SARAN New Vinylidene Chloride Resins
W. C. GOGGIN The Dow Chemical Co. Midland, Mich. Above. Vinylidene chloride extruded resins are used in this transportation seating manufactured bv the Heywood Wakefield Co. Left. These moderately high softening point resins are used advantageously in an abrasive wheel recently developed by the Norton Co. Lower left. Its high tensile strength, flexibility, claritv, and water resistance make vinylidene chloride resins suitable for fashing leaders, snells, and trolling lines such as those pictured, made by Weber Lifelike Fly Co.
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HE year 1940 has seen many advances in the plastic art—among them the introduction of a group of new thermoplastic resins, based on vinylidene chloride, more commonly known by the trade name, "Saran". The product has as its raw materials the almost limitless domestic supplies of crude oil and brine. History is not generally familiar with vinylidene chloride, and it is barely mentioned in a recent comprehensive survey of resinous materials. For some time, however, it has been investigated in a few industrial research laboratories and is now directly or indirectly the subject of some 40 patents. Vinylidene chloride is a clear, colorless liquid with a characteristic odor. It boils at 31.7° C. and has the structural formula:
The liquid monomer may be poly-
merized in a long linear chain by direct linking of the monomer molecules to form an insoluble, white crystalline powder which may be represented as follows:
A wide range of properties may be obtained either by controlling the length of the chain or by using a copolymerizing agent or both. A suitable copolymerizing agent might be a vinyl type monomer, such as vinyl chloride:
In this process the two materials become activated together and so polymerize to form the straight-chain copolymer having the possible structural formula:
923
Through a variation in the type and quantity of copolymerizing agents an almost infinite number of resins having widely diversified properties may be obtained. Resins formed through copolymerization range from a flexible, moderately soluble material having a softening point around 70° C. to a hard, tough, thermoplastic solid with a softening point of at least 180° C. To a greater or lesser degree, these resins exhibit crystallinity of structure. This unusual property may be demonstrated readily through use of the x-ray diffraction pattern. The higher softening pouit resins show the greater degree of crystallinity. Normally, the so-called fibrous crystals are arranged in a heterogeneous manner so that the plastic has only ordinary properties. Such unoriented Saran may show a tensile strength of 8000 pounds per square inch. Under proper conditions, the fibrous crystals may be oriented into an orderly linear pattern. In this manner the tensile strength may be increased to 60,000 pounds per square inch, accompanied by much greater flexibility. The altera* tion of crystalline arrangement results in a change in the modulus of elasticity, but even more striking is the great flexing fatigue life of oriented vinylidene chloride. In a series of tests this resin withstood 250,000 flexes through an sngle of 180° over a 0.125-inch mandrel without breaking. Saran resins are characterized by their
924 extreme chemical resistance. The highest softening point resins exhibit the greatest chemical resistance, and the lower softening point materials lesser resistance. As an example of its inertness, the intermediate softening point material is entirely unaffected by water, inorganic salts, acids, or alkalies in any concentration at ordinary temperatures. The resin is solvated only by the more active oxygen* bearing organic solvents, the oxides and ethers. These resins in the oriented form exhibit even greater chemical resistance than the unoriented type. Sjiran will not bum, it is odorless, tasteless, and nontoxic. The resin has a high index of refraction. Hardness and toughness are determined by the resin used and t he method of fabrication. Because of the incompatibility of this type of resin with must organic materials, only a limited group of plasticizers offers any advantages. In comparison with other plastics, relatively small amounts of plasticixer are required for facilitating fabrication. The basic re?in is essentially clear, making it possible through the use of dyes and pigments to obtain almost any shade of color or range of opacity. Although vinylidene chloride resins were not introduced until late in 1940, several applications already have been noted. Taking advantage of the extreme strength, toughness, and flexibility available in oriented Saran strands, new leaders, trolling lines, and snells made from this material have been enthusiastically received by both commercial and sport fishermen. Equivalent wet or dry strength, invisibility in water, durability, and availability in long continuous lengths have been decisive factors in the use of Saran resins, under the trade name, "Vec", to replace imported Japanese synthetic gut and best grade Spanish silkworm gut leaders. A late development is the use of a special twisted construction of several filaments to form a flexible and strong snell for saltwater fishing. An effective use of Saran is in transportation seating. Under the severe conditions to which pubway seats are exposed, Saran has stood up remarkably well. Again crystalline orientation is employed to produce strong, flexible, rattan-like strands which are woven into cheerfully colored, durable seat covering which may be easily cleaned. Attractive woven bulkhead panels of this material are being used in a number of new airliners. The possibilities of woven, braided, or twisted strands of Saran become almost unlimited when the utilitarian markets are considered. In addition, decorative features greatly expand the field of the material's usefulness. However, neither the plastic nor tK- market is limited to extruded sections. 8aran, as a pure thermoplastic resinous bonding agent, has become an essential ingredient in a new type of abrasive wheel, recently introduced to industry. Promising applications, based on the material's extreme
NEWS
EDITION
Vol. 18, No. 21
Rene* of Physical Properties of Serin Resins Compression molding, ° F. Lb./sq. in.
