Patent Application
20080014440
The present invention relates to composite fibers of a polyoxadiazole and a flexible chain polymer and the preparation thereof.
For purposes herein, the term “fiber” is used herein interchangeably with “filament”, and means a relatively flexible, macroscopically homogeneous body having a high ratio of length to width across its cross-sectional area perpendicular to its length. The fiber cross section can be any shape, but is often somewhat circular. Fiber spun onto a bobbin in a package is referred to as continuous fiber. Fiber can be cut into short lengths called staple fiber. Fiber can be cut into even smaller lengths called floc. Multifilament yarns can be combined to form cords. Yarn can be intertwined and/or twisted.
The term spin as used herein refers to the extrusion of a polymer solution through a spinneret.
Polyoxadiazole useful in this invention include any polyoxadiazole polymer which has suitable properties to allow it to be solution spun into a fiber from a solvent in which the second polymer can similarly be spun into a fiber can be used to produce composite fibers of this invention. Preferably, the polyoxadiazole polymers are 1,3,4-polyoxadiazole polymers or copolymers. More preferably, the polyoxadiazole polymers including copolymers include but are not limited to polyoxadiazoles comprising the repeat units:
Processes for the production of polyoxadiazole polymers are well known in the art. Examples of processes for the production of polyoxadiazole (POD) polymers can be found in the Journal of Polymer Science: Part A, 3, 45-54 (1965), Journal of Polymer Science: Part A-1, 6, 3357-3370, (1968), Advanced Materials, 9(8), 601-613, (1997) and U.S. patent application Ser. No. 11/415,026. It is preferred to have a polyoxadiazole polymer of high inherent viscosity such as those produced by the method disclosed in U.S. patent application Ser. No. 11/415,026.
The second polymer can be any polymer selected from known flexible chain polymers which include copolymers, but preferred polymers are those that form isotropic solutions in mineral acids, including chlorosulfonic acid and fluorosulfonic acid, particularly sulfuric acid. A highly preferred polymer for use in the isotropic solution is polyvinylpyrrolidione (PVP). Examples of suitable polymers include aliphatic polyamides (e.g., 6-nylon, 6,6-nylon, and 6,12-nylon), polyaniline, polyether ketone ketone (PEKK), aromatic polyamides (MPD-I, MPD-I/T), and copolymers of PVP, such as PVP/VA (Vinyl Acetate).
Polyoxadiazole polymers and flexible chain polymers can be combined in any ratio that allows the solution to be spun into a fiber. Typically, any ratio of polyoxadiazole polymer to flexible chain polymer can be spun into a fiber. One in the art will typically use the rule of mixtures to determine the ratio of the polymers that will produce a fiber with desired properties. Typically, each polymer will be present by weight in the amount of at least 2 percent in order to produce a measureable change in properties of the resulting composite fiber.
Composite fibers of this invention can be spun by the process of continuously combining an isotropic polymer solution of a polyoxadiazole polymer and an isotropic solution of a second polymer to form a combined polymer solution; passing the combined polymer solution through at least one static mixer to form a spin dope; and extruding the spin dope through a spinneret to form a composite fiber. Additionally, the process can further include passing the composite fiber through an air gap; contacting the composite dope fiber with a quench solution to form a coagulated composite fiber; contacting the coagulated composite fiber with a wash solution; contacting the washed composite fiber with a neutralization solution to form a neutralized and washed composite fiber; drying the neutralized and washed composite fiber; and winding up the dried composite fiber. The dried composite fiber can be wound onto a bobbin on a windup device. Extrusion processes suitable for use in making composite fibers within the scope of the present invention are disclosed in U.S. Pat. Nos. 4,340,559, 4,298,565 and 4,965,033.
The polyoxadiazole composite fibers exhibit improved dyeability over fibers of polyoxadiazole polymers alone. The composite fibers can be solution dyed using both basic or acidic dyes. Basic dyes (or cationic dyes) are used to check the dyeability of the composite fibers. Cationic dyes such as Basacryl Red GL (Basic Red 29 by Color Index) are frequently used for this purpose because of the depth of the color it generates. Dyes are usually soluble in most of organic solvent and in aqueous medium, but dyeability was tested in aqueous medium. Slight acidity (pH of 4-6) is required to achieve level dyeing with basic dyes.
Without being bound to any theory it is believed that improved dyeability of the composite fiber is due to a diffusive channel created by chain mobility of the flexible chain polymer.
The UV stability of polyoxadiazole composite fibers is typically improved over fibers of polyoxadiazole alone. Polyoxadiazole fibers alone when exposed to a Xenon lamp for 20 hours typically do not exhibit measureable tenacity. Composite fibers of polyoxadiazoles having at least 2 percent by weight of the second polymer when exposed to UV radiation using a Xenon lamp for 20 hours can retain measureable tenacity. Preferably, polyoxadiazole composite fibers contain a sufficient amount of the second polymer to retain greater than 20 percent of their tenacity after 20 hours of exposure to a Xenon lamp. More preferably, polyoxadiazole composite fibers contain a sufficient amount of the second polymer to retain greater than 35 percent of their tenacity after 20 hours of exposure to a Xenon lamp. Most preferably, polyoxadiazole composite fibers contain a sufficient amount of the second polymer to retain greater than 50 percent of their tenacity after 20 hours of exposure to a Xenon lamp.
Each polymer solution and/or the combined stream can contain additives such as anti-oxidants, lubricants, ultra-violet screening agents, colorants and the like which are commonly incorporated.
All percentages are by weight unless otherwise indicated.
A polyoxadiazole copolymer was prepared by mixing 86.885 grams (0.668 moles) solid hydrazine sulfate, 88.74 grams (0.534 moles) of solid terephthalic acid, and 22.18 grams (0.133 moles) of solid isophthalic acid were mixed and blended together in a mixer for 30 min. To this blended mixture of solids was added a first addition of 30% Oleum, 534 grams Oleum (2.001 moles of SO3) at 25 degrees Celsius.
The mixture was mechanically stirred at 25 degrees Celsius for 15 minutes to dissolve the solids and form a solution. The solution was then heated to 120 degrees Celsius with mechanical stirring until a constant torque (constant viscosity) was observed on the mixer (60 minutes).
To this solution was added a second addition of 30% Oleum, 611 grams oleum (2.290 moles of SO3) at 130 degrees Celsius. The temperature was maintained at 130 degrees Celsius for 2 hours until the viscosity of the solution reached a plateau. The solution was then cooled to room temperature.
A small sample was removed from the cooled solution and added to water at 0 degrees Celsius to precipitate the polymer. The polymer was washed with water until a neutral pH was reached. The polymer was dried under vacuum and an inherent viscosity of 2.60. The solution was diluted to 5.0% solid by adding 581 grams of concentrated sulfuric acid.
To the rest of polymer solution prepared above, 5.06 grams of K-90 polyvinylpyrrolidone powder with a weight average molecular weight of about 90,000 was added at room temperature and stirred until all added solid was dissolved. The solution showed some shear opalescence and silky appearance. This solution was spun into fiber by air-gap spinning into coagulation bath of 7% sulfuric acid solution at room temperature followed by washing and neutralized in sodium bicarbonate. The resulting fiber was dried overnight in 120 C oven. Dyeability of the fiber was tested in 0.5% Basacryl Red GL (a basic dye) solution in acidic pH=4-5. The fiber was dyed deep, while the fiber prepared without added PVP was not dyed.
The fiber sample prepared the same way except that low molecular weight PVP (K-30 with a weight average molecular weight of about 60,000) instead of K-90, was also dyed deep with Basacryl Red GL (a basic dye).
