Study of selected thermal characteristics of polypropylene/polyethylene binary blends using DSC and TGA

doi:10.1016/S0142-9418(01)00144-1

Polymer Testing

Volume 21, Issue 6, 2002, Pages 691-696

https://doi.org/10.1016/S0142-9418(01)00144-1 Get rights and content

Abstract

The characteristics of polypropylene/polyethylene (PP/PE) binary blends at the microscopic level have been widely studied by different researchers over the years. This communication discusses the empirical results obtained from a series of DSC and TGA tests on the selected thermal properties of PP/PE blends. Using DSC in our investigation is aimed at revealing the effects of different blending ratios of PP and PE on the melting and crystallinity behaviour of the blend systems, while the application of TGA is to study the degradation characteristics of the blends in terms of their induction time. An empirical equation is proposed and has been proved to offer a convenient means for the estimation of the overall crystallinity percent of a PP/PE system. It largely requires the knowledge of blend ratios and the densities of the pure components, and eliminates the tedious graphical integration process on determining areas under curves of thermograms. The TGA study shows that the effect of temperature on induction time of PP/PE blends follows the trend of the Arrhenius equation.

Introduction

Blending of different plastic resins has long been practised in the manufacturing industry for various reasons including: (i) tailor-made blends to meet specific processing and performance requirements which cannot be satisfied by a single component; (ii) scientific interests; and (iii) financial incentives. Over the years, blends of polypropylene (PP) and polyethylene (PE) are among those binary systems that have attracted a lot of attention. The huge worldwide annual consumption requirements of PP and PE is also thought to be responsible for the continuous research efforts directed towards the various blending issues of these two resins. The interests and needs in this area of polymer science and engineering have grown even further since the success of the UNIPOL process which came into practice in the late 1970s and early 1980s. The UNIPOL process is a polymerisation process licensed by Union Carbide for the production of linear type polyethylene.

This communication describes work focused on the application of: (i) differential scanning calorimetry (DSC) to reveal the effects of different blending ratios of PP and PE on their melting and crystallinity behaviour; and (ii) thermogravimetry (TGA) to reveal the degradation characteristics of the blends in terms of their induction time.

Section snippets

Experimental

The basic physical properties of the polymers selected for the study are shown in Table 1. While PP was chosen as the blending base, the different PEs were selected as the blend partner for the investigation of the branching effects — LDPE has the largest degree of molecular branching whereas HDPE has the least. PP and its blending partner were carefully weighed separately prior to charging them into a PRISM 16 mm diameter co-rotating twin-screw extruder for compounding and pelletising. The

DSC — melting and crystallinity

Perhaps one of the most obvious effects brought about by the blending is on the density of the blends. A Techne Density Gradient Column was employed for density measurement. It was found that the density of the blends may be accurately described by the following additive rule (Fig. 1) which was reported by Wong [1] to be applicable for PE/PE systems: $ρ_{blend} =∑^{i=n}_{i=1} χ_{i} ρ_{i}$ where ρ is the density, x the weight fraction, and subscript i represents the blending component.

A Polymer Laboratory DSC was

Conclusion

Employing the techniques of DSC and TGA, some of the thermal properties of PP/PE blends have been revealed and are reported in this communication. An equation originally developed for PE/PE systems was modified for the prediction of the overall crystallinity of PP/PE systems. All these efforts have offered additional information to the pool of existing knowledge and experience accumulated by other workers in similar fields.

Acknowledgements

The authors would like to thank the CRCG committee of The University of Hong Kong for their generous funding support for this project.

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Material CharacterisationStudy of selected thermal characteristics of polypropylene/polyethylene binary blends using DSC and TGA

Abstract

Introduction

Section snippets

Experimental

DSC — melting and crystallinity

Conclusion

Acknowledgements

The study of the relationships between melt index, density and blend ratio of binary polyethylene blends

Polym. Eng. Sci.

The compatibility of linear low density polyethylene–polypropylene blends: viscosity ratio plots

Polym. Eng. Sci.

Crystallization, melting behavior, and morphology of BPP/HDPE blend

J. Appl. Polym. Sci.

Mechanical properties and morphology of polyethylene–polypropylene blends with controlled thermal history

J. Appl. Polym. Sci.

Drawing behaviour of polyethylene–polypropylene blends

J. Appl. Polym. Sci.

A correction function to determine the β-fusion heat in a mixture of α- and β-PP

J. Therm. Analy. Calor.

Material Characterisation
Study of selected thermal characteristics of polypropylene/polyethylene binary blends using DSC and TGA