between the virgin polymer and the polymer after a recovery test by DMTA (dynamic mechanical thermal analysis) and by Cole–Cole method has illustrated that the polymer does not obtain its initial properties even when it was totally regained its initial shape. These results have been confirmed by three successive shape memory tests on the same sample and by comparing the mechanical characteristics of different cycles because ‘‘shape memory effect’’ and ‘‘properties memory effect’’ do not follow the same mechanisms

Micro-mechanisms of fatigue in short glass fiber reinforced polyamide 66: A multi-scale experimental analysis

The objective of this work is to identify and to analyze the main micro-mechanisms which govern the fatigue behavior of a short glass fiber reinforced polyamide 66 composite through a multi-scale experimental analysis. Tension-tension fatigue tests have been performed at different applied maximum stress and have been analyzed at both microscopic and macroscopic scale. Together with the progressive stiffness reduction, the temperature rise due to self-heating during cyclic loading has been measured using an infrared camera. Moreover, SEM fractography observations have been performed to assess the chronology of deformation mechanisms. Two principal mechanisms have been identified: matrix deformation due to self-heating and fiber-matrix interface damage. In addition, localized deformation zones have been observed around the fibers. The evolution of the size of these micro-ductile areas have been statistically related to the maximum applied stress. Finally, a competition between thermal fatigue and mechanical fatigue have been shown according to the loading amplitude

Some New Concepts of Shape Memory Effect of Polymers

In this study some new concepts regarding certain aspects related to shape memory polymers are presented. A blend of polylactic acid (PLA) (80%) and polybutylene succinate (PBS) (20%) was prepared first by extrusion, then by injection molding to obtain the samples. Tensile, stress-relaxation and recovery tests were performed on these samples at 70 °C. The results indicated that the blend can only regain 24% of its initial shape. It was shown that, this partial shape memory effect could be improved by successive cycles of shape memory tests. After a fourth cycle, the blend is able to regain 82% of its shape. These original results indicated that a polymer without (or with partial) shape memory effect may be transformed into a shape memory polymer without any chemical modification. In this work, we have also shown the relationship between shape memory and property memory effect. Mono and multi-frequency DMA (dynamic mechanical analyzer) tests on virgin and 100% recovered samples of polyurethane (PU) revealed that the polymer at the end of the shape memory tests regains 100% of its initial form without regaining some of its physical properties like glass transition temperature, tensile modulus, heat expansion coefficient and free volume fraction. Shape memory (with and without stress-relaxation) tests were performed on the samples in order to show the role of residual stresses during recovery tests. On the basis of the results we have tried to show the origin of the driving force responsible for shape memory effect

Fatigue Behavior of Polyamide 66/Glass Fiber Under Various Kinds of Applied Load

In this study, the fatigue behavior of polyamide 66 reinforced with short glass fibers and especially the role of glass fibers has been investigated under two kinds of cyclic loading. tension–tension fatigue tests with stress controlled and alternative flexural fatigue test with strain controlled were carried out. The main topics include microscope damage observation, described by fiber/matrix debonding and interfacial failure, endurance limit with Wohler curves, effect of self-heating temperature. For both tests, the surface temperature increases with an increasing applied load. The results show that the self-heating has an important effect in the failure point where the Wohler curves join each other. The fracture surface was analyzed by scanning electron microscope for both applied loads. The stress ratio is −1 for alternative flexural fatigue test and 0.1 and 0.3 for tension–tension fatigue test ones at frequencies ranging 2–60 Hz

Modélisation du mécanisme de coalescence des grains de polymère

Dans le procédé du rotomoulage, le phénomène physique majeur lors de l’écoulement des poudres est la coalescence et densification des grains. La coalescence est la formation d’une seule particule elliptique à partir de deux particules sous l’effet de la température et des forces de tension surfacique. Nous intéressons dans cette étude en particulier au mécanisme de coalescence des grains de poudre de PVDF. Les résultats de cette étude permettent de déterminer des paramètres tel que la vitesse de la coalescence pour l’optimisation du procédé

Rheokinetic of polyurethane crosslinking time-temperature-transformation diagram for rotational molding

In this work, the rheokinetic of polyurethane crosslinking was studied by different methods: differential scanning calorimetric (DSC), rheometry, and infrared spectrometry. The conversion ratio and the glass transition temperature were followed by time of reaction. The results of the isothermal and nonisothermal test were compared. The evolution of viscosity was measured at different frequencies. The intersection of these curves is considered as gel point. A simplified mechanism has been proposed for crosslinking reactions. Based on this mechanism, a kinetic model describing the evolution of reactive system was developed. This model then was compared with the results of experiments performed by infrared spectrometry. The time-temperature- transformation diagram was established showing the evolution of physical state change of the reactive system. This diagram may be used to evaluate the zone of rotomoldability of the reactive polyurethane

Kinetic modeling of polypropylene thermal oxidation during its processing by rotational molding

The main drawback of rotational molding is a long stay (several dozens of minutes) of polymer in melt state at high temperature in atmospheric air. To prevent any significant polymer thermal degradation, it is necessary to define, preliminary, a processing window in a temperature-molar mass map. The objective of this article is to elaborate and check the validity of a general thermal degradation model devoted to determine, in a near future, some important boundaries of this processing window.This model is composed of two distinct levels: (i) The first level is derived from the thermal transfer mechanisms occurring during a processing operation, polymer phase changes (i.e., melting and crystallization) being simulated by the enthalpy method; and (ii) The second level is derived from the oxidation mechanistic scheme of free additive polymer in melt state established in a previous study, but completed, here, by adding the main stabilization reactions of a common synergistic blend of antioxidants, widely used for rotational molding polymer grades. By juxtaposing such "thermal" and "chemical" levels, it is possible to predict the polymer thermal degradation during a whole processing operation. The validity of both levels is successfully checked in real rotational molding conditions for polypropylen

The effect of multi-walled carbon nanotubes on the mechanical behavior of basalt fibers metal laminates: An experimental study

Fiber metal laminates (FMLs) are a group of hybrid composite materials consisting of metal and fiber-reinforced polymer layers. In this study, the effects of multi-walled carbon nanotubes (MWCNTs) on the flexural and high-velocity impact behavior of FMLs made up of aluminum 2024-T3 and basalt fibers/epoxy layers were investigated. The fracture surfaces of samples were analyzed by scanning electron microscopy (SEM). Results showed that the adhesion of composite plies, as well as the interfaces between aluminum and basalt fibers/epoxy layers, were significantly affected by the inclusion of the MWCNTs. The good adhesion of MWCNTs within the body of FMLs caused considerable improvement in the flexural properties. In this regard, the optimal content of MWCNTs was 0.5 wt%, and compared to the samples without MWCNTs, the flexural strength and flexural modulus values improved 36.62% and 60.16%, respectively. However, contrary to the effectiveness of MWCNTs on the flexural performance of samples, the high-velocity impact properties in terms of specific absorbed energy and limit velocity values were affected adversely