Polystyrene with rubber

Much better differentiation of plastic waste from general refuse and segregation of the recovered plastic materials according to resin type is obtained by presorting of the waste at the householder level. As already discussed in connection with the properties of mixtures of PVC and poly(vinyl acetate), or polystyrene with rubber, crude mixtures of two or more polymers usually result in degraded properties relative to those achievable from any of the more rigorously segregated component materials. For this reason, for... 

As SR decreases, 1 must be decreased too (and thereby also the inlet pressure loss/total pressure ratio is decreased). This is what is really observed when dispersed fillers are added to polymer [182,190,193,194], The rubber phase in heat resistant polystyrene behaves much like a dispersed filler it also diminishes the inlet correction [195]. For polystyrene with different fillers the following relationship was found to be valid [196] ... 

Block copolymers of polystyrene with rubbery polymers are made by polymerizing styrene in the presence of an unsaturated rubber such as 1,4 polybutadiene or polystyrene co-butadiene. Some of the growing polystyrene chains incorporate vinyl groups from the rubbers to create block copolymers of the type shown in Fig. 21.4. The combination of incompatible hard polystyrene blocks and soft rubber blocks creates a material in which the different molecular blocks segregate into discrete phases. The chemical composition and lengths of the block controls the phase morphology. When polystyrene dominates, the rubber particles form... 

We most often encounter polystyrene in one of three forms, each of which displays characteristic properties. In its pure solid state, polystyrene is a hard, brittle material. When toughened with rubber particles, it can absorb significant mechanical energy prior to failure. Lastly, in its foamed state, it is versatile, light weight thermal insulator. 

One of the principal weaknesses of pure polystyrene is its low impact resistance. To counteract this problem, we toughen it with various types of rubber. This is most effective when a portion of the rubber is chemically grafted to the polystyrene. The rubber forms small inclusions within a matrix of polystyrene. The presence of rubber also improves polystyrene s extensibility, ductility, and resistance to environmental stress cracking. 

One of the most important outcomes of these efforts was impact-resistant polystyrene, which was obtained by modifying the brittle material with rubber. The first products were blends of polystyrene and synthetic rubbers recourse was soon made, however, to a principle that Ostromislensky (29) had suggested as early as 1927 styrene monomer was polymerized in the presence of rubber dissolved in it. 

Transparent block copolymers of styrene and butadiene, having polystyrene character (Phillips). Weather-resistant, impact-resistant polystyrene with EPDM rubber (Mitsui Toatsu, Hoechst). 

Berlin and coworkers (5,56) desired to obtain a material with an increased mechanical strength. They carried out a plasticization of bulk ami emulsion polystyrene molecular weight 80000 and 200000 respectively at 150-160° C, with polyisobutylene, butyl rubber, polychloroprene, polybutadiene, styrene rubber (SKS-30) and nitrile rubber (SKN 18 and SKN 40). The best results were obtained with the blends polystyrene-styrene rubber and polystyrene-nitrile rubber. An increase of rubber content above 20-25% was not useful, as the strength properties were lowered. An increase in the content of the polar comonomer, acrylonitrile, prevents the reaction with polystyrene and decreases the probability of macroradical combination. This feature lowers the strength, see Fig. 14. It was also observed that certain dyes acts as macroradical acceptors, due to the mobile atoms of hydrogen of halogens in the dye, AX ... 

Cross-links limit the mobility of macromolecular chains, and thus give rise to an increase in Tg. With a very low concentration of cross-links this effect is hardly detectable. Experiments with the system polystyrene + divinyl benzene showed that at a concentration of 0.4 % of DVB and higher a detectable increase of Tg occurred. With rubbers, vulcanized with sulphur, the detection limit for an increase of Tg appeared to be at 1 to 2 % of sulphur, so that for a technically vulcanized rubber the level of Tg is hardly influenced by the vulcanization process. 

Poly(phenylene sulphide) Polypropylene Polystyrene toughened with rubber Styrene-acrylonitrile... 

Polystyrene may be extruded to produce film and other transparent articles with high gloss finish but in commercial practice the formulations toughened with rubber are used to a greater extent (extruded transparent film is toughened by stretching and orientation while it is still hot from the die). 

