Dispersion, rubber particles

Id. Thus, it is expected that in the modified PRP-EVA blend, probably due to interface modification by reactive processing, a transesterification between the pendant MAH group in MAH-PP, and acetate groups in the EVA elastomer, as predicted in reaction Scheme 1, the dispersed rubber particles become more efficient in craze initiation. 

In order to obtain a finely sized dispersed phase in the PET matrix, the use of reactive compatibilization has been found to be important. Small dispersed rubber particles and a small interparticle distance are necessary to induce high toughness. For effective rubber toughening of PET, it is important that the rubber domains be less than 3 im in diameter (and preferably less than 1 xm) and that the interparticle distance be between 50-300 nm. 

Phase separation through NG mechanism cannot be observed for polymer-polymer blend systems that show interfacial tension lying in the range 0.5-11 mN/m. In addition, they predicted that a secondary phase separation could take place inside dispersed rubber particles in the case when the average composition of dispersed domains lies in the unstable region at the end of the phase separation [2], They were not able to observe a phase separation inside dispersed domains with TEM micrographs however, they concluded that there are two phases inside the dispersed domains by the fact that the glass transition temperature of the rubber-... 

The partial agglomeration technique has been described in detail elsewhere (15). The colloidal stability of the dispersed polymer particles is not destroyed in the partial agglomeration process. The agglomeration step involves treatment of the dispersed rubber particles at a stage where they have no outer protective layer of non-rubbery, i.e., rigid polymer to prevent the massive or complete coalescence of the rubber particles (13). 

In a rubber modified styrenic resin the rubber particles are dispersed. The particle size of the dispersed rubber particles has a large influence on the quality of the products. The smaller the particle size of the dispersed rubber particles, the better the gloss of molded articles that is obtained therefrom. 

Processing Stability. As with elastomers or other rubber modified polymers, the presence of double bonds in the elastomeric phase increases sensitivity to thermal oxidation either during processing or end use. Antioxidants are generally added at the compounding step to ensure retention of physical properties. Physical effects can also have marked effects on mechanical properties due to orientation, molded-in stress, and the agglomeration of dispersed rubber particles under very severe conditions. Proper drying conditions are essential to prevent... 

Blends of polymers are manufactured and applied at an increasing scale. Only in exceptional cases are polymers soluble in each other and can form a homogeneous blend (an example PPE + PS, a blend known as Noryl ). In most cases blends are, therefore, dispersions. Rubber particles are dispersed in brittle polymers to improve their impact strength (toughened PS and PP, ABS etc.), but also hard polymers are combined to reach a favourable compromise between properties (and price). 

The aim of any grafting is to increase the rubber efficiency, i.e. the ratio between the gel content and the rubber content, and to enable the rubber particles to bond to the polystyrene phase in order to ensure the transmission of external forces from the energy-elastic phase to the entropy-elastic phase. The graft polymer acts as emulsifier and stabilizes the dispersed rubber particles in the two-phase system. 

In rubber-modified polymers like high impact polystyrene or acrylonitrile-butadiene-styrene (ABS) resins, the toughening effect of the dispersed rubber particles appears only in the presence of block or graft copolymers. These copolymers regulate the particle size of the rubber dispersion and achieve adhesion of the two phases. Hence, graft copolymers are of practical importance in polymer alloys. 

In heterophase polymeric materials such as rubber modified polystyrene or acrylonitrile-butadiene-styrene (ABS) resins, outstanding mechanical properties can be obtained only by regulating the dispersed rubber particle size and by achieving adhesion between the rubber and the resin phase. This can usually be achieved by adding block or graft copolymers, or by their formation in situ, as in industry. 

A study of various PS-PMM polyblends in which the dispersed PS phase was selectively plasticized demonstrated that the impact resistance, R, varies in the same way as the occupation density, D (see Table III). Since the dispersed rubber particles are practically spherical, a simple relationship for R and D is ... 

Martuscelli [1984] and Bartczak et al. [1984] have calculated the energies dissipated by growing PP sphemUtes in a blend with dispersed rubber particles for all the above mentioned phenomena that may disturb the spherulite growth (Table 3.20). It can be concluded that mainly rejection of small... 

Figure 11.121. Formation of flocculated and tubular structures above critical concentration fnjm physically dispersed rubber particles dispersed means completely surrounded by a monomolecular matrix polymer layer (dashed line). [Reproduced from ref. 89 with kind permission of Huthig and Wepf publishers,]...

Vf is the relative volume of the rubber phase, % C is the mean size of dispersed rubber particles X is the polybutadiene content (6+ 2%) X2 is the polymerization temperature at the first stage (120+ lO C) X3 is the polymerization extent after the first stage completion (50+ 15%) X4 is the concentration of n-lauryl mercaptan... 

HIPS and ABS are heterogeneous materials containing dispersed rubber particles in continuous vitreous matrixes. Figure 4.4(a) and (b) exhibit the typical salami morphologies of HIPS and ABS when produced in bulk processes with PBD rubber. These products are nontransparent, due to their relatively large particle sizes. Figure 4.5 compares the stress-strain curves of PS, poly(styrene-co-acrylonitrile) (SAN), HIPS and ABS. The area under... 

On melt mixing of the thermoplastic and rubbery polymers under high stress, the less viscous thermoplastic tends to become the continuous phase with the more viscous rubber dispersed in it. The dispersed rubber particles are then vulcanized and form a three-dimensional polymer network within each particle they cannot recombine or agglomerate into larger particles. The most common polymer system in TPVs is PP/EPDM rubber, however, a number of other polymer systems have been used commercially. These include NBR/PP, IIR/PP, and NR/PP. 

In the absence of a rubber modifier, the shear deformation would be confined to local regions where the stress is very high and the structural features allow slip. This would not dissipate much energy. When an impact modifier is used, yielding becomes much more widespread and is accompanied by the formation of small cavities in the dispersed rubber particles, provided that they are small enough. This cavitation can occur either before or after the polymer yields. Shear yielding sometimes occms preferentially in certain zones of a specimen or component, rather than uniformly. 

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