Thermal, Rheological and Basic Properties Laboratory


Thermal analysis by differential scanning calorimetry (DSC)

Differential scanning calorimetry is a thermoanalytical technique that measures the difference in the amount of heat required to increase the temperature of a sample and an inert reference as a function of temperature. Both the sample and the inert reference are maintained at the same temperature throughout the experiment by a controlled temperature program. This technique can be used to evaluate chemical reactions (such as thermal degradations or oxidation processes), identification of primary transitions (melting and crystallization processes), and second-order transitions such as glass transitions which can occur in the sample under certain analysis conditions.

LATEP has a high sensitivity DSC 822e equipment from Mettler Toledo, which works in a temperature range from -150 to 500 °C.

Thermogravimetric analysis (TGA)

Thermogravimetric analysis is a method in which changes in physical and chemical properties of materials are measured as a function of increasing temperature ramp (with constant heating rate), generally extended to its decomposition temperature. The weight loss curve (TGA) and its first derivative (DTGA) is used to evaluate the weight loss of a sample.

Most of TGA curves show weight loss, which it is associated to chemical reactions (decomposition and separation of crystallization water, combustion, reduction of metallic oxides) and physical transformations (evaporation, vaporization, sublimation, desorption, drying). Exceptionally, weight gains may be observed due to reactions with gaseous components of the purge gas yielding non-volatile compounds, adsorption of gaseous products in the samples.

LATEP has a robotized TGA/DSC1 equipment from Mettler Toledo, which works in a temperature range from room temperature to 1100 °C.

Heat deflection temperature (HDT)

The heat deflection temperature (HDT) is the temperature at which a specimen of plastic material, that is rigid at room temperature, deforms under a specified load (0.45, 1.8 or 8.0 MPa) as a consequence of a controlled increasing temperature ramp (heating rate of 50 or 120 °C/h). This method can only be applied to materials which are rigid at room temperature. The test procedure is described in ISO 75 and ASTM D648 standards.

LATEP has a HDT6/VICAT equipment from Ceast. This instrument has six independent test stations, and works in a temperature range from room temperature to 300 °C.


VICAT softening point

Vicat softening point is the temperature at which a standard indenter (3 mm long, circular cross section, and area 1.000 ± 0.015 mm2) penetrates 1 mm into the surface of a plastic test specimen, that is rigid at room temperature, under definite load conditions (10 N or 50 N) and when the temperature is raised at a uniform rate (50 ºC/hour or 120 ºC/hour). The test procedure is described in ISO 306 and ASTM D1525 standards.

LATEP has a HDT6/VICAT equipment from Ceast. This instrument has six independent test stations, and works in a temperature range from room temperature to 300 °C.

Melt flow index (MFI)

Melt flow index is defined as the mass of polymer, in grams, flowing in ten minutes through a nozzle of a specific inner diameter (2.095 mm) and length (8 mm) under certain conditions of stress and temperature.

The value of the melt flow index depends on the molecular structure of the polymer (molecular weight, molecular weight distribution, degree of chain branching, etc.). This value is an indirect measure of molecular weight. The melt flow index, along with the analysis of possible distortions at the extrudate will determine the processing method for the polymer. The test procedure is described in ISO 1133 standard.

LATEP has a melt flow tester 2000 from Ceast, which works in a temperature range from 23 to 400 °C. Additionally, the laboratory has an automatic melt indexer MI-ROBO 86.07 equipment from Göttfert, which automates the evaluation of up to 30 consecutive samples.

Capillary Rheometry

Rheology studies the relationship between force and deformation in a material. Capillary rheometer is designed for characterizing polymer melts at high shear rates and it is the most effective instrument for measuring shear viscosity at high shear rates. The polymer melt is forced through a capillary of known dimensions. Knowing the dimensions, the flow-rate can be converted into a value for the shear rate and the pressure drop into a value for the shear stress. The true stress – true shear rate curve of the polymeric material under study can be determined. These tests are carried out outside the limits of linear viscoelastic region (LVR) and the capillary flow process resembles many industrial processes such as extrusion and injection moulding. The test procedure is described in ISO 11443 standard.

LATEP has a twin bore barrel rheometer from Malvern Instruments (model Rosand RH 7), which works in a temperature range from room temperature to 400 °C and the maximum shear rate produced by the rheometer is 500 mm/min.


Dynamic Rheology

Rheology studies the relationship between force and deformation in a material. Oscillatory rheometer is a versatile equipment to study polymers in the melt state. It can perform tests in oscillation, flow or creep modes. This kind of rheometer allows to work in the linear viscoelastic region (LVR) or outside the limits of LVR. In this equipment, the specimen is held between two parallel plate. The specimen is subjected to a sinusoidal torque. In the oscillation mode, the viscoelastic properties of a material are determined from the measured torque, the displacement, and the specimen dimensions. The test procedure is described in ISO 6721 standard.

LATEP has an oscillatory rheometer with a parallel-plate geometry from TA Instruments (model DHR-2) which works in the angular frequency range from 0 to 300 rad/s. Also, the rheometer has an environmental test chamber (ETC) accessory which employs a combination of radiant and convective heating and has a temperature range of 23 °C to 600 °C.



Fourier transform infrared spectroscopy (FTIR)

Infrared spectroscopy is a relevant tool for the identification of a polymer through the study of its vibration spectrum after the interaction with infrared radiation. The vibration frequency depends on the chemical nature of the atoms involved in the vibration, and on the vibration mode (stretching or bending). Infrared radiation wavelengths extend from 1.0 mm to 714 nm (10-4000 cm-1), although the most commonly used is the mid-wavelength infrared, between 2.5 and 20.5 μm (4000-400 cm-1).

LATEP has a Varian Excalibur 3100 FT-IR spectrophotometer which operates in transmission mode or in attenuated total reflectance (ATR) mode.

Density

The density is a basic physical property of the material that is directly related to other physical properties and its final application. In LATEP’s facilities there are two different methods for determining the density of solid specimens.

One of the methods is a density gradient column where a linear density gradient is obtained inside the 1m tall, conditioned, columns. The columns are prepared with ethanol and water solutions, which allow measurements of densities from 0.7900 to 1.0000 g/cm3. Moreover, there is a hydrostatic balance to evaluate density by the immersion method. In this method, first of all the specimen is weighed in the air, and then the same specimen is dipped into water or ethanol to measure its apparent weight. These two measurements are compared to determine the density. Both methods are described in ISO 1183 standard.