Rubber Particle Morphology

Adams ME, Buckley DJ, Colbom RE, England WP, Schissel DN (1993) Acrylonitrile-Butadiene-Styrene Polymers. Rapra Review Reports, Vol. 6, No. 10. 

Bovey FA, KolthoffIM, Medalia IM, Meehan EJ (1955) Emulsion Polymerization, Interscience, New York. 

Burkhardt F, Majer H, Kuhn W (1960) Helv. Chim. Acta 43, 1192. 

Llauro MF (1970) Thesis, Ecole Superieure de Chimie, Mulhouse. 

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Additional information on elastomer and SAN microstmcture is provided by C-nmr analysis (100). Rubber particle composition may be inferred from glass-transition data provided by thermal or mechanochemical analysis. Rubber particle morphology as obtained by transmission or scanning electron microscopy (101) is indicative of the ABS manufacturing process (77). (See Figs. 1 and 2.)... 

Rubber particle cavitation, 20 353 Rubber particles, morphology of,... 

In HIPS a wide variety of rubber particle morphology is possible. Echte et al. summarized this in an excellent review (see Figure 14.5) [41]. The key to these different structures is the composition of the styrene-butadiene block rubber, which is an emulsifier for the polystyrene-polybutadiene system. Additional grafting can generate a shift from one structure to another. 

In the case of mass ABS, the variety of rubber particle morphology is less diverse. Typical examples of morphology are shown in Figure 14.6. If polybutadiene rubber is used (linear or star), cellular particles are obtained with SAN occlusions. In the case of styrene-butadiene block rubber (typically 30% styrene) also cellular particles are obtained but besides the SAN occlusions, polystyrene domains are clearly visible in the particles. To be able to make the other morphologies that are possible in HIPS, the interfacial tension has to be manipulated. Controlling the grafting reaction is a way to achieve this but the possibilities are limited with the tools (mainly initiator) that are currently available. 

Figure 14.5 Possible rubber particle morphology in HIPS...

Figure 14.6 Rubber particle morphology in mass ABS as function of rubber type...

Morphological examination of the reaction products also provided evidence that, with EPDM elastomers, the grafted and crosslinked rubber remained dispersed in the matrix as particles with an average diameter of 2-5(i. The structure remained unaltered, even after mechanical actions such as those required for transformation into manufactured articles. On the other hand, with EP rubbers, particle morphology was markedly altered under the same transformation conditions. 

The structure of ABS is similar to that of HIPS but with a SAN matrix instead of the PSt matrix in HIPS. PB grafted with SAN acts as a compatibilizer between the rubber particles and the SAN matrix. The rubber particle morphology in ABS can be similar to that in HIPS, with salami-type particles, but ABS particles can also be of the core-shell type, with a core of solid PB and a shell of graft copolymer, especially if the ABS is produced by the emulsion process [34]. In addition to craze formation, an important fracture mechanism in ABS polymers is shear yielding, which leads to tougher materials [46]. 

Rubber particle morphology has also been shown by Keskkula and Traylor [130] who removed the rubber from impact polystyrene (IPS) and ABS polymers and examined their surface topography... 

At high conversions, the solvation of the rubber and the gel effect (Trommsdorf effect) cause an increase in the molecular weight of the grafted polystyrene. The viscosity change with styrene conversion in the manufacture of HIPS is shown in Fig. 10 with typical rubber particle morphology [34]. 

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