Clear Blends

The polymer most commonly blended with SBC is crystal polystyrene. Crystal polystyrene and SBC do have a significant difference in refractive index, but the polystyrene is miscible in the polystyrene domains of the SBC. Hence the blended part, if well mixed, will have good optical properties. Crystal polystyrene is desirable as a blend resin for SBC because it is of lower cost and also offers advantages in temperature resistance, stiffness and surface hardness. The major disadvantage in blends of SBC with crystal polystyrene is a significant decrease in impact strength as the polystyrene content is increased. 

In thermoformed cups, the SBC content can vary significantly. The SBC content is often close to 50 %, but in many cases there is more crystal polystyrene than SBC in the final part. Hence selection of an optimum crystal 

Some packaging applications may be particularly sensitive to styrene or other volatile components. SBC and crystal polystyrene blends, even with low residual monomer levels in the polystyrene, may be unacceptable for these applications. In this case one possible solution may be to co-extrude a thin food contact layer on the surface of the blended sheet. Studies have indicated that by co-extruding a thin layer of crystal polystyrene on the surface of an SBC and crystal polystyrene blend, the styrenic volatiles and the odor can be significantly reduced. However, the downside is that the added layer of crystal polystyrene can serve to make the blended part more brittle. Another option that could reduce odor, but not have a deleterious effect on impact, is a thin coextruded layer of PETG [20]. 

The molecular weight of crystal polystyrene can also play an important role in blend properties. There is a trade-off between impact and clarity, with higher molecular weight giving better impact and lower molecular weight providing better clarity. The converter can select the proper crystal polystyrene to match specific performance requirements. 

Another polymer that has been very successful in blends with SBC is polystyrene-methyl methacrylate (SMMA), a styrene acrylic copolymer. Compared with SBC, SMMA offers significantly higher stiffness, surface hardness and temperature resistance. The refractive index of these copolymers can be 

---

PVB combinations with the thermoplastic resins nitrocellulose or shellac have been used as sealers for wood finishing. In these applications the PVB component adds flexibility and adhesion. Tough, optically clear blends have been made with aliphatic polyurethanes. Thermosets are prepared with cross-linkers that form covalent bonds with hydroxy] groups. 

Deli cups with a clear blend of performance and price , Packaging Dig., January (1994). 

Clearly, blending is an important technique to obtain conducting materials based on intrinsically conductive polymers and conventional as well as rubbery plastics. In a recent study, Martins et al. (2006) prepared an electrically conductive thermoplastic elastomer by blending butadiene-styrene copolymer (SBR) and... 

Emulsifier, solvent degreaser, drycleaning detergent. Oil-soluble sulfonate capable of forming clear blends of water and... 

Features Forms clear blends of water and kerosene... 

Figure B3.6.2. Local mterface position in a binary polymer blend. After averaging the interfacial profile over small lateral patches, the interface can be described by a single-valued function u r. (Monge representation). Thennal fluctuations of the local interface position are clearly visible. From Wemer et al [49].

These surfactants, in conjunction with soap, produce bars that may possess superior lathering and rinsing in hard water, greater lather stabiUty, and improved skin effects. Beauty and skin care bars are becoming very complex formulations. A review of the Hterature clearly demonstrates the complexity of these very mild formulations, where it is not uncommon to find a mixture of synthetic surfactants, each of which is specifically added to modify various properties of the product. Eor example, one approach commonly reported is to blend a low level of soap (for product firmness), a mild primary surfactant (such as sodium cocoyl isethionate), a high lathering or lather-boosting cosurfactant, eg, cocamidopropyl betaine or AGS, and potentially an emollient like stearic acid (27). Such benefits come at a cost to the consumer because these materials are considerably more expensive than simple soaps. 

NB Some technical reviews refer to polymer composites being used in film manufacture when it is not always obvious whether the reference is to the use of a physical blend of the component polymers or whether the polymers are separated in layers (as in coaxial extrusion) or in some combination. Clearly the effects can be quite different.]... 

---