Thermal and Rheological Properties of Polyethylene Blends with Bimodal Molecular Weight Distribution Hong-Wang Shen, Bang-Hu Xie, Wei Yang, Ming-Bo Yang College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, Sichuan 610065, People’s Republic of China Correspondence to: B.-H. Xie (E-mail: xiebangh@tom.com) ABSTRACT: Polyethylene blends with bimodal molecular weight distribution were prepared by blending a high molecular weight poly- ethylene and a low molecular weight polyethylene in different ratios in xylene solution. The blends and their components were char- acterized by the high temperature gel permeation chromatograph (GPC), different scanning calorimetry (DSC), and small amplitude oscillatory shear experiments. The results showed that the dependence of zero-shear viscosity (g 0 ) on molecular weight followed a power law equation with an exponent of 3.3. The correlations between characteristic frequency (x 0 ) and polydispersity index, and between dynamic cross-point (G x ) and polydispersity index were established. The complex viscosity (g * ) at different frequencies fol- lowed the log-additivity rule, and the Han-plots were independent of component and temperature, which indicated that the HMW/ LMW blends were miscible in the melt state. Moreover, the thermal properties were very similar to a single component system, sug- gesting that the blends were miscible in the crystalline state. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000–000, 2013 KEYWORDS: bimodal polyethylene; dynamic rheology; solution blending; miscibility Received 17 September 2012; accepted 19 November 2012; published online DOI: 10.1002/app.38850 INTRODUCTION There is no doubt that polyethylene (PE) is one of the most im- portant plastic materials with utilities in industry, agriculture and other fields. The properties of polyolefine mainly depend on the polymer structure, especially the molecular weight and molecular weight distribution (MWD). 1–4 Generally, higher mo- lecular weight will bring about better final mechanical proper- ties, but it also gives rise to high melt viscosity and poor processability, which limits the application of PE. Recently, polyethylene with bimodal molecular weight distribution (defined as bimodal PE) can resolve the conflict between me- chanical properties and processability very well. Because of their good processing characteristics and excellent mechanical properties, bimodal PE arouses the researchers’ in- terest quickly. This bimodal PE is composed of low molecular weight PE fraction and high molecular weight PE fraction. In bimodal PE, the low molecular weight fraction guarantees the stiffness and creep resistance in crystalline state, and reduces the melt viscosity during processing. Meanwhile, the high molecular weight fraction acts as the tie molecular that connect the crystal lamella mainly formed by the low molecular weight fraction, and so the impact strength and stress cracking resistance are enhanced. The combined action of these two fractions results in a good balance between mechanical properties and processabil- ity. 5–7 At present, bimodal PE is produced through two methods in industry: the reactor in series configuration and the single reactor with dual site catalysts. 8–11 And yet for all that, both of the two methods are complex and expensive, and it is difficult to produce a series of bimodal PE with continuously variable MWD. Essentially bimodal PE can be considered as a blend of two PE components with different molecular weight and MWD. Therefore, a melt blending is better suited to prepare a series of bimodal PE with continuously variable MWD in laboratory, but the bad mixed effect may seriously affect the research results. So a solution blending has been applied and proved to work well in PE blending for research purpose because of the most inti- mate mixing at the molecular level. 12–15 At present, there are many reports about the effect of molecular weight, MWD and comonomer on the properties of polyole- fin. 1,5,16–26 But for bimodal PE, the research mainly focuses on the synthetic technology and performance comparison to unim- odal PE, while the study about the effect of bimodal MWD characteristic on the properties is relatively rare. 14,15 In our previous works, 27,28 the bimodal MWD characteristic was regulated by blending bimodal PE with unimodal PE, but the range of regulation was very limited. In this paper, two V C 2013 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2013, DOI: 10.1002/APP.38850 1