EPL-0000007_article (PS POE Blend)
Definition of the interparticle distance (
Figure 3.Variation of Charpy impact strength with the POE content [wt%] for PS/POE blends
It can be seen for all blend compositions (Figure5a–5d) that the phase structure of these blends is inho-mogeneous and that the blend composition influ-ences the extent of dispersion of the two phases. Figure5a showed a micrograph of the surface of the 90/10 PS/POE blend. In this blend, PS forms a continuous phase, while the POE forms a discrete phase, indicating immiscible behavior of the blends. The POE phase presents droplets with dif-ferent sizes in the blend and poor adhesion between phases can be observed. Figure5b and 5c depicts the morphology of 80/20 PS/POE blend. It can be seen that the POE phases change partially continu-ous long fibrils and the POE domain size becomes bigger. The micrograph revealed a change in the distribution of the dispersed POE particles, with many of them starting to form aggregate-like elon-gated structures. According to the differences of the structure and shape between Figure5a, 5b and 5c, therefore, when POE content is about 20wt%, the volume fraction of stress volumes has already exceeded the percolation threshold, and the stress volume has overlapped. With the composition of PS/POE increasing to 70/30 (Figure5d), the aggre-gates were more obvious and the fiber diameters were coarser. The percolation phenomenon went on in the blends. However, when POE content increased to 40%, POE phase became completely continuous and PS/POE blends showed the co-con-tinuous structures, as shown in Figure5e.
3.4. The continuity of POE
POE can be well dissolved in n-heptane and PS is not dissolved in n-heptane. Therefore, the continu-ous POE phase in PS/POE blends can be extracted by n-heptane and we can calculate the continuity of POE from Equation3. Figure6 presents the evolu-tion of the continuity of POE with the composition of the PS/POE blends. At 90/10 PS/POE the level
Figure 5.SEM micrographs of PS/POE blends: a) PS/POE=90/10; b) and c) PS/POE=80/20; d) PS/POE=70/30; and
e) PS/POE=60/40
of continuity of POE is nearly zero, consisting with the typical matrix-droplet structure in morphology as shown in F igure5a. As the content of POE increasing, the continuity is also increasing, reflect-ing in morphology (Figure5c and 5d) as the POE particles elongating. When the content of POE is about 40%, the continuity has been beyond 50%, corresponding to the co-continuous morphology structure in Figure5e. The content of 20% POE seems a threshold of continuity increasing dramati-cally, indicating that the percolation phenomenon has already started. This result gives the additional evidence to the morphology observation for the gradual coarsening of fiber diameters up to the phase inversion region.
4. Conclusions
The percolation model has been applied to the study on brittle to ductile transition (BDT) of the PS/POE blends. According to the interparticle dis-tance theory and percolation model, the relations of stress volume (V s), volume fraction (V r) and S/d were achieved. It was predicted that the percolation threshold (V sc) varied from π/6 to 0.65. The curve of Charpy impact strength and content of POE showed a typical brittle to ductile transition phe-nomenon. The 14wt% POE content was a critical point at which the BDT in PS/POE blends was induced and the percolation threshold of PS/POE blends was showed within 0.53~0.64, correspon-ding to the theoretical value. It was well shown the percolation point and phase inversion through mor-phology observations of SEM and TEM and conti-nuity of POE by selective dissolution. References
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