HIPS, additives Rubber

Indeed, as obvious from both exemples given in Fig. 2, the transition could thus be determined accurately within 0.1-0.2 decades of test speeds with few samples in a relative short time frame. Moreover, as the apparent values (Kimax) are always lower than the effective parameters (Keff), none of the material descriptor would be overestimated. In addition, since Kjmax-values have been shown to provide a semi-quantitative evaluation (in terms of test speed or temperature) of fracture resistance parameters, a coherent material comparison would be possible over the whole investigated range. This remark remains true as long as the grades have similar rp. For iPP grades, it should be checked (and considered with more caution) when materials exhibit different particle and matrix melt flow rates, or different crystalline structures. It should also be investigated in detail when different polymer families (ABS versus HIPS or rubber modified iPP) are compared. 

The prepolymerization reactor for HIPS is similar ( ). A solution of rubber and styrene monomer is charged to the reactor along with catalysts, antioxidants, and other additives, and the temperature program is carried out until the desired conversion is reached. This is usually close to the point where increasing viscosity seriously limits mixing and temperature control. 

Cortes et al. [975] have used on-line p,SEC-CGC for rapid determination of a great variety of additives in an emulsion ABS-PVC blend, HIPS and a styrene-acrylate-ethylene rubber polymer. These systems are difficult to analyse, because of the high levels of insolubles such as fillers, pigments, or rubber modifiers. The additives were separated from the polymer fraction in a polymer/additive dissolution using p,SEC, and were... 

Polycarbonate is blended with a number of polymers including PET, PBT, acrylonitrile-butadiene-styrene terpolymer (ABS) rubber, and styrene-maleic anhydride (SMA) copolymer. The blends have lower costs compared to polycarbonate and, in addition, show some property improvement. PET and PBT impart better chemical resistance and processability, ABS imparts improved processability, and SMA imparts better retention of properties on aging at high temperature. Poly(phenylene oxide) blended with high-impact polystyrene (HIPS) (polybutadiene-gra/f-polystyrene) has improved toughness and processability. The impact strength of polyamides is improved by blending with an ethylene copolymer or ABS rubber. 

The potential problem of styrene taint in foods is well known and documented in the literature (Saxby 1996). Styrene (see Chapter 2) is the monomer that is polymerized to make polystyrene (PS) (also known as general purpose or GPPS grade). It is also commonly used with butadiene rubber (5-20 % w/w) as a block copolymer to form high impact polystyrene (HIPS). In addition there are less common copolymer grades such as acrylonitrile-butadiene-styrene (ABS) having a mixture of 25 %, 15-25 % and 50-65 % of each monomer respectively or a copolymer with acrylonitrile (styrene-acrylonitrile, SAN). 

The production of HIPS begins with the granulating and dissolving of rubber and other additives in styrene monomer (1) and then transferring the rubber solution to a storage tank (2). For general-purpose product, controlled amounts of ingredients are fed directly to the feed preheater (3). 

In GPPS systems, these peroxides mainly supplemented the free radicals generated by thermal initiation, whereas in the HIPS process, it was found that they could enhance the grafting of styrene to unsaturated rubbers, such as polybutadiene. Additional benefits of organic peroxide initiators were increased production per unit reactor volume, reduction of styrene oligomers and lower reactor temperatures. The instantaneous removal of peroxide feed to a runaway reactor also provides a safety mechanism. Peroxide-initiated systems have higher reaction rates owing to shorter reactor residence times, so the ability to remove one source of radical initiation quickly is important. 

In HIPS a wide variety of rubber particle morphology is possible. Echte et al. summarized this in an excellent review (see Figure 14.5) [41]. The key to these different structures is the composition of the styrene-butadiene block rubber, which is an emulsifier for the polystyrene-polybutadiene system. Additional grafting can generate a shift from one structure to another. 

For the rubber modified copolymer, ABS, we have carried out fatigue studies over a range of stress amplitudes and frequencies under reversed tension-compression cycling in addition, some tests have been made under cycUc tension. Results will be presented first for tests carried out under different applied amplitudes and comparisons will be made between ABS and SAN, between ABS and HIPS, and between our data on ABS and that of others... 

An additional problem arises in attenqiting to predict the moduli of rubber-modified dastics the rubber particles are themselves composite in structure. A typfeal hi inqiact polystyrene (HIPS) m t contain only 6 v(d.% of pcdybutadi-ene, whereas the volume fraction of rubber particles is between 20 and 30%. The additional vcdume comes from sniall sub-inclusions of polystyrene (PS) embedded in the rubber. The problem of relating modulus to structure in rubber-toughened plastics is discussed in a recent review ). 

Phase-separated polymers are of practical importance. An example is the way that a brittle polymer such as polystyrene may be toughened by the addition of an incompatible rubber that undergoes phase separation. Provided that this is done with attention to the interface between the two phases, a rubber-toughened high-impact polystyrene (HIPS) will result. 

Stress State at Particles. If the modifier particles consist of rubber-like material, they act as stress concentrators as in HIPS and ABS. Whereas in HIPS and related polymers the maximum stress component, aee, at the equatorial regions around the particles is responsible for initiating crazes, in polymers with a tendency to shear deformation the maximum shear stress at the particles, yielding the formation of shear bands, must be considered (see Figure 17a). But in contrast to crazes, which have a stress-concentrating ability, shear bands to not increase the stress between particles as effectively. Therefore, the formation of microvoids inside the particles is necessary as an additional mechanism to increase the stress at and between particles. To make the polymeric material between particles yield, not only is the stress concentration at particles necessary (as in craze formation), but so is the stress field between particles. 

The addition of rubber significantly complicates the picture. Rubbers commonly used for HIPS and ABS have various microstructures depending on the method of manufacture ( ... 

The structure of ABS is similar to that of HIPS but with a SAN matrix instead of the PSt matrix in HIPS. PB grafted with SAN acts as a compatibilizer between the rubber particles and the SAN matrix. The rubber particle morphology in ABS can be similar to that in HIPS, with salami-type particles, but ABS particles can also be of the core-shell type, with a core of solid PB and a shell of graft copolymer, especially if the ABS is produced by the emulsion process [34]. In addition to craze formation, an important fracture mechanism in ABS polymers is shear yielding, which leads to tougher materials [46]. 

Other Impact-Modified Commercial Grafting-Based Polymers Typical HIPS and ABS polymers are opaque materials however, MABS (methyl methacrylate-acrylonitrile-butadiene-styrene) polymers, which are produced by processes similar to those used in the production of ABS, are transparent materials. This property is obtained by the addition of methyl methacrylate (MMA) to the recipe in order to impart transparency to the polymer by equalizing the refracting index of the rubber particles to that of the matrix. These materials find applications... 

Acrylonitrile/Butadiene/Styrene (ABS) Acry-lonitrile/butadiene/styrene (ABS) polymers are not true terpolymers. As HIPS they are multipolymer composite materials, also called polyblends. Continuous ABS is made by the copolymerization of styrene and acrylonitrile (SAN) in the presence of dissolved PB rubber. It is common to make further physical blends of ABS with different amounts of SAN copolymers to tailor product properties. Similar to the bulk continuous HIPS process, in the ABS process, high di-PB (>50%, >85% 1,4-addition) is dissolved in styrene monomer, or in the process solvent, and fed continuously to a CSTR where streams of AN monomer, recycled S/AN blends from the evaporator and separation stages, peroxide or azo initiators, antioxidants and additives are continuously metered according to the required mass balance to keep the copolymer composition constant over time at steady state. 

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