Structure and mechanical properties of a multilayer biomedical shaft tubing: effect of layer composition

Abstract

Trilayer polymer tubes were manufactured through an extrusion process using Pebax 6333 and high density polyethylene (HDPE) as outer and inner layer, respectively. A maleic grafted linear low-density polyethylene (LLDPE) was used as the bonding layer or tie-layer. Three types of multilayer tubes were produced: (1) outer layer (Pebax) at 70% of the total wall thickness (WT), (2) outer layer at 90% of WT, and (3) outer layer at 20% of WT. The analysis of mechanical properties showed that the inner layer contributes to strength and rigidity of the tube while the outer layer provides flexibility. Melt rheology behavior for HDPE and Pebax were studied, and HDPE showed a more pronounced shear thinning behavior compared to Pebax. Orientations of the tubes were assessed using Fourier transform infrared spectroscopy (FTIR) and it was found that HDPE layer is more sensitive to molecular orientation when extruded compared to Pebax material. Melting behavior for the tubes was investigated using dynamic scanning calorimetry (DSC). The tubes showed two melting temperatures: one associated with HDPE and one with Pebax. The HDPE peak showed a specific shift to a higher melting point for tubes as a result of molecular orientation during processing. Burst and compression testing were performed on the tubes and results demonstrated that the HDPE-rich extrusion showed the highest burst pressure and compression resistance.