Citation: Yun-Fan Mei, Bao-Hua Guo, Jun Xu. Detection of long-chain branches in polyethylene via rheological measurements[J]. Chinese Chemical Letters, ;2016, 27(4): 588-592. shu

Detection of long-chain branches in polyethylene via rheological measurements

Department of Chemical Engineering, Tsinghua University, Beijing 100084, China

Received Date: 28 December 2015
Revised Date: 4 February 2016

Fund Project: This work was financially supported by the National Natural Science Foundation of China (No. 21374054) and the Sino-German Center for Research Promotion.

The detection of long-chain branches (LCB) in polyethylene is of considerable importance as the processing properties of polyethylene are strongly affected by even a small amount of LCB. While the conventional characterization techniques such as GPC-MALS and ¹³C NMR fail or take very long time to detect low content of LCB, we turn to the rheological method, which is more sensitive to LCB. In our study, we performed oscillatory shear test, creep test and stress relaxation test on two series of metallocene linear low density polyethylene (LLDPE), revealing that the resins with LCB show higher zero-shear-rate viscosity, retarded relaxation and higher flow activation energy than those without or with less LCB. The resins with LCB showed shear thinning at very low shear rate and their zero-shear-rate viscosities were obtained via creep test. The content of LCB was quantitatively estimated from the flow activation energy. In addition, the modulus-time curves during stress relaxation of melt of the different resins obeyed the power law. The exponent of the resins with more LCB was -0.7, different from that of the resins with less LCB, around -1.7.
- Metallocene polyethylene,
- Long-chain branch,
- Rheology,
- Stress relaxation
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