Paul J. DesLauriers

Wall slip of HDPEs: Molecular weight and molecular weight distribution effects

The slip behavior of several high-density polyethylenes (HDPEs) is studied as a function of molecular weight (Mw) and its distribution for broad molecular weight distribution metallocene and Ziegler–Natta catalyst resins. It is found that slip depends strongly on Mw and its distribution. First, the slip velocity increases with decrease of molecular weight, which is expected to decay to zero as the Mw approaches a value with characteristic molecular dimension similar to surface asperities. For HDPEs that exhibit stick–slip transition, the slip velocity has been found to increase with increase of polydispersity. The opposite dependence is shown for HDPEs of wider molecular weight distribution that do not exhibit stick–slip transition. A criterion is also discussed as to the occurrence or not of the stick–slip transition which is found to depend strongly on Mw and its distribution.

Chemometric Methods for Estimating the Strain Hardening Modulus in Polyethylene Resins

The feasibility of using multiway or N-way partial least square (NPLS) methods to estimate physical properties of 1-butene and 1-hexene polyethylene (PE) copolymers directly from multidimensional data obtained from size exclusion chromatography coupled to a Fourier transform infrared detector (SEC FT-IR) was explored. Digital sample sets of horizontal slices (slabs) of two-dimensional data simulating the molecular weight distribution and the corresponding orthogonal FT-IR spectra were correlated to a particular Y-block response using NPLS. The NPLS results were compared to those obtained through separate estimations using various algorithms and exploratory response surface methods. The estimated strain hardening modulus () for bimodal PE-like digital structures could adequately be modeled using both the linear response surface method (RSM) and NPLS. Although different input values were used, the predicted values for  by NPLS was found to mirror both the analytical results and the expected structural effects obtained using linear RSM models.