Multi-component polymer blends

Fig. 10.60 Compressive stress-strain behavior of PS and LLDPE at 25°C and crosshead speed of 25.4 mm/min. At a compressive stress level of 20 MPa the deformation of the soft LLDPE is large, in the dissipative region and nearly twenty times the PS deformation, which is of the order of 0.04, in the elastic nondissipative range. [Reprinted by permission from B. Qian, D. B. Todd, and C. G. Gogos, Plastic Energy Dissipation (PED) and its Role in Heating/Melting of Single Component Polymers and Multi-component Polymer Blends, Adv. Polym. Techn., 22, 85-95 (2003).]...

B. Qian, D. B. Todd, and C. G. Gogos, Plastic Energy Dissipation and its Role on Heating/ Melting of Single-component Polymers and Multi-component Polymer Blends, Adv. Polym. Technol., 22, 85-95 (2003). 

Prasanth R, Aravindan V, Srinivasan M (2012) Novel polymer electrolyte based on cobweb electrospun multi component polymer blend of polyacrylonitrile/poly(methyl methacry-late)/polystyrene for hthium ion batteries-Preparation and electrochemical characterization. J Power Sources 202 299-307. doi 10.1016/j.jpowsour.2011.11.057... 

The objective of this paper is to examine interfacially driven structure formation in multi-component polymer blends. The effects of selective interfacial modification and annealing time will be studied. 

Here the primary interest is in the plasticity of single-component glassy polymers well below the glass-transition temperature. We consider no heterogeneous blends and multi-component polymers. Some consideration of such polymers for purposes of toughening is deferred to Chapter 13. 

A natural evolution of past work is to extend the benefits of processing in CO2 to multi-component polymer systems. Potential applications include the modification and orientation of block copolymers, the preparation of homogeneous blends, and improving the efficiency of melt-phase blend compatibilization reactions. In this chapter, we show that for these systems, CO2 sorption not only influences molecular mobility, but can also have a dramatic effect on polymer/polymer compatibility that can... 

At first glance, one might consider the effect of compressed CO2 on the phase behavior of multi-component polymer systems to be a simple combination of the known effects of liquid solvents and hydrostatic pressure. Solvent effects are primarily enthapic in nature and typically manifest in upper critical solution behavior. Common solvents mitigate unfavorable interactions between dissimilar segments and enhance miscibility. In blends, the addition of highly selective solvents, e.g. a non-solvent for one component, can lead to precipitation of the unfavored species at high dilution. In block copolymers, the effect of selective solvents is less clear, but studies to date reveal a collection of the solvent at the domain interface, selective dilation of one phase, and stabilization of the disordered phase via depression of the UODT. The systems we have studied each exhibit a lower critical transition. For these specific systems, previous work indicates the hydrostatic pressure suppresses free volume differences between the components and expands the region of miscibility. 

Rgure 12.35 (1) summarizes the state of the art of polymeric and multi-component polymer materials from the point of view of the role of surfaces and interfaces. The three main types of surfaces and interfaces are (a) free surfaces, (b) polymer blend interfaces, and (c) polymer composite interfaces. While the dilute solution-colloid interfaces are noifree in the ordinary sense, the fluid phase exhibits a low viscosity allowing rapid diffusion similar in some ways to the free air surface, and is classified as such for the present purposes. The concepts of polymer blends and composites will be further developed in Chapter 13. 

Polymer blending is nearly as old as the polymers themselves. However, the literature dedicated to this technology is relatively recent, and it focuses primarily on the academic aspects of polymer hlends. It seems that there is a dichotomy of efforts. On the one hand, annually the industry generates about 30 million tons of blends, and on the other, academia produces over 10,000 publications dedicated mainly to studies of model systems. The only place where these two streams meet is a laboratory of industrial researcher who tries to build a better blend using the accessible data. It is not an easy task to convert the published information into a commercial, multi-component polymer alloy. 

