Stretchability and Properties of LLDPE Blends for Biaxially Oriented Film

In order to improve the stretchability of linear low density polyethylene (LLDPE) for double bubble tubular film (DBTF), the blending of LLDPEs have been investigated. Three LLDPEs of varying densities were blended, and several films having different densities, molecular-weight distributions and composition distributions were produced. The stretchability and properties of these films were investigated and the relationship between the stretchability and the material properties were also discussed. The material properties of LLDPE which showed better stretchability were reported. Furthermore, the stretchability of LLDPE by using the laboratory tenter stretched film (LTSF) and the DBTF were compared. The prediction of the stretchability for the DBTF by using the LTSF was reported.

Bi-axially Oriented Blown Film Technology

A set of commercial polyethylenes (three LDPE and three LLDPE) was rheological characterized and processed in a laboratory double bubble extrusion line with the purpose of investigating: i) whether their relative processability could be predicted in the laboratory and ii) the effect of operating and machine variables on processability. Oscillatory shear and extensional measurements were able to differentiate the various materials, who also behaved quite differently upon processing. Those with a stronger shear thinning behaviour, higher elasticity and higher melt strength were the most suited to the process. Bubble stability and thickness uniformity were assumed as the main requirements for processability. The former was estimated by monitoring the time required to stabilize the bubble and examining any variation/oscillation in size/shape. Bubble stability depends on the interaction between various parameters, the most relevant being those related with the film cooling stage, namely the axial position of the air rings, the air flow rate and air velocity. The study was preceded by an assessment of the performance of the re-heating oven and die/calibration/centring, as these parameters could also narrow the practical operating window.

Physical properties of biaxially oriented PA6 film for simultaneous stretching and sequential processing

There are two different stretching processes that produce the biaxially oriented film, namely the tenter process and double bubble tubular film process. Furthermore, there are two tenter processes, i.e., the sequential biaxial stretching process and simultaneous biaxial stretching process. There is no report describing the difference among film physical properties of the three different processes. The biaxially oriented polyamide film using the double bubble tubular process has good balanced physical property and high impact strength, thus it is used for proper applications utilizing their advantage properties. In this report, the influence of each biaxial stretching process on film physical properties of polyamide, which has hydrogen bond, was studied in detail. As a result, the tentering process film has anisotropic tensile properties between machine direction (MD) and transverse direction (TD). This result was influenced by a later stretching process, namely TD stretching. On the contrary, the double bubble tubular film has good balanced properties, especially thermal shrinkage and impact strength. Tentering simultaneous stretching film has much larger shrinkage in MD than in TD. The sequential stretching film has larger shrinkage in TD than in MD. The double bubble tubular film has high impact strength, because it corresponds to the balanced molecular orientation.