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Characterization of plastics

Nowadays, the large range of plastics that now exists and the constant appearance of different resources is increasing the use of plastics for the manufacture of any part in all sectors. These materials shows a enormous variety of very diverse properties, and knowing his behavior, you can obtain much information for every particular application.

The knowledge of its features allows manufacturers to better understand the technical specifications of each material, which can lead to save energy and raw materials during processing, and help in the design and manufacture of molds, for example.
The experimental techniques allow us to know virtually all the properties of plastics: Physical, mechanical, thermal, electrical, environmenta, etc.. The measuring of all these properties are mostly field of study to national and international standards.

These properties depends on the internal structure of plastics itself, which can be classified into three main groups: Thermoplastics, thermosets and rubbers or elastomers. For example, elastomers have a lattice structure that provides elasticity at room temperature, and its molecular chains makes them infusible and insoluble. The reticulation of thermoset materials is even more dense which gives them rigidity and fragility. The thermoplastic materials, with no lattice structure, also have unusual behaviors depending on amorphous (such as PC, PMMA, PS, PVC ...) or partially crystallized (PA, PP, PE, POM ...).

Types of characterization tests

AIJU are available in a variety of testing equipment for characterization of plastics, either to assess the adequacy of these particular rules or to learn about different properties of interest depending on the application it is intended for the product.

For the mechanical behavior of materials are ordinarily carried out tensile, compression or bending, which evaluates the plastic strength to bend and the magnitude of the deflection at the point where it breaks the material and the point which it changes its behavior from elastic to plastic behavior. We also collect information from its modulus of elasticity, which indicates whether the material is rigid or flexible.

Impact tests (Izod, Charpy, high-velocity impact, drop test ...) allow us to know the amount of energy that the material is able to absorb when it receives a blow. Another feature, as the resistance of the material, can be determined by durometer (Shore hardness) or the Rockwell method (penetration of a ball). The mechanical behavior of reinforced plastics is diverse depending on the amount and type of load they contain.

Thermal Characterization

Given the high sensitivity, which presents the plastic versus temperature, thermal characterization is as significant as the mechanics. Thermoan lysis techniques provide a wealth of information on the structure and composition of the plastic.
For example, using thermogravimetry (TG) we can know if the material is unadulterated or contains loads or other inorganic materials. The amorphous or crystalline structure of thermoplastics is evidently observed by DSC and the melting temperature, in the case of partially crystalline glass transition temperature, specific heat, enthalpy of fusion and so on. The determination of melt flow rate provides information on the molecular weight of polymer and its fluidity in the molten state, and another of the interesting features and practical application is the softening temperature of the material, which gives us an appreciation of the temperature range. This temperature can be obtained by the Vicat method, thermo-mechanical analysis or deflection under load.

Accelerated aging

These tests are provides us a valuable way to know the capability duration and / or behavior of a part or finished product, when its subjected to an environment or under specific conditions. Depending on the structure of plastics and the environment in which they are placed, it will behave differently. Using cameras for testing (salt spray, aging and environmental chamber to light) can reproduce the influence of solar radiation, temperature, rainfall, humidity, etc.. And check whether the material breaks down, changes color, if it has tensions in their structure, if the coating or paint, if any, is attacked or not well adhered, and so on.

Qualitative and quantitative composition of the formulations  is analyzed by more sophisticated techniques, which require more elaborate sample preparation and for identifying different plastics containing additives such as dyes, plasticizers, stabilizers, perfumes, and others. This is available spectroscopic techniques (infrared spectroscopy, IR, and UV-visible), chromatographic (gas chromatography and high resolution liquid, HPLC), mass spectrometry, supercritical fluid extractor, microwave. IR spectroscopy and also by HPLC identifies the structure and components of plastic material being able to know if it is a mixture of plastics.

Apart from these techniques has AIJU traditional laboratory and the rules governing the characterization of plastics, on which to advise companies that request it. UltimatelyFind Article, the main issue when there is a characterization of a plastic is to know what you're looking for and choose the most appropriate technique for this.

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Felipe Garcia consultant of Ibertest Internacional Materials Testing

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