Solvent resistant polymer blends

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. 

Standard-grade PSAs are usually made from styrene-butadiene rubber (SBR), natural rubber, or blends thereof in solution. In addition to rubbers, polyacrylates, polymethylacrylates, polyfvinyl ethers), polychloroprene, and polyisobutenes are often components of the system ([198], pp. 25-39). These are often modified with phenolic resins, or resins based on rosin esters, coumarones, or hydrocarbons. Phenolic resins improve temperature resistance, solvent resistance, and cohesive strength of PSA ([196], pp. 276-278). Antioxidants and tackifiers are also essential components. Sometimes the tackifier will be a lower molecular weight component of the high polymer system. The phenolic resins may be standard resoles, alkyl phenolics, or terpene-phenolic systems ([198], pp. 25-39 and 80-81). Pressure-sensitive dispersions are normally comprised of special acrylic ester copolymers with resin modifiers. The high polymer base used determines adhesive and cohesive properties of the PSA. 

An IPN has different properties from either a copolymer or a polymer blend. It may swell in solvents, but will not dissolve it will resist creep or flow to a greater extent than copolymers or blends. Some differences in the physical properties of IPNs compared with polymer blends can be seen in Table 10.3. The major reason for the differences in properties between polymer blends and IPNs is that the latter have greater adhesion and better mixing. 

PET can be blended with PBT or polycarbonate (PC) to make blends or alloys. Polycarbonate is a high Tg (150 °C) ductile, high-impact-strength polymer but has rather poor solvent resistance because of its amorphous nature. PET/PC blends have therefore proved advantageous because they combine the solvent-resistance... 

Most polystyrene products are not homopolystyrene since the latter is relatively brittle with low impact and solvent resistance (Secs. 3-14b, 6-la). Various combinations of copolymerization and blending are used to improve the properties of polystyrene [Moore, 1989]. Copolymerization of styrene with 1,3-butadiene imparts sufficient flexibility to yield elastomeric products [styrene-1,3-butadiene rubbers (SBR)]. Most SBR rubbers (trade names Buna, GR-S, Philprene) are about 25% styrene-75% 1,3-butadiene copolymer produced by emulsion polymerization some are produced by anionic polymerization. About 2 billion pounds per year are produced in the United States. SBR is similar to natural rubber in tensile strength, has somewhat better ozone resistance and weatherability but has poorer resilience and greater heat buildup. SBR can be blended with oil (referred to as oil-extended SBR) to lower raw material costs without excessive loss of physical properties. SBR is also blended with other polymers to combine properties. The major use for SBR is in tires. Other uses include belting, hose, molded and extruded goods, flooring, shoe soles, coated fabrics, and electrical insulation. 

Most commercial fluorocarbon elastomers have brittle points between -25°C (-13°F) and -40°C (-40°F). The low-temperature flexibility depends on the chemical structure of the polymer and cannot be improved markedly by compounding. The use of plasticizers may help somewhat, but at a cost of reduced heat stability and worsened aging. Peroxide-curable polymers may be blended with fluorosilicones, but such blends exhibit considerably lower high-temperature stability and solvent resistance and are considerably more expensive than the pure fluorocarbon polymer. Viton GLT is a product with a low brittle point of -51°C (-59°F) [48]. Tecnoflon for containing a stable fluorinated amide plasticizer reportedly exhibits improved low-temperature hardness, brittle point, and compression set without sacrificing physical properties [66]. Low-temperature characteristics of selected fluorocarbon elastomers are listed in Table 5.13 [9]. 

To overcome the main drawbacks of sPS (e.g. poor impact resistance) without impairing the other thermo-mechanical properties (e.g. modulus, heat distortion temperature) and solvent resistance, extensive research has been carried out by blending and compounding it with suitable polymeric and inorganic components. Several patents have been issued on polymer blends having sPS as a main component. Table 20.1 reports the most relevant of them published by the US Patent Office in the period 1985-2000. 

A second important factor in polymer polymer blend device design is the degree of vertical segregation of donor and acceptor polymers. This can be controlled by choice of solvent and processing (Arias et al, 2002), by thermal post-treatments (Veenstra et al, 2004) or by solution casting of consecutive layers. Vertical segregation can greatly improve the device shunt resistance. Currently, the best efficiencies for polymer-polymer solar cells is 1.5% for a blend of a PPV polymer with a red... 

Fig. 4c) can be compared to lamellar blending of small amounts of immiscible higher barrier polymers (Fig. 4f) by consideration of Chapters 14, 15 and 13, resp.(81-83) The efficacies of the various treatments for the preparation of solvent resistant automotive gasoline tanks and hydrocarbon storage bottles are treated in these chapters. 

Earlier work done in these laboratories has shown that polymer blends wherein the barrier polymers are dispersed as thin platelets parallel to the surface of the fabricated article, have significantly improved permeability barrier properties than the conventional "homogeneous", uniform, dispersions (1,2). The high barriers demonstrated were then achieved by blending 15-20% polyamides with a linear polyethylene, which achieved performance comparable to that obtained by adding as much as 50% nylon by conventional blending. While this performance has been satisfactory for a variety of applications, some of the more demanding uses require that the barrier polymer be used more efficiently. Described here are such blend compositions which show substantial resistance to permeation of hydrocarbon solvents and their mixtures. 

In addition to, or instead of, polystyrene and oils, polymers such as polypropylene, polyethylene, or ethylene-vinyl acetate copolymer can be blended with these block copolymers. Blends with S-B-S or (S-B) -X block polymers usually show greatly improved ozone resistance (S-EB-S already has excellent ozone resistance). In addition, these blends have some solvent resistance. In certain cases, some oils that are stable to UV radiation reduce the stability of the blends however, the effects can be minimized by the use of UV stabilizers and absorptive or reflective pigments (e.g., carbon black or titanium dioxide). 

PPS and PEEK blended with a fluoro(co)-polymers and reinforced with either CF or GF were wear resistant with a short break-in period for forming a self lubricating film [Davies and Hatton, 1994]. Many commercial blends contain fluoropolymers (primarily PTFE) for the improved weatherability, wear and solvent resistance SUPEC — self-lubricating blend of crystalline PPS with PTFE and 30 wt% GF, Lubricomp blends from LNP and similar/JTP blends from RTP Co. (e.g., 15 wt% PTFE, 30 wt% GF and any of the following resins ABS, PA, PEST, PC, PE, PEI, POM, PP, PPE, PPS, PS, PSF, PVDF, SAN, TPU, PEEK, PES, etc.), Sumiploy from Sumitomo Chem. Co., etc. [Utracki, 1994]. 

Quite generally, the goal in any blending of polymers is to obtain one or all of the following benefits higher heat distortion temperature (HDT), improved variable temperature impact resistance, solvent resistance, dimensional tolerance, higher flow, utilization of recycle/regrind, and lower cost. 

Blend properties strongly depend on which polymer is the continuous phase. The majority of commercially important compatibilized blends of semi-crystalline polymers with amorphous polymers are prepared with compositions such that the semi-crystalline component is the matrix and the amorphous component is the dispersed phase. The blends show adequate solvent resistance since in this morphology the surface consists largely of the dominant, matrix phase,. 

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