Glossary PP
This glossary contains an overview of the most used terms in the polypropylenes business.
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| M |
| Masterbatch |
A virgin material with a high concentration of additives that can be diluted by blending with a certain amount of base material to obtain, after extruding, some desired properties in the final product.
When a masterbatch is used no powders (e.g. pigments) need to be used during processing, resulting in easier handling and improved homogeny. A more technical description is the following: a masterbatch is a previously prepared mixture consisting of a base material and a high percentage of ingredients (usually a dry powder) that is critical to the product being manufactured. Masterbatches are used to get a good disperison of the additives.
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| Melt extension |
Elongation of a molten plastic.
Melt extensibility relates to the behaviour of a plastic when extruding it, e.g. to bubble stability and draw-down properties.
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| Melt flow index |
The amount (in grams) of thermoplastic material which can be forced through an orifice of 0.0825 inch diameter when subjected to a force of e.g. 2160 grams in ten minutes at 180°C.
The MFI increases with decreasing molecular weight. A high MFI corresponds to a low viscosity and occurs in plastics with short chain molecules. A lower MFI usually gives a higher yield point and a lower elongation at break.
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| Melt fracture |
The occurence of surface defects in a plastic film.
Melt fracture leads to poor optics. This mainly occurs in plastics with a low MFI and a narrow MWD, when a certain critical shear rate is exceeded.
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| Melting point |
For crystalline materials, the melting point is the temperature at which a solid begins go transform into a liquid. For plastics, it is the temperature at which crystallinity is reduced to 0%.
The melting point or solidification point of a pure substance is the temperature at which its crystals are in equilibrium with the liquid phase at atmospheric pressure. The melting point usually increases with density. Plastics have a melting range rather than one melting temperature.
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| Migration |
The transfer, usually undesirable, of a substance from a plastic to a contacting material or an interface due to natural forces.
Migration is caused by concentration differences (the migrating substances will move to the contacting material with a lower concentration) and by differences in both materials (some materials have a greater affinity to certain substances than others). Of course, the layer thickness of the plastic, and the total contact surface between the plastic and the contacting materials also have an influence.
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| Modulus of elasticity |
The quotient of stress and elongation in the first, linear part of the tensile curve.
This modulus is measured as the material is deformed under dynamic load: the tangent of the angle between the horizontal axis and the tensile curve is the modulus of elasticity. It is a measure for the softness or stiffness of the material. The modulus of elasticity of amorphous materials is temperature-dependent. It is usually higher at higher densities.
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| Molecular Weight Distribution |
A graph indicating the number of polymer molecules per weight class, for each weight class.
The MWD is related to the zero viscosity of a material and to its flow, sealing and processing behaviour.
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| Molecules |
A molecule is the smallest portion to which a substance can be reduced by subdivision without losing its chemical identity.
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| Monofilament |
Endlessly spun filament consisting of one thread.
Applications: sewing yarn a.o. for medical purposes. As woven fabric for filter cloth. As pile yarn for artificial grass.
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| Multi-layer |
Consisting of several layers.
Multi-layer film is obtained by either of the following processes: Lamination: cementing films together by applying glue or heat, and pressure; Coating: applying a film layer in a fluid state (on a substrate). Between two layers: extrusion lamination; Coextrusion: extruding all layers at the same time: all materials are heated and meet each other at the end of or before the die.
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| Multifilament |
Yarns consisting of many endlessly spun filaments.
Application: Woven fabrics for technical applications.
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