Temperature flexibility, plastic

For many applications low-temperature flexibility of the plasticized composition is also important. Plasticizers of low viscosity and low viscosity-temperature gradient are usually effective at low temperature. There is also a close relationship betv/een rate of oil extraction and low-temperature flexibility plasticizers effective at low temperature are usually rather readily extracted from the resin. Plasticizers containing linear alkyl chains are generally more effective at low temperature than those containing rings. Low-temperature performance is evaluated by measuremen t of stiffness in flexure or torsion or by measurement of second-order transition point, brittle point or peak dielectric loss factor. 

Figure 2.16 Typical stress/strain graphs. Clockwise rigid plastic, Tj >> room temperature flexible plastic, Tg s room temperature elastomer, Tg room temperature = rupture.

Because nitrile rubbers are polar elastomers, their vulcanizates are very resistant to swelling in hot oil, gasoline, grease, and other nonpolar substances. The resistance to swelling in nonpolar oils, solvents, and so on, is improved greatly with increasing nitrile content. Here we see the need for compromises increasing nitrile content improves oil resistance but reduces elasticity and set resistance and most severely reduces low-temperature flexibility. Plasticizers are very necessary to surmount this problem. 

Example of an HACCP System. The HACCP system can be used to ensure production of a safe cooked, sHced turkey breast with gravy, which has been vacuum packaged in a flexible plastic pouch and subjected to a final heat treatment prior to distribution (37). Raw turkey breasts are trimmed, then injected with a solution containing sodium chloride and sodium phosphate. Next, the meat is placed into a tumbler. After tumbling, the meat is stuffed into a casing, placed onto racks, and moved into a cook tank, where it is cooked to an internal temperature of at least 71.1°C (160°F). After... 

Polymer thick films also perform conductor, resistor, and dielectric functions, but here the polymeric resias remain an iategral part after cuting. Owiag to the relatively low (120—165°C) processiag temperatures, both plastic and ceramic substrates can be used, lea ding to overall low costs ia materials and fabrication. A common conductive composition for flexible membrane switches ia touch keyboards uses fine silver particles ia a thermoplastic or thermoset polymeric biader. 

The PSA formulator can also take advantage of plasticizers. For example, polyether-based plasticizers have both good low-temperature flexibility and good hydrophilicity. Using these properties, acrylic PSAs have been formulated with these types of plasticizers to obtain high adhesion to food packages stored under refrigerated conditions [102]. Similarly, polyether plasticized acrylics have been used to make repulpable PSAs [103]. 

Alk l chain. The increase in the alkyl chain length and linearity improves the efficiency of the plasticizer and the low-temperature flexibility of the plasticized polymers. 

Material added to a plastic to increase its workability and flexibility. Plasticizers tend to lower the melt viscosity, the glass transition temperature and/or the elastic modulus. 

Low-density polyethylene (polythene) is a relatively cheap, tough, flexible plastic. It has a low softening point and is not suitable for use above about 60°C. The higher density polymer (950 kg/m3) is stiffer, and can be used at higher temperatures. Polypropylene is a stronger material than the polyethylenes and can be used at temperatures up to 120°C. The chemical resistance of the polyolefines is similar to that of PVC. 

The plastic bottle and dispensing tip is made of low-density polyethylene (LDPE) resin, which provides the necessary flexibility and inertness. Because these components are in contact with the product during its shelf life, they must be carefully chosen and tested for their suitability for ophthalmic use. In addition to stability studies on the product in the container over a range of normal and accelerated temperatures, the plastic resins must pass the USP biological and chemical tests for... 

There are several plasticizers for PVC that may be used in propellants. Weil (19) mentions sebacates, phthalates, adipates, and glycol esters of higher fatty acids as being desirable. Dibutyl sebacate, dioctyl sebacate, and 2-ethylhexyl adipate are all good. The plasticizer has a most important effect on the physical properties of the cured propellant and the variation of these properties with temperature. Long chain, aliphatic plasticizers impart improved low temperature flexibility, and hence are preferable to aromatic plasticizers such as the phthalates. An increase in plasticizer viscosity leads to an increase in viscosity of the mixed pro-... 

Internally plasticized systems consisting of simple random copolymers, designed for use in flexible plastic articles, generally have an unsatisfactorily narrow use temperature range, since they soften more sharply than analogous externally plasticized systems or polyblends (mixtures of two or more polymers). 

Since there were no commercially available phthalate plasticizers comparable to the linear heptyl and nonvl derivatives, they were bracketed between the even numbered oxo phthalates for comparison. Table IV shows that DL7P was the most efficient of all the plasticizers tested and is superior to DHP and DIOP in low temperature flexibility. It is considerably less volatile than DHP and only slightly... 

Low Temperature Performance. The ability of plasticized PVC to remain dexible at low temperatures is of great importance in certain applications, eg, external tarpaulins or underground cables. For this property the choice of the acid constituent of the plasticizer ester is also important. The linear aliphatic adipic, sebacic, and azeleic acids give excellent low temperature flexibility compared to the corresponding phthalates and trimellitates (Fig. 3). 

Phthalates. These esters, prepared from o-phthalic anhydride, constitute the most important group of plasticizers from the stand-point of production and sales volume. Among these the dioctyl phthalates are the most widely used in vinyl chloride resins, where they are preferred because they offer a good compromise with respect to a wide range of properties satisfactory volatility, good compatibility, fair low-temperature flexibility,... 

Phosphites. The phosphates, second only to phthalates in production volume, are favored for flame resistance and low volatility. Tricresyl phosphate (mixed meta and para isomers) is the most popular it is used in polyvinyl chloride and in nitrocellulose lacquers. Resins plasticized with tricresyl phosphate are deficient in low-temperature flexibility. Diphenyl cresyl phosphate and triphenyl phosphate are other examples, the former for polyvinyl chloride, the latter for cellulose acetate. Diphenyl-2-ethylhexylphosphate is preferred to tricresyl phosphate in polyvinyl chloride where its low toxicity and improved low-temperature flexibility are required. Tn(2-elliylliexyl)-phosphale is outstanding among phosphates used in polyvinyl chloride with respect to low-temperature flexibility in flame- and oil resistance, however, it is inferior to tricresyl phosphate. Tri(butoxvethyl)phosphate finds some use in synthetic rubber. 

Primary plasticizers may be further subdivided. The phthalate types me by far the most popular due to cost and ease of incorporation. Dioctyl phthalate and diisooctyl phthalate are typical of this class, They exhibit good general -purpose properties. Phosphate plasticizers are also important for general-purpose use. Typical of these are tritolyl phosphate and trixylenyl phosphate. These plasticizers also impart fire retardant properties. Low-temperature plasticizers, such as dibntyl sebacate, are used where good low-temperature flexibility is required, For maximum... 

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