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TN1 – Glossary of Terms

YEONJIN 2020-08-07 06:28:02 406
The identiPol QA2
  • Amorphous : A  material  with  no  regular  crystalline  structure.  Such  plastics  exhibit  a  glass transition or softening point, but have no melting point. Polystyrene and polycarbonate are examples of amorphous plastics.  

 

  • Differential Scanning Calorimeter (DSC) :  A Thermal Analysis instrument frequently used for the melting point determination of plastics. It also yields the energy of a melting process, which can be used to assess the level of crystallinity in a plastic (see Level of crystallinity).  

 

  • End Point : This parameter in the identiPolQA refers to the point where the plastic no longer registers on the stiffness measurement, i.e. the plastic is a liquid. It can be correlated to the Vicat softening temperature and is a very reliable indicator of plastics’ properties. A difference of 1°C is frequently significant. 

 

  • Glass transition, Tg: The temperature where the molecules of a plastic start to become mobile. Depending on the nature of the plastic, it may soften slightly, e.g. high viscosity PVC used for extrusion, or flow easily, e.g, Polystyrene and polycarbonate. Tg is a softening point, but not a  melting point (see Melting Point). 

 

  •  Level of crystallinity : In semi-crystalline plastics the level of crystallinity can have a big effect on the mechanical properties of a product. Therefore differences in plastic molecular weight and addition of nucleating agents can make large differences to product performance, e.g. impact strength. 

 

  • Melt Flow Index ((MFI or MFR) : Is defined as the mass of plastic flowing through a capillary die of a specific diameter and length. A prescribed temperature and mass are used and details can be found in ASTM D1238 and ISO 1133. The result is the mass of plastic flowing from the die in ten minutes. This gives an indication of the processability of the plastic, in terms of how easily it will flow when softened. E.g. for PP extrusion grades the MFI is low, e.g. ≈0.3g/10 min, whereas for moulding grades it is higher ≈12 g/10 min. 

 

  • Melting Point, Tm :  The temperature at which a crystalline plastic melts. Due to the high and disperse molecular weights of plastics, this is usually a broad melting peak, unlike the sharp transition seen for simple molecules, e.g ice/water. The energy evolved when a plastic melts can be used to assess the level of crystallinity in a DSC instrument (see Differential Scanning Calorimeter).

 

  • Quality Index Score : The QIS is a number that is an indication of similarity when using the identiPol QA2 in Confirmation Mode and is derived using a Chemometrics analysis algorithm based on comparing Tan δ curves vs temperature. Simply, a value of 10 indicates that samples are identical, whilst 0 means that it is the wrong material. An acceptance threshold level can be set (typically 7), where any sample scoring above the threshold is a PASS and any  scoring below this level is a FAIL. 

 

  • Semi-crystalline : Many common plastics are semi-crystalline, e.g. polyethylene, polypropylene and polyamides (nylons). They are composed of two phases, one crystalline and the other amorphous (see Amorphous). These phases are chemically identical, but have different physical properties. The amorphous phase exhibits a glass transition, Tg, which is always below the melting point of the crystalline phase. The amount of softening seen at Tg will decrease in proporon to the amount of crystalline phase present.


Download Technical Note: TN1 – Glossary of Terms