Blending of HDPE with LLDPE, Alkamax Metallocene MLLDPE and LDPE
The last post explored the blending of certain polymer grades to create optimum film packaging. This blog post does the same, but compares combining HDPE with LLDPE, Alkamax Metallocene MLLDPE and LDPE.
Some film applications require a combination of stiffness and toughness, which may be achieved by blending LLDPE or mLLDPE with HDPE. For example, the addition of LLDPE to HDPE will improve impact strength, tear resistance and can improve sealing properties. Even greater improvements are typically achieved if mLLDPE is used.
Alternatively, the addition of HDPE to LLDPE or mLLDPE will improve stiffness and creep resistance, with some sacrifice of toughness properties.
The choice of HDPE grade depends on the film properties required. Where toughness and creep resistance are important, a low MFI grade is preferred. However, in some extrusion lines, low MFI HDPE grades may not mix well with higher MFI LLDPE grades. In this case, a higher MFI grade of HDPE may be necessary. The higher MFI grade of HDPE will still improve the film stiffness, but there will be a reduction in film toughness.
For some applications, a blend of HDPE, LLDPE and LDPE may be required. Typical examples may include films where a low proportion of HDPE is added to a blend of LLDPE and LDPE to improve stiffness or creep resistance. As noted in the previous section, the appropriate HDPE grade depends on the toughness required and the extrudability. Combinations including LDPE and low MFI HDPE are more prone to show poor dispersion. Hence, some work may be required to find the optimum blend and extrusion conditions for the application and extrusion line.