Blend properties lower cost

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 crystalline polymers such as PPS, LCP, PEEK offer the additional advantages of high solvent resistance. Due to the inherently high cost of the specialty polymers, very few blends have been developed for commercial applications. The only driving force for the development of even the few blends of specialty polymers has been the desire to reduce the cost of the base resins by blending with lower cost engineering plastics, although this invariably results in a lower DTUL. Nevertheless, a few commercial blends of specialty polymers exist and their properties will be discussed below ... 

Very few blends of PEI have been commercialized because blending a lower-cost polymer invariably compromises the transparency and high-performance properties of the neat PEI resin. 

Synthetic polymers have become extremely important as materials over the past 50 years and have replaced other materials because they possess high strength-to-weight ratios, easy processabiUty, and other desirable features. Used in appHcations previously dominated by metals, ceramics, and natural fibers, polymers make up much of the sales in the automotive, durables, and clothing markets. In these appHcations, polymers possess desired attributes, often at a much lower cost than the materials they replace. The emphasis in research has shifted from developing new synthetic macromolecules toward preparation of cost-effective multicomponent systems (ie, copolymers, polymer blends, and composites) rather than preparation of new and frequendy more expensive homopolymers. These multicomponent systems can be "tuned" to achieve the desired properties (within limits, of course) much easier than through the total synthesis of new macromolecules. 

Because of increased production and the lower cost of raw material, thermoplastic elastomeric materials are a significant and growing part of the total polymers market. World consumption in 1995 is estimated to approach 1,000,000 metric tons (3). However, because the melt to soHd transition is reversible, some properties of thermoplastic elastomers, eg, compression set, solvent resistance, and resistance to deformation at high temperatures, are usually not as good as those of the conventional vulcanized mbbers. AppHcations of thermoplastic elastomers are, therefore, in areas where these properties are less important, eg, footwear, wine insulation, adhesives, polymer blending, and not in areas such as automobile tires. 

The use of ABS has in recent years met considerable competition on two fronts, particularly in automotive applications. For lower cost applications, where demands of finish and heat resistance are not too severe, blends of polypropylene and ethylene-propylene rubbers have found application (see Chapters 11 and 31). On the other hand, where enhanced heat resistance and surface hardness are required in conjunction with excellent impact properties, polycarbonate-ABS alloys (see Section 20.8) have found many applications. These materials have also replaced ABS in a number of electrical fittings and housings for business and domestic applications. Where improved heat distortion temperature and good electrical insulation properties (including tracking resistance) are important, then ABS may be replaced by poly(butylene terephthalate). 

Product development and improvement has a crucial role to play in the further development of the biodegradable polymers market. These include development of more reliable and lower cost raw materials for manufacture of biodegradable polymers, improvement in performance properties vis-a-vis standard thermoplastics, improvement in processing performance and development of new polymers and 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. 

The references noted well demonstrate the ability to utilize polymer blend technology to achieve the desired balance of mechanical properties and conductivity. The promise of electrical conductive polymers with lower cost, processability, and mechanical durability can thus be envisioned for applications such as electrical dissipative coatings, printable circuits, electromagnetic shielding, resistive heating, conductive sheathing, battery applications, elastomeric conductors, fuses, electronic uses, sensors, specialty electrical devices for corrosive atmospheres, photovoltaic devices, catalysts, optical switches, and semiconductor devices. 

Polyolefin blends are a subset of polymer blends that emerged as a result of the need to meet apphcation requirements not satisfied by synthesized neat polyolefins. In comparison to other subsets of polymer blends, polyolefin blends have distinct advantages of lower density, lower cost, processing ease, and good combination of chemical, physical, and mechanical properties. In the last several years, research and usage of polyolefin blends have increased due to new application opportunities (e.g., in medical and packaging) and the development of novel polyolefins. 

For many years polymer blends have been seen as means to combine the best properties of the two homopolymers, or as means of improving the fabrication method and at a lower cost by incorporating fillers. Miscible blends can be seen to be one continuous phase with resultant properties between those of its two components. Immiscible blends can... 

The main reason for polymer blending is economy. If a material can be produced at a lower cost with properties meeting specifications, the manufacturer must use it to remain competitive. The main and most difficult task in polyblend production is the development of materials with a full set of desired... 

Standard SBR materials are made from an emulsion polymerization process and are available in more than 100 grades, but only a few are used as a base for adhesives. The two basic processes for producing these many grades can be either a hot or cold process, depending on the polymerization temperature, with hot polymerization being the preferred process. Hot polymerized SBR typically yields a lower molecular weight polymer, but with a wider molecular weight distribution which provides for a more balanced polymer. The styrene content can also be varied to enhance certain properties. Emulsion process polymers are often called random SBR because there is no control of the attachment sites for the styrene monomer when polymerized. These polymers are often blended with other polymers to lower cost and increase compatibility with various resins, plasticizers, and fillers. 

Blending two or more polymers offers yet another method of tailoring resins to a specific application. Because blends are only physical mixtures, the resulting polymer usually has physical and mechanical properties that lie somewhere between the values of its constiment materials. For instance, an automotive bumper made from a blend of PC resin and thermoplastic polyurethane elastomer gains rigidity from the PC resin and retains most of the flexibility and paintability of the polyurethane elastomer. For business machine housings, a blend of PC and ABS (acrylonitrile—butadiene—styrene copolymer) resins offers the enhanced performance of PC flame retar-dance and ultraviolet (UV) stability at a lower cost. 

TPOs (olefinic blends) comprise a lower-performance, lower-cost class of TPEs (Fig. 4.39). Their performance and properties are generally inferior to those of thermoset rubbers. Yef they are suitable for uses where (1) the maximum service temperature is modest (below 80°C), (2) nonpolar flnid resistance is not needed, and (3) a high level of creep and set can be tolerated. Thns, TPOs are marketed more on the basis of cost rather than performance, competing directly with the lower-cost general-purpose rubbers (NR, SBR, and the hke). TPOs are associated with the traditional practice of rnbber componnd-ing and mixing. They can be prepared by the same techniques and equipment as for thermoset mbber however, they need to be processed at temperatures above the of the thermoplastic hard phase. The amounts of elastomer, rigid thermoplastic, plasticizer, and other ingredients can be varied to achieve specific properties in much the same manner as with rnbber componnds. 

Although H-PP is often used as a blend for making TPO, or filled with short or long fibers, and so forth, there is very little direct H-PP application in the automotive industry. These applications take advantage of the lower cost and scratch resistance of H-PP. PP may also go into some of the fibers used in antomotive components. In contrast, ICPs, with their excellent balance of toughness, rigidity, and processability, have made enormous inroads into automotive applications over the last two decades, becoming a dominant interior thermoplastic. (Clearly, the economics of hydrocarbon-based resins plays an important role.) Table 9.3 shows some characteristic properties of homo, copolymer, and impact copolymer PPs. 

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