Commercial Elastomer Blends

The most important commercial use of elastomer blends is in the huge tire market. These blends are generally phase separated and represent one of the largest single applications for immiscible or miscible blends. Ckjmpatibilization is achieved via crosslinking reactions across the interface. The use of SBR/PB (polybutadiene) and NR(natural rubber)/PB for tread, NR/SBR/PB and NR/PB for carcass, NR/PB and NR/SBR for sidewall and NR/SBR/PIB 

Additional examples of commercial elastomeric blends are given in Table 7.1. 

EPDM/siUcone rubber Rogers Corp. Document handling equipment 20 

Silicone rubber/various polymers Multibase Crosslinked silicone phase dispersed in various polymers automotive and industrial tubing applications ws 

SEBS/polyolefins Teknor Apex Tradename Tekron medical tubing, seals, gaskets cushions 21 

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Immiscible Blends. Rubber. Elastomer/elastomer blends are used extensively for commercial applications, particularly in the construction of automobile tires. There is an extensive patent and technological literature on this subject. A recent review (see chapter 19 of Ref. 19 by McDonel, Baranwal, and Andries) summarizes a great deal of this... 

PET/elastomer blends have been used commercially either filled or reinforced. Owing to slow crystallization of PET in these blends, unfilled grades would be very difficult to mold. In warm molds, the cycle would be too long, the parts would tend to stick and distort when removed, making the process expensive. In cold molds, amorphous parts with low heat deflection temperatures, would be produced, reducing the usefulness of the blends. 

Many commercial polymer blends often include an elastomer, to improve the impact strength of the blend under conditions of stress concentration (notched Izod impact strength) and to lower the ductile-brittle transition temperature of the blend. The elastomeric dispersions are judiciously employed either in the matrix phase, in the dispersed polymer phase, or in both phases, depending upon the requirement and the fracture behavior of the blend. As a general rule, the more brittle component in a given polymer blend has a greater need for rubber toughening. 

Although commercial twin-screw extruders can be as large as 300 mm size, capable of compounding up to 40 ton/hr, the acmal type and size of the equipment used depends on the type of the polymer blend and the production volume. Normally, for engineering polymer blends, twin-screw extmders of about D = 90 mm size (L/D = 30 to 40) and capable of compounding at 700 to 1000 kg/hr, are used. For blending PVC or elastomer blends other types of compounding equipment are used, e.g. Farrell continuous mixer (FCM), Buss co-kneader, or a batch mixer, such as Banbury. 

Blends of butadiene-acrylonitrile copolymer rubber (nitrile rubber or NBR) and PVC are among the oldest known examples of commercial elastomer/ thermoplastic blends. The shortage of natural rubber during World War II stimulated research in the USA on the compounding and modification of synthetic polymers to produce rubber-like materials. An outcome of this research was the commercial introduction of NBR/PVC blends by B.F. Goodrich in 1947 under the trade name of Geon Polyblends [Pittenger and Cohan, 1947]. The blend showed improved ozone resistance and melt processability compared to the nitrile rubber (Table 15.12). 

Table 15.13. Key properties of commercial thermoplastic elastomer blends based on polypropylene/elastomer dynamic vulcanizates...

The outstanding impact toughness of the commercial impact modified polyamides is attributed to the small particle size of rubber dispersion and their good degree of adhesion to the polyamide matrix. Typical morphologies of compatibilized polyamide/elastomer blends are shown in Figure... 

Table 15.17. Properties of some commercial polyamide/elastomer blends...

Commercial impact modified (elastomer blended) polycarbonates are used for the production of protective headgear, sporting goods, bobbins for textile industry and automotive components requiring high toughness. Impact modified PC has to compete with the more solvent resistant impact modified PBT/PC, PET/PC blends and polyamides in some of the applications. 

Table 15.29. Properties of commercial acetal/elastomer blends vs. acetal...

PET/Elastomer blends have not been commercialized in the unfilled form, due to the slow rate... 

Table 15.32. Commercial PBT/polyester elastomer blends vs. PBT and polyester elastomer...

A new method known as reactive mixing has developed recently to increase the cure rate of EPDM by modifying the EPDM phase to make it more reactive toward curatives, using commercially available sulfur donors such as bis-alkylphe-noldisulphide (BAPD), in combination with dithiocaprolactam (DTDC) and/or dithiomorpholine (DTDM). The refinement of reactive mixing process with cost effective sulfur donors is one of the challenges in the maximum utilization of these elastomer blends. 

