PS/rubber blends

Figures Storage modulus of PS/Rubber blends for various values of hh micrograph for the 90/10 PS/Rubber blend. ...

Experimental data for 10/90 and 90/10 PS/PMMA blends clearty demonstrate that the increase in blend s elasticity and the longer relaxation times observed in the terminal zone are due to the deformability of the suspended droplets. On the other hand, results obtained for PMMA/Rubber and PS/Rubber blends illustrate limitations of the Palierne model. For these blends, the model does not even qualitatively predict the secondary plateau arising at low frequencies for high rubber contents. The model does not account for particle-particle interactions. For volume fraction of rubber larger than 15 %, the particles form a network-type structure. For rubber particles concentration of 15 % and larger the elasticity of the network structure is satisfactorily described by the percolation theory. For PS/Rubber blends, a network is observed at a particles concentration of 10%. This is not predicted by the percolation theory. 

Blend of (1) and (2) type categories mostly include the modification of engineering thermoplastics with another thermoplastic or rubber. PS-EPDM blends using a low-molecular weight compound (catalyst) Lewis acid have been developed [126]. Plastic-plastic blends, alloys of industrial importance, thermoplastic elastomers made by dynamic vulcanization, and rubber-rubber blends are produced by this method. 

Figure 6 Dependence of Izod impact strength on the DMAE concentration in 80 20 PS-bromo butyl rubber blends. Source Ref. 53.

The formation of the polyalloy results in improvement in the performance of the blends. This system is similar to the production of high-impact polystyrene (HIPS) where a rubber is dissolved in styrene monomer and then polymerized in the usual way. Even though the impact strength of the compatibilized PS-PE blend was higher than that of PS, it was much less than that of HIPS. In another study. Van Ballegooie and [55] have confirmed... 

The important factors that affect the rubber toughening are (1) interfacial adhesion, (2) nature of the matrix, (3) concentration of the rubber phase, and (4) shape and size of the rubber particles. In the PS-XNBR blend containing OPS, due to the reaction between oxazoline groups of OPS and carboxylic groups of XNBR, the interfacial adhesion increases and as a result, the minor rubber phase becomes more dispersed. The immiscible blend needs an optimum interfacial adhesion and particle size for maximum impact property. In PS-XNBR, a very small concentration of OPS provides this optimum interfacial adhesion and particle size. The interfacial adhesion beyond this point does not necessarily result in further toughening. 

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). 

As mentioned extensively, PPE is not mainly used as such, but in polymeric blends and copolymers to faciUtate the fabrication. Some of these copolymers act also as impact modifiers for example, block copolymers built from styrene, ethylene, butylene, and propylene. Naturally, the impact can be improved by using high impact poly(styrene) (HIPS) instead of ordinary PS in blends. Other impact modifiers include rubbery materials, such as poly(octenylene), and ethylene propylene diene monomer rubber. 

In the same manner, blends containing (100% to 90%) polystyrene and (0% to 10%) styrene-butadiene rubber (SBR) exhibited improved impact properties after gamma irradiation at a dose of 100 kGy. FTIR provided evidence that irradiation produced a radical in the benzene ring of PS that could react with the double bond of polybutadiene producing a metasubstituted benzene (Figure 9.5). Hence, this chemical link between the two polymers gave rise to the increase in Izod impact strength parhcularly for 100 kGy y-irradiated 90/10 PS-SBR blend. 

Starting in the 1980 s, a number of governmental recycling policies created a demand for recycled thermoplastic olefin (TPO) for post-consumer applications. Since polystyrenes and TPOs are not miscible, polystyrene-TPO diblock copolymers are being developed to reduce the interfacial tension in PS/TPO blends. TPOs are tough materials with low stififiiess properties. If blended with polystyrene, they improve the toughness of polystyrenes. If compatibilized, the properties of PS/TPO should be similar to styrene-hydrogenated polybutadiene rubbers. 

Another commercial application is in PS foams, where it is used as a cell-nucleating agent. In rubber blends, talc is used as an antitack agent to prevent newly formed goods from sticking together. In some specialty elastomers, it reduces air and fluid permeability [5]. 

Phase separation studies Song and co-workers [348] used microthermal analysis to study the phase separation process in a 50 50 (by weight) PS/polyvinylmethylether blend and nitrile rubber. Microthermal analysis will image the composition in the near-surface region or surface region of multi-component materials if the resolution is high enough. 

Figure 2. Top topography (left top), adhesion (right top), and elastic modulus (left bottom) images of the PS/PB blend (15 x 15 pm). Force-distance curves are shown for rubber and glassy phases (right bottom). All mappings are done with the 64 x 64 pixel lateral resolution. Two histograms (bottom) of elastic modulus distribution and adhesive forces show two distinctive peaks for rubber and glassy phases.

The development of compormds and blends of polymers dates back almost two centmies to the early rubber and plastics industry, when rubber was mixed with substances ranging from pitch [3] to gutta percha [4]. As each new plastic has been developed, its blends with previously existing materials have been explored. Thus, synthetic rubbers, in the early period of the plastics industry, were mixed into natural rubber and formd to produce superior performance in tire components. Polystyrene (PS) was blended with natiual and synthetic rubbers after its commercialization, and this led to high impact polystyrenes (HIPS), which now hold a... 

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