PP-PS Blend

FIGURE 3.69 SEM micrographs of cross section of (a) 92/2 and (b) 92/8 PP-PS blend fibers spun at 800m/min. (From Wang, Y.H. Xing, Q. Zhu, M.F. Chen, Y.M. Piontech, J. Adler, H.J. International S5miposium on Polymer Physics, DaU, China, June 1-5, 2004, p. 190.) 

PP-PS drawn fibers were prepared from the as-spun fibers in a heated tunnel above the Fg of polypropylene and polystyrene. This implies the two components can undergo deformation readily and thereby influence the fiber structure. 

The diameter of as-spun fiber decreased from around 20-30 p,m to about 15 pm after drawing, while the size of the polystyrene morphology reduced about 10%. This indicates the drawing process did not effectively deform the solid dispersed phase, because it is difficult for the draw stress to transfer from the matrix to the dispersed phase through the solid interface, and the free space for the polystyrene phase deformation is limited. 

---

Bartlett D.W., Paul D.R., and Barlow, J.W. Additive improves properties of scrap PP/PS blends. Mod... 

Inmiscible blends of HDPE or LDPE with PS have been compatibilised with various graft copolymers, such as PS-graft-PE, PS-graft-EPDM or block copolymers such as SBS triblocks, SEBS, PS-block-polybutadiene [53, 54]. The same block copolymers are suitable for PP-PS blends [55]. 

Figure 3.34. Influence of the amount of dispersed phase, mixing time, and T on the amount of nuclei per volume unit in the immiscible PP/PS blend a) after 2x mixing, b) after 3x mixing was set to 190°C (open symbols) or 220°C (filled symbols) r for experiments was 125°C (circles) or 130°C (blocks) [Bartczak etal, 1987],...

Figure 3.35. Influence of the amount of dispersed phase, mixing time and crystallization temperature, T, on the amount primary nuclei active for crystallization at T in a PP/PS blend. All samples have been molten up at 220°C a) 2x mixing, b) 3x mixing T was set to 119X (V), 123°C (A), 125X (o) and 130°C ( ) [Bartczak et al, 1987],...

Figure 3.43. DSC cooling curves (10°C/min) for PP/PS blends difference in the crystallization behavior in blends with PP as a matrix phase and as a dispersed phase [Santana and Muller, 1994],...

The most commonly used compatibilizers for PP/PS blends are also di- or triblock copolymers of styrene and butadiene (SB and SBS) and their hydrogenated products (SEB and SEBS) (160-164). They form dispersed phases in both pure PP and PS. In PP/PS blends, they locate at the interface to connect both PP and PS phase together. Thus, the interfacial tension is decreased and the dispersed phase sizes are greatly decreased. 

Polystyrene-b-poly (ethylene-co-propylene) block copolymers were also used to compatibilize PP/PS blends (165,166). They showed similar effect to block copolymers of styrene and butadiene. Fig. 2.10 indicates that they locate in the blend interface. 

Graft and block copolymers of propylene and styrene have been developed to compatabilize PP/PS blends. Del Giudice et al. (167) and Xu and Lin (168) have synthesized PP-b-PS. Kim et al. (169) and Li et al. (170) first polymerized propylene together with some functional monomers, then polymerized styrene from these monomers units to form polystyrene branches. Diaz et al. (171,172) grafted PP chains onto PS chains based on F-C alkylation reaction when mixing PP/PS blends in the presence of AICI3 catalyst and styrene. All these copolymers help form very... 

An attractive route to compatibilize thermoplastic blends, hke polyolehn-PS, is the Friedel-Crafts ahcylahon (F-C). By this reaction, a hydrocarbon chain can be chemically bonded to the PS benzene ring through an aromatic electrophilic substitution. The graft copolymer formed (polyolefin-g-PS), situated at the interphase, will behave as an in situ compatibilizer. The present work discusses the binary (PE/PS, PP/PS) and ternary (PE/PP/PS) blends compatibihzation by F-C reactions. Detailed smdies were performed on the F-C and side reaction characterization, blend morphological aspects, and final mechanical properties. 

The morphology of PP/PS blends was studied following the emulsification behavior as explained in Section 20.3.1.2. Figure 20.10 shows that the emulsification curve follows a typical trace, which was frequently reported for compatibilization of immiscible blends (28-30). It is clear that after a significant drop in particle size, an equilibrium value is reached at about 0.7% AICI3. This value has been taken as the cmc condition. It has to be remarked that the particle size decreases to one third of its initial value, reaching an equilibrium diameter of about 0.5 pm. Also, the particle size homogeneity increases with the catalyst content. It is shown by the decrease in error bars in Fig. 20.10. From these results, it is foreseen that the copolymer formed by the F-C reaction behaves as an efficient in situ compatibi-lizer for the PP/PS blend. 

Figure 20.11 SEM micrographs from PP/PS blends, (a) PB, (b) RB0.3, (c) RB0.7, and (d) RBl.O. (Erom Reference 41 with permission from John Wiley Sons, Inc.)...

Figure 20.12 Variation of elongation at break and yield strength with decatalyst content for PP/PS blends under tensile test. (From Reference 42 with permission from Elsevier.)...

Figure 20.15 shows b of PE/PP/PS blends as a function of catalyst concentration. The TPB reveals a fragile behavior, with only 4% of b. To assess the effect of PP in these TPBs, and taking into account their relative component amounts, this ternary blend can be considered as a binary 80/20 PE/PS blend with a small amount of PP. As was shown before (Fig. 20.7), the PE/PS physical blend exhibits Cb of about 120%, much greater than the value for the ternary blend. It is clear that the low ductility of PE/PP/PS blend must be related to the PE-PP interphase. 

In order to improve the compatibility of PE-PP interphase the F-C reaction was applied to PE-b-PP/PP/PS physical blend, where the PP-PE interphase is already compatibilized by a block copolymer EPR (PE-b-PP). Figure 20.16 shows fractured surfaces of these modified blends before and after the F-C reaction. It has to be noted that in these PE-b-PP/PP/PS blends the continuous phase is PP. In Fig. 20.16a, for the TPB, the PS particles appear unbounded from the matrix and the fracture mode is interparticle indicating, as was expected, a poor adhesion at the PP-PS interphase. 

The results of ductility are presented in Fig. 20.17 as a function of catalyst concentration, of PE-b-PP/PP/PS reactive blends shows a maximum for 0.5% AICI3, which is three times greater than the value for the corresponding TPB, and then a drop at higher catalyst concentrations. This drop can be assigned to PP chain scission in the same way as above for the PP/PS blends (Fig. 20.12). 

The compatibUization of binary PE/PS and PP/PS blends by the E-C reaction was shown to be simple and effective. This route offers a proper combination of one-step and solvent-free process that uses a low amount of low cost reactants. 

An interesting publication by Martini et al. (2006) describes a method for separating a reactively compatibilized PP/PS blend into its individual polymeric components for analysis. The method involved use of high-temperature, high-pressure, near-critical... 

---