Grade Selection Of Polymer Grades For Film Extrusion
Alkamax film polymer grades cover a wide range of MFIs (Melt Flow Index) and densities and so deciding which to use is very important. One dimension that determines the polymer performance is the class of polyethylene (PE).
In film extrusion, different classes of PE produce different film properties, even if the MFI and density are equivalent. In this blog post, the different type of polymer grades will be compared by highlighting the differing properties of film produced for each one.
Compared to Alkathene LDPE, an Alkatuff LLDPE with similar MFI and density will typically produce films for product packaging with:
- Higher stiffness
- Higher tensile strength at break
- Higher tear strength
- Higher puncture resistance
- Better heat sealing properties, superior hot tack
- Higher impact strength, especially at low temperatures
- Higher softening point and hence higher heat resistance
- Better drawdown
However, an Alkamax metallocene (mLLDPE), also with similar MI and density, will typically produce films with:
- Much higher impact strength
- Further improved heat sealing properties, especially hot tack performance
On the other hand, the Alkathene LDPE will typically show the following benefits;
- Lower extruder power consumption
- Lower melt temperature
- Lower tendency to suffer from melt fracture
- Improved bubble stability
- Higher film clarity
Alkatane HDPE grades have significantly higher density than LDPE and LLDPE grades. Films produced with HDPE will typically show:
- Much higher stiffness
- Much higher yield strength
- Improved creep resistance
- Lower permeability to gases
However, it is not always just the case of choosing one film polymer grade based on the properties as the differences between films produced with different classes of PE are often combined in a film to obtain the best balance of properties for the application. Products can be combined by blending and by coextrusion. This table highlights the differences between the films based on their class of PE so it is easier to see how they can be merged for the best possible outcome, based on the needs.
The next blog post will explore the blending together of polymer grades in even greater depth, such as which are the best to combine to give the best results.