Numerous nylon blends prepared by compatibilization or reactive blending are commercially successful. The modifiers fiequenfly utilized in commercial nylon blends include polyolefin, thermoplastic polyolefin, thermoplastic polyunethane, ionomer, elastomer, ethylene-propylene rubber, nitrile mbber, polyftetrafluoroethylene), poly (phenylene ether), poly(ether amide), silicone, glass fiber, and carbon fiber. The nonpolar modifiers such as polyolefin, maleic anhydride or a polar vinyl monomer such as acrylic acid, methaciylic acid and fimiaric acid is fiequently incorporated to introduce reactive sites in nylon. 

Blends of elastomers are of technological and commercial importance since they allow the user to access properties of the final blended and vulcanized elastomer that are not accessible from a single, commercially available elastomer alone. These potentially improved properties include chemical, physical, and processing benefits. In reality, all blends show compositionally correlated changes in all of these properties compared to the blend components. The technology of elastomer blends is largely focused on the choice of individual elastomers and the creation of the blends to achieve a set of final properties. This chapter shows some of the instances of the uses of elastomer blends. Empirical guidelines for the creation of novel blends of elastomers is a comparatively more difficult proposition. 

The EP thermoplastic elastomers are distinguished from the crossUnked analogues, which are not thermoplastics since reforming is impossible. A very important thermoplastic elastomer is comprised of a blend of an EP copolymer with an ethylene-propylene-diene (EPDM) terpolymer. This latter material is, of course, a crosslinkable thermoset however, these materials can be processed as thermoplastics if the crosslinkable component is present at low enough concentration to be present as an isolated phase. Melt-processing causes the formation of chemical bonds within the isolated rubber phase, a process called dynamic vulcanization. A commercial example of this type of material is Santoprene [4] manufactured by Advanced Elastomer Systems. Other blends of noncrosslinkable TPEs with crosslinkable materials are used commercially. These materials are classified as elastomer blends and are the subject of Chapter 12. 

PPCP blends with commercial elastomers/ plastomers (EXACT 5371, ENR 7370, ENGAGE 8150, VERSIFY 2300, NORDEL IP 4760P, NORDEL IP 4770P, Chemtura EPDMIM 7565) DSC, Delta heat of fusion, delta heat of crystallization, T, Charpy impact strength (notched) raised up to 70 kJ/m in case of Engage-8150, Nradel-4760, N[Pg.1129]

In contrast to the rigid TPOs described above, low-modulus/flexible grades of TPO blends are also produced commercially. In flexible TPOs, the rubber content can be as high as 60 %, and in some cases, the dispersed rubber may also be partially cross-linked during the mixing without losing the thermoplastic character of the matrix. However, the latter type of dynamically vulcanized elastomeric alloys or thermoplastic vulcanizate rubbers (TPVs) are considered as a separate class of elastomeric materials and hence will be discussed under elastomer blends. On the other hand, the soft TPO blends discussed here contain a low-modulus olefln copolymer elastomer as the major component with some polypropylene added to impart melt processability. 

Thermoplastic polyolefin (TPO) blends of metallocene-based polyolefin elastomers (POE) with polypropylenes have gained commercial significance because of the improved melt flow and toughness compared to the conventional TPOs based oti EPR or EPDM blends made with high melt-flow PP (Toensmeier 1994). in comparative tests with 70/30 PP/elastomer blends, the blends with POE maintained ductile behavior at —29 °C even with high melt flow index PP (MFl = 35), while the corresponding EPR-based blends were brittle with PP of MFl = 20. In addition, they showed improved knit-line strengths. 

Table 19.11 Properties of commercial SMA/elastomer blends (impact modified SMA resins) ...

Table 19.23 Properties of commercial, low-modulus, semi-flexible PA6/elastomer blends ...

Currently, ABS/PA blends are commercially available primarily from Styrolution under the trade name of Terblend N and Ineos ABS tmder the trade name of Triax . In general, ABS/PA blends exhibit excellent notched Izod impact (>850 J/m or >65 KJ/m )) at room temperature (Table 19.9). These impact properties are equivalent to those of impact-modified polyamide (Table 19.22). However, the DTULs (0.45 MPa) of ABS/PA blends are relatively low compared to those of impact-modified nylons. The key difference being that in ABS/polyamide blends, due to the significant level of ABS, a substantial drop in the modulus occurs at the Tg of ABS (SAN), and hence the blend exhibits lower DTUL at 0.45 MPa than the impact-modified polyamide. The latter blends are polyamide-rich (>75 %) elastomer blends and hence maintain a higher level of heat resistance due to the higher level of the crystalline PA phase. 

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