Characterization of plastic materials
Today almost all of the properties of a plastic can be known
Given the wide range of plastics than exists at present and the constant appearance of new materials, is increasing the use of plastics for the manufacture of any piece in all sectors. These materials are a huge variety of very different properties, and knowing its behavior, you can get much information for each specific application.
Knowledge of characteristics allows manufacturers the better understanding of each material data sheets, which may lead to a saving of energy and raw material during the transformation, and aid in the design and manufacture of mouldsfor example.
The current experimental characterization techniques allow to know virtually all the properties of a plastic: physical, mechanical, thermal, electrical, properties behavior to environmental agents, etc. The extent of all these properties are most subject to national and international standards.
These properties depend on the internal structure with plastics, which can be classified into three main groups: thermoplastics, thermosetting and rubbers or elastomers. For example, elastomers have a reticulated structure which gives them elasticity at room temperature, and in turn, these points of Union among their molecular chains make them infusibles and insoluble. The cross-linking of thermoset materials is even more dense that gives rigidity and fragility. Thermoplastic materials, not reticulated structure, also have different behaviors depending on amorphous (such as the PC, PMMA, PS, PVC...) or partially crystalline (PA, PP, PE, POM...).
Types of characterization tests
AIJU provides a wide variety of equipment for testing of plastic material characterization, well to assess the adequacy of these specific rules, well to learn about different properties of interest depending on the application that is designed the product.
The mechanical behavior - To learn about the mechanical behaviour of materials are usually performed tests of traction, compression or bending, which evaluates the resistance of the plastic to be deformed and the magnitude of the distortion at the point where the material is broken, if it is the case, and at the point where it changes its behavior from elastic behavior to plastic. We also obtain information of its modulus of elasticity, which indicates whether the material is rigid or flexible.
Through tests of impact (Izod, Charpy, impact at high speed, trials of fall...) determines the amount of energy which is able to absorb the material when it receives a blow. Another feature, such as the hardness of the material can be determined through durometer (Shore hardness) or the Rockwell (penetration of a ball) method. The mechanical behavior of reinforced plastics is different depending on the amount and type of cargo they contain.
Thermal - characterization Given the great sensitivity with plastics to the temperature, the thermal characterization is as important as the mechanics. The techniques of termoanálisis provide lots of information on the structure and composition of the plastic.
For example, using termogravimetría (TG) we can know if the material is pure or contains loads or other inorganic materials. The amorphous or crystalline structure of thermoplastics can clearly see by DSC, as well as the melting temperature, in the case of the partially crystalline, glass transition temperature, heat capacity, enthalpies of fusion etc. The determination of fluidity index provides information on the molecular weight of the polymer and its fluidity in the molten state; and another interesting feature in vista to a practical application is the temperature of softening of the material, which gives us an idea about the range of temperature. This temperature can obtain the Vicat, thermomechanical or deflection under load analysis method.
Accelerated ageing - These tests are helpful to learn about the potential length and/or behavior of a piece or finished product, when they are subjected to an environment or certain conditions. Depending on the structure of the plastic and the environment in which is found, it will behave differently. Using cameras in trial (saline fog, Chamber climate and ageing to light) you can play the influence of solar radiation, temperature, rain, humidity, etc. and check if the material is degraded, it changes color, if you have tensions in its structureIf the coating or painting, if this is the case, is attacked or is not well attached, etc.
Qualitative and quantitative formulations composition - is analysed by other more sophisticated techniques, which require a more elaborate sample preparation and that allows to identify the various additives that contain plastics, such as dyes, plasticizers, stabilizers, perfumes, and others. Spectroscopic techniques are available for this (infrared spectroscopy, go, and ultraviolet), chromatographic (gas chromatography and liquid of high resolution, HPLC), mass spectrometry, supercritical fluid extractor, microwave. Also using IR spectroscopy and HPLC identifies the structure and components of the plastic material and can know if it's a mixture of plastics.
Apart from these techniques AIJU offers the traditional laboratory, as well as the rules for the characterization of plastics, which can assist those companies that request. In the latter case, the main issue when you are going to the characterization of a plastic is knowing what you are looking for and choose the most appropriate technique to do so.
SUNY Martínez García
Laboratory of AIJU
Proyectos@aiju.es
