Sample Preparation Laboratory

Homogeneization by polymer calendering

Some materials such as polyethylene, polypropylene copolymers, as well as some thermoplastic rubbers, are often obtained by compression molding in order to obtain plaques with normalized width that can be used to conduct the required characterization tests to determine their properties. For this purpose, it is necessary to perform a process of polymer calendering in laboratory's rollers previously to homogenize and compact the original material (generally pellets or flakes), and to mix it with antioxidants and antidegradants.

Compression molding

After the homogenization process, the obtained polymer is introduced in a mold and into a hot-plate hydraulic press to carry out the compression molding process at certain pressure and temperature (always above its melting point). After a definite period of time at the molding pressure and temperature, a cooling ramp is applied (generally at 15 °C/min) until room temperature is achieved. It is essential to control the cooling ramp in order to control the process of crystallization of the material, as it will have a relevant influence on its physical properties.

LATEP has two hot-plate hydraulic presses (Collin P300M, IQAP-LAP Pla 30) equipped with cooling groups that guarantee a precise control of the cooling ramp, as specified in ISO 293, ISO 1872-2, ISO 1873-2 standards.

Milling and punching of specimens

In order to obtain normalized specimens from previously molded plaques, LATEP uses a triaxial-control robotized milling machine and an automatic hollow die punch. These equipments are able to reproduce any previously designed specimen (whose dimensions are specified in the corresponding standards) on the compression molded plaque.

Notching of specimens

Some tests require performing controlled defects on the materials in order to concentrate tensions in a region. These notches must be performed in a thoroughly controlled manner, attending both to their geometry (angle, radius, etc.) and to the performance process (notching speed). For this purpose, LATEP has a number of equipments which allow an exhaustive control of the notching process. In addition, LATEP has a profile projector for the subsequent verification of the notches according to the corresponding standards for each test.

Polymer extrusion

Polymer extrusion is a common process for both mixing and moulding polymeric materials. First, the polymer in the molten state is forced to pass through a head, by the rotating action of a screw that rotates concentrically in a temperature-controlled chamber. This technique is very useful for the preparation of mixtures between different plastic resins, for example, blends of recycled materials with virgin resins.

LATEP has a Collins ZK50 co-rotating twin-screw extruder, with a screw diameter of 50 mm and an estimated production of between 2 and 20 kg/h. This model allows a better homogenization of the materials, as well as reducing the shear effect that a counter-rotating model would have.