Transparent ABS

Transparent ABS is a quaternary copolymer composed of butadiene, styrene, acrylonitrile, and methyl methacrylate. It is composed of a core-shell structure, where the core component uses butadiene rubber or 

The refractive index of the respective component is 1.516 to 1.518 for polybutadiene, about 1.49 for poly(methyl methacrylate), 1.592 for polystyrene, and about 1.52 for polyacrylonitrile. The refractive index (RI) of the grafting copolymer can be calculated according to 

RIa = refractive index (1.52) of polyacrylonitrile Wts = weight percent of styrene RIs = refractive index (1.592) of polystyrene Wtjvf = weight percent of methyl methacrylate RIm= refractive index (1.49) of poly(methyl methacrylate) 

The composition of each respective component can be calculated so that the refractive index of the grafting copolymer as calculated from the above 

Blow process Plug assist process Cooling extraction 

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Blending of ABS with an acrylic material such as poly(methyl methacrylate) can in some cases allow a matching of the refractive indices of the rubbery and glassy phases and providing that there is a low level of contaminating material such as soap and an absence of insoluble additives a reasonable transparent ABS-type polymer may be obtained. More sophisticated are the complex terpolymers and blends of the MBS type considered below. Seldom used on their own, they are primarily of use as impact modifiers for unplasticised PVC. 

This ABA block copolymer consists of stiff polystyrene (PS) and resilient polybutadiene blocks. The domains of these TPEs have characteristic Tt values of 100 and —80 C, respectively. The polybutadiene blocks retain their flexibility at low temperatures, and the polystyrene blocks lose their stiffness when the polymer is heated above 110 C. A related thermoplastic is a transparent AB block copolymer of styrene and butadiene (K-resin). 

Transparent ABS Acrylic (PMMA) Ally dielvcol carbonate Cellulosics Good impact properties, good processibility Excellent resistance to outdoor exposure, crystal clarity Good abrasion/chemical resistance, thermoset Heat sensitive, limited chemical resistance, good toughness... 

The next evolution in ABS technology was the need to produce a transparent ABS. Existing ABS was opaque owing to the scattering of light by the rubber domains. While producing smaller domains would make the system clear, it led to a loss of impact strength. The answer was to modify the refractive index of the components so that the various phases were less optically different. A fourth monomer , methyl methacrylate, was used to minimize the refractive index variation in the ABS and a clear impact-resistant thermoplastic named Cyclolac CIT was achieved [20]. 

Optical clarity has received considerable attention from the research community, as well as industry, especially, since transparent ABS was introduced to the market. Although success in this area has been limited, nevertheless this property frequenfly is pertinent when considering blend suitability to a particular application. The chapter concludes with a discussion of this aspect. 

Optical properties Usually opaque but may be transparent. ABS has a good surface finish with high gloss. 

Figure 2.30 Izod impact strength vs. temperature for Toray Plastics Toyolac transparent ABS resins.

The final ABS resins completed by compounding grafted ABS and SAN copolymer have been prepared by subdividing into general-purpose ABS, flame-retardant ABS, extrusion ABS, heat-resistant ABS, transparent ABS, weatherable ABS, etc., depending on the raw materials and additives as applied. 

ABS resin bas excellent physical properties including impact strength as well as excellent processability. Transparent ABS is structurally similar to such ABS resin and therefore maintains the balance between mechanical properties and processability properties. Of course, although there is a small change in properties by providing the transparency, it maintains the balanced properties in comparison to other transparent resins. 

Table 6.10 shows the general properties of transparent ABS. Since the characteristics differ according to the makers and the grades, only the most representative properties are listed. In addition, to show how the properties of the present transparent ABS are different from those of other transparent resins, the properties of the different kinds of transparent resins are also described. 

ASTM test Unit Transparent ABS PMMA (general- purpose) PMMA (impact resistance) PC... 

Other products having properties similar to those of the transparent ABS, transparent HIPS, transparent MBS, etc., can be included. Since such similar products have the properties and qualities similar to those of the transparent ABS, the names used may be the same, but the manufacturing methods and compositions differ somewhat. 

As can be seen from Table 6.12, the transparent ABS uses polybutadiene rubber, whereas transparent HIPS or transparent MBS uses poly(stjn-ene-butadiene) copolymer. Although such a difference in the rubber used does not bave a great influence on properties, it creates a difference in the refractive index, which in turn creates a difference in the composition of the shell. The refractive index of poly(stjn-ene-butadiene)... 

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