220 to 250 500 to 2000
Injection molding, ° F. Lb./aq. in. Mold shrinkage, in./in. Specific gravity Specific volume, cu. in./lb. Refractive index, no Tensile strength, lb./eq. in. Elongation, % Modulus of elasticity, lb./sq. in. X 10* Flexural strength, lb./sq. in. Impact strength, ft. lb. energy to break 0 . 5 X 0 . 6 in. bar, 1 unnotched Hardness, Rockwell superficial Thermal conductivity, 10* cal./sec./sq. cm./° C./cm. Specific heat, cal. / ° C./g. Resistance to heat (continuous), ° F. Softening point, ° F. Distortion under heat, ° F Tendency to cold flow Volume resistivity, ohm cm., 50% relative humidity and 25° C. Breakdown voltage, 60 cycles, volte/mil (instantaneous) Dielectric constant, 60 cycles, 10* cycles, and 10* cycles
275 to 350 5000 to 40,000 0.013 1.6 to 1.75 17.3 to 15.8 1.60 to 1.63 Up to 60,000 25 0.4 X 2 . 4 15,000 to 17,000 1 to4 15 y 65 to 95 2.2 0.32 160 to 200 200 to 325 150 to 200 Slight 6 X 10" 500 to 2500 3.0to5.0
Power factor, 60 cycles 10* cycles 10* cycles
0.03 toO.08 0.03 toO.15 0.03 to 0.05
Water absorption, immersion, 24 hr. Burning rate
0.00 None
Effect of Age Weak acids Strong acids Weak alkalies Sunlight Organic solvents Strong alkalies
Becomes stronger None None None Slight Highly resistant None
Effect on metal inserts Machining qualities Clarity Color possibilities
Inert Excellent Transparent to opaque Unlimited
chemical resistance, include extruded tubing and other shapes as well as compression and injection molded articles. These items find application in chemical plants, paint and lacquer manufacturing units, and other industrial processes. Much experimental fabrication work has been done on this form of processing. Special techniques and equipment have been developed by material suppliers to enable accurate control of properties and shapes of extruded sections. As with extrusion, injection and compression molding can be accomplished through method* developed by material suppliers. The outstanding properties of Saran resins may be made to vary over a rather wide range but can be summarized generally as follows: extreme tensile strength; high fatigue and abrasion resistance; toughness; great water and chemical resistance; nonfiammability; high dielectric strength; ease of machining; colorabilitv.
Magnesium Output P L A N T expansion, which will triple its fabricated magnesium output to cope with the demands of national defense, is being made by the American Magnesium Corp. Most of the plants of the company are operating on a three-shift-a-day, full capacity basis, and others will be on that basis as soon as personnel can be trained. Additional construction and equipment, now under way, will break all magnesium fabrication records in this country. The foundry at Cleveland, Ohio, where castings for aircraft engines, wheels for bombing planes, and other defense necessities are manufactured, is producing 350 per cent more magnesium products than a year ago. The magnesium powder plant, also at Cleveland, will soon be manufacturing ten times normal peace requirements, for use in tracer bullets and flares. The new foundry in Buffalo, N. Y., now in its second month of operation, is geared into high-speed production and as soon as the necessary skilled labor is obtained will have an output exceeding that of the Cleveland plant. A plant erected in Los Angeles, Calif., a year ago, is being expanded to twice its previous capacity. A new die-casting plant has been erected and equipped at Garwood, N. J. At New Kensington, Penna., the mill which was completed two months *go for magnesium sheet production is in operation.
