Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
2000-01-14
2002-03-19
Mullis, Jeffrey (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C525S063000, C008S115560, C008S115620, C008S115650
Reexamination Certificate
active
06358451
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to grafted aramid fibers for improvement of adhesion between the fibers and rubber matrixes which the fibers are to reinforce. The aramid fibers are subjected to grafting while still containing water from the fiber manufacture.
2. Description of the Prior Art
U.S. Pat. No. 5,310,824, issued May 10, 1994, discloses poly(p-phenylene terephthalamide) fibers with fluoroalkyl groups grafted thereto and a process for performing the grafting reaction. The fibers are dry and there is no water in the grafting system.
Japanese Pat. Publication (Kokai) 62-81426 published Apr. 14, 1987 and Japanese Pat. Publication (Kokai) 62-91542, published Apr. 27, 1987 published Apr. 14, 1987, disclose a surface treatment of aramid by grafting reactions. The aramid can be poly(p-phenylene terephthalamide) fibers; but the reactions are anhydrous and dried fibers are used.
An article in The Journal of Adhesion Science, Volume 6, No. 12, pp. 1303-1323 (1992), titled “Wettability And Adhesion Studies Of Grafted Poly(P-Phenylene Terephthalamide) Fiber Surfaces”, by Ravichandran and Obendorf, discloses that increased fiber-to-matrix adhesion can be obtained by grafting various materials onto the surface of fibers. The fibers are dry and the grafting reactions are free from water.
SUMMARY OF THE INVENTION
This invention relates to a fiber of poly(p-phenylene terephthalamide) having nitrobenzyl groups or nitrostilbene groups grafted thereto. It also relates to a fiber reinforced rubber composition comprising a rubber matrix material with, embedded therein, fibers of poly(p-phenylene terephthalamide) having nitrobenzyl, allyl, or nitrostilbene groups grafted thereto. There is, also, a process for making grafted poly(p-phenylene terephthalamide) fibers comprising the steps of: spinning a solution of poly(p-phenylene terephthalamide) into an aqueous coagulating bath to make coagulated fibers having 20% to 400% water, based on the weight of poly(p-phenylene terephthalamide) material in the fibers; contacting the coagulated fibers, along with the water therein, with a solution of strong base to make base-activated fibers; optionally, quenching the fibers with a nonaqueous solvent to remove any excess base; and contacting the base-activated fibers with a grafting solution of allyl halide, nitrobenzyl halide, or nitrostilbene halide grafting agents. The grafted fibers can be washed with water. Strong bases are those which exhibit a Pka greater than 12 in dimethyl sulfoxide. Potassium tert-butoxide is preferred.
DETAILED DESCRIPTION
Due to high strength and modulus, poly(p-phenylene terephthalamide) (PPD-T) fibers are particularly useful as a reinforcement for rubber. One troublesome aspect of the use of PPD-T fibers as a rubber reinforcement has, in the past, been a lack of good adhesion between the rubber matrix and the PPD-T fibers which reinforce it.
In the past, PPD-T fibers have been coated by two materials, individually, to achieve acceptable rubber adhesion properties. The fibers were treated by a complicated process—first, by an epoxy subcoating and, after drying and curing the subcoating, next by a resorcinol-formaldehyde topcoating which must, also, be dried and cured.
The inventor herein has found a treatment means for the PPD-T which requires only a single step and which can be conducted on the PPD-T fibers in a wet or never-dried state. The treatment of this invention can, thus, be conducted on PPD-T fibers on a continuous basis as an additional step in the fiber spinning process. This not only provides fibers of improved rubber adhesion, it provides these fibers by a considerably simplified process as a part of the fiber manufacture.
By PPD-T is meant the homopolymer resulting from mole-for-mole polymerization of p-phenylene diamine and terephthaloyl chloride and, also, copolymers resulting from incorporation of small amounts of other diamines with the p-phenylene diamine and of small amounts of other diacid chlorides with the terephthaloyl chloride. As a general rule, other diamines and other diacid chlorides can be used in amounts up to as much as about 10 mole percent of the p-phenylene diamine or the terephthaloyl chloride, or perhaps slightly higher, provided only that the other diamines and diacid chlorides have no reactive groups which interfere with the polymerization reaction. PPD-T, also, means copolymers resulting from incorporation of other aromatic diamines and other aromatic diacid chlorides such as, for example, 2,6-naphthaloyl chloride or chloro- or dichloroterephthaloyl chloride; provided, only that the other aromatic diamines and aromatic diacid chlorides be present in amounts which do not compromise the required properties of the polymer. The PPD-T has amide linkages (—CO—NH—) resulting from the chemical combination of the amine groups of the diamines and the carboxyl groups of the terephthaloyl chlorides and at least 85% of the amide linkages are attached directly to two aromatic rings.
Additives can be used with the components of the PPD-T and it has been found that up to as much as 10 percent, by weight, of other polymeric material can be blended with the PPD-T.
The PPD-T fibers of this invention have allyl groups (AL), nitrobenzyl groups (NB), or nitrostilbene groups (NS), as grafting agents, grafted to the PPD-T by replacement of the hydrogen at amide groups (—CO—N(AL/NB/NS)—). The nitrostilbene group has the advantage of being a bifunctional structure including both the allyl and the nitrobenzyl groups. The grafting reaction is performed by deprotonation and metallation of —NH groups using a reagent prepared by an interaction of potassium tert-butoxide with dimethyl sulfoxide (DMSO) to yield a polyanion structure. The metallated polyanions can then be subjected to nucleophilic substitution of AL, NB, or NS groups. The overall reaction sequences are known as the deprotonation grafting reaction of this invention.
It has been concluded that the PPD-T polymer in the fibers of this invention should be subjected to the deprotonation grafting reaction after formation or spinning of the fibers because such permits the most advantageous use of the grafted materials. However, it would be possible to make the grafted fibers of this invention by grafting the PPD-T prior to formation of the fibers.
The fibers are generally spun from an anisotropic spin dope using an air gap spinning process such as is well known and is described in U.S. Pat. Nos. 3,767,756 or 4,340,559. Fibers are spun from an anisotropic spin dope, through an air gap, into an aqueous coagulating bath, and through an aqueous rinse and wash. The resulting fibers are so-called “never-dried” and include from 20 to 400%, by weight, water. While the fibers to be used may be partially dried, it is important that they have been newly-spun and have never been dried to less than 20 percent moisture prior to the grafting. Fibers which have been previously dried to less than 20 percent moisture have had their molecular structure irreversibly collapsed and ordered into a compact fiber. Never-dried fibers are important for use in this invention because they are more wettable, individually and in yarn bundles, by the grafting reagents and provide more porosity and increased accessibility of the grafting reagents to the —NH reaction centers.
The grafting process of this invention involves the formation of a metallated PPD-T polyanion as a precursor to the grafted polymer. Up to this time, it has been the accepted practice to conduct grafting processes such as this one in dry conditions to minimize the competitive reprotonation by water which could reduce the grafting reaction yield.
The grafting process of this invention utilizes a strong base material and it has been determined that potassium tert-butoxide is preferred because it will function in the water-containing polymer material on which the grafts are to be made. Other strong bases may be used which exhibit a Pka greater than 12 in DMSO or an equivalent aprotic solvent. Other suitable bases are sodium met
E. I. du Pont de Nemours and Company
Mullis Jeffrey
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