Flow rate

The Melt Flow Index (MFI) is the amount of polymer that flows in the melt through a standard nozzle (2,0955 x 8 mm) at a given temperature, under the weight of standard masses that press on a piston. Basically, it is a measure of the flow rate of the polymer melt, and indirectly, its viscosity and molecular weight. The flow index is measured according to ISO 1133 or ASTM 1238. The polymer flow can be measured mass (ISO 1133-A / MFR – Melt Flow Rate, expressed in g / 10 min) or volumetric (ISO 1133-B / MVR – Melt Volumetric Rate, expressed in cmc / 10 min). Method B is useful for filler polymers. The temperature and reference weights of the test masses are chosen according to the polymer tested in order to best characterize its rheological properties.

The most common specific test conditions are (ISO 1133):
Polymer Temp / Mass
Polyethylene 190 ºC / 2,16 Kg 190 ºC / 5,00 Kg 190 ºC / 21,6 Kg
Polypropylene 230 ºC / 2,16 Kg
Polystyrene 200 ºC / 5,00 Kg
ABS 220 ºC / 10,0 Kg
Polycarbonate 300 ºC / 1,20 Kg
POM 190 ºC / 2,16 Kg
PMMA 230 ºC / 3,80 Kg

Flexural modulus

The bending modulus (bending strength) represents the bending force of the material in relation to the elongation under load. It is practically a measure of the rigidity of the material, of its resistance to deformation. The higher the flexural modulus of a material, the more rigid it is. The SI unit of measurement is Pa (N / m2). In the field of plastics, the usual values are of the order of megapascals (MPa = N / mm2) or gigapascals.

Typical values of the flexural modulus:
Material Flexural Modulus [Mpa]
ABS 2.500
ABS + 30% GF 7.000
Acetal Copolime 2.500
Acetal Copolimer + 30% GF 7.500
PA 6 2.300
PC 2.300
PE 700
PET 1.000
PP 1.500
GPPS 2.500


The contraction of the polymers is due to the change in their volume during the transition from the melt to the solid phase, and subsequently the cooling in this phase, and is expressed as a percentage, as a variation of the volume (shrinkage index). In the molten state, all polymers have a random distribution of macromolecules. Below the vitrifying temperature (Tg), however, crystalline polymers (actually – semicrystalline) tend to arrange macromolecules, so that crystalline polymers will have a more significant reduction in volume in the solid state than amorphous ones, and thus a shrinkage index. bigger. In general, the density of semicrystalline polymers in the melt is about 80% of the density in the solid state, while that of amorphous ones is about 90%.

Also, a polymer with a higher molecular weight will have a higher tendency for the macromolecule to relax after the stress it is subjected to during the injection, leading to a higher shrinkage, and generally differentiated in the direction of flow from that. transversal. Copolymers and filler polymers generally have lower shrinkage rates.

Typical values ​​of contraction indices:
Material Type Degree of crystallinity Shrinkage index
HDPE Semi-crystalline 70 – 80 2 – 6
LDPE Semi-crystalline 45 – 55
Polypropylene Semi-crystalline 70 – 80 1 – 2,5
Polypropylene 40% GF Semi-crystalline 0,2 – 0,8
PA 6 Semi-crystalline 0,5 – 1,5
PA 6.6 Semi-crystalline 35 – 45 0,8 – 1,5
POM Semi-crystalline 70 – 80 2 – 2,5
PEEK Semi-crystalline 0,7 – 1,9
ABS Amorphous 0,4 – 0,9
PC Amorphous 0,5 – 0,7
PS Amorphous 0,4 – 0,7
PMMA 0,1 – 0,4


RoHS (Restriction of Hazardous Substances) is a European standard (CE / 2002/95) restricting the use of certain hazardous substances in electrical and electronic equipment. RoHS seeks to reduce the amount of hazardous materials entering electronic products and is closely related to the EC / 2002/96 Directive on waste electrical and electronic equipment (WEEE).

Annex II contains the list of restricted substances:
Substance Acronym Conc max(MCV)
LED Pb <1000 ppm
Mercury Hg <100 ppm
Cadmium Cd <100 ppm
Hexavalent chromium Cr (VI) <1000 ppm
Polybrominated biphenyls PBB <1000 ppm
Polybrominated diphenyl ethers PBDE <1000 ppm
Di (2-ethylhexyl) phthalate DEHP [Ro: DOF] <1000 ppm
Benzyl butylphthalate BBP <1000 ppm
Dibutylphthalate DBP [Ro: DBF] <1000 ppm
Diisobutylphthalate DIBP [Ro: DIBF] <1000 ppm
The RoHS list remains open, depending on future proposals and other substances will be included, while there are some exceptions where these substances cannot be replaced efficiently, such as: mercury in many types of fluorescent lamps. , lead in steel and aluminum alloys, lead in some types of soldering and military applications.

The editions published so far are:
Edition EU standard Remarks
1 RoHS CE/2002/95 Restrict the first six substances in the list.
2 RoHS 2 CE/2011/65 Enter the CE marking of the products.
3 RoHS 3 CE/2015/863 Add phthalates to the list of restricted substances.