Untitled

The influence of paraffin-wax type and content on the properties of its blends with HDPE, LDPE, and LLDPE was investigated. Melt-mixing of HDPE with wax gave rise to completely miscible blends for both 10 and 20% wax contents. A wax content of 30% gave rise to a partially miscible blend. These observations were supported by the thermal fractionation (stepwise cooling) results. Melt-mixing of LDPE with hard paraffin wax gave rise to a partially miscible blend for all wax contents investigated, while complete miscibility was observed for the 10% oxidized hard paraffin wax containing blend. Complete miscibility was observed for all the LLDPE/A1 wax blends, with A1 wax as an oxidized hard paraffin wax. This indicates possible cocrystalli-zation of this wax with LLDPE, which was also evident from the thermal fractionation curves. LLDPE blends with hard paraffin wax were, however, partially miscible for all wax contents. All the observations were supported by the surface free energy results. It is further clear from the thermal fractionation results that the presence of wax changed the crystallization behavior of LDPE and LLDPE. Changes in the tensile properties are explained in terms of the miscibility and proposed morphologies of the blends.

Section: Introductionmentioning

confidence: 99%

Thermal fractionation and properties of different polyethylene/wax blends

Hato

Luyt

2007

“…The heterogeneity of isotactic PP can be determined in a much shorter time using the DSC fractionation method compared to TREF and similar compositional information is obtained, although the curves are not identical. This has been used to study intermolecular heterogeneity in short‐chain branched polyethylenes 14, 15. For PP, this technique has thus far been used only by Hardy et al16 for achieving a better separation between different crystal modifications (α/β).…”

Section: Introductionmentioning

confidence: 99%

Propylene–ethylene random copolymers: Comonomer effects on crystallinity and application properties

Gahleitner

Jääskeläinen²,

Ratajski

et al. 2005

117

110

For understanding the correlation chain from the polymer structure to the final application properties of propylene-ethylene random copolymers, four commercial grades with different ethylene content (0 -8 mol %) but identical molecular weight distributions were investigated. Structural investigations concerning the comonomer distribution, using two different techniques (temperature rising elution fractionation and stepwise isothermal segregation), showed an increase of inhomogeneity with the total comonomer content, which was reflected for temperature rising elution fractionation in a widening of the elution temperature range. Crystallinity and crystallization speed studies confirmed the reduced overall crystallinity and increase of ␥-modification content as reported previously, but they also showed the reason for these effects in the distinctive decrease of the spherulitic growth speed. Good correlations of all these parameters to the mechanical performance of the four materials were obtained.

“…The previous thermal effects were removed by heating the samples from room temperature to 140°C; followed by a hold up at 140°C for 5 min. All samples were cooled to subambient temperatures for complete evaluation of crystallization 25. The samples were cooled from 140° to 5°C at a rate of 2°C/min, 6°C/min, and 10°C/min.…”

Section: Methodsmentioning

confidence: 99%

“…The previous research has primarily focused on the study of the influence of molecular weight ( M w ), molecular weight distribution (MWD), branch type, branch content (BC), and crystallization conditions on the crystallization behavior of ethylene/α‐olefin copolymers 16–28. Most of these studies used Ziegler–Natta linear low density polyethylenes (ZN‐LLDPEs).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Nonisothermal crystallization kinetics study of LDPE/MWCNT nanocomposites: Effect of aspect ratio and surface modification

Hussein

Parvez

2010

In this article, the effect of aspect ratio and chemical modification of multiwall carbon nanotubes (MWCNT) on the nonisothermal crystallization kinetics of LDPE/MWCNT nanocomposites was studied. Nine different samples were prepared using different MWCNT to study both effects. The cooling rate (R) was varied in the range 2-10 C/min. In this article, the effect of CNT loading, surface modification, and aspect ratio were studied. For the same MWCNT concentration, aspect ratio and ACOOH modification had weak influence on both the peak crystallization temperature and the crystallization onset temperature. However, the crystallization onset temperature was significantly affected by the amount of MWCNT. The rate parameters in the modified Avrami method and Mo method [F(T)] of analyses show a very good fit of data. The Vyazovkin and Sbirrazzuoli method of analysis, which is based on Hoffman-Lauritzen theory for secondary crystallization, was also used. Temperature dependency of activation energy was obtained for 30-75% relative crystallinity of the produced nanocomposites. Activation energy based on calculations of Hoffman-Lauritzen theory showed a decrease with the increase in the concentration of MWCNT and crystallization temperature. A proposed model of the form E ¼ a exp (-bXT) which relates the activation energy, E, to relative crystallinity, X, and crystallization temperature, T, was able to fit the whole set of data. Incorporation of MWCNT in nanocomposites lowers the activation energy; hence enhances the initial crystallization process as suggested by the different methods of data analyses.