Polymer blends viscoelastic behaviour

The viscoelastic behaviour of dilute blends of polymers of different length and narrow molecular weight distributions was investigated experimentally for polybutadiene by Yanovski et al. (1982) and by Jackson and Winter (1995) and for polystyrene by Watanabe and Kotaka (1984) and Watanabe et al. (1985) (the results can be found in the work by Jackson and Winter (1995)). The results for polybutadiene were approximated by Pokrovskii and Kokorin (1984) by the dependencies... 

Pokrovskii VN, Chuprinka VI (1973) The effect of internal viscosity of macromolecules on the viscoelastic behaviour of polymer solutions. Fluid Dyn 8(1) 13-19 Pokrovskii VN, Kokorin YuK (1984) Theory of viscoelasticity of dilute blends of linear polymers. Vysokomolek Soedin B 26 573-577 (in Russian)... 

The simplest type of viscoelastic behaviour as shown by single-phase amorphous polymers is described in this article. Polymers that crystallize or form multiple phases such as blends, block copolymers, particulate or fibre-filled polymers show more complex behaviour, since each amorphous region will show its own viscoelastic response to deformation. 

Takayanagi [17] devised series-parallel and parallel-series models as an aid to understanding the viscoelastic behaviour of a blend of two isotropic amorphous polymers in terms of the properties of the individual components. For an A phase dispersed in a B phase there are two extreme possibilities for the stress transfer. For efficient stress transfer perpendicular to the direction of tensile stress we have the series-parallel model (Figure 8.9(a)) in which the overall modulus is given by the contribution for the two lower components in parallel (as in Equation (8.3)) in series with the contribution for the upper component (as in Equation (8.5)) ... 

The field of polymer science and technology has undergone an enormous expansion over recent decades primarily as a result of chemical diversity. Dilute solution behaviour, elasticity, tacticity, single crystal formation, viscoelastic behaviour, etc., attained the prime interest from past researchers. The concept of physically blending two or more existing polymers to obtain new products is now attracting widespread interest and commercial utilization. 

The mechanical and viscoelastic behaviours of natural rubber based blends and interpenetrating polymer networks (IPNs) are fimctions of their structures or morphologies. These properties of blended materials are generally not constant and depend on the chemical nature and type of the polymer blends, and also enviromnental faetors involved with any measurements. Preparations of natural rubber blends and IPNs are well known as effeetive modifieation methods used to improve the original meehanieal and viscoelastie properties of one or both of the eomponents, or to obtain new natural rubber blended materials that exhibit widely variable properties. The most common consideration for their mechanical properties include strength, duetility, hardness, impact resistance and fracture toughness, each of which can be deformed by tension, compression, shear, flexure, torsion and impaet methods, or a eombination of two or more methods. Moreover, the viseoelastieity theory is a way to predict the behaviours of deformation of natural rubber blends and IPNs. The time and... 

Natural rubber based-blends and IPNs have been developed to improve the physical and chemical properties of conventional natural rubber for applications in many industrial products. They can provide different materials that express various improved properties by blending with several types of polymer such as thermoplastics, thermosets, synthetic rubbers, and biopolymers, and may also adding some compatibilizers. However, the level of these blends also directly affects their mechanical and viscoelastic properties. The mechanical properties of these polymer blended materials can be determined by several mechanical instruments such as tensile machine and Shore durometer. In addition, the viscoelastic properties can mostly be determined by some thermal analyser such as dynamic mechanical thermal analysis and dynamic mechanical analysis to provide the glass transition temperature values of polymer blends. For most of these natural rubber blends and IPNs, increasing the level of polymer and compatibilizer blends resulted in an increase of the mechanical properties until reached an optimum level, and then their values decreased. On the other hand, the viscoelastic behaviours mainly depended on the intermolecular forces of each material blend that can be used to investigate the miscibility of them. Therefore, the natural rubber blends and IPNs with different components should be specifically investigated in their mechanical and viscoelastic properties to obtain the optimum blended materials for use in several applications. 

Takayanagi [50] devised series-parallel and parallel-series models as an aid to understanding the viscoelastic behaviour of a blend of two isotropic amorphous polymers in terms of the... 

The same enhancement of elasticity is observed for PS/PVME blends at temperatures above the critical temperature of phase separation. For temperatures lower than 140 C, the components are totally miscible and the linear viscoelastic behaviour of these blends is typical of an homogeneous polymer melt. 

Various workers have discussed aspects other than those mentioned above in studies of the viscoelastic properties of polymers. These include PVOH [62], hydroxy-terminated polybutadiene [63], styrene-butadiene and neoprene-type blends [64], and polyamidoimides [65]. Other aspects of viscoelasticity that have been studied include relaxation phenomena in PP [66] and methylmethacrylate-N-methyl glutarimide copolymers [67], shear flow of high-density polyethylene [68], Tg of PMMA and its copolymers with N-substituted maleimide [69] and ethylene-vinyl acetate copolymers [70], and creep behaviour of poly(p-phenylene terephthalate) [71] and PE [72]. 

---