Heat capacity, enthalpy and crystallinity for a linear polyethylene obtained by DSC

Abstract

By means of computer-controlled DSC, heat-capacity measurements were performed on NBS SRM 1484 between --70~ and 250~ in heating as well as cooling. By using stepwise and continuous measuring methods together with enthalpy calculations, an insight was obtained into the intrinsic consistency end the accuracy of the measurements. The reference states of polyethylene within the two-phase model were used to determine the crystallinity as a function of temperature, and to evaluate various other methods employed for the same purpose.For many years the DSC technique has been generally used in the thermal analysis of materials. Computerization has enlarged the possibilities of control and data manipulation, so that not only have measurements and evaluation been speeded up, but accuracy has increased as well. Meanwhile the point has been reached where accuracy is no longer restricted by peripheral apparatus, but only by the calorimeter itself.This will be illustrated with reference to Cp measurements on polyethylene.Although polyethylene has long been a subject of study [1,2], hardly any quantitative measurements are known for the interval from room temperature through the whole of the melting range, the very area to which by far the greater part of the present calorimetric studies relate, and, indeed, the area in which Cp and crystallinity show strong changes.This article presents findings in the range from -70 ~ to 250 ~ measured by step- The results are discussed within the framework given by the so-called reference states of purely amorphous and purely crystalline polyethylene [2].

Non‐isothermal crystallization of polypropylene with sorbitol‐type nucleating agents at cooling rates used in processing

“…For measurement of the crystallinity by conventional DSC all samples were cooled at 60 K min −1 from the melt (220 °C) to below the glass transition temperature (−40 °C) and subsequently heated at 20 K min −1 . The enthalpy of melting is determined using a method proposed by Mathot and Pijpers . The baseline for evaluation of the heat flow peak is the extrapolated line from the melt to 87 °C.…”

The effect of poly(4‐methyl‐1‐pentene) on the nonisothermal crystallization kinetics of polypropylene

“…To be exact, the crystallization determination as described above is known to be insufficient because the temperature dependence on the heat of fusion and the intersection between the baseline and the trace are not considered in Equation (3). However, according to a previous study, [22] these influences for calculating the crystallinity are negligible. For this reason, we After that, the crystallization of PMP proceeds perpendicular to the surface.…”

A comparative DSC, X-Ray and NMR study on the crystallinity of isomeric aliphatic polyamides

“…Heating curves were recorded at 10 C/min from 50 up to 260 C on 5 mg samples in Perkin Elmer standard aluminum pans. The c p (T) based mass fraction crystallinity, w c (T), was calculated as a function of temperature according to [2,14]:…”