Polymer-filler interphase

The model for a filled system is different. The filler is, as before, represented by a cube with side a. The cube is coated with a polymer film of thickness d it is assumed that d is independent of the filler concentration. The filler modulus is much higher than that of the d-thick coat. A third layer of thickness c overlies the previous one and simulates the polymeric matrix. The characteristics of the layers d and c are prescribed as before, and the calculation is carried out in two steps at first, the characteristics of the filler (a) - interphase (d) system are calculated then this system is treated as an integral whole and, again, as part of the two component system (filler + interphase) — matrix. From geometric... 

Jancar J (1998) Mechanical properhes of thermoplastic composites with engineered interphases in Polypropylene Handbook , H. Karian Ed.,M. Dekker, New York 1998 Tong SN, Chen ML (199l) Analysis of transihon temperatnres in polymer-filler systems. In Mitchell J (ed) Applied polymer analysis and characterization, vol II. Hanser, Munich, chap 5, p 329... 

This work investigates the behaviour of elastomeric chains (polybutadienes of identical molecular weight but different microstructures) in the close vicinity of carbon black surfaces in order to attain a better understanding of the structure and properties of interphases. Elastomer-filler interactions are assessed through the study of the thermal properties and NMR relaxation characteristics of the corresponding materials. MAS solid-state NMR provides information on the effect exerted by polymer-filler interactions on the mobility of the various constitutive species of the macromolecular backbone. 

With emerging nanoscale fillers where the particle sizes are in the l(X)s of nanometers, the specific snrface area of filler particles can be orders of magnitude larger than that for conventional fillers. As fractional volume of matrix-filler interphase determines the level of reinforcement achieved in the composite, nanofillers can achieve superior properties at relatively low volume fractions, provided they are adequately dispersed in the base polymer. 

For modification of polymer/filler surfaces to improve properties like adhesion, fluid absorbancy and wetting properties "exposure of the surfaces to proper electrical glow discharge method is usually and succesfully employed. This technique can also be employed in polymer composite systems to modify interfaces and interphases to improve properties. 

The results of research conducted dining the last decade confirm the nucleating character of UgnoceUulosic filler in polymeric composites. Natural fibers added to polymeric composites are the active source of creating a nucleus of crystallization. The addition of the filler reduces the interphase energy semicrystalline polymer-filler and cOTisequently makes the crystallization process easier. A foreign surface as the filler structure, by its presence, makes it possible. 

Observations of polypropylene crystallization by polarized light microscopy helped to understand phenomena on interphase of polymer-filler. When analyzing the influence of the filler, many researchers noted transciystallization of the polypropylene as a result of high enough nucleation density rai the filler s surface and also in the presence polypropylene fibers. The addition of both mineral substances and natural composites containing lignocellulosic material can induce formation of TCL. 

Figure 7.16 shows interface formation with painted substrate. The mechanism of organization was discussed in the previous section. The alignment in the polymer layer plays a large part in polymer-filler interaction in the adjacent layers. The way in which polymer is configured on the substrate surface determines if polymer chains are readily available for interaction with filler. This example shows that it is not only the filler and the matrix which play a role in the interphase organization. 

Many packaging materials and containers are produced by the combination of more than one plastic material. Common configurations include multilayer structures, two-phase polymer blends, and plastics with fillers. While multilayer structures offer the lowest permeability for a given composition, the performance of two phase-blends depends on which polymer provides the continuous phase. The effectiveness of a flUer to enhance or diminish the barrier value of a polymer depends on the adhesivity and wetting interphase characteristics of the polymer-filler pair. 

Rheological methods of measuring the interphase thickness have become very popular in science [50, 62-71]. Usually they use the viscosity versus concentration relationships in the form proposed by Einstein for the purpose [62-66], The factor K0 in Einstein s equation typical of particles of a given shape is evaluated from measurements of dispersion of the filler in question in a low-molecular liquid [61, 62], e.g., in transformer oil [61], Then the viscosity of a suspension of the same filler in a polymer melt or solution is determined, the value of Keff is obtained, and the adsorbed layer thickness is calculated by this formula [61,63,64] ... 

Thus a strong bond is not always desirable. We can see this from Table 7 and 8. The authors of [100] interpreted their experimental data as follows the rigidity of specimens increases with increasing PVC-filler interaction as a result the rate of relaxation of stresses arising at interphases in the course of deformation decreases. The overstressed states at the interphases may, in the authors opinion, promote separation of the polymer from the filler surface. That is, it is more desirable that the matrix-filler bond is not rigid but labile. 

The important yet unexpected result is that in NR-s-SBR (solution) blends, carbon black preferably locates in the interphase, especially when the rubber-filler interaction is similar for both polymers. In this case, the carbon black volume fraction is 0.6 for the interphase, 0.24 for s-SBR phase, and only 0.09 in the NR phase. The higher amount in SBR phase could be due to the presence of aromatic structure both in the black and the rubber. Further, carbon black is less compatible with NR-cE-1,4 BR blend than NR-s-SBR blend because of the crystallization tendency of the former blend. There is a preferential partition of carbon black in favor of cis-1,4 BR, a significant lower partition coefficient compared to NR-s-SBR. Further, it was observed that the partition coefficient decreases with increased filler loading. In the EPDM-BR blend, the partition coefficient is as large as 3 in favor of BR. 

The characteristics of particulate filled polymers are determined by the properties of their components, composition, structure and interactions [2]. These four factors are equally important and their effects are interconnected. The specific surface area of the filler, for example, determines the size of the contact surface between the filler and the polymer, thus the amount of the interphase formed. Surface energetics influence structure, and also the effect of composition on properties, as well as the mode of deformation. A relevant discussion of adhesion and interaction in particulate filled polymers cannot be carried out without defining the role of all factors which influence the properties of the composite and the interrelation among them. 

This chapter focuses its attention on the discussion of the most relevant questions of interfacial adhesion and its modification in particulate filled polymers. However, because of the reasons mentioned in the previous paragraph, the four factors determining the properties of particulate filled polymers will be discussed in the first section. Interactions can be divided into two groups, parti-cle/particle and matrix/filler interactions. The first is often neglected although it may determine the properties of the composite and often the only reason for surface modification is to hinder its occurrence. Similarly important, but a very contradictory question is the formation and properties of the interphase a separate section will address this question. The importance of interfacial adhesion... 

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