Über die Wirkung thermoplastischer Elastomere als Additive zur Unterdrückung des Sharkskin-Effekts

Meer over het boek

The extrusion rate of polyethylene is constrained by melt fracture, with sharkskin being the initial surface defect. While common polymer processing aids, primarily fluoropolymers, can delay sharkskin onset, they are costly and raise environmental concerns. Kulikov (2005) proposed thermoplastic elastomers (TPE) as an alternative for sharkskin suppression, and Müller (2009) demonstrated the effectiveness of certain TPEs as processing aids. Both authors classified TPEs based on their efficiency in this regard. This work aims to uncover the reasons behind the varying efficiencies of TPEs for sharkskin suppression. Rheological evaluations of slip velocities for various TPEs against steel and in a polyethylene (PE) and TPE interface were conducted. Low viscosity TPEs exhibited higher slip velocities against steel, which were consistent in the polymeric interface and directly proportional to applied shear stress. Measurements of the first normal stress difference were consistent with empirical rules from Laun (1978, 1986). However, neither slip velocities nor normal stress differences accounted for the varying efficiencies. Instead, interfacial tension between PE and TPE emerged as the key factor. The chemical structure of TPE soft segments influences the dispersion of TPE droplets in the PE matrix, with TPEs based on polyester or silicone displaying coarser structures. This phase segregation enhances efficiency, as larger droplet s