Color and Gloss
Why the Assessment of Color and Gloss is Crucial
The assessment of changes to a component through testing is usually initially purely visual. For this purpose, the surface is compared under standardized lighting conditions with the initial state or a reference sample. Anomalies such as blistering or paint detachment are also recorded in the report.
Visual Assessment
The assessment of changes to a component through testing is usually initially purely visual. For this purpose, the surface is compared with the initial state or a master sample under standardized lighting conditions. Rating panels or a gray scale are often taken into account during the assessment. Anomalies such as blistering or paint detachment are also noted in the report.
Color Measurement and Gloss Measurement
Alternatively, color changes during batch changes or due to environmental influences can be quantified using color and gloss measuring devices. The measurement geometries are standardized to obtain comparable values. In gloss measurement, the directed component of a surface’s reflection is determined. Various standardized measurement geometries (20°, 60°, and 90°) are available for measurement to cover the entire measurement range from deep matte to high gloss in accordance with standards. In color measurement, either color values in the CIE-Lab color space or spectral curves are obtained.
Solution Viscosity
Viscosity Number and Intrinsic Viscosity
The solution viscosity is a measure of the average molecular weight of a plastic. The determination is carried out on dissolved polymer, using different solvents (formic acid, m-cresol, tetrachloroethane, …) and concentrations. Measurement in a capillary viscometer yields the viscosity number VN (ml/g).
The viscosity number allows for control of the processing and performance properties of plastics. Thermal stress on the polymer, aging processes, or the action of chemicals, weathering, and light can be investigated through comparative measurements.
The method is standardized for common plastics, for example in DIN EN ISO 307 for polyamides and DIN ISO 1628-5 for polyesters.
Further characteristic values include relative viscosity and specific viscosity, which describe the change in the viscosity of the pure solvent due to the polymer.
The intrinsic viscosity (also limiting viscosity or Staudinger index) is the extrapolation of the viscosity number VN for vanishing polymer concentrations. It can be estimated from series of measurements or by using suitable approximation methods (e.g., Billmeyer).
Melt Flow Index
Volume Flow Rate and Mass Flow Rate
The melt flow index is often also referred to by the English abbreviations MFI (melt flow index) or MI (melt index). It serves to characterize the flow behavior of a thermoplastic and thus its degree of polymerization. Through comparative measurements, the MFI is suitable for detecting material impurities and processing errors. Therefore, the melt flow index is routinely used in quality assurance or damage analysis.
A distinction is made between the volume flow rate (MVR, melt volume-flow rate) and the mass flow rate MFR (melt mass-flow rate). Both are linked via the melt density; the measurement method is described in DIN EN ISO 1133 and is a routine procedure in plastics analysis.
Soxhlet Extraction
Extraction by Organic Solvents
DIN EN ISO 6427 describes a variety of possible methods for a wide range of plastics and solvents. The method to be used depends on the material and the specific question. The extracts allow conclusions to be drawn regarding dissolved mono- and oligomers, plasticizers, uncrosslinked resin components, emulsifiers, …
Moisture Content of Polymer Granulates
Residual moisture is an important parameter in the processing of plastics. Excessive moisture during processing leads to injection molding defects or even polymer degradation. Using the Karl Fischer method described in DIN EN ISO 15512, the water content is specifically and quantitatively determined by titration. Other emissions during the heating of the granulate are not included in the measurement. The plastic sample is heated in an airtight sealed vessel, and the released moisture is transferred to the titration unit via a carrier gas stream.Ignition Residue / Ash Content
The ignition residue describes the residual mass of an organic substance after combustion and continuous heating at high temperatures until constant mass is achieved. It is a measure of the content of inorganic components in the polymer, such as glass fibers.
DIN EN ISO 3451-1 describes several methods for determining this residual mass, referred to as ash or sulfated ash (depending on the method).