Ductile matrix polymers

The composite systems studied by Takayanagi et al. (1980) used the polyaramides poly(p-phenylene terephthamide), PPDT, or pol.y-p-benzamide (PBA) as the reinforcing component with nylon 6 or nylon 66 as the ductile matrix polymer. Block copolymers of one of the aromatic polyamides with one of the nylon polymers were also evaluated. The blends were prepared by extruding the sulfuric acid solutions of polymers into a... 

The matrix polymers can be divided into brittie or ductile categories, each having specific requirements for achieving toughness (Table 3). Numerous variations are possible. For instance, often mbber particles that vary in both size and kind are desirable for optimum performance. In these cases, the requirements of the mbber phase and the toughening mechanisms are complex. 

Kikuchi Y., Eukui T., Okada T., and Inoue T. Origin of rubber elasticity in thermoplastic elastomers consisting of crossUnked rubber particles and ductile matrix, J. Appl. Polym. Sci., Appl. Polym. Symp., 50, 261, 1992. 

Figure 5.89 Schematic illustration of stress-strain curves for continuous, unidirectional fiber-reinforced composites containing brittle fibers in a ductile matrix. Contributions from fibers and matrix are shown as dashed lines at (a) low fiber volume fractions and (b) high fiber volume fractions. Adapted from N. G. McCrum, C. P. Buckley, and C. B. Bucknall, Principles of Polymer Engineering, 2nd ed., p. 267. Copyright 1997 by Oxford University Press.

Adding to this, there may be alternative polymer combinations - the matrix does not have to be PLLA. In fact, there may even be biodegradable polymer combinations for MFC in which, for example, PLLA is the reinforcing component surrounded by a ductile matrix. Furthermore, additional drawing steps could be added to maximize the orientation of the reinforcing polymer as well as decrease fibril diameters. A very interesting overlap of MFCs and particulate composites provides even more potential for Improvement and scope for future work because, as mentioned before, nanoparticles could be used to modify the reinforcing polymer s thermal properties to enhance creep resistance. 

Fig. 4.36 SEM images of representative fractured, dispersed phase polymer specimens (A) has obvious dispersed phase particles in a ductile matrix that have poor adhesion (B) has much finer dispersed phase particles (C) has particles and holes where particles pulled out and are on the other fracture face - the adhesion is much better in this case compared to (A) (D) has barely distinguishable particles, although over 20% elastomer is present.

Because fibre composites frequently fail in this statistical manner by accumulating local damage, the methods of fracture mechanics are often not too useful. If, on the other hand, a sufficiently long crack in a fibre composite forms, it may propagate. In this case, the fracture toughness Kic of composites with ductile matrix is often smaller than in the pure matrix material because the fibres cause the stress state to be triaxial (see section 3.5.3). This happens in some polymer matrix composites, but mostly in metal matrix composites in which the fracture toughness may be halved compared to the matrix material [62]. 

One of the exciting concepts in the field of blend/composite materials is the reinforcement of flexible-chain polymers by highly rigid rod-like macromolecules with a persistence length Lp > lOnm. The basic principle of these blends, which are known as molecular composites , is dispersion of rigid-chain polymers in a random coil chain, ductile matrix. The basic principles, advantages, and difficulties of molecular reinforcement, and the available data on this problem were summarized... 

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