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Rheological Study of Linear and Nonlinear Viscoelastic Behavior for Silica-Reinforced Polybutadiene and Polystyrene

Thompson, Thaddeus
http://rave.ohiolink.edu/etdc/view?acc_num=akron1134566032

Abstract Details

2005, Master of Science, University of Akron, Polymer Science.
The incorporation of filler particles into a polymeric system causes an increase in the elastic modulus, G’ at low strain amplitudes, but G' decreases as the strain is increased, commonly referred to as the Payne effect. This nonlinear behavior was explored in terms of the matrix molecular weight, filler loading, and time scales used to probe the viscoelasticity of filled melts. Use of monodisperse, uncrosslinked 1, 4-polybutadiene (PBD) along with a silica filler allowed for the illustration of different mechanisms of filler reinforcement in the elastic and liquid regimes. Oscillatory shear results showed that the addition of higher molecular weight chains bridged the gaps between particles creating an enhanced network of filler-filler agglomerates. This effect became less significant as the chains became sufficiently long, resulting in the same level of reinforcement between samples. Standard strain sweep experiments at a given oscillatory shear frequency showed that the filled systems demonstrated the expected Payne effect in addition to liquid-like behavior (G’<G”) at low strain amplitudes, switching to solid-like (G’>G”) behavior as the strain amplitude was increased. In comparing experiments involving filled systems of short chains versus long chains, the long chain system was able to withstand disruption of its filler network as a result of increasing strain. However, the short chain system was able to return to its enhanced value of G’ at a faster rate. Ramp-up and ramp-down experiments showed a permanent loss in each system due to a large scale disruption of the filler-filler network and filler spatial rearrangement under oscillatory shear. After the high strain amplitude stage, the filler structure was capable of repairing itself upon returning to low strain, recovering most of the reinforcement it had lost. The increased moduli at higher strain for the long chain systems further support the idea of chain bridging. Creep measurements of the filled systems showed that the onset of shear-thinning behavior is at a much lower stress for the short chain system. The lack of a sharp shear rate transition as a function of applied stress implied a wide spectrum of filler-filler structures in terms of strength. The two-step relaxation behavior seen for the filled systems was believed to be due to filler structural disintegration followed by the standard relaxation of the polymer melt. Due to the extremely low glass transition temperature of polybutadiene, polystyrene was used to explore the low mobility shell theories of filler reinforcement. DMTA results showed that as the chain dynamics around the filler particles begins to slow, they served to broaden the glass transition values instead of shifting them. Static DSC results confirmed these findings. These combined results indicate that filler-filler network dissociation is the major cause for nonlinear behavior in filled polymer systems as a result of increased shear stress and that the addition of long chains greatly increases the reinforcement of the system. Dynamic and static experiments show no evidence that the Payne effect is affected by the existence of a low mobility shell.
Shi-Qing Wang (Advisor)
71 p.
filler; phr; 12K; PBD; polymer; G'; rad/s

Recommended Citations

Citations

  • Thompson, T. (2005). Rheological Study of Linear and Nonlinear Viscoelastic Behavior for Silica-Reinforced Polybutadiene and Polystyrene [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1134566032

    APA Style (7th edition)

  • Thompson, Thaddeus. Rheological Study of Linear and Nonlinear Viscoelastic Behavior for Silica-Reinforced Polybutadiene and Polystyrene. 2005. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1134566032.

    MLA Style (8th edition)

  • Thompson, Thaddeus. "Rheological Study of Linear and Nonlinear Viscoelastic Behavior for Silica-Reinforced Polybutadiene and Polystyrene." Master's thesis, University of Akron, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=akron1134566032

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.