No / Small-angle neutron scattering measurements on a series of monodisperse linear entangled polystyrene melts in nonlinear flow through an abrupt 4:1 contraction have been made. Clear signatures of melt deformation and subsequent relaxation can be observed in the scattering patterns, which were taken along the centerline. These data are compared with the predictions of a recently derived molecular theory. Two levels of molecular theory are used: a detailed equation describing the evolution of molecular structure over all length scales relevant to the scattering data and a simplified version of the model, which is suitable for finite element computations. The velocity field for the complex melt flow is computed using the simplified model and scattering predictions are made by feeding these flow histories into the detailed model. The modeling quantitatively captures the full scattering intensity patterns over a broad range of data with independent variation of position within the contraction geometry, bulk flow rate and melt molecular weight. The study provides a strong, quantitative validation of current theoretical ideas concerning the microscopic dynamics of entangled polymers which builds upon existing comparisons with nonlinear mechanical stress data. Furthermore, we are able to confirm the appreciable length scale dependence of relaxation in polymer melts and highlight some wider implications of this phenomenon.

Recycled material produced during three months from packing polyethylene foils coming from three suppliers was analysed together with one recycled material under complaint from the point of melt flow index (MFI), composition and mechanical properties. The addition of linear low density polyethylene (LLDPE) into the recycled material was studied as well. It was measured melt flow index (MFI), Differential scanning calorimetry (DSC) together with Thermogravimetry methods were used to determine composition. Selected materials were pressed to obtain films with the thickness of 1 mm to determine tensile properties. Recycled materials contained 40–65% LLDPE, small amount of polypropylene as well as chalk. The content of LDPE and LLDPE varied within one supplier and thus mechanical properties did. The results showed the difference in quality of PE films separation among all suppliers. The problems with workability of material under complaint were caused by the material composition – the amount of LLDPE predominated. The addition of LLDPE into the recycled material in the range of 5–20 % increased MFI by 13-78%. Mechanical properties of blends rich in LLDPE were similar to those of clear LLDPE. The presence of LDPE influenced more markedly only the strength to break. The blends of LDPE and LLDPE were evaluated as immiscible but with high affinity of the components with increasing contend of LLDPE. No material was chemically degraded. The methods commonly performed in manufacture, especially MFI, are not able to differentiate LDPE form LLDPE – recommended is DSC.