At this point it will not be necessary to provide details of polymer blends, nor of their fabrication routes and applications, as this entire book is devoted to such information. Indeed, a plethora of reference material describing different aspects of the materials science and engineering of polymer blends is available [1-11], with many references - both direct and indirect - being made to electron microscopy (EM) and/or atomic force microscopy (AFM) for such purpose. But this simply highlights the significance of microscopy in the characterization of multi-component polymers, polymer blends, and their composites. 

Multicomponent melts that are commonly found in such varied situations as material fabrification, reinforcement, blending, and so on are discussed in the chapter by Muller ( Computational Approaches for Structure Formation in Multi-component Polymer Melts ). Only equilibrium properties are discussed along with computational approaches for coarse-grained models in the mean field approximation. Both hard-core and soft-core models are used to cover a multitude of scales of length, time, and energy. Attention is also paid to methods that go beyond the mean field approximation. 

This approach was further explored by Hakemi who prepared blends that contain both a wholly aromatic and an aromatic-aliphatic LCP that are miscible with each other. The ultimate goal of this approach was to develop multi-component miscible blends that have components of thermoplastics. The miscible blends could be useful as reinforcing agents for the thermoplastic matrix polymer, and because LCPs contain some of the components of the thermoplastic polymer, improved adhesion between the LCP portion and the matrix portion of the mixture is expected. This is another example of an attempt to balance the phase separation inherent in high temperature polymer blends due to molecular conformation differences by enforcing the enthalpic interactions between the two polymers. 

In addition, patterns created by surface instabilities can be used to pattern polymer films with a lateral resolution down to 100 nm [7]. Here, I summarize various possible approaches that show how instabilities that may take place during the manufacture of thin films can be harnessed to replicate surface patterns in a controlled fashion. Two different approaches are reviewed, together with possible applications (a) patterns that are formed by the demixing of a multi-component blend and (b) pattern formation by capillary instabilities. 

While the demixing patterns in Fig. 1.2 are conceptually simple and exhibit only one characteristic length scale, more complex phase morphologies are obtained by the demixing of a multi-component blend [16]. With more than two polymers in a film, the pattern formation is (in addition to the factors discussed in the previous section) governed by the mutual wetting behavior of the components. Two different scenarios are shown in Fig. 1.4 [ 17]. While both films in Fig. 1.4(a) and (b) consist of the same three polymers, their mutual interaction was modulated by preparing the films under different humidity conditions [15],... 

Polymer nanocomposites and polymer blends are an extremely important class of materials due to the expected synergistic enhancement of properties and potential multi-functionality. However, the immiscibility of most of the polymers results in poor interfacial interaction between the individual components which severely affects the hnal properties. A deeper insight into the spatial heterogeneity and morphology of the individual components at a microscopic level and their inhuence on the macroscopic properties is important for their rational design (such as choice and volume fraction of individual components, surface chemistry, and processing... 

Jenekhe. Electroluminescence of multi-component conjugated polymers. 2. photophysics and enhancement of electroluminescence from blends of polyquinolines. Macromolecules, 35(2) 382—393,... 

The multi-component, multiphase nature of polymer blends affects crystallization kinetics, crystalhne morphology and level of crystallinity [Nadkami and Jog, 1991]. In particular, the presence of one polymer may affect the crystallization of the other, the phase boundary enhancing nucleation of crystalhzation. If the two blend components have different crystalhzation temperatures, which is likely, the solid particles of the higher melting component will nucleate crystalhzation of the lower melting component. 

The universal compatibilizers are multi-component copolymers, with parts that either are soluble in some components of the blend, chemically bond to chain ends, or have a tendency for hydrogen bonding. Because of the universality, these materials are rather expensive to use. A better chance offers the proprietary compatibilizers-cwm-impact modifiers, formulated for specific types of polymer mixtures, viz. Blendex (polybutadiene-type compatibilizer for styrenics, PVC, TPU, PET), EXL (an acrylic-based additive for PEST), Fusabond (maleated-PO compatibilizer for PO/PET blends), Vector (is SBS-type block copolymer with stabilizers, designed for PO/PS commingled mixtures), and many others. 

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