PVC can be blended with numerous other polymers to give it better processability and impact resistance. For the manufacture of food contact materials the following polymerizates and/or polymer mixtures from polymers manufactured from the above mentioned starting materials can be used Chlorinated polyolefins blends of styrene and graft copolymers and mixtures of polystyrene with polymerisate blends butadiene-acrylonitrile-copolymer blends (hard rubber) blends of ethylene and propylene, butylene, vinyl ester, and unsaturated aliphatic acids as well as salts and esters plasticizerfrec blends of methacrylic acid esters and acrylic acid esters with monofunctional saturated alcohols (Ci-C18) as well as blends of the esters of methacrylic acid butadiene and styrene as well as polymer blends of acrylic acid butyl ester and vinylpyrrolidone polyurethane manufactured from 1,6-hexamethylene diisocyanate, 1.4-butandiol and aliphatic polyesters from adipic acid and glycols. 

From the pure component data it is possible to calculate the expected a behavior as a function of temperature for a blend of the two polymers using the equation ah = sas + < rar, where the subscripts b, s, and r refer to the blend, polystyrene, and rubber, respectively, and the < s represent the volume fractions of the two components in the blend. The calculated curves (Figure 7) are reasonably smooth and exhibit only the polystyrene Tg. The calculated curve for TR-41-2445 is in good agreement with that found experimentally for the solution-blended material. The only significant difference is that below the polystyrene Tg the calculated values of a are about 0.5 X 10 4 deg1 lower than the experimentally determined data points. This may be attributable to the density differences in the samples, particularly for the blended material where density variations and void formation can occur at the interfaces between the polymer phases. 

Van Henten, at the Shell Plastic Laboratories (II), showed that styrene-butadiene block polymers can be blended with commercial HIPS to upgrade its impact strength to 5.8 ft-lbs/inch. Childers, at Phillips Petroleum (12), blended commercial polystyrene with block polymers in a Brabender plastograph. To control rubber particle size he added a peroxide during the blending operation, thereby creating crosslinks. With this technique he achieved an impact strength of 5.9 ft-lbs/inch. 

High Impact Polystyrene (UPS) obtained by means of copolymerization of styrene with rubber represents heterogeneous system consisting of polystyrene matrix and the particles of rubber phase dispersed in it the particles in their turn keep the graft copolymer and a great number of occluded polystyrene O/,Physical and mechanical properties of HIPS are defined... 

When comparing them with the photos obtained with the help of generally known Kato method (10). one can see beside similarity of general picture ofrubber distribution also difference membranes between occluded polystyrene and rubber particles in our picture are much thicker. In our opinion it can be explained by the fact that when being worked out one can see only contracted with osmium-tetroxide rubber and in fig. 1 b membranes be-tween occlusions represent rubber together with the intermediate layer, consisting of graft polymer of poly(styrene-gr-bu tadiene). 

Figure 3.4 Ternary phase diagram for the system styrene-polystyrene-polybutadiene rubber. Reproduced with permission from Encyclopedia of Polymer Science and Engineering, Mark (Ed.), John Wiley Sons, NY. Copyright John Wiley Sons...

While formulations with rubber compounded into the GPPS are effective, grafting the elastomer into the continuous phase is preferred. Commercial polymerization processes produce a polymer system that not only has an elastomer incorporated, but also a grafted species where short polystyrene side chains have been attached to the rubber domains. This grafting anchors... 

Polystyrene (PS) in its atactic and syndiotactic forms is a brittle thermoplastic, even in an orientated state [4]. To improve the toughness of aPS, impact modification has been practised for a long time, either by polymerizing the styrene in the presence of a polybutadiene rubber leading to high-impact polystyrene, commonly called HIPS, or by blending the polystyrene with multi-block copolymers, mainly of the styrene-butadiene-styrene (S-B-S) type. 

In rubber-modified polystyrenes, the rubber is dispersed in the polystyrene matrix in the form of discrete particles. The two-phase nature of rubber-modified polystyrene was first suggested by Buchdahl and Nielsen [47] based on data on dynamic mechanical properties obtained with a torsion pendulum. The existence of two prominent loss peaks led to this conclusion, one at low temperatures which is due to the a relaxation of the rubber (e.g. 193 K for polybutadiene) and one at high temperatures which is due to the a relaxation of the matrix (e.g. 373 K for polystyrene). Later, microscopy provided proof of the existence of the rubber phase as a discrete dispersed phase in polystyrene [48]. 

There are a number of flame-retardant styrenic polymers that will be covered in this chapter. These include polystyrene itself, rubber-modified polystyrene [high-impact polystyrene (HIPS)] and rubber-modified styrene-acrylonitrile copolymer [acrylonitrile-butadiene-styrene (ABS)]. Blends with styrenic... 

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