M.Ll. Maspoch

Influence of annealing on the microstructural, tensile and fracture properties of polypropylene films

Abstract The influence of annealing temperature on the fracture properties of iPP films (one homopolymer and two propylene–ethylene block copolymers) is presented. The fracture behaviour is studied by means of the Essential Work of Fracture (EWF) procedure, and is complemented by the study of the effect of thermal treatment on tensile properties and microstructure, using differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). It is shown that the initial metastable phase of quenched iPP films, widely known as smectic, transforms gradually into the monoclinic form as the annealing temperature is increased, resulting in an important improvement of the tensile properties, whereas the fracture parameters have different evolutions depending on the ethylene content. The reasons for a decrease in the essential work term and an increase in the plastic term as the crystal perfection grows are discussed on the basis of the microstructural changes of the crystalline phase and the smectic–monoclinic strain-induced phase transformation.

Effects of recycling on the microstructure and the mechanical properties of isotactic polypropylene

Polypropylene (PP) was injection moulded several times to mimic the effect of recycling procedures. The influence of the recycling was studied by following changes in chemical structure, melt viscosity, crystallisation behaviour, and tensile and fracture properties. The main effect of recycling is the lowering of the melt viscosity, which is attributed to molecular weight decrease. Recycled PP exhibits greater crystallisation rate, higher crystallinity and equilibrium melting temperature than those measured for virgin PP. Elastic modulus and yield stress increase with the number of recycling steps. However, elongation at break and fracture toughness decrease.

Essential work of fracture on PET films: influence of the thickness and the orientation

Abstract This paper presents the fracture behaviour of films of a bioriented poly(ethylene terephthalate) (BOPET), that was studied by the Essential Work of Fracture (EWF) method. The influence of specimen thickness and molecular orientation was investigated. The results show that this method is a useful alternative for studying the plane-stress fracture of this material, finding that the specific essential work of fracture is strongly affected by the orientation [ w e was smaller in the direction of extrusion (MD) than in the perpendicular one (TD)], but independent of the specimen thickness in a range from 50 to 250 μm. On the other hand, the plastic work item is sensitive to variations of thickness but does not depend on orientation.

Effects of injection moulding induced morphology on the fracture behaviour of virgin and recycled polypropylene

Abstract The effect of injection moulding induced morphology on the fracture behaviour of virgin and recycled polypropylene (PP) has been studied. Skin-core morphology has been analysed by microhardness measurements, since the microhardness and the degree of crystallinity are directly related. Virgin PP has shown higher microhardness values and bigger plastically deformed zone at the crack tip than recycled one. These two differences are due to the higher crystallinity of the recycled PP. Otherwise, in both materials, skin layer has shown lower microhardness values and smaller plastic zone extension than the core region. The former phenomenon is suggested to be governed by the different degrees of crystallinity between both regions, whereas the latter is related to the stress-state (triaxial stress-state) rather than to morphological parameters.

Milled Glass Fiber Filled-Poly(Ethylene Terephthalate-co-Isophthalate) Composites - Thermal and Mechanical Properties

Fracture and thermal behavior of injection-molded poly (ethylene terephthalate-co-isophthalate) filled with milled glass fiber has been studied as a function of fiber content in the range 0-40% by weight. Composite Youngs modulus and tensile strength increased with fiber percentage, and good agreement was found with theoretical predictions. Low rate fracture tests were carried out on injection-molded SENB specimens. Fracture toughness (K ic ) and fracture energy (G ic ) could be obtained by applying Linear Elastic Fracture Mechanics (LEFM). Results seemed to indicate improved fracture toughness if compared with homopolymer poly (ethylene terephthalate) composites. The reason was attributed to a lower crystallinity developed in the matrix, which promoted higher plastic strain.

Mechanical Properties and Morphology of Multifunctional Polypropylene Foams

One of the actual trends in polymer foams consists in the development of new materials by combining density reduction through foaming with the incorporation of functional fillers. This would enable to obtain materials with improved specific properties and added functionalities. There is also a growing interest in the use of environmentally-friendly materials obtained from renewable sources, thus coming as a logical step to combine both in order to create novel biocomposite foams. This work presents an overview of our recent results regarding the preparation and structural and thermo-mechanical characterizations of rigid polypropylene-based composite foams, with the main goal of developing new lightweight materials with tailor-made properties (multifunctional foams). Several reinforcements have been considered, from renewable cellulose fibres to nanometric-sized reinforcements such as silicate-layered nanoclays and carbon nanofibres.

Methane hydrate: shifting the coexistence temperature to higher temperatures with an external electric field

In the present work, we used molecular dynamic simulations of the equilibrium NPT ensemble to examine the effect of an external electric field on the three-phase coexistence temperature of methane gas, liquid water and methane hydrate. For these simulations, we used the TIP4P/Ice rigid water model and a single-site model for methane. The simulations were implemented at two pressures, 400 and 250 bar, over temperatures ranging from 285 to 320 K and from 280 to 315 K, respectively. The application of an external electric field in the range of 0.1–0.9 caused the effect of the thermal vibrations of the water molecules to become attenuated. This resulted in a shift of the three-phase coexistence temperature to higher temperatures. Electric fields below this range did not cause a difference in the coexistence temperature, and electric fields above this range enhanced the thermal effect. The shift had a magnitude of 22.5 K on average.