Blends interfaces

The efficiency of the copolymers, either block or graft, acting as the compatibilizer depends on the structure of the copolymers. One of the primary requirements to get maximum efficiency is that the copolymer should be located, preferentially at the blend interface (Figs. 2a, b, and c). There are three possible conformations, as shown in the figure. Many researchers [10-12] found that the actual conformation is neither fully extended nor flat (Fig. 2c). A portion of the copolymers penetrates into the corresponding homopolymer and the rest re-... 

Figure 2 Conformation of copolymer at the blend interface (a) completely extended, (b) completely flat, and (c) neither completely extended nor completely flat.

Cho D et al. (2000) Segregation dynamics of block copolymers to immiscible polymer blend interfaces. Macromolecules 33( 14) 5245—5251... 

In the completed study, exact amounts of the powdered materials were sprinkled onto the wood-resin surface. Analysis of the test specimens revealed that under the press times and temperatures used the phase transition of the polystyrene side chains on the graft polymer was not efficient. Further, in order for the graft polymer to be effective as a interfacial agent, it must locate preferentially at the blend interface (SI), The research team hopes to develop procedures in the future to allow the polystyrene and graft polymers to be dissolved in an organic solvent for application to the wood resin surface. This should allow the graft polymer to locate at the blend interface and improve bonding efficiency. 

Polystyrene-b-poly (ethylene-co-propylene) block copolymers were also used to compatibilize PP/PS blends (165,166). They showed similar effect to block copolymers of styrene and butadiene. Fig. 2.10 indicates that they locate in the blend interface. 

The crystallization behavior and kinetics under isothermal conditions of iPP/SBH and HDPE/SBH blends, compatibilized with PP-g-SBH and PE-g-SBH copolymers, respectively, have been investigated (71). It has been established that the LCP dispersed phase in the blends plays a nucleation role for the polyolefin matrix crystallization. This effect is more pronounced in the polypropylene matrix than in the polyethylene matrix, due to the lower crystallization rate of the former. The addition of PP-g-SBH copolymers (2.5-10 wt%) to 90/10 and 80/20 iPP/SBH blends provokes a drastic increase of the overall crystallization rate of the iPP matrix and of the degree of crystallinity. Table 17.4 collects the isothermal crystallization parameters for uncompatibilized and compatibilized iPP/SBH blends (71). On the contrary, the addition of PE-g-SBH copolymers (COP or COP 120) (2.5-8 wt%) to 80/20 HDPE/SBH blends almost does not change or only slightly decreases the PE overall crystallization rate (71). This is due to some difference in the compatibilization mechanism and efficiency of both types of graft copolymers (PP-g-SBH and PE-g-SBH). The two polyolefin-g-SBH copolymers migrate to blend interfaces and... 

To improve compatibilization, it is required that the copolymer preferentially locates at the blend interface. 

Liao et al. [261] reported biodegradable nanocomposites prepared from poly(lactic acid) (PLA) or acrylic acid grafted poly(lactic acid) (PLA-g-AA), titanium tetraisopropylate, and starch. Arroyo et al. [262] reported that thermoplastic starch (TPS) and polylactic acid (PLA) were compounded with natural montmorillonite (MMT). The TPS can intercalate the clay structure and that the clay was preferentially located in the TPS phase or at the blend interface. This led to an improvement in tensile modulus and strength, but a reduction in fracture toughness. 

It is imperative to mention that component polymer surfaces and interfaces play a major role in the properties and applications of blends such as in biocompatibility, switching, or adaptive properties. Whether it is an everyday plastic part or parts in automotives or in an airplane, not only the development of interfacial morphology but also the analyses of blends interfaces are equally important. The compatibilizing effect is primarily due to the interfacial activity of the constituent partners. This in turn raises the question of what are the effects of the molecular weight, concentration, temperature, and molecular architecture of the... 

PBT/HDPE PBT 1 to 90 wt% Nanofil 919 PBT phase and interface based on blend composition The MMT particles located at the blend interface reduce the interfacial tension between blend components. The addition of organoclay also increases the thermal stabilization of blend morphology Hong et al. 2006a, b... 

This chapter discusses the role of nanofillers as a compatibilizer for immiscible blends when located at the blend interface or as an aid to reduce coalescence of dispersed particles when located in the continuous phase of blends. The presence of... 

Fig. 19.10 Schematic illustration of interfacial graft copolymers in polyamide/reactive rubber blends (Note Balanced end group PA (1-amine/chain) forms a mono-graft copolymer. A diamine terminated PA forms di-graft copolymers. The latter can lead to entanglement at interface. Both graft copolymers stabilize and strengthen the blend interface)...

M. Sprenger, S. Walheim, A. Budkowski, U. Steiner, Hierarchic structure formation in binary and ternary polymer blends. Interface Science 11 (2(X)3) 225-235. 

One approach to obtain the energy to break single chains involves placing them across a polymer blend interface. Polymer interfaces between two polymers, however well annealed, are often weak see Chapter 12. One way to strengthen an interface is to put small quantities of block copolymers at the interface. Usually the two blocks are identical to or at least soluble in their... 

Helfand and Tagami (10) derived thermodynamically based equations for the interfacial tension at a polymer blend interface. 

Figure 12.18 The density profile of a polymer blend interface goes through a minimum if the polymers are immiscible. The quantity is a function of the compressibility.

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. 

There are specific structural and spatial problems in whieh Raman spectroscopy plays a dominant and important role based on higher sensitivity (due to resonance enhancement) and higher spatial resolution than FTIR. Specifically, micro-Raman spectroscopy has been applied in the analysis of (glass) fibres and their surface treatments, fibre composites, multilayer plastic films, foils and coatings, polymer blends, interfaces in eomposites, contaminant and paints/pigments [488]. 

Hu et al. [48] studied the addition of PS-h-PDMS diblock copolymer to the PS/PDMS blend. A maximum interfacial tension reduction of 82% was achieved at a critical concentration of 0.002% diblock added to the PDMS phase. At a fixed PS homopolymer molecular weight, the reduction in interfacial tension increases with increasing the molecular weight of PDMS homopolymer. Moreover, the degree of interfacial tension reduction was found to depend on the homopolymer the diblock is mixed with when the copolymer was mixed into the PS phase, the interfacial tension reduction was much less than that when the copolymer was blended into the PDMS phase. This behavior suggested that the polymer blend interface may act as a kinetic trap that limits the attainment of global equilibrium in these systems. 

Adedeji A, Lyu S, Macosco CW (2001) Block copolymers in homopolymer blends interface vs micelles. Macromolecules 34 8663-8668... 

The concept of co-continuous polymer blends with carbon black preferentially located in one of the continuous polymer phases or at the polymer-blend interface has been studied for more than a decade with an aim to reduce the percolation threshold. Examples of this kind are the work by Geuskens et al. in as early as 1987 [31], which shows that for the same carbon loading, the resistivity of the co-continuous polymer/rubber blends is several orders of magnitude smaller than that of the single polymer/carbon black composites. Recent works on polymer/elastomer combinations [32,33] and on polymer/polymer systems [34- 1] have also shown that the... 

This chapter covers various aspects of reactive polymer blending and compati-bilization starting with a comparison between physical and reactive blending. Issues related to chemical reactions encountered in reactive blending are considered including reaction kinetics. The inter-relation between the reaction events and morphology development is discussed. The last part of this chapter deals with the characterization of the blend interface including measurement of interfacial tension and the interface thickness. 

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