Methods of treating polymeric materials, methods of forming...

Details Methods of treating polymeric materials, methods of forming... Methods of treating polymeric materials, methods of forming...

2000-02-03

2001-11-13

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S152000, C522S156000, C522S154000, C522S104000, C522S108000, C522S090000, C522S173000, C528S480000

Reexamination Certificate

active

06316518

ABSTRACT:

TECHNICAL FIELD
The invention pertains to methods of treating polymeric materials. The invention includes methods of increasing polymerization within polyamide, polyester, polyurethane, copolymers thereof, and condensation polymers in general, as well as methods of forming nylon. Additionally, the invention encompasses apparatuses configured for treating feed materials with radiation, such as, for example, radio-frequency (RF) electromagnetic radiation.
BACKGROUND OF THE INVENTION
A commercially important polymeric material is the polyamide known as nylon. A form of nylon (specifically, nylon-6) can be produced from caprolactam (CPL) utilizing the process described in FIG.
1
. At a first step, CPL is mixed with water and initiators (such as, for example acetic acid). It is noted that the initiators are optional. It is also noted that other optional materials can be mixed with the CPL and water, including terminators and additives.
In a second step, a temperature of the mixture is increased to about 200° C. under pressure, which causes the ring of CPL to open. The ring opening is shown below in reaction 1, and forms 6-aminohexanoic acid (6-AHA).
CPL+H
2
O&rlarr2;H
2
N—(CH
2
)
5
—COOH (6-aminohexanoic acid, 6-AHA) (monomer, n=1)  I
In a third step of the
FIG. 1
process, the monomeric 6-AHA is heated to from about 240° C. about 260° C. to form polymers comprising 15 to 20 of the monomeric units. The reactions occurring during the initial polymerization comprise the addition reactions shown below as reactions II-IV, and condensation reactions shown below as reactions V and VI. The reactions referred to as “addition” (specifically, reactions II-VI) are identical in principle to the reactions referred to as “condensation” (specifically, reactions V and VI). However, an important distinction between the addition reactions and the condensation reactions is that condensation enables rapid chain growth with emission of only a single water molecule, whereas addition enables chain growth of only one monomeric unit per water molecule formed. This can enable condensation reactions to yield a greater rate of polymer growth than addition reactions. However, such is not always the case, as kinetics can become limited by the relative scarcity of available groups to perform polymerization as monomers become incorporated into polymeric units.
2(6-AHA)&rlarr2;H
2
N—(CH
2
)
5
—CO—NH—(CH
2
)5—COOH+H
2
O (dimer, n=2)  II.
dimer+6-AHA&rlarr2;H
2
N—((CH
2
)
5
—CO—NH)
2
—(CH
2
)
5
—COOH+H
2
O (trimer, n=3)  III.
trimer+6-AHA&rlarr2;H
2
N—((CH
2
)
5
—CO—NH)
3
—(CH
2
)
5
—COOH+H
2
O (tetramer, n=4)  IV.
pentamer+hexamer&rlarr2;undecamer (n=11)+H
2
O  V.
undecamer+octamer&rlarr2;nonadecamer (n=19)+H
2
O  VI.
In the above reactions I-VI, “n” equals the number of monomeric units in a chain. Generally, addition reactions produce chain links wherein “n” is from about 5 units to about 20 units, and then the reaction changes character so that condensation (sometimes referred to as polycondensation) begins to predominate. Reactions I-VI are all fully reversible, with equilibrium constants somewhat greater than 1 for the reactions as written.
It is noted that the above-described reaction I utilizes water as a reactant, and reactions II-VI generate water as a by-product. The presence of water in the reaction mixture allows the reversal of every step of the polymerization processes of reactions II-VI, and accordingly the reacting materials utilized in reactions II-VI are typically flushed with a gas during the reactions to remove water from the reacting materials. The gas typically is a material which is inert relative to reaction with the materials of reactions II-VI, and can comprise, for example, nitrogen or argon. Because water is necessary for reaction I, and yet causes reversal of reactions II-VI, water is allowed to escape from the reaction chamber as steam after reaction I. The reaction chamber may also be sparged with an inert gas during this time to aid in the steam's escape. Removal of water can be an important determinant on the rate and degree of polymerization occurring under particular reaction conditions. (Mallon and Ray, Journ. of Applied Polymer Science 69, 1203 (1998); and U.S. Pat. No. 5,269,980). The rates of two amidation reactions can, in practices frequently be determined by a rate of water removal under a variety of conditions, including melt conditions, solid state polymerization (SSP) conditions, or conditions wherein the reactions are in the form of small droplets (see, for example, U.S. Pat. No. 5,269,980). Mallon and Ray have shown that the rate of solid state polymerization of polyamides can be dependent on the diffusion rate of water generated by an amidation reaction, and specifically by the rate at which water diffuses to the surface of chips of solid nylon and escapes into a surrounding environment.
Steps
1
-
3
of
FIG. 1
typically occur in a pressurized vessel. The steps are described as separate steps because they are chemically distinct stages of a reaction process. However, it is to be understood that the steps typically do not comprise separate manipulations of a reacting mixture, but rather comprise different stages along a reaction continuum.
Referring to step
4
of the
FIG. 1
process, a pressure of a vessel comprising the reacting mixture is reduced and water is vented. Such venting and reduction of pressure can be accomplished by, for example, opening a valve of a pressurized reacting vessel to allow escape of water vapor and other gases from the vessel. The de-pressurized reacting mixture is maintained at a temperature of from about 240° C. to about 260° C. to encourage condensation within the mixture and form polymers comprising from about 50 to about 200 monomeric units. The material formed in step
4
is extruded, cooled and chopped to form nylon chips in processing labeled as step
5
of FIG.
1
. It is noted that the material of step
4
typically comprises a thick, sticky substance, and such substance is typically extruded through a number of holes to form long strands. The strands are then cooled and chopped to form chips on the order of about ⅛ inch in length and about ⅛ inch in diameter.
Referring to step
6
of
FIG. 1
, the chips are leached in hot water in a multiple-step process that takes from 15 to 20 hours to leach unreacted CPL from within the chips. The chips typically comprise about 10% unreacted CPL, as a result of the reactions I-IV being in equilibrium, and the leaching enables such CPL to be reclaimed from the chips. The leaching typically occurs at from 105° C. to 120° C.
Referring to step
7
, the chips from step
6
of
FIG. 1
are dried. Such drying typically comprises exposing the chips to warm nitrogen in a tumble dryer under a partial vacuum in a process that typically takes a number of hours.
After the chips are dried, they can be utilized in one or more of the
FIG. 1
steps
8
,
9
and
10
; which comprise subjecting the chips to a solid state polymerization (SSP), selling the chips, and using the chips to form nylon products, respectively.
A quality of nylon chips is measured by a so-called formic acid viscosity (FAV) value, a measure of relative viscosity that reflects an average chain length within the nylon material. The formic acid viscosity value is determined with an 8.4% (weight/weight) solution of the nylon material in 88% formic acid, and reflects a viscosity of such solution. Higher FAV values typically indicate longer chain lengths within the nylon chips, and correspond to chips having higher value than would chips with lower FAV values.
The FAV values of chips at the processing of step
7
of
FIG. 1
are typically about 40. If the chips are subjected to the SSP of step
8
, the FAV values can be increased to 200 or higher. Nylon-66 undergoes SSP more rapidly and can reach FAV values of 500 or more. FAV values greater than 200 could, in theory, be

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