Page 30 - Handbook of Adhesion Promoters

2.7 Crystalline properties 23

Figure 2.20. Schematic illustration of the interphase formation between PP and GF. [Adapted, by permission,
from Luo, G; Li, W; Liang, W; Liu, G; Ma, Y; Niu, Y; Li, G, Compos. Part B: Eng., 111, 190-9, 2017.]
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transfer between the glass fiber and the matrix. A schematic mechanism including
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molecular interaction and polymer chain motion is illustrated in Figure 2.20. When poly-
propylene is melted, the compatibilizer (maleic anhydride) chains move to the surface of
glass fiber because they have shorter relaxation time and diffuse much faster than the lon-
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ger chains. The diffusion of the shorter chains also drives the movement of the longer
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chains. The nucleating agent increases
crystallization and contributes to the forma-
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tion of transcrystalline layer. The diffu-
sivity of polymer chains and the interaction
between matrix and glass fiber are key fac-
tors for the formation of the interface,
which has dominating effects on the
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mechanical properties of the composite.
Polyamide-66, an aliphatic semicrys-
talline polyamide, was reinforced with E-
glass fibers and high-modulus carbon
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fibers. An interphase was composed of
Figure 2.21. The transcrystalline interphase in a high- transcrystallinity developed due to the high
modulus carbon-fiber-reinforced polyamide-66 com- nucleation density of the polymer on the
posite (unsized carbon fiber embedded in a polyamide- fiber surface (Figure 2.21). Composites
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66 matrix melt-crystallized at 235°C). [Adapted, by per-
mission, from Clark, RL; Kander, RG; Sauer, BB, Com- containing transcrystallinity have higher
pos. Part A: Appl. Sci. Manufact., 30, 1, 27-36, 1999.] interfacial shear strength values than those
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that do not contain this interphase.
Short glass fiber was coated with electrically conducting polyaniline by in situ chem-
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ical polymerization. The coated fiber was melt-compounded with isotactic polypropyl-
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ene grafted with maleic anhydride as an adhesion promoter. Scanning electron
microscopy showed the improvement in wetting and dispersion of the fibers when the