Characterization of polymeric materials

Study of the Slow Crack Growth (SCG) process in high density polyethylene for pipe application

High density polyethylene (HDPE) pipes are used extensively for gas and water transportation and distribution. This market is continually growing, seeking higher operating pressures and requiring superior performance materials with good resistance to failure. The most common failure mode in polyethylene pipes is the Slow Crack Growth (SCG) process. SCG generally starts at the surface of the material in a point of stress concentration. After a certain period of time a craze is formed in the material, leading to a crack which grows inside the pipe up to the final failure. To control this failure mechanism and to know the influence of the different physical and molecular parameters that take part is the main aim of this research line, where the LATEP has been working for years with fruitful results.

Alternative fast methods to evaluate the long-term performance in polyethylene resins

Slow Crack Growth (SCG) is the most critical failure mechanism in high density polyethylene used in pipe applications to determine the long-term performance of the resin. The most common methods for evaluating the SCG resistance are the Pennsylvania Edge Notched Tensile (PENT), Full Notch Creep Test (FNCT) and the Notched Pipe Test (NPT). LATEP has developed a modified PENT test with higher load and temperature conditions (2.8 MPa and 90 °C) which provides a failure time reduction around six times guaranteeing a SCG process. On the other hand, the strain hardening (SH) modulus determination through the tensile test is confirmed as a very good method to correlate with conventional SCG tests. LATEP carries out SH test following the international ISO/PRF 18488 standard and also other alternative methodologies developed by the laboratory during the last years.

Photo as a courtesy of J. L. Municio - IPCE

Properties of plastics used for the conservation of the Cultural Heritage

This research line comes up due to the current interest on the polymeric materials in the conservation of the Cultural Heritage, replacing the classic materials. The search of materials with adequate properties and with a proper resistance to the environmental factors, fulfilling all the time their initial function, is the main aim of this research line. The LATEP takes part in this project in collaboration with the Laboratory of Applied Chemistry of the Fine Arts Faculty (Complutense University) and the Laboratory of Material Analysis of the Spanish Cultural Heritage Institute.

Heterophasic polypropylenes characterization

This research line arises from industry companies since they took a real interest in connecting some variations found in mechanical properties, such as impact and tensile resistance, of several commercial polypropylene heterophasic copolymers (HETCOs) with their molecular properties, crystallization kinetic and phase morphology. Using fractionation techniques in solution, isolation of each phase from raw copolymer has been achieved. This fact allows to search synergistic effects caused by the presence or not of different phases, effects that play an important role in the final properties and applications of HETCOs.

Fractionation techniques in solution based on composition and molecular weight applied to polyolefins

Areas such as medicine, automotive and aerospace require materials lighter and with specific features. Nowadays, both academia and industry are searching cheaper production processes of these kinds of materials by physical or chemical blended of "commodity" polymers. These processes produce materials with broad distributions in molecular weight or composition. That is why it is indispensable the use of fractionation techniques in solution based on molecular weight or composition, in order to separate each component of these mixtures to analyze them individually from a molecular and physical point of view. This allows to control those experimental parameters in order to improve the synthesis of new materials for specific applications.

Atomic force microscopy (AFM) characterization of polymeric materials

Atomic force microscopy (AFM) is a technique used to study many materials and which can be used for the characterization of polymeric materials. For many materials, such as for PE film, it is very difficult to characterize their structure at the micro and nano-scale using optical or electron microscopy. For these materials, AFM has emerged as a technique that allows observing their internal structure without the need of making any specific preparation of the samples used, hence avoiding the changes that this preparation would induce in them. AFM has allowed recording the topography of the samples at the nanometre scale. Thus, in the case of PE films, the nanoscale topography has been determined and the morphology of the film has been observed to be a combination of spherulites constituted by fibres with diameters in the nanometre scale. From these observations, the relationships between structure and several properties for several materials have been derived.

Evaluation of ionomeric polymers as self-healing materials

In the last years, it has been observed that some ionomeric materials exhibit self-healing ability when they suffer high energy damage, i.e. after suffering a breaking process in which the material is forced to absorb a large amount of energy it is capable of recovering their morphology and eliminate large macroscopic fractures induced in them. This process is intrinsic for this type of material and it is associated with the mobility of the ionomeric polymer chains. To advance in the knowledge of these materials will allow to improve the control of their properties and to improve their applicability in many uses, providing to many pieces extended durability and improved visual quality for